Any Ideas?

I have my Nats plane. A geo bolt wing with a 26% stab. Big flaps. 9" nose and 17 3/4" tail moment. It has a 65 in it. The CG is pretty far aft and it will turn easy even in heavy winds. It never has a the feel of "Loaded" controls.

I have virtually the same plane excpet the nose is a 1/4" shorter. the tail area and tail moment are exactly the same. The wing is same. The tips are different but the span is within an inch of the nats plane. It carries in it a Saito 72. It has a very heavy feel in the cotrols. Sometimes it is very "loaded" I feel like I am pulling for all my life sometimes to keep the plane off the ground.

Easy right sneak the CG back all should be fine right? WRONG! I checked last night and the CGs are almost identicle. The 4s plane having the cg actaully just hair back further. I even added in more elevator than flap and it still has this really loaded up and nose heavy feel in the turns.

What is going on?

You would think with the CGs really close the feel would be about the same. If I move it(cg)forward to match the Nats plane it is even worse. I dont get it. It should turn about the same.

I am leaning towards the fact you have all 20oz crammed right in the nose and the negative pitching movement of the large flaps coupled with trying to change the 20oz of weight into a different direction are killing the elevator power.

Leaning towards adding in counter balances and very tiny flaps. Tiny flaps mean very light weight building. But the negative pitching of the small flaps will be very small and wont work so hard against the elevators. Ala...Berringer. He uses a smaller tail area to move CL forward so that flying with a far forward CG isnt such a bad thing becasue the CG and the CL are still relatively close. I discussed this with GZ at length yesterday. Interesting conversation for sure. It just dumbfounds me that 2 planes with identicle CGs turn so vastly different.

Oh I can't forget the 72 plane has a 14" Prop and the nats plane only has a 12" prop. I know that has some effect but I wouldnt think it was this large of an effect. In the wind this plane really loads up. I can still fly it but it is hard work.

Any ideas???

Hi Doug,
My guess is a combination of the things you mentioned...in particular, bar bell effect of 20 oz. in the nose in conjunction with bigger prop. Also, this planes weighs about half a pound more than your piped 65 ship right! More weight, more pull. Maybe you have to much engine offset in conjuntion with right rudder offset and or LO location also. Its worth checking!?

The difference in flying my Dads 66 oz. Chevelle and my own 61 oz. is quite drastic where the stump pulling feel is concerned. Had to rest and massage my arm between flights on his plane. It doesnt allow for typical bent elbow flying such as I like to use. The only way I could not get a spasm was to leave my arm fully extended during flight.

Personally, although others will dispute it, I'd be pointing the finger at the 14" prop. On a piped setup there is quite a difference in corner rate between a 12" and a 12.5", so naturally the difference between a 12 and 14 is going to be noticable. I know some people have this theory that the large props on the 4s doesn't load up the corners, but it seems obvious here.

Not only do you have a bigger prop, but I'll assume you're also using more pitch as well with the 4S motor. I would think both these factors would have an effect on the plane's rate of turn.

Also, while the plane may essentially be balancing at the same CG ... that doesn't mean that the nose can be turned with the same amount of force. The tail (stab/elev) is what forces the plane to turn. Despite the fact that you're turning a heavier motor a shorter distance (due to the shorter nose moment), that doesn't necessarily mean that the force generated by the tail will move the mass of the piped nose and the mass of the 4S nose equally. I would suspect that the 20 oz in the nose of the 4S ship need much more force in order to turn than would the (relatively) lighter piped motor.

LAST EDITED ON Apr-01-03 AT 09:59 PM (CDT)
 
Doug, I think you have your answer in the above posts. The prop is dampening your turn rate. The extra pitch is winding up and also increasing the elevator loads. I know this goes against the thinking in Dallas on 4 strokes but when I flew 4 strokes 2 years ago I started with a 13-4 APC on my 72. It flew great. Sometimes you have to think outside the box and try what seems to be contrary to accepted absolutes. I am a try and fly kind of guy and suggest that sometimes this is the only way to get where you are going. When I started flying stunt I heard a lot of "tried that, it does not work". I tried anyway and found numerous times it Did Work. The big 13-4 Bill Lee 3 blade with heavy undercamber was a great prop. Email me if you want to hear the rest of my 4 stroke experiences(about 500 flights).

>Not only do you have a bigger prop, but I'll assume you're
>also using more pitch as well with the 4S motor. I would
>think both these factors would have an effect on the plane's
>rate of turn.
>
>Also, while the plane may essentially be balancing at the
>same CG ... that doesn't mean that the nose can be turned
>with the same amount of force. The tail (stab/elev) is what
>forces the plane to turn. Despite the fact that you're
>turning a heavier motor a shorter distance (due to the
>shorter nose moment), that doesn't necessarily mean that the
>force generated by the tail will move the mass of the piped
>nose and the mass of the 4S nose equally. I would suspect
>that the 20 oz in the nose of the 4S ship need much more
>force in order to turn than would the (relatively) lighter
>piped motor.
>
>
>
>

NOT SHOUTING HERE...JUST USING THE NASA COMPUTER WHICH ONLY ALLOWS FOR CAPS...SORRY.

THERE REALLY IS SOMETHING TO THIS MOMENT OF INERTIAL STUFF YOU'RE DEALING WITH. CONSIDER THE FOLLOWING.

YOU'VE GOT TWO BICYCLE WHEELS OF THE SAME TOTAL WEIGHT...LET'S JUST SAY 10 POUNDS (OK, OK, IT'S A REAL OLD BUT HEAVY BICYCLE) ON ONE THE WEIGHT IS CONCENTRATED AT THE AXLE IN THE FORM OF GEARS, ETC. ON THE SECOND THE TIRE IS MADE OF TUNGSTEN CARBIDE OR GOLD OR SOMETHING EQUALLY HEAVY.

THE CENTER OF GRAVITY OF EACH WILL BE IN EXACTLY THE SAME PLACE...RIGHT AT THE AXLE. STARTING AND STOPPING ROTATION, HOWEVER, WILL BE MUCH DIFFERENT.

THE HEAVY HUBBED VERSION WILL BE FAIRLY EASY TO START AND STOP. THE HEAVY RIMMED VERSION WILL TAKE SOME EFFORT TO START AND WILL BE MUCH MORE DIFFICULT TO STOP ONCE IT IS MOVING.

CG'S IDENTICAL MOMENT OF INERTIA MUCH DIFFERENT.

FOR WHAT IT'S WORTH I ALSO AGREE THAT THE GREATER DIAMETER PROP IS DETRIMENTAL TO RAPID PITCH CHANGE AS WELL. THERE'S A REASON P.W. FOUGHT THE BIG PROPS ON HIS IMPACTS FOR SO MANY YEARS (I KNOW, I KNOW THE MUSTANG'S A DIFFERENT STORY AND I AGREE...IN MORE WAYS THAN ONE!)

A LARGE PART OF THE REASON FOR THE PROP'S EFFECT IS GYROSCOPIC INERTIA...THE SAME PHENOMENA WHICH KEEPS A GYROSCOPE SPINNING IN PLACE EVEN WHEN SITTING ON THE SIDE OF A STRING, FOR INSTANCE.

NOW, PROBABLY, IF YOU MADE THE WHOLE AIRPLANE LARGER SO THAT THE TOTAL MASS DISTRIBUTION IS SIMILAR TO THE PIPED/SMALLER PROPPED SHIP THE RESPONSE WOULD BE MORE SIMILAR. OF COURSE, THEN YOU'D HAVE TO GET INTO THE WHOLE THING OF CONTROL SYSTEM GEOMETRY, CONTROL LOADS ETC. ALL OVER AGAIN.

BIGGER MAY OR MAY NOT BE BETTER...BUT IT IS CERTAINLY DIFFERENT.

TED

>CG'S IDENTICAL MOMENT OF INERTIA MUCH DIFFERENT.

Posted from another thread:

I don't think the MOI is a factor. If indeed the CG is EXACTLY the same as the equivalent 2 cycle setup, the nose MUST BE SHORTER. If the nose is shortened to statically balance the model at the same point, the MOI of a 4 cycle plane is actually lower than a 2 cycle airplane. (BTW I am not sure MOI is truly static, but I am using it that way).

I posted this MOI calculation once before. I received no comments:

We will assume a center of lift 3 inches back from the leading edge of the wing to start. This assumed number would bring the airplane into perfect balance. For a typical 2-cycle stunt nose, we assume the ever-popular 10 inches from the leading edge.

