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How to do what I want without using a 3LS design ?

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Vigilant1

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This is one area that technology has finally caught up with us dreamers. The rotax 915 offers a true single lever FADEC automatic constant speed prop system from a certified engine now. Jet engine like control simplicity. It's also a big part of the dream. Lose an engine and you pull one lever back. Everything wired into a Garmin or Dynon that will flash warnings at you as it monitors engine stats. Pair of turbo 140hp engines on a 2 seat twin is plenty of power for excellent performance on two or one engine.
Two Rotax 915s plus two controllable pitch props? Oops, I think I stumbled into the wrong tax bracket thread. 280 HP in a two place airplane--so, what is the mission? With that much power and just two seats it sounds like you either want to climb quite quickly or go quite fast (250+ MPH would be quite doable with this power and a clean airplane, even with the big-ish wing required for acceptable SE climb). If you want to go fast, then retractable gear starts to get attractive, and a low wing makes a nice spot to stow landing gear. At least one of the engineers who designed the Cessna Skymaster said that they would have used a low wing if they'd known from the start that the planes would eventually have retractable gear.

Definitely going to take a rethink at the push/pull set-up. How hard is it do a cantilever wing with booms ? Is designing a structure that can pass through all the different loads the wing spar now has to handle hard to deal with ?
Sorry, I don't know. The subject did come up before in the Beetlemaster thread. I thought wing lift struts would be handy for managing the tail boom loads, Autoreply suggested that feeding them into the wing skins would be more appropriate (assumed composite construction?). More here (including a link to an article based on interviews of the Cessna 336 designers) and here.
 
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TFF

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The point of the Skymaster was to build a twin in the lucrative single engine plant, not the twin plant. A lot of issues like paralleling generators and bad buss management has known fixes on the twin line. Mainly the single engine designers had to relearn what was known down the street. Kind of sucks when the design gets locked because of certification.
 

rbarnes

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Two Rotax 915s plus two controllable pitch props? Oops, I think I stumbled into the wrong tax bracket thread. 280 HP in a two place airplane--so, what is the mission? With that much power and just two seats it sounds like you either want to climb quite quickly or go quite fast (250+ MPH would be quite doable with this power and a clean airplane, even with the big-ish wing required for acceptable SE climb). If you want to go fast, then retractable gear starts to get attractive, and a low wing makes a nice spot to stow landing gear. At least one of the engineers who designed the Cessna Skymaster said that they would have used a low wing if they'd known from the start that the planes would eventually have retractable gear.
Yes to both. Strong climb and cruise. Mission goal is fast, efficient, low pilot workload, night or day / rugged mountains or open water cross country cruiser
At the end of the day the whole point of having two engines is single engine performance in an emergency. In that scenario there is no such thing as too much power. I am hoping to have a plane that can do 200kts at 10-12,000' and 500 fpm single engine climb up to 12,000+ Density Alt. I wish the 915's were cheaper and something like the Apex engines or big bore Rotax 912 should power the airframe quite easily. If I ever do get to a flying prototype stage (not holding my breath, but will strive for it over the years) it will probably startout with a pair of cheaper 912s to keep cost in check while testing aerodynamics.

With the current dream of a 3LS layout I envision something about the size and shape of the small Velocity SE (with more shoulder room), with a wing and interconnected flap layout like the Eagle 150 (low canard up front, center mount for main-wing and conventional T-tail), Twin pusher Rotax 915's, and landing gear from Cessna 177/182 (circa Lancair IV). The flap interconnect system between the two wings has already been figured out in the Eagle 150, just need to see how they did it and make something similar. Same with the gear retract. No need to reinvent the wheel with these sub-systems.
 

sming

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it will probably startout with a pair of cheaper 912s to keep cost in check while testing aerodynamics.
That remind me that i saw a rotax powered Defiant for sale in France in the last few months.
I think it was a 2 places one of a kind and apparently had some Rutan approval...
The (old and retiring from aviation) gentleman was selling it 90k€ to a good home...
Let me see if i can find the ad again.
 

wsimpso1

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Yes to both. Strong climb and cruise. Mission goal is fast, efficient, low pilot workload, night or day / rugged mountains or open water cross country cruiser
At the end of the day the whole point of having two engines is single engine performance in an emergency. In that scenario there is no such thing as too much power. I am hoping to have a plane that can do 200kts at 10-12,000' and 500 fpm single engine climb up to 12,000+ Density Alt. I wish the 915's were cheaper and something like the Apex engines or big bore Rotax 912 should power the airframe quite easily. If I ever do get to a flying prototype stage (not holding my breath, but will strive for it over the years) it will probably startout with a pair of cheaper 912s to keep cost in check while testing aerodynamics.

