Roll rate testing

[ChiefPilot]

For the experienced test pilots on the board - how exactly is maximum roll rate determined? I've seen wildly different numbers for RV roll rates - as low as 90?/sec and as high as 190?. I suspect the difference lies in airspeed, whether the roll was unloaded or not, and so on.

My question really centers around what is done for certificated aircraft? Is the roll rate checked at 1G at a specific airspeed (Va perhaps)?

 

[Flying again!]

At USAF Test Pilot School (a long time ago, Class 85A) we had a matrix of configurations and airspeeds we used to obtain roll rate. You are correct in that roll rate will vary with speed, altitude, configuration, etc.

For the T-38 at each altitude/KCAS point we would do 1/4, 1/2, 3/4 and full stick deflections rolls left and right. As I recall with flaps down, we would time from +/- 60 deg. in clean configuration we would do a full roll right and then left. We taped a reference on the panel to help get the same deflection each time.

For lower performance aircraft like the RV-3/4/6/7/8 I would use +/- 60 deg bank though you could use the full roll technique. Choose altitudes you are comfortable with 5k, 7k, 9k and a/s such as 100KIAS, 120KIAS, 130KIAS etc. up to manuevering speed.

For any flaps down use only +/- 45deg roll.

Stating the obvious, it is very important that you reach the aileron deflection you are testing (1/2 deflection, full deflection) very rapidly (and consistently) instead of gradually as this greatly impacts the results/time you record. keep the a/s within 1-2 knots for a valid data point and altitude within 50-100 ft.

After a full flight of roll testing the T-38 in the clean configuration at the higher speeds your internal gyro would be uncaged (max roll rate of 720deg/sec!).

When you plot the data you can look at changes in roll rate vs a/s for a given deflection, altitude versus deflection etc. I think on the RV-6/7/8 you will see the roll rate is non-linear with deflection with not as much change between 3/4 and full as between 1/2 and 3/4 deflection.

Hope this helps. post the results if you decide to do a full test, might find some interesting results.

TJ

 

[Lindamon]

Use a video camera

I like to measure it using a video camera, then when you edit it you can see on the computer timeline exactly how long it takes. I do it at full throttle, level flight, I don't pay any attention to the altitude other than it being legal and safe. I do on point aileron roles, which means using elevator and rudder during the roll to keep the nose of the plane exactly on a point directly in front of you as you roll, no barrel rolling. You will go from +1g to -1 g throughout the roll.

I find that it takes at least two rolls for the roll speed to stabilize. I use full aileron, applied as quickly as I can. I have only done this in Pitts and Extras, my RV 7 will hopefully be ready to fly by next month, and this will be a Phase 1 test for sure. I understand that the RV 7 has some aileron "snatch" when using full aileron, I will explore this, and also test the rate at less deflection. I will post a video and results when I get them, and look forward to it.

In the meantime, here is a short video of a double roll in my old Extra 300 to give you an idea. BTW, I don't remember what Extra advertises as the max roll rate, but I could never get anything better than 270 degrees/sec at 160 knots level flight - I suspect they dive them to Vne and roll them to get max rate!

Damon

http://youtu.be/rT9vnmVuCiY

 

[sandifer]

My question really centers around what is done for certificated aircraft? Is the roll rate checked at 1G at a specific airspeed (Va perhaps)?

There are so many variables, I wouldn't be too concerned about testing roll rate. It doesn't mean much. I know my Pitts rolls about 180 deg/sec. at top speed in straight and level flight, and that the rate varies widely across other airspeeds. But straight and level is not where roll rate really matters when you're trying to fly through a routine that challenges the airplane's performance. Here, low speed roll rate is much more advantageous - especially in competition. There's no way I believe manufacturers use standardized roll rate test methods. I've never heard of one. Advertised roll rates for many airplanes (especially some experimentals) are a little optimistic, meaning that there is no way roll rate testing is certainly not limited to Va. Some listed roll rates could only possibly be achieved by full aileron at Vne. 90 deg/sec should be about right for full aileron in an RV at Va. I've seen numbers on certain airplanes that are just not physically possible with ailerons alone. BTW, in an RV, the only way you'd get 190 deg/sec would be to snap it. In this case, my Pitts really will roll 400 deg/sec.

 

[ChiefPilot]

TJ - Thank you so much! This is exactly the kind of information I was looking for. I had considered various speeds but didn't think about a matrix of speeds vs. altitudes. I'll be sure to post back the data after I get it completed.

Damon - Using a camera is definitely the way to go. In fact, that was what sparked by original question. During my phase one flights, I had one or sometimes two GoPros in the cockpit. After reading somewhere that the -6A has a roll rate of only 90? per second, I checked the video from one of the flights where I rolled it and found that I had 115? per second just by using the frame rate and time elapsed for half the roll.

Thanks!
Brad

 

[johnfurey]

TJ

TJ, I went to high school in Ohio with a guy named Bill Mannecke who flew
T38s in San Antonio. He is now flying for Fed Ex. Didn't happen to know him did you?

 

[WillyEyeBall]

better video

Damon,
I liked your video, but I think the other two are better. This one shows a better attitude for rolling: http://www.youtube.com/watch?v=JxreiysDpwo ;that is unless someone wants to accuse you of child abuse. I like that guitar playing one too, and would love to use that music for background on a youtube video. Hope to see you at Sebring and maybe buy you lunch for another critique session.
Cheers,
Bill McLean
RV-4 slider
lower Alabama