ST 60 = 13 oz with muffler (we will omit pads for the sake of this discussion). We will assume the CG of the engine is 2" back from the spinner backplate. We will also assume a spinner and prop weight of 1.5 oz. So, the total MOI for the engine would be the following:

14.5 OZ x (10” – 2” + 3”) = 14.5 OZ (11”)**2 = 1754.5 oz*inch**2 total moment of inertia to the CG of the airplane due to the engine, prop, spinner, and muffler

Now we will calculate the moment of the tank and the fuel. We will assume 7 oz of fuel, utilizing a standard stunt wedge of 7” in length. We will also assume that the CG of the tank is 3.5” ahead of the leading edge of the wing (6.5” in front of the CG of the airplane). We will assume 1 oz of fuel weighs 1 oz. We will assume the tank weighs 2.5 oz.

(7 oz ) x (6.5”)**2 = 295.75 oz*inch**2 total moment of inertia from the fuel
(7 oz + 2.5 oz) x (6.5”)**2 = 487.5 oz*inch**2 total moment from the fuel and tank

Total moment of the ST 60 with a 10” nose = 295.75 + 487.5 + 1754.5= 2537.75 oz*inch**2.

That being the case, the fuel represents 11.7% of the total moment or inertia.

Now we calculate the MOI for a Saito 72 using the known nose length 8.72” that we found from the moment calculation. We will assume the Saito 72 weighs 17.2 oz with muffler. The spinner and prop weighs 2.8 oz (I use a 2 ½” spinner and 14” wood prop). We will assume the CG of the engine is 2" back from the spinner backplate. We will assume a center of lift 3 inches back from the leading edge of the wing (for example). This assumed number would bring the airplane into perfect balance. So, the total moment for the engine would be the following:

(20 oz ) x (8.72 -2” + 3”)**2 = 20 oz (9.72”)**2 = 1889.57 oz inch**2.

Now we will calculate the MOI of the tank and the fuel. We will assume 4.5 oz of fuel (some claim far less), utilizing a Sullivan 6-oz clunk tank of 4” in length. Just for fun, we will assume that the front of the fuel tank has to be 5.25” back from the spinner backplate to clear the engine (this is actually true). We will assume that the fuel tank weighs 1.5 oz.

The MOI of the fuel tank with fuel = (4.5 oz + 1.5 oz) x ((8.72– (5.25” + 2”) +3”)**2 = 6 oz (4.47”)**2 = 119 oz inch**2

The MOI of the fuel alone = (4.5) x (8.72-4.25) = 89.9 oz inch**2

The total MOI for the 4 cycle setup is 1889.57 + 119 + 89.9 = 2098.48 oz inch **2

This is a reduction of about 17% over the 2 cycle setup.

This means the total MOI of the fuel in the EQUIVALENT 4 cycle setup is only 4.2%.

That’s around a third of the 2 cycle setup.

>>CG'S IDENTICAL MOMENT OF INERTIA MUCH DIFFERENT.
>
>Posted from another thread:
>
>I don't think the MOI is a factor. If indeed the CG is
>EXACTLY the same as the equivalent 2 cycle setup, the nose
>MUST BE SHORTER. If the nose is shortened to statically
>balance the model at the same point, the MOI of a 4 cycle
>plane is actually lower than a 2 cycle airplane. (BTW I am
>not sure MOI is truly static, but I am using it that way).

But I don't think this is the situation in this case, is it? The nose on the 4-stroke airplane is only 1/4" shorter, and that's only 3%. But the engine is far from 3% heavier. This can only mean that that to get the same CG there is some more weight in the aft end as well (either intentional or from building variations). Your analysis only works if you have otherwise identical mass properties and then adjust the nose length to get the same CG. If you add weight, or just have more weight, in the tail, this has to be included in the moment of inertia calculation. Then, you have another 18" radius of gyration to account for the tail weight in addition to the radius of gyration from the engine (reduced by 3-4% due the 1/4"). A given amount of weight in the tail has ~5x the effect on the moment of inertia that the same weight in the nose. But there is only about a ~2x difference in the moment arm for CG purposes, so adding weight to the tail to balance the engine has disproportionate effect on the moment of inertia. It's sort of the reverse of your argument for the engine.

Seems like to me that the nose needs to be a lot shorter than 1/4" to balance properly with otherwise identical mass properties, and if you don't have it short enough, the "advantage" of the shorter nose in terms of moment of inertia goes away.

But it seem clear to me that the gigantic prop is probably the source of Doug's observation. Might be worth calculating the moment of inertia of the prop - see Dr. Soule's website for assistance.

>
> Seems like to me that the nose needs to be a lot shorter
>than 1/4" to balance properly with otherwise identical mass
>properties, and if you don't have it short enough, the
>"advantage" of the shorter nose in terms of moment of
>inertia goes away.
>

I agree. How did the new plane balance at nearly the same point?

BTW Doug's nose is still pretty short compared to most.

>>
>> Seems like to me that the nose needs to be a lot shorter
>>than 1/4" to balance properly with otherwise identical mass
>>properties, and if you don't have it short enough, the
>>"advantage" of the shorter nose in terms of moment of
>>inertia goes away.
>>
>
>I agree. How did the new plane balance at nearly the same
>point?
>
>BTW Doug's nose is still pretty short compared to most.

One way to start finding out would be to take out the engine and tank, and find where they balance empty.

Given all the parts in hand, and an airplane known to (on average) balance with, say, a PA61, it would be a simple matter to calculate the required nose length to make it balance with a Saito 72.

LAST EDITED ON Apr-03-03 AT 05:06 PM (CDT)
 
>BIGGER MAY OR MAY NOT BE BETTER...BUT IT IS CERTAINLY
>DIFFERENT.
>

Exactly...

I heard the AMA is going to pass the larger motors for CLPA. This means those venturing down the larger motor path may have to rethink their stunt ideas in order to get the feel they like of their smaller stunt planes that they have now. A .91 turning a 16" prop is going to take some real force to have any kind of corner.

It seems to me it all has a little something to do with it. Which has more effect I dont know. Some claim this some claim that. I will have to find out on my own huh? Maybe a long shaft extension would relieve some of this barbell effect and a harder corner could be attained with the 14" prop while still getting the pull from the 14" prop. Best of both worlds...maybe...

Just thoughts...

>NOT SHOUTING HERE...JUST USING THE NASA COMPUTER WHICH ONLY
>ALLOWS FOR CAPS...SORRY.

Oh please do tell! There's got to be a great story behind this. Don't tell me they're still using teletypes? Even the old VT-52 and Televideo terminals we used in the old days had shift keys! What sort of web browser do you use on the old computer?

>>NOT SHOUTING HERE...JUST USING THE NASA COMPUTER WHICH ONLY
>>ALLOWS FOR CAPS...SORRY.
>
>Oh please do tell! There's got to be a great story behind
>this. Don't tell me they're still using teletypes? Even the
>old VT-52 and Televideo terminals we used in the old days
>had shift keys! What sort of web browser do you use on the
>old computer?
>
>

Way too complicated for me, Isky.

It's a Mac which I've never used before and is configured to handle the flight safety reports that I help to diagnose and enter into a data base. For whatever reason they have it set up so that no matter what buttons I push everything comes up in caps.

Doug,

Brett, please step on in here, you are the expert in this
category. I have been thinking about this and part of the
explanation must be the prop and pitch, but the 20 OZ of engine
weight is distributed further forward than that of the 65 pipe
set up. Could the more forward mass of the 4S engine be dampening
the effectiveness of the stabalizer like Doug mentioned?

>Doug,
>
>Brett, please step on in here, you are the expert in this
>category. I have been thinking about this and part of the
>explanation must be the prop and pitch, but the 20 OZ of
>engine
>weight is distributed further forward than that of the 65
>pipe
>set up. Could the more forward mass of the 4S engine be
>dampening
>the effectiveness of the stabalizer like Doug mentioned?

Well, my 4-stroke experience is quite limited. But there's no doubt that having a 20 oz engine and whatever it takes to balance it in the tail will certainly increase the pitch moment of inertia, meaning it will take more deflection/force to both start and stop the corners. Without flying the airplane, and fiddling around with it, I can't really tell of this is the issue or not.

But don't overlook the prop - this is a huge, huge factor. Richard's prop experience seems to be far more in line with what I have seen work locally than the New Jersey style high-pitch setup. I don't know if lower pitch will reduce the control loads or not. If nothing else, more than about 4.5" of pitch seems to lead to very high level flight speeds with any reasonable venturi.

