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Thread: Turboprop or Turbofan powered experimentals

  1. #1
    steveinindy's Avatar
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    Turboprop or Turbofan powered experimentals

    Has anyone on the forums- or anyone you know personally off the forums- designed and built an experimental powered by a turboprop or turbofan engine? I have some generic technical questions for someone with this sort of background, especially with regards to the design aspects. Any assistance would be greatly appreciated.

  2. #2
    Hi Steve,

    Where you wanting to know about Engine Design, or engine installation on an airframe design?

    I may be able to help you.

    Spencer G

    EAA Technical Counselor # 5426

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    steveinindy's Avatar
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    Spencer,
    My questions mainly pertain to the installation aspects of it or, more accurately, how one designs the installation for a turboprop engine on a new design. I can't seem to find good references to this in any of the reference books I have.

  4. #4
    Do you have a particular turbo prop in mind? I spent years around the outside of a PWC PT-6 on a meridians when I used to work for Piper, I'm on my smart phone right now so it's cumbersome to write lengthy stuff but I'll type up some more stuff on my pc. I've been a TC on a few engine installs and there are some quarks to turbo prop installs compared to a lycon or cont installSg

  5. #5
    steveinindy's Avatar
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    I'm primarily looking at one of the RR M250-B17Fs at the moment although I might talk to the PWC folks next week at Airventure about what they have to offer. The original plan was to use an aviation diesel but that doesn't seem feasible due to a lack of sufficient horsepower in the currently available models with the exception of one.

    One of the major issues is that my design is a canard design so it has a pusher arrangement. Once I realized that the diesel option was more or less not viable, the first option I considered was putting a turbofan into the design, but from a fuel consumption standpoint that doesn't seem particularly viable either. My desire not to use a 100LL powered engine for safety reasons (not to mention avoiding having to re-engine once 100LL goes away) limits me to either a diesel or a turboprop then.

  6. #6

    Goggles

    Hello, Finally at my PC,

    One thing to consider about going to jet A for safety over AV gas is traditionally piston to turboprop conversions typically gain weight not lose it as a general trend when all things are weighed up. If your wings stay the same it will drive up your wing loading. Increasing your wing loading particularly in a homebuilt is most often the biggest danger factor you can get, stall speed and impact energy are both equal to velocity squared. And higher weights must be addressed with higher velocity.

    Some new Certified & Experimental piston engines are multi fuel compatible, the biggest challenge is dealing with ethanol in a composite tank, hoses, seals etc.

    As for the propeller in the back particularly for a single engine I would make sure you have a propeller to main wing trailing edge proportions similar to the Ez’s and Velocity’s the incoming air into the propeller has been tainted by all the things in front of it. Stalling canard, antennas any aerodynamic boo boos etc. these can cycle the engine, prop, barings and baring shaft surfaces for every revolution so you want to make it as aerodynamically clean in front of the propeller.

    One big issue with a piston to turbine app is the propeller typically ends up further from the CG on turbines, (normal Mirage vs a Turbo Mirage / Meridian, Bonanza vs Turbo Bonanza etc) all this will reduce your take off propeller tip clearance on a pusher config. The AIAA Raymer design book has good geometric layout info for landing gear & prop clearance.

    Another thing to consider with the prop clearance issues is it may be tempting to raise the prop thrust line for more clearance, however raising it above the CG will increase the nose down power on pitching moment this will become another player in the stall / stability calculations for a Canard. This will in short increase the power on stall speed for a given canard config, as the canard is designed to work as hard as it can and stall first. Nose down power pitching moments will add to what it has to carry.

    Some turbo props such as the PT-6 have a ~mid mount vertical dynafocal configuration option which is good for vibration, its similar looking to a Lycoming install. Same generic rules fallow on a Turbo prop as they would on a piston Engine should be mounted on some sort of elastrometric isolation mount, the vibrating engine should clear all fixed structure, cowl openings etc. all lines going from the ridged airframe structure to the engine should be flexible, with in the specified heat and approved for Fuel & Oil exposure. Electronic sensors should be accessible & rated for the thermal / vibration environment its placed in.

