A complicated question
A complicated question
(OP)
If I were to mount a mini-jet engine vertically and direct it's thrust (say 100Lbs) through nozzles at the end of a pair of rotors, via a rotating swivel joint, could I make a mini helicopter capable of lifting someone? The idea being that there would be no torque reaction and only one moving engine part. I guess the question is- would 100Lbs of thrust acting on the ends of the rotors be enough to produce the required lift? (say 300Lbs load) If not, how much thrust would be required?
Anybody care to make an educated guess? I just thought it might be a neat way to make an ultralight flying machine.
Anybody care to make an educated guess? I just thought it might be a neat way to make an ultralight flying machine.





RE: A complicated question
RE: A complicated question
htt
Meh, it could even work
RE: A complicated question
KENAT,
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RE: A complicated question
My idea was to use a micro jet with a long 'split' tailpipe so that the air could be cooled/noise abated before it reached the tips. If I get the time I'll try and make a simple drawing of what I mean. In terms of overall noise it should be possible to make something much quieter than the jet engine itself?
RE: A complicated question
RE: A complicated question
RE: A complicated question
Remember the jet exhaust may be in the high hundreds of degrees Farenheit, which won't do much to help the structural integrity of the rotor, an already highly stressed device.
RE: A complicated question
KENAT,
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RE: A complicated question
RE: A complicated question
Mmm, kind of. But the path would be more of a gentle 90Deg radius. The rotors would also be slightly curved to help with gas routing. Also I was thinking of using a bypass turbine as more of an 'air pump'? I'm sure there would be some losses, but even if they were 50% (!) , it would only need a 100Lbs or aprox 40Kg thrust to make a feasable single person helicopter. Like I say, I'll draw something up when I get the time.
RE: A complicated question
Mike Halloran
Pembroke Pines, FL, USA
RE: A complicated question
RE: A complicated question
However, by using rearward curved blades would centripital force not help 'move' the air mass towards the end of rotor? And thus help reduce back pressure? Or does air not work like that?
RE: A complicated question
A man named Gluhareff designed and built Propane fuelled jet engines without any moving parts. Really clever designs.
The smaller versions could be tip-mounted on a rotor fitted to the back of the pilot (or victim?).
See if he is still in business.
D
RE: A complicated question
annddd, noooo ... i think you need the pressure in the collector to force the air along the blades.
i have pictured having the fixed engine exhaust into a "tank" that has four exits. what about blending the four orifices so there is little flat plate surface ... there'd be some sort of roller race, maybe a flange outside of the exhaust ... this would minimise the back pressure, 'cause the flow is being directed out along the blades ... sort of like you might've been thinking about (now that i've written it all out !!) ... the problem could well be maintaining the exhaust area from the jet eflux to the blades (i see the blade area being much smaller than the jet exhaust)
RE: A complicated question
Anyhow, I had 10mins so I knocked up a very crude drawing to show what I mean. Gota love MS paint
link- http://fi
RE: A complicated question
You may be able to find some information on any problems this causes.
KENAT,
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RE: A complicated question
I hate raining on parades. But I did extensive aerothermodynamic analysis of a device that acted much as your ducted jet rotor did. The fluid passing down a rotor blade can be imagined to be passing through a stationary coiled tube, whose bending radius gets progressively smaller. Think of it as "coriolis" forces...but analogies don't work very well. This causes the flow to swirl axially, incurring very large head losses, which tend to eat up any pressure head generated by centrifugal forces.
What is worse, the fluid in the long tube tends to set up oscillations, the rotor is acting like an amplifier for any perturbations at the rotor inlet. When this happens, the flow through the rotor essentially stalls repetitively, causing a lot of racket (acoustic noise) and damage to surrounding structures.
NASA did a lot of studies back in the '50's on supersonic compressors, including radial vane compressors. You should be able to find many of the reports on the NASA servers. They can be hard to read, but informative.
RE: A complicated question
btw- I did link to a very crude drawing in my last post.
RE: A complicated question
Yes, you said you had knocked it up...thus I asked when it was due...ba-dum.
The degree of axial rotation of the flow is countered to a slight degree by the aft-ward sweep of the channel, as you've drawn, but it doesn't go away, any more than the centrifugal forces will go away.
RE: A complicated question
- It has to be unnecessarily heavy to keep from straigtening out or fracturing from centrifugal force.
- That gets particularly troublesome, as does the thrust vectoring, when you try to translate the bird by cyclic alteration of the AOA.
Mike Halloran
Pembroke Pines, FL, USA
RE: A complicated question
D
RE: A complicated question
"Yes, you said you had knocked it up...thus I asked when it was due...ba-dum."
LOL, very dry..my bad for missing it
RE: A complicated question
If the same amount of power were directed at driving rotors that had half the weight, one would think that you'd get better overall performance.
TTFN
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RE: A complicated question
RE: A complicated question
KENAT,
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RE: A complicated question
RE: A complicated question
How can you lift 300 lbs with 100 lbs of thrust?
Surely you need 300 lbs of thrust!
RE: A complicated question
Think about that long and hard.
How much thrust does say a 747 have. How heavy is it.
KENAT,
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RE: A complicated question
RE: A complicated question
There have been a couple of A/C with vaguely similar configurations, I doubt they all had unity thrust to weight.
KENAT,
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