VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics


Go Back   VAF Forums > Main > RV General Discussion/News
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #21  
Old 11-29-2006, 08:22 PM
garnt.piper's Avatar
garnt.piper garnt.piper is offline
 
Join Date: Mar 2005
Location: Australia
Posts: 152
Default Rolling G

Conventional wisdom, which comes from FAR Pt23 I believe, is 2/3 maximum symmetrical g with full aileron deflection at Va.

re. earlier discussion, I have a finite element analysis of my G-200 wing which shows the highest stresses at about 40% span.
__________________
Grant Piper
SAAA #727 (TC)
RV-4 VH-PIO ~600hrs
G-200 VH-OVR ~250hrs
Reply With Quote
  #22  
Old 11-29-2006, 08:23 PM
jcoloccia jcoloccia is offline
 
Join Date: Sep 2005
Posts: 1,110
Default

Incidentally, if you want to speculate on ANYTHING it's interesting to note that the NTSB found a broken elevator trim clevis. I think they also found the trim motor at full extension (i.e. full up tab...full DOWN trim). It's not a stretch to think that plane was trimmed full down for whatever reason, the clevis broke and suddenly all that stick force that went into maintiaining level flight caused a massive pitch up and subsequent wing failure.

I don't know...I haven't read the NTSB report in almost 2 years and I'm much too lazy to look it up now, so maybe I have my accidents confused. Look it up and decide for yourself.

Anyhow, my guess is the answer to the question asked is "as light as possible and just barely strong enough to keep most pilots from killing themselves".

Remember....RV's are overengineered. There's a big difference between that and overbuilt. Overengineered implies redundancy in the design and tolerance for some sloppy work. That doesn't mean it's way stronger than it needs to be....it means you can be a little off and still make it just as strong as it was designed to be. Big difference....
__________________
John Coloccia
www.ballofshame.com
Former builder, but still lurking 'cause you're a pretty cool bunch...

Last edited by jcoloccia : 11-29-2006 at 08:27 PM.
Reply With Quote
  #23  
Old 11-30-2006, 10:29 AM
gmcjetpilot's Avatar
gmcjetpilot gmcjetpilot is offline
 
Join Date: Jan 2005
Posts: 3,668
Default 10! Ten

Quote:
Originally Posted by cruzer
I have been inspecting aircraft since 1978 and have found only 2 small cracks in certified aircraft engine mounts. The 12 years I worked at Vans there were 10 times plus that many accounts of cracks and damaged mounts on the factory demo aircraft. I also personally have welded 7 customer mounts for RV aircraft that had fatigue cracks in the dyna-cup rings and supporting tubes. It is dangerous for anyone to think any aircraft or part is overbuilt and therefore routine inspection of it isn't needed. Also for the record on the RV8 wing. The flutter test that was conducted at Vans was on the RV6A which had a different spar in it than the RV8 that crashed. The load test after the crash was done on a pair of customer wings that the builder abandoned, they also had a different spar than the crash aircraft. The crash aircraft had a different aileron on the right wing, it had a different D section shape. No one knows FOR SURE what happened. The speculation on this subject is just that.
Interesting statistics 10 cracks! May be it's the way the plane is flown?

Well in 20 years of being around 30 RV's there has been few cracks. I flew at a field with at least 15-20 RV's flying at any one time. Over many years I don't recall any one with engine mount complaints, except one older RV-4, whose firewall fittings cracked. It had older style firewall engine mount that where upgraded many years ago. The engine mount itself was OK.

While I am thinking about the older RV's like the RV-4 used very thin skin for the elevator (0.016). They would crack near the trim tab cutout typically. IT seemed it was fine with a little 150HP engine and wood prop, but when more people started using bigger engines and constant speed props the problem was more prevalent. Van LONG ago went to (0.20) thick elevator.
__________________
George
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767

Last edited by gmcjetpilot : 11-30-2006 at 10:35 AM.
Reply With Quote
  #24  
Old 11-30-2006, 10:34 AM
gmcjetpilot's Avatar
gmcjetpilot gmcjetpilot is offline
 
Join Date: Jan 2005
Posts: 3,668
Default Loss of control?

P, what clevis, the trim tab? Yea I don't like that plastic trim tab clevis either.

You mention uncontrollable plane? Is there an accident report or what. There are like 5,000 built and flown and we know they really fly wonderfully. Very few if any RV's have crashed due to the airframe failure. Some engine issues, sure, but as far as airframe structure and controls, I can't think of any. I have over 1000 hour in RV's. What RV are you flying P.

(I did a quick check and there have been a few control jams, this is one that is scary, ball point pen and jar under floor boards caused greif to this RV).

RV-8, June 05, 2005, NY, N61TW
The pilot/owner of the homebuilt airplane began the takeoff roll. At rotation, the airplane pulled “hard” to the left, and pitched up “more aggressively” than a standard takeoff. The pilot applied full down elevator, “but the nose would not come down.” The airplane then pitched nose down, the pilot applied full up elevator, and the airplane attained a level pitch attitude prior to ground contact. When asked about the performance and handling of the airplane, the pilot/owner said, “Everything was perfect with the engine.” He added that about the time of rotation, he felt a bump, and surmised that he had struck a runway light or that a wheel brake had locked. Examination of the airplane revealed an ink pen lodged beneath the rudder bar. As a result, more force was required for a right rudder input than a left rudder input. The pilot/owner said he routinely stored pens, unsecured, on the ledge next to his right knee. Further examination revealed a 50-ounce glass jar beneath the front seat, in close proximity to the forward control stick. The jar’s lid displayed indentations that the pilot said had not been there prior to the accident. He said the jar was kept in the airplane as a relief container, and that it was placed on a ledge, unsecured, prior to takeoff. report: http://www.ntsb.gov/ntsb/brief.asp?e...09X00746&key=1
__________________
George
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767

