A question occurred to me in relation to Ted's famous (and very interesting to me) experiment.  If it were possible to produce a scaled-up 60-size version of Ted's Tucker in which all else is identical: balsa density, number of dope coats, proportionally higher engine weight, etc. is it likely that the same need for extra weight would occur?

In other words, would the larger control surfaces require sufficiently greater control force so that additional weight might be required, OR, would the greater absolute mass of the larger plane without ballast alone be sufficient to eliminate the problem?  Thanks in advance for replies.  

Quote from: Kim Mortimore on September 28, 2013, 12:25:18 PM
A question occurred to me in relation to Ted's famous (and very interesting to me) experiment.  If it were possible to produce a scaled-up 60-size version of Ted's Tucker in which all else was identical: balsa density, number of dope coats, proportionally higher engine weight, etc. is it likely that the same need for extra weight would occur?

In other words, would the larger control surfaces require sufficiently greater control force that additional weight might be required, OR, would the greater absolute mass of the larger plane without ballast alone be sufficient to eliminate the problem?  Thanks in advance for replies. 

   Maybe not, because as you scale something, the area goes up as the square of the linear dimensions, and the weight goes up as the cube of the dimensions.

     I'd have to think about it. I have seen a few somewhat larger airplanes that suffered greatly from being built too light and too powerful which made the trimming beyond the capabilities of the pilot to diagnose and correct.

    Brett

I am far from an expert in this kind of thing, but I think there is an optimum weight for every plane. I have an old Nobler that was given to me that weighs 52 ounces and is the best cornering plane I have ever flown. It turns extremely tight corners with no bounce and comes out right on line. Even with the Fox 35 that's in it.

When you increase the size of an airframe, unless you are building with solid wood, the final density of the skinned and finished airplane will be lower than a smaller ship.  This is a large function of built up construction containing mostly air volume. 

A large plane that is too light may benefit from ballast at the CG...although how much in CL?  I know RC gliders, particularly slope gliders, will benefit from ballast under windy conditions. 

The general rule of lighter is better probably still holds.

Phil

Quote from: Jim Kraft on September 28, 2013, 04:38:54 PM
I am far from an expert in this kind of thing, but I think there is an optimum weight for every plane. I have an old Nobler that was given to me that weighs 52 ounces and is the best cornering plane I have ever flown. It turns extremely tight corners with no bounce and comes out right on line. Even with the Fox 35 that's in it.

BINGO! That is exactly what I was trying to express in the other (DELETED) thread.  

Brett, Not being an AE I like that squared & cubed thing....  I have experienced it in my past (Glider Competitons) The bigger ships fly better for that application.

Will we see you in Napa on the 6th?

Cheers, Jerry

Quote from: Gerald Arana on September 28, 2013, 06:27:36 PM
BINGO! That is exactly what I was trying to express in the other (DELETED) thread.  

Brett, Not being an AE I like that squared & cubed thing....  I have experienced it in my past (Glider Competitons) The bigger ships fly better for that application.

Will we see you in Napa on the 6th?]

    Perhaps, judging as usual, but likely not flying.

     Brett

Quote from: Phil Krankowski on September 28, 2013, 06:26:40 PM
When you increase the size of an airframe, unless you are building with solid wood, the final density of the skinned and finished airplane will be lower than a smaller ship.  This is a large function of built up construction containing mostly air volume. 

A large plane that is too light may benefit from ballast at the CG...although how much in CL?  I know RC gliders, particularly slope gliders, will benefit from ballast under windy conditions. 

The general rule of lighter is better probably still holds.

Phil

    The fraction of "air/balsa" is constant if you scale everything up (including the wood thicknesses).

    The Tucker experiment definitively showed that lighter was not always better. That doesn't mean that heavier is always better, either. It depends on a multiplicity of things far beyond the overall mass or wing loading.

    Brett

Is there an article on this experiment available?  I don't find anything with a Stunt Hanger search. 

Quote from: Brett Buck on September 28, 2013, 11:09:29 PM
   The fraction of "air/balsa" is constant if you scale everything up (including the wood thicknesses).

   The Tucker experiment definitively showed that lighter was not always better. That doesn't mean that heavier is always better, either. It depends on a multiplicity of things far beyond the overall mass or wing loading.

   Brett

No.  It's not.  If you have a round hole, and increase the diameter by 2x, it has 4x the area but only 2x the perimeter.
 
If the material sizes are increased by the same percentage as the increase of overall scale the density is still going to be reduced.

Phil

A general reminder here to no one in particular---if we get into controversy, please play nice to avoid having this thread get bounced.  Thanks in advance.

