# Unlimited Aluminum Aeorbatic Aircraft

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#### jbourke

##### Member
And while I honestly feel a 100-130hp acro mount will never be competitive in Unlimited, I do hope people keep trying, even though the market is miniscule.
Very well said, John. All of it.

Jim

#### autoreply

##### Well-Known Member
I've been attending IAC competitions since 1997. During that time there have been a myriad of low cost, low power aircraft available on the market to whoever wanted them. Everything from the Cessna Aerobat, RANS S-9 & -10, Sonex, RV-3's, Stits, etc., etc.. In those 18 years I've seen only two Cessna Aerobats and one Sonex in the box. Whether it be the folks who own them don't feel they are up to perceived competition standards, or that competition is not their cup of tea, who knows. Fact of the matter is that the airframes exist, but don't show up.
None of those would qualify as even "fully aerobatic" in my box.
Every few years there's the call for an affordable, top tier aerobatic airplane. But we're not a culture of builders anymore, the vast majority gravitate to factory Pitts, Extra, Yak and Sukhoi for their mounts in Advanced and Unlimited. I've only seen one Zenith, the Eigenhawk (a one off), Laser, and various Pitts S-1's as homebuilts in the top two levels.
Makes sense. So without a kit (so plans), there's essentially no market.
Presentation through size and horsepower is the determining factor. And while I honestly feel a 100-130hp acro mount will never be competitive in Unlimited, I do hope people keep trying, even though the market is miniscule.
I'm mostly interested in why it hasn't worked. Why, not how to. Because understanding why it didn't work (till now) is the only way to discover what needs to be changed, or possibly that you'd better find a realistic proposition.

Not trying to split hairs here but just to make sure the details are clear, the Extra 300 is not an unlimited class airplane and also has 300hp. It is often flown in Advanced but only rarely seen in unlimited and it is completely outclassed. It is also a two seat airplane, so it is heavier than most.

My Extra 330LX is lighter than the 300 and rolls much faster. It weighs somewhere just over 1400 lbs. It is two seat also, but capable of unlimited. It would not do well enough in international competition but is acceptable for regional unlimited competition.

The Extra 330SC is the top of the line single seat unlimited class aircraft today. They typically come in at around 1300 lbs. It is common to pump up the engines on these planes which puts them at 350hp or more.

So your target power:weight ratio is a bit higher than it might have seemed at first, but that depends on whether you are looking for something to fly at the very highest levels. There is more to it than power:weight because presentation is also extremely important.
So we're talking about this right:

 Extra 330SC Proposal Power 350 130 EW 1300 400 Pilot 200 200 Fuel 175 65 AUW 1675 665 power/weight 0,209 0,195 Prop dia 1980 1700 Prop disk 3,08 2,27 Disk loading 114 57

With such disk loading, the proposal might end up on top (I'm baselining with the UL350iS), assuming 1.5 hours of fuel, same pilot etc. Disk loading in the end defines how much trust you have, which is a major contributer to low and mid-speed performance.

I'm interested in a deeper breakdown of the weights if you have time for it. Maybe a new thread.
I only have one for a design with similar engine weight (Rotax 912S/914), but otherwise different. Without building it, little point in argueing it though. Would there be a market for such a design if say the complete kit plus engine plus hydraulic prop and bare instruments was available for say 60K US$? #### jbourke ##### Member I'm mostly interested in why it hasn't worked. Why, not how to. Because understanding why it didn't work (till now) is the only way to discover what needs to be changed, or possibly that you'd better find a realistic proposition. There might simply be an opening that hasn't been explored yet, since the people flying and designing planes are probably not the same people flying advanced aerobatics. When the Pitts was designed it was based on an engine that by today's standards is very heavy. The more modern designs like the Giles were built around the engine used by the Pitts, essentially. If there are new options then it makes sense to go back to basics. With such disk loading, the proposal might end up on top (I'm baselining with the UL350iS), assuming 1.5 hours of fuel, same pilot etc. Disk loading in the end defines how much trust you have, which is a major contributer to low and mid-speed performance. Within reason, yes. We need to do elements that require crispness, like point rolls, and that requires airflow over the wings, so we can't just tractor our way through a sequence. Would there be a market for such a design if say the complete kit plus engine plus hydraulic prop and bare instruments was available for say 60K US$?
Probably not. (edit: but who am I to say??)

One aircraft we forgot to consider in comparison is the Rans S-9. If you haven't reviewed the specs on that it is worth a look.

Jim