FAI 15cc Engine Ruling

The new FAI rules allow for a 15cc or .91 maximum engine size, 2 or 4 stroke. What is your take on this new ruling and how do you feel it will effect plane design. Keep in mind, Windy Urtnowski has already placed 5th at the 2001 Nats with a Saito 91, so we have an actual successful contestant with this size motor.

My own take is that plane size probably won't go up too much. Our airplanes are limited by the space they are given, and, well, that is that. The 90 size engines are a bit on the large size, also. Even Windy had to admit that, and there is nobody building dedicated 4-strokes for us to engineer a lighter one for us which could be done. These are all being made for the RC fraternity.

I would look for one or two larger 2-stroke engines coming out in the next year or so, however, based pretty much on the same cases we have now. They won't go all the way to .90 because that would demand a larger case size. But it is not unrealistic to stretch the present engines to 70 or even 75. The more engine you cram into the same size case, the better the power to weight ratio becomes.

However, that doesn't mean that the smaller engines are dead. Look for lighter versions of these as well. I see smaller planes also making a "comeback" with new smaller, lighter power plants to move them. Remember, the PA (Nelson) and Jett 40 size engines started life as pylon engines made for high rpm use. They do not need to be made that hefty for our PA stunt use. Put the same power into a smaller case, and, again, the power to weight ratio goes up.

Karnac has spoken. Now can I put the Mayonaise jar back on Funk and Wagnell's porch? (A little Johnny Carson humor in case you don't remember.)

LAST EDITED ON Nov-07-03 AT 00:18 AM (CST)
 
I'd like to see what can be done with a "Fox Stunt .90"..

Imagine all the oil spewing out of one of those... you can run really rich and still have plenty of power.

Len,
I used to think the larger motor would just "go in" the planes we already have. But the more I mess with the bigger 72 the more I realize it is really going to need it's own plane. Or a set of numbers I should say. The wings may go up just 15% larger but the fuse will be a whole differen ballgame if you decide on one of the larger 91 motors. First of all you arent fitting a 2"spinner on one probably more like 3" second they are heavy enough to demand new fuse numbers to get kind of performance "we" aft cg guys are used to. Remember the MOI it is a huge player here when trying to balance out one of these pups. You have to use alot of weight to move the cg when the front three inches of the plane weighs 22oz. I know Windy had god results VERY good results with his 91 but he has moved on. Truth is he was swinging the same prop I had on my 56. It seemed as though he flew it very tamed. The motor is so large and heavy it will need larger spinners larger mounts and so on. It all adds up. You couple taht with normal numbers and it wont perform like we are used to. However up the size a bit and it will be a plane again not just a motor hanging out there.

About the smaller plane come back. I dont see it. I know Curt does real good with the Satona but it has more span that a Normal Geiske Bear at 56" Longer than a Saturn even. And those are 650+. Ted and Brett and David and Paul all fly planes that are normal 60 sizers and Billys and mine and Bob's and Mike Scotts are all larger models. All the SV series except for the Satona are all 650 or bigger.

As usual Leonard we are seeing things differently. But as ALWAYS in a pure friendly discussion.

IMHO I think the planes will keep getting larger. The motors are all making more power and more power will haul larger models. And you have to admitt it is easier to fly a larger model if it is adequetly powered.

I still want to see a top dawg bring a classic plane to the Nats and compete in open. I want to see a direct comparison.

>As usual Leonard we are seeing things differently. But as
>ALWAYS in a pure friendly discussion.
>
>IMHO I think the planes will keep getting larger. The
>motors are all making more power and more power will haul
>larger models. And you have to admitt it is easier to fly a
>larger model if it is adequetly powered.
>
>I still want to see a top dawg bring a classic plane to the
>Nats and compete in open. I want to see a direct
>comparison.

I don't think we are seeing things too much differently on this one, Doug. I totally agree that the 90 size motors are going to get heavier and demand a larger size plane. As such, they may not be feasable (at least in the eyes of the majority). Since a lot of flyers are not flying on the full 70 foot lines allotted to them, it may be possible to make the plane a bit larger, go the full distance, and still fit the pattern in. However, I believe it is possible to get the 70 or 75 size engine in the same, approximate, case size. You could do it without increasing the stroke--just increase the bore--or, perhaps, you could widen the case by a couple of thousandths, which, I believe, is the practical limit without increasing the mounting width, etc.

Can we fly on a 61 size engine if we limited it to that? Certainly. And if everybody is limited to that maximum size, nobody is hurting. But going up to a 65 does make a difference, as will going to a 70 or 75, should those become available, and in the same size engine package. If you have to increase the weight and bulk of the engine, then it is a different story.

And, if you don't have a great deal of difference in size or weight between a 40 or a 70, which will give the better power to weight difference? And I like to point out that there is a lot of stuff that remains constant, (the wheels, the controls, to a degree even the engine mount and tank) between the systems. So there is a fair amount of fixed weight (including the engine when the size and weights are equal) no matter which system you choose, giving the advantage to the bigger engine (not to mention the added advantage of wind penetration).

However, if the 40 size engine could be put into a smaller case, perhaps the nose does not have to be built quite as beefy, it uses a smaller tank (not a great deal of difference here. And I don't really count the extra fuel because it is burnt off during the flight and the difference becomes less critical during the verticals and overheads) then a slightly smaller plane with the smaller engine package makes sense as an option. However, it remains as an option only.

I, like you, still see the bigger planes dominating *unless* the smaller package such as Curt is using or Bob used proves to be better in turbulent conditions.

The jury's out. It is all a crystal ball. But I think the future will be in using somewhat larger engines in plane packages very similar in size to what we have today. Power is king if you can do it without adding weight. However, losing weight is good (yeah, just listen to my doctor) if you can do it without losing power. That's where I see offering a smaller engine of the 40 size, producing the same power as today's 40, also offering an option.

And I agree, that although you see the "top dawgs" producing some fine scores in classic competition, I believe those scores are a bit inflated because they are merely being compared to others using the same type planes. If the same flyer took the same classic ship into the present day Nats or Worlds competition, and especially if you gave him some adverse conditions to fly in, he would not do as well against his competitors using the best of today's equipment that is available to them.

Or, to put it another way, George Aldrich or Don Still, in their prime, flying their winning Noblers or Stukas of that day, would probably not even qualify for the top 20 in today's Nats.

I would love to see a "star" come to the Nat's in expert with a classic ship. My guess, it would have to be someone like Billy Werwage with his Aero .36 powered Vulcan. That seems to be the best combo of plane and pilot that could actually win it. I am not sure if a Les Mcdonald Stilletto 660 is Classic Legal, but that ship with a PA .50 side exhaust on long lines has got to be able to take care of serious business.

Of course, these are all just assumptions, but one possible scenario is larger engine sizes may do away with the need for tune pipes. More power out of the larger motors may allow for the same high rpm low-pitch prop setups we have been seeing without the weight, cost, complexity, and pipe tunnel construction. Relatively light weight "PA .80's" with Bolly 12x 3.4's would possibly provide even greater performance without the pipe penalty. Or even, a Saito .91 in a .72 case! I would be all over that one! Quite possibly, we may all be flying in "low gear" one day.

