Unlimited Aluminum Aeorbatic Aircraft

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Toobuilder

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How the aircraft "presents" to the judge on the ground is an important component of competition aerobatics. I understand that the biplanes have fallen out of favor mainly due to this aspect rather than their raw aerobatic capability. I suspect that a "sub scale" Extra would be at a disadvantage right out of the gate. I'm not versed in competition aerobatics enough to back this up, but hopefully someone can clarify/dispute.
 
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Himat

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If full scale aerobatics is like F3A radio control model airplane aerobatic, I second Toobuilder.
How the aircraft "presents" to the judges is an important component of the competition. A smaller airplane may look "wrong" to the judges and score less.
 

Vector

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This may explain why the One Design never really picked up despite the roll rate and low budget cost. From what I have been told, it is really hard to judge from the ground. But then again, the average Pitts is not that much bigger if at all.
 

BJC

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How the aircraft "presents" to the judge on the ground is an important component of competition aerobatics. I understand that the biplanes have fallen out of favor mainly due to this aspect rather than their raw aerobatic capability. I suspect that a "sub scale" Extra would be at a disadvantage right out of the gate. I'm not versed in competition aerobatics enough to back this up, but hopefully someone can clarify/dispute.
You got it right. Part of presentation is the judge's ability to accurately judge the line of the airplane. It is much easier to judge the line of an Edge or MX than it is the relatively stubby shape of a Pitts fusleage or even a small monoplane such as the One Design.


BJC
 

jbourke

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I'm flying in Advanced and Unlimited with my Extra 330LX and I've thought about this subject a bit. Maybe my thoughts will help.

If you are on a budget and want to build a competition airplane then you are going to want to go with 4 cylinders.

The obvious starting point is the Pitts. There are a ton of them out there. They fly well. If you build it like everyone else does it almost certainly won't kill you. They make great aircraft for competition up to the Advanced level. The main downsides are that they are small and draggy. The drag eats up energy so Pitts pilots get used to starting the sequence high and working their way down. Since they start high and they are small they just don't present as well as cleaner aircraft. I love the Pitts but that's my honest impression as a judge. It's very hard to fly a Pitts well enough to make up for the fact that the judges are squinting to see it.

There are several monoplane options. The Giles and the One Design are great airplanes, but I prefer the Laser 200. There are some pilots out of the San Francisco area flying a 4 cylinder Laser to good effect in Unlimited, so I know it is capable.

It would be very hard for any 4-cylinder airplane to compete at the National or International level but if your interest is in flying successfully in regional competition a 4-cylinder airplane is plenty.

So I would suggest start with the Laser 200 and start improving on that design. The wing tips could be improved, but the wing itself is fine. The cockpit could be more ergonomic. You could squeeze some more range into it and clean up the drag. Pretty soon you'd have a really nice sport plane that could hang with the 6 cylinder composite aircraft like mine.

The Slick 360 is an example of such an effort.

Jim
 
S

Sasho

Being among the top performers these days, even the newest models of Extra still resemble some structural features of their predecessor the Stephens Akro. WAC's have been won with airplanes of all constructions- tube and fabric, sheet metal, wood, composite and their combinations. Material choice is heavily influenced by traditions for each manufacturer. Yak50-55 and Zlin-50 are products of relatively massive organizations, seasoned at designing and building in sheet metal. Pitts, Laser, Extra roots are in homebuilding or small private enterprises. The producers of modern all composite airplanes have their own considerations, which in my opinion include appearance and fashion together with performance. Do we have an all composite winner of WAC yet?
 

jbourke

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You can find out about what aircraft are flown in international competition at Aerobatic Championship Results

This last year in France is right here: Known*compulsory*programme

Top 3 positions went to the Extra 330SC.

Generally speaking you will find mostly Extra and Sukhoi aircraft at the top of the list. The French team flies Extras. The Russians fly the Sukhois. There is more variation in aircraft from other countries, but certainly all 6-cylinder.

Few of the aircraft are entirely composite, but of course Rob Holland flies his MX to great success and some choose the XtremeAir. There aren't many pure composite aircraft to choose from!

Jim
 

autoreply

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How the aircraft "presents" to the judge on the ground is an important component of competition aerobatics. I understand that the biplanes have fallen out of favor mainly due to this aspect rather than their raw aerobatic capability. I suspect that a "sub scale" Extra would be at a disadvantage right out of the gate. I'm not versed in competition aerobatics enough to back this up, but hopefully someone can clarify/dispute.
That never even occured to me. (I can fly all standard aerobatic figures, but I've never even seen a contest)

Say you scale down the Extra 300 to 70% of all dimensions and keep to the earlier mentioned weights and power. That'd give you about 35% lower wing loading, so tighter figures if we assume penetration (mass over drag) remains the same. Could allow performing at a lower altitude. Would that work for an unlimited ship, or is that not realistic?
 

jbourke

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Say you scale down the Extra 300 to 70% of all dimensions and keep to the earlier mentioned weights and power. That'd give you about 35% lower wing loading, so tighter figures if we assume penetration (mass over drag) remains the same.
That's pretty much what the One Design is. It's probably pretty close to 70% in each dimension.

Could allow performing at a lower altitude. Would that work for an unlimited ship, or is that not realistic?
In aerobatic competition you must fly in a box. The box is 1000 meters x 1000 meters. The height of the box floor depends on the category. In Unlimited the floor is at 100 meters.

There is no point in going lower than that. It just results in a penalty.

We are also not allowed to go out of the top of the box. Also a penalty.

There are various figures allowed in competition. Each figure has "elements" which includes rolls and snap rolls of various directions, sometimes alternating.

