Weight and Balance

[Abid]

Abid, sounds like you have your design dialed in. Nice!

...

Well it still slows down 6 knots but it used to slowdown up to 10 knots. But it is safer this way and this is lower with lower HP engines as well (like 912 and 914). When you lower the power to idle you will nose down a little and it will accelerate and increase speed about 5 to 6 knots and thus you may want to retrim there a tiny second also. So power/thrust is going over the tail and having an effect. In my opinion it should be in this direction not the other direction. Gyroplanes do not stall so slowing down 5 to 6 knots isn't going to be dangerous and loads the rotors. In an airplane I may want this the other way on balance.

 

[Mike Leimetter]

Abid, sounds like you have your design dialed in. Nice!

In my limited time in a Magni-configuration gyro, I did notice that initial nose-dip upon power-up. The effect is small and apparently harmless; just irritating to a stability nerd. What may be the case with those gyros is that the H-stab as installed has no negative incidence, and the nose must dip a little before the H-stab starts to "bite."

I found that a -3 deg. incidence on the Gyrobee (with a small engine, 2-3 inches HTL and a 6 sq. ft. immersed H-stab) produced Scenario #2. OTOH, my 912S tandem Dominator, with substantial LTL plus an immersed H-stab, was over-compensated for power changes -- powering up from cruise power to full power required quite a large trim change to avoid slowing down. Scenario #3 on steroids. More examples:

The earliest model lowrider Air Command would fly very nose-low at high airspeeds. I noticed this both in flying mine and in flight videos of a friend flying his. This is an example of a gyro that was laid out using Bensen's hang specs, but its uncompensated HTL actually demanded a different hang spec. Once you add the factory H-stab to the lowrider Air Command, though, it becomes a different aircraft. The "low-nose syndrome" largely disappears. (My dinky 447 lowrider Air Command would do over 80 IAS using a high-pitched prop, but was twitchy and scary at that speed pre-H-stab. It became quite solid after the H-stab upgrade.)

IIR, the hang spec for an original RAF-2000 was around 4-5 degrees nose-down (recall that Bensen's was -12). This is an example of departing from the classic hang spec in order to enable a very HTL gyro to fly level. An RAF-2000 with a seriously-compensating H-stab would need to revert to something like the Bensen spec. Otherwise, it would fly way nose-UP.

According to my RAF manual, it should be between 4.5 to 12.5 degree's nose down depending on what position the CG adjuster is at. That’s with the original design. How do I correct for the Boyer Stab that I have? Use the same but on the higher end?

 

[Abid]

According to my RAF manual, it should be between 4.5 to 12.5 degree's nose down depending on what position the CG adjuster is at. That’s with the original design. How do I correct for the Boyer Stab that I have? Use the same but on the higher end?

You may want to ask Larry Boyer. I think he has substantial time flying RAF with the stab. He just called me an hour ago to tell me he bought one of the gyroplanes I had sold in 2016.

 

[Bob Gregory]

Recipe for Hanging a Gyro.
Before the reason for this recipe, lets set new mandates or rules for settings. This stems from blades we use. Most blades fly at 9-10 degrees, Skywheel fly at 8 degrees and Dragon Wings at 7 degrees. More efficiency will come from setting the hang down angle of incidence at the blade dangle angle. Super efficient blades may fly at 4 degrees. Ken Wallis or Dick DeGraw may have already done this.
Mandate 2, design main wheel location to be 15-17 degrees to cg to prevent swapping ends for tail draggers.
Mandate 3, design thrust line to be 100 mm or 3.9” below vertical cg according to Glasgow University.
Mandate 4, consider down thrust line in degrees to come in lower than incidence of wing or rotor for efficiency.
Any discrepancies in this narrative (Refer to mandate).

Reason: To insure there is enough control authority of the rotor head arc front to back. The controls must hang in the center of the arc of the rotor head and joystick to allow the rotor blades to come back for the landing flare. To check if teeter towers are hanging parallel with the cheek plates which are set at 9 degrees back when flying level. (Refer to mandate).

Prerequisites: Level gyro. Set rotor head and cheek plates at 9 degrees back.(Refer to mandate). RAF's are set different, follow instructions of manual. Some are set at about 7 degrees.

