Stunt Design

I'd like to start a discussion on stunt design philosophy. Not anything specific, just some thoughts about overall philosophy of approach. What is mostly seen at contests are, I hate to say it this way, but "cookie cutter" designs. Different paint, different aesthetics, but essentially the same couple of designs repeated. Now, there is obviously a good reason for this. When a top flyer comes up with something that works, others tend to follow suit. Here in the Northwest, we tend to see a million (well, maybe not a million, but a lot) of variations on Fancher and Walker designs with a bit of Windy thrown in. These designers put in a tremendous amount of work and flight testing on their respective designs and others have taken those designs and used them as a basis for what they are flying. Hey, they work and it's human nature to follow the successful. But, as a recent thread in RCOnline points out, there are other approaches that can also be successful.

Right now, I have 2 planes underway that each take very different approaches to accomplishing certain goals. One is a serious departure from the norm and the other is more conventional, but has some concepts I've learned over the past few years that will likely set it somewhat apart from the norm. The first is entirely my own design, from the airfoil and layout to the moments and areas. The other is based (loosely) on a successful design. Now, I don't know if either will ultimately work out, but I put quite a lot of thought into each.

The idea for me was to not just follow the successful, although, I'd be stupid not to take what I've learned from successful designs. I wanted to use what I've learned the last few years in building a lot of different designs (some mine, some variations on successful designs) and come up with an alternate approach that, in my mind, might be successful.

I know I'm not likely to end up in the Top 20 this way (as Al Resinger has pointed out to me on several occations), but I probably wouldn't anyway. I do want to find something that makes me happy and flies with the characteristics that I'm looking for but that's not a recycled design that someone else has flown to glory

Any thoughts from folks out there on design philosophy?

"1/2% of the total package"

and

"There's a reason they all look alike"

"Because that's the way we've always done it"

You certainly don't give the rest of us much credit.

Brett --

Now, boys, let's not fight! Randy just wants to build something different that flies as well as the top line stunters today, and do it in a different way. That gives full credit to past designs and their success. The truth is nobody is going to come up with a new design that is head and shoulders above what is out there today. The design challenge is to match all the smart guys with a different model.

I still think we could increase airfoil thickness. We could increase tail moments or tail area. Perhaps, go so far as to have the back tail (wing) larger than the front (A Canard, as Bob Hunt is attempting to prove or disprove.) We could put a canard wing in front of the present wing up by the prop. With the power we have today, we could build a biplane design with coupled flaps. We could try moveable, coupled leading edge slats. Or how about a couppled moveable nose where the engine would pivot into the turn?

Now, I am not about to suggest that any of these ideas is going to "fly". Even with the greatest development program in the world, they may all prove to be no better and maybe a lot worse than what we are already flying today. Or a new breakthrough might be made as radical as when coupled flaps were first applied to our stunt ships.

I would never want to quickly write off any of these ideas (or others that have not fully been tried) and, like most others, I will be flying within the "proven window" of airplane design. But people are constantly jumping on the bandwagon of the "winner", even though, in many cases (as was demonstrated by Todd's success at last year's Nats) the "newest" and "greatest" is not, necessarily, any better. But it doesn't mean it is any worse, either. There is room for diversity of opinion and I, for one, welcome any new design pholosophy and a desire to leave the "cookie cutter" mold.

I don't know if the judges will agree, however, and that is another point. Sometimes, there is a lack of acceptance because it is different.

Now, there you go.

>>We could try moveable, coupled leading edge slats.<<

What would be the advantage (if you could get it to work) at the speeds we fly?

When I started thinking about building a plane for this year, I spent a lot of time thinking about what we were trying to accomplish. Forget for minute about weather conditions, power or anything else. Just basic concepts of what we are trying to do. I know that I want a plane that is stable first. I want to be able to point it and it will pretty stay there until I tell it to move. I want a plane that is responsive, but not so jumpy that you breath on the handle and the plane moves. I want a plane that is predictable. And I want a plane that I like to look at.

Your note on judges acceptance is a good one. My buddy Pat and I had a great discussion the other day about the "cool" factor in stunt. It was never so obvious as when Paul showed up with a B-17. Turned out it flew pretty well too, but the initial impression was "WOW!" Like it or not, this effects the judges preception. I think this is a factor that can also work against a design. Show up with someting that is far enough out of the mainstream and the judges look at it and write it off. I don't think this happens on any sort of conscious level, but they believe your not a "Serious Stunt Pilot". Tough to overcome, but I suppose I believe that if you keep coming back and putting in competent flights, eventually the judges will accept it.

