90 MPH in an Air Command?

NoWingsAttached

Unobtainium Member
Joined
May 21, 2006
Messages
4,871
Location
Columbia, SC
Aircraft
Air Command Tandem w/ Arrow 100hp; GyroBee w/ Hirth 65hp; Air Command Tandem w/ Yamaha 150hp
Total Flight Time
>350
I have hit 90 a couple of times, briefly, while mostly cruising around 80-85 when I am in a hurry. This is IAS, not GPS. My ASI is accurate. But I've never gone faster than ~90 straight and level in my tandem Air Command, sustained for very long.

Once I did two low, high-speed passes, starting at 20 feet off the deck, from the north end heading down RW 18. The first one I kept it at 90 mph for the last half of the distance. The second time I went over 90, hitting 92 by mid-field and sustaining it the entire length until something started to flutter in the rear and I backed it off (control push tubes? I'll need to figure out what made the noise, of course).

Now this was at 8800-8900 RPM, so somewhere in the 135HP range, WOT, typical climb power. I don't know of anyone else who has flown a Tandem Air Command with a similar power-to-weight ratio, and I am wondering if anyone has ever flown one of these (very draggy) AC gyrocopters and been able to maintain over 90MPH S&L like this before. If so, any vibrations? Issues? Safety concerns? Everything seemed fine until I got that flutter...It didn't come through my pedals, I didn't notice excessive stick shake, but did feel it through my seat and heard it outside of my helmet, behind me.

When I flew after that I took it REAL cool, and the stick seemed to have more shake than usual. An inspection of the Skywheels and the rotor head turned up nothing. No hardware was loose, bearings tight the ship passed a thorough ground inspection. The teeter bolt tower bushes are a tad sloppy, probably time to replace them, but they have been that way for a while now and I didn't think it was anything to be too concerned with since stick shake has remained very light & nominal.

I ran the engine on the ground, taxiied up and down the pavement but nothing seemed out of place, no PSRU or engine vibrations or noises. So I am thinking perhaps it had to do with air turbulence...

Any comments or insights would be appreciated, especially from any Air Command specialists.
 
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Approach this carefully. If it's aerodynamic flutter from the rudder or even possibly HS, it's nothing to take lightly. Things can go bad really quickly. Control surfaces could be counter balanced with weights or can be made more stiffer to solve this issue. Be safe.
Some machines are made to go at speed and some can get there for small amount of time but are not meant to be there for long. Best to remain within the safe operating range.
 
update:

Discussed the flutter with Jake at length, and although we both had already reached the conclusion, separately, that the flutter was likely induced by the airfoils on the control rod push tubes high up on the mast, he explained some things to me about the "hunting" of the entire fuselage at high speed which might also have been the major contributing factor leading to the phenomenon.

The Air Command builder's handbook does state that a placard is to be placed on the instrument panel indicating a VNE of 90 MPH.

These limitations were tested and written with a stock Air Command tail. I had thought that a larger empenage, a full-height cruciform flying tail, would improve the VNE significantly.

I have changed the VNE back to the manufacturer's suggested 90 MPH until further testing can be completed to determine anything different. As mentioned, I have not experienced any issues up to and including 90 MPH, so we are good.
 
In my opinion if an aircraft begins to behave badly at 90 miles per hour then the Vne should be set lower than that. It is not unusual to encounter a 10 or 15 mph wind shear particularly at low altitudes so the Vne should probably set ten or fifteen miles per hour below the speed the aircraft misbehaves.

If the problem is flutter the flutter may escalate rapidly as the speed increases leading to a catastrophic failure of the fluttering surfaces.

In my opinion low altitude is not the best place to explore Vne.

I wish people would fly within their skill and experience limitations at events.

A crash spoils the event for everyone attending and adds to the bad reputation of gyroplanes.

I don’t try things out at air shows for this reason.
 
Greg, Ken Brock said that gyros are very draggy........What makes your tandem, partially enclosed gyro so draggy ? (compared to others)

Have you tried Dragon Wings on it ?

Have you done any thrust tests ? If so how much ?

How fast can an RAF or Sparrowhawk go ?

I have done thrust tests on a few RAFs & the numbers were very low (cabin? )
 
Be careful

Be careful

I have a friend that used to have an Air Command and he decided one day he was going to see what it would do.
He pushed it to the point it snapped nose up vertical rudder pointing directly at the ground. He thought it was going to tip over backwards but an angel must have been with him because he recovered and never tried it again.
 
I have had the control rods go into resonance a few times. This rapidly started feeding into the rotor head and back into the control stick. Quite alarming how quick it happens. I changed from alloy control rods to chromolly to stiffen them and never happened again. Two piece rods will work too...
 
Greg, Ken Brock said that gyros are very draggy........What makes your tandem, partially enclosed gyro so draggy ? (compared to others)

Have you tried Dragon Wings on it ?

Have you done any thrust tests ? If so how much ?

How fast can an RAF or Sparrowhawk go ?

I have done thrust tests on a few RAFs & the numbers were very low (cabin? )

The Air Command Tandem has a lot of frontal area exposed. Whenever you put two tubes close to each other they act more like one large, wide object in the air rather than two separate ones. Take a look at the photo, and you can quickly see how this affects overall drag with this gyro, more so than, say, a Snobird tandem which has no forward tubes attaching the rotor head assembly. Also note the landing gear struts - there are three pieces, and the tube is all 1-1/2" diameter. Next, a tall tail creates more drag than a shorty tail.

