Tailwheel a pussycat on grass but a wild animal on pavement

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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azsportpilot
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Tailwheel a pussycat on grass but a wild animal on pavement

Postby azsportpilot » Wed May 04, 2016 11:53 am

I am a Sport Pilot CFI with over 500 hours of tail-wheel time in quite a few different models, but this one is really challenging

I have a new student with a 1999 Kitfox 3 w/ 80hp 912

You could not ask for a more stable, gentle tailwheel plane when on the grass, but paved runways are a different story

The mains track straight and true but as soon as the tailwheel touches down it swerves radically from left to right, as it slows down it gets even worse

I have flown Kitfox’s before but I don’t remember any abnormal handling characteristics

When preflighting, the tailwheel assembly and associated cables & springs all appears normal

Any ideas?

(I chose the "ASK THE MECHANIC" area in this forum as the problem is "mechanical" in nature, moderator please move if it belongs elsewhere)
John Sarra CFI-S
1946 Aeronca Chief

-Mankind has a perfect record in aviation; we never left one up there!

3Dreaming
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Location: noble, IL USA

Re: Tailwheel a pussycat on grass but a wild animal on pavem

Postby 3Dreaming » Wed May 04, 2016 12:34 pm

It could be either the tailwheel set up or main gear alignment. Most tailwheel issues don't lead to steering problems, unless the tailwheel is not aligned with the rudder. The more likely culprit is the change in toe from the level flight position to the three point position. In the 3 point position with someone sitting in the airplane roll the airplane aft 25-30 feet. Now measure the distance between the main gear. Now roll the airplane forward and re-measure. If you get a significant difference between the 2, you have an alignment issue.

The reason you are seeing the difference on grass compared to pavement is because the gear will slide on the grass, but it grips the pavement.

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azsportpilot
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Re: Tailwheel a pussycat on grass but a wild animal on pavem

Postby azsportpilot » Thu May 05, 2016 10:36 am

3Dreaming wrote:It could be either the tailwheel set up or main gear alignment. Most tailwheel issues don't lead to steering problems, unless the tailwheel is not aligned with the rudder. The more likely culprit is the change in toe from the level flight position to the three point position. In the 3 point position with someone sitting in the airplane roll the airplane aft 25-30 feet. Now measure the distance between the main gear. Now roll the airplane forward and re-measure. If you get a significant difference between the 2, you have an alignment issue.

The reason you are seeing the difference on grass compared to pavement is because the gear will slide on the grass, but it grips the pavement.


we will check the alignment (toe & Camber) this weekend

whats your opinion on toe?.... piper used to build in a tiny amount of toe-in at the factory

many people today say a bit of toe-out makes the plane more stable on runways, though it accelerates tire wear

not knowing which camp is correct, I'm inclined to shoot for 0 degrees of toe
John Sarra CFI-S
1946 Aeronca Chief

-Mankind has a perfect record in aviation; we never left one up there!

3Dreaming
Posts: 1992
Joined: Sun Jan 10, 2010 6:13 pm
Location: noble, IL USA

Re: Tailwheel a pussycat on grass but a wild animal on pavem

Postby 3Dreaming » Thu May 05, 2016 1:03 pm

I would look to see where it is first, and then make adjustments from there. Just remember angles change from level to three point.

JimC
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Re: Tailwheel a pussycat on grass but a wild animal on pavem

Postby JimC » Wed Aug 31, 2016 6:45 am

Have you checked the kingpost angle?


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