RV7Ron
Well Known Member
I saw the same number which I can not even imagine what must have been like over 10K FPM decend.
It actually states a max rate of 12,000 fpm...which comes out to about 136mph if my math is correct.
I saw the same number which I can not even imagine what must have been like over 10K FPM decend.
It actually states a max rate of 12,000 fpm...which comes out to about 136mph if my math is correct.
During a pull-out from a rapid descent, there was a sudden onset of an airframe vibration (shuddering around the longitudinal axis), which was followed by a yawing motion, a roll and ground impact.
The report was quite clear in this regard.
Top of page 4:
It actually states a max rate of 12,000 fpm...which comes out to about 136mph if my math is correct.
Yep, that's what I was going to say. The only thing is, that only applies if the airplane is pointed straight down. If that 12,000 fpm descent includes a forward component, then it could be significantly faster. Obviously the only relevence here is the forward speed of the airplane.
Vne for the -9/9A is 210 MPH.... Ive been asking alot of "dumb" questions about Vne, and stuff for a 9A, and the real differences in the 7A/9A flight packages...
Not likely a fastener failure. If it had been, then the hinge brackets would not have been ripped off the VS....Could this have been a fastener failure, metal failure, skin failure?...
Not likely. A few years back a -9A in South America had a wire strike which cut the VS and rudder right off, equal with the top of the fuselage, IIRC. The pilot was able to fly the plane and made an uneventful landing.Here?s my theory:
At way past Vne, the rudder counterbalance tore off, maybe due to a bit of flutter and the resulting aerodynamic load on the surface ahead of the hinge line when it got in the slipstream.
...
There is no trim tab on the rudder, and that is what failed, not the elevator.Thanks Brantel.
Still leaves open the possibility of a fluttering trim tab...
160 knots velocity at 45 degrees nose down equates to approximately 12,000 FPM descent rate.
According to the report, 12000 fpm descent with a max pitch of 45 degrees would have yielded a 192 mph if my math is good.
edit: Skylor beat me to it
Bill, I'm referring to the commonly used fixed tabs that balance aerodynamic forces on many RV rudders and trims them to balanced flight. Very common.
The point is the failure mode of the rudder is almost an irrelevant. At 20% above Vne you are a test pilot and along for the ride.
Right...you guys are missing my point. I'm trying to say that 12,000 fpm descent is not in and of itself a bad thing. Even as you pointed out, at a 45-degree angle, you're still not even getting close to Vne. An earlier post mentioned the descent rate in a "holy cow!" type of tone, but I am trying to convey that those rates are not unusual. I think I passed 11,000 feet ASCENT on a loop during Phase 1 testing with an aerobatic test pilot. Entry speed of 175 mph and a 4G pull...going up the front side of that loop is a high rate, as is going down the backside.
My over-all point is that no-one should focus on that number (fpm descent), but they should be looking at the pilot's Vne.
Quick question regarding what someone should do in the event they're pointed down (let's say on the back side of a loop or a split S) and you're rapidly approaching Vne. Let's say your doing over 200 mph pointed straight down. But, as in this case, you're only pulling 3 G's. I would think that loading up your wings to 4.5 or even 5 G's would better your situation, assuming you could grunt through it without blacking out. Wouldn't you be managing your speed at the cost of increased drag?
I hope I never have to find out, but I would think the safer thing to do is pull as many G's as the airframe could take to keep your speed under control. Thoughts?
I disagree with the findings of the report (page 11).
1. Exact balance is not required of a control surface to prevent flutter.
2. There is no evidence provided that flutter occurred.
3. Not reweighing after paint did not cause this accident.
4. Being over gross did not cause the rudder to fail.
The #1 cause of this accident was doing acro well beyond Va and Vne. This is pure speculation on my part but if they were rat racing, well beyond Vne, its easily possible that the rudder/VS failed when this aircraft entered turbulent air or the wake of another aircraft.
10,000 - 12,000 FPM descent is not trivial when you are at 2650 feet AGL.
So I have this airplane project and the <strike>rudder</strike> elevator is not perfectly balanced. Why? Who knows why but it is aft heavy and when you add in the manual trim cable it is even more aft heavy. It's not painted, of course, but the tips are done.
Should I be cracking those emp tips open and starting over with adding more weight?
This paint... balance is BS !!! Fly by Van's numbers and everything will be fine balanced/painted or NOT.
Guys and Gals,
This paint... balance is BS !!! Fly by Van's numbers and everything will be fine balanced/painted or NOT.
imagine if an aerobatic manoever goes TU and you end up pointing downhill
.........Please don't fly your RV hard and fast. Feel free to personally attack me again for expressing that opinion, but I'm alive after all these decades and there are plenty of people who disagree with me, who aren't.
balancing the control surfaces, after painting, gives you an increased margin of safety
THE SPEED IN THE CANADIAN CASE WAS A RESULT OF THE WAY THE PLANE WAS FLOWN JUST AS MUCH AS THE INFLIGHT BREAKUP. LET'S FOCUS ON THE CAUSE WHICH IS THE WAY THE PLANE WAS FLOWN AND TREAT RESULTS AS RESULTS.
Bob Axsom
Guys and Gals,
This paint... balance is BS !!! Fly by Van's numbers and everything will be fine balanced/painted or NOT.
I could not believe my eyes when I saw that this was posted by an EAA tech councillor.
Surly, balancing the flying surface after its been painted, increases the margin of safety. I know thats what I would want. Just imagine if an aerobatic manoever goes TU and you end up pointing downhill. It is very easy to exceed vne and maybe get close to non balanced flutter speed.
I could not believe my eyes when I saw that this was posted by an EAA tech councillor.
Surly, balancing the flying surface after its been painted, increases the margin of safety. I know thats what I would want. Just imagine if an aerobatic manoever goes TU and you end up pointing downhill. It is very easy to exceed vne and maybe get close to non balanced flutter speed.