Quote from: Brett Buck on September 28, 2013, 01:12:54 PM
......I have seen a few somewhat larger airplanes that suffered greatly from being built too light and too powerful which made the trimming beyond the capabilities of the pilot to diagnose and correct.

    Brett

Brett,
Do these planes all tend to have the same problems, or are the problems all over the place? 

Quote from: Brett Buck on September 28, 2013, 11:05:42 PM
    Perhaps, judging as usual, but likely not flying.

     Brett

C'mon Brett.  You can beat me with the Ruffy again.  I added 10oz to the CG and it flies grrrrrrreat!

Ted

p.s.  Actually, I was just joking about the weight.  It's fine at 42 (the Tucker was 34 before adding the lead).  I did, however, make some changes that you'll find salubrious.

Quote from: Ted Fancher on October 01, 2013, 12:14:54 PM

.....salubrious.

Does wearing a bib help?

Quote from: Ted Fancher on October 01, 2013, 12:14:54 PM
C'mon Brett.  You can beat me with the Ruffy again.  I added 10oz to the CG and it flies grrrrrrreat!

Ted

p.s.  Actually, I was just joking about the weight.  It's fine at 42 (the Tucker was 34 before adding the lead).  I did, however, make some changes that you'll find salubrious.

   I will likely not find out this weekend, seeing as how I will be at work 10PM-6AM both days. I supposed I could sleep on the drive up, but I am not sure the other people on 680 would be too happy with me.

   Brett

Quote from: Ted Fancher on October 01, 2013, 12:14:54 PM
C'mon Brett.  You can beat me with the Ruffy again.  I added 10oz to the CG and it flies grrrrrrreat!
Ted
p.s.  Actually, I was just joking about the weight.  It's fine at 42 (the Tucker was 34 before adding the lead).  I did, however, make some changes that you'll find salubrious.

I don't have the higher math skills that some of you have on this forum but I always thought if you took 34 and added 10 it would be 44. Is this some new math or a form of calculus?

Just poken at ya

Quote from: Robert  Storick on October 02, 2013, 08:36:22 PM
I don't have the higher math skills that some of you have on this forum but I always thought if you took 34 and added 10 it would be 44. Is this some new math or a form of calculus?

Just poken at ya

   It was 8 ounces added at least when Ted and I were doing it.  I recall different starting and ending numbers.

     Ted was referring to adding 10 OZ to the Ruffy (to "help" me, no doubt, at this weekends contest, while he flies something else). The only number 10 that I recall associated with the Ruffy was the $10 I won when Ted and I both flew it at the NWR.  Some wagering was involved. The recollection is really vague, it came out something like this:

CLASSIC STUNT (15 entries)
1. Brett Buck, 549 (no appearance points)
2. Ted Fancher, 537.5  (17 appearance points)

   I paid for it the next day in real stunt.

    Adding 10 oz to the Ruffy may possibly be less than advantageous, but I am sure my ole buddy wouldn't be steering me wrong here. Alas and alak, we won't know since I am on graves for the weekend and going to contests from 8 to 4 with 2-hour drives each way is not in the plan.

   Seriously, however, given that the Ruffy has no problem deflecting the small control surfaces with the available line tension, it does appear to suffer severely with induced drag due to the low aspect ratio. Adding 25% more induced drag (needed to overcome the weight) doesn't solve any problem the airplane has and exacerbates the one it does have, so not likely to be a good idea. You diagnose and solve the problem you have, and it's not always the same problem, so the solution is not the same every time.

     Brett

I have thought about this for awhile now and I am wondering how you got it to balance latterly? 10 ounces in the belly I am assuming you put it below the wing didn't the out board wing fly high? As far as I know centrifugal force would raise the out board wing. How did you get that to balance? Add more wing tip weight?

I now have personal experience with 10 ounces of dead weight (the battery) with my electric plane. I know for a fact that 10 ounces above or below tether will make the plane roll.

Quote from: Robert  Storick on October 02, 2013, 09:09:55 PM
I have thought about this for awhile now and I am wondering how you got it to balance latterly? 10 ounces in the belly I am assuming you put it below the wing didn't the out board wing fly high? As far as I know centrifugal force would raise the out board wing. How did you get that to balance? Add more wing tip weight?

      Equally spaced strips of Prather stick-on weights top and bottom, inboard and outboard, right at the CG, and right up next to the fuse sides. I think that 4 "blocks" of weights in 4 strips was 2 ounces, so it went in 2-ounce increments. I think they are still on there, Ted could check. I know that some of them fell off at the Northwest Regionals a few weeks later, so it may be down to +7 3/4 ounces. And yes, Ted did tell on himself for dropping parts.

In any case, when you do something like this, it is important to remove as many of the other variables as possible, and to make a big enough change that you can be sure you can tell that it did something.