Last edited by DeltaRomeo : 07-16-2007 at 06:09 PM.
Reply With Quote
  #25  
Old 11-30-2006, 05:08 PM
kentb's Avatar
kentb kentb is offline
 
Join Date: May 2005
Location: Canby, Oregon
Posts: 1,786
Wink

Quote:
Originally Posted by gmcjetpilot
. He said the jar was kept in the airplane as a relief container, and that it was placed on a ledge, unsecured, prior to takeoff[/u]. [/i] report: http://www.ntsb.gov/ntsb/brief.asp?e...09X00746&key=1
Man, wouldn't that pis* you off..


Kent
__________________
Kent Byerley
RV9A N94KJ - IO320, CS, tipup
AFS 3500, TT AP, FLYING....
Canby, Or
Reply With Quote
  #26  
Old 12-05-2006, 03:40 PM
jstiegel jstiegel is offline
 
Join Date: Sep 2005
Location: Vinton, Iowa
Posts: 20
Default wing failure

[quote=JonathanCook]What happened to the 8 wing that broke after the fuel tank does not happen from pulling too many Gs. I know that this goes against what Van's says, but this kind of failure is probably due to flutter.

This may not be the same RV-8 accident, but the one I remember the wing failed in straight and level flight. So, this was very probably due to overstressing the airframe and not doing a through inspection afterwards and at frequent intervals to see stress fractures develop. If you go back to the structural breakup of TWA Flt 800, '96' I believe when the nose came off the rest of the aircraft pitched up rapidly. This caused the wings to fail at some point outboard of the wing root. I believe at some point outboard of the flap line. The wing destruct in this case was not flutter. Not saying you are wrong in your analysis, but over stress does cause premature failure.
Former USAF Pilot, Retired TWA Captain. No engineer just a flyer.
Regards,
John S.
__________________
Where tillage begins, other arts follow.
John Stiegelmeyer
Reply With Quote
  #27  
Old 12-05-2006, 04:48 PM
gmcjetpilot's Avatar
gmcjetpilot gmcjetpilot is offline
 
Join Date: Jan 2005
Posts: 3,668
Default I think apples oranges

John Stiegelmeyer: Yea I get you but of course TWA 800 was a totally different deal, and doubt any RV nose fell off causing a pitch iup. As far as level flight, unlike the big gets the little plane can change directions very fast. In level flight, if you are going fast enough, and pull hard enough the wing will fail. From a ground observer it may seem like the plane was going level at the time.

Here is the RV-8 prototype accident (notice one eye witness says plane was level):

Summary
http://www.ntsb.gov/ntsb/brief.asp?e...11X10121&key=1

Factual detail
http://www.ntsb.gov/ntsb/GenPDF.asp?...98FA171&rpt=fa

Prob cause:
http://www.ntsb.gov/ntsb/GenPDF.asp?...98FA171&rpt=fi

Airframe deficincy was not found to be a probelm. This was following metilurgical analysis of the wing and Van's static load test subsiquent to the accident with a pair of RV-8 wings built (badly) by a customer, representaive of the wing on the prototype.
__________________
George
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767

Last edited by gmcjetpilot : 12-05-2006 at 08:09 PM.
Reply With Quote
  #28  
Old 12-05-2006, 05:25 PM
Mike S's Avatar
Mike S Mike S is offline
Senior Curmudgeon
 
Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 14,280
Default I wonder if-------

This is all conjecture, as I haven't yet built a RV wing, but I am wondering------

Is the fuel tank a load carrying member of the total wing structure????

The tank just bolts on to the spar, and doesn't appear to help carry the full span flight loads. Therefore, the inner part of the wing must carry the flight loads with the spars and rear skin only, while the outboard section of the wing utilizes the "D" tube of the front ribs/skin also---------and in an area of lower stress to boot.

So, I would expect the spar to be reinforced in the inboard end------------and yes, in fact it appears to be.

Now, if the inner portion reinforcement was terminated incorrectly (too soon, or too abruptly) just where the flight loads would transition from the entire wing structure to just the spar rearward, at the outboard end of the tank. Seems to be an ideal failure point.

Now throw in a few violent maneuvers-----------

Any of you engineer types have input??

Mike

Last edited by Mike S : 12-05-2006 at 05:31 PM. Reason: additional thoughts
Reply With Quote
  #29  
Old 12-05-2006, 09:02 PM
tclaire tclaire is offline
 
Join Date: Nov 2005
Location: Rayville Mo Midland Tx
Posts: 74
Default

Has any one replaced the plastic clevis on the trim with metal clevis and where did you purchase them at
Reply With Quote
  #30  
Old 12-05-2006, 10:02 PM
jcoloccia jcoloccia is offline
 
Join Date: Sep 2005
Posts: 1,110
Default

I don't think a clevis has ever broken. Even if it was a broken clevis on that one aircraft, the report states that the clevis was modified with a notch (definate no-no).

I'm sorry I even started the thread down this path. The only point I was trying to make is that for whatever reason, someone yanked on that elevator to break that wing...simple as that. The structure performed exactly as intended. The whole clevis thing was more of a mental exercise and I regret even mentioning it at this point.

The stock clevis is perfectly OK
__________________
John Coloccia
www.ballofshame.com
Former builder, but still lurking 'cause you're a pretty cool bunch...
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 11:03 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.