da Rock

Too simple by far.

Aspect ratio is not just short versus long.

combatpigg

My Feedback: (3)

Not all speed contests with airplanes are done in circles. Let's consider straight line speed over a short distance after a dive....just flat out speed.
Let's speak from actual experience from time spent in the speed trap with the 2 different wing types, similar weight and similar power.

da Rock

Let's speak from any experience with 2 different wing types, similar weight and similar power that is applicable.

I woulda' thought combat experience was perfectly applicable. Almost exactly the same weight and absolutely exact same power, and an environment where extremely accurate measurement is possible. CL provides an excellent test environment that is very accurate with the tools available to most modelers.

Higher aspect ratio combat wings always kept their speed significantly better in the turns than the low aspect ratio wings. Level speeds did not vary significantly.

rmh

Well- a wing on a string is one thing
Awing which has to maneuver whilst keepng speed is quite another.
Note that F1 cars are designed to turn and hold speed -etc..
straight line speed - is just a tiny aspect (pun intended ) of good wing design.

HighPlains

My Feedback: (1)

The so called straight line speed events run in Germany have proven that the models do slow down significantly during the pull out to the beginning of the speed trap. They continue to slow through the trap. A large part of the slow down during the pull out is due to induced drag because of their short spans used in their present designs.

If you compare the performance of the F3D designs with 40 sized engines to their .91 powered designs, you can see that the pylon designs go faster through the traps than the other designs when you use normalized power. In other words, even though the large engines have twice the HP, their speed is not 26% faster, but barely 10% faster.

rmh

OK- what that proove?

It is obvious that long skinny wings have best l/d
what is apparantly not accepted is that these setups are worhless as teats on a boar for a fast maneuverable setup -
As race courses got longer - the wing requirements changed

combatpigg

My Feedback: (3)

Through decades of trial and work with stop watches and wings of every conceivable design, this is the state of the art.

The contro line speed plane has a "venetian blind slat" for a wing and the RC Speed plane pictured was a Speed Cup winner going through the end of a 200 meter trap at about 220 mph.

Control line combat planes had evolved to a pretty high level of speed and agility. Howard Rush's foamies were fairly high aspect and the best flyers around......until the Russians came out with their own low aspect design that ended up as the single design to survive this very Darwinian event.

da Rock

Having flown combat wing's on strings, I understand that the characteristic they exhibit due to aspect ration is just about 100% pertinent to the discussion we're having PLUS flying on strings provides a modeler a test system the likes of which the RC modeler won't ever approach. So what we experienced was easy to see and quite easy to prove reliably.

Wasn't talking about straight line (pun intended) speed at all. The speed loss with low aspect ratio wing combat wings was significant when they turned. Significant and very easy to judge as most times the LAR wing was up with either an average AR wing. About the time the LAR wings were tried, HAR wings were tried. Why? Because the loss in performance was so obvious, there should certainly be improvement, and there was. However, the improvement wasn't as great. Why? Because it's like everything in aerodynamics, nothing is that simple.

BMatthews

Now we're comparing apples to avacadoes. Control line speed models do not use the long high aspect ratio wings because they need the improvement in L/D or reduction in induced drag. They went to the extreme shown in CP's pic purely because the wing shrouds and streamlines as much of the very draggy round wire control line as possbile. And control line combat has gone to as high an aspect ratio as the structures can comfortably manage due to the need to pull massive G loads for direction changes while losing as little speed as possible. In that respect they can be compared to a pylon racer but not to an open course pure speed design. Just different requirements leading to different answers.

Dick, if it was purely about straight line speed then some lower aspect ratio would likely be found to be best. I say "lower" instead of just "low" because daRock is right in that there's always more to the picture than we include in discussions on fundementals such as this.

But the interesting point is when it comes to our models is that we still need to be able to turn them so as to keep them in sight for control. As shown at extreme speeds even a big open "county size" turn can generate enough load that the wing is asked to work harder and some loss is found. So even for these pure speed models there's an optimum aspect ratio. It may well be that this can be stubbier than a purpose built pylon racer and make a gain.

I find it a little funny that over in the Extreme Prop Speed forum it's all about the delta models. Yet those designs are pretty much the worst possible planform for bleeding off speed in a turn. Even a big open turn. I guess a smaller and harder to see model with a honkin' big engine on it that looks faster than it really is generates enough adrenaline to stir the soul....

HighPlains

My Feedback: (1)

But they land like a manhole cover.

rmh

Each "SPEED' setup dictates which planform works best
Controline speed is TOTALLY it's own thing simply because a snap roll is really not going to happen
The odd one winged thing is really a control line only thing-
not much more than the lines grouped n smoothed with an engine at the outer end- BUT suitable for that "speed" approach.
Very nimble and fast acclerating models shaped like that would never exist
A fast fuel rail is shaped entirely different than a fast F1 car etc., etc.,
A delta planform may look ungainly but they do displace a big chunk of air and can hold a low angle of atack -and keep speed up
Way back when - we tried a DeBolt Speedwagon - after one flight -I dismissed the speed setup as just a rock on a string .
I like fast setups but I also want a model to be flyable at less than full throttle
I have been helping a friend with a big Sundowner - finally got his engine on a pipe setup which works - very high top end yet fully tractable at lwo throttle. ( a muffler pressure closed loop setup)
He tried a "stall turn and said - "this thing falls all over it's self- it's only good for making big turns "
My reply "what did you expect"

combatpigg

My Feedback: (3)

The RC deltas and "near deltas" can at least in spurts get up to the same speeds as their higher AR brethren. I've seen very comparable speeds [to AMA pylon racers] turned in by the deltas with identical power.

