taildragger toe-in vs toe-out AGAIN

OK, I've researched this a fair bit and am still hearing two definite
different views. One one hand you have those that swear you need
toe-out and then on the other you have (among others- these are the
few I'm certain about) Cessna 100 series, Huskies, and Pitt's that all
are set with slight toe-in by the factory. Granted these are set
without weight on the aircraft and the toe-in may change slightly when
under load.

I think it boils down to what wins when you start to go into a turn
with a taildragger- does the toed-in outside wheel "drag" and thus
want to straighten you back out or does the toed-out outside wheel get
weight transferred to it and tend to straighten you out (vs tightening
the turn)?

Anybody with some definite answers based on physics? There's lots of
emperical and experiential opinions out there, anybody with some more
factual answers to the argument?

J oa

On 14 Nov 2003 10:07:59 -0800, (Joa) wrote:

OK, I've researched this a fair bit and am still hearing two definite
different views. One one hand you have those that swear you need
toe-out and then on the other you have (among others- these are the
few I'm certain about) Cessna 100 series, Huskies, and Pitt's that all
are set with slight toe-in by the factory. Granted these are set
without weight on the aircraft and the toe-in may change slightly when
under load.

I think it boils down to what wins when you start to go into a turn
with a taildragger- does the toed-in outside wheel "drag" and thus
want to straighten you back out or does the toed-out outside wheel get
weight transferred to it and tend to straighten you out (vs tightening
the turn)?

Anybody with some definite answers based on physics? There's lots of
emperical and experiential opinions out there, anybody with some more
factual answers to the argument?

J oa

What's wrong with putting the wheels on straight?

What's wrong with putting the wheels on straight?


Or not even fixed - like crosswind gear?

Seems to me that there might be a few parameters to many to make a "scientific"
generalization. This may be an area where it's best to just go with the
conventional wisdom, hope it works, and if it doesn't, do a bit of
experimenting.

The conventional wisdom does not work with my brand of 'dragger, but then it's
kind of odd. Q

There's lots of
emperical and experiential opinions out there, anybody with some more
factual answers to the argument?

I've pondered this thing myself. Problem with tail draggers (actually a
characteristic of aircraft and their need to have flexible gear way out on
spindly aerodynamic legs) is that toe out could change to toe in depending on
the load. This also changes during the transition from ground to flight. Worse
yet (the big problem with my plane) is the toe change as I bring the tail up on
take off or transition down during landing. Suffice to unscientificlly say that
20 years in the automotive alignment business has shown me that cars with toe
out tend to be a bit more twitchy than those with toe in. Have no idea if that
translates to aircraft because taildragger pilots EXPECT the plane to try to
swap ends.

Jim

Suffice to unscientificlly say that
20 years in the automotive alignment business has shown me that cars with toe
out tend to be a bit more twitchy than those with toe in. Have no idea if that
translates to aircraft

It does not. You want a small amount of toe out with the weight on the
wheels. Do a deja search and find some good posts on the topic.

One of the key points has to do with which way the wheels point when one
wing is up.

Ed Wischmeyer

On 15 Nov 2003 00:22:09 GMT, (JFLEISC) wrote:

There's lots of
emperical and experiential opinions out there, anybody with some more
factual answers to the argument?

I've pondered this thing myself. Problem with tail draggers (actually a
characteristic of aircraft and their need to have flexible gear way out on
spindly aerodynamic legs) is that toe out could change to toe in depending on
the load. This also changes during the transition from ground to flight. Worse
yet (the big problem with my plane) is the toe change as I bring the tail up on
take off or transition down during landing. Suffice to unscientificlly say that
20 years in the automotive alignment business has shown me that cars with toe
out tend to be a bit more twitchy than those with toe in. Have no idea if that
translates to aircraft because taildragger pilots EXPECT the plane to try to
swap ends.

Jim
+++++++++++++++++++++++

TOE IN is a NO-NO for tail draggers.
Just the reverse of cars.

Read the archives.
This has been beaten to death.
Many times.


Barnyard BOb -

On Fri, 14 Nov 2003 19:12:31 -0600, - Barnyard BOb -
wrote:

On 15 Nov 2003 00:22:09 GMT, (JFLEISC) wrote:

There's lots of
emperical and experiential opinions out there, anybody with some more
factual answers to the argument?

I've pondered this thing myself. Problem with tail draggers (actually a
characteristic of aircraft and their need to have flexible gear way out on
spindly aerodynamic legs) is that toe out could change to toe in depending on
the load. This also changes during the transition from ground to flight. Worse
yet (the big problem with my plane) is the toe change as I bring the tail up on
take off or transition down during landing. Suffice to unscientificlly say that
20 years in the automotive alignment business has shown me that cars with toe
out tend to be a bit more twitchy than those with toe in. Have no idea if that
translates to aircraft because taildragger pilots EXPECT the plane to try to
swap ends.

Jim
+++++++++++++++++++++++

TOE IN is a NO-NO for tail draggers.
Just the reverse of cars.

