G testing "Bump" question

bobmarkert · #1 06-05-2015, 06:59 AM

Phase 1 testing is going extremely well. Today I was expanding the G envelope at max aerobatic weight. Using incremental steps I was working my way to the limit of 6 Gs in ? G steps. AT 5 ? Gs I experienced to solid bumps. It felt like it was more aerodynamic than mechanical,... as if I went through my own wake?. but I was in a straight pull so it wasn?t wake (at least not mine). Any thoughts (accelerated stall?)? Will be looking over the aircraft thoroughly but the post flight showed nothing abnormal

fixnflyguy · #2 06-05-2015, 07:18 AM

I have not had my 4 past 5Gs in straight and level or turns, but when doing full aileron deflection rolls you will get bumps as the ailerons stall and recover. It feels very weird the first time you do it, and bumps every 2 seconds or so. It is possible your elevator is doing the same thing. I have not experienced any "G" related bumps.

sailvi767 · #3 06-05-2015, 07:25 AM

You may have stalled the aircraft. At what airspeed were you performing the test? You need to look at the speed when the bumps occurred. At a high G loading if you were in a level turn it will be bleeding airspeed rapidly.
G

bobmarkert · #4 06-05-2015, 07:31 AM

Bill, I am familiar with the aileron bump and mine is typical. When the ailerons go Bump (in the night) I can feel it feeding back through the stick. This felt like it originated in the wings not the tail and there was no feedback in the stick. I will download the Garmin data stream and look at the speeds

ColoRv · #5 06-05-2015, 07:36 AM

Bob, what was your AOA saying at the time? I've done 5.5 (straight pull) and didn't have a bump, not that that means anything.

bobmarkert · #6 06-05-2015, 07:40 AM

Billiam,
I was in a straight pull from a dive. I was also at 10,000' (4,500 agl) so that didn't help. Testing in Denver can be challenging due to altitude, as you know.

skylor · #7 06-05-2015, 08:12 AM

Quote:

Originally Posted by bobmarkert

Billiam,
I was in a straight pull from a dive. I was also at 10,000' (4,500 agl) so that didn't help. Testing in Denver can be challenging due to altitude, as you know.

What was your indicated airspeed at the time of the bump? If it was much less than 123 KIAS (I assume you were under gross), then it was most definitely accelerated stall. In my -8, the onset of accelerated stall feels just as you've described...a noticeable "bump".

In one -7 that I've flown, accelerated stall felt like driving over "washboard".

Skylor
RV-8

bobmarkert · #8 06-05-2015, 09:18 AM

After looking at the data stream, I'm confident it was an accelerated stall. Next flight I'll increase onset rate (wary of G overshoot) with a slicing turn (no rolling moment). Then comes the interesting test....... negative 3......

RV Jerry · #9 06-05-2015, 09:23 AM

I had an rv-6 that did the same thing coming out of loop at bottom at 10,000 ft, it wouuld stall causing bump the G pull was less than 5,5

skylor · #10 06-05-2015, 11:38 AM

Quote:

Originally Posted by RV Jerry

I had an rv-6 that did the same thing coming out of loop at bottom at 10,000 ft, it wouuld stall causing bump the G pull was less than 5,5

Coming out of the bottom of a loop, I would be much more inclined to believe you experienced your own wake turbulence, which also feels like a sudden vertical "bump". This is common on loops, Cuban 8's and steep 360 degree turns.

Skylor