BMatthews

Ah, but you won't see those delta wing models flying in a pylon race.

Of course if they are flown in big wide patterns so they don't load up they will still be fast. Over a long enough straight line I bet they are faster than a high aspect ratio model. As Dick says it's a case of picking our poison and then flying it in a manner that leads with the strong aspects and minimizes the weaker ones.

pimmnz

Funnily enough, way back when pylon was first flown and there was an engine and span limit, deltas ended up being banned cause they were faster than anything else and the promoters always wanted scale looking airplanes. In model sizes they do have several advantages over 'normal' models...
Evan, WB #12.

BMatthews

I believe that they were fast more due to the super low wing loading of those early pylon racing deltas. If you go back and look at the designs they were HUGE in wing area while still being quite clean due to having nothing but a wing. They were also built very light for their size thanks to the building skills of all those modelers of the day that learned their chops in the free flight field before going into radio control. Yes that's a shameless plug for free flight....

Also many of them had tip chords sizable enough to be more accurately classed as tapered flying wings. It's not that these pylon racing model delta designs were better than regular planforms. They just used the existing rules to slide around and come out better due to the circumstances of the rules. The pylon class in those days also used very small engines. .19's were the max size as I recall for that brief period. So there may well be a lot of apples to cumquats in making such a comparison.

HighPlains

My Feedback: (1)

The early pylon was a displacement vs area formula. And the winner in 1958 or so was a conventional design.

If the delta planform held any performance advantage, the Germans would be using them in their speed competitions. They don't.

Making lift and an anti-pitching moment with one airfoil does not lend itself to good drag polars.

The one area that delta planforms do well is landing. Easy to operate at a high angle of attack without falling off in a stall, makes landing easy. A clean conventional speed design takes much more pilot skill in landing.

Mike Connor

My Feedback: (5)

I have noticed the Germans are starting to use some modified flying wings that are fairly competitive. Maybe the deltas are next. I guess we owe combatpigg a real pat on the back for taking a $60 build up delta kit to 200 mph last month. [X(]

HighPlains

My Feedback: (1)

Yes, that was pretty good that CP got it up to 200. The same engine would have put any Q40 model above 210-215 in a simular dive.

combatpigg

My Feedback: (3)

215 mph with a .40....7x7 prop....32,000 rpm...4 HP...just to put that in perspective.

rmh

Is that speed clocked from a stabilized, level flight approach of a given distance ,or is it a speed built from some sort of a dive?
The way some speeds are produced ,seem to vary with the "class".

There seems to be two distinct schools of thought on what makes a good speed setup.
1- a bullet with minimal wing or
2- an all wing setup.
Either setup is a bag of compromises.
Of course with enough power
no lifting surfaces are need.
Fire when ready, Gridley-

HighPlains

My Feedback: (1)

The big numbers for prop driven models are always out of dives. A really strong racing engine can produce about 7 hp/cu in, so the rest of the energy comes from converting potential energy to kinetic. This is why the Germans limit the wing loading to 75g/dm^2 or about 24.6 oz/sq in.

A year or so back, there was a guy in the speed forum with a Patriot that he radared at 170 mph in a dive. It sounded rather difficult to believe, but the physics did work out when the hp of the engine, prop efficiency, dive angle, and model's weight were all factored into the calculations. In level flight he was able to reach around 140 mph.

The German event has pretty much any dive angle, but do have a course with gates of a maximum height, and a distance to go before the measurement traps. So they see a large difference between radar speed and trap speed.

Part of the question of maintaining a high trap speed is pulling out of the dive. If we look at the big iron which is pushing 400 km/hr or about 250 mph or about 365 ft/sec. Now assume that the pull out from the dive has a 200 ft radius. This would require a g load of about 22 g, an area where the high aspect wing does better.

If you think that a 200 ft radius is rather big, let's decrease it to 150 feet. Now the load goes up to around 29 g.

Let's tighten it up more because the ground is close to just 100 feet. Now the load is over 42 g.

combatpigg

My Feedback: (3)

This specialized event was developed based on what people wanted to see and hear. To make the event faster than pylon racing, something different had to be allowed, so diving is part of the game. The pilot needs to set up a perfect slope from an entry height of 50 feet and maintain a gradual slope to [15?] feet at the end of 200 meters. To get the maximum unloading but also enough thrust to maintain speed through the course, the event becomes a quest to find [make] the magic prop after all the other hoops have been jumped through.
One advantage of the stretched out conventional designs that I see is being able to thread the needle through the timing zone with less input. Deltas are amazingly smooth and precise,[in spite of themselves] but it's a matter of degree that I'm talking about here.

rmh

I guess this is why the "speeds" are so high

I should do my engine rpm tests the same way

Which brings up another funny point
Some guys think the engine is developing more power just because it runs faster in a dive.
I watched a guy leaning out his golw engine to get more revs in a split S- the engine actually put out LESS power as he went - but revved harder in the dive.

combatpigg

My Feedback: (3)

The engine does develope more power in a dive. It is partly fueled by the fuel in the tank and partly fueled by stored energy of the plane, but the prop doesn't turn faster because of magic.

X prop at X rpm = X horsepower

HighPlains

My Feedback: (1)

Perhaps, perhaps not.

The HP can go down with higher rpm because the torque goes down. That's why there are graphs of peak torque and peak hp.