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Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268
In a tube cut off, its the tsr tip speed ratio, the tips will turn slower cut off, but a comment I made that Ashsmall ruled off a rackets system that allows more air one the tube, say 1:10 ratio, will allow more mass, which turbines, cyntrycill pumps allow but not pressure which piston's are good. I had a idea of using a blower to supply the air for methane to heat pipes were, turpentine got raised to 600°C then a piston compressor injected into the chamber. It broke even, but 200kg would need to be upscaled.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
We typically cut the tips off a triple blade prop then put it in a tube as in an A-10 or F-16. That was before the premade electric turbines became cheap enuff for any idiot to buy.
i was thinking of a 18" diameter triple blade variable pitch prop driven by a rotary wankel engine.
something like this : but this small version :
General characteristics
Type: Aircraft Wankel engine Dry weight: 27 kg (60 lb)
60lbs @ 80HP = 1.3 hp/lb is really tempting compared with the 8" diameter turbines which are really under throttled most of the time for a M 0.9 capable drone which normally cruises and operates at M 0.3 (80% mission time).
Turbines can beat otto/diesel cycle engines in overall speed and power density, but they dont seem to scale in physical size or specific fuel consumption which is paramount above all other features in sub 1000 lbs drones.
the dimensions are surprisingly good:
Type: Twin rotor, four stroke Wankel aircraft engine, 105 hp @ 7,500 rpm Displacement: 588 cc (35.9 cu in) Length: 720 mm (28.3 in) Width: 530 mm (20.9 in) Height: 420 mm (16.5 in) Dry weight: 54 kg (119.0 lb)
For a piston aircraft engine, though not by comparing turbine to piston directly. Absolute power density always favors the turbine even with the ancillary operating junk we build into the plane the get the turbine to run, which isnt needed for the piston power plants.
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268
For a plane its normally four times the motor HP, that the aircraft can weight. So 80*4 =320lb 160 kg. Last I speced that was a 200hp Cessna engine, with three for a VTOL,did get far, the blades were $3000 . Rotors engine are used for compact power output, but maintance is high, guessing but I'll try design a a car engine say 1100-1300Cc , 80hp is quite a big aircraft, any question not asked?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
the Mazda car and motor cycle engines are bigger than there wankle air-optimized cousins. These dimensions are perfect for a 600 lbs fixed wing Mach 0.5 drone.
Length: 720 mm (28.3 in) Width: 530 mm (20.9 in) Height: 420 mm (16.5 in)
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268
I was about to post a single engine in the centre wants to turn to the left, but its twin rotor going opposite directions? A rotary engine would have better performance, but design wise I would test with a cheap $500 overweight engine. Aircraft engines have the turbo to match the air desinty,.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Im not worried about cost (well other than finding the money). $200,000 is what we're thinking this is going to take for the first three aircraft. Even If its feasible we may not follow through with the fixed wing first. We may focus on our ultra-high altitude thrust vectored rocket. That initial effort and success would help with fund raising for this and other projects. Its also easier to get FAA approval for rocket flights several times a year.
Yes they would counter rotate, but we're thinking of a single engine driving two turbines. So maybe both "internal" turbines turn clockwise, but the rotatory pistons turn clockwise, as you suggest to minimize unwanted torque. Im not sure how the force vectors add up, my brain is still doing some mental drooling from the difficulty.
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Turbine vs Piston Thermodynamics