    Brett

Quote from: Kim Mortimore on September 29, 2013, 02:13:56 PM
A general reminder here to no one in particular---if we get into controversy, please play nice to avoid having this thread get bounced.  Thanks in advance.

Brett,
Do these planes all tend to have the same problems, or are the problems all over the place?  

 Not all the same. The problems with what I will suggest are "too light" airplanes tend to fall into two categories - inadequate line tension to move the controls, and/or inadequate roll and yaw restoring force. A thrid category of "too light" might also be called "too much flap" and can be solved with trim, so lets forget about that one for this discussion.

  The Tucker is an example of the first problem  - just not enough tension to move the controls far enough. Speeding it up increased the line tension but also increased the control force necessary so it didn't help very much. Let's assume that Ted Fancher and his caddy know how to trim a stunt airplane and would have fixed any underlying trim issues. Adding weight to the airplane and changing nothing else increased the ratio of the line tension to the speed, so the control authority went up with more weight, and the control effort stayed the same, so it came out ahead. In fact, the extra weight allowed the airplane to fly more slowly because it could be slowed down and still have adequate line tension for other reasons, so the end result was much slower lap times and much better cornering. I want to say the last flight without was around 4.6 seconds, and the best flights in the same conditions were around 5.2 with the full 8 ounces. At no point was the lift inadequate to the task, to no harm came from that issue, and it had no problems making it to the top of the circle with a Rustler-Merco 40/Tornado 10-4 3b, so no harm there, either.

  The second issue is that with low line tension, there is less roll/yaw restoring force, particularly roll. Yaw get some passive stability from the aerodynamics (rudder/fin), but there's not much in roll aside from the line tension. That's why tipweight is so critical. If you have a large engine with a large prop, there's a lot of roll and yaw torque variatons, but there's not much line tension available to keep the nose pointed the right direction, nor is there a lot of tolerance for any sort of slightly-off trim condition. Speeding up the airplane does help some depending on the problem but many of the possible disturbances are speed-dependent, too. Changing the line tension at the same speed provides more restoring force and is more robust.

  An example of the latter- two airplanes, both about 585 or so square inches, both with PA65s. They aren't the same design, but not way off. One weighs 54, the other 66 ounces. The first was essentially untrimmable, because the massive amounts of torque, p-factor, etc, cannot be handled with the light line tension available. It may also have the "not enough line tension to move the controls" issue but that doesn't make any difference if it can't be put into proper trim.  The second suffers a bit from weight in hot conditions but is otherwise a solid flier. Both airplanes have stellar vertical performance, a PA65 is still just loafing in either case.

   The first airplane could benefit greatly from several changes - either put on a smaller prop and smaller venturi, and let the PA65 8-stroke at 11,000 rpm, replace the PA65 with a 40VF and run it with the small prop, same effect, or, add ballast (like maybe 6-8 ounces) to increase the line tension without the speed.

  The second airplane would likely benefit from being 4-6 ounces lighter, it would increase the sensitivity to trim errors but eliminate the cornering issues in hot weather. It has also benefitted from a different engine setup that reduces the prop diameter, and removes some of the power variation, but not nearly to the degree that would be needed to fix the first airplane.

   Brett

p.s. in the first case someone might also be tempted to "trim for more line tension". Usually, that is a loser in almost any case, because if you have to manufacture line tension with trim tricks (like lots of rudder offset or excessive tip weight) you get wild variations on the line tension as the speed changes.

I was talking to Ron and he said they flew their 32 ounce planes at 5.8 -6 second laps with fox 35s in the wind no line tension problems. I find that interesting. My guess is one could say ENGINE OFFSET as they did when that plane was designed.

Brett,
Thanks kindly for your detailed response to my question.  The concept of dependence on weight for roll recovery is new to me, but seems intuitive once pointed out.  Looks like the BHE approach (Big Honkin' Engine) is not an unmixed blessing.  I find this kind of high-level trim analysis fascinating and informative. 

Quote from: Brett Buck on October 03, 2013, 02:15:43 AM

..... Let's assume that Ted Fancher and his caddy know how to trim a stunt airplane and would have fixed any underlying trim issues......

This does seems like a....uhhhhh....fairly reasonable assumption.   

Quote from: Robert  Storick on October 03, 2013, 09:47:02 AM
I was talking to Ron and he said they flew their 32 ounce planes at 5.8 -6 second laps with fox 35s in the wind no line tension problems. I find that interesting. My guess is one could say ENGINE OFFSET as they did when that plane was designed.