Meanwhile there is a limit to what the pilot can tolerate. 10 gs or more for brief periods is possible. We can't let the plane get too fast or it is not possible to corner within the box without knocking out the pilot. The higher the roll rate the better but there is a limit there as well. My aircraft rolls quite a bit faster than one roll per second. It's a blur at high speeds but at low speeds I sometimes wish I had just a tad more roll available.

It works out pretty simply that we just want:
- a very light airplane so we can turn tightly with as little g as possible
- enough horsepower that we can reach the top of the box from the bottom
- the highest roll rate we can get so we can fit all the elements in

Jim
 

bmcj

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We are also not allowed to go out of the top of the box. Also a penalty.
I'm familiar with the box and the rules, but how do they detect excursions out through the top of the box?


The higher the roll rate the better but there is a limit there as well. My aircraft rolls quite a bit faster than one roll per second. It's a blur at high speeds but at low speeds I sometimes wish I had just a tad more roll available.
You haven't had fun until you've roll at 720 degrees per second. :gig:
 

jbourke

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I'm familiar with the box and the rules, but how do they detect excursions out through the top of the box?
There is at least one example I'm aware of where the officials used a radar system, but in general it is up to the judges to make "high" and "low" calls. Consequently it is very hard to earn a "high" call since it is a matter of judgement and not a safety issue. Low calls are more common.

You haven't had fun until you've roll at 720 degrees per second. :gig:
Sounds fun! My plane has a paltry 420 dps. I got a good whack on the head the first time I tried it but it's perfectly manageable now.

Jim
 

Vector

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From what I am told, you have to park the T-38 stick and hold it there for a few turns to really get the 720. The aircraft is amazing going fast in a straight line.
 
S

Sasho

Basically judges should not judge the roll rate. Higher roll rate makes mistakes less visible. The airplanes with extremely high roll rate tend to score poorly in the hands of inexperienced pilots. Experienced pilots have nothing much to hide.
 

autoreply

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That's pretty much what the One Design is. It's probably pretty close to 70% in each dimension.
True, however it seems to be off on at least power/weight ratio, compared to what I proposed.

It seems the One design is an admirable design, but doesn't get close enough to the true unlimited birds.
In aerobatic competition you must fly in a box. The box is 1000 meters x 1000 meters. The height of the box floor depends on the category. In Unlimited the floor is at 100 meters.

There is no point in going lower than that. It just results in a penalty.

We are also not allowed to go out of the top of the box. Also a penalty.

There are various figures allowed in competition. Each figure has "elements" which includes rolls and snap rolls of various directions, sometimes alternating.
I'm aware of the basics and did limited practise in a box myself. Never seen a formal competition though.

So, assume we have our design that has the same power/weight, same aerobatic capabilities and is 70% of the original dimensions of an Extra or sukhoi, while wing loading is considerably lower, such that you can make tighter figures. Would in that case performing manouvres at lower altitude absolve that point?

The more I think about it, the more an extremely light (100-ish HP) unlimited aerobatic bird makes sense.
 

BJC

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True, however it seems to be off on at least power/weight ratio, compared to what I proposed.

It seems the One design is an admirable design, but doesn't get close enough to the true unlimited birds.

I'm aware of the basics and did limited practise in a box myself. Never seen a formal competition though.

So, assume we have our design that has the same power/weight, same aerobatic capabilities and is 70% of the original dimensions of an Extra or sukhoi, while wing loading is considerably lower, such that you can make tighter figures. Would in that case performing manouvres at lower altitude absolve that point?

The more I think about it, the more an extremely light (100-ish HP) unlimited aerobatic bird makes sense.
The lower categories of competition have higher minimum altitudes, so visibility for judging would still be a factor. The thrust to weight ratio that is needed for the higher categories will not be achieved with a 100HP engine hauling around 275 pounds of pilot, parachute and fuel.

I would love to see a good 100 HP aerobatic airplane. A Cassutt with a sport wing and a clipped wing Taylorcraft are two that come to mind, but I have always wanted to see something like a Cassutt with a high AR wing and larger tail surfaces. Yes, I have seen Pete Meyers modified Cassutt, but that is not what I have in mind.


BJC
 

autoreply

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The lower categories of competition have higher minimum altitudes, so visibility for judging would still be a factor.
Any idea of what kind of altitudes we're roughly talking about?
The thrust to weight ratio that is needed for the higher categories will not be achieved with a 100HP engine hauling around 275 pounds of pilot, parachute and fuel.
The Extra 300 is roughly 1500 lbs empty, so say 1800 loaded, bare minimums fuel with 315 hp.
With 100 hp, you'd be at 570 lbs, or about 300 lbs empty. If we assume* 400 lbs empty is possible, power/weight is about 15% lower (or you'd need 17% more power). Sounds like with a light ULpower (130-ish hp) it is possible to match power/weight of an unlimited, but with 100 hp it's impossible.

*To avoid a discussion. For an optimal composite, FG aerobatic ship, I think that's about the lowest realistic weight you can achieve with a 912S and a variable pitch prop, but obviously opinions might disagree.
I would love to see a good 100 HP aerobatic airplane. A Cassutt with a sport wing and a clipped wing Taylorcraft are two that come to mind, but I have always wanted to see something like a Cassutt with a high AR wing and larger tail surfaces. Yes, I have seen Pete Meyers modified Cassutt, but that is not what I have in mind.
It never occurred to me till now that aerobatic ships don't necessarily have to be such big powerful airframes. You'd think more people would have thought/designed/built in this direction, given the popularity of the Pitts.
 
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