Hang test questions

fiveboy

I FLY THE JUNGLE JET!
Joined
Jan 28, 2007
Messages
2,324
Location
Panama City Central America
Aircraft
AC Tandem Elite F30
Total Flight Time
Almost 200 hours
This has no doubt been covered before but rather than wade through years of arguing back and forth to find nuggets I thought I might ask some specific questions and reopen the subject, allowing that the gyro community will indulge me:

If the machine is hung from the teeter bolt, how does one center the point on the bolt that the rope is attached to make sure it hangs right? I would think that off to either side would have an influence.

Are the degrees of hang different for each machine, or is there a universal range to hit on all?

When measuring this angle, is it the angle of the keel to the assumed 90degrees of the ground below? Or the angle of the mast off from 90d to the ground?

What is the most accurate way to determine that angle?

It is done with pilot in full uniform (helmet) with full tanks? If there are two tanks are both to be filled? Should it be done with one tank full first and then the second and then average the angles....?

If a tandem machine, should it be done with a passenger (or bag of cement to the load limit) in the rear seat as well?

If the angle is off, how does one correct that? My understanding is that the cheek plates need to be moved. I would also assume that just drilling more holes in the existing cheek plates could weaken them(?)... so new ones need to be made?

How does one realize the angular correction via new cheek plate position? Is there a formula that applies to all? E.g.: Move the holes back a half inch = 2d of nose down... or?

As I approach mounting a different engine etc on my machine, these are the things I am thinking about and need to fully understand.

Thanks to all
 
I am no expert, but have done hang tests on a number of machines now that fly, so I'll take a wag at it. I will not be offended in the least if someone feels inclined to overturn or correct any of my assertions:

The rotorhead hangs straight (laterally) and once pressure is on the strap or hook, lateral "drift" has never been a problem. I suppose you could use washers or spacers if you wanted to mitigate this. I don't think it would make a measurable differenence if it was off left or right. You are measuring front to back angle. Keeping the rotorhead centered, front to back, is more important. I use wooden shims at the rotorhead rather than to rely on the pilot.

Each manufacturer has their own instructions. Generally, for those machines that have masts at a 9 degree back-angle from the keel, the MAST should hang 0-3 degrees nose down when loaded. This assumes a check with the stick centered. Some test prefer the stick full forward or full aft. Since the range of movement of a normal gyro rotor head is 18 degrees, the non-center results should be corrected 9 degrees plus or minus as appropriate. Machines with other than 9 degree mast angles (such as the a stock bee, for example) may need different values, depending on what has been done with cheek plate angles or other adjustments.

I assume in question 3 you are referring to your own personal indicator. The MAST should PHYSICALLY be near to 90 degrees from good ole' earth. Some indicators may read 90 degrees when placed on the keel. If that is so, you will have to correct for your indicator.

The stock answer is pilot in full normal gear and a half tank of fuel (all tanks). If you want to be sure you don't have a condition that puts you in a bad hang angle, try all conditions that may apply. There are machines that are nearly "out of hang" at full fuel...or dead empty...but are fine at half tank. This is especially true with auxillary tanks, so I recommend testing all conditions, especially if you have a complex fuel system.

You need to do testing in a tandem machine with and without a passenger. Simulated passengers just aren't as good. Legs weigh a lot, especially in a large person. That leg weight, forward of the seat, is difficult to duplicate in a simulated "person." It would be bad to find that you were "out of hang" the moment a passenger was in the seat..and worse to find that you MUST have a passenger in the seat to be in the safe range.

The rotorhead, and ultimately the teeter bolt, must be moved forward or backward to correct an errant hang angle. You may be able to drill addition holes in existing cheek plates. You may not. This all depends on how far away the new holes are and the material is used in your cheek plates. Some cheek plates already have multiple holes at regular intervals to allow one to move the rotorhead to the next position forward or aft. Some do not. This will vary by style and manufacture. If your hang is way off nose-down, you may have to build new cheek plates of more robust material to extend forward. You may also want to consider other design aspects that may have it that far off and correct those. If you are building a stock design and find your hang way off, you may have done something wrong. Best to contact the manufacture or ask specific questions here before attacking the cheek plates. That said, it is not unusual to have to build new cheek plates, especially for a heavy pilot.

There may be a spreadsheed available available for each different make and model of gyro. I do not have one. Results will differ by make, model, pilot and powerplant and fuel system, so the only way to be sure is to make a custom mathematical model for your gyro. Most gyros that I have seen with multiple holes on cheek plates for "stock" hang adjustments have a 1" spacing. There is nothing saying that would be right for any given gyro and pilot.

*JC*
 
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Each manufacturer has their own instructions. Generally, for those machines that have masts at a 9 degree back-angle from the keel, the keel should hang 0-3 degrees nose down when loaded. This assumes a check with the stick centered. Some test prefer the stick full forward or full aft. Since the range of movement of a normal gyro rotor head is 18 degrees, the non-center results should be corrected 9 degrees plus or minus as appropriate. Machines with other than 9 degree mast angles (such as the a stock bee, for example) may need different values, depending on what has been done with cheek plate angles or other adjustments.