>Of course, these are all just assumptions, but one possible
>scenario is larger engine sizes may do away with the need
>for tune pipes. More power out of the larger motors may
>allow for the same high rpm low-pitch prop setups we have
>been seeing without the weight, cost, complexity, and pipe
>tunnel construction. Relatively light weight "PA .80's" with
>Bolly 12x 3.4's would possibly provide even greater
>performance without the pipe penalty. Or even, a Saito .91
>in a .72 case! I would be all over that one! Quite possibly,
>we may all be flying in "low gear" one day.

The pipes dont add power they just control the engine better. The size of the motor is really not the issue.

I sure would like to see a 91 crammed in a 72 also!

However we are still limited by AMA to 65 size 2 strokes --right??

>However we are still limited by AMA to 65 size 2 strokes
>--right??

Under the current AMA rules, 2-stroke engines for CL Aerobatics are limited to .65 cu in. From the rule book: "Sixty percent of the actual piston displacement of four-stroke cycle engines shall be taken for copetition classification purposes." That means that a 1.08 cu in four-stroke engine could be used in AMA PA Aerobatics.

There is a change proposal to change the AMA rules to adopt the same rule proposal being submitted to the FAI that places the displacement limit for all engines to 15 cc. This equates to approximately .92 cu in. If this rule passes the AMA CL Aerobatics Contest Board, the new limits for our AMA CL PA event will be in the 2005 rulebook.

What we may be missing here is that larger non-pipe engines could possibly open up a whole new avenue for say, semi scale stunt ships. Keith Trostle's Focke Wolfe TA 52 was a beautiful airplane. How about that same ship with a 72" wing span and a Saito 90!. What was once a really nice semi scale stunt ship would become an absolutely spectacular stunt ship! While Bill Werwage's P47 "Razorback" or Charles Parrot P47 are nice ships, I don't quite feel that the "Jug" has ever been done the way it could or should be. I think that Windy was ahead of the game with his big Typhoon with Saito .91 power. I for one, would not mind doing a "honkin" Sukhoi with full cockpit detail and not have to sweat the weight so much because I had some real power in the nose. Corresponding longer lines; say, a 75 foot max, would pretty much put us back in place. CLPA could start to see the equivalent of the big RC T.O.C. ships. Quite possibly, a two meter limit, as applied in RC pattern would govern max size.

>The new FAI rules allow for a 15cc or .91 maximum engine
>size, 2 or 4 stroke. What is your take on this new ruling
>and how do you feel it will effect plane design.

I think it's not particularly important, and none. Somebody, or a few people, will build airplanes for 91 2-strokes, or 91 4-strokes, and try to fly them. Big trend? I doubt it.

If I ever build any more airplanes, they won't be powered by 91's, and they probably won't be larger.

Big trend?
>I doubt it.

> Brett

The only way a trend gets started is when something is really proven out then everybody jumps on. Look at the pipes. When it first came around I am sure there are many who fly a pipe today that thought it was a ridiculous idea in the first place. It took its time get in and it wasnt so welcome from the get go. Larger planes for 91s. It will take along time for that to be a trend but I bet some will try for sure. I think it will be cool to see more more different motors in the game. When the AMA proposal goes through Randy gets to punch out the 65 case even more and add a whole new line of motors,.

New trend...I always wonder what the next one will be...what will be the next jump in performance...what will move "the crowd"...dont you wonder that too sometimes??? Sometimes I even try to think of it but then I get tired head and go onto to bed like I am doing now...

I already have engines in the works. When all the numbers were crunched I can make an 80 in the same case and it will be the same weight as the 61/65, about 11.5 ounces. Big bore, slightly longer stroke. This is the BSE case. The cast case just won't do it. With the bar stoke cases we can make a 90 but it will be a couple of ounces heavier after making the case a little larger. Estimating the 90 to be 14 ounces. I also agree it will help the guys who just do not want to run a pipe.
Doug here is where we disagree, the pipe does increase the power. You could not fly your plane the way you do without the pipe unless you set it up to have a hard break to get over the top. You can do it now with no break or light break. This is from the pipe giving you more power. It also does it on less fuel when working right. The only way the pipe can control you motor is if it is working. If it is working(on tune) then it has to produce more power. If no power then it is just a muffler (to long) and controlling nothing. When it gets to short for stunt it makes way to much power and heat for what we want. We just operate it at the bottom of the curve(long).
Richard Oliver

Richard,

I can run a motor on the pipe and it will regulate better than it does with no pipe. Like an FP 40 for example. On the pipe it a true sewing machine. Extremely regulated and very steady and strong. Off the pipe the power is more up and down and sometimes runs away. However they swing the same prop. The same take off rpm and everything. Same plane also. The pipe just controls it better but it deosnt seem to have more power. And yes it was in tune, you can tell how the motor reacts and how it stays in place. I have setup many FPs on the pipe it really makes it such a nice little stunt motor to learn pipe running on.

I think I could fly my plane just as a I do now on a rear muffler. I dont have one to try but I would like to sometime. If the chamber is correct it will work just fine. It will have more peaks and valleys but less power I dont think. The tune keeps it more regulated on the curve but it doesnt change the power curve. "narrows the rpm rage" The real reason I can get away with the way I am running my motor is the higher compression and the venturi coupled with higher nitro. The high compression setup will always makes more power. That is true in all combustion motors. Brett took your 61 and pumped up the compression and it only got better. Trick is controlling the power increase. That is where the pipe comes in. I wouldnt go so far to say that the pipe gives you more power but the pipe lets you use more of the available power without getting out "control" of you motor.

80! That would be cool. But what props and stuff. I already draw 8 oz through a 65 what will happen with an 80? So we are going to have 60 stunt planes running 80 on 16" props. The pipes are going to that much larger also. Wow that is whole new host of trim problems waiting to happen. Or just tame the crap out of it to run similar props we have now. Then whats the point? That is why I think larger planes will come along behind the larger motors. Ted touched on this a while back. Sooner or later the motor will outgrow the frame and new numbers will have to come. Then if the model is larger you can build it (plane and motor) heavier and keep the same wing loading and it wont fly like a big brick...

To make it effective, I suspose we'd need longer lines...and bigger arms.

Any advantage with these for Muncie '03?

>Any advantage with these for Muncie '03?
>

For the 18 millionth time, GETTING THROUGH THE MANEUVERS was not a problem with existing equipment. Mine was pulling my arm off even in the top of the vertical 8. What was an issue was SPEED in level flight. More speed to get through the upwind side of the circle. All the diameter, torque, whatever, in the world doesn't help you run at zero or negative airspeeds. In fact, LESS effective propulsion might have helped that particular problem, and been a net positive. All it would have taken was for more people (myself included) to realize what the real problem was going to be, and tweak the needle 1/4 turn (or one of half a dozen other things). It's not like there wasn't enough power on tap - it's probably a 1.25 horse engine even in stunt trim, and we are running it at .35. If you have a 90, you'll still be running it at .35 Hp.

