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Old Oct 09, 2008, 06:17 PM
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Tilt rotor VTOL

Here is my VTOL project so far.

I still need to work on the left tilt section. I screwed up the control horn angle (not in sync with the right tilt section), but this gives you an idea.

My build blog with few additional details.

http://www.rcgroups.com/forums/showthread.php?t=898966


Bench testing of tilt mechanism.


Project VTOL - Part 4
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Old Oct 10, 2008, 04:40 AM
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You will still need a way to control pitch. I don't think you can rely on the "pendulum effect" for that, you will either have to add a small horizontal prop on the tail like on the CL 84 or to have cyclic control on your rotors. Maybe the portion of ailerons that is left in the prop stream could be used to control pitch, if they are low enough with relation to the CG
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Old Oct 10, 2008, 11:45 AM
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Interesting point. For now, I'm planning to setup gyro in such a way the it holds the direction (angle) of the tilt, not to correct the pendulum effect. If I let the gyro correct the pendulum effect then I see your point comes true.

What you think if I just hold the position of the tilt using gyros and let the plane settle itself?

Important point, this plane has dihederal (another simple but new change I came up after studying all other projects) and when I violently swing the plane by holding the motor mount sticks, the plane settled the pendulum effect in less than 2 seconds. This happens without the gyro

Here is one more unique mod. Most of the weight of the plane is in the wings. The fuselage is pretty much empty, just the receiver, a receiver power pack and the gyros and rudder and elev servos. This is another new design feature I came up with. So I believe the pendulum effect will be drastically reduced because the fuselage doesn't have any mass compared to the wings.
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Old Oct 10, 2008, 04:09 PM
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the pitch control is a universal problem with vtols
i like your idea about trying to keep the rotors vertical with gyros and it may work but i guarantee i will take a lot of fine tuning if ti works at all

i did see you have control surfaces in the tilted portion of the wing and actuating those in the prop wash will give a torque the could be used for pitch control, weather its is enough is the primary question.
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Old Jan 07, 2009, 09:43 PM
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Question for those who have really thought this thru....

If a plane (twin motor) has two 12 X 6 props then does the total thrust and pitch becomes 24 X 6?

Thanks
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Old Jan 07, 2009, 09:58 PM
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No, 2- 12" props won't have the same area as a 24" prop so the thrust wouldn't be the same, don't know what your trying to figure out from your question, there are other factors involved, rpm, etc.

Pitch is just how far the prop "screws" forward per 1 revolution.
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Old Jan 07, 2009, 10:12 PM
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If what you are saying is true what's the advantage of twin motor planes?

Why a twinjet with two motors has close to double thrust than funjet with same but one motor?
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Old Jan 08, 2009, 04:39 AM
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twin motor or jets don't have half of the wing in their road when they are working just for airplane mode
When the airplane props swings over the wing ... that area has no lift at all .
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Old Jan 08, 2009, 06:13 AM
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Still not sure what your trying to figure out, yes 2 motors with a 12x6 prop would give double the thrust as 1 motor with a 12x6 prop, but the 12 is just the diameter of the prop, not the thrust.
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Old Jan 08, 2009, 12:16 PM
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Yep. I meant to ask if two 12 X 6 props would roughly equate to one 24 X 6 prop in terms of thrust and pitch speed.

I'm trying to calculate roughly how much thrust and pitch speed I need when the tilt is at 45 degrees. At this point the plane has to move forward fast enough to get lift over the wings and at the same time it must have enough thrust negate gravity.

In other words I want enough thrust and speed for the plane to behave in airplane mode and hover mode at the same time (is, when the tilt is at 45 dgree and moving forward).
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Old Jan 08, 2009, 12:36 PM
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Quote:
Originally Posted by v22chap
When the airplane props swings over the wing ... that area has no lift at all .
Well, Doesn't that depend on how high the prop is from the wing surface? Osprey has them very high in the hover position.
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Old Jan 08, 2009, 01:10 PM
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If you're trying to find the ideal prop, in general, a larger prop will give better static thrust for hover, and slower cruise speed using the same motor. There's no free ride, you'll have to find a balance that meets your purpose. A 24x6 prop will be too large for a motor that usually spins a 12x6 prop, you would have to change to a larger motor.

Since you're tilting your wing, blocking the thrust wouldn't be too much of an issue, I think 12" prop should be close to what you need.
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Old Jan 08, 2009, 01:11 PM
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Don't make any difference how high .... it still has to push some air down to bring more air in over the top and it still stalls that area of the rotor disc quite a bit .
The osprey is what I am familar with and have been experiencing that effect for almost 18 yrs now
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Old Jan 08, 2009, 01:48 PM
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v22chap,

I don't doubt your experience at all. I've followed all your posts and studied them carefully and learnt a lot.

I'm just a pair of fresh new eyes approaching the problem from a different perspective. I have a clear understanding of how real Osprey works and what my plane lacks and trying to substitute or come up with alternatives.

maxvtol,

My intention is not to use a 24 X 6 prop on a motor capable of 12 X 6.

Quote:
a larger prop will give better static thrust for hover, and slower cruise speed using the same motor
This is exactly where I'm pulling my hair now and doing some number crunching.
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Old Jan 08, 2009, 02:14 PM
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Number crunching is good to get you in the ballpark, but you'll need to do some testing. Lot of props and motors have been tested in this forum. If you can be more specific in what you want to do (the weight you have to lift and forward speed for cruise flight), somebody may have already tested what you're looking for.
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