Go Back  PPRuNe Forums > Non-Airline Forums > Private Flying
Reload this Page >

Big Crash at Reno

Private Flying LAA/BMAA/BGA/BPA The sheer pleasure of flight.

Big Crash at Reno

Old 3rd Oct 2011, 23:48
  #261 (permalink)  
 
Join Date: Sep 2011
Location: Nevada
Age: 57
Posts: 18
Likes: 0
Received 0 Likes on 0 Posts
Quote: Lyman "Wouldn't that be conducive to torsional vibration on the elevator hinge?"

I think that is what I was sort of asking towards the end of my long post. But hadn't considered the vibration aspect, just a simple twisting of the elevators in relationship to each other. I've seen the question regarding the use of only one TT and a reason for it, asked on numerous forums but not ever have I read an inkling of reason for doing it.
xmh53wrench is offline  
Old 4th Oct 2011, 01:15
  #262 (permalink)  
 
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 81
Posts: 1,454
Likes: 0
Received 0 Likes on 0 Posts
One trim tab on the left elevator only.
Information I've seen on other forums indicates that this might be better stated as one functional trim tab only. I have seen pictures that I will post a link to that indicate the port and starboard elevators are interchangeable on the P-51. When built back up after its substantial overhaul, GG had trim tabs in both positions. The bellcrank on the starboard elevator tab is on the top surface, and on the port elevator tab, the bottom surface. The starboard trim tab may have still been ground adjustable even if that tab was fixed. For pictures of the GG rebuild, see WarbirdAeroPress.com
and
WarbirdAeroPress.com
Wow, what an extensive rebuild!!

Last edited by Machinbird; 4th Oct 2011 at 01:26.
Machinbird is offline  
Old 4th Oct 2011, 02:03
  #263 (permalink)  
 
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,074
Likes: 0
Received 0 Likes on 0 Posts
The F-16 has Stabilators. They articulate on separate pins that allow deflection in opposite direction, to enhance (to put it mildly!) Roll. They of course deflect in concert, when selected for Pitch only.

If GG had one Tab fixed in ground-only aspect, and the other operable in flight, one gets the 'same' effect, though obviously the poor mans' version. Roll is enhanced along with Pitch trim. I'm going to assume the elevators remain affixed to the single Tube/hinge barrel that carries both, aligned identically.

Interesting trick. Under severe load, one can imagine an asymmetrical span wise loading on this Tube, and the potential for vibration, even flutter, or buzz. The drag of Trim, on the left, is spent on Yaw capture when turning, and makes elegant use of Drag that would otherwise go to waste. If the pilot is flying trim, mechanically, this sytem has some issues relative to load (torsional) on the tube, and on the HS bellcrank, and cables. When back driven, the system would be subject to variable loading, unless damped in some fashion, and this set up would want some serious monitoring.

Unlikely, but possible, is the loss of Elevator continuity, if the actuating frame had a break in the attach to the tube. Since control is asssumed to have been pilot/unavailable anyway, it isn't impossible that the Elevators were flapping in the airstream, following, instead of leading the flight path.

The flight path after the snap looks eerily ballistic, it is too smooth to have controls inputting directional leads.

wrench, I missed your bit about the asym tab purpose, but does this proposition sound in any way applicable?
Lyman is offline  
Old 4th Oct 2011, 02:33
  #264 (permalink)  
 
Join Date: Jul 2004
Location: Found in Toronto
Posts: 615
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Machinbird
Information I've seen on other forums indicates that this might be better stated as one functional trim tab only. I have seen pictures that I will post a link to that indicate the port and starboard elevators are interchangeable on the P-51. When built back up after its substantial overhaul, GG had trim tabs in both positions. The bellcrank on the starboard elevator tab is on the top surface, and on the port elevator tab, the bottom surface. The starboard trim tab may have still been ground adjustable even if that tab was fixed. For pictures of the GG rebuild, see WarbirdAeroPress.com
and
WarbirdAeroPress.com

Wow, what an extensive rebuild!!
Thanks for the link. Lots of good photos there:









Lost in Saigon is offline  
Old 4th Oct 2011, 04:50
  #265 (permalink)  
 
Join Date: Sep 2011
Location: Nevada
Age: 57
Posts: 18
Likes: 0
Received 0 Likes on 0 Posts
Lyman: thanks for the explination, you would think since I spent my racing career turning right to go left, than all of that would make sense to me, but having the right TT fixed still seems backwards to me, but I will take your explanation.

Lost in Saigon: How did you manage to extract those photos? I just ordered a 1/32 kit and they would be a great source of detail, and I would like to save them to my laptop before they disappear. Thanks

Also, new long distance vid, but really shows the pitch up.