List of items: Come-a-long, hook for teeter bolt (pad with electric tape), camera, broom stick and plumb bob, rope and chocks to prevent swinging, Ladder. Helmet, half tank of fuel. Level. Wood shims to center rotor head.
Laser if available. Hardware stores or Walgreens have inexpensive ( 5.99) lasers with built in levels now.

1. Setting the Dangle Angle for the controls to be in the center of the arc.
Remove the rotor blades and hub bar and set them aside.
Wedge the rotor head with wood shims (less damage to aluminum) to eliminate the gimbal head offset from pulling the joystick to the full forward position. Place the towers to the side. Hook in center of bolt. (a short 2 piece of steel pipe with a chain link welded to it will support the bolt much better without the fear of bending the bolt or damaging the teeter towers, just put it in place of the rotor hub bar and lift by the welded chain link.)
Raise the gyro off the ground via the come-a-long from the teeter bolt.
The gyro should now hang keel down 9 to 12 degrees. (Refer to mandate).
If head is not wedged it will pull forward and the Dangle Angle will not be accurate for the controls.
Put lead in nose or tail if only a little is required. Other wise, change the cheek plates.
Ideal Dangle Angle is 10 degrees. (Refer to mandate).
If angle is 12.1 or more, move the head forward. If angle is 9 or less move head backward. (Refer to mandate).
Temporary plywood cheek plates can be made to help find the right bolt position. Then transfer to aluminum plate once the position is assured.

2. Setting the Joy Stick for Neutral.

Good time to adjust the joy stick while the rotor head is wedged and hanging.
Lengthen or shorten control rods to what is comfortable to your hand.
Adjust control rods to center joystick after flying.
If stick is to right, shorten left control rod.
Check rotor head movement after adjusting to make sure you have full movement side to side and front to back.

3a. Finding the Center of Gravity.....( Horizontal and Vertical center of mass ( COM or CG ) ).

While hanging, take a picture from some distance to eliminate the parallax of the camera.
Get down low and line up with the main axles and get the hanging cable in the picture.
Have the broomstick with the hanging plumb bob across your lap in the picture.
Or have the laser leveled vertically on the cable and take the picture.
Put the finished picture in "Paint" and draw line from upper cable down parallel to plumb bob line.
This will show the horizontal cg and some place on that line, is the vertical cg.

3b. Finding the vertical center of mass.
Install rotor blades and sit in seat with all flying gear for all up weight.
Balance a pusher gyro on car ramps by lifting up on the nose with pilot in seat with helmet and all flying gear.
Rotate the gyro frame on the axles to reach the point of balance where the gyro wants to fall over backwards or forwards. That is the balance point, so be careful!
You can lose control and drop the gyro so get assistance if possible to block it.

Tractor gyro will balance on the mains by lifting up on tail with pilot in the seat with helmet and gear. Block rear wheel at height and record height.
While balanced, take picture from some distance to eliminate the parallax of the camera.
Get down low and line up with the main axles and get the picture.
Have the broomstick with the hanging plumb bob across your lap in the picture.
Or have the laser leveled vertically on the axle and take the picture.
Put the finished picture in "Paint" and draw line from the axle upward parallel to plumb bob line.
This will show the vertical cg some place on that line.

4. Setting the Thrust Line Offset.

Where the two lines cross in the combined "Paint" pictures, is the Center of Gravity. Hcg and Vcg are in same place.
The CG should be in line with the propeller thrust line of a properly designed gyro. (Refer to mandate).

The propeller thrust line is an imaginary line through the center of the prop at 90 degrees to the propeller disk.
If the offset is small ( 2 inches or less ), washers can be used to alter the motor mount.
This will angle the thrust line to intersect the CG.
Example: Thrust offset is 2 inch. Propeller to CG is 24 inch. ATAN(2/24)*180/PI() = 4.8 degrees.
Motor Mount fore and aft is 6 inch. Raise rear mount of pusher 0.5 inch. ATAN(0.5/6)*180PI() = 4.8 degrees.
Motor Mount fore and aft is 8 inch. Raise rear mount of pusher 0.67 inch. ATAN(0.67/8)*180PI() = 4.8 degrees.

