Single engine 300-400hp pusher

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KC135DELTA

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It's been awhile but I have been running a little design through my head the past month or so. Sorry if the write up is rough, please bear with me.

The basic concept is; high horsepower (300-400hp) turbo normalized water cooled single engine mated to the rear of an extremely efficient pressurized 6 place carbon composite fuselage in center line thrust fashion with the main wing spar passing below the rear bench seat.

Think scaled down learfan



With the only major difference being the intake would probably be a NACA duct and the cooling radiator would essentially be the vertical stab in a T tail configuration in order to get the horizontal stab outside of the prop diameter so we can get a cleaner less interrupted airflow.

Benefits of this design include
-clean jet like visibility
-far less noise as the propwash and turbulence is simply carried off into the airstream
-more efficient as the propwash is no longer destroying the airflow over the fuselage

very rough idea but the idea is to keep it light (1,800lbs empty/3,600lbs gross) and efficient with higher wing loading. One difficult issue I foresee is the wing design as the high wing loading will probably have to integrate some kind of electric flap system (hydraulics too heavy) in order to get stall speeds ~65knts


Thoughts?
 
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Autodidact

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It seems to me that the usual problem with a conventional (non canard) pusher is to get the power from the engine back to the tail where the propeller is. Could you put a turbocharged wankel back at the end of the tail cone so as to avoid the shaft drive and still have enough weight in front of the wing?
Also, 9 lb/hp, possibly 6 lb/hp lightly loaded - whats this gonna be, a six passenger point defense interceptor?:grin:
 

bmcj

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Certainly doable. I like the Learfan, but I'm not a big fan (pardon the pun) of T-tails. Despite having 3 surfaces in front of the prop, it offers an arrangement that works and provides protection against a prop strike. Build in a little distance between the prop and tail, design to minimize control deflection in steady-state trimmed flight, and go with 4 blades to keep from pulsing all 3 blades at the same time (instead, you get 12 smaller pulses in each revolution).
 

wsimpso1

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Warning! Big issues happen when you try to drive a prop with either a PSRU or a shaft or both. You will need to do your dynamics homework on the powertrain, design it to drive the torsional resonance modes outside of the operating range if you can, and tame any remaining modes with tuned absorbers or other devices if you can not. Serious engineering effort may be required, and I can not emphasize this enough, you are unlikely to beat resonance without an analysis based engineering effort. Cut and try really will not do it...

Tail design and number of prop blades should be driven by the resonant modes and frequencies too. Resonant modes are excited when either of engine firing order or twice firing order or prop blades passing through the wake of the tail surfaces occur at the smae frequency as a resoance mode. Serious homework ahead.

Billski
 

KC135DELTA

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It seems to me that the usual problem with a conventional (non canard) pusher is to get the power from the engine back to the tail where the propeller is. Could you put a turbocharged wankel back at the end of the tail cone so as to avoid the shaft drive and still have enough weight in front of the wing?
Also, 9 lb/hp, possibly 6 lb/hp lightly loaded - whats this gonna be, a six passenger point defense interceptor?:grin:
Putting the engine too far to the rear will make it very difficult to balance and keep in CG when the fuel burns off. This issue will be even more prominent considering the high aspect ratio needed for the more efficient wing.

But yes it will be quick, think of it as the VLJ alternative, or assassin. Your choice :roll:

Warning! Big issues happen when you try to drive a prop with either a PSRU or a shaft or both. You will need to do your dynamics homework on the powertrain, design it to drive the torsional resonance modes outside of the operating range if you can, and tame any remaining modes with tuned absorbers or other devices if you can not. Serious engineering effort may be required, and I can not emphasize this enough, you are unlikely to beat resonance without an analysis based engineering effort. Cut and try really will not do it...

Tail design and number of prop blades should be driven by the resonant modes and frequencies too. Resonant modes are excited when either of engine firing order or twice firing order or prop blades passing through the wake of the tail surfaces occur at the smae frequency as a resoance mode. Serious homework ahead.

Billski
Your concern is grounded in a bedrock of truth. The original learfans biggest argument (between the thick headed bill and his engineering staff) was to drop the transmission and go with each of the turboprop engines turning counter rotating props, but it was understood that if one power train were operating at max power and the other at a different interval the aircraft could be rattled to carbon bits. Then the FAA poked its eyes out after seeing the transmission arrangement but that's a different story.

Very complicated subject that will require outside expert engineering expertise. The whole power train is exotic to begin with, this will just be more icing on the cake.
 

DaveK

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I would immediatley question the possibility of building a 6 passenger aircraft with 400 hp that has an empty weight of only 1800 lbs. I see that you show gross of 3600 lbs which implies 1800 lbs of useful load, which. 6 FAA standard people is 1020 lbs add fuel for 5 hrs of flight at around 750 lbs and you have your 1800 lbs and you still have baggage to account for. So do you really think you can get the empty weight for a slick, complex, and pressurized airplane to be equal to your useful load? Only a handful of aircraft have ever done this and they tend to be much simpler aircraft or very specialized (Voyager).
 

KC135DELTA

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I would immediatley question the possibility of building a 6 passenger aircraft with 400 hp that has an empty weight of only 1800 lbs. I see that you show gross of 3600 lbs which implies 1800 lbs of useful load, which. 6 FAA standard people is 1020 lbs add fuel for 5 hrs of flight at around 750 lbs and you have your 1800 lbs and you still have baggage to account for. So do you really think you can get the empty weight for a slick, complex, and pressurized airplane to be equal to your useful load? Only a handful of aircraft have ever done this and they tend to be much simpler aircraft or very specialized (Voyager).
Long story short.
Yes.