With the current dream of a 3LS layout I envision something about the size and shape of the small Velocity SE (with more shoulder room), with a wing and interconnected flap layout like the Eagle 150 (low canard up front, center mount for main-wing and conventional T-tail), Twin pusher Rotax 915's, and landing gear from Cessna 177/182 (circa Lancair IV). The flap interconnect system between the two wings has already been figured out in the Eagle 150, just need to see how they did it and make something similar. Same with the gear retract. No need to reinvent the wheel with these sub-systems.
Sounds mighty complicated compared to the Boomerang layout. Have fun...

Billski
 

rbarnes

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Sounds mighty complicated compared to the Boomerang layout. Have fun...

Billski
Nothing written in stone. That's why I'm here bouncing ideas off you guys. I may end up with a simple conventional twin like the Derringer or maybe something that looks like a 177RG with two engines on the wing, or a push/pull set-up. Following unrealistic dreams is a surefire way to a dead end road .... lesson learned from the Raptor project... (and Beech Starship) to not try and force the mission to fit the plane you have locked in your head.

Keep em coming, I'm listening... I knew about the Derringer, but had forgotten about it.
 

rbarnes

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What about an engine and fuselage layout like the infamous Pond Racer ? CG balance headaches ?
 

bmcj

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If you set a canard Incidence to stall above VMC, then you have set that higher minimum speed (and landing speed) for all flight regimes, even when both engines are still running.

What about putting both engines close together so that the prop arcs are almost touching? That can be done with forward engines (and maybe prop shaft extenders) and balance it out with fuselage length and rear loaded payloads on a tractor config. You can do it on a canard too.
 

Brünner

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Yes to both. Strong climb and cruise. Mission goal is fast, efficient, low pilot workload, night or day / rugged mountains or open water cross country cruiser
At the end of the day the whole point of having two engines is single engine performance in an emergency.
....................
May I suggest a Seneca? A friend of mine is selling his Seneca III (I think), because he's upgrading.
 

rbarnes

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What about putting both engines close together so that the prop arcs are almost touching? That can be done with forward engines (and maybe prop shaft extenders) and balance it out with fuselage length and rear loaded payloads on a tractor config. You can do it on a canard too.
Hence my question on the Pond Racer style set-up. CG balance concerns ? I would want to lose the two engine booms though and just have a fuselage behind the wing.

pond.jpg
 

Victor Bravo

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Dornier 335 layout with two aluminum V8 engines would solve several problems, good structural efficiency and short load paths, be a little easier to engineer. It would importantly allow fairly high aspect and efficient wings (without the intersection drag of engine nacelles), giving you the cruise performance you want, and give you a pretty good chance of safe handling with an engine out. Liquid cooling would eliminate the biggest issue that the Cessna Skymaster had to deal with (bad airflow to the rear engine). The only really exotic part is that the horizontal stabilizer carry-through and attach system would have to be part of the rear engine mount.

But any new high performance twin engine airplane is going to be a significant engineering effort, whether it lookslike a Short Skyvan or a Dornier 335. The Dornier will be the most aerodynamically clean, and if you want to go thundering across oceans, that efficiency will be worth whatever extra cost. With the V8 engines you need to have some sort of redrive of course.
 

rbarnes

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Yeah, I'm rethinking the push/pull idea. Really seems the simplist way to go. KISS !. I was sketching some ideas last night similar to the D-335 with tail mounted around the engine. No need for big V8's. Keep it light. Pair of turbo rotax or Apex engines and 2 seats with a big baggage area.
 

Victor Bravo

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OK, this might be a good case for the Apex engines, there's a few high brain function people here who can make a CAD rendering of this layout, sized for the Apex....
 

rbarnes

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Someone had same idea for an LSA sized plane.... "127ktns on a pair of 40hp 2 stroke engines"

aerielle.jpg
 
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