Last edited by xmh53wrench; 4th Oct 2011 at 05:01. Reason: Add link
xmh53wrench is offline  
Old 4th Oct 2011, 05:53
  #266 (permalink)  
 
Join Date: Jul 2004
Location: Found in Toronto
Posts: 615
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by xmh53wrench
Lost in Saigon: How did you manage to extract those photos? I just ordered a 1/32 kit and they would be a great source of detail, and I would like to save them to my laptop before they disappear. Thanks
It is quite easy to do. Just hit "Print Screen" on your keyboard, and you take a snapshot of what is displayed on your monitor. Then open "PAINT" or a photo-viewing program like "Irfanview"(free download) and hit "Control V" to paste it. You then crop it to size and save the file.

More info: Print screen - Wikipedia, the free encyclopedia
Lost in Saigon is offline  
Old 4th Oct 2011, 11:02
  #267 (permalink)  
 
Join Date: Jan 2008
Location: Atlanta, GA, USA
Posts: 349
Likes: 0
Received 0 Likes on 0 Posts
Alt-PrintScreen is better - it just copies the focused application (active window), not the entire screen. There is probably a Mac and Linux equivalent.

-drl
deSitter is offline  
Old 4th Oct 2011, 12:06
  #268 (permalink)  
 
Join Date: Mar 2009
Location: Perth Western Australia
Age: 57
Posts: 808
Likes: 0
Received 0 Likes on 0 Posts
There is probably a Mac and Linux equivalent.

In Ubuntu Linux if you alt print screen it will actually open a image viewer with the captured window in it, you can save straight to disk from that
rh200 is offline  
Old 4th Oct 2011, 15:18
  #269 (permalink)  
 
Join Date: Dec 2007
Location: Cape Town
Age: 70
Posts: 440
Likes: 0
Received 0 Likes on 0 Posts
The thing that niggles me wrt to the single functional trim tab is this statement from the link I posted earlier.

"He was warned about the forces being put on that one tab."

Did the previous incident of trim tab failure not give cause for concern?

I know it's a human trait to believe that it can't happen to you and I hope that the rest of the racers are making suitable modifications to their awe inspiring aircraft.

Incidententally, does anyone know what happened to Learfang, the P51 with Lear jet wings?
skwinty is offline  
Old 4th Oct 2011, 15:36
  #270 (permalink)  
 
Join Date: Jul 2004
Location: Found in Toronto
Posts: 615
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by skwinty
Incidententally, does anyone know what happened to Learfang, the P51 with Lear jet wings?


Crashed in 1999: P-51 Mustang Survivors: " Miss Ashley " , N57LR - serial #: 87-1002 Sights, Sounds, History.

N57LR plane crash in NV details :: PlaneCrashMap

Lost in Saigon is offline  
Old 4th Oct 2011, 15:46
  #271 (permalink)  
 
Join Date: Dec 2007
Location: Cape Town
Age: 70
Posts: 440
Likes: 0
Received 0 Likes on 0 Posts
Thanks for that Lost in Saigon.
skwinty is offline  
Old 4th Oct 2011, 21:10
  #272 (permalink)  
 
Join Date: Sep 2011
Location: Nevada
Age: 57
Posts: 18
Likes: 0
Received 0 Likes on 0 Posts
Lyman....did you get the chance to look at that 18 photo sequence? Am I mistaken or a does it look like the TT is in major flutter in #7a, if the GG is rolling to its right why are the ailerons showing roll to the left in #15a? or am I just all twisted around? Just curious on your take.
xmh53wrench is offline  
Old 4th Oct 2011, 21:17
  #273 (permalink)  
 
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,074
Likes: 0
Received 0 Likes on 0 Posts
If you have anything with the sort of resolution you allude to, I'd love to see them? PM is good.

thanks wrench
Lyman is offline  
Old 4th Oct 2011, 22:15
  #274 (permalink)  
 
Join Date: Jul 2004
Location: Found in Toronto
Posts: 615
Likes: 0
Received 0 Likes on 0 Posts
More photos of the tail area:













Lost in Saigon is offline  
Old 5th Oct 2011, 00:54
  #275 (permalink)  
 
Join Date: Jun 2009
Location: ATL
Age: 67
Posts: 131
Likes: 0
Received 0 Likes on 0 Posts
Trying to catch up. Before this tragedy happened, I had been talking to some teams about reducing compressibility drag on the Mustang Unlimteds, so I might have some unique contributions.

Haven't had time to study the video frame-by-frame but can comment in areas. Like everyone here, still putting the pieces together.

- "Could it occur, but not for long enough for the aircraft to actually stall at that G load and relieve itself?"

Dynamic stall can result in higher CLmax than the FAA demonstrated one knot/sec deceleration to the stall by hysteresis. Though on some other boards, there are claims of the telemetry being limited to 8g's. Don't know if we'll get the right number until the report, unless someone takes the time to convert the geometric flight path to g's. Since the tailwheel pops out before wings level, this might not capture the max.

- Remember a report in the past about older people being able to handle g better than the younger ones if they have any hardening of the arteries since the airteries don't expand as much to accept blood. This probably wouldn't matter much at 10+ g's, but the discussion should preclude age.