    One additional piece of equipment is what is called an Inertial Separator, its not just for FEKI ops but general sand / partial erosion. The goal is partials with mass, ice, hail, sand, FOD etc want to keep going in the same direction, the separator lets these objects go past the intake and exit the nacelle, the intake pulls in air from the side. All these small objects reek havoc on the Compressor / Turbine blades and stators. Although a good separator will not filter out everything, it filters out the bulk. Not an “IC” will not protect you from volcanic ash, Some people in Europe tried that last summer and it did not work out too well for the internals of the jet / turbo engines.


    One weird thing with Jet A is you need protective measures against Fungus, sounds really odd but can grow in that environment, if dislodged it can plug incoming fuel. all fuel system coatings, materials & plumbing should be rated for a Kerosene / Diesel / Jet A environment.

    With modern lower cost CAD packages (Albrie, Rhino Cad) I would have a detailed 3D CAD mockup of the whole fire wall aft area to make sure you have room for everything before one part is built and get an accurate weight rollup.

    Martin Hollmann wrote a good book called boggie with a turbo prop it should have some additional helpful hints. http://www.aircraftdesigns.com/Books...craft.tpl.html

    Hope this helps, Let me know if you need to know any particulars.

    Spencer

    TC #5426

  7. #7
    steveinindy's Avatar
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    One thing to consider about going to jet A for safety over AV gas is traditionally piston to turboprop conversions typically gain weight not lose it as a general trend when all things are weighed up.
    Compared to an aviation rated diesel, there is a savings both in weight and fuel load necessary for a given mission (due to higher power- read as 'higher potential airspeed'- and comparable to slightly better fuel consumption).

    Some new Certified & Experimental piston engines are multi fuel compatible, the biggest challenge is dealing with ethanol in a composite tank, hoses, seals etc.
    Yeah, there's no way in hell I am getting anywhere near automotive grade fuel as fuel source. The two big reasons I want a Jet-A (or something similar) powered engine are:
    -To avoid having to pop a new engine on this thing when 100LL goes away
    -Reduction of fire risk in the event of a crash

    A secondary reason is why would I want to use automotive gasoline when there are other alternatives out there? It's like someone offers you a glass of 200 year old quality scotch and you decide to drink a bottle of Cutty Sark instead because it's a little cheaper and, after all, they are same type of alcohol.

    One weird thing with Jet A is you need protective measures against Fungus, sounds really odd but can grow in that environment, if dislodged it can plug incoming fuel. all fuel system coatings, materials & plumbing should be rated for a Kerosene / Diesel / Jet A environment.
    Not a problem. I wasn't planning on going for anything other than rated fuel lines anyhow.

    If your wings stay the same it will drive up your wing loading.
    Which is why I'm designing it from the word go to operate with a turboprop.

    As for the propeller in the back particularly for a single engine
    Actually after running it through a couple of simulations, I decided that having a tractor design is much more practical not only due to the aerodynamic issues but for the purposes of cooling the engine.

    Martin Hollmann wrote a good book called boggie with a turbo prop it should have some additional helpful hints. http://www.aircraftdesigns.com/Books...craft.tpl.html
    Thanks for the suggestion. I will have to check it out.

    Hope this helps, Let me know if you need to know any particulars.
    Will do. I am just trying to get the weights and other specs figured out. I have pretty much selected the engine I want to use so that's one less thing to worry about. Luckily, the dang thing is produced right here in Indy so I'm close to the manufacturer if I have any questions about that particular model of engine specifically.

  8. #8
    Pat_Panzera's Avatar
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    Here's a great article we published in Experimenter:
    http://www.eaa.ca/experimenter/articles/2010-01_turbines.asp


  9. #9
    steveinindy's Avatar
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    Thank you Pat. I appreciate the help.

  10. #10
    Auburntsts's Avatar
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    Steve,
    You might want to contact the folks at CompAir http://www.aerocompinc.com/ and Epic Aircraft http://www.epicaircraft.com/index.html. These are the only 2 kit compaines that I know of that offer turbo-prop E-AB kit aircraft. They might be able to give some insight into what you're after.
    Todd Stovall
    Aka tsts4 on POA & Matronics, and Auburntsts on VAF, RV Airspace, AOPA, & Purple Pilots
    PP ASEL
    Building an RV-10 N728TT
    My builder's log (which is woefully out of date): www.mykitlog.com/auburntsts
    WAR DAMN EAGLE!

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