Duh! let me see if I understand your Statement.
The real problem is not power but airspeed.into the wind vs. downwind.
In a 30 m.p.h. wind a 5000 hp eng.will not wind up or down (properly
tuned).
This being the case the plane will go faster downwind and less than
30 mph normal speed into the wind,which I comprehend as meaning,unless your plane is hauling freight downwind it will be
getting pretty near stall speed into the wind.
As I seee it the problem lies in the ability(lack of) to govern the speed of the airplane, not the eng,into the wind and downwind.
I have tried to envision an eng. to wind speed throttle, of course as the plane went faster the wind speed would increase an speed up the engine. I just don;t see a bigger engine as the answer, unless maybe in a quarter scale.
If all ths seems wacky, please cut me some slack;As a child I was ran down by a runaway mule cart driven by a c/l modler the culprit was never found.We are still looking for clues.
Best Regards

>Duh! let me see if I understand your Statement.
>The real problem is not power but airspeed.into the wind vs.
>downwind.
>In a 30 m.p.h. wind a 5000 hp eng.will not wind up or down
>(properly
>tuned).
>This being the case the plane will go faster downwind and
>less than
>30 mph normal speed into the wind,which I comprehend as
>meaning,unless your plane is hauling freight downwind it
>will be
>getting pretty near stall speed into the wind.

Not at stall speed - relative to the air, anyway. The more "power" you have (I use the word "power" in the stunt fliers sense, not the engineering sense) the closer the airplane will hold a constant airspeed. It''s going 49 mph pretty much all the time, relative to the air. Unfortunately, we care a lot about , too - since we care about line tension as a result of standing on the ground. This is what varied wildly as the airplane went around. Nose into the wind, my airplane was going *maybe* 15 fps, (and Geiseke's was close to 0). Dead upwind, it was close to normal speed, maybe 75 fps. Tail into the wind, mine was probably going 120-130 fps, and dead downwind it was normal speed again (except when exiting maneuvers).

Of course, we were also getting severe crosswinds, too. The problem area, or at least the worst problem area, was about 45 degrees prior to dead upwind. The combination of very low groundspeed, and a very severe crosswind component, resulted in very little or no line tension. Of course, the judges were standing upwind and this created tremendous turbulence, but if I got past the 45 degree point I was OK.

Ironically, the tremendous airspeed regulation power of piped engines with low-pitch props, and in this case, ram air into the uniflow, made it relatively easy to get through the maneuvers with tension to spare. I was very, very impressed with my PA61 in these conditions. I was worried about the vertical 8, but no problem. But the very same characteristics made it much worse just flying around level. That's why "torque", "power", etc. wasn't gonna help, in fact, it probably would have made it worse in the area that most people were having a problem. A Nobler with a Fox would have had a better chance because it wouldn't have had as steady an airspeed, and then maybe would have "gotten a run" at upwind. Of course, it wouldn't have stood a snowball's chance in the maneuvers (based on my 2000+ flight with such a combo).

The solution was to either reduce the airpspeed stability (in my case, probably would have been enough to hook the tank vent to the pressure tap, thus reducing the ram air effect that was making the engine go rich in the wind - although it might have blown the wings off in the maneuvers), or increase the airspeed until it could make it around safely (and then maybe blow the wings off anyway).

I understand. Thanks Brett.

>If all ths seems wacky, please cut me some slack;As a child
>I was ran down by a runaway mule cart driven by a c/l modler
>the culprit was never found.We are still looking for clues.
> Best Regards

Hey Charlie, did that event happen to occur in or around Asheville, NC??? I seem to remeber some little kid with glasses getting in the way one day on a trip into town. We'uns had a great big laugh!
Bill <><

The Police have been notified!
Have a good building season.
Incidentally , your flight at Hville was very good!

Best Regards to you and Aaron.

Brett,
Windy talked to me about the evolution of the PA engine in terms of size. He said, " the guys started out using the .40', then they went to the .50's, then they went to the .60's". He mentioned that that he had seen this ALL before. What seems to happen is that if the 15cc limit ever applies to the United States, some top flyer is going to start cleaning every bodies clock with a honking .80 or .85 with a lighter plane because of no pipe or pipe tunnel and as sure as I am writing this thread, every other top flyer is going to jump on board. Gilbert and Remi Beringer took care of serious business with the Saito 4 stroke, and as fast as you can blink your eyes, we have a new United States National Champion using a Saito 4 stroke. People did not leave the Fox 35 neccesarily because they wanted to; they did because they HAD to. I personally watched the Fox start to get blown out the door by the O.S. Max 35s and then the ST46. If you showed up at a contest with a Fox 35 in the nose, you were dead! Maverick, who I believe is Rich Oliver, already stated that he has a killer motor waiting in the wings just waiting for a ruling change. A Rojett .80 or .85 in side exhaust mode with the weights that he is suggesting would make me seriously consider abandoning my beloved Saito 72! I absolutely would not want to face someone with say, a well built Impact with an engine like that in the nose. My guess is he is going to go through turbulence like a "hot knife through butter".

>What seems to happen is that if the 15cc limit ever applies
>to the United States, some top flyer is going to start
>cleaning every bodies clock with a honking .80 or .85 with a
>lighter plane because of no pipe or pipe tunnel and as sure
>as I am writing this thread, every other top flyer is going
>to jump on board.

I am skeptical - and I have at least some small insight into what "top fliers" think about it.

But, by all means, knock youself out! If you want a 90 in a 33 oz airplane, please don't let me stand in your way. You might even be able to get it to fly as well as a 65 Oz Impact with a 40VF, if you try really hard.

Richard Oliver isn't the only one playing with larger engines. They may not be 80 or 85, but, yes, they will be there. And if they are built on the same (approximate) case size, they will offer a power to weight advantage.

My only question is, why do you think they will be without a pipe? All of the engines are already available without a pipe. If there was an advantage to NOT using a pipe, don't you think that, one of the guys currently using a 61 with a pipe might not have shifted to a 65 without a pipe? Larger engine. No pipe. More power, less weight. Why not? Yeah, why not?

If there is a reason to use the pipe, they will continue to use it, larger engine or no, simply because the reason to use the pipe will continue to exist.

Just remember, the pipe tunnel is not a big deal. And the pipe itself, not a great deal of difference in weight between it and a tube muffler. The only thing is, there is more to fiddle with when you have a pipe, but the top guys are going to do it.

Leonard,
I suspect you may be correct. If the rules do indeed change, my guess is that we will see .80 or .85 with the pipe or some other device, say an integral engine pump, all the same simply because, the nature of competition is to use "the maximum allowed". If an .80 or .85 performs better with a pipe than a .80 or .85 without, then suffice to say, we will see "the max equipment" allowed.

I would still like to know what you are looking for? Going from a 61 to 65 is a cool jump. The 65 will turn the same props as the 61 but with just a bit more authority and no noticable loss in the heat and winds compaered to the 61. The 65 just hangs in there better. The props are so close to the same that the plane stays the same.

What are you going to do with an 80 in 60 sized model? Are you going to run the same prop? Why on earth would you do that? You wouldnt. The 80-85 is going to be large enough to spin props that are going to cause trim issues. If the planes dont change a Rabe rudder will be on every model out there. And improperly adjusted ones are worse than not having it at all.

Think about it...and Impact on 11.75"-13" props will trim out with no real issues. Start bolting on 16" props and you are in for a real surprise. Not only will the clearance be a problem but I think the yaw issues will be huge on a airframes of taht size with props that are 2"-3" longer than what we run now. Not to mention VCG with the extra long gear and the new larger pipes hanging below. Just thoughts on my part. Going from a 65 to 72 2s on pipe might not demand whole new trim but go up to 80 and above and I bet new things are going to start popping up. I wonder what will really happen. Cant wait to see...

But still...what is the goal with going to an 80 if you dont want to build larger planes...????

Read thread #17.

Proparc,

I was asking Len what he wanted with an 80. He doesnt want to build larger planes or thinks that larger planes will be in the owrks but yet he thinks 80s would be good. I was just wondering what his and others angle is with the way larger motor without getting in to larger planes.