One thing I have noticed - most of the principles of props seem to work pretty much exactly the same on 4-strokes as they do on 2-strokes, with the exception of the feedback effects on the mixture. In particular, pitch distribution effects seem to be pretty much identical - the average pitch sets the level flight speed, and the pitch at the tips seems to set the speed in the corners - just like it did for the last 40 years on two-strokes!

"...the average pitch sets the level flight speed, and the pitch at the tips seems to set the speed in the corners..."

Brett, would you elaborate on this, please? I've been trying to understand props.

>"...the average pitch sets the level flight speed, and the
>pitch at the tips seems to set the speed in the corners..."
>
>Brett, would you elaborate on this, please? I've been
>trying to understand props.

I hope you aren't asking me *why*, because I don't know to the level of detail that you (and I) would accept. I have a vague notion about the change in prop AoA at varying airspeeds (less change in the tips than the root, due to the velocity) but it's nothing more.

But, empirically, take the old Impact out, and fly it with the usual 11.3-4, then with a 11.3-3.75 that washes in to 4.25 over the last inch, and see what happens. I think you'll see what I mean.

It might be a thing called moment of inertia, which determines how much effort is needed to rotate a body. The Center of Gravity is only the static balance point of all the distributed weight of the plane.
The dynamic balance point can be different depending on how the weight is distruted.

>It might be a thing called moment of inertia, which
>determines how much effort is needed to rotate a body. The
>Center of Gravity is only the static balance point of all
>the distributed weight of the plane.
>The dynamic balance point can be different depending on how
>the weight is distruted.

What you said reflects my idea of the major problem despite short nose moment...ie Gialdini Olympic article written when I was a tot....Bar bell effect. I think Doug seems to explain that the plane turns fine but G force in the corner is hard to handle much less level flight line tension.

Good timing. I just posted on flitelines about my combat ships turning different with different props. The 9in prop plane needs the Cg back 1/4in to turn as well as the 8in prop plane. Also, the big prop plane allways feels heavy on the handle, the small prop is light . The higher polar moment(weight in the ends) does make for a slower turn as well.
The gyro effect loads up the plane a lot.(from back to back test)
I have one engine ( FOX CS 35) that can use either prop and it is pretty dramatic, the difference in the turn. I would guess that the lighter the ship the more effect the prop can make. MY combat planes are less than 19oz and 408sq.
Maybe try a lighter , slightly smaller prop. or 4blade?? Anything to reduce the prop"s Gyro effect should show up really fast in your case.

RE; Polar moment measurement can be done. They used to measure twelve meter sail boats by the "swing test". Hang you best plane by two strings, One from the prop nut(with prop on)the other from the spot just before the tail. The strings must be attached to a very solid object and the same object each time. For stunt use the outboard tip needs to be straight down. Rotate the ship a measured amount one way and release it. Time it for a certain number of swings, back and forth. This will give a good reference point and I'll bet that the best planes swing the fastest.
Your results may vary. But hey it gives you stunt guys something else to measure. HAHA. .03MM

> RE; Polar moment measurement can be done. They used to
>measure twelve meter sail boats by the "swing test". Hang
>you best plane by two strings, One from the prop nut(with
>prop on)the other from the spot just before the tail. The
>strings must be attached to a very solid object and the same
>object each time. For stunt use the outboard tip needs to be
>straight down. Rotate the ship a measured amount one way
>and release it. Time it for a certain number of swings,
>back and forth. This will give a good reference point and
>I'll bet that the best planes swing the fastest.
> Your results may vary. But hey it gives you stunt guys
>something else to measure. HAHA. .03MM

This is the old "bifilar pendulum". I actually prefer a torsion spring because it's easier to explain.

I would definitely not jump to the conclusion that the lowest moment of inertia is necessarily the best - there is just too much that goes into a "good airplane" to simply limit it to one parameter.

Doug, the large prop is definitely, problem, but there is also linkage solution. There was already written lot about flaps and feedback. CG position, flap to elevator ratio do not change it too much. Smaller flaps will definitely help, on cost of worse flying properties. But you have still chance to change bellcrank/flap ratio. If you use short arm on bellcrank or longer on flap, you will limit feedback and push Netzeband wall to smaller radius even with that large prop. It will cost you more lines spacing on handle.

However, my limited experience with 4C and large prop is, that it really likes less flaps and more elevator deflection and rather aft CG position. I think it is exactly that gyro stabilizing moment. If you want turn the same radius at the same flap deflection, you must give more elevator deflection if your prop stabilizes too much. When I went to my pipe prop BE 12x3.5 3 bl on 4C engine Os Max .52, everything was back and the model got exactly the same “pipe” feeling I knew with that prop on piped .50. Does not matter what engine you use 2C or 4C – the prop is the point.

Brett, As most of these planes are built and balanced the same. I dont expect a big difference in the numbers. I do expect the hardest turning plane to have the lowest polar#(IE fastest swing times), all else the same.
Please give us a few test results.
my test is that I have built and flown about ten of the same ship with varying power. The lightest 15 engine turns the smallest prop and needs the CG at 2.25" from LE. The heaviest engine turns the largest prop and the CG is 2.75in (and could be back further).
The 15 turns 10ft loops , and the planes progress as they they gain polar moment(and weight). The three speedlimit planes all fly 77mph+-2 and the lightest prop turns inside the rest.(12ftloops) I have not added weight to the small ones to test. I could add weight to the ends and then move it to the middle for test.
If we could measure them with the engine running. That would be a huge reference. It's possible that going to a larger, slower prop would reduce the gyro. I doubt it tho as the thrust required is the same, and I guess that test would show that the thrust is very lineir with Gyro.
4 or 5 blade props on 4 strokes should be the stunt best.IMHO
( math wise)

>Doug, the large prop is definitely, problem, but there is
>also linkage solution. There was already written lot about
>flaps and feedback. CG position, flap to elevator ratio do

>...Does not matter what
>engine you use 2C or 4C – the prop is the point.
>
>igor

I am not ready to vote totally for prop when it comes to loss of turn. That heavy weight concentrated in the nose does make a difference. Our experience with big props is they will give you more pull. Just going from an 11 inch to a 12 inch on the 35 FP made a tremendous difference. Going from a 12 to a 12.5 made a noticeable difference. With the pipe ship, going from a 13 inch three blade to a 13.5 inch three blade made a difference. It will help the pull. So, if you have got pull, well, that's part of the "blessing."

On the corner, the prop will make some difference. I don't know that it will make that much difference. The extra nose weight will also make some difference. I am not ready to say which would be worse.

With Matt's ships, he has had to increase elevator movement (reduce flap movement) on his last several designs. On his latest, he has shortened the flaps to less than full span for the first time, while leaving the elevator the same. It hasn't flown yet, so, can't tell you anything beyond that. It is the reincarnation of the white ship that folded at the FAI trials a year and a half ago. Same wing (including area), same tail size, shape, and area (same tail), just reduced flap length (with incorporation of RABE rudder and a few other minor "tweaks".)

But, all this said about the prop, the extra weight concentrated in the nose will make a noticeable difference. Don't discount it when comparing ships.

One thing you didn't mention was weight. What is the weight difference between the two planes? If the pipe ship weighs less, can you add weight to it, just to see what effect this has? Add it all at the CG and fly it. Then move the weight to the nose and extreme tail to balance and try again. See what your difference is.

As to prop, here is the simplest of all. Put a 13 inch three blade on the 4-stroke and try it out. Make sure the pitch is pretty much the same or it will throw things off, but the load should otherwise be pretty equal. Fly it once with the 14 inch and then with the 13 inch and report back.

(Your assignment, if you choose to accept it, has been given to you. As always, if you experience difficulties in carrying out your mission, particularly if you should encounter the ground in an unusuall attitude while in flight, this contributor will disavow any knowledge of your aforementioned experiments.)

Len, I do not understand what exactly you mean. But I wrote about ONE model, ONE engine and two different props – large two blade 13x6 with wide tips and smaller 12x3.5 3 bl.

If you speak that larger is better – yes sometimes yes – it brings better pull, but sometimes is also smaller better if it brings better run of engine. However the stabilizing effect of large rotating prop is counterproductive, because it acts well at high pitching rates – in corner – where we do not need it, while it does not act in level flight or in straight segment, where it would be beneficial. So I think it is rather parasitic, and if model needs more stability, the larger tail, or forward CG will be much better.