*JC*

Good, but not quite right JC

On a typical gyro, the mast is tilted back at 9 degrees to the keel. The Rotorhead is mounted 90 degrees to the mast.

On a typical gyro when you hang test it, your looking for a nose down angle on the keel, BUT MEASURED ON THE MAST of zero degrees up to 5 degrees.

So if your gyro had the typical 9 degree mast/ keel arrangement, and were hanging with a read of 0 degrees, this would mean the mast is perfectly straight. With 5 degrees nose down, the top front of the mast would be further forward than the bottom front of the mast.

You can take these same measurements on the keel itself, but you have to add 9 degrees to the 'Zero to Five" you would want to see on the mast. So it would be 9 degrees to 14 degrees nose down on the keel.

This is all assuming the controls are more or less centered. I have found that controls being slightly out of center don't affect the hang angle in any measureable amount. Same with making sure the strap the gyro is hanging from on the teeter bolt, when it is not centered.

A gyro like a Gyrobee has a mast that is zero degrees of tilt in relation to the keel. It does have the rotorhead tilted back at 9 degrees though, just like it would be on a typical 9 degree masted gyro with the rotorhead at 90 degrees to the mast. On a gyrobee you would just hang it like any other gyro and look for the 9-14 degrees nose down on the keel.
 
I have always hung mine 9 degrees nose down. I see the angle can be a bit more but 9 degrees has worked well for me. Half fuel, stick at halfway. If its a two seater I guess half a passenger plus pilot.

That is 9 degrees nose down from level flight at 50-60knts when the keel should be level. If you are changing the engine the hang point may only move an inch or so.

Use a set of dummy plates to test then its usually just a matter of checking with another hang test when the rotor head is mounted.
 
9 degrees nose down..............what is your angle of mast in relation to keel.

( vertical to keel, or angled back at ??? )
 
GyroRon said:
Good, but not quite right JC

Thank you, Ron, and quite correct. I have edited my post above to correct the error and prevent someone reading it and becoming confused. I had meant to say 0-3 degrees on the mast. For 9 degree masts, that translates to 9-11 on the keel, nose down. I'm not sure I like 5 degrees as an outside measure for nose down because of the human factor.

Excessive nose down reduces your "back-stick." I fly the GyRonimo at the outside end of the scale (11 degrees nose down). I know that in winter I probably exceeded that by a few degrees for winter gear. If I had started at 9 degrees and weight moved me to 11...no problem. But I started at 11 and added weight to who knows where. Had I started at 14, I might have been at issue with winter gear. It would fair to say I should have done a winter gear hang test. No longer an issue now, as I have dropped 20 pounds.

Where I went wrong in the initial post above was in considering a discussion of the reason for a hang test in the first place. That discussion would have included the keel's "normal" level flight condition of near parallel to the ground, leading to discussion of the problem with too much nose up or nose down in normal "level" flight. I dismissed that idea, considering that it might be better placed in another thread, but the level keel thing must have stuck in my head. Thinking about that as I typed, and having just finished installing the crown molding in the kitchen was too much cyphering for my poor little brain at the time, I suppose.

Good catch. Thanks, again.

*JC*
 
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Robert glad you asked the question as we are about to make some dummy cheeks plates and do the hang test.

The Hornet like the Bee has a vertical mast so if I have understoodwhat Ron and JC have said correctly we will be looking for a hang with the nose around 9-14 degrees low when measured from the keel. This with fully dressed pilot in the seat, half fuel and centered controls which we will center first then shim into place with wooden wedges to maintain that position.

I will add the question, about head movement fore aft and side to side. We are intending to have Pitch rage -1 forward to approx 18 degrees aft and Roll 9 degrees either side. We will also be checking to see that we have adequate ? rotor clearance with the prop and ground behind the gyro with these.

We have a 62'' prop and 23' blades but appreciate the geometry will also depend on what height we end up with with the cheek plates final rotor head height and engine mount position/prop tip height/position.

Any remarks/helpful advice here greatly welcomed for example how best to do the head movement limiting, the range we are envisaging using.

P.S JC we will be summer only so no heavy clothing, on the Hornet similar to your Gyronimo would 9 degrees down be a better starting point?
 
The primary relevance of a hang test is the rotorhead angle with controls centered. The rotorhead should hang ~2º nose down at whatever the angles of mast and keel happen to be.

This will ensure there is sufficient stick travel for all flight conditions.

Secondary issues are engine and landing gear angles.

The engine should hang ~11º nose down to ensure that propeller thrust is parallel to the flight path.

Landing gear angle should be ~9º nose down to ensure that touchdown is main wheels first.

Gyros that have a large misalignment between CG and propeller thrust line are often specified at different hang angles but the critical factor remains one of having sufficient stick travel in the event of engine failure. Engine off, all gyros are the same.
 
