Crazy idea of the week - Scale Magister

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Aircar

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Gordo- I still have your photocopy of the recuperative ARL turbine but have mislaid your address --please PM me and I'll send it to you ,

(and the other bloke for the Lysander Delanne report --lost his address also but the report sitting here looking accusingly at me -he uses the flying flea avatar and has "rabat Morocco' as address but hasn't posted for a while )

How about real micro turbines mounted on a prop at the tips (model aircraft variety ) --provided they were well faired the efficiency at high subsonic speed and the mass flow multiplication like a turbo prop would do something for SFC ?
 

Aircar

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PS the comment about Darryl Stinton's forward swept jet design proposal sells him a bit short in my view --I have book open in front of me and studying the calcs on it --the engine specified is the Microturbo TRS 18 --225lbf thrust and 82 lbs dry weight --2 off , he goes through his preliminary feasibility checks and does revise it to sweep back and to increase fuel volume -quotes 280 lb per hour each at max continuous thrust --the primary effect of scaling down anything is to lose much more volume than area of course.
 

Himat

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First a comment on the thread drift part. Quite a few manufacturer claim that their airplane are able to "supercruise", and then define this cruising at a speed higher than sound without afterburners as "supercruise". The period of time their airplanes are able to do this is is usually not mentioned. This as there are very few airplanes that have the ability to cruise at supersonic speeds at any amount of time. The Concorde, Tu144 and Sr71 are the one I guess is on the list of aircraft that can or rather could as none are operational today. I have yet to see information on that any of the "new" supercruising airplanes are able to cover a longer distance at supersonic speed than the old Mig31 and the like.

Next, the idea of a "curcuit special" airplane sounds kinda fun. Just for the thrill, a fast manouverable plane. With fuel for 45 minutes you are not going far, but it might be great fun anyway. Then, what performance do we look at? Single seat and twin engines.
 

autoreply

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How about real micro turbines mounted on a prop at the tips (model aircraft variety ) --provided they were well faired the efficiency at high subsonic speed and the mass flow multiplication like a turbo prop would do something for SFC ?
If I recall correctly G-forces make that pretty close to impossible. I've written a few articles about the Rotodyne, but even ramjets and rockets must be ridiculously sturdy to keep in shape.

On the other hand, as a gas generator you might have a massively powerful prop without much complexity. So have the jet near the prop axle and exhaust it into the blades with small exits near the tip. It should be fairly efficient because the tips are running around the exhaust speed of the jet, so very high efficiency (relative to a turbojet). Which temperatures can affordable steel (no special alloys) props withstand? Is this ever been tried with a turbojet? (I know of ramjets and rockets)
 

Aircar

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I have seen the "pinwheel" concept in the 40s in old Aviation (now Av week etc) mags and my old boss Dick Schreder tried out the concept for a self launcher using the pulse jet principle in the hub with a flapper valve and centrifugal fuel spray --the blades were edge welded stainless steel hand beaten into kirksite dies by Morry Hummel (of Hummelbird and 1/2 VW fame ) --it was tested some time after I had left Bryan aircraft but didn't work for whatever reason . I did some preliminary calculations (or tried to anyway using 'Aero 101' knowledge) seeing if the blade would have enough mass flow possible or of supersonic internal flows would choke it or even blow it apart -- synchronizing the explosions and the mass flow down each blade would be a likely problem (a single bladed prop might have been better ) -- without real compression of the charge the thermodynamic cycle had to be pretty poor and heat losses enormous .

A free piston engine as a gas generator couple to a hollow prop with tip discharge is another option --a wankel hooked up to a pinwheel type torque generator and prop was shown in a 1960 Ostiv paper on self launching concepts --a German professor was behind it from memory .
 

oriol

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turbinepoweredcricri.jpgShogun Cri Cri.jpgcricri.jpg


According to wikipedia the cri cri with its two 15 HP engines is capable of 220 Km/h cruise. The turbine version is credited to have a top speed of 240 Km/h.
Colomban Cri-cri - Wikipedia, the free encyclopedia



Here you can watch a turbine powered french cri cri flying radio controlled to obtain its flying certificate.




Oriol
 
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Autodidact

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PS the comment about Darryl Stinton's forward swept jet design proposal sells him a bit short in my view --I have book open in front of me and studying the calcs on it --the engine specified is the Microturbo TRS 18 --225lbf thrust and 82 lbs dry weight --2 off , he goes through his preliminary feasibility checks and does revise it to sweep back and to increase fuel volume -quotes 280 lb per hour each at max continuous thrust --the primary effect of scaling down anything is to lose much more volume than area of course.

Ah, well..., I didn't mean to sell him short. To me, forward swept wing is a difficult problem; you'd have to locate the shear center so that the wing twists under load to create washout or at least maintain washout as the tips flex up, wouldn't you? And then worry about flutter, aileron reversal, bleah - worms all over the place. I just meant that it is a really neat concept and perfect for a small twin jet. The planform is "somewhat" academic compared to packaging the people and engines. The new edition of that book has a Fouga on the cover :grin:.
 

autoreply

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Just to finish off on this small turbine engine and its impossible performance numbers...
You're "finishing off" AMT...LOL. A reputable company that's been building those engines with great success over 2 decades.

The simple fact of the matter is that they work as advertised. They do deliver those trust figures, as verified by many, no matter how much number-crunching you do. A simple Google search will show you universities doing extensive tests on those very engines, up to and including the top models.

Stop arguing solely the theoretical aspect and start thinking where your assumptions go wrong, since they're disproven by reality. I can point out at least half a dozen reasons. Give AMT or NASA a phonecall, share your doubts with them and listen to what they have to say. You might learn something, either about your assumptions, or about their engine...



You rightfully point out the very high price. Nevertheless, everybody who's in this business for a while buys AMT's and willingly pays that much money. In the real world, that means they're much better as cheaper alternatives. The ones I know got annoyed by the continuous tinkering that homebuilt or other competing turbojets required and their immense unreliability. Converting turbochargers works fine... in theory. In reality... not so much apparently...
 
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topspeed100

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Only reason why there isn't really a small jet engines between models and trainer's Marbores is that the military industry needs bigger engines to carry payload, e-seats, weapons, radar etc....and they cost a lot too to build and use of course.
 

Topaz

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Since it's virtually certain that nobody here is actually going to build a little jet based off of this engine, how about we assume, for the moment, that this engine actually performs as-advertised. That is not an endorsement of the company or the product but, short of someone buying one of these engines and doing their own independent test, this sidebar argument is pointless and isn't going to be resolved here.

The thread was started by the OP with regards to designing an airplane around such an engine. That's a fine exercise, and if any of you don't believe the engine's performance, consider this a thought exercise as if that engine actually exists. Or simply don't participate. If you want to argue the merits or demerits of this engine as a topic, my first recommendation would be to do it via PM. Or start a separate thread specifically about this engine. This thread is meant to be about an airframe designed to suit this engine, on the assumption that it does what the manufacturer claims. Derailing it into an argument about the engine itself is off-topic, and further posts in that direction will be moderated.
 
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