Other wise, a large down loaded stabilizer is necessary to counteract any PowerPushOver tendencies.

5. We are not done. Find the Center of Pressure on the Side and Top. Use new or old manila folders for cutouts, they are stiff enough for cutouts.

Take a copy of the picture and cut out around the pilot, frame, wheels (the side view).
If there are two tails.....cut an extra tail area right above the tail. Idea is to get the full side area.
Now balance it on the scissors at the Rotor / CG axis..................Mark it.
Ideal is 6 to 12 inches back from Rotor / CG axis.
This shows that aerodynamically the gyro is stable from the side.

Now do a scale top view of the gyro using the picture as a guide. Real simple.......Length, width and horizontal.
Mark the cg with circle and rotor head with X.........1/2 way between is the Rotor / CG axis.
Cut it out, balance on the scissors. Is the horizontal sized to balance at 6 to 12 inches behind the Rotor / CG axis?

Plagiarized by Bob Gregory from I Bensen, P Bruty, P Johnson, D Riley, R Taggart, C Beaty and Hey-Abbott.

Quick List Review for Printing......................Take to the field.
List of items: Come-a-long, hook for teeter bolt (pad with electric tape), camera, broom stick and plumb bob, rope and chocks to prevent swinging, Ladder. Helmet, half tank of fuel. Level. Wood shims to center rotor head.

1. Set the Dangle Angle for the controls to be in the center of the arc.
Wedge the rotor head with wood shims.
Place the towers to the side. Raise the gyro.
The gyro should now hang keel down 9 to 12 degrees. The ideal Dangle Angle is 10 degrees,. (Refer to mandate).

2. Setting the Joy Stick for Neutral.
While the rotor head is wedged and hanging.
Lengthen or shorten control rods to what is comfortable to your hand.
Adjust control rods to center joystick after flying.
If stick is to right, shorten left control rod.

3a. Finding the Center of Gravity.....( Horizontal and Vertical center of mass ( COM or CG ) ).
While hanging, take a picture from some distance to eliminate the parallax of the camera.
Get down low and line up with the main axles and get the hanging cable in the picture.
Have the broomstick with the hanging plumb bob across your lap in the picture.
Or have the laser leveled vertically on the cable and take the picture.

3b. Finding the vertical center of mass.
Install rotor blades and sit in seat with all flying gear for all up weight.
Balance a pusher gyro on car ramps by lifting up on the nose.

Tractor gyro will balance on the mains by lifting up on tail with pilot.
While balanced, take picture from some distance to eliminate the parallax of the camera.
Get down low and line up with the main axles and get the picture.
Have the broomstick with the hanging plumb bob across your lap in the picture.
Or have the laser leveled vertically on the axle and take the picture.

 

[Abid]

Sky wheels and Dominator rotors both fly at around 10 degrees in flight. We tested Skywheels on AR-1. They were terrible and completely divergent past 70 mph.

How do you get that these rotors fly at lower angles. Did you setup a measurement and if so how? I’d love to know how these angles came about

 

[Bob Gregory]

Sky wheels and Dominator rotors both fly at around 10 degrees in flight. We tested Skywheels on AR-1. They were terrible and completely divergent past 70 mph.

How do you get that these rotors fly at lower angles. Did you setup a measurement abd if so how?

Don't know where I found that. Might have been around 2009. Remember Chuck Beatty checking rotors at 50 mph from a post in the ground at some flyin, and recording the data. His data about Dragon Wings was 7 degrees, the rest at 9 to 12 deg. Many pictures of wings, UL to jets come out about 7.13 degrees.

 

[Bob Gregory]

Can't get to work, tomorrow,

 

[Abid]

Don't know where I found that. Might have been around 2009. Remember Chuck Beatty checking rotors at 50 mph from a post in the ground at some flyin, and recording the data. His data about Dragon Wings was 7 degrees, the rest at 9 to 12 deg. Many pictures of wings, UL to jets come out about 7.13 degrees.

That is some calculation. I was hoping for a measurement. Engineering is after all an applied science.
I do not think Chuck Beaty measured this . Dominator rotor disc flies at about the same angle as anything else.
Just FYI, Glascow university report had many things not quite correct and according to their main researcher Magni M16 was a centerline thrust gyroplane.

