Gyro Tilting Mast for Variable CG Pilot Loads?

RotoPlane

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This thread http://www.rotaryforum.com/forum/showthread.php?t=23855 got me thinking (I know, that can be a bad thing) about using a rotorhead assembly that would be attached to the top of a tubular mast. This mast would be able to pivot at or near its bottom end allowing the rotorhead to be adjusted for best CG location. This ability would allow one gyro to serve more than one person's ideal weight position and also make for an easier hang-test. The weight positions would be pre-determined by hang tests and labeled.

This quick drawing (will zoom) shows two ways (without a bunch of details) too adjustably fix the mast at the best position….one with angles and the other with a bolt though the triangular gussets (which could be slotted). The seat and engine assemblies would be self supporting and not attached to the mast. This could also help to lower the mast for shorter door openings. Another possible advantage may be that by using this size mast tube, the 2/rev may possibly be reduced with less stick shake (refer to the above thread). It's not an UL…..and possibly just a dumb misguided idea.
 
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The drawing is low contrast when I view it but it looks like you are using multiple holes or a slotted arc at the bottom of the mast and mast tilt to eliminate cheek plates. That is essentially what I did with my gyro. What you'll find is that the way you are showing with the holes will provide too much movement at the top to be practical, it's difficult to get the holes close enough together to be precise while keeping some material between them, and most of the holes will have the top of the mast out of practical range. Raising the top of the seat angles (changing the pivot location) will constrain the range at the top some. I personally don't like the idea of using a slotted arc but you may figure out a way to make it work well. If you look at most gyros, you'll see that the teeterbolt is within only a few degrees of the mast to keel connection almost regardless of the mast angle. If you remove the gyros with unusual layouts of fuel tank, battery, seat or engine placement, the angular range goes down further. The tighter the range, the easier it becomes set the CG with seat and engine placement, and fine tune it with the placement of other stuff like battery, fuel tank, etc. IMLE
(In My Limited Experience)
 
Yes John, I agree about the holes in an arc and your other comments. A slot can work with the proper clamping washers but I thought using something like Bonanza uses at the wing trailing edge spar...a concentric washer to vary the pitch. It would eliminate the cheek plate hassles. I should have known you would have thought this out…some time ago ;). I don't know why your drawing lines are dim....they are bright and crisp on my monitor.....
 
One of the Spagnoleti's (sp) from Texas already developed a sliding rotorhead for a S/S gyro. This was to compensate for passenger/no passenger. He flew it at Mentone several years ago.

Basically from what I remember. The whole rotorhead slid by removing and replacing a few pins.
 
you also have to remmber that pivoting the mast changes the teeter stop angles.
 
Chuck - I wanted a sliding head/mast assembly on the one I'm building now…but I just wouldn't be able to meet the UL weight. It is, IMO, a practical addition for a tandem, or a trainer.

Paul - You are of course right and I probably should have at least implied that. I would have added adjustable teeter stops to the head.

I am building my own now, so this idea was for whoever may be thinking along the same lines….as twisted as it may be. Sometimes a "dumb" idea may spark a good idea in someone else.
 
I'm viewing it on my Linux box using document viewer. Its probably my fault I can't see it better.
 
This was in an old issue of Rotorcraft. The large knob turns a screw that slides the head for C.G. adjustment, then the bolts were re-tightened. This allowed the gyro to be flown single or with two side by side.
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Yes that is what I want to do Alan. Nothing is new…..The only difference is that mine had a v-rail on each side in an arc and the head has dolly-wheels riding on the top and bottom of this rail. The head is pushed and pulled by a linear-actuator and can be adjusted in flight. The arced rails keep the RTV pointing to the ideal CG location. Thank you for the picture!
 
seems like a good idea....why then, are these not used more often??

Because most 1-2 seat designs have a large enough allowable CG range that they don't really need such a device over a pretty large passenger weight range.

Most 4+ seaters would just deal with it by shifting between fwd/aft seats as required.

The Hiller 12E's I used to fly (with a single bench seat for 3 people) had a 9 lb steel ballast weight that could be shifted between either the cabin floor or the end of the tailboom as needed, with quick release pins it took a few seconds to move. In our case we didn't need it in the back over our entire normal operating range since we never had that much weight in the seat so it was removed entirely to save those 9 lbs...
 
seems like a good idea....why then, are these not used more often??

I think it is like the Dominator tail Mark….someone does it, it works well and looks good, and so others begin to use it. Weight of course is also a factor for most gyros. My gyro uses a wing which is sized to carry the added stuff and the fuel at cruise. Therefore the rotor can do its thing without the added weight imposed on it and the engine is better off because the wing can carry that weight with less drag. The wing does little lifting below cruise but I don't care about the extra rotor drag at low speeds. If my rotor system and wing work well on the UL, then I will definitely be using a shifting head on my next gyro…plus all the other stuff I can't use on the UL now.
 
Because most 1-2 seat designs have a large enough allowable CG range that they don't really need such a device over a pretty large passenger weight range.

When I did weight & balance on my tandem, I found it was not acceptable if I was in the aft seat and my front seat passenger varied between 90 and 300 lbs., and then do a jump takeoff. That’s when I decided to incorporate the in-flight shifting head. This also takes the load off the HS at cruise.
 
That's why most tandems pushers are flown solo from the front seat, hard to do it the other way given the general layout without what you're looking at. Variable passenger weight is easier dealt with the closer it is to the CG :)
 
Yes Brett, that is normally a true statement....but how about during flight training? It is a different flight experience, between the two seats.....well at least in my opinion ;).
 
but how about during flight training? It is a different flight experience, between the two seats.....well at least in my opinion

I normally fly my tandem gyro with fuel only in the rear seat tank with students. But if I have a lighter than average student then I can compensate by adding up to 7 gallons of fuel in the front seat tank.
 
I haven't flown any tandems, but switching between left/right/center was a non-issue for me. Biggest difference is what I could see in a turn :)
 
I normally fly my tandem gyro with fuel only in the rear seat tank with students. But if I have a lighter than average student then I can compensate by adding up to 7 gallons of fuel in the front seat tank.

Well there you go Chuck….think of all the hassles you'd save if you could push a button and CG level that sucker out….nor be concerned that you may forget to change something. :)
 
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