   Running it with a Fox presents a fundamentally different issue than running it with a RM40, mostly, that you had to make it light as possible for vertical performance. Adding significant rudder offset and engine offset (which is very ineffective at increasing line tension, but less offensive in terms of trim than rudder offset) to "manufacture" more tension may well be a good compromise if you have a Fox. It's a very poor compromise if you have much more power - say, enough power to get even a 8-ounce ballasted airplane around the corners and through the hourglass.

    I think the example 54-ounce/585 square inch/PA65 airplane suffered severely from some trim settings that were an attempt to "manufacture" line tension that just made the situation far worse, unnecessarily so. I know it had substantial rudder offset.

   I am not claiming and have never claimed that adding weight is always a good idea.  I merely note that adding weight made it far better in this and several other cases. That proves definitively that always making it lighter doesn't help.

   I will leave the 6-second-lap part to other budding physicists.

     Brett

Quote from: Kim Mortimore on October 03, 2013, 04:35:47 PM
Thanks kindly for your detailed response to my question.  The concept of dependence on weight for roll recovery is new to me, but seems intuitive once pointed out.  Looks like the BHE approach (Big Honkin' Engine) is not an unmixed blessing. 

   It's the dependence on line tension for roll recovery, and if there were some way to make more line tension without adding weight, and without causing the roll and yaw forcing functions to go up too (like lots of rudder offset, engine offset, or tip weight), then you would be set. With very limited power, like Sparky's example, then you might be willing to live with some of the trim issues to create more line tension than you would have otherwise. With overkill power, there's no reason to have to make that compromise since adding weight causes no problems but solves the Netzeband wall and roll restoring force issues. It was not a close call in any way, it was WAY better with more weight.

     Brett

Quote from: Robert  Storick on October 02, 2013, 08:36:22 PM
I don't have the higher math skills that some of you have on this forum but I always thought if you took 34 and added 10 it would be 44. Is this some new math or a form of calculus?

Just poken at ya

Hi Sparky.  No secret math.  I was kidding about the Ruffy which has pretty much always weighed 42 oz.  Built strictly stock.  It was my Tucker Special that was built ultra light (lots of 1/32 wood and not much of a finish with a very light Rustler .40 engine) that weighed 34 oz off the bench and to which I added eight ounces on the CG, split above and below the wing.  The primary improvement came from a much more predictable control input/response output due to the increased line tension versus hinge moments (control air loads).  Wing loading continued to be a non-issue.  The resulting patterns were every bit as good as the best without the weight and something like 100% more repeatable.

I am, once again, a fan of enough lift to do the job...or put the other way, no less weight that is required to optimize the pattern and the resulting flight scores.  different strokes, etc.

Ted

Quote from: Robert  Storick on October 03, 2013, 09:47:02 AM
I was talking to Ron and he said they flew their 32 ounce planes at 5.8 -6 second laps with fox 35s in the wind no line tension problems. I find that interesting. My guess is one could say ENGINE OFFSET as they did when that plane was designed.

Sparky,

One of my favorite stunt memories was flying as a junior at the 1959 Nats where watching the Tucker Specials from St Louis was one of "the" best parts.  One of the things that doesn't belong in those memories is any instance of people "timing" laps at the stunt circle.  I've heard others (George Aldrich, for instance) say they flew Fox .35 stunters at six second laps but, with all due credit for their skills, I simply don't buy the numbers.  I remember George flying his replicated Nobler at a VSC at or around six seconds a lap and being unable to complete a pattern, let alone a competitive one.  Billy Werwage won the Walker Cup that year with the Ares/Fox .35 flying smoothly but almost certainly closer to five than six seconds a lap.

In more recent times I remember Bob Gieseke flying 5.5 laps competitively with the Gieseke Nobler.  Big difference from the Tucker, however.  Very small chord flaps... and quite large with very soft corners.  The difference was most everyone was flying that way back then.  That is no longer true.

Bottom line, I've flown stunt competitively since about 1957 and never even considered buying a stop watch to do so until I started attending the Nats regularly in the mid '70s and the whole 5.5 second lap thing surfaced via the Bear.

I believe the real secret to lower lap times isn't light weight as much as it is power train (within reason).  The slowest I ever flew competitive stunt was with the original Trivial Pursuit (650-60 squares at 68 to 70 oz) at the 1992 Nats where it finished second.  It was powered by a VF .40 revving more or less 12K with a 3.25 pitch Bolly.  I still didn't time it, by the way.  Randy Smith, many years later told me he had video tapes he had timed and the lap times were 5.8...which surprised me although I knew they were slower than I flew my previous ST .46 ships with-generally-six pitch props.

Don't get me wrong.  I'm not a fan of "heavy" airplanes.  I do, however, believe that wing loadings lighter than necessary to fly competitively may be more of a problem than a solution.

Ted