Some tailwheel questions/comments

On 25 Sep, 20:35, john smith wrote:
In article . com,

wrote:
What my instructor seemed to imply (and things didn't really sink in
till about a day after the flying) was that the takeoff roll is more
stable when the tail is up. So I was wondering if the CG shifts
forward when the tail is raised because this is a more stable
configuration than when the CG is behind the main wheels.

This is basic piloting 101.
Have you calculated the takeoff CG?
What can you do to make the CG change?
How is what you described above going to influence the CG location on
takeoff or landing?
Answer those questions and you will have answered your own.


He means that the CG changes in relation to it's distance from the
mains, which it does, but it isn't really significant to what he was
taling about anyway.

Bertie

On 25 Sep, 20:47, wrote:
This is basic piloting 101.
Have you calculated the takeoff CG?
What can you do to make the CG change?
How is what you described above going to influence the CG location on
takeoff or landing?
Answer those questions and you will have answered your own.

The airplane is