|
-
POSTING RULES

-
Donate yearly (please).
-
Advertise in here!
-
Today's Posts
|
Insert Pics
|

09-22-2010, 11:30 PM
|
|
|
|
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,351
|
|
I have been following this with much interest and since I am a fairly new pilot (450+ hours) and have little engineering knowledge, hesitate to offer an opinion. However, for my personal use and comfort, I have taken a few small/inexpensive and easy steps to increase my odds. These are such as small wood dampener, Matco axle and keeping my air pressure where it needs to be. I also ALWAYS follow safe technique for RV-A flying such as keeping the NG up as long as it stays up and always have the stick in my tummy while taxing. It seems trying to fix this NG issue is like wanting to fix a tail dragger from its inherent risk and unfriendliness. We all take more care landing a tail dragger and if it ground loops, the blame goes to the operator. How is that different with the NG model?
If there is a redesign that proves to be safer but does not require a major overhaul, then I will change it. But if I am back to building stage and specially the improvements are not significant then I will keep flying and practice safe piloting.
__________________
Mehrdad
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
|

09-23-2010, 06:15 AM
|
 |
Moderator/Tech Counselor
|
|
Join Date: Jan 2005
Location: East Troy, WI
Posts: 1,983
|
|
I did not torque the axle, but rather tightened to remove any slop in the assembly. The torque Van's recommended was to secure the bearings from turning in the yoke. The staking prevented that and allowed you to relieve the bearings so that the tire and wheel could spin easier.
I like the new style spacers some of you guys have developed and I would recommend that method. I always liked the Piper nose wheel design and this is similar. The Piper axle tube went through the yoke to machined plugs that went into the axle tube spacers, providing a way to adjust for bearing slop. The axle bolt went through the whole assembly from plug to plug and allowed preloading the bearings while still fully supporting the bearings. The picture attached is a little unclear, but the axle is a tube and the axle bolt is separate. The picture sort of implies it is intregal to the axle.
My best recommendation would be to copy what Piper did.
I have attached an SB that shows how the axle is configured. This SB was generated after a failure of one of the cups from overtightening. Just shows how important is is to remove slop from wheel bearings, but be wary of over torqueing them.
Roberta
http://www.aaib.gov.uk/cms_resources...GT%2005-06.pdf
__________________
Roberta Hegy
Built/Flew an RV-7A
Air Troy Estates, East Troy, WI
Ford Expedition and TRICE "Q"
Built Glen L "ZIP" Classic Outboard Runabout and Super Spartan Hydroplane
Glen L Torpedo
Last edited by robertahegy : 09-23-2010 at 06:20 AM.
|

09-23-2010, 06:51 AM
|
 |
|
|
Join Date: Apr 2005
Location: KSLC
Posts: 4,021
|
|
Quote:
Originally Posted by Zero4Zulu
I was just measuring the NG for an idea I have for a bolt on damper/stopper to limit the aft movement of the NG.
The failure occurrs when the gear is deflected aft to a point it can't recover and gives way. The whole nut thing is when the failure is imminent. Just imagine the angle that would have to be present to have the nut contact earth.
I measured the diameter at the lower bend(1.010 dia.). 8" up the leg (.910 dia.) and at the socket it tapers up to 1.125". The leg is actually reduced in diameter .100" right where they appear to fail. That seems and actually looks pretty dramatic. Just slide your and up and down the leg and you can feel the thin area.
If the gear leg was just an even taper from the lower bend up to the socket that would be a pretty substantial strength improvement. Any engineering thoughts about this? I know it would remove some spring from the leg.
****, right now they are designed to fail if you ask me. I know, I know, keep the stick in your gut.
|
Have you seen the Van's video from around the year 1999, when they re-designed the nose gear? They had a large spinning wheel designed like a cam lobe that would spin at high speed & constantly beat against the gear leg & wheel. The new leg held up, where the old design failed rather quickly. Considering the leg is the shock absorber, I'm not convinced that removing some of it's "spring" ability, is the right approach. Afterall, RV's do drop through the flare once and a while.
L.Adamson --- RV6A
|

