Level flight by FW P.97 Triebflugel


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1 May 2007
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I have always wanted to know, how lift was supposed to be generated for level flight of Focke-Wulf Triebflugel. If they are shown in artworks in level flight, the take off and landing rotor blades generate both, thrust and lift (the latter as wings in the less perverse desings). But lift cannot be generated this way, while the falling blade would generate a positive lift indeed, the ascending one would generate the negative lift. Were the blades intended to be stopped at this mode, and set at high angle of attack?
The whole concept of this machine looks absurd to me anyway.
I think, the principle is just the same as in a helicopter, where the rotor (or
better the rotation plane) is tilted slightly forward to produce a forward motion.
As the rotating wings couldn't be tilted and AFAIK there was no possibility to
achieve a cyclic pitch, the rotation axis of the wings, and so the whole aircraft
would have to be kept at un upward angle for forward flight. ???


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I understand (more or less) the whole idea of transition into the level flight Jemiba, but I cannot see how lift was supposed to be generated in level flight. See attached my rough sketch.


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mattrix said:
I understand (more or less) the whole idea of transition into the level flight Jemiba, but I cannot see how lift was supposed to be generated in level flight. See attached my rough sketch.

Thrust is generated by the whole rotating wing assembly much like a regular propellor, just very large. When flying straight and level, it would fly at some angle of attack... with the result being that most of the trust was directed aft, but some down. To maintain level flight, forward thrust (X) must equal drag, and lift (Y) must equal weight. Simple vector math will tell you at what angle of attack you must fly if you produce a certain amount of thrust and weight so much.

Additionally, the fuselage will also produce lift if it is flown at some angle of attack, so you have to add that in as well.

If you fly *directly* into the wind, you're going to drop, as there'll be no net lift.


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Thank you guys for your explanation (I was not trolling here). So it is impossible to show on my sketch the components generated by the airscrew which would contribute to the lift. There will not be any in this view as my sketch simply does not show the Triebflugel viewed along the flight direction. The whole machine is rather small but the propeller - enormous, so slight tilting in level flight would suffice to balance the weight and assure stable flight.
As for vertical to level flight transition, the whole rotor disk was to be tilted probably the same way as in Lockeed XFV-1 or Convair Pogo, by deflecting rotor downwash by the empennage.
Would the Triebflugel develop any radial lft, like the Curtiss X-19?

I am afraid I was too quick to subscribe to your explanations. Still the whole idea of Triebflugel seems to me unfeasible, no matter how elegant (in its simplicity) it appered at first glance. That jet tip-driven rotor/propeller with moderate disc load, would probably work fine at ascent or hover, but would not as a, more or less, regular propeller - It would generate enormous drag making the whole propeller just inefficient.
Few days ago I have found a picture posted by Justo Miranda (cannot find it now) of the Triebflugel at level flight. The rotor blades were pictured stopped in a feathered, inverted "Y" position so as to have the tip jets operating aligned (as in any jet plane). What bothers me this time is the asymmetric lift generated by rotor blades/wings due to e.g. geometric twist of the blade.
Does anybody know if they did foresee for the Trieblugel to be flown level in two alternative modes (propeller/jet)?

Many German VTOL concepts were further researched during the post-war period, but I have never seen any continuation of the Triebflugel concept, maybe because of this flaw.
Can you name your source for the designation FW P.97? It´s totally new for me...
Can you name your source for the designation FW P.97? It´s totally new for me...

It is embarrasing dear Maverick, but I cannot be very helpful in this matter. I am sorry. The only source of information on Triebflugel for me is something as patently unreliable as internet.
When I started collecting pieces of data on Triebflugel, it took considerable time for me (at least 2 years), to finally get this P-number (do not know where from though). So I am absolutely prepared to admit that it is a false designation.
Sorry for reviving this old thread, but here http://www.secretprojects.co.uk/forum/index.php/topic,21466.msg212084.html#msg212084
Martin provided us with a link to a dedicated Triebflüger site ( http://paralympic-ph.com/germanvtol/tribflugfolder/triebf.html),
stating "There was some speculation by other authors that the wings could be tilted in flight. Take-off would be accomplished by tilting
the wings (blades) to a +3 degree angle. Once in level flight the blades would gradually be angled until reaching 90 degrees, thus transforming
the blades into wings for level flight."
Can anybody tell me a concrete source for that ? Furthermore, on that site a prone position for the pilot is mentioned. That would be new
to me, AFAIK the pilot was seated in a normal position.

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