I fully understand what you are saying in #17 and I think so too. But I believe the engines will have pipes.

When you talked to Windy did he discuss how it felt holding on to his original sweeper, 88"span and 100oz wt? Wonder if he will dust off his old(or build another) sweeper when he can install a 80-90 size 2 stroke. I would expect that the weight will be a limiting factor as the heavier plane will pull harder especially if the line limits remain the same. Would we fly these on 18thousand lines or have to go to 21thousand as the combat guys have done.

I believe that it is not the weight of the planes that is the limiting factor or even the size. Line length limitations are holding up the works.

>I believe that it is not the weight of the planes that is
>the limiting factor or even the size. Line length
>limitations are holding up the works.

I personally think the limiting factor is the strength of the back of the flyer.

I am running the Saito 72 at WOT, and no one around here wants to fly it much. It "pulls too hard" is the comment I keep hearing. Believe me, an .85 RO Jett is going to have a ton of line tension (even though all the rocket scientists will tell me that there is no basis for this statement), and some guys had better hit the gym if they want to run these big boys.

The beauty of the larger displacement in the same case is that the motor could be set up EVEN MORE MILD and still pull the SAME PROPS as the 61 and 65, and could be dropped into the same airplane. Simply raising the displacement is going to raise the torque, so the power delivery could be made even more mild and predictable. That is simply a WIN-WIN for everyone.

I think basically Windy overcame a lot of the shortcomings of the 4 cycle (whose development was simply in its absolute infancy) by going to a huge displacement. Like Doug said we are pulling the same props on the Saito 56 that Windy was using on a 91, but the 91 was easier to figure out in a short period of time. Larger engines are simply more forgiving.

As far as what the "big boys" use. I think they will run whatever Billy runs...

I believe the heavy pull you are getting from SP is from the motor being out at full nose length. 20oz in the first three inches of your plane at 10" or further out is going to pull like hell going 60 mph. As the motor goes back the line tension will soften a bit. When I had a 72 in the Furias at nose length of 8.75 I started adding tail weight by the oz and as the cg crept back the tension started to soften a bit. Before I could get the plane to fly like I wanted it started with the MOI stuff. The new one at just over 7" nose and 21" tail should have a much more steady but not so hard. At least I think that is what will happen...

Brad, Doug, I think both of you can be "right" on your assessment of pull. Extra weight is going to add to pull. Extra power is going to add to pull. But trim can definitely affect it as well. If the plane is yawing out, it is going to pull. More power, more weight, more pull. Yet, no matter what the power or weight, if you trim the plane to turn in the path of a circle at the same rate of turn as the line length, it can have zero pull. A full size P51 on lines at full speed, if set to turn left at the same rate of turn as demanded by your line length would have zero pull.

But to demonstrate "power", we have changed props on a fully trimmed ship, and without changing anything other than the prop (and appropriate rpm and pipe length)--and that means maintaining the same lap speed--the larger prop gave more pull. The smaller prop, even with lower pitch and higher rpm (and pipe readjusted) did not equal the tension of the larger prop. And maintaining rpm with the same pitch (making it easier) was a quick demonstration of the value of more diameter.

But each engine has its limit, and that is where you have to quit.

> Believe me, an .85 RO Jett is going to have a
>ton of line tension (even though all the rocket scientists
>will tell me that there is no basis for this statement)

This rocket scientist didn't - it's a well-documented observation However, I still don't see the mechanism. I do know some things that it pretty conclusively IS NOT:

torque
power (engineering sense)
prop diameter
prop blade area
anything that the engine is NOT CURRENTLY EXHIBITING (i.e. "potential torque")

Counter arguments should include proposed mechanism of effect.

>> Believe me, an .85 RO Jett is going to have a
>>ton of line tension (even though all the rocket scientists
>>will tell me that there is no basis for this statement)
>
>This rocket scientist didn't - it's a well-documented
>observation However, I still don't see the mechanism. I do
>know some things that it pretty conclusively IS NOT:
>
>torque
>power (engineering sense)
>prop diameter
>prop blade area
>anything that the engine is NOT CURRENTLY EXHIBITING (i.e.
>"potential torque")
>
> Counter arguments should include proposed mechanism of
>effect.
>
> Brett

Brett, I do not understand what you are saying here. You agree that the larger engine will produce more pull (tension). Then you say things it is not and include torque, power, blade area, and diameter.

I agree that potential means nothing. But without power (or torque, or however you measure it) there is not even potential, much less fact. Some of the early large engines are a good example. They had the cubic inches, but not the power.

And we have argued for years about diameter, but this is an observable fact. Keep everything else equal and increase diameter and you will increase thrust. You can develop all the power in the world, but if you have no means to convert it into thrust, it is meaningless. That is like putting bicycle tires on the drive wheels of a dragster. For them it is width. For us it is diameter.

Of course, if you are talking about spinning one prop at 40,000 rpm and another at 5,000 there will be a difference. But use the same type prop with the same pitch and rpm, the larger diameter is going to win out.

There are other things to consider in proping an engine, and that is why some choose not to use the largest prop available. But, if you keep the rest of the equation equal, a larger diameter or wider blade (or multiple blades) will produce more thrust. And, with proper trim, that can be transformed into greater "pull".

>>> Believe me, an .85 RO Jett is going to have a
>>>ton of line tension (even though all the rocket scientists
>>>will tell me that there is no basis for this statement)
>>
>>This rocket scientist didn't - it's a well-documented
>>observation However, I still don't see the mechanism. I do
>>know some things that it pretty conclusively IS NOT:
>>
>>torque
>>power (engineering sense)
>>prop diameter
>>prop blade area
>>anything that the engine is NOT CURRENTLY EXHIBITING (i.e.
>>"potential torque")
>>
>> Counter arguments should include proposed mechanism of
>>effect.
>>
>> Brett
>
>Brett, I do not understand what you are saying here. You
>agree that the larger engine will produce more pull
>(tension). Then you say things it is not and include
>torque, power, blade area, and diameter.
>
>I agree that potential means nothing. But without power (or
>torque, or however you measure it) there is not even
>potential, much less fact. Some of the early large engines
>are a good example. They had the cubic inches, but not the
>power.
>
>And we have argued for years about diameter, but this is an
>observable fact. Keep everything else equal and increase
>diameter and you will increase thrust.

Only the static thrust. It has no effect on the thrust while flying around level - because you only require so much thrust to fly the airplane at a constant speed. If you have a 20' diameter prop, on an airplane that generates 12 oz of drag in level flight at a particular speed, that 20' diameter prop only produces 12 oz of thrust. Yet the "strong engine" effect may (or may not) still occur.

>There are other things to consider in proping an engine, and
>that is why some choose not to use the largest prop
>available. But, if you keep the rest of the equation equal,
>a larger diameter or wider blade (or multiple blades) will
>produce more thrust. And, with proper trim, that can be
>transformed into greater "pull".

How does this work, given that the *thrust* is the same in level flight*? Does the airplane, flying around level, "know" somehow that if it were to slow to a stop, you might have more thrust?

