Trim questions.

I have a trim question.

My Nats plane the one I fly in competition has never had a good neutral setting. I have tried all kinds of settings on teh handle. It is very close but wont come in.

I fly on a bar handle. I have tried a Ted handle on cables and it will not come in no matter how I set it up. I think the bar handle is masking a bigger problem.

The thing is it is so hard to tell which the controls are out. There is something out on the pushrod as far as how long it needs to be. I just dont know which way to go. I can make the controls to fast up or down by adjusting the length of the lines. How do you really know which the controls are out? It hunts inverted and isnt that much better upright. It can still fly it very well and just work my rear off to hold it level during the judged laps.

I have decided to start over at the begining and retrim the whole plane. However this level flight and equal turn issue is still a question I cant resolve.

Any tips on where to start?

I have Walker's chart but I still cant tell which way to go...???

Brad says I might want to try down thrust. I am going to add in down thrust into the motor and work from there like it is a brand new plane.

Well Doug,

Need more info. Does the stab have any negative incidence. If not, there could possibly some incidenice disagreements? One known way of fixing things is to set up the elevator with some down bias with the flaps exactly neutral. The other way is putting some down incidence in the engine. With fully adjustable controls, I think I would opt for the elevator down bias. How many flights do you have on this plane anyway? It's just a little late to do a complete re-trimming job before the Nats. After you get it where it needs to be, there is the practice needed with that setting of course. Sounds like you are going through a bummer period here?

>Well Doug,
>
>Need more info. Does the stab have any negative incidence.

As far as I know there is no there is no Neg incidence in the stab.

>If not, there could possibly some incidenice disagreements?
>One known way of fixing things is to set up the elevator
>with some down bias with the flaps exactly neutral.

Yes I love this way of setting up the elevator. All of mine are this including this one. However I am still fighting it. I have even had it so far that it raises the tail in flight.

The
>other way is putting some down incidence in the engine.
>With fully adjustable controls, I think I would opt for the
>elevator down bias. How many flights do you have on this
>plane anyway?

Oh, around 500-600. Yes this is a lingering problem from day one back in '02. It was just so far beyond anything I had at the time I could work with it.

It's just a little late to do a complete
>re-trimming job before the Nats. After you get it where it
>needs to be, there is the practice needed with that setting
>of course. Sounds like you are going through a bummer
>period here?
>
>Jim Pollock

I cant stay for the Nats this year so it isnt a problem. I think I have been flying the plane out of trim for a long time.

Funny thing is in Muncie the problems are almost totaly gone. But here it is a battle and I am tired of it.

Here is a pic of the plane. It is the one on the back left.

Doug,
Here's a simple test before you add the downthrust (2 questions). Is the hunting mild? Does the hunting seem to go away or decrease toward the end of the flight? If so it is nose heavy. You might be on the fine edge of finding the perfect CG. First try moving the leadouts forward 1/8" at a time and you just might cure the problem without adding weight aft the CG. If not try adding small amounts of weight aft the CG about midway between the flaps and stab.

>Doug,
>Here's a simple test before you add the downthrust (2
>questions). Is the hunting mild? Does the hunting seem to
>go away or decrease toward the end of the flight? If so it
>is nose heavy.

If Doug's plane is nose heavy, I am soooo screwed.

I would however, agree with Phil that an accurate measure of the CG location is the FIRST THING I WOULD DO. All of Brett and Ted's recommendations rely on an accurate measure of the CG location.

I have a CG Machine.

The CG is 25% MAC. I have moved it forward and backward and the hunting will not go away. However that doesnt mean that I wont try it again.

Brad,

Why would you be screwed if I am nose heavy?

LAST EDITED ON Jul-01-04 AT 12:10 PM (CDT)
 
>The CG is 25% MAC. I have moved it forward and backward and
>the hunting will not go away. However that doesnt mean that
>I wont try it again.

OK. I am going to be Missouri mule here. You will have to "show me" how this is possible.

What is your nose moment? 9.25"?
Tail moment=17.75"
Tail is 26% plus with tiplets and is 1/2" thick.
The wing is notched to allow a PLASTIC TANK to be shoved back into the wing!!!

All this and you are saying your CG is in the same spot as Ted, David, and Brett, who all use 10" noses minimum (at least---from my memory and the TP plans) and 7" long metal tanks.

I simply do not see how this is possible!!!! The numbers do not add up to me.

Your CG should be at least a 1/2" behind say, a typical TP considering the placement of the wing. Windy's Strega has a 10 1/2" nose moment and the same tail moment as your plane. That would mean that there would be a 4-5% difference in CG between a Windy plane and yours. I would say Windy's planes are also around 24% to 25% (from memory).

>Why would you be screwed if I am nose heavy?