So in my eyes – if more prop load or thrust, than by more blades, not by large diameter. Especially if large two blade prop is killer for plain bearing, as I wrote some weeks ago.

Igor, I think that is what I was trying to say. I am agreeing that the larger prop could add thrust and pull (as he is experiencing) but could also contribute to less corner. Matt has compensated by reducing flap and increasing elevator movement as well as widening the handle spacing. So Matt's planes will corner quite well. But if Doug's planes are both set up the same, he could be experiencing a difference because he hasn't trimmed the 4-stroke to compensate.

I am suggesting that the "bar bell" effect is in play as well--extra weight at the extremes which will also slow the corners.

I was suggesting one test for this (add weight to the extremes of the pipe ship) and one test for the larger prop. A 13 inch three blade prop should have about the same load as a 14 inch two blade (if the same pitch and blade and, well, there are a lot of "ifs")

I was suggesting that Doug try the 4-stroke plane with a smaller diameter three blade prop and just see what difference that makes in the turn. I am curious myself and thought both were easy tests just to see what the effect would be. Besides, Doug has a lot of time because the weather is perfect down there in Texas this time of year.

LAST EDITED ON Apr-02-03 AT 10:21 AM (CDT)
 
The difference in weight is 7 OZ. I know this is a contributing factor. It would be hard to add 7oz to the pipe plane at the cg.

After reading all the respones I am coming to the conclusion that running a 14" prop on a 20oz motor is going to take some design mods to get the feel that I like. Maybe that feel isnt for everyone. I like it hot and snappy. I have no doubt that it can be done. It will just take some figuring out.

There are alot of good suggestions on this board and I think they all have merit. Dia, extreme weight in the nose, large flaps, pitch of the prop. The elvator has to turn all of that. It is going to take a strong one to do so.

Len, I was thinking back this morning about a smaller pipe plane I have. When the 12" dia is on there it turns good. When the 13" is on there it pulls more yes but turns less and I tend to have to hit hard to get it to go. Now I take it one step further and add another inch and Bam it is really wanting to stay on the path it is traveling and the elevator has to work that much harder. Number of blades seems to have no effect on this. As the 12" has 4 blades and turns alot easier than the 3 blade 13" on the same plane. On the 4s I use a 2 blade.

Thanks for all the input.

If you have more keep it coming.

>The difference in weight is 7 OZ.

Nope. The "wet weight" difference is only 3 oz. The fuel use is half.

That is really no difference at all.

It is not the barbell effect, even though everyone must realize that Doug's Nats plane has a nose moment of 9" and almost an 18" tail moment with the fuel tank cut back into the front of the wing. Couple this with a 26% tail (with RUDDERLETS to make it more powerful) and pipe behind the CG and I think you will see his CG is way far back, much more than is possible with a 10" or longer nose, even on the West Coast stunters, without a substantial amount of tail weight.

Sure, the weight of the engine of the engine is a factor, but compared to what?

The 4 cycle is inherently more stable, coupled with a big prop, it is very very stable.

Its apples and oranges. An apple will NEVER be an orange.

Ask Paul Walker, if you want a "flip turn" or "snappy" or "light feel" maybe stick to pipe motors... PA's, VF's, etc.

If you want "stable" or "driving" or "Mack Truck" try a Saito 72.

>>The difference in weight is 7 OZ.
>
>Nope. The "wet weight" difference is only 3 oz. The fuel
>use is half.

At the end of the flight the difference IS 7 oz. The wet weight is always changing through the flight.

>
>The 4 cycle is inherently more stable, coupled with a big
>prop, it is very very stable.
>
>Its apples and oranges. An apple will NEVER be an orange.

I think you are missing the point. It isnt about making the 4s a 2s or vice versa. What this is all about is trying to get my plane to have the flight characteristics I like. With the any motor that is in there.

>
>Ask Paul Walker, if you want a "flip turn" or "snappy" or
>"light feel" maybe stick to pipe motors... PA's, VF's, etc.
>
>If you want "stable" or "driving" or "Mack Truck" try a
>Saito 72.

You said many times the 4s gives up less in the corners than the 2s correct? If that is the case then I would think you could corner it even THAT much harder and get no stall from the airplane or tip stall.

I am trying to do something totaly different here. I want to be able to get the flight characterestics I like from either motor. Is that a bad thing?

Your statement above seems to say it is one or the other. Are you saying that you cant get a flippy sharp corner with a 4s? I started this thread to see if I could get any ideas, and have a cool discussion about airplanes. So far so good.

I will keep working on it and see what I can find. Wouldn't it be beneficial to be able to set it up either way? Your statement makes it sound as if you dont think it can be setup the other way.

I mean you arent limited in the world of 2s motors. Low pitch high rpm or high pitch lower rpm whatever is your liking in that game.

>I am trying to do something totaly different here. I want
>to be able to get the flight characterestics I like from
>either motor. Is that a bad thing?

No. That is a good thing. I am just glad YOU CAN DO THE TESTING. I figure we have a "duel pronged approach".

I also figure if you are happy, almost every human being on the planet will be content with one setup or the other...

LAST EDITED ON Apr-09-03 AT 07:39 AM (CDT)
 
I am just glad YOU CAN DO THE
>TESTING. I figure we have a "duel pronged approach".

So when I come down and say I dont like it or it isnt there yet for me. Dont get frustrated with me and start telling me to put a 2s in there. I am trying to set this up for me the way I like it. It will take time to get the hard corner from the .72. Simply because it is going to take alot of prop to load it as you already know. It is going to be something different for sure to give it the characteristics I want.

Sounds like Paul is exploring this very same thing.

Small Diameter lots of load...hmmmm...Windy had a 5 blade once didnt he?? Anyone got one??

Sounds like Paul is exploring this very same thing.

However you might come down and like yours right out of the gate.

>
>I also figure if you are happy, almost every human being on
>the planet will be content with one setup or the other...

Content...Who wants to be content

It will take time to get the hard corner
>from the .72.

What???????????????????????????????????????????

Are you insane? What is a "hard" corner???????????????????

I obviously don't know.... I give up.

Somebody hand me an ARF....

Have you completely missed the entire point of the thread? Yes it corners hard but it is alot of work to do it. I am trying to reduce the amount of work needed to get the hard corner. Right now if you went out a flew it for fun and didnt really work at it it would not corner worth a darn.

It is exhausting after about 3-4 flights. You said this about sheer panic last year. More than 4 flights and you were tired from the plane. I dont feel the plane should always feel like it is working against you. But that's just me.

There have been many good ideas and discussions on this thread.

One thing we have found with the larger diameter is that you can move the cg back further without it getting jumpy. That, in turn, brings back the corner. The CG location is kind of funny, also. We measure and think it is about right, but add a little tail weight, the CG doesn't seem to move, but it makes a difference in the turn. There is a spot you have to go back to, I guess.

On the adding weight theory, if you have a fuselage mounted gear you might be able to bolt some weight there. Then add a little tail weight to balance. Or add tail weight (solder on the tail strut) and nose weight while keeping the balance. It would be interesting to see how the two planes would react if you brought the pipe ship up to the same weight by adding weight to the extremeties. I am sure it would slow the turn.

I know Bob Gieseke now likes the 4-blade prop, but Matt prefers the larger 3-blade. If you would have access to a 12 inch 4-blade, it would be interesting to see what difference you would find using it on the 4-stroke. You would need to keep the pitch about the same, however, or rpm could through off the experiment as well.

Yes - now I understand Len. My LA powered piped model uses 12x3.5 two blade prop. I tested the same just three blade prop. The engine did not work so well, but it still acceptable. I did not touch pipe, carb even needle was as I have it for 2 blade. The level speed did not drop down, but overhead tension was lower. However signifficant difference was in corners - it was more open, and I also feeled worse repeatability - it was more difficult to hit 90 degrees every time. I note that it was only difference of 3 grams.

>Yes - now I understand Len. My LA powered piped model uses
>12x3.5 two blade prop. I tested the same just three blade
>prop. The engine did not work so well, but it still
>acceptable. I did not touch pipe, carb even needle was as I
>have it for 2 blade. The level speed did not drop down, but
>overhead tension was lower. However signifficant difference
>was in corners - it was more open, and I also feeled worse
>repeatability - it was more difficult to hit 90 degrees
>every time. I note that it was only difference of 3 grams.