Yes, I use Dragon Wings, have a set on my other Air Command Tandem as well as a set on my Honey Bee. This gyro has the Skywheels on it.

It's been a while since I did any thrust testing, but last time I did it with a 2.58:1 Arrow PSRU I got 500 lbs at 2850 prop RPM, and 520 lbs at 3050 PRPM, which is a lot for a gyro which only weighs 595 lbs. The problem I have testing thrust here in Savannah is that there is too much ground friction, and no good, level ground to set up the test. Everything is grass or gravel.

Good thrust tests must be done on perfectly level, clean, pavement or - better yet - concrete, with absolutely zero wind and nothing behind the gyro to catch the prop wash and create a pressure bubble which would artificially inflate test results.

Something like tying the gyro to the hitch on the back of a pickup truck with a long length of rope works well. Tying off with the gyro backed up to a hangar wall with a short freight strap, not so well.

It also makes sense to record pressure altitude at the time of the test.
 

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I have a friend that used to have an Air Command and he decided one day he was going to see what it would do.
He pushed it to the point it snapped nose up vertical rudder pointing directly at the ground. He thought it was going to tip over backwards but an angel must have been with him because he recovered and never tried it again.

This is a good post. Do you recall any details, such as what kind of rotor wings he was flying at the time? Was this a single or tandem? Stock Air Command tail or tall tail? With or w/o HS? Body pod or bare?
 
In my opinion if an aircraft begins to behave badly at 90 miles per hour then the Vne should be set lower than that. It is not unusual to encounter a 10 or 15 mph wind shear particularly at low altitudes so the Vne should probably set ten or fifteen miles per hour below the speed the aircraft misbehaves.

If the problem is flutter the flutter may escalate rapidly as the speed increases leading to a catastrophic failure of the fluttering surfaces.

In my opinion low altitude is not the best place to explore Vne.

I wish people would fly within their skill and experience limitations at events.

A crash spoils the event for everyone attending and adds to the bad reputation of gyroplanes.

I don’t try things out at air shows for this reason.


I posted this thread to get feedback from other pilots who may have some experience to share with this sort of thing.

Ever had anything like this happen in the past?

Any insights, anything else to add to the topic of pushing a gyrocopter's speed envelope?
 
I have had the control rods go into resonance a few times. This rapidly started feeding into the rotor head and back into the control stick. Quite alarming how quick it happens. I changed from alloy control rods to chromolly to stiffen them and never happened again. Two piece rods will work too...

This makes a LOT of sense.

I am really interested in scissors tubes, having just built a set on a single place Air Command for a customer's YG4 conversion. When I flew that gyro, the stick was wonderful.

I am hooked, and willing to bet this is the best answer.

The Wicked is about to get a new set of scissors push tubes, folks!

I wanna come visit you in Hokitika and do some gyro flyin! It must be amazing to fly that area.
 
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Ok, Mr. Dummy here....

Please explain scissors push tubes and how they differ from conventional push tubes.

Cheers,

Dave
 
Greg,

I also had a buddy who flew a tandem Air Command with the tall tail, and Skywheels. He was out flying fast, with a heavy passenger, doing somewhere near 90mph, when the gyro abruptly stood up on it's tail. The pilot immediately reacted by rolling off to the side, which probably saved them.

They both got bruised pretty good, and had to change their shorts when they got on the ground.

He said it was a dead calm evening, and there was no prior warning. One minute they were screaming along, and the next they were both slammed forward, looking straight up, is how he tells it.

It looks like you have Skwheels on your machine, so you may have gotten a prior warning that you were about to experience the same event.

Something to think about the next time you try checking out what your top safe speed is.
 
Does this occur with skywheels only or has this happened with other blade types?
 
Skywheels rotorblades are tail heavy, CG being at ~ 35% of chord whereas the aerodynamic center is at ~ 26% of chord.

That’s what causes the mid air flares with heavy load.

It also makes a rotor unstable Vs angle of attack. That effect is often misinterpreted as “high lift.”

It also helps cushion the landing by providing a form of collective pitch; during the landing flare, as the load is increased, the tail heavy blades twist nose up.
 
Thank You Chuck for that. I wonder what blades are more suited to high speed flight

or are all gyro rotors susceptible to this effect.
 
For rotorcraft, blades must be balanced about their aerodynamic center, nominally the ¼ chord point and have zero pitching moment; that is, they shouldn’t pitch nose up or nose down as they move through the air at high speed.

The old standby for helicopter blades has been the NACA symmetrical types, such as 0012 or 0015 but modern helicopters have switched over to cambered blades with reflexed trailing edges to balance the nosedown pitching moment resulting from the camber.

Most any modern helicopter rotorblade, properly configured, would be satisfactory for high speed gyro flight.
 

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Excellent info Chuck. Thank You for providing this valuable knowledge.
 
Sure would add to this post if someone with the talent and knowledge could add all the currently known gyro blade manufactures blade profiles in a graphic like the one above that Mr. Beaty provided.
 
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