 

[Jean Claude]

When I designed my first radio control gyro which was a tractor configuration, I figured out the horizontal CG by aligning the blades for and aft.
The balancing the entire aircraft from a point on the front blade that bisected the disk at 30% of the disk area.
The rotor head was not direct control, it was a rudder elevator aircraft.
When I switched to direct control, I locked the head with a couple of shims.
After balancing at 30%, I would add a bit of nose weight to bring it to 27% for stability on the first flight, then reduce the weight until it flew the way I wanted it too.
I use the same process on fixed wings, except I tend to keep moving the CG back until it gets unstable, then move it slightly forward of that point for maximum efficiency.
Obviously you can not do this to full sized aircraft, the rotor is not strong enough...
The other interesting thing was that when balanced this way, it would hang as expected when suspended from the center of the rotor head.
Here is a diagram (Not a tractor) to explain the balance point.
I basically treated the rotor as a round wing and balanced it accordingly.....

You're misinterpreting your experiments.

The rotor's thrust is almost on its axis. Therefore this on it where GC should be placed (in the absence of other disturbances such as tail or fuselage thrust).

So, contrary to your interpretation, the balance is not altered by the diameter of the rotor, but by the vertical position of the head.


This is also why the hang test by the rotor head is relevant, since it gives an airframe angle relative to the vertical identical to the angle the airframe will take relative to the plane of the blade tip in flight.

 

[Abid]

Here is a CG on an AR-1 via a double hang test. One can see that the thrust line of the prop/engine is about 4 inches above the CG. To do this correctly was not easy. We had to weld a special weldment to be able to hang the gyroplane from a second point besides the usual teeter bolt. It also coincided fairly closely with predicted CG location.

 

[Aerofoam]

You're misinterpreting your experiments.

The rotor's thrust is almost on its axis. Therefore this on it where GC should be placed (in the absence of other disturbances such as tail or fuselage thrust).

So, contrary to your interpretation, the balance is not altered by the diameter of the rotor, but by the vertical position of the head.

View attachment 1161507
This is also why the hang test by the rotor head is relevant, since it gives an airframe angle relative to the vertical identical to the angle the airframe will take relative to the plane of the blade tip in flight.

I pointed out that I initially did this on a tractor (actually 4 of them) with a fixed head, so the diagram I provided was not the best tool for the concept.
I did do it on a pusher and the results were the same.
My point being that on all the models I have built, the disk could be treated as a wing and it ended up working properly and also hanging at about 12deg. So it seems to be another path to the same finish line.
So the interpretation may be wrong, but the process works. I never had a failure and the final tuning was very minor.

 

[okikuma]

Here is a CG on an AR-1 via a double hang test. One can see that the thrust line of the prop/engine is about 4 inches above the CG. To do this correctly was not easy. We had to weld a special weldment to be able to hang the gyroplane from a second point besides the usual teeter bolt. It also coincided fairly closely with predicted CG location.

Abid,

Instead of creating a special weldment to hang the gyro, you could have just raised up the gyro up on some blocks. Then rock the gyro back on it's main wheels (raising the nose) until the balance point is found between the nose falling back down or falling rearward onto the tail.

Wayne

 

[Abid]

Abid,

Instead of creating a special weldment to hang the gyro, you could have just raised up the gyro up on some blocks. Then rock the gyro back on it's main wheels (raising the nose) until the balance point is found between the nose falling back down or falling rearward onto the tail.

Wayne

Yes but when I did that the result was not the same. Kind of close but not exactly. If you really want to know the CG you have to do it right or no point really. Maybe we screwed up something but making the weldment was easy enough for us.

 

[Jean Claude]

In both cases, the second vertical line requires installation of the rotor. Bending the blades at rest lowers its own center of gravity, and thus modifies that of the aircraft as a whole (one inch perhaps?)

 

[Abid]

In both cases, the second vertical line requires installation of the rotor. Bending the blades at rest lowers its own center of gravity, and thus modifies that of the aircraft as a whole (one inch perhaps?)

Yes we had the rotors on. I did not think about rotors not being coned up but that makes sense. In that case I would guess AR-1 is high thrustline by about 3.5 inches

 

[Aerofoam]

You're misinterpreting your experiments.