We had to spend a lot of time on the "learning curve" with the pipe ship. We ran everything from 2 to 4 blade props and from diameters of 11.5 to (now) 13.5. We found that with less load using a 2-blade or shorter diameter 3-blade we had to run shorter pipe lengths and higher launch rpms. With the big 3-blade prop we had to lengthen the pipe to get the proper run. This might be why you experienced less overhead tension. Lengthening the pipe may help.

Of course, you are running the LA, so what it will turn I don't know. You may have hit the limit for the engine and started to strain it. But, all things considered, the bigger prop just needed to have a slightly (and I do mean slightly) wider handle spacing to get the same corner. We have switched back and forth between the 12.5 and 13.5 inch prop and the 13.5 gives the better overhead tension without any loss in the corner. Matt has the cg pretty far back and I don't recall it needing a lot of hand pressure to make it turn, either. We had too much overhang on the handle for a while which then made for excessive pressure from the handle, but shortening the overhang solved that. I don't know if that would help Doug, or not, but that is another thought for the equation.

Hi Doug,

Well, you certainly have a lot of advice. I've done better with 4S engines by using smaller props with wider blades, but could just be me. Can't wait to test out a home made prop I'm building that is done from RevUp 15x5 THP props. Will be a 12.5 3 blade re-pitched to 4.25. Should be interesting.

So, try a smaller, multi-blade prop. I'd think about bigger elevators rather than smaller flaps. But that's probably just me.

>So, try a smaller, multi-blade prop. I'd think about bigger
>elevators rather than smaller flaps. But that's probably
>just me.

Good Call!!

Counter balances are also getting a close look down here in TX. Even small ones seem to have a major effect on the turn abilities. I would add some but I have stablets on my plane. It makes it tough to put those on without surgery.

Doug,

I ran into this exact thing when I switched from a 56 to a 72 saito. The difference turned out to be the PROP. The 56 used a 13.5 * 5.0 3 blade with fairly thin blades and the 72 used a 14.25 * 5.0 2 blade with fairly wide blades. The 72 would barely turn the plane with the 14.25 prop, and when changed to the other 3 blade, most of the corner came back even with the 2 ounce heavier engine.

Try a smaller 3 blade and see if that helps.

Also, the new Mustang this year is 10 ounces lighter than last years (yes, 10 oz lighter). It is night and day different than last years. It will now almost corner with one of my good Impacts. 30 degree patterns, no problem. This with a 72 and 13.5" 3 blade prop. Weight is also a factor in corner.

Listen to Godzilla ....Don't give up on the 4-stroke yet, BUT it is an entirely different feel than any piped plane I have flown. It WILL take some getting used to. I now fly a piped plane and wonder what happened to all the power I thought they used to have, yet they still hang out there!

I have found that there are many variables in considering how two "identical" planes behave. I have build numerous Impacts and there are good ones, and ones that are not as good. They are all within 2 ounces of each other, come out of the same jigs, but there are lots of areas where little differences can add up to make a big difference. A better comparison would be to take the piped setup out of the plane and drop in the 4-stroke. This eliminates many variables.

I mentioned above about measuring the gyro affect/polar moment with the engine running. Some quick math and a book or two show that the prop is the larger hinderance to the turn than the minor polar moment difference. Bearing in mind that a larger engine will always require a larger tail effort to turn it.
I also thought that if you bolted a engine /prop/tank to a swival chair base and measured the torque required to rotate it while running... The gyro effect of the props could be measured against each other. Dont foreget that a four stroker has more whirly gigs inside and thus has more designed in gyro stablity.
RE; balanced controls raise the Netzband wall because of the reduced control loads.
.03MM

Paul,

I agree. Seems to me, from my own limited experience that smaller diameter props, particularly 3 blades, with somewhat wider blades do better. Problem I've had is that in order to extract the more power out of the engine, I've gone to somewhat bigger venturis and that usually means, with the 4S I've used anyway, more rpm (and fuel consumption) on the same prop. So I've gone to wider blades to put a bit more load on the engine and bring the rpm down and transmit more of the additional torque garnered with more fuel and air running through the engine.

But even with pretty large diameter props, I haven't had much problem with turning, per se. But that's probably because I've been using ridiculously long tail moments with really large stabs and elevators. But the "feel" of the plane is much better with the smaller diameter, wide blade props. Just seems more under control with a lot less load on the controls.

Just a neophyte's view of experience.

>Also, the new Mustang this year is 10 ounces lighter than
>last years (yes, 10 oz lighter). It is night and day
>different than last years. It will now almost corner with
>one of my good Impacts. 30 degree patterns, no problem.
>This with a 72 and 13.5" 3 blade prop. Weight is also a
>factor in corner.

Wow 10oz. That is huge! It must be so much more friendly to fly. It must be so much more nimble.

I am making my first attempt at take apart construction. It is coming out nice but I think it is going to be heavy. Oh well the journey continues...

>
>Listen to Godzilla

Do I have to (Just kidding Brad) He keeps handing me these 14" 2 blades that look like they were made in Heaven. Just works or art! However he says he has 2 smaller three blades he wants me to try out. I can't wait to get a few runs on them. I let you all know what I find. I am sure it act just as you say.

What I would really like to have is a smallish diameter 4 blade. 12" to 12.5" undercambered. Man that would rule. I could go back to a more forgiving 1:1 ratio.

If it would ever quit blowing we could try them out. We may not get to fly again until June. It did this last year. 20mph steady with 30mph gusts until mid to late May. It is very frustrating.

>
>If it would ever quit blowing we could try them out. We may
>not get to fly again until June. It did this last year.
>20mph steady with 30mph gusts until mid to late May. It is
>very frustrating.

Oh.....You would prefer the rain we have instead?

Paul,

And the wind, you forgot about the wind. I love flying whenthe rain comes in horizontal.

Hey, it will stop raining eventually. If like most years, should stop the weekend after July 4th.

>>Listen to Godzilla
>
>Do I have to (Just kidding Brad)

Yuck it up, Moon Pie...

Doug,

After reading and re-reading 'zilla's moment of inertia thread that concluded that the 4S would have somewhat less of a moment of inertia due to fuel load being less and such - I am wondering how identical planes except for the engine got to be 7 ounces different? Of course that amount of mass out on the end of the lines is going to change just about everything! Including amount of corner available. I bet if you could find a way to lighten it up about 4 ounces it will do much better corners and have a lot better overall feel. Using a 13" four blade prop would probably also help a good bit. Keep working at it you'll get it flying and feeling better - it just takes time with something that's fairly new.

LAST EDITED ON Apr-04-03 AT 09:07 AM (CDT)
 
>Doug,
>
>After reading and re-reading 'zilla's moment of inertia
>thread that concluded that the 4S would have somewhat less
>of a moment of inertia due to fuel load being less and such

Cool. Somebody actuallly read it (I was starting to wonder). I keep posting the same calculations. Every time I do the board goes silent...

Basically it is the shorter nose.

The moment of inertia is proportional to the SQUARE of the distance. Once the nose length is set to balance the airplane at the same spot as with the lighter 2 cycle engine, actually the moment of inertia is reduced.

>- I am wondering how identical planes except for the engine
>got to be 7 ounces different?

They are not identical. The Furias has a much bigger fuselage and a lot more beef in the front. It also has a nearly 2 oz spinner (that is nearly 1.5 oz gain right there).

Also, like I said before the wet weight (true weight)is only 3 oz different.

>I bet if
>you could find a way to lighten it up about 4 ounces it will
>do much better corners and have a lot better overall feel.

????????
This airplane already corners like a maniac.

>Using a 13" four blade prop would probably also help a good
>bit.

I am going to make Doug a 12.5" 4 blade just to shut him up (I have one at the house). I am sure it will work just fine.

Let me explain something. I told Doug the same thing. I never really worked on trying to make the 4 cycle feel like a piped motor (nirvana right?). I certainly feel this is possible, and should be not be a real trick with a smaller diameter prop (I have several). I just simply had no interest in making the Saito 72 "feel" like a 40/60 piped motor. In my opinion, the 4 cycle is capable of an entire new level of "feel", one that has yet to be attained. It will not be a piped motor feel, that is for sure. Some will say that is too bad, because the piped motor is better.

Doug kind of hit the nail on the head. A 91 Saito swinging a 16" prop on a 60 oz plane that will groove like a freight train and turn hard and smooth. Bring on the wind, bring on the junk...