And many cars actually DO have a toe out spec.
The ideal is for the wheels to roll 100% straight down the road.
Depending on steering geometry, they will try to toe out, or in. The
spec is to set them toed in if they tend to toe out, and out if they
tend to toe in, so that the natural forces pull the wheels towards the
straight ahead position. GENERALLY, vehicles with front wheel drive
tend to have toe out specs. ( Austin mini (old) was 0.062 inch toe
out) - but more and more you are seeing spec of 0 +/-.
The position of the tie rod, either ahead of or behind the steering
axis had some effect, as does the position of the intersection between
the KPI and the wheel centerline (camber).

Positive camber contributes to a toe-out tendancy ( that's why cars
tend to pull to the side with the most positive camber) (also think
about the handling of a bicycle)and Negative caster has the same
tendancy.
On an aircraft landing gear, the camber is self evident - and the
"effective" camber changes with load, and is effected by "unballanced"
landings (one wheel first). If the landing gear has "caster" it
changes between tail-up and tail-down attitudes. The different
combinations of uneven loading and landing attitudes will all effect
the "toe" behaviour of the wheel - so it is dangerous to make a
statement that either toe out or toe in is NECESSARILY more desirable
on a particular plane.


Read the archives.
This has been beaten to death.
Many times.


Barnyard BOb -

On 14 Nov 2003 04:12 PM, - Barnyard BOb - posted the following:

TOE IN is a NO-NO for tail draggers.
Just the reverse of cars.

One of the instructors at the local A&P school tried to convince me
otherwise, unsuccessfully, I might add.

----------------------------------------------------
Del Rawlins-
Remove _kills_spammers_ to reply via email.
Unofficial Bearhawk FAQ website:
http://www.rawlinsbrothers.org/bhfaq/

(Joa) wrote in message . com...
OK, I've researched this a fair bit and am still hearing two definite
different views. One one hand you have those that swear you need
toe-out and then on the other you have (among others- these are the
few I'm certain about) Cessna 100 series, Huskies, and Pitt's that all
are set with slight toe-in by the factory. Granted these are set
without weight on the aircraft and the toe-in may change slightly when
under load.

I just pulled out my copy of Ladislao Pazmanys "Landing Gear Design
For Light Aircraft, Volume I", and he comes to no conclusion either.

I think it boils down to what wins when you start to go into a turn
with a taildragger- does the toed-in outside wheel "drag" and thus
want to straighten you back out or does the toed-out outside wheel get
weight transferred to it and tend to straighten you out (vs tightening
the turn)?

My take on the physics is that the inertial forces generated in even
an incipient groundloop are WAY bigger than the restoring forces that
either of these possible mechanisms could generate.

Anybody with some definite answers based on physics? There's lots of
emperical and experiential opinions out there, anybody with some more
factual answers to the argument?

Not that I'm aware of.

Chapter 3 of this reference does go into the forces and couples
involved in a ground loop, in a qualatative way. Simply put, the
gross geometry of the airplane seems to have more to do with it than
the fine geometery of the wheel alignment.

On 14 Nov 2003 10:07:59 -0800, (Joa) wrote:

OK, I've researched this a fair bit and am still hearing two definite
different views. One one hand you have those that swear you need
toe-out and then on the other you have (among others- these are the
few I'm certain about) Cessna 100 series, Huskies, and Pitt's that all
are set with slight toe-in by the factory. Granted these are set
without weight on the aircraft and the toe-in may change slightly when
under load.

I think it boils down to what wins when you start to go into a turn
with a taildragger- does the toed-in outside wheel "drag" and thus
want to straighten you back out or does the toed-out outside wheel get
weight transferred to it and tend to straighten you out (vs tightening
the turn)?

Anybody with some definite answers based on physics? There's lots of
emperical and experiential opinions out there, anybody with some more
factual answers to the argument?

J oa

this has been done to death with adherents in both camps who may not
have ever flown taildraggers.

I fly a Wittman W8 Tailwind. (about 220 hours now)

my experience is that the geometry of the undercart does not correct
for groundloop tendency. it's influences in the forces at play are
fairly minor, HOWEVER having slight toe out is buckets better than
slight toe in because in the swerve of an impending groundloop the
inertia of the aircraft will lift all the weight off of the inboard
wheel (so it doesnt matter where it points really) and will place all
the weight on the outboard (outer edge of the turn) wheel. in this
condition slight toe out will have the wheel pointing in the direction
of forward travel and so it will not be working against your efforts
with rudder to straighten out the aircraft. toe in would provide just
that little bit more of a tendency to groundloop that you need to
overcome with rudder force.

now the order of toe out on my tailwind is not extreme.
in tail up takeoff position with the full aircraft weight on the
axles, ( the aircraft sitting with the bare axles on pine boards and
the fuselage level, ie without the 5.00x5 wheels on) the axles are
slightly lower at the outer end than the inner (about 5mm) and are
slightly more aft at the outer end than the inner end (again about
5mm).

while that setup works ok with the tailwind and it's taper spring legs
you might want to look closely at other aircraft with similar gear
geometries to what you are interested in before deciding.
I've been told that the RV6 has interesting gear behaviour under
deflection which is different from the tailwind.
Stealth Pilot