Read and re-read again: "IN LEVEL FLIGHT AT A PARTICULAR CONSTANT SPEED, A GIVEN AIRPLANE WILL REQUIRE THE SAME THE SAME AMOUNT OF THRUST NO MATTER HOW IT IS DELIVERED". Unless you have somehow decided that the laws of physics are to be suspended for stunt planes - or that the airplane is psychic and somehow "anticipates" that if you pull into a wingover the thrust might go up. While we are at it, an unavoidable corrolary to this is that "IN LEVEL FLIGHT AT A PARTICULAR CONSTANT SPEED, A GIVEN AIRPLANE WILL REQUIRE THE SAME THE SAME AMOUNT OF HORSEPOWER NO MATTER HOW IT IS DELIVERED". Although how it is delivered may effect the horsepower required from the engine.

Even more contradictory to your premise, the effect we are talking about happens *even if you use the same prop on a different, stronger engine*.

It's obviously not (based on easily-proven reasoning and exhibited behavior):

torque
power (engineering sense)
prop diameter
prop blade area
anything that the engine is NOT CURRENTLY EXHIBITING (i.e.
"potential torque")

> Even more contradictory to your premise, the effect we
>are talking about happens *even if you use the same prop on
>a different, stronger engine*.

That's what I am talking about.

Given that the power reserve would be higher, the ability to deliver power could be more closely monitored, as opposed to the constant pursuit of "more power". I keep trying to make this point about the 4 cycle (and I suppose any engine really). We seem to have plenty of power, what we lack is constant power (and I mean truly constant).

This, I believe has very little to do with not having enough power.

Going to a larger engine on the same prop will further mask these symptoms, and will also invariably lead to a more powerful "feel" on the handle.

>(snip) Read and re-read again: "IN LEVEL FLIGHT AT A PARTICULAR
>CONSTANT SPEED, A GIVEN AIRPLANE WILL REQUIRE THE SAME THE
>SAME AMOUNT OF THRUST NO MATTER HOW IT IS DELIVERED". Unless
>you have somehow decided that the laws of physics are to be
>suspended for stunt planes - or that the airplane is psychic
>and somehow "anticipates" that if you pull into a wingover
>the thrust might go up. While we are at it, an unavoidable
>corrolary to this is that "IN LEVEL FLIGHT AT A PARTICULAR
>CONSTANT SPEED, A GIVEN AIRPLANE WILL REQUIRE THE SAME THE
>SAME AMOUNT OF HORSEPOWER NO MATTER HOW IT IS DELIVERED".
>Although how it is delivered may effect the horsepower
>required from the engine.
>
> Even more contradictory to your premise, the effect we
>are talking about happens *even if you use the same prop on
>a different, stronger engine*.
>
> It's obviously not (based on easily-proven reasoning and
>exhibited behavior):
>
>
>torque
>power (engineering sense)
>prop diameter
>prop blade area
>anything that the engine is NOT CURRENTLY EXHIBITING (i.e.
>"potential torque")
>
> Brett

Maybe you should read and reread my premise, Brett. I am no longer talking about how much power is needed to propel an airplane at a given speed, even though the bigger prop will "slip" less and have the ability to bring the plane back up to speed should there be a slow down, and to deliver more thrust in situations like when the plane goes straight up and the force of gravity is added to the drag of the plane, or to serve as a brake on the way down.

What we are talking about is "pull" now, pull on the lines. Some (much, most, choose one) of the thrust from the engine/prop is used to propel the airplane through the air. The more drag there is on the plane, the more "slippage" there will be. (Some people like to use different terms. I just happen to like slippage because it is descriptive of what is happening.) The bigger the prop. the less slippage. The more drag, the more yaw (which is also drag), the more the slippage. But some of that slippage becomes extra thrust and can be transferred into "pull" on the lines. In an extreme case, if we tied the lines to the tail of the plane and aimed it away from us, the plane would not be moving at all. There would be no drag, in the normal sense at least (the airframe would still be interfering with the slip stream) but there would definitely be a certain amount of "pull" on the lines. No airspeed, no movement, but pull. When the airplane is flying, some of that prop thrust is being transferred into pull on the lines. It may be "wasted" in the sense that it is doing no work (other than holding the airplane out on the lines) but it is making you do work in holding onto the handle, and sometimes rather tightly. So, I guess, there is work being done after all. The bigger prop has more thrust available which, in addition to what is needed to fly the airplane, can then be transferred to pull on the lines. In effect, the amount of thrust produced is equal to the drag on the plane plus the pull on the lines.

As I said in another thread, you can trim the airplane so that even a P-51 flying on the lines would exhibit no pull on the lines. You could make any plane fly very light on the lines, big prop or no. Or you could make it fly so heavy that it would jerk the handle out of your hand. Whatever "pull" there is on the lines is thrust that is over and above what is needed to propel the airplane through the air.

From personal experience, and this is how we test, we have taken a plane and trimmed it out with a smaller prop, and then, with no additional trim changes of any kind, and no increase of lap speed, changed to a bigger prop and found that there is a noticeable increase in "pull" on the lines. Call it what you want. Call it "wasted" thrust. But it is added thrust that is used to tug against the handle and hold the airplane out on the lines.

Does it make any difference in "normal" flying? Probably not (except for the added thrust available for going uphill.) But when you have to fly the plane upwind in a heavy breeze, it can make a decided difference.

And again, if you don't trim for it, it won't be there to help.

>What we are talking about is "pull" now, pull on the lines.
>Some (much, most, choose one) of the thrust from the
>engine/prop is used to propel the airplane through the air.
>The more drag there is on the plane, the more "slippage"
>there will be. (Some people like to use different terms. I
>just happen to like slippage because it is descriptive of
>what is happening.) The bigger the prop. the less slippage.
> The more drag, the more yaw (which is also drag), the more
>the slippage.

Why does more drag relate to more yaw? More yaw=more drag, but I don't see the inverse.

>But some of that slippage becomes extra
>thrust and can be transferred into "pull" on the lines. In
>an extreme case, if we tied the lines to the tail of the
>plane and aimed it away from us, the plane would not be
>moving at all. There would be no drag, in the normal sense
>at least (the airframe would still be interfering with the
>slip stream) but there would definitely be a certain amount
>of "pull" on the lines. No airspeed, no movement, but pull.
> When the airplane is flying, some of that prop thrust is
>being transferred into pull on the lines. It may be
>"wasted" in the sense that it is doing no work (other than
>holding the airplane out on the lines) but it is making you
>do work in holding onto the handle, and sometimes rather
>tightly. So, I guess, there is work being done after all.

No work is being done if nothing is moving. Work is defined as force time distance, horsepower is the rate at which work is being performed. No horsepower is going into the airframe in this situation. A force is being applied to the airplane, but the engine horsepower is going into air movement, not into the airframe, and thus the efficiency of the propellor in this case is 0.

So your mechanism that relates "stronger engine" to "more line tension" is the yaw angle? How come a "stronger engine" makes the airplane yaw out further? How come the same airplane with the same size prop and same, but a "stronger" version of the same engine still exhibits the effect?

It's NOT the yaw angle.

>The bigger prop has more thrust available which, in addition
>to what is needed to fly the airplane, can then be
>transferred to pull on the lines. In effect, the amount of
>thrust produced is equal to the drag on the plane plus the
>pull on the lines.

>Whatever "pull" there is on the lines is thrust that is over
>and above what is needed to propel the airplane through the
>air.

How does a force that doesn't exist in level flight, and that even if it did, has no component in the direction of the line tension, effect it? If you have more thrust than you have drag, will the airplane not accelerate until they *are* equal?