Something else to think about.

Here are my thoughts: With coupled, moveable flaps, as we now use them, they move the center of lift back and cause a pitching motion which needs to be countered by the stabilizer and elevator. This, in part, is why we need longer tail moments and larger tail surfaces. Moving the flap, also, changes the angle of attack on the wing, which, in effect, puts down throust on the engine which, then, also works against the turn.

Moveable slats on the front of the wing along with moveable flaps on the rear of the wing, would add to the lift of the wing without appreciable changing the center of lift or the angle of attack. Using these 0ne would probably need even less movement on the flaps and less on the elevator to achieve the same rate of turn.

The mechanics of such a system are not going to be simple, however, as it would need to be an integral part of the airfoil, not like the flat flap on the rear, and there would be structural problems to deal with as well.

I am not saying this is practical, just saying it would be interesting to see developed.

Adding a canard to the nose along with the conventional tail in the rear, I would think would be much easier to achieve. This, also, adds lift while actually moving the center of lift forward, and it would, also, act as a thrust deflector, negating some of the effect of the changing angle of attack caused by the deflection of the flap. Archie Adamisin tried this one year and got some sort of an achievement award, and I haven't heard of anyone trying it since. Why not?

Go for it Randy. Innovate. Lead the pack. Show what can be done. You can do it. (I love to egg other people on, or haven't you noticed?)

Yea, fine. I've stuck my neck out enough.

One good point was made (well, several, but one in particular), I'm not looking to come up with some new world beater design that will catapult me to stardom or whatever. Just looking at using some alternative ideas to overcome certain problems and hopefully come up with something competitive.

You can have all the credit if you want

Look Brett, I've seen your planes and I've seen you fly. Your a great pilot and I've been very impressed with your planes. I was just watching a video of you flying at the 1999 Nats. You don't do things unless they are well thought out and your fairly certain they will be successful. I also know that your not afraid to experiment within certain bounds. When I was having trouble with an engine run last year, everyone pointed to you because you have gained a lot of experience and know your stuff. So, what made you experiment and not just build a carbon copy of something else? I pretty sure you weren't just peeing in the wind but had some specific idea of a problem you wanted to overcome or area you wanted to improve.

Just showing up with some radical new design isn't very often the way it happens. You start off with something, perhaps a copy of something else, but over time you improve something here or solve a problem there and pretty soon, it's a new design. I once saw Paul fly a design of his called the Seahawk (now that was interesting). This plane was near the start of a design cycle that ultimately produced the Impact, a successful and very much copied design. But the Impact still started off as an idea; try to produce something better than what was available at the time. Why didn't he just fly one of Ted's designs?

So, what's the main concept behind your current design? If I remember correctly, you started off a couple of years ago with design criteria from Ted's Imitation, right. So, what did you change and why?

Randy (determined to get SOMEBODY to talk about this stuff)

You could kind of see what was leading up to the Nobler, with the All Americans and the Zilches. But sort of, at best.

Look at the Depperdusin (pre WW 1) full size race plane, and tell me how much prop driven planes have changed in 90 years. Rutan stuff excepted, of course. Now there's a genius.

Just thinking out loud:

Paul Walker's B-17. Not a design trend, but a pure engineering feat that no one wanted to take on...

The Ridiculous and the Humbug? Proved a point, but they're not contest competitive...

As time went on, we got .40s, .45s, and .60s, and piped jobs, and spans that exceeded 60",. but did the designs change that much? Construction techniques and materials certainly did, granted...

No Nats/World Champs competitive bipes to date, at least to my knowledge...

No canards...

When Jets become competitive in price, and light to boot...Who knows...?

You did half a post. What is your design? What are you doing differently? I agree that we are in somewhat of a design rut, and maybe mainstream will stay in that rut. But some fun people may want to go out and play. As you admitted they may not be winners. What the heck? If you come up with something that is "pretty darned good" and is different, I would call that a success and a worthwhile effort.

One is a large, highly tapered, somewhat high aspect (about 6.8 to 1) plane sort of along the lines of Beringer's idea (though the airfoil is differnt and it has slighly bigger flaps - 2/3 span at about 12%). It has a very long tail moment with an airfoiled stab and a forward CG. After experimenting most of the winter with a power setup, I came up with something that I hope will deliver something like consistent power). It's about 700 squre inches with about 23% tailplane. I wish now I had given it a bit more side area, but it has a pretty big fin and rudder pushed pretty far back, so I hope that compensates. Looks pretty cool anyway.