- Leaning towards the structural failure causing the left wing drop since wake turbulance would be unlikely since the wind was coming from the direction it was and was strong from the flags flying in various videos.

- "Roll Rate on this a/c is rapid, far higher than the factory model with ten feet less span. Similarly, the ailerons are half length, and it would be interesting to know if they were clipped Out/In, or In/Out. This is critical, since ailerons are airfoils, and subject to STALL just as any other."

Roll rate capability is a function of wing span-to-aileron span, and would be reduced due to the clipped wings at the tip, but at these q's, the airplane had plenty of control authority. Ailerons don't stall like wings since the leading edge is protected by the slot, but the upper surface can separate at high enough deflections.

- The racing Mustangs have an aft cg, so the elevator is deflected for nose down moment at race speeds. Some of the guys have changed the incidence to alleviate this requirement. Leeward had the one port trim tab. Voodoo had the elevator shear the torque tube fasteners on the lost trim tab side. Probably from the violent act of the trim tab fluttering and departing.

- The trim requirements in the turns and straights tend to balance out due to the aft movement of the center-of-pressure due to a shock wave forming on the inboard wing at 4 g's in the turn. Haven't analyzed it yet, and Leeeward was banked pretty good in the turn, but 6 or 7 g's probably wouldn't cause Mach buffet, looking at the pressure distribution at 4 g's. Yes, the Unlimteds are seeing compressibility drag due to the original subsonic airfoil selection.

This seems like a forum with informed, and talented individuals, and will try to contribute as I read through the thread.

Last edited by ClippedCub; 5th Oct 2011 at 01:05.
ClippedCub is offline  
Old 5th Oct 2011, 13:44
  #276 (permalink)  
 
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,074
Likes: 0
Received 0 Likes on 0 Posts
Roll rate is dependent on wing area/aileron/area, among other things. I see your point, as the area of the wing was not "halved" as was the aileron area. Good point.

Having a shorter wingspan reduces the inertia of the rolling moment? Less energy is needed to start, maintain roll? The aircraft is also less stable in roll.

The rapidity of the wing drop is what captivates me, not the impulse strength of the ailerons. I doubt the snap left was controls induced, more like a wing drop from loss of net lift v/v the right wing? Wake turbulence remains a possibility? Torque from the loss of structural integrity at the Tail?

Clipped wings, quick turns, eh? I am waiting for the next gen Mustang to show up with anhedral?

As to airfoil, the aileron is just a wing with a humongous cuff. And the laminar flow Mustang is sensitive to interruptions in local airflow?
Lyman is offline  
Old 5th Oct 2011, 22:16
  #277 (permalink)  
 
Join Date: Jun 2009
Location: ATL
Age: 67
Posts: 131
Likes: 0
Received 0 Likes on 0 Posts
Google for the basic aerodynamic and control theory answers of wings.

Could have been turbulence from ground based items/structures, but to conclude the initial dip was from wake turbulence of the lead airplanes is unwarranted due to the wind conditions. Am sure there are some weather history websites that would have the atmospheric conditions to the hour. For this reason, am leaning toward the left wing drop as being an artifact of the mechanical failure.

Whatever the cause, Leeward did an excellent job of arresting the left roll with the right amount of finesse. Reflexes like a cat from muscle and experience memory developed over the years. If nothing else, he can be remembered for his skill.
ClippedCub is offline  
Old 5th Oct 2011, 23:17
  #278 (permalink)  
 
Join Date: Jun 2009
Location: ATL
Age: 67
Posts: 131
Likes: 0
Received 0 Likes on 0 Posts
In response to the just prior post, that's missing now, on discrete roll rates in the turn;

There's a small right roll rate well before the left wing drop with a slight left roll rate immediately before the left wing drop. Consider these excursions to be positioning corrections. Ailerons are rate controls, as opposed to attitude controls, i.e., once a bank angle is established, aileron deflection is zero to maintain bank angle. The aircraft stopped rolling at wings level indicating the ailerons returned to neutral. The roll resumed during/after the wings level pull up.
ClippedCub is offline  
Old 6th Oct 2011, 01:07
  #279 (permalink)  
 
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,074
Likes: 0
Received 0 Likes on 0 Posts
Should you include the "slight correction" needed each time to arrest the roll? Could these have been merely imprecise, instead of "positioning" inputs? Not a criticism, certainly, this is a hot a/c.

There is no shame in "hunting" a roll at 475 mph.
Lyman is offline  
Old 6th Oct 2011, 02:06
  #280 (permalink)  
 
Join Date: Jun 2009
Location: ATL
Age: 67
Posts: 131
Likes: 0
Received 0 Likes on 0 Posts
Lyman, you're not a pilot, are you. No offense, but what's your background? You seem to have a Wiki knowledge of aircraft, their workings, and their operation.

Last edited by ClippedCub; 6th Oct 2011 at 03:48.
ClippedCub is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.