byoungplumbing(at)gmail.c
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 Posted: Fri Feb 18, 2011 7:35 pm Post subject: kolb toe in |
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ok kolbers..
my toe in numbers are in. this is quite long,,, and if you are not interested hit delete now.
my starting numbers may not be as accurate as I would have liked them to be, my measuring technique improved with time. but not with standing this is what I have.
the camber of both wheels was a neg 3 deg. this was due to the way the axels were bent at the factory, when the plane was hoisted in the air the axels were parallel to the ground, and when the weight of the aircraft was put on them, both wheels went neg, and when I climbed in with a passenger it went to 4 1/2 deg neg, the tops of the tires were angled in and the gear looked squatted down.
recent post about toe in had me wondering. and I had quoted what was in the mkiii construction manual for "toe in". which was "neutral, and if you have to err, err on the side of toe out."
a while back my son bought a very nice pipe bender. so I had him bring it over and we did some work on the gear.
my original measurements which may not be as accurate as I would have liked,, best I knew how at the time, were:
left wheel .70 deg toe in,,, right wheel 1.000 deg toe in total for both wheels of 1.70 with neg 3 deg camber each side. with the air pressure in the tires low (6 to 8 psi) it drove around what I thought was ok... if I pumped the air pressure up to 15 it would dart across the runway and made it hard to keep the white line between the tires. so for 600 hours I ran low tire pressure.
I figured if I was going to put in a bit of positive camber, I could correct the toe in at the same time. so my son and I proceeded to bend steel. and by varying the bend angle, I could adjust for camber and toe in at the same time with one bend. what we ended up with was about 3/4 deg pos camber on the right and 1 deg pos camber on the other right (left), and the toe in was neutral on both sides,,, I was quite thrilled, until I took it out for a drive.
from the neutral toe in as I started rolling for take off, the rolling resistance pulled the gear back till I was in a toe out condition. at that time the drag on the wheel increased and the gear flexed back till the tire started sliding, and the gear would spring forward.. it felt like I was riding a jack hammer. so back to the drawing board.
a friend and I went out this afternoon and started bending some "toe in" back in the gear. what we ended up with was:
left wheel .78 deg right wheel .70 deg both wheels 1.48 deg... my goal was 1.5 deg,, I came real close. it was less then my 1.7 I started with,,, I went for a test taxi and it would dart across the runway,, not as bad as before,,,, and the jack hammer was gone,, I figured if I lowered the tire pressure it would be ok... but we tried one more time. this time we only bent 1 gear, and I ended up with
left .52 deg "toe in" and right stayed .7 deg "toe in" total for both wheels 1.22 deg,,, I increased the camber to 1.5 deg pos camber each side. with my friend sitting on the side each side would go to neutral camber. I went for another taxi test,,, the darting across the runway went from manageable to barely noticeable.. but there was a tiny bit of shake in the right side when I hit the brakes. I am quite certain that if I lower the air pressure it will go away. a test for another day. I ran out of daylight.
from my experience and if I had computerized bending equipment, I would go with .625 deg toe in per side for 1.25 deg for the combined figure. or I would redesign the landing gear sockets to make them adjustable. for "toe in" then you could dial in exactly what you need. I will fly like this for a while.. but I may experiment again with the tubular steel, hardened to 48 rockwell.
my gear is the solid tapered spring steel gear legs that the new kolb company sold for the mark iii. your mileage may vary. the aluminum gear (i think) would not be as flexable, so less toe in would be required.
I took a few pictures if any one is interested.. I will have to get them off the camera, resized and posted.
boyd young
mkiii
utah
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