Brad wrote:
>
>Basically it is the shorter nose.
>
>The moment of inertia is proportional to the SQUARE of the
>distance. Once the nose length is set to balance the
>airplane at the same spot as with the lighter 2 cycle
>engine, actually the moment of inertia is reduced.
>
Ok Brad....as interpretted from Websters a " Moment" in mechanical terms is A." A tendency to produce motion, esp. about an axis" and B." the product of a physical quantity and its distance from an axis"

....and Inertia, "the property of matter by which it retains its state of rest or its (velocity) along a straight line so long as it is not acted upon by an external force." ..Velocity......with gravity being the one constant external force upon this state of rest, wouldn't this thereby reduce the amount of reaction time or quick reflexes necessary to return a flying model to its normal flight path? Therefore, causing some problem given a certain shorter moment distance forward of the CG. Especially, when headed toward terra firma and executing a 10G turn with say 3 to 5 more oz.!

It seems to me that this could act equal and opposite of a positively balanced, slightly tail heavy model airplane. This would concentrate into the short moment, from the CG forward, making the task of appropriate balance more critical than a slightly tail heavy airplane. Also making nirvana that much more incrementally hard to find!

Also, a positively stable model has a fairly wide range from tail heavy to nose heavy, which is easier to adjust about the CG from the tail than the nose.

In short, but grudgingly so, given the already mentioned weight....if prop does not cure Dougs problem.....I would add minute amounts of tail weight until it turns like Doug wants it to without dragging him out of the circle.

Here you go:

http://www.umich.edu/~amophys/125/eighteen/node5.html
http://moon.ouhsc.edu/dthompso/gait/kinetics/mominert.htm
http://www.scientia.org/cadonline/Physics/equilibrium/moment.ASP

I have read the MOI posting of Brads many times. Yeah the fuel load is less but the load of the motor is more by a fair amount. But the total is very comparable. You remove some of the load of the fuel and just dump it up on the nose of the plane. And at the end of the pattern the MOI has to be different because there is no fuel in either plane and the 4s plane then has a much heavier front three inches. MOI seems like it would have something to do with it. I cant prove it but it makes sense to me. It seems to me after thinking about it that if the first 3" of your plane weighs 20oz then it is deffinently going to be harder to turn than a plane with similar nose moments where the first 3" is weighing only say 14-15oz. Just seems like it would.

I still think the prop has more to do with it. Ted is right. If the props become much larger the designs might have to as well. With a much larger plane this would not even be an issue.

Believe me I know it(4s) is different. I have been messing with 4s motors for about 5 years now. I have had many different 4s motors in many different planes, Saito 50,56,72, Enya 53 with a cool starting choke, OS 26,26c,53, YS 63 with on a pipe(VERY FAST), and tried lots of different fuels. Now I have built a 2s design with a few minor changes for the sole use of the 4s. Before it was always retro fits or profiles. It will take some time.

The plane is already really close I just have to fiddle with it. I am very picky when it comes to getting it flying like I want it to. I love to talk about planes so why not start a thread about mine? Brad says I tend to over complain about the little things, and would sometimes rather slap me in the eye and tell me to get out there and fly it again. (Maybe sometimes I do need a slap in the eye , thank god it hasnt happened yet) Well I see it as trying to get it as close as I can to what would be the best trim for a certain plane. If I come down and complain and comment on the bad stuff about the plane there are usually some very talented flyers at our field and they always have some good advice and most of troubles get worked out. Trim out can go quickly with many sets of good eyes around the circle, believe me I am very thankful for this and do not take it for granted. I know there is a happy medium for all setups so I just get it as close as I can then practice practice practice...

By the way Paul, now we have the wind and the rain...Thanks

Doug replied: By the way Paul, now we have the wind and the rain...Thanks

Glad I could be of service!!

I was out this weekend with my new Mustang and played with props. Very interesting considering the timing of this thread.

I basically used 4 props.
1) Standard prop from last year's Mustang. Bolly 3 blade ~13.5 dia, 5.0 pitch (constant).
2) Same prop but at 5.25 pitch
3) 4 blade Bolly, ~13.0 dia, 5.0 pitch (constant).
4) Eather 3 blade (flatback) 13.0 * 5.0 pitch (droping slightly at tips). Blade is wider than a Bolly 3 blade.

ALL props tracked in level flight and rounds almost the same. The corners is where the varied. The tightest corners came from...

Prop 1) Clearly the best in corners. Next best...
Prop 2) Almost, but a little more stick force in corner, slightly larger radius. Next best...
Prop 4) Eather prop did slow the corners noticeablly...And finally,
Prop 3) 4 Blade was a total bust...Very large increase in stick force and larger radius.

The bollys' turned tighter even at their larger diameter. They didn't hurt for line tension in the overheads, so it seems to be a win-win situation here. The 4 blade has approximately the same blade shape as the 3 blade, but an extra 33% inertia over the 3 blade. Pitch also slowed the corner.

I have tried the 14.24 * 5, 2 blade bolly in the past and that was MUCH worse than the 4 blade. Considering that D^2 is dominant, it is no surprise that this prop with it's big wide blade would be a problem (in this context).

Bottom line: If you want corner you need to minimize the props inertia...Smaller diameter and less pitch......

Now........How about a 11.3 * 4.0 prop on the same size plane. Wow!! Where have I seen this before?

LAST EDITED ON Apr-07-03 AT 02:11 PM (CDT)
 
>
>Doug replied: By the way Paul, now we have the wind and the
>rain...Thanks
>
>Glad I could be of service!!

You even gave us same Tennis Ball sized Hail at Brad's house..I am sure his jeep thanks you for it...

>
>
>I was out this weekend with my new Mustang and played with
>props. Very interesting considering the timing of this
>thread.
>
>I basically used 4 props.
>1) Standard prop from last year's Mustang. Bolly 3 blade
>~13.5 dia, 5.0 pitch (constant).
>2) Same prop but at 5.25 pitch
>3) 4 blade Bolly, ~13.0 dia, 5.0 pitch (constant).
>4) Eather 3 blade (flatback) 13.0 * 5.0 pitch (droping
>slightly at tips). Blade is wider than a Bolly 3 blade.

What kind of RPM range are you running in? Do you get the same range in all of your props. By range I mean 200-300 rpm, or is all over the place?

>
>ALL props tracked in level flight and rounds almost the
>same. The corners is where the varied. The tightest
>corners came from...
>
>
>
>Prop 1) Clearly the best in corners. Next best...
>Prop 2) Almost, but a little more stick force in corner,
>slightly larger radius. Next best...
>Prop 4) Eather prop did slow the corners noticeablly...And
>finally,
>Prop 3) 4 Blade was a total bust...Very large increase in
>stick force and larger radius.
>
>The bollys' turned tighter even at their larger diameter.
>They didn't hurt for line tension in the overheads, so it
>seems to be a win-win situation here. The 4 blade has
>approximately the same blade shape as the 3 blade, but an
>extra 33% inertia over the 3 blade. Pitch also slowed the
>corner.
>
>I have tried the 14.24 * 5, 2 blade bolly in the past and
>that was MUCH worse than the 4 blade. Considering that D^2
>is dominant, it is no surprise that this prop with it's big
>wide blade would be a problem (in this context).
>
>Bottom line: If you want corner you need to minimize the
>props inertia...Smaller diameter and less pitch......

But you said Prop 1 had the best corner and it had the largest Diamter right??? Pitch creating intertia between prop one and two.

I guess blade area is really coming into play here???

Seeing as how the 4b was smallest diameter but the corner was a "Bust" the blade area of 4b is more than 3b thus causing more prop intertia? The pitch was the same as prop one so if it were totaly diameter related it would turn the same as prop one.

Depending on the rpm maybe a little less pitch or length or both on the 4 blade and you could still keep the motor loaded enough to run correct then you really get laser corners.

Of course you already know all about laser corners as your last statement and your style and your record tells us.

It all works together. As John Grigsby says "It all VooDoo aerodynamics in control line."

>
>Now........How about a 11.3 * 4.0 prop on the same size
>plane. Wow!! Where have I seen this before?
>
>P. Walker

I think we all have seen that before...

I have a dumb question for you Paul. Matt has been using that 13.5 diameter 3-blade Bolly with close to stock 4.25 pitch and a little extra at the tips with his PA 61. There is an extended version that goes out to 14+ inches with the tips almost coming to a point. Matt tried that with his PA 61 but it started to bog it down with the same number 9 venturi and 5% nitro fuel that he was running. A larger venturi or more nitro might have done it.

