MATCO pneumatic 6" Tailwheel 'wobble'

Ade Kentzer · Post by **Ade Kentzer** » Mon Aug 22, 2011 11:32 am

Perhaps 'wobble' is the incorrect term to be used but heres the symptoms, that I hope someone will be able to steer me in the right direction for a remedy.

I fly a CH601XL taildragger and have noticed only when landing on tarmac (which I don't do often) that the tailwheel 'feels' like its oscillating or doing the duff supermarket trolley castor wheel wobble. This is only happening on landing, whereas takeof is as smooth as silk.

Is this down to my landing technique or could it be down to excess play on the bearings / spacers in the Matco setup? Admittedly, my landings on tarmac have been at higher speeds than normal as there has been so much runway to 'play' with that I have tended not to use flap or have reduced flap compared to landing on short grass strips.
The tyre is now looking a little feathered after landing at Caernarfon yesterday so a new one will be ordered today.
Any help will be much appreciated.
Ade

G.Dawes · Post by **G.Dawes** » Mon Aug 22, 2011 9:00 pm

Shimmy is the problem and can be reduced by using differing spring tensions on the springs, one stronger than the other but the same length.
Graham

John Clarke · Post by **John Clarke** » Tue Aug 23, 2011 12:12 am

Interesting problem, Ade...we're going to have to meet up to compare tailwheels!

I've not had your problem but I've recently burst the inner tube after landing at an airfield (hard surface) that could be described as "bumpy" to put it mildly. I recently bought a Matco solid tailwheel but I really can't recommend it for the 601...it makes for very uncomfortable and noisy taxying. My plan is to refit the pneumatic wheel and keep the solid one in the aircraft all the while as a spare. The drawings etc. for this wheel are on the Matco website, if you haven't found them already. There is also a service bulletin on the website describing how to set the pre-load on the vertical axle.

The tyre and tube for this wheel has to be ordered together as a single item from LAS. If you can find the tube separately then please let me know as I can't get one in the UK. It took 5 weeks for LAS to get the new tyre and tube, which I admit is unusual for them.

The biggest problem I have with the Matco wheel is that, once it "breaks out" (about 40 degrees I think) I have a devil of a job to get it to straighten out again.

John.

tnowak · Post by **tnowak** » Tue Aug 23, 2011 8:06 am

Although not familiar with the Matco tailwheel I suggest you check the geometry of tailspring and tailwheel. The tailwheel pivot angle (usually) shouldn't be 90 deg relative to the ground but a few degrees less. Also, as a previous poster mentioned, different tension springs is another classic means of reducing or eliminating shimmy.
Tony Nowak

Ade Kentzer · Post by **Ade Kentzer** » Tue Aug 23, 2011 1:35 pm

Thanks for the replies chaps. I've had a look at the Matco tech bulleteins and it looks like there is a certain amount of adjustment in the vertical plane area via 'friction' washers and nipping up via the castle nut.

Graham / Tony, by having different spring tensions, do you mean a higher rated tension on one side rather than both, OR, increase the tension but retaining identical tension on both sides.

John, Ive ordered a new tyre and tube set from http://www.aircraftspruce.eu/?gclid=COK ... 4QodkGHd6A
They are in stock and cost 33 euros (including shipping).

Ade

Brian Hope · Post by **Brian Hope** » Tue Aug 23, 2011 4:20 pm

Hi Ade, what's being suggested are Maule type rudder/tailwheel springs. they are doubled up (an inner and an outer spring) and are of different tensions one side to the other. You can get them from LAS.
I use them and they have solved a shimmy problem I had. On the Jodel the swivel axis was said to be best when it was vertical with the a/c sitting on the ground. Mine is and works, though I can see that a little trail seems theoretically better. The rudder springs need to have a bit of tension when fitted and wheel is straight. The tyre on my and many Jodels is hard rubber and gives no problems, I've never ad a puncture!

ColinC · Post by **ColinC** » Tue Aug 23, 2011 9:38 pm

Hi,

just a thought:

it is worth checking that the castor angle is in the right direction. With weight on the wheel is there positive castor? i.e. if you draw a line through the pivot axis is it forward at the bottom and aft at the top? That makes the wheel self-centre. If the other way then it would be a problem.

The reverse is what causes that trolley wobble effect. Perhaps over time the spring has flattened out which would reduce the castor angle, particularly when the spring is being compressed under load.

The dual rate Maule spring may not be the answer if the geometry is incorrrect.

ThePipster · Post by **ThePipster** » Tue Aug 23, 2011 9:38 pm

I have noticed that Airworld UK (Pete Smoothy) has them for a bit less than LAS......

Pipster

(not connected with any vendor, just got a nose for a better price!)

Ade Kentzer · Post by **Ade Kentzer** » Wed Aug 31, 2011 10:31 am

Many thanks for the replies, I've had a tinker with the t/wheel setup and re-adjusted the top castle nut by a good 3/4 turn as there was a bit of play in the vertical post. Also the mounting nut on the trailing arm/leaf spring was 'nipped' up as this wasn't overly tight either. Just waiting for a TARMAC landing now and I'll post the results. Hopefully Sywell this weekend !

Ade