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Old 01-17-2014, 12:08 PM
RetroAcro is offline
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Pitts Strut Cam

Just a mashup of clips with the camera on the strut last Sunday. Awesome clear day to be up.

Pitts Strut Cam (2 min 31 sec)


Hey Earle - question. My airplane behaves oddly (in my opinion) during negative right rudder snaps on level or 45 uplines. If I let it go more than 1 rotation as if I'm attempting a 1-1/2 snap, it goes into an end-over-end tumble, and once this starts, opposite rudder has no influence on the recovery. It's literally out of control and won't recover until the airplane has enough vertical down trajectory and airspeed to block the tumbling action. Below is another video showing the sequence of snap tests with rudder applied at different times. Entry speeds were 110 mph. If I apply left recovery rudder between 1/2 and 3/4 rotation, I can stop the snap on 1 rotation (1st clip). But if I apply this left recovery rudder at or after 1 rotation of the snap, this 'tumblesnap' just continues (2nd clip). Happens the same if I just hold the original right snap rudder and let it go (3rd clip here).

My CG is pretty much on the aft limit when flying acro. Curious if you know what's happening here, or what I'm doing wrong. I mounted the camera on the strut to capure the control inputs. I'm holding some typical left aileron through these snaps. I can do a 1 turn vertical snap down with a nice crisp stop, but again, if I let it go past 1 turn, the character of the snap changes and recovery is not as clean. Doesn't tumble of course going straight down. This behavior is very different from inside snap behavior. It flies straight out of a left rudder snap between 1.5 and 2 rotations. Completely predictable recovery snapping inside. I need to mess around with left rudder negative snaps to compare. BTW, I'm running a 3-blade composite Catto prop that weighs 12 lbs. There's not much torque or gyroscopic influence with this prop compared to a metal Sensenich. Eric

Note - video below is loud. Mute or turn sound down first.

Outside Tumblesnaps (0 min 27 sec)
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Old 01-17-2014, 05:12 PM
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A couple of thoughts. First….great videos but it’s really weird to see these maneuvers from that POV…just an entirely different perspective!

Not sure what’s happening but some observations.

I’m surprised to see 1) that much up elev applied during negative snaps and 2) that much down during pos snaps! If memory serves me correct, after feeling the initial stall break I would relax the elev input through the rest of the rotation, but the stick would be around neutral. Your seems to be much farther fore or aft?

My S1-T had the Hartzell 2-blade and generally tended to snap well at 130-140mph (pos or neg), except on up or down lines where you have another G of “grace” because you’re starting at 0 instead of +1 or -1 (So you can up the snap speed a bit more). Higher entry speeds will give you faster and cleaner snaps….of course you don’t want to push it too far!! At 110 it was pretty sluggish and of course you’re losing speed during the snap.

I know that to get a clean triple avalanche I needed about 210 entry speed at the bottom and a clean but hard pull to retain enough speed and energy at the top. 220 would get you 4 snaps, but the last one wallows around a bit as so much speed is being scrubbed off.

Where is your throttle during the snaps? Mine was basically wide-open on anything except a vertical down, and even then I had somewhere around half or more throttle to help with control over the tail feathers. After a vertical down snap you can always chop the throttle to limit airspeed gain during the rest of the line.

Hard to see the ailerons on the vids, but I would always use FULL aileron with the snap roll rotation direction….pos=same and neg=opposite. My "T" would stop a smidge after I released the aileron and hit opposite rudder. Was very easy to hit your mark.

I guess maybe I’d try more entry speed and not so much opposite elev after the stall break. See how that works out. It will of course alter your timing that you’re used to, but give those a chance and see what you think.

Thanks for giving me a look back in time! Other than memories and pictures here's the only thing I have left of that wonderful airplane! It's on the wall in my studio just above my desk.
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Old 01-17-2014, 05:57 PM
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Not being a pilot... I was amazed at how much you had to wag the rudder after you landed. I've head that this was required on a Pitts, but never been able to see it on video.
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Old 01-17-2014, 07:00 PM
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Ahh....the "Dance"!

As the Garth Brooks song goes; "Yes my life is better left to chance,
I could have missed the pain, but I'd have had to miss the dance."
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Old 01-17-2014, 08:08 PM
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The aft limit CG may also be a contributor to the negative recovery. My Pitts was a little slow to recover from multi turn spins, and I too had a pretty aft CG.

Tom
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Old 01-17-2014, 08:12 PM
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Old 01-18-2014, 05:15 PM
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Thanks for the reply Earle. Yeah, I may be excessively unloading the snaps. I've tried deliberately unloading positive snaps to around neutral, and it didn't really change the character or recovery of the snap, but what I haven't paid much attention to is if I could possibly get through the snap with a little less energy loss by not unloading so far. But I do think half snaps benefit from unloading forward of neutral to minimize the heading issues. I'll also try less aft unloading for the negative snaps and see what happens. Lots to play around with. I was at full throttle for all the snaps.
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Old 01-18-2014, 07:14 PM
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You're welcome. Don't forget to try some higher entry speeds as well. Full elev, rudder and aileron, then unload the elev to neutral....see how that works at 130-140mph. If I recall correctly the manuevering speed of an S1 is around 140?
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Old 01-20-2014, 11:43 AM
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Quote:
Originally Posted by Pistolera View Post
Don't forget to try some higher entry speeds as well. Full elev, rudder and aileron, then unload the elev to neutral....see how that works at 130-140mph. If I recall correctly the manuevering speed of an S1 is around 140?
I'll inside snap it up to about 120 mph, even though the book says it can be inside snapped up to 140. I have no plans to snap it that fast. My airplane doesn't have the strut braces on the horizontal stab, but not sure if that's really an issue. The book says a 110 mph limit on negative snaps. I guess I don't have much reason to push any of this, since this airplane isn't going to get me through Unlimited. It currently does well in Advanced, so I'm only messing around with outside snaps for fun. Trying not to beat the airplane up too bad.
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Old 01-20-2014, 12:07 PM
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Certainly good points. I know flying one and being competitive in Unlimited took its toll on the airfame and prop hubs . Mine was completely rebuilt at around 800 hrs TT....with many other repairs prior to that during the off-seasons. Looking back on it, I'm always amazed at the amount of abuse a Pitts can take!
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