But I am wondering on your 4-stroke if you have one of these to try. There wouldn't be a lot of extra weight out there with that prop, but the extra diameter does add thrust. Matt said he could definitely feel the difference. Just a thought since you said the 13.5 so far was your best prop.

I am also wondering if you tried the heavier pitch at the same rpm or slowed the engine down a bit to maintain the same lap times. Trying to understand how this affected the turns.

> Pitch also slowed the
>corner.

?????? More pitch?

>Bottom line: If you want corner you need to minimize the
>props inertia...Smaller diameter and less pitch......

Diameter, OK. Pitch? With a 4 stroke? I think most will definately misread this statement to mean high RPM low pitch like a pipe.

this looks like a prop problem, related to the gyroscopic effect of the prop. I got as far as calculating the angular momentum(mvd) of a 12 in. prop(17.2) and a 14 in. prop(30.6). I didn't go back and dig out all the math for calculating gyro effects, but the force required to turn a gyro has to be related directly to the angular momentum. This kind of calculation confirms that bigger props take a lot more control force to turn. It's also related to the prop mass. These were wood props. An APC weighs over twice as much and would change the angmom. proportionately. So just as a rough approx. the stab needs to be twice as effective and generate twice as much lift to make the plane turn as easily with a 14 in. prop vs. a 12 in. prop.

You can fudge some(and people probably do every day) by adding some tail weight. That reduces the stability but also reduces the aerodynamic forces the stab has to overcome, leaving more to turn move the prop.

LAST EDITED ON Apr-06-03 AT 06:38 PM (CDT) by LNeumann (admin)
 
Mr Grogan's post got erased because I got tired of him.

"grogan", you say it is your first time on this forum. It will be your last if you keep insulting everyone you post under. This is the third posting of yours that I have deleted in this your first day. You have no e-mail so I cannot contact you directly. But I expect that everyone on this board will act decently. There is no excuse for these insulting, "know it all" remarks, and I will not tolerate them on this board.

grogan,

Doug Moon did place in the top 10 at the US nats last year, a great achievement, not something a goose as you put it would do easily. The fact that he is prepared to post a question, no matter how basic it seems to someone else doesn't mean he deserves ridicule. Your comments aren't very fair.

Yes we do have a flier here in Australia who beats us all with a profile model. Simply put he practices a lot with reasonably sound gear. If the rest of us pulled our fingers out and flew a bit more regularly things would be closer, but yes it is frustrating, but someone has to win, and someone has to come last.

LAST EDITED ON Apr-07-03 AT 09:01 AM (CDT) by LNeumann (admin)
 
"yep I got an idea," (and grogan's idea got deleted.)

This is the fourth delete "Mr" Grogan. Please register, tell us who you are, and act in a civilized fashion. Otherwise, you are not wanted on this board.

Humor is one thing. We do joke around a lot on this board. I do not expect people to inslult, however, especially when you don't even know the people. I have better things to do than to follow you around and constantly delete. So...

Please register, tell us who you are, and act in a civilized fashion. Otherwise, you are not wanted on this board.

Enough warnings, OK?

Grogan???

Since you are going to come on flame people why dont you be MAN enough to use your real name? Or did your momma forget to teach you how to be a man?

Doug Moon

LAST EDITED ON Apr-08-03 AT 08:29 AM (CDT)
 
Doug,

Well, I think he was trying to get a rise out of you...and he did. Shades of Floyd!!!

>yep I got an idea, someone feed that Moon runt a hamburger,
>looks like his mumma didn't teach him how to eat. Hows a
>little weed like that supposed to hold onto a 72. does the
>stunter fly him, or does he try to fly it?

I know, I know, in YOUR WORLD you's a funny man...

I know I get a chuckle...

...especially at the thought of planting of my size 13 Nikes across your neck and watching you kick and scream like the BIG GIRL that you are...

Sorry, Len. Couldn't stop myself.

Doug, 'zilla,

Grogan seems to be of the Rickles humor crowd. Of course I never found anything humorous about dandy Don. Could this really, be Floyd in disguise?

Fer, di d you find some real numbers? can one maybe reduce the Gyro force and increase the thrust by changing to a smaller prop and higher Rpm??
ow about a large,slow prop ?? 4 blade carbon? vs two blade carbon with equal thrust.
Maybe we should fly ducted fans??
MM
Pre post edit. My planes all require the same thrust to fly at 77mph.
the 9x6 has the most rearward Cg and the biggest turn.: I should state that the thrust is the same as the smaller prop but the Gyro # is much greater,Correct?. The bigger prop cuts more streamers. MM

>Fer, did you find some real numbers? can one maybe
>reduce the Gyro force and increase the thrust by changing to
>a smaller prop and higher Rpm??

I don't have numbers, but, remember, higher rpm also increases the gyro force. Using the same prop, one with higher pitch and lower rpm and one with lower pitch and higher rpm, the one with higher rpm would have more gyro force.

> How about a large,slow prop ??

See above.

>4 blade carbon? vs two blade carbon with equal thrust.

If the blades are of equal size and the prop is turning the same speed, lap times will remain the same, available thrust will be vastly improved with the 4-blade, and gyro force will be proportionally larger.

> Maybe we should fly ducted fans??
>MM

I realize this is "tongue-in-cheek", but I have mentioned this in previous posts concerning the efficiency of larger props. Ducted fans are whirrling at extremely high rpms and their engines, generally, are turning out tremendous horsepower numbers, but their efficiency is nowhere near what that kind of power would produce in terms of thrust if harnessed to a larger prop.

>Pre post edit. My planes all require the same thrust to
>fly at 77mph.

Just remember, you are talking about the amount of thrust used to maintain that 77 mph in level flight. It is the same argument as say putting a small 4-cylinder engine in a car like, say, a Pontiac Bonneville and also using their standard larger 6-cylinder engine. Either engine could run the car nicely at the 65 mph speed limit down a level interstate highway. But, when the car comes to a hill, the car being "towed" by the smaller engine will bog down while the larger engine car will just cruise right on up. The same thing happens to our planes. It is not just level flight, but how much we slow down in the turns and the corners, or even in the vertical eight and the hourglass (or whatever else you do with a combat ship. When you go "up" you need more available thrust. And if it is not there, it is not there. Even acceleration in combat is important.)

>the 9x6 has the most rearward Cg and the biggest turn.: I
>should state that the thrust is the same as the smaller prop
>but the Gyro # is much greater,Correct?.

The thrust being used in level flight, maybe. The available thrust when needed for acceleration out of a tight turn or when flying uphill, no!

>The bigger prop cuts more streamers. MM

That is an argument I have always considered. Even if you could somehow turn tighter with the smaller prop, the bigger prop on the combat shjip will give you a bigger cannon with which to shoot the other guy when you have him in your gunsight. It might be a deciding factor. (Remember, the extra inch, or whatever, is not only in the up and down direction, but right and left as well. Do you always have your hand directly in line with your opponent? I hope not. You make yourself too easy of a target.

LAST EDITED ON Apr-09-03 AT 11:28 AM (CDT)
 
Boy this thread is getting long. Forgive me if this is reduntant to someone else's input.

Doug, Here's an idea you might want to try. Assuming there is validity to pretty much all the input you've received there is a reasonable way to experiment without the use of knives on balsa wood. Here's what I'm thinking.

All the things we've discussed, MOI, prop gyro inertia, smaller flaps, etc. point toward a need to get more elevator authority without, hopefully, increasing stick forces event further. Tiny flaps will reduce stick forces for sure and simultaneously reduce adverse pitching moment...all well and good until you address the issue of wing loading and the lost lift coefficient that comes with the use of effective high lift devices (the cambering effect of the flaps). As noted, weight (wing loading) becomes critical even though power loading is almost excessive. Not a good combination.

Reducing flap movement is probably better than the tiny flaps but it is still a matter of degree and the wing loading issue will be less but no less real.

The aero balances on the elevator would seem to have merit and should be tried. If they're added to the tips of the existing elevator they should unload the controls pretty effectively which will solve part of the problem.

The other issue, simply getting enough lift out of the tail to overcome the MOI involved requires a slightly different approach. You can certainly go to a bigger stab/elevator area but, especially at the same aspect ratio as the existing one, control loads due to deflection will be even greater.