The rotor's thrust is almost on its axis. Therefore this on it where GC should be placed (in the absence of other disturbances such as tail or fuselage thrust).

So, contrary to your interpretation, the balance is not altered by the diameter of the rotor, but by the vertical position of the head.

View attachment 1161507
This is also why the hang test by the rotor head is relevant, since it gives an airframe angle relative to the vertical identical to the angle the airframe will take relative to the plane of the blade tip in flight.

Hmmmmm........

 

[Jean Claude]

According your method, the balance depends on the rotor diameter !

 

[Aerofoam]

According your method, the balance depends on the rotor diameter !

View attachment 1161520

Given the slight range of diameters for a specific sized gyrocopter, I don't think it can vary enough to get you out of the ballpark.
I started with the disk area and designed the rest from there, maybe not the proper method, but it worked....
I used this method to set initial balance. it also produced the proper hang angle within a degree or 2.
The first tractor version flew slightly nose high, so I added down thrust at the engine, because at idle it seemed to glide only slightly nose down, so I assumed the balance was OK and it was a thrust line issue.

 

[Doug Riley]

Abid, Chuck B. did measure rotor disk angles -- as well as could be done using very simple items.

His apparatus consisted of a vertical post set in the ground, with a horizontal beam crossing it at eye level, capable of pivoting like a seesaw. He could pivot the beam while standing a distance away from it, using a control "cable" running from each end of the seesaw down to a fairlead on the ground and then out to the spot where he stood.

A good pilot would fly the gyro at a few feet altitude, behind and past the apparatus at cruise speed and power. Chuck would use his cables to pivot the crossbeam to the observed angle of the rotor disk. He'd measure the crossbar's angle to the horizontal using a bubble protractor.

It might have been easier and more accurate to take a video with a level reference beam in the frame, then measure the disk angle frame by frame.
* * *

Foam, I know of no aerodynamic basis for treating a rotor disk as you would a fixed wing -- that is, with a presumed center of pressure somewhere around 30% of diameter aft of the disk's leading edge. This cannot be. Were it somehow the case, the disk would flip nose-up violently and the rear of the disk would collide with the prop and tail.

The thrust forces on each blade are very, very close to equal, thanks to the flapping or teeter hinge(s). As a result, the rotor's thrust is, as Jean Claude points out, essentially centered on the rotor's rotational axis. No matter where the rotor head is mounted, the airframe will hang at an angle that puts the CG on the rotor's thrust line (unless some other force displaces it). We'd like this hang angle to result in a level airframe in cruise flight.

 

[Aerofoam]

Abid, Chuck B. did measure rotor disk angles -- as well as could be done using very simple items.

His apparatus consisted of a vertical post set in the ground, with a horizontal beam crossing it at eye level, capable of pivoting like a seesaw. He could pivot the beam while standing a distance away from it, using a control "cable" running from each end of the seesaw down to a fairlead on the ground and then out to the spot where he stood.

A good pilot would fly the gyro at a few feet altitude, behind and past the apparatus at cruise speed and power. Chuck would use his cables to pivot the crossbeam to the observed angle of the rotor disk. He'd measure the crossbar's angle to the horizontal using a bubble protractor.

It might have been easier and more accurate to take a video with a level reference beam in the frame, then measure the disk angle frame by frame.
* * *

Foam, I know of no aerodynamic basis for treating a rotor disk as you would a fixed wing -- that is, with a presumed center of pressure somewhere around 30% of diameter aft of the disk's leading edge. This cannot be. Were it somehow the case, the disk would flip nose-up violently and the rear of the disk would collide with the prop and tail.

The thrust forces on each blade are very, very close to equal, thanks to the flapping or teeter hinge(s). As a result, the rotor's thrust is, as Jean Claude points out, essentially centered on the rotor's rotational axis. No matter where the rotor head is mounted, the airframe will hang at an angle that puts the CG on the rotor's thrust line (unless some other force displaces it). We'd like this hang angle to result in a level airframe in cruise flight.

Understood, but when treated this way, it also hangs correctly.
Not debating whether it is proper, just saying it worked.