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Old Feb 21, 2012, 04:50 PM
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Old Feb 21, 2012, 06:00 PM
I'm a pilot... 100 yrs to late
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Tail dragger doesnt have any effect on incidence... (in my opinion) The wheels sound to be in a good spot. I usually put my conversions where the front of the whell is just peeking out beyong the leading edge when looking straight down. But ballpark will work fine. You just don't want it to far back where it will nose over easily so you want the pivot ahead of the CG.

The tail will come up quickly and the incidence is the same as a trike at that point. You'll need to apply right rudder as you increase power on takeoff.. different planes take different amounts.
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Old Feb 21, 2012, 07:15 PM
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where's my axle?

You did good! the axle always wants to be a skoche ahead of the wing leading edge for starters...and if you're not happy with that,shim it a little till you are.

There was a formula that we used,'way back,prolly still works.Mark the thrust line on the fuse with tape,momentarily.Find the C/G,and draw a line square off the thrust line to the C/G...from that dot,mark a line at 17 degrees down to the axle.
This method takes into account the relationship of the axle with the C/G,in the case of tapered wings or low wings....and especially biplanes.

If I confused you ,sorry...your way is good,also.
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Old Feb 21, 2012, 09:51 PM
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Old Feb 21, 2012, 09:57 PM
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You are OK with the gear where you put it. A couple of my planes have the axle a tad forward of the leading edge and ground track well. It helps if you put a small amount of toe in on the wheels.
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Old Feb 21, 2012, 11:24 PM
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Old Feb 23, 2012, 10:42 AM
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Quote:
Originally Posted by Fokker DII View Post
You are OK with the gear where you put it. A couple of my planes have the axle a tad forward of the leading edge and ground track well. It helps if you put a small amount of toe in on the wheels.
Don't want to start a debate, but if you have a problem with ground-loops you might want to try toe-out, per EAA article.
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Old Feb 23, 2012, 11:15 AM
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Originally Posted by gyrocptr View Post
Don't want to start a debate, but if you have a problem with ground-loops you might want to try toe-out, per EAA article.
Chickens and eggs again.I'm no toe stepper-onner,so let's be adult right at the beginning..I'm not going to try to convince anyone what is correct..I will,however say what works for me. Let's add toe out,1/8 inch,on a 1/4 scale taildragger.A 'ground loop' is when the tail decides to be first,even if you don't want it to be.(should always be the prop first)
When you start the take-off roll,both wheels are now pointed at their own side of the runway,but they're dragging sideways a little bit.If the airplane starts to the right,(for example)then the LEFT wheel is rolling straight down the runway with no side-scuffing.But the right one is scuffing harder now,so that wheel is dragging back,increasing the right turn until you spin around,unless you CAN correct with Rudder or Brake.
But if you have 1/8" toe IN,then if the aircraft drifts to the right,now the LEFT wheel is scuffing,and helps pull it back straight...
.Ideally,at tail-up takeoff position NO offset is present in the wheels,so that the rudder only has to overcome drift,not wheel drag.
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Old Feb 23, 2012, 11:23 AM
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Originally Posted by epoxyearl View Post
Chickens and eggs again.I'm no toe stepper-onner,so let's be adult right at the beginning..I'm not going to try to convince anyone what is correct..I will,however say what works for me. Let's add toe out,1/8 inch,on a 1/4 scale taildragger.A 'ground loop' is when the tail decides to be first,even if you don't want it to be.(should always be the prop first)
When you start the take-off roll,both wheels are now pointed at their own side of the runway,but they're dragging sideways a little bit.If the airplane starts to the right,(for example)then the LEFT wheel is rolling straight down the runway with no side-scuffing.But the right one is scuffing harder now,so that wheel is dragging back,increasing the right turn until you spin around,unless you CAN correct with Rudder or Brake.
But if you have 1/8" toe IN,then if the aircraft drifts to the right,now the LEFT wheel is scuffing,and helps pull it back straight...
.Ideally,at tail-up takeoff position NO offset is present in the wheels,so that the rudder only has to overcome drift,not wheel drag.
To each his own. Each person can read the rationale in the EAA article, and use the setup that works for him.
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Old Feb 23, 2012, 12:01 PM
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Just my experience but I have always found toe in to be beneficial and toe out a recipe for ground loops, especially on short coupled bipes.
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Old Feb 23, 2012, 05:32 PM
Zor
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interesting articles