Am I to understand that you consider that (Fstatic-Fdrag)+centrifugal force=F(linetension)? Never mind that the Fstatic is a "potential thrust", not inflight thrust, and never mind that as long as the current thrust > than Fdrag, the airplane will speed up until they are equal - are you suggesting that two forces perpendicular to each other add in such a way that one component is increased?

I think you need to go back and think this theory through for a while.

>(snip) The bigger the prop. the less slippage.
>> The more drag, the more yaw (which is also drag), the more
>>the slippage.
>
>Why does more drag relate to more yaw? More yaw=more drag,
>but I don't see the inverse.

I was using a comma here in place of an "and/or". I meant "the more drag and/or the more yaw", then the more slippage there will be. On this we should be agreed.

We have argued this whole thing about the big prop before and we will probably be at odds on it for a while longer. But others are starting to beat the drums for bigger props as well.

Part of the problem in our discussions, I think, is this definition of work being done (or no work if there is no movement). But if you and I were to have a tug of war with a big rope, you take one end, I take the other, and we both pull as hard as we can...well, I'd lose. Bad idea. Maybe if I tied my end of the rope around a tree and let you pull on the other end, that would be better. You could pull as hard as you want, break out into a sweat, and neither the tree nor the rope would go anywhere. But there would be pull on that rope. And you would think you were working even though no work was being done.

Now, I'll go grab a couple of friends, and we'll all pull on your end of the rope. Well, we still wouldn't get anywhere, but we would now all break out into a sweat doing "nothing". We have, however, increased the pull. At this point we will let you untie the other end and hang onto it and see what happens. Even though you could overpower me alone, once I have a couple of helpers at my end, we could easily out pull you.

Now, were we doing more work pulling against the tree, or were we doing more work pulling against you (because you moved)? I think we are getting bogged down arguing whether or not work is being done when all we are trying to do is define pull against a stationary point (our hand in the handle). But you and I can run all the theory we want, use all the formulas we can, it doesn't make any difference. What really counts is when we try it. And in all the tests that we have done, the bigger prop has produced more pull.

There are other advantages (and disadvantages) but this was all I wanted to say here. If the bigger prop didn't do more, then we don't need the horsepower because we can't harness it. It isn't just a matter of having sufficient thrust for level flight. We could take a 60 ounce pipe ship and fly it on an OS 20 FP with enough thrust for level flight. What we need is enough for when the plane is in the verticals and to keep it from slowing down escessively in the maneuvers.

There is more than one way to set our power packages up, I will grant that. And there is more than one way to achieve success. I just happen to be a fan of the bigger prop approach. And, quite frankly, I think it is the ability to turn the bigger prop that has given the appeal to the 4-strokes as well.

>We have argued this whole thing about the big prop before
>and we will probably be at odds on it for a while longer.

The problem is that you insist on your opinion - yet the proposed mechanisms seem to violate fairly-well-established, and fairly easy-to-understand physical laws and principles of aviation, bordering on mysticism (see previous counter-argument). Then, I give you actual measured data (like the 12-6/8000 vs. 12-4/12000 thrust data Ted and I took), and when it contradicts your initial idea, you don't beleive it.

This is not arguing fairly - just denying it and clamping your jaw on it like a bulldog doesn't change the reality. And, the fact that the most successful stunt engine system in the history of the event uses a prop you probably consider too small for break-in doesn't seem to soak in. I don't claim any particular approach is the "ONE RIGHT WAY" - but I do at least look at all of them.

I don't particularly care what you do - but to simply dismiss anything that doesn't agree with your consciously and intentionally limited preconceived notion, and justifying it with physical arguments that are (charitably) not valid, and completely refusing to even respond to the counter-arguments (other than simply repeating the initial premise, and arguing by reference), really does grate.

Brett & Len,

You have to look what is happening with prop. If you have constant RPM and constant model speed, you have also constant drag and thus also constant thrust of prop in level flight. Does not matter what is the engine power, torque, pitch diameter or whatever.

The only real question is, what is happening if we fly uphill or downhill – means what is happening if we add or subtract some force to the drag – or - if prop must balance that force by thrust.

So by other words what is the speed stability at changing force against the thrust.

Simplest way to understand it is to analyze what is happening if the model slows down say 10% (uphill).

Slowing down at equivalent RPM makes higher AoA on blade and it makes more lift – more than that lift at nominal speed. Does not matter what was the original lift.

If you do very simple analyze only by lift as I described it – means without downwash, tip vortex, efficiency and so, you will quickly see that:

1/ More blade area (wide) as well as more blades make thrust higher – just because of more “wing” area – linear response.

2/ Bigger prop (in diameter) also makes more area (like in 1/) but tip speed is also higher and at that higher tip speed you make lift with quadrate of that speed. Result is much better thrust.

3/ Pitch is little confusing – less pitch needs more RPM, angular change is lower at higher tip speed, but tip speed is higher and the response is quadratic, so the result is that lower pitch keeps speed better.

It all means that if you have more power, you can replace bigger prop with the same pitch and you have better thrust response after slowing down, thus you have better speed stability, thus you have higher speed uphill and thus you have better tension overhead.

But it is not the only way. You can go to less pitch at higher RPM. The 2C engine gives more POWER!!! (even torque goes down). You use only little smaller prop, with less pitch and thus you have better speed stability with the same engine and with smaller prop.

I already wrote one example – the same thrust response you can expect at 12x6 and 10x4 – means if you can use 12x6 and engine is able to twist 11x4, you will get better line tension.

But AGAIN AGAIN AGAIN – it is ONLY at constant RPM!!! It all depends what the engine does. It can easily happen that engine itself will make better self regulation with smaller prop and thus usage of bigger can be still counter productive. It is the same like to think that only power curve shape solves all. That is not true, it must be analyzed together – it is because curve regulates better at high rpm and prop regulates better at large diameter – means lower RPM. It is necessary to find optimum.

>Brett & Len,
>
>You have to look what is happening with prop. If you have
>constant RPM and constant model speed, you have also
>constant drag and thus also constant thrust of prop in level
>flight. Does not matter what is the engine power, torque,
>pitch diameter or whatever.

Well, that's what you might expect to happen. But, the effect we are arguing about undeniably exists - specifically, some engines generate more line tension than others, regardless of the other factors staying the same. Used to happen with ST46's all the time, still happens with PA61s. Put in a "stronger" engine (the defintion of "stronger" being the principle point of debate) with the same prop at the same airspeed, and every other trim setting the same, and it pulls harder, even in level flight. It's the mechanism that eludes us all.

Happened to me as recently as 3 weeks ago. I thought my PA was getting a bit tired (after having run some debris through it last year at a contest). It was always way "stronger" than the others. So, I borrowed Ted's fresh from rework motor. It has better compression, still has a "pinch" at the top, far fewer "rattles" - but even with the exact same prop, same venturi, same speed, same everything else, it just didn't pull as hard. To even it up, I had to run something like 2/10 second a lap faster. I emphasize that this was still in level flight - never mind what it did in maneuvers. There's just something about my engine that makes it "stronger", in that it seems to generate more line tension.

>
>The only real question is, what is happening if we fly
>uphill or downhill – means what is happening if we add or
>subtract some force to the drag – or - if prop must balance
>that force by thrust.
>
>So by other words what is the speed stability at changing
>force against the thrust.
>

This does seem to be pretty unambiguously true as far as propulsion and vertical performance- it the partial derivative of the thrust with respect to velocity that seem to determine the performance, and it's relatively easy to see the mechanism that relates it to diameter, pitch, and RPM (Leonard's disbelief notwithstanding).