The other is a fairly low aspect (about 4 to 1), highly tapered (22% at the root, 10% at the tip tapered eliptically), eliptical design based very, very, VERY loosely on Dave Gierke's Novi IV. I started off with the Novi and then pretty radically changed it. Different airfoil, different moments, somewhat changed plan form with a much longer tail moment (about 4 inches longer!) and a not even similar fuselage. The tailplane is about 30%. I had some help from Mark McLaughlin who also experimented with this design (he talked me into the larger tailplane based on his experience). In the end, it is not really a very radical design compared to most modern stunt ships. It's about 580 square inches and is coming out pretty light. Will use a piped 40 for power and is likely to be my main squeeze if the larger plane doesn't fly as well as I hope.

So, there you have it. As soon as these are done, I'm back to the 4 stroke powered semi-scale of the Rare Bear.

I have a flying wing design I call the "Agile Arrow". It has some similarities to Red Reinhardt's Stunt Wing, (an excellent flying airplane) and is influenced by some of the modern combat designs. Span 60 in, tapered wing with squarish tips, 720 squares, twin rudders, high aspect ratio elevator, inverted cowled engine (K&B 40). The original is retired after about 800 flights. The one I plan to start on shortly will have trike gear, and may or may not be a modified I-beamer.

I think I was stimulated by some of the ideas noted on RCOnline's discusison of the Sukhoi that placed 2nd at the World Champs.

Funny, everyone seems to want to copy Beringer's (sp?) design. The rush to 4 strokes is interesting to watch. Again, folks see a successful design and want to follow it. I read the outline of design criteria and philosophy posted there and it seemed well thought out. But not in the standard mold. I liked the idea of a very long tail moment to give some muscle to a turn on a plane with a CG pretty far forward to allow for a smoother flight path. The airfoil discussion was also interesting.

Look, classic design works. No question about it. As was said, it's been refined over the past 30 years. But it isn't the only way it can be done as Beringer has shown. I was more interested in that than in his actual design. The Sukhoi is quite a departure, but still within the bounds of general design philosophy that has proven to work. That's all I'm talking about. I think there is a design window into which all successful designs must fall. I probably think that window is a lot wider than others think it is, but the window is still there. Within that window, what can be done?

I suppose we'll see if my ideas function. After building renditions of other's designs the past couple of years, I'm trying something new. Both planes I'm working on are coming from very different design philosopies. I'm pretty sure Number 2 will fly pretty well. It's not that big of a departure (if any). Number 1 is pretty radical, while still falling within the window, as I see it anyway.

Hi Scott,

No, I'm certainly not trying to re-invent the wheel. I'm not going to show up at a contest with a carnard, bi-plane pusher and claim this is the future of stunt (as much as I know you'd enjoy that). As I said, The point of the thread was just to discuss design philosophy and approach, certainly not to bash classical design or claim that all designs over the past 30 years are somehow lacking. That's clearly not the case. I watch Paul fly and I'm always impressed by the not only his superb flying, but the way in which his designs handle certain aerodynamic problems.

OK, let's try this. I've messed with higher aspect designs in the past. everything from moderate (6.5 to 1) to ricdiculous (10 to 1). There are some advantages and disadvantages. One of the disadvantages was that they were more suceptable to roll in maneuvers. I suspect this was because of flexing in the wing structure or in full span flaps. Short, wide wings are easier to build without flex than long, narrow ones. There are other reasons too. A while back in another thread, Brett talked about the use of rudder in trimming roll (a great explanation too, Brett), it got me to thinking that rudder and fuselage side area may be more critical to a high aspect designs. Perhaps it's not just an issue of flex, but that greater side area or rudder area would aid in solving that particular problem. All my high aspect designs tended to have long, narrow fuselages.

What do you think?

In the aritcle Homa posted on RCOnline concerning Beringer's Sukhoi, there was a explanation his theory of the CG, airfoil and moments. I thought this was quite interesting. All designs rely on combination of factors to achieve stability and maneuverability. CG, rudder and engine trim, leadouts, control throw, incidence and a host of other factors. Most planes I have built over the past several years required a pretty far aft CG in order to turn smoothly. This often became (for me, anyway) a balance between turn and hunt. Seemed to me the aft CG, while providing a great turn, magnified other problems. I could trim with a more forward CG and many problems, most notably hunt but also some other problems went away, but the turn suffered. Now, in a perfect world with an perfectly straight plane, maybe this wouldn't occur. But I doubt it. All trim, I think, is a series of compromise. Give up some of this to get some of that. Beringer seemed to solve the above noted problem by thinning the airfoil, pushing the CG forward and overcoming the turn difficuties by pushing the tail moment back (a lot) to give more leverge. He claims that it provides stability and turning over a much wider range of conditions than most conventional designs. And without as much triming to change in conditions.

