Hang Balance VS. Flight Test Pilot of different weight

[Brian Jackson]

I didn't want to go off topic asking this in another thread. When my build is eventually finished I will be hiring an experienced gyro pilot to test fly my ship. I'm a small guy that might squeak in at 145 over the winter months. If a test pilot were, say, 185 lbs, how would he adjust to a ship with cheek plates designed to balance a lighter pilot? And on that train of thought, how easy is it for people of different weights to fly each other's gyros? Are there typically weight "ranges" that are deemed safe before new cheek plates need be installed? The designer in me is almost envisioning an adjustable-position rotorhead but that's an area I have no practical knowledge of. Thanks.

Brian

 

[Vance]

This is a challenge in The Predator as I change from the front to the back. I am near the maximum front seat weight and I have had clients in the front seat from a hundred thirty five pounds to two hundred fifty pounds. Full fuel also moves the CG slightly forward.

All aircraft should have a forward and aft CG limit and on an experimental that will need to be determined in phase one flight testing.

If I was hanging; on most gyroplanes I would probably use a maximum of eleven degrees nose down to three degrees nose down.

I have not flown a gyroplane outside of the maximum nose down angle so I cannot describe what trouble looks like.

I did fly a gyroplane that hung at zero and balancing on the mains was problematic. I don’t know if this was because of the locating of the mains or the rotor head.

 

[Alan_Cheatham]

I would suggest that if there is a significant weight difference between you and the test pilot that a second set of cheek plates be made for the test flying phase.

 

[Illini85]

Not an engineer here so take this for what it's worth. Part of the consideration in a balanced machine is having the cyclic centered in straight and level flight so as to have full range of control input primarily fore and aft. A machine balanced for you but with a substantially heavier test pilot as you propose should still be able to fly straight and level however the cyclic location (further back) in doing so would be different and hence closer to the stop thereby limiting range of control motion. I would think that a counterbalancing weight placed in such a way as to center the cyclic for the test pilot would be an appropriate consideration. Obviously the further back it could be located the less it would have to weigh thereby softening the effects of adding even more weight to other considerations of flight performance.

This is what Jim Fields with the 2-place Honeybee G2 had in mind with the electrically controlled sliding mast design; he and his team developed. See photo attached. This was to address the anticipated applications involving substantially varying weights. The design made it off paper to actual flight tests and Jim reported as he would shift the mast forward and back the orientation of the craft wouldn't change but the cyclic position would shift.

 

[Gyro Technic]

The most important aspect of a hang test is to assure your CG lies slightly ahead of your rotor thrust vector for dynamic stability.
An unbalanced machine can have the controls adjusted to be centered for straight and level flight, but possibly sacrificing a great level of safety.

 

[Brian Jackson]

Thank you all for the insights. I take away from this that the issue is more pronounced in 2-place tandems due to the mechanical advantage of the pilot out front. So weight changes at this moment arm will have a more dramatic effect than of a close-coupled single-seater where the varying pilot weight is closer to the CG. If I'm understanding this correctly then I will scratch that off my list of things to worry about. There's enough of those already. Much obliged, gentlemen.

Brian

 

[Vance]

Thank you all for the insights. I take away from this that the issue is more pronounced in 2-place tandems due to the mechanical advantage of the pilot out front. So weight changes at this moment arm will have a more dramatic effect than of a close-coupled single-seater where the varying pilot weight is closer to the CG. If I'm understanding this correctly then I will scratch that off my list of things to worry about. There's enough of those already. Much obliged, gentlemen.

Brian

Your aircraft is lighter so a little more weight makes more difference as a percentage of the takeoff weight.
The leverage does come into play.
Hang it with the big kid in it so your have more data on what your weight and balance limits are.

 

[Rowdyflyer1903!]

When the FAA/DAR visits you for the inspection to give their approval, what kind of weight and balance data is expected? It seems a fixed wing (FW) weight and balance determination is more straight forward. What do we show? Also where would be a good place to find a good example of a Pilot Operating Handbook for a scratch built machine?

 

[Vance]

You can do the weight and balance just like a fixed wing with a datum point and a CG range.
You will find some guidance here.

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/faa-h-8083-1.pdf

Some people do a gyroplane with a hang test with a minimum and maximum nose down angle.

I have it both ways in The Predator; a one of a kind gyroplane and I have not had anyone from the FAA demonstrate an understanding of either.

Many kit gyroplanes use a minimum and maximum seat weight with a maximum takeoff weight.

I had the FAA accept that too.

Assuming your fuel is close to your center of gravity maximum seat weight works just fine.

 

[Doug Riley]

A note regarding Post #6:

The location of the rotor on the frame has no effect on whether the CG is ahead of, or behind, the rotor thrustline. The aircraft will position itself in the air so that the net forces and moments on the frame are zero in unaccelerated flight. IOW, the CG will end up behind or ahead of the rotor thrustline, dependent only on where the other forces on the frame dictate that it end up. The aircraft will adopt whatever stance in the air is necessary for this to occur.

Trouble is, this in-air stance, if very nose-down or nose-up, may put the fore-aft control stops out of center, relative to the rotor's spindle angle, just as others have posted. You could run out of fore-aft control.

My original, no-HS low-rider Air Command was designed around Bensen specs, including rotor head position. Unlike a Bensen, however, the Air Command had a 6-7" high prop thrustline. This meant that the rotor thrustline HAD to come down in front of the CG to hold the nose up against prop thrust (which was trying to push the nose down). At high throttle settings and airspeeds, the resulting "hang angle" in the sky was very nose-down. In Bensen at the same speed and power but with nearly CLT, the aircraft would have flown more level. A H-stab would have levelled the nose, too.

The stock RAF 2000, with an enormous HTL, has a specified hang angle several degrees less than a Bensen.

 

[C. Beaty]

To reiterate Doug’s comments about dangle angle; it has no direct influence on the location of rotor thrust line to CG; the main purpose is to properly center the stick. It is totally unrelated to FW weight and balance determination.

As a secondary effect, dangle angle affects incidence angle of the horizontal stabilizer.

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[OuterMarker]

There is a program on this site which calculates the vertical CG point. Aircraft scales should be used but bathroom scales have also been used. I would trust scales over guessing an intersecting point via eyesight. However, if you are going to use the hang method, make sure the procedure is followed and the rotor head is contained firmly in the center of the rotorhead travel.

 

[Rowdyflyer1903!]

Are you referring to the F.A.A. Site : https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/faa-h-8083-1.pdf

 

[Rowdyflyer1903!]

Found this handy dandy Document https://cdn.shopify.com/s/files/1/0002/3737/1457/files/Weight_and_Balance_Information.pdf

 

[Rowdyflyer1903!]

Also http://www.md-ra.com/docs/C17HG_E.pdf

 

[OuterMarker]

Attachments

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  CG5.1(1)gyro.xls
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  Rotor Blade Lift HP3.xls
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[C. Beaty]

CG (center of gravity) is a point that can only be located in space by specifying 3 dimensions; horizontal, lateral and vertical.

What is commonly called CG for a weight and balance check only specifies a plane where the CG is located; or if lateral balance is also specified, locates CG along a line.

Stability of an aircraft requires knowledge of the actual CG location so that moments acting about the CG may be determined.

 

[wolfy]

To reiterate Doug’s comments about dangle angle; it has no direct influence on the location of rotor thrust line to CG; the main purpose is to properly center the stick. It is totally unrelated to FW weight and balance determination.

As a secondary effect, dangle angle affects incidence angle of the horizontal stabilizer.

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Chuck could you elaborate about the effects of hang angle on stab incidence.

wolfy