Since my airplane has the same nose moment as you and has a 18 oz engine in it, I would say I am pretty darn nose heavy!

>>The CG is 25% MAC. I have moved it forward and backward and
>>the hunting will not go away. However that doesnt mean that
>>I wont try it again.
>
>OK. I am going to be Missouri mule here. You will have to
>"show me" how this is possible.

You are comparing apples and oranges here. However if you want to do this you need to get the numbers straight.

>
>What is your nose moment? 9.25"?

9"

>Tail moment=17.75"

Yes.

>Tail is 26% plus with tiplets and is 1/2" thick.

Yes.

>The wing is notched to allow a PLASTIC TANK to be shoved
>back into the wing!!!

Yes or it wont fit.

>
>All this and you are saying your CG is in the same spot as
>Ted, David, and Brett, who all use 10" noses minimum (at
>least---from my memory and the TP plans) and 7" long metal
>tanks.

Ted uses 10 1/8 nose, 18 1/4 tail. From the plans I have.

>
>I simply do not see how this is possible!!!! The numbers do
>not add up to me.

Here is where the apples and oranges part comes in. If I had chaged the nose on a TP and you compared it to his then yes you would be right but I didnt do that. Let's compare all the numbers and see where we differ.

Ted's NM is 10 1/8
Doug's NM is 9

Ted's TM is 18 1/4
Doug's TM is 17 3/4 AND the entire tail section elevators and stab and tipplates and the horn weighed just 7/8oz before installation. the lightest of the 13 such stabs like that I have built.

Ted's span is 60"
Doug's span is 63"

Ted's gross area is 666
Doug's gross area is 714

Ted's weight on the purple plane I heard was in the 66oz range.
Doug's at the time of that pic was 58.75oz.

The overall weight of the planes makes a big difference. If I am going to build a much larger and longer plane than Ted but have it come out 7.25 oz. lighter I am going to have to save weight in the extremeties. We use the same drive train. The tanks are within grams of each other. Wheels, mine are heavier. I think my prop is heavier... It has an extra blade you know..

There is a huge difference there. Anyway it is not a TP CG vs another TP CG that is why we use the MAC to compare the planes.

>
>Your CG should be at least a 1/2" behind say, a typical TP
>considering the placement of the wing. Windy's Strega has a
>10 1/2" nose moment and the same tail moment as your plane.

Maybe it is the other way around??? Maybe they are not as far back as they think they are????

Windy actually has a shorter tail by .75" and they are sheeted and I have seen on the video where he says three oz. before installation is acceptable. Do you see where I am going with this? I am saying installation because that is at the same stage of building. After installation he covers with SS where I use PS. The weights of these two materials on a surface of this size is comparable. I use nitrate all the way through where is using Butyrate which has a gloss hardener in it. Any weight from the SS over the PS is lost due to the type of dope used. But do you see where there is a huge difference from the get go?

>That would mean that there would be a 4-5% difference in CG
>between a Windy plane and yours. I would say Windy's planes
>are also around 24% to 25% (from memory).

Yes I think MAII is in the 25% range but the plan I got didnt show where it(cg) goes. But the style of plane would dictate that setup with a 24% tail section.

>
>>Why would you be screwed if I am nose heavy?
>
>Since my airplane has the same nose moment as you and has a
>18 oz engine in it, I would say I am pretty darn nose heavy!

But your CG machine is telling you where you are. What my plane is set at means nothing in DIRECT relation. I am headed to the garage right now to figure it out again. I will report back with my findings. I have a CG thinggy-ma-jig that hangs the plane. But I already know where it is but I will do it again just to make sure.

Remember apples and oranges. CG between me and Mike now that is comparable. Since the planes are indenticle accept for the top block shape and the type of cowl used. But yours and mine are worlds apart. As far as DIRECT comparisons go.

PS sorry I never answer the phone. Today you caught me with a client and then later on the way home my phone died, as usual, Darn POS!

NO expert here, but I do recall that this can be eliminated by letting a little "slop" in the control horn at the elevator. This works fine on three of mine that were constantly hunting. One was a tad tail heavy, the others were at the CG. Works great on my TEOSAWKI that I got from Kent Tysor. It flies dead level and makes me look goood.

I'm sure this isn't really kosher, but it does work (slop, I mean). When I flew RatRace years ago we had one that hunted. Seemed incurable. Easily controllable but affected the speed a little. We finally (on another racer's advice) reamed out the hole in the elevator horn and it sat in a groove like it was on rails. I have no idea why this works but have done it on a few other stubborn "hunters" and it has always been successful. The down side, of course, is that an oversize hole will then "wallow out" even bigger with time, finally wearing all the way through. No, I didn't learn this the hard way.
--Ray

Ah yes the wonderful world of SLOP! I use slop when I can. This model started life with no slop and a slight hunt. Now some slop has worn into it and it doesnt seemed to have had an affect either good or bad. Still feels the same. Thing about adding it is that you cant take it back out should it make it worse...