The primary relevance of a hang test is the rotorhead angle with controls centered. The rotorhead should hang ~2º nose down at whatever the angles of mast and keel happen to be.



So with the rotor head shimmed( to hold it in place) to 2 degrees nose down when the gyro is sitting level and controls centered, and I then hang the gyro and adjust the cheek plates so that I have a nine degrees nose down angle measured from the keel, have I got a correct cheek plate geometry?
 
Just to clarify:

I shim my rotorhead for hang testing at the center of rotorhead travel. If the controls are proper, this gives me a centered cyclic. If it doesn't give me a centered cyclic, there are control adjustment issues...but that's another thread.

*JC*
 
So with the rotor head shimmed( to hold it in place) to 2 degrees nose down when the gyro is sitting level and controls centered, and I then hang the gyro and adjust the cheek plates so that I have a nine degrees nose down angle measured from the keel, have I got a correct cheek plate geometry?
No. The rotor is shimmed to center it midway between stops. Saw wood wedges and lightly tap in between torque bar and pitch stops, making sure it’s centered between stops.

Then with the thing hanging from a rope attached to the center of the teeter bolt, with pilot in the seat and a half tank of gas, the rotor head should be ~2º nose down. Most anything in the range of zero to –4º will do.

Keel and mast angles can be useful references if relative angles are known but what does one do with a LittleWing or other machine with space frame of small diameter tubes running at all sorts of angles?
 
Thank you for clearing that bit up for me Mr Beaty.

So the keel angle/mast angle would seem to be not as important as the head angle.

Our mast is a vertical one 90 degrees to the keel. So with the gyro dangling from the rope and the rotor head (shimmed to center) with the controls central, now inclined forward between 2 and 4 degrees hopefully I will find that the keel is approximately 11 degrees down giving me a good engine thrust line, but this is secondary?

I am going to try to arrange that the forward pitch stop for the head will allow 1 degree and the back stop to limit the head at a point that gives good blade clearance over the prop and rotor tip to ground clearance. Any advice on these clearances?

I do apologize if I am being a bit obtuse about this but I do want to make sure I am doing it correctly.
 
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What would any of you recommend as a support beam (ie a-frame) to hang a sparrow hawk. I do not have access to a crane. I am concerned about hanging the craft from a hanger support. I am upgrading the landing gear to the sparrow hawk three configuration. It seems that hanging the craft would be the safest way to allow the change.
 
HAWK PILOT : Red neck crane: A oak tree limb.:noidea:
Fork lift
I am sure if you can find a person with a backhoe, front end loader, ect that they might swap you for hanging it up for a ride in it!
 
engine hang?

engine hang?

The engine should hang ~11º nose down to ensure that propeller thrust is parallel to the flight path. Landing gear angle should be ~9º nose down to ensure that touchdown is main wheels first.(QUOTE]

Chuck, are you saying that the keel should be 11* nose down of the crankshaft regardless of what engine it is? That a gyro should fly 11* nose down?
 
No. Using Bensen’s dimensions with the keel hanging 11º nose down, the engine should also be 11º nosedown; that is, parallel to the keel.

Bensen actually had the engine 2º nosedown (by nose, I mean the end opposite the propeller) relative to the keel to get the line of propeller thrust to pass through the CG or at least nearer.

If the gyro happens to fly with keel level, ideally the engine should also be level with the keel to ensure the engine thrust line is parallel to the flight path.

Small deviations of engine thrust line don’t do a great deal of harm but consider the case with propeller thrust line inclined 10º downward relative to the flight path:

Say the engine thrust is 300 lb:

The horizontal component is equal to the cosine of 10º which is 0.985 or 295 lb. parallel to the flight path. No big thing.

The downward component is equal to the sin of 10º which is 0.174 or 52 lb. of extra load. That is a big thing.
 
Bensen actually had the engine 2º nosedown (by nose, I mean the end opposite the propeller) relative to the keel to get the line of propeller thrust to pass through the CG or at least nearer.

Excellant, this is exactly what Racer did with his engine as prior the engine wanted to lift the mains first. I plan to duplicate his machine but with a different frame. It's easy to complicate this simple stuff. Thank-you.
 
The primary relevance of a hang test is the
Landing gear angle should be ~9º nose down to ensure that touchdown is main wheels first.
.

Chuck,
would you do one of your famous drawings to show me what you mean about 9 degrees nose down angle?
 
Mark, I was bass ackwards on that.

What I should have said; “resting on the wheels, the keel should be about 2º nose up.”

That helps with rotor starting and still permits main wheel first touchdown during the landing flare.
 
Mark, I was bass ackwards on that.

What I should have said; “resting on the wheels, the keel should be about 2º nose up.”

That helps with rotor starting and still permits main wheel first touchdown during the landing flare.


Thank you, I often fly bass ackwards, but I wasn't sure if I was 9 degrees nose down. :usa2:
 
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