09-23-2010, 07:30 AM
|
 |
|
|
Join Date: Feb 2005
Location: Huskerland, USA
Posts: 5,862
|
|
Quote:
Originally Posted by Leland
Last Thanksgiving I landed too slow at an airport I was unfamiliar with. My -9A stalled a foot or so above the runway, hit hard on the mains, and then immediately banged the nosewheel so that it "twanged". My best landings are done coming over the fence at 60 knots and rounding out until the mains kiss the runway, holding the nose off until elevator authority is nearly gone, and then lowering it. Full stall landings are not the way to go here.
Leland
|
[quote=GrayHawk;134726]
Quote:
|
Originally Posted by Leland
Agreed! I took no stalling as a given, but will modify the list. I usually am at 80 mph over the fence, 70 mph over the numbers, which is about the same as your 60 knots. (5040' elevation airport) Also good point on gently lowering nose before elevator authority is gone.
|
I am certainly no expert, but I have flown a bunch of RV's so my experience level is slightly higher than some, and I notice the way others fly. It is rare that I see a pilot in an -XA RV roll out with the elevator in the nose up position. If they don't bang the nose gear down, they relax the stick immediately after nose touch down. Even after there is "no elevator authority" the elevator still has the ability to reduce the pressure on the nose wheel on roll out. Watch the video of the RV flip over and you can plainly see the elevator in the neutral position.
Basically, the above can be condensed into: "Keep the stick in your gut until engine shut down." It will relieve some pressure off the nose wheel even when the engine is just idling and stoped. The prop wash gives some air over the elevator. Try moving the stick forward and back at 1500 RPM (or slightly above) and watch the nose of the plane.
The last point I would like to make is is that the effect of these bad landings is cummulative. Meaning, you might get away with several dozen bad landings, until the gear gives out. It's not just a one time occurance that breaks the nose wheel.
__________________
RV-7 : In the hangar
RV-10 : In the hangar
RV-12 : Built and sold
RV-44 : 4 place helicopter on order.
Last edited by Geico266 : 09-23-2010 at 07:33 AM.
|

09-23-2010, 07:44 AM
|
|
|
|
Join Date: Jul 2007
Location: Rock Hill, SC
Posts: 390
|
|
Certified standards
Rather than approaching this in a "problem investigation - solution" manner, I think starting with the standards for certified aircraft nose gear in (14CFR23.477 et seq.) would be logical.
http://www.access.gpo.gov/nara/cfr/w...4cfr23_10.html
__________________
Jonathan Hines
Charlotte, NC
|

09-23-2010, 07:59 AM
|
|
|
|
Join Date: Feb 2005
Location: Chesterfield, Missouri
Posts: 4,514
|
|
Quote:
Originally Posted by L.Adamson
Have you seen the Van's video from around the year 1999, when they re-designed the nose gear? They had a large spinning wheel designed like a cam lobe that would spin at high speed & constantly beat against the gear leg & wheel. The new leg held up, where the old design failed rather quickly. Considering the leg is the shock absorber, I'm not convinced that removing some of it's "spring" ability, is the right approach. Afterall, RV's do drop through the flare once and a while.
L.Adamson --- RV6A
|
Larry, a most relevant observation. I did not know about the spinning wheel test and the strut.
It does support my feeling that the strut is most adequate, the challenge is keeping the nose of the NG from digging into a soft surface or catching an irregular lip or hole, and bending aft.
In every failed NG, that is what happens. It may be aggravated by tight bearings acting like a brake, or the tire low on pressure getting caught on a wheel pant with little clearance, a very hard landing, but the end result is the nose of assembly getting caught on something and bending the bottom of the strut aft.
That is what led to the modification that raised the nut one inch. The idea did not come from this forum, it came from a study by a guy at the NTSB. Consequently, Van's had to act on it. Raising the nut certainly provided for a greater margin of deflection before the bending occurred but it did not provide any improvement if the deflection was such that the nut made contact with what ever was being run over.
The attached image is of from my event in 2003.
Uploaded with ImageShack.us
I did not save the strut, but clearly it was mostly bent at the wheel. The upper part of the strut was bent slightly.
My perception of the problem may be in error and I may well be bitten again, but as of today after flying with the system for the past 5+ years, mostly off of turf, I feel comfortable with it. I do not worry about it. But I do try to be aware of surface conditions and make every effort to not land on the NG but only the main wheels.
__________________
RV-12 Build Helper
RV-7A...Sold #70374
The RV-8...Sold #83261
I'm in, dues paid 2019 This place is worth it!
|

