My nosegear incident.

I have posted this on the RVSQN board, and will post it here also for general info:

Well it happenened to me today......
Some of you may have followed my trouble getting the old nosegear off
to fit the new one. With all the trouble, we had resigned ourselves
to leaving it to the couple of weeks prior to the permit renewal
(December), so we could continue to fly the aircraft over the summer.
Today, went from Mount Airy to Eddsfield, had a coffe and came back.
Landed 07, uneventfully (I may go so far as to say skillfully, as I
was doing my best to impress my wife, who hardly ever comes with
me!!!). We finished the roll out, and back tracked.
Coming onto the apron area, there is a very slight uneveness to the
surface. The aircraft started to pitch up and down, and then the
grinding noise started. Chunks of mud started coming into the air
with the pitch up movement. At no stage did I think we were going to
nose over, but it was in the front of me mind, as I have been
paranoid about this for months.
Thankfully all settled back down, and be managed a taxi to our
hangar, with a few more slight grinds.
I knew instantly what the end result would be..... a yolk that had
tucked under.
The conditions were firm / hard grass due to chalk under bed and a
hot dry week. Speed - normal taxi speed, no faster. Stick back ,
power idle. Nose wheel pressure 35 psi 8 days ago when I last
checked, but it retains pressure very well. I will check it tomorrow
when I go back to investigate this further.
The main problem is Stick back does nothing whatsoever at normal /
slow taxi speed, with power at idle. I am sure it lightens the
nosewheel with more than 1200rpm, or 20mph+, but otherwise not.
If this had happened at higher speed, it would have flipped.
I have a few phots but can not post till tomorrow, when I get away
from work. Hopefully, I can also go back to the strip, and check the
area inch by inch.
I had a few misgivings about leaving the nosegear this long, and I
remember Roys posts previously about changing gear prior to the CDRM
flip.
It is clear in my mind now that it is not pilot technique for the
main part. Nearly all grass strips will have some area of unevenness
somewhere similar to this. The wrong speed and power, and the stick
position becomes academic.......
Others may disagree.

Justin

Hi Justin:

Thanks for sharing your experience. I'm not sure which RV you're flying, but I can tell you that with my -7A at taxi speeds (~1000rpm) load IS most definately taken off the nose wheel with the stick full back. I can move the stick fore and aft full deflection and the nose will pitch up and down slightly. Also you can *feel* the load on the elevators in the stick. If you can feel load there, there's weight being taken off the nosewheel, however insignificant it may be.

Best,
Jamie

Its a 9a with FP Sensenich cruise prop.

I'm sorry to hear about your plane. Very glad that there was no flip and that you and your wife are okay.

Best,

Everything Bryan said, Justin.

b,
dr

Bryan Wood said:

I'm sorry to hear about your plane. Very glad that there was no flip and that you and your wife are okay.

Best,

Click to expand...

I'd dispute that full aft stick at 1000 rpm and taxi speeds unloads the nose gear any useful amount. Perhaps 30-40 lbs. max where something like 300+ lbs is resting on the nose gear statically. It is just a feel good thing.

It takes full power and at least 20-25 knots to lift the nose gear off on most RVs I've flown.

Glad nothing really bad happened.

In my RV7A, At 1000rpm, with my feet on the brakes, I can most definitely move the nose up and down a noticeable amount with full elevator deflection. It's not a feel good thing, you can pick a spot on the horizon and watch it move up and down as you move the stick. Maybe I'm not unloading the nose gear when I do this...but I'm definitely moving the airplane. I don't know about "300+ lbs" resting on the nosegear, my RV weighed closer to 270 lbs up there...but it definitely makes a difference. Having said all that, I normally don't taxi above 750RPM. YMMV

Hello Bob,

Bob Brown said:

In my RV7A, At 1000rpm, with my feet on the brakes, I can most definitely move the nose up and down a noticeable amount with full elevator deflection. It's not a feel good thing, you can pick a spot on the horizon and watch it move up and down as you move the stick. Maybe I'm not unloading the nose gear when I do this...but I'm definitely moving the airplane. I don't know about "300+ lbs" resting on the nosegear, my RV weighed closer to 270 lbs up there...but it definitely makes a difference. Having said all that, I normally don't taxi above 750RPM. YMMV

Click to expand...

