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rexjan(at)bigpond.com
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 Posted: Tue Nov 28, 2006 4:09 pm Post subject: Directional stabilitty |
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The tricycle gear handles differently no doubt.... But directionally more
stable. I think directional stability will be the result of a number of
factors. E.g. the speed of taxi, the number of wheels on the ground, the
direction and speed of the wind, the condition and length of the runway and
lets not forget the experience of the pilot.
Noel, the main reason for directional stabilitty of the tri-cycle undercarriage is due to the weight being in front of the main wheels dragging behind. As soon as you touch the deck the weight pulls the plane straight. Whereas in a tail dragger the bulk of the weight [ C of G ] is behind the main wheels so it has to push them. If you are not dead square with direction of travel the weight tries, and does. come around in front of the mains. As this happens it is called a ground loop.
Rex.
[quote][b]
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Tue Nov 28, 2006 5:23 pm Post subject: Directional stabilitty |
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Ok Rex:
first what you are saying is to an extent true. But...The amount of weight on the tail wheel is only a fraction of the mains. In order to ground loop you have to let the the swing develop past a point of no return and you have to do this just before the tail wheel touches the ground. To counter this slight instability ( displayed only for a few seconds of a flight ) the mains can be slightly toed out, then as the plane starts to wander off straight the mains will actually act to pull it straight again. Tricycle gear planes sometimes have a slight toe in to do the exact same thing.
During almost all other aspects of ground handling except taxiing with a strong wind into a forward quarter the tail wheel should be superior. The centre of gravity is lower, the wheel base between the mains and the steering wheels is longer. Down wind it is almost impossible to trip a conventional gear plane. The tricycle counterpart better be careful.
What can make a conventional gear plane squirrelly is putting a great heavy weight close to the tail wheel. My fathers plane had the battery installed almost right over the tail wheel. It was next to impossible to not crack the tail spring off at regular intervals. Inertia of the battery mass over the tail wheel would make any plane squirrelly on the ground in almost any conditions. I gave him the fix for his ground instability and he refused to try it. The plane was a VJ22 Sportsman which had a Lycoming 125 Hp tractor installed. Corrections for the added weight forward of the CG were not calculated and to bring the CG in line they had to put the battery far, and I mean FAR aft. What he had was a high wing plane with a high CG and a huge mass in its tail. Nobody liked it on land... on the water that was another story.
Lets hear some concrete figures on ground accidents in Kitfoxes. Include nose overs, tricycle trips, ground loops, wing overs etc.etc... I'll bet you will find there are probably more accidents per capita in tricycle gear small planes than are in their conventional counter parts. Also, as has been mentioned here when there is a minor accident (broken tail wheel) with a conventional gear plane it is usually a cheaper fix than a collapsed nose wheel which can end up costing a new crank/prop/engine mount/firewall amongst other things.
Noel [quote]
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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
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