09-23-2010, 08:28 AM
|
|
|
|
Join Date: Mar 2009
Location: Suffolk, UK
Posts: 7
|
|
Although my Rv is an 8, I'm getting on in years now and I thought about a 7A for my old age - if I ever keeled over my bride could put a side-by-side nose-wheel back on the ground quite safely and she deserves to see the side of my head after all these years! It would also give me an excuse to become a repeat-offender, two van man. And guess what, I could always sell it and keep the 'DUDE'.
However, I have flown lots of the A variety and once when testing a new US import here in UK I did have a near miss withthe nose-wheel issue. It was a 7A with a 180hp engine and constant speed prop. It also was airways equipped and weighed in at about 1150lbs(forward cg & lots of weight on the noseleg). I flew my 8 over to the grass strip where it was located and noticed that although the ground was reasonably smooth, there were a series of ridges rather like a swell at sea.
There were no problems with the take off or in the air but I was very, very careful when landing to be on speed (60kts) and tried to avoid the bumps by lading at the very start of the strip. I held it off and got the stick right back after touchdown. Nevertheless I was unable to prevent the nosewheel hitting one of the 'waves' in the ground. This kicked the nose wheel back into the air and I almost hit the tail bumper. As I struggled to maintain a nose up attitude the ground came up and hit me again! Up went the nose again, even higher and I thought how stupid I was going to look upside down.
Anyway the beast calmed down and the everything was well. The point of this post (what I learned) is that I suspect that the smooth ridges on the ground in some way coincided with the natural harmonic of the nosewheel leg and even though I was decelerating this caused the pitching to be amplified. So there's bumps and there's different bumps! The next time I flew from there I waited till the wind was from the other end!
I'll still build the 7A and be very careful - I'm still learning after 50 years of flying.
|

09-23-2010, 09:04 AM
|
 |
|
|
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
|
|
Can an ME confirm this?
Quote:
Originally Posted by Geico266
.....
The last point I would like to make is is that the effect of these bad landings is cummulative. Meaning, you might get away with several dozen bad landings, until the gear gives out. It's not just a one time occurance that breaks the nose wheel.
|
Few (none?) of the failures seem to involve a physically broken nose gear leg, so cracking caused by previous bad landings is not likely. Most failures are extreme bending.
So, can a piece of spring steel be reduced in strength by previous large deflections if no permanant set has taken place?
A permanent set would be visible in how the plane sits and the ground, and a change in the pivot angle would probably affect taxying...
Can an ME help here?
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
|

09-23-2010, 09:31 AM
|
|
|
|
Join Date: Sep 2010
Location: Sao Paulo, Brasil
Posts: 72
|
|
Quote:
Originally Posted by FresnoR
So just for arguments' sake, what would it take to get the RV-10 nose gear assembly on a 7 or 9?

|
Weight and balance, I guess ...
|

09-23-2010, 10:27 AM
|
|
|
|
Join Date: Dec 2008
Location: Colorado
Posts: 33
|
|
I think as well as weight and balance, also size/complexity/space limitations inside the cowl that deter this type of nose gear.
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
All times are GMT -6. The time now is 06:51 AM.
|