It is real easy how it works. The slop lets you add in down flap(while flying you dont see this happening) while the elevator stays near neutral. This gives you a positive AoA at the wing with a near level setting at the elevator. Positive stab incidence or down elevator while the flap is flat does pretty much the same thing.

>
>It is real easy how it works. The slop lets you add in down
>flap(while flying you dont see this happening) while the
>elevator stays near neutral. This gives you a positive AoA
>at the wing with a near level setting at the elevator.
>Positive stab incidence or down elevator while the flap is
>flat does pretty much the same thing.

Except a Rat Racer doesn't have flaps...nor did any other plane I ever tried this trick on (I don't fly *serious* stunt, sorry).
--Ray

Doug,
Check to see if your leadouts aren't dragging on any part of the wing and that the controls are free. Could the hinge gap sealing tape cause this problem (binding the controls ever so slightly)? Might want to look at how it was applied?

Doug,

It is never too late, no model has enough time on it, to resist getting that sucker up on a flat surface and checking the alignment yet again.

I have seen the man I regard very highly, many regard as the best of the best, show up with a well-flown model which of a sudden had lots of spinner-to-fuselage mismatch. The thing had downthrust from the beginning...

I only mention this because rememberance of the happening has frequently made it easier for me to go back and check stuff, with the (sometimes) helpful perspective of having flown the model quite a lot.

Crist,

Never thought of that. I have been calling that plane Ole' squeaker or a while now. I hear the LOs squeaking against a rib. Sounds like an old squeaky door. You hear if when the plane is on the ground. It has always been that way. It doesnt seem to make them not smooth but under pressure that could be locking on the line. I will look at how I can get the out of there. Good call!!

LAST EDITED ON Jul-02-04 AT 01:05 AM (CDT)
 
I went to this website...

http://www.moleski.net/rc/WingMAC.htm

And found the MAC on the plane. Then I used the mark I found while the plane was suspended and I came up with the CG at.......................................................................................... 29.7% Pretty far back I would say. Just like old Brad said "4-5% points behind..."

Make sure I am right on this. The total chord with flaps at MAC is 11.75. The CG measures at 3.5 back from the LE at MAC. Divide 3.5 by 11.75 and you get 29.7???

I think before I was finding it at mid span and that skews the numbers just a tad.

Score one for GZ!

However I still think the controls are out one way or the other. I guess that will be a trial by error game.

Or I could just be wrong and a further forward CG would be a better move. It will be an easier test for sure.

Brad, just think the Furias had the CG even a 1/4" behind that! It was WAY more stable with all of the engines weight in the first three inches of the plane and the larger prop too. Makes you wonder about things huh?

Here is the rig hanging in the CG Machine. I got it from the July August issue of SN. I dont know who wrote the article. It doesnt say.

Sorry but I just cant keep from throwing in a pic of the little helper...All the pics are in the same folder so when I am uploading I just add one in for fun...

> 29.7% Pretty far back I would say. Just like old Brad
>said "4-5% points behind..."
>
>Make sure I am right on this. The total chord with flaps at
>MAC is 11.75. The CG measures at 3.5 back from the LE at
>MAC. Divide 3.5 by 11.75 and you get 29.7???

>I think before I was finding it at mid span and that skews
>the numbers just a tad.
>
>Score one for GZ!

OK. Now balance the plane at 25-6-26% and tell us how much lead it took to move the balance point. You should have to move the balance point approximately 1/2".

>Brad, just think the Furias had the CG even a 1/4" behind
>that! It was WAY more stable with all of the engines weight
>in the first three inches of the plane and the larger prop
>too. Makes you wonder about things huh?

New secret weapon?

LAST EDITED ON Jul-02-04 AT 05:06 AM (CDT)
 
hey doug
as you know i am flying close to the same plane with the only real difference being my wing/stab is inline.

mine has tried to "hunt" some as well but it really only seems to happen on hot days while flying over blacktop... when i fly at the softball field here locally (take off on infield and fly over outfield) the hunting doesnt seem to be as bad... also at brodak it wasnt that bad and we were flying over grass.

i really can't describe it as "hunting" in the true sense that i understand hunting because it doesnt do it in manuvers only in level flight and not as bad as some other things i have flown.

mine is not hingeline tape because i havent taped them, it could possibly be where the leadouts exit because i was reading my satana plans (which is close to being finished) and it mentions that the opening should be 3/8 (going from memory) and i dont think my leadout opening is 3/8.

