Out and About finally! U/C resonance.(aka landing gear shimmy)

Its over 4 years since G-IKON was ready for the first overseas trip but family illness prevented it. Last week, she finally did 3 new countries in two days: France, Germany & Austria. There are a few pictures here going through the Alps.

For many of you this will be odd but it was only my second or third experience of landing on a hard runway, not grass. At both Calais and Zell am See, after touch down the aircraft developed a quite strong resonance. I presume the toe out is pulling the legs apart, then springing back in and repeating. Short lived but disconcerting. How familiar is this to RV4 folk? Is it a feature? No, I dont have the gear leg stiffeners installed. I would welcome comments though. If I remember correctly the toe out is effectively set by the kit?

Common

Steve,

Shimmy is common during deceleration when landing on a hard surface. Grass provides a scrubbing action that mitigates it. Tires balanced and lower air pressure helps (I use 24-26 PSI). I don't recommend stiffeners, since that transfers stress to the engine mount and may lead to fatigue cracking in the lower corners. There's some discussion on this topic in the POH for our -4 posted on that section of the site. There is also some info in the old RVator as well as discussion on VAF.

Looks like a great trip!

Cheers,

Vac

Gear shimmy

Steve,

I fly off a hard surface runway with a -4 and had the same problem until I did some research. I tried balancing the tires, swapping sides and checked the gear. Couldn't solve the problem until someone told me about Wilkerson tires. They are retreads and since installing them the airplane is smooth as glass on landing. No shimmy, no vibration and going on 50 hours now. Take a look at their website below or give them a call.

http://wilkersonaircrafttires.com/

Oly

You missed to visit Switzerland!

Sorry, I had to make this remark
Hope to see you next time here! You would be welcome.

Steve Sampson said:

Its over 4 years since G-IKON was ready for the first overseas trip but family illness prevented it. Last week, she finally did 3 new countries in two days: France, Germany & Austria. There are a few pictures here going through the Alps.

For many of you this will be odd but it was only my second or third experience of landing on a hard runway, not grass. At both Calais and Zell am See, after touch down the aircraft developed a quite strong resonance. I presume the toe out is pulling the legs apart, then springing back in and repeating. Short lived but disconcerting. How familiar is this to RV4 folk? Is it a feature? No, I dont have the gear leg stiffeners installed. I would welcome comments though. If I remember correctly the toe out is effectively set by the kit?

Click to expand...

Great hearing from you Steve!
Yes, gear shimmy is an age old event in RV"s. I found on my RV4 that stiffeners helped with the problem but over time I realized they created their own issues. An engineer friend showed how stiffeners transferred the torsional loads from the legs to the gear sockets on the engine mount. Being a grass strip (and less optimum surfaces) guy, this was important. After experimentation I found with my (and your) 380X150X5 tires that air pressure and brake application was much more critical than leg stiffness. 30 psi I found to be ideal. 25 is better for pavement but not as easy to move the airplane around by yourself.

Great photos, looking forward to a visit someday soon!

Seeya!
Smokey

feedback

My experience...
Short gear, 5.00X5 wheels, PR wheels pants, Desser retreads (and a variety of other tires).
No shimmy on pavement.

Any issues during landing and rollout were all mine.

U/C resonance.

Thanks for the replies guys.

As a first step I will drop the pressures. From memory I am up at 36 or 38. I will give 26 a try for starters since the aircraft does not have to be pulled around much down here in Zell. I assume you were saying hard braking excited it Smoky? These metal runways appear to be infinite after my 1000' of grass so maybe I will just try and forget I have brakes.

Hey Cloudancer. I have forgotten where are you in Switzerland. Which airfield? Customs? Grass? Just possible........ Since I wrote that last sentence I have realised its quite a challenge having looked at the chart. The length of Austria, from here, the min. safe altitude much of the time is above 11000'. Also Innsbruck airspace is a bit in the wayStill it would be a great flight. I'll have a more detailed look.

Nice pictures of the Alps Steve! How much is fuel in Austria? Did you pay any fees in Europe?

32-34 psi works for me. I suggest dropping the pressure a couple of pounds at a time till you find what suits your aeroplane. Lions will go down though.

Vlad said:

Nice pictures of the Alps Steve! How much is fuel in Austria? Did you pay any fees in Europe?

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Vlad, I havnt refilled it yet, so dont know. It was €2.26 at Tannheim. It will be cheaper here I think. Landing was €9.70. Best not to think about it.

Doug, I cant see a reason not to go down and then come up bit by bit.

Trip to Switzerland?

Steve;

I have to apologize that I did not respond earlier. I did not realize that you are still on travel.

My home airfield is Langenthal (LSPL) and is located nearly mid of Switzerland. It's an AFIS airfield and during the week you will normally get no answer on the radio. We have a 585x18m paved runway and a small 335x20 grass runway in parallel (in fact the grass strip is longer, but the offficial runway has that length). You can find all the information on www.lspl.ch. On the homepage everything is written in German. But the most important information you will find as well in English under: http://aecs.lspl.ch/index.php?id=140
Customs: There is a link on the webpage for online customs announcements (Zoll). They have to be done 18:00 on the day before arrival latest.

Landing fees are rather expensive, but I would take care of that ;-) On the airfield we have some homebuilt and aerobatic aircraft (no RV for instance), a lot of gliders and as well quiet a lot of oldtimers (among them 5 B?cker Jungmanns and 1 B?cker Jungmeister).

I drop you a PM with my contact data in case you're interested to visit.

Andreas

Doug said:

Lions will go down though.

Click to expand...

Doug, I am not much into sport so perhaps you can explain this to me?

Also, Wimbledon, how did the Australians do?

RIP Aust rugby. I couldn't watch, and I'm not expecting too much more in the ashes.

BTW on the subject that matters, I find that getting the stick all the way back after the tailwheel is on the ground seems to stop any main gear shimmy. I'm not sure why this works, perhaps it damps the resonance or possibly just marginally reduces the load on the gear legs.