Quote:
Originally Posted by epoxyearl View Post
Chickens and eggs again.I'm no toe stepper-onner,so let's be adult right at the beginning..I'm not going to try to convince anyone what is correct..I will,however say what works for me. Let's add toe out,1/8 inch,on a 1/4 scale taildragger.A 'ground loop' is when the tail decides to be first,even if you don't want it to be.(should always be the prop first)
When you start the take-off roll,both wheels are now pointed at their own side of the runway,but they're dragging sideways a little bit.If the airplane starts to the right,(for example)then the LEFT wheel is rolling straight down the runway with no side-scuffing.But the right one is scuffing harder now,so that wheel is dragging back,increasing the right turn until you spin around,unless you CAN correct with Rudder or Brake.
But if you have 1/8" toe IN,then if the aircraft drifts to the right,now the LEFT wheel is scuffing,and helps pull it back straight...
.Ideally,at tail-up takeoff position NO offset is present in the wheels,so that the rudder only has to overcome drift,not wheel drag.
I find this article (above) quite interesting because of its technical nature and also because of its limitations.

The toe in and toe out is a matter of angle and not a matter of dimensional figure.

We cannot talk of 1/8 inch without taking into account the diameter of the wheels.

I realize the reference is of a 1/4 scale tail dragger but there is no assurance that the wheels are exact scale and it leaves us searching for the diameter of the wheels so we have a fair idea of the angle involved.

Some factors that logically affect the results are not taken into account.

The subject of toe in versus toe out is tryng to analize the results of their effect. One article says that toe in has the effect of decreasing the turn (yaw) because on a turn (either way) the wheel outside the turn has more angle to the trajectory while the inner wheel beocmes better lined up so the friction of the outer wheel help bring the trajectory opposie the initial turn.

That seems to make some good sense.

The pdf article seem to emphasize the weight distribution on the wheels due to the CG being higher than the ground contact of the wheels.

The wheel resistance to rotation would not be much affected by the weight it is supporting if we consider its rotation in its orientation.

True enough that with a toe out the initial yaw would bring the outer wheel more in line with the trajectory but we cannot neglect the drag on the inner wheel even if it has a bit less weight to support.

The drag of this inner wheel can be just as much rearward whether it is supporitn 50% of the main gears weight or only 40% and even less.

The outer wheel of the toe out has nearly no backward resistance but the inner wheel still has more than the outer wheel due to its trying to steer to its own direction (orientation) and scrapping partly sideway.

From the above reasoning I vote in favor of the toe in.

I observed that both articles are NOT discussing the amount of angle of the toe in and toe out nor such things as tire flexing sideways.

Now let us have a look as to why a toe in is desirable and at the amount of angle that should be used.

Our landing gears must have some flexibility to absorb the landing impact.
It means that some elasticity exist. since the impact is not only upward but often rearward (nose too far down) and the wheels are outside the axle support then he wheels have a endency to turn outward on impact.

As the wheels turn outward it has a tendency to spread out the wheel to wheel distance reducing the impact absorbtion. The toe in partly cancel that effect by trying to bring the wheels closer together.

How much toe in ?
I is not critical. Usually 1 to 2 degrees for each wheel is a good general practice. Who decides that ? YOU DO .

Zor
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Old Feb 25, 2012, 10:27 PM
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aha

Zor; I do not delve as deeply as others into the inner workings of many systems in the model aircraft and engines,and especially the radios.
I'm more of an experimenter. "let's try this".In the case of toe-in versus toe out, when I investigated my wheel alignment,there was noticeable toe-out...and since I didn't like the ground looping tendency,my reasoning was simple-that ain't working.
Hmm..what shall we do?Let's try the opposite! no paper work,no engineering,and no measuring of angles...just bend it the other way! That worked!...It's fixed.
I appreciate your explanation of the theory..but I don't know if 1/8" toe-in between two 4" wheels is any different than,say,2 degrees..My point,to the layman,is 'try this'..if you've cured the unwanted tendency,WE WIN.!
I'm unwilling to say that I have the correct amount,because I haven't tried a different setting.
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Old Feb 25, 2012, 10:36 PM
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Old Feb 25, 2012, 11:07 PM
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gone in 60 seconds

Cherokeenut..sorry about the short flight,man.

Maybe a ground loop would have been better...OH NO he dih-nt.
sorry man-it was right there!lol

Yeah you can't know to check for every thing..were they supposed to be screwed in place?
or how are they fastened in there?
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Old Feb 25, 2012, 11:17 PM
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