EDIT: after looking at your pics, i dont know if the leadout thing would make a difference or not since you used the eyelets which i didnt use because i have had kind of a hard time with that on two airplanes because i make the holes to big and the eyelets come out in flight.. INSTANT FUN!

also great baby picture, we find out whether number 2 is a boy or a girl today... END EDIT

anyway just my two cents man
let me know what you find out

later
a.l.

>hey doug
>as you know i am flying close to the same plane with the
>only real difference being my wing/stab is inline.
>
>mine has tried to "hunt" some as well but it really only
>seems to happen on hot days while flying over blacktop...
>when i fly at the softball field here locally (take off on
>infield and fly over outfield) the hunting doesnt seem to be
>as bad... also at brodak it wasnt that bad and we were
>flying over grass.

Yes I have noticed this too! It is very frustrating to say the least.

>
>i really can't describe it as "hunting" in the true sense
>that i understand hunting because it doesnt do it in
>manuvers only in level flight and not as bad as some other
>things i have flown.

EXACTLY! It isnt really hunting like any other plane I have had. I would call it more like wondering. But in the maneuver it seems to be fine. I dont know on this one.

>
>mine is not hingeline tape because i havent taped them, it
>could possibly be where the leadouts exit because i was
>reading my satana plans (which is close to being finished)
>and it mentions that the opening should be 3/8 (going from
>memory) and i dont think my leadout opening is 3/8.

I dont have mine taped either.

>
>EDIT: after looking at your pics, i dont know if the leadout
>thing would make a difference or not since you used the
>eyelets which i didnt use because i have had kind of a hard
>time with that on two airplanes because i make the holes to
>big and the eyelets come out in flight.. INSTANT FUN!

I use nylon 4/40 screws with a hole drilled in them for the LOs. Then I insert a piece of basswood in the tip and drill holes and thread them and connect them. The screw holding the LO threads into the wingtip. It has worked pretty good so far. I dont like eyelets either. They always move or come loose. Too scary.

>
>also great baby picture, we find out whether number 2 is a
>boy or a girl today... END EDIT
>
>anyway just my two cents man
>let me know what you find out
>
>later
>a.l.

That will be so much fun!

LAST EDITED ON Jul-03-04 AT 01:28 PM (CDT)
 
have you tried a little down elevator!!!

Greg,

I have tried a little and alot of down elevator.

Still wonders around.

Doug,

Are the hingelines taped?

>Doug,
>
>Are the hingelines taped?

No.

It only weighs 58.75 oz and has 714 sqrs. There really is no lift issue there. I have taped many hingelines and the only planes it seems to help are the heavy ones. At least that is what I have noticed.

What would taping the hingelines do to help my problem?

Hi!

Since you seem to have tried everything else, it may be time to add down down thrust.

My flying buddy and I had a similar problem this (Sunday) afternoon with a 40-VF powered "Imitation".

We tried changing the flap/elev from 50/50 to a little down/down, lead-out rake, CG, everything.

One washer under the front engine mounting bolts transformed the ship from an untrustworthy, hunting, mess, into a groovy, eyes-off delight. what an eye-opener!

Give it a try.

Bigs

" What constitutes the dignity of a craft is that it creates a fellowship, that it binds men together and fashions for them a common language. For there is but one problem - the problem of human relations."

Doug,

I've had this fix the hunting problem on 2 or 3 airplanes including my current one. The plane had a slight tendency to hunt, especially coming into the wind. Taping the hingeline cured it. I suspect that air bleeding through the hingeline was causing airflow disruption and making the thing bounce around on me. Or it was demons. Either way, taping the hinge line on both the flaps and elevators did the job.

Again, just a thought.

I do not have much experience in this area but here are a couple ideas to consider.

1. As mentioned earlier, stiff gap seals or stick gap seals can cause problems. Fix, is to interlace gap seal material top and bottom like cloth hinges.

2. I asked this hunting question to a local very well known competitor and his matter of fact response was. "You will not have a hunting problem if your plane is straight." So I proceeded to check out my assumed straight plane. Thank you Derek Moran. He loaned me his classy incidence meter and a device to add to the engine shaft. Guess what? the wing was twisted plus or minus 1/2 degree at four points and slightly misalligned WRT the engine thrust line. So a heat gun to straighten out the wing and zero it to the thrust line and eyeballed the stab; flew the bird and it behaved nicely. I also found out that upwind and downwind rising/falling was significantly reduced or eliminated. So I recommend you use a mechanical device to check the incidence of your wing at different station points along the wing. These warps and twists mysteriously appear.

Bob Smiley
N94RJ

Bob,

Where you using an incednece meter, Robart maybe? How do you use it when you have flaps and elevators on the plane? How do you lock them in place?