So, What do you think of this?

Doesn't anyone else ever think about this stuff?

I know you haven't been flying that long, but you've spent a lot of time on the handle. What do you think? I know you have some sense of what seems to work with your own planes and what doesn't.

What do you think about Beringer's notion? Doesn't matter if you agree or disagree.

>>It would seem that high aspect ratio surfaces would not require flaps.<<

Well, I can tell you that really big flaps don't work. And that full span flaps are at best, problematic. I'll let you know how 2/3 span flaps work in about a month. Hey, at least the thing is relatively light. I'll also let you know how stupid long tail moments with probably too big tail surfaces work. Pretty wierd gear too.

How about a piped twin boom ship? I have thought about such an animal myself! I have always liked the looks of the Crusader and the Gobbleshwants. A few changes here and there could produce a piped version don't you think?

On the other hand, from the FF days, I have been designing thicker tip airfoils to cut down tip stall. this seems to be the general thought in stunt these days.

I wonder two things. High aspect ratio airplanes are said to be more succeptable to wind upset. How about thinning down the tip airfoil on high aspect ratio wings to control this? Also, how about doing different thickness tip airfoils on inboard and outboard wing. Would this accomplish anything?

I can't remember the name of the mathematician who said, "When I die, I have two questions for God. First, why turbulence? Second, why relativity? I suspect He can answer the second question."

Pushing my memory to the limit I have these pictures of coefficient of lift graphs where airfoils fall off a cliff at low Reynold's Numbers. It is not gradual, it is indeed a cliff. The FF world crosses RN ranges with a high speed climb and a slow (low RN) glide. At low RNs, the turbulator, sharp LE (remember "Lucky Lindy" FF?) approaches can do wonders. I don't think any turbulator approach will work in our RN ranges. I would like to see someone try it. I think our wings are too big, and our speeds are too high to get to the low RNs where turbulators might help. It is indeed true that turbulence can make air "stickier" than laminar flow, given the right conditions. This is what I recall, and I might not have remembered all this right.

That sort of quote seems to be loosely attributed to several people. The best documented version I can find assigns it to Sir Horace Lamb, in an address to the British Association for the Advancement of Science in 1932. He said:
"I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic."

Well, Werwage went after it another way. Ever look at the airfoil on the wing and stab of the USA-1 and subsequent planes? Very thin airfoil with the high point very far forward. Very Berringer-esque. Another idea...

Funny you should bring that up. My current ship, which is fairly high aspect as things go (about 6.8 to 1), has a 24% airfoil at the root and about 11% at the tip. Gues we'll find out. I never noticed the rocking or similar stability problems in the wind with previous such designs. Biggest problems was variable control response based on how hard the wind was blowing. You just never knew where the thing would turn at. I think I've gotten that solved by 1) creating a much sturdier control system, 2) cutting down on the flap length (the current plane has 2/3 span (or about 12%) flaps and 3)much stiffer overall construction. The thing ain't going to flex. Now we'll see if the other assumptions and ideas work out. My biggest concern is a largely untested power system. But I have high hopes (and set it up to take another proven power system if the primary fails).

>Jim, I like the looks of them (twin-boomers) too, but the
control system is the real hangup. Putting the force into
the flaps and elevator anyplace other than in the center
or on both ends simultaneously is asking for problems,
IMHO.

About 25 or 30 years ago, I built two modified Humbugs that I was far less than happy with. The second had a "full cable pull-pull system" that was duplicated in each of its twin booms (not trips as per the Baron plan). I had two bellcranks, each of which had twinned acting arms, one in each boom. At each end of a flying stab, I had horns on either side.

The control system wasn't what I had trouble with after it was installed. As a matter of fact, that part worked very well!

Kiwi

P. S. (Added in Edit) OK, then, for what it's worth, I used the same (Veco Series 200 19BB) engine that Baron did, the same prop, and the second of the pair was lighter than his prototype, but both needed to go "too fast" in order to perform, and I was quite surprised to find that 60+ mph maneuvering was much harder when you care about the SHAPES of things than when you're just having fun with something fast, like one of my Streaks at those speeds.

I "needed" to slow down one more notch or so to 55 mph (I cannot recall ever hearing any single lap's times ever mentioned before the mid to late 1980's, but we did occasionally clock some for six or seven laps, and the Humbugs weren't super fast, but just enough harder to track with), that I didn't rebuild either one after crashing due to pilot errors.