Just because it will seat a max of 6 does not mean it will carry that amount every flight. I believe the average is 2-3 persons per private flight.

Also don't confuse complex concepts with a complex airplane. In terms of number of systems (which would be modular btw) and weight It will be simpler than a T-210 in practice.
 

Autodidact

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I was just thinking, the Aerostar balances because they put the pressurization equipment far back in the tailcone. You could put it in the nose and balance out an engine that is at the tail with no drive shaft. The closer you get to no driveshaft, the closer this comes to being reality. "Simplicate and add lightness."
 

Autodidact

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Let it be said that I have nothing against Fourier analysis.

Except for the fact that I don't know how to do it.:whistle:

And heres a cutaway of the Aerostar, mainly 'cause I just like cutaways:
 

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Starman

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Good, it could be offensive to some people. I'm low on sleep and in a bit of an offensive mood so decided to cut my losses.

anyway, I always loved those 3D cutaways that you used to see so often in the old days.
 

autoreply

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Designing a pusher with a PSRU or long driveshaft is close to impossible as Billski has pointed out. For a turbine that's no problem at all which might be a good reason to move over there.

My personal design has some things in common with yours. If you're willing to shift over to a highly swept T-tail you can build the engine in the back as long as it's diameter (and weight) is limited). In your weightclass the Falconer V12 comes to mind (watercooled and compact). Aircooled pushers do have cooling problems.

If you do put the engine completely in the back you need to pay attention to the risk of short-coupling. In my design I can get away with that because the engines are pretty light while the payload (passengers) are comparatively heavy. The swept t-tail reduces (ground) noise and vibrations quite a bit.
Note that you have quite a lot of empty room in this configuration behind the main spar.

As for your weight estimate, I'd say it's optimistic. Pressurisation doesn't cost any significant weight (maybe 50 lbs structural over a non-pressurized fuselage), but all the extra fuzz (pumps, vents, sealings) do cost quite a lot of weight.
 

wsimpso1

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I did not mean that it was close to impossible, but it will require serious engineering and should have a serious ground test series. Is it possible to avoid all of that? Maybe, but there are lots of sets of conditions that will break stuff, so you had better not be trying to check it out during flight test...

Think on the consequences of not doing a proper design and ground test program: If the prop shaft breaks at the prop, it departs, and can take out control surfaces as it does so; If the shaft going aft fails, it flails around, potentionally cutting the empennage from the fuselage; and if the PSRU packs it in, these other failures can immediately follow too. All of these failure modes are made likely by resonant vibration, and you will have several modes in such a bird. To be safe, all modes would have to be outside of the operating regime... Sure, you can put the prop well aft of the tail, and put hoops on both ends of the shaft to contain it, but you still are faced with a forced landing in what I imagine to be a high landing speed airplane. Better to do it right..

Billski
 

autoreply

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I did not mean that it was close to impossible, but it will require serious engineering and should have a serious ground test series. Is it possible to avoid all of that? Maybe, but there are lots of sets of conditions that will break stuff, so you had better not be trying to check it out during flight test...
I should have pointed out the "close to impossible" comment was mine.

Having said that though, which succesfull driveshaft aircraft flew?

Mini-Imp and Stemme SV-10 are about the only ones I can think of. The latter - while certified - is known for problems with the driveshaft. Since it has an L/Dmax of 50 engine failure isn't such a concern.

Billski, do you share my idea that for a turboprop a driveshaft isn't a problem at all?
 
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orion

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Based on the experience of one local company (Soloy), even turbines exhibit rotational resonance problems that can cause significant problems with drivetrain components. True, the problems are somewhat different than what you'd see with recips but they still introduce design variables that need to be understood and addressed.
 

Dan Thomas

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anyway, I always loved those 3D cutaways that you used to see so often in the old days.
A bit off topic, but you're right; we used to see those in the old days. Not now. People don't care (or can't comprehend) what's under the skin of any mechanical device and are attracted only by style. Old TV commercials for cars used to highlight engine and drivetrain and suspension technology, explaining how they worked; now they highlight body style, interior flashiness and gimmicks.

A couple of more recent ads prove how they're playing on marketplace ignorance: Toyota has some deep-voiced guy bragging about their trucks' "big ol' leaf springs," as if this is something new. My 1951 International pickup has leaf springs all around, just like the new Toyota. Another ad for a car talks about "all-wheel drive when you need it and rear-wheel performance when you don't." As if rear-wheel drive has just been invented and the front-wheel drive we were told was so great 30 years ago is now less than the best. Don't people know anything any more? Are they really that gullible?

Dan
 

Dana

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Speaking of the Learfan which was mentioned in a totally irrelevant bit of trivia, did you know that December 1980 had 32 days? Production for the Learfan was planed for Belfast, Northern Ireland, with money from he British government to build the factory. The stipulation was the first flight had to happen before the end of 1980 or the funding would expire. They were down to the wire, but the weather was too bad on December 31. The first flight was made the next day, and cooperative British officials recorded it as "December 32, 1980".

Alas, even that wasn't enough to save the program.

-Dana

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