On the other hand, you could add area only to the stab...tape on a doubled over piece of cardboard to the leading edge thus increasing the stab chord by, say, 3/4". This will increase the total area of the horizontal stab/elevator and make any deflection you apply produce more lift. More lift = greater torque about the CG which = a tighter turn for the same deflection. As a result you should be able to achieve your desired turn rate at lesser deflection thus reducing stick forces.

What d'ya think? Worth a try?

To take the idea a step further (and include the use of knives and sandpaper) you can make a stab/elevator of the same area require less stick force by increasing the aspect ratio. Air loads go up by something like the square of the chord of the deflecting surface. Thus an elevator of a given area that is long and narrow will produce require much lower control forces than will one of identical area that is short and long.

An added benefit of the increased AR is the fact that for a given area the higher AR will produce more lift for a given angle of attack (in the case of a stab/elevator, a given angle of deflection).

Thus, you can get the lift you need to overcome the problems inherent in your 4C ship with likely less control force required than the piped ship by simply reshaping the tail and, if you choose, using a lower percentage of the chord for the movable surface (down to about 25% if you want to get crazy about it...I think 35 or 40% is a better choice.

You probably wonder why I'm advocating the higher AR when I have clearly argued the case for low AR in the past. Understand, I'm addressing the specific issue in question. Given the ability to achieve the turn you desire with control forces you can live with I'd still advocate as low an AR as will achieve that goal.

The low AR produces more drag for a given amount of lift produced and I believe moving the center of drag aft when maneuvering is valuable...as long as you can move the elevator!

Which brings us to...larger bellcranks....maybe another time. Shareen just announced hors d'ouerves and cocktails on the dock...wonderful what attention you get after one's spouse flattens one's Nobler! Almost worth it....almost.

Dougie,

I've done some experimenting this weekend the results of which may be of some help to you.

Your using the tip plates/rudderlets on your tailplane.

I went out and flew my old Bear, on which I had extended these 3/8 both top and bottom. It has made quite a noticable difference to the effectiveness of the tailplane. My reasoning for this came about when I had observed that the tail seemed to stall if I used more control. I taped a piece of paper to the fuse side, and a spring loaded marker to the root of the elevator. I flew the model with lower movement and marked the extent of the movement, then had another flight with wider handle spacing, in which the tailplane appeard to stall. The interesting observation came that the lower movement flight didn't have the elevators move above or below the tip plates, whereas the larger movement flight they did. The obvious conclusion being that once the elevators go beyond those tip plate their use is negated. The extended tip plates have allowed me to use the wider spacing without the aparrent tail stall of before. Also of note is that even lower movement manouvers like loops seem to have benefited. This is where I tought of you post here. If you were to extend these in a similar manner you may get the same corner with slightly reduced movement, and thus less control system load.

A note here that the tail on my Bear is 1" more span than the plan.

just thought I'd share this with you. It's possibly less relavent on models with larger tail areas, but significant on models like the Bear which have small tails.

thought I'd share this with you. It's possibly less
>relavent on models with larger tail areas, but significant
>on models like the Bear which have small tails.
>
>BRI

That is a cool post. I just love "taping stuff to the plane" stories. Some tape and some scrap balsa can prove more in an afternoon than 5000 hours of debate over "theories".

good stuff...

>That is a cool post. I just love "taping stuff to the
>plane" stories. Some tape and some scrap balsa can prove
>more in an afternoon than 5000 hours of debate over
>"theories".
>
>good stuff...

I agree. Some of these ideas just need to be tried. I would be interested, myself, to see what the result is, even though, at present, I am not a 4-cycle enthusiast.

LAST EDITED ON Apr-18-03 AT 11:01 PM (CDT)
 
Correction. The CG on the 72 plane was further forward than initially thought. However, at times I had it moved back and the plane became very unstable yet handle loading in hard corners was very high. The tendancy to wheelie out a of a corner was always present with the far aft CG on the 72. It takes alot of handle load to turn it then all of a sudden it pops through and a wheelie occurs.

As Brett said before adding tail weight has a much larger effect on the model then reducing nose weight. At times when I would have the cg aft with the 72, by adding tail weight. I was trying to make up for the engine's weight and add some corner. It would cause it to get jumpy before I could get the cg as far back as I thought I would need it to get light handle loading. This proves his point perfectly. In this situation you could not add enough tail weight to make up for the the weight of the 72 and get light handle loading. All that aft weight gets to moving and it doesn't want to stop. Then the wheelies start.

MOI is a HUGE factor!!!! How do I know this?

Yesterday I bolted in Bob Reeves' Saito 56 with the largest Venturi that UHP offers installed on a UHP manifold. I had tested it on the bench and it turned the very same 14" prop I was using on the 72 300 rpms faster! Bob reeves your 56 is a Monster. My 72 has the smallest venturi in it to get it slowed down to a decent lap time. Depitching to slow the lap times can lead to a racing and over revving engine. Load is key in the 4s land. Using venturi sizes is a very good way to regulate speed. Basically changing the "Throttle" opening the slow way. Getting needles becomes a snap. You just set it balls out and go!

Now the nose of the plane is 3oz lighter than before! Also bringing the overall weight down to 63oz.!

Now the CG is further aft than it ever was with the 72.

At this point I am fearful it will be very unstable and very hard to fly. I should have known ahead of time that this CG was going to be ok. The Nats plane a very close cousin has a further aft cg still, not by much though. I know from the many posts here on SSW that the static margin between the CG and the CL on this particular design was still great enough with the 56 installed to create a stable flight path. Not to mention it will be swinging a 14" prop. I was running into troubles before due to excessive ADDED weight way back in the tail causing unwanted gyrations and all kinds of funny stuff. See Ted and Brett someone is reading and learning. At least I think I am...

Nothing else changed! Not one thing! Kept the same prop, fuel tank setup, lines, handle, everything the exact same!!!

Went and flew it yesterday, 4/16. 4 flights. The lap times were actually a little faster, 5.10-5.25, however, the plane turns on a dime with HUGE reduction in handle loads! I even had it slowed down to a 5.5 lap for a couple of flights and it was actually very very sensitive. The first square turned into a triangle due to over control. The corner was very snappy to say the least.

Yes 3oz redution on the nose moves the CG way back but it is still stable. I could never get the cg this far aft with the 72 close but not as far as I needed. All the added tail weight would have very adverse effects in hard corners. Yet with the 56 and the WAY aft cg it would cruise along nicely.

Now I feel I can go back to a 1:1 control system and get more consistancy with it. If it loads up a again I can make the changes to lighten it up.

One of the most impressive things of the day was the 56 pounding out the power. I have now installed the mid sized venturi trying to get the max RPM to yeild the 5.4 lap time. It should be right in there close. With the large reduction in nose weight yet the same large 14" prop it shows real promise. It was the most fun I had with that plane yet!

I will keep you posted on any other findings. Like the 1:1 controls...

Brett mentioned in an earlier post about equal masses just change the nose length to accomodate the weight of the motor to get the desired CG. This is a great thing to remember when trying for a new design. I did not know how to do this when I was building this plane. I just thought .25" would help. I knew it wouldn't be far enough but I didn't want to end up to short. I should have done more research to get the plane setup to hold the 72 at the desired cg. Al Rabe mentioned on another thread about how he comes up with a tail moment prior to building. I think I will do some more research before I start agian on a new design. However, this has been a great learning experience. Lots to think about as I watch the 30mph winds blow and the new PA 65 eat a gallon of fuel on the stand...

Doug,

Well, now you know why my Saito 56 has a .320 venturi and a force feed fuel system. The more fuel and air you can stuff through, the more power you get. To a point anyway. I was using an Eather 3 blade undercamber prop and the engine was a monster in the wind.

Doug, Thanks for the update. Cool

1:1 proved out just as I thought. It slowed it down of course but it became very predictable. Handle is about the same. The movement needed was more as expected.

I added a little tail weight to see what it would do and 3/8oz helped it some and there were no adverse effects.

The over head performance between the two motors is almost identicle.

The two motors are now setup to turn the very same prop at the exact same rpms. 8400-8500 rpms. This being the case I see no reason at this time to put the larger motor back in. All it does is add 3oz to the nose and hole bunch of unwanted line tension and handle load.

The 56 souped up and the 72 choked down. I think in this one I will take the 56 for now...it stiil has to get hot down here....

The jury is still out but I am now really having fun.

Now comes the tough part. Stopping the exit acceleration. I think I got an idea on that one...

Keep you posted.

MOI is a HUGE player!