My plane won't move in the grass at 750 rpm. I usually taxi at 900-1000 until I get to paved surface.
My nose wheel (empty) had 283 lb on it (IO320/CS). The pilot and passenger are over the wheel so that shouldn't change the nose wheel weight, but the fuel is forward of the mains. If fuel is full on my plane (RV9A) we have 216 lbs. Quick guess is that about 25% will show up on the nose wheel, EI 54 lbs. That gives 337 lb in my plane. Anything in the baggage will help reduce this some.

Kent

Data point

Please look at the area where the problem occurred, take pictures, measure ruts, etc to help determine what happened.

Hmm...sounds like time for an experiment.

It would be interesting if someone could get their -A model RV up on scales and do a static run-up. The numbers are probably useless but I would be interested in seeing them.

Ron,
I have not had time to post any pics yet, but spent the morning pacing the area, and taking photos.
I can not find a specific pot hole or surface obstruction to cause this, but there is certainly some uneveness to the grass. More to follow.

Yep, ya caught me in sleep mode on that one...I'm sure you're closer to correct on nosegear weight with fuel and people...I just looked over at my wt and bal form and noted the (less fuel and people) weight...300+ is probably a good real world number.

rv6ejguy said:

I(snip}. Perhaps 30-40 lbs. max where something like 300+ lbs is resting on the nose gear statically. It is just a feel good thing.

[snip]
Glad nothing really bad happened.

Click to expand...

I hesitate to post, since I don't really have a dog in this fight, but I wonder if the most useful mod might be to sweep the mains forward a little so they take proportionately more of the load.

I've certainly flown tricycle-gear airplanes that were very light on the nose. It might make the airplane more prone to tail strikes on landing, but that strikes me as more benign than the current issues.

Is there something I'm not thinking through?

flyeyes said:

I hesitate to post, since I don't really have a dog in this fight, but I wonder if the most useful mod might be to sweep the mains forward a little so they take proportionately more of the load.

I've certainly flown tricycle-gear airplanes that were very light on the nose. It might make the airplane more prone to tail strikes on landing, but that strikes me as more benign than the current issues.

Is there something I'm not thinking through?

Click to expand...

Good point, but there is one thing - ingress and egress of the plane - if you moved the gear - as you try to board it might have a tendency to tip the tail on the ground. OK for a Rans S-12, but maybe not so good on a much heavier RV with an easily damanged thin aluminum structure on the elevator or rudder bottom.

Must be careful here.

If the main gear would be move forward much, you would experience balance problem when loading and unloading. IE as it is if two large people step on the boarding step at the same time the tail will go down. This will even happen in the RV10. In fact the RV10 can be even more prone to tip-back if you have back seat passengers.

On the two seat planes you may be able to move the main forward a small amount. What would be nice is if you could adjust the position of the mains after loading and before taxi. Then when you are lined up on the runway adjust them back for takeoff and landing.

Kent

Like the -6A maybe??

Ever notice how much lower the tail is on the -6A's, compared to the -7A and 9A? The shorter mains on the -6A have got to help unload the nosegear, maybe why you don't see this type of incident as much on the 6's? Never have fiqured out why they did this in the first place. Maybe have something to do with the slightly longer fuse on the -7s and -9s?

It would be interesting if someone could get their -A model RV up on scales and do a static run-up. The numbers are probably useless but I would be interested in seeing them.

Click to expand...

Jamie, I can get the scales, if you want to try this sometime. We might could even arrange to do it on a 6A also, to see how the two compare. I don't think the numbers would be unless. If you saw a huge nose weight difference between these two models, it could very well provide a better understanding of whats going on!