But this doesn't explain the "stronger engine effect".

> (snip) This does seem to be pretty unambiguously true as far as
>propulsion and vertical performance- it the partial
>derivative of the thrust with respect to velocity that seem
>to determine the performance, and it's relatively easy to
>see the mechanism that relates it to diameter, pitch, and
>RPM (Leonard's disbelief notwithstanding).
>
> But this doesn't explain the "stronger engine effect".
>
>Brett

I guess I am just as much in the dark as to your adamant disbelief that diameter could have anything to do with it. But that said, I do recognize your "stronger engine effect" without totally understanding it. Ted's engine probably wasn't broken in enough yet. They get stronger during the first 7 or 8 hours of running. It just may need more time. But Matt will sometimes complain that the plane just doesn't have enough drive. I am timing him and lap times are "there". He leans it a smidgeon and then says, "that's it". But lap times remain the same. Just leaning it that small amount didn't change lap times, but did increase the drive that he felt. Of course, I think it also kicked in a bit more in the verticals as well, which was part of it.

>
>> (snip) This does seem to be pretty unambiguously true as far as
>>propulsion and vertical performance- it the partial
>>derivative of the thrust with respect to velocity that seem
>>to determine the performance, and it's relatively easy to
>>see the mechanism that relates it to diameter, pitch, and
>>RPM (Leonard's disbelief notwithstanding).
>>
>> But this doesn't explain the "stronger engine effect".
>>
>>Brett
>
>I guess I am just as much in the dark as to your adamant
>disbelief that diameter could have anything to do with it.

Because it occurs WITHOUT CHANGING THE PROP. Therefore it's not a function of diameter.

Diameter effects are A DIFFERENT question - which you seem to recognize only one direction of (see Igor's post for an example that I assume you don't beleive any more than the measured thrust data I sent you a while back). The effect Igor is discussing is reasonably well-grounded and seems to fit very well with observation.

>But that said, I do recognize your "stronger engine effect"
>without totally understanding it. Ted's engine probably
>wasn't broken in enough yet. They get stronger during the
>first 7 or 8 hours of running.

Or, they get weaker - since we have no idea what creates the effect we are discussing (although it's clear enough that a lot of things DON'T cause it). I've seen it a lot of ways.

Until we come up with a plausible mechanism - vague notions about "not being rocks on a string" with no technical explanation of why you think that's true don't count - it's still an open question.

>(snip) I don't particularly care what you do - but to simply
>dismiss anything that doesn't agree with your consciously
>and intentionally limited preconceived notion, and
>justifying it with physical arguments that are (charitably)
>not valid, and completely refusing to even respond to the
>counter-arguments (other than simply repeating the initial
>premise, and arguing by reference), really does grate.
>
> Brett

Brett, it sounds like you are having a bad day. I am sorry if I upset you if that's the case.

The interesting thing is, we didn't just dismiss all of the prevailing theories and claims. We tried over a thousand dollars worth of props with different rpms and different pipe settings. We tried 2-blade, 3-blade, 4-blade. We tried 11 inch, 12 inch, 13 inch and stuff in between. We tried the underchambered, the Eathers, the Bollys about 3 or 4 specialty props. It is not like we just stuck one prop on the plane and said, "well, that's it." I am one who loves to experiment. I want to see what happens when we try this or that. Matt would rather fly, but he does want to improve the product. And moving from a 13 inch to a 13.5 inch blade was a noticeable improvement for him. He felt the difference. And that is what counts.

Our airplanes are more than a rock on a string, and we can get more pull than can be simply calculated by weight and lap speed. There is something else that also generates tension and that is why it is not just a matter of thrust = airframe drag and no more.

But, be that as it may, Igor has part of the answer--the ability to keep the plane flying at its speed when drag increases as you aim the airplane up. Right now Matt is running about 4.5 inch pitch and launching about 10000 rpm. And all I know is that with the increased diameter there was increased thrust. It is not a matter of sticking the head in the sand. It is a matter of putting the hand in the handle.

Maybe next time around, if the weather is good, you can get a chance to fly Matt's plane. Matt would love to have you do it and make your comments, good or bad. We all have our preferences, but it is good sometimes just to see what the other guy is doing or to get his comments on what you are doing.

I have experienced what Len is talking about first hand. I run the 12" 4 blade and the tension is good. I run the 13" 3 blade and there is more tension. Not the best flying prop for my rig but I am talkikng about how the bigger diameter has created more tension.

I think there is a simple answer.

Simple fact is even though Len is not changing one thing in his setup by changing the prop he is changing the output of his engine. Larger props demand more power. So the real reason there is more line tension is there is more output from the motor.

Lets take a 4s for instance. You run an Eather 12X4 4 blade on a 72 and it turns it at 10800 rpms. Backside of the curve for sure(read that losing power as rpms increase). Now take the same motor(dont change a thing) and strap on an Eather 14X5 UC 2 blade. You are only pulling 8800 rpms and drinking alot more fuel to do so. This is on the rising side of the curve(gaining power as rpms increase). It cant spin it way up like it can the smaller prop. The lower power it is making at higher rpms just cant turn the prop.

In 2s land it isnt that drastic but the effect is the same. Since we dont run our 2 motors at full blast it is easy to lose sight of what is really happening. I think it is simply making more power to trun the larger prop. IMHO that is where the gain in tension comes from.

I know in setting up the 61/65 the more power I get out of it the more tension I get.

Also when my model is yawed out I feel less tension. Only when I realy draw the nose in and get it as close to tangent to the circle do I really get the heavy duty line tension.

One other thought I have had on this, is that the larger prop makes it harder to pull the airplane out of its "groove".

We can probably agree that it takes a certain amount of power (call it thrust) to pull a car at 55 mph. Now, if we pulled the car on dry pavement or on slippery ice, it would still, so long as the wheels are not spinning once we are up to speed, take only a certain amount of power to maintain that 55 mph speed. (Now there is a second side of this story, too. Better grip on the tires is going to get you up to speed quicker on slippery ice, which is what the bigger prop is also going to be able to do in flight.)

But, having agreed that it takes a certain amount of power (call it thrust) to maintain the constant speed, it would be much easier to push the car sideways on ice. It won't maintain its groove as well. Better tires, better grip, is the only thing that is going to help. The bigger prop should have the greater ability to hold the groove--to keep it from slipping sideways.

So, even if we aren't adding tension--pulling us out of the circle as in the rope illustration--whenever we add input to the airplane, we are doing a little tug to pull it in. An airplane that is light on the lines will pull in quite easily (half-A, for instance). But an airplane that is solid in the groove will not pull in as easily. We can thus fly it without overtiring our arm or being pulled out of the circle, but also have a very solid feel on the lines and be able to input control whenever and wherever we want to.

Of course, the big prop adds more "P" factor (actually, the lower the pitch and the greater the rpm, the greater the effect of "P" factor as well) and precession problems, but then, we have the Rabe rudder and other trim "thingies" at our disposal to deal with this.

And I will admit, there are trade-offs to anything. Just putting a real P-51 into the air can be an exciting experience because of the "P" factor in play when lifting the tail.

>>>I run the 12" 4 blade and the tension is good. I run the 13" 3 blade and there is more tension.<<<

And Doug do you know that your larger prop has also higher effective pitch at tip? So it will need little less RPM for the same speed (probably 200)? Means if you have all the same, your model is quicker and so clearly makes more line tension ...

>Whatever "pull" there is on the lines is thrust that is over and above what is needed to
>propel the airplane through the air.

Len-

Disregarding any horizontal aerodynamic forces, the pull you feel as line tension from an unyawed model (the centrifugal reaction on you to the centripetal force YOU exert on the plane through the lines to keep it circling) is the inertially derived force the plane exerts on you due to its reluctance to change direction. It is not a component of thrust. Now, if you yaw the plane modestly outward, then you can employ a component of your thrust to create more line tension - at least around level flight. As has been remarked often on this forum and as I have demonstrated to myself at the field, this can reduce line tension at higher altitudes, due to loss of speed hrough reduced thrust, thus reducing the mv^2/r force at a time when an inward gravitational component also exists.

If you were to yaw your full-sized P-51 inward to reduce line tension, then you also lose thrust. This is because you have used a component of your thrust to take over the job of your pull through the lines to centripetally accelerate the plane in a circular path.

I have no really relevant experience yet with my lower powered models; so I do not know the relative amounts of increased line tension you are experiencing from using larger props or how much change you experience at various attitudes and altitudes (angles to horizontal in the hemisphere). Is it possible that some of this change comes from increased prop mass and the associated forward movement of the c.g.? The high speed of the constantly accelerated mass at the longer tips must cause some resistance to the plane's change of direction, but I suppose this is manifested as the upward force from gyroscopic precession. I guess too that the instantaneous differences between attack angles of the inward directed blades vs. the outward directed blades is changed with increased diameter. I'll have to think further on this. What I'm sure of is that the increased tension doesn't come from thrust or power, if speed remains the same. I am guessing that it must come from inertial forces, asymmetrical prop dynamics, or subtle trim changes.

SK

>As far as what the "big boys" use. I think they will run
>whatever Billy runs...

Well....Some of them...Maybe....!

>
>>As far as what the "big boys" use. I think they will run
>>whatever Billy runs...
>
>
>Well....Some of them...Maybe....!

Well, sure.

I just mean that the well spring of all things pipe engine related somehow always seem to point in that direction.

>>
>>>As far as what the "big boys" use. I think they will run
>>>whatever Billy runs...
>>
>>
>>Well....Some of them...Maybe....!
>
>Well, sure.
>
>I just mean that the well spring of all things pipe engine
>related somehow always seem to point in that direction.

It looks like a certain Texas flyer better stay away from certain Northern California and Pacific Northwest contests!

>>
>>>As far as what the "big boys" use. I think they will run
>>>whatever Billy runs...
>>
>>
>>Well....Some of them...Maybe....!
>
>Well, sure.
>
>I just mean that the well spring of all things pipe engine
>related somehow always seem to point in that direction.

Huh? I have the utmost respect for Billy's skill and accomplishments, and I pay attention to his approach - but there aren't very many people copying it. Most of the airplanes and engine seutps I see come from a *very* different underlying concept and design lineage. Maybe that's to our detriment, but that's the reality.

> Huh? I have the utmost respect for Billy's skill and
>accomplishments, and I pay attention to his approach - but
>there aren't very many people copying it.

Everyone who runs a PA and uses a Billy pipe is copying his approach to some extent. I think Bob Hunt might agree (you could ask Dean Pappas or Randy Smith also).

Billy has probably tested everything out there, and there are a lot of people who are listening downstream. I do not know Mr. Werwage personally, but I see his influence.

I certainly will not argue the fact. Think what you want. I will think different...

PS: Why do I care? I run 4 strokes.

>
> Huh? I have the utmost respect for Billy's skill and
>accomplishments, and I pay attention to his approach - but
>there aren't very many people copying it. Most of the
>airplanes and engine seutps I see come from a *very*
>different underlying concept and design lineage. Maybe
>that's to our detriment, but that's the reality.
>
> Brett

I'm sorry Brett, but look again. How many SV/TBolt wings are out there? And how many PA/Aero pipe Combos are flying in competition?

What Billy does has a huge influence on what is concidered to work well in this event.

>>
>> Huh? I have the utmost respect for Billy's skill and
>>accomplishments, and I pay attention to his approach - but
>>there aren't very many people copying it. Most of the
>>airplanes and engine seutps I see come from a *very*
>>different underlying concept and design lineage. Maybe
>>that's to our detriment, but that's the reality.
>>
>> Brett
>
>I'm sorry Brett, but look again. How many SV/TBolt wings are
>out there? And how many PA/Aero pipe Combos are flying in
>competition?

I don't know - I guess I don't see a lot of Thunderbolt wings, and I would have no idea where to even get the plans for one, other than the obvious expedient of calling Billy directly. I hardly ever see SV-series locally. And, I thought me and my buddies were running the PA's "all wrong" - which would suggest some deviation from the plan.

None of this is a criticism. But compare, say, Ted's Trivial Pursuit with a modified PA running an Eather prop and an Eather Pipe to a Thunderbolt. Then compare Paul's Mustang with a Saito 72. Heck, for that matter, compare an Infinity with a R0-Jett and an Eather prop. Do any of these look like they come from the same design tradition?

>What Billy does has a huge influence on what is concidered
>to work well in this event.

When did I say otherwise? I merely pointed out that Billy is not the sole source of this. I watch what he does, and try to understand it, and see if it would work for me. Then I look at what Paul is doing, and try to understand it, and see if it would work for me. Then I look at what Ted is doing, and.... but why belabor it.

I've probably ripped off Paul more than anyone, but that just proves my point.

Maybe I'm stupid, maybe I'm making a competitive mistake, but I'm not copying anybody. Maybe that's why I'm such a loser. But stunt is not a cult.

I have nothing but respect for Billy and his accomplishments in this event - so don't "spin" or filter it to suggest otherwise.

Brett,
Maybe that is one of the best aspects of this event. We have so many guys that are proven winners to steal from! Each has his own ideas and set ups, and we develope our *style* from what we observe and try. This Paul W. guy.... 9 Walker Cups (is that why it's called the "Walker" Cup??)wins them with .60, .40FSR, pipes, 4 strokes, and flies a 4 X 15FP ENGINED B-17 At the World's!....Kinda impressive. The other esteemed gentlemen have somewhat similar "stories", too. (except for that 4 engined B-17 LOL!!)
Any of the Walker Cup winners/Team members from the recent past have to know quite a bit about what works for them, right? I think it is great that they are willing to share their knowledge with all who ask.
Bill <><

"cold hearted orb rules the night.... robs the colors from our sight.... red is gray and yellow white, and who's to say which is right and which is an illusion"

> I think it is great that they are willing to share
>their knowledge with all who ask.

That's the truly amazing part of this event - the hot-shots are perfectly willing to tell you what they are doing, sometime to a fault, and still be fierce competitors.

Ted, David, and I are such close collaborators that I would have a tough time figuring out all the stuff I've ripped-off, copied, learned, whatever from them. And I think I have done a reasonable share of contributing, as well. But when it comes to the contest, there's hardly anyone I want to beat more! But we all go home friends.

In general, I think the hero-worship/designated cheering section/"my guy right or wrong" factor is not the most appealing side of the event - but if you were picking heros, you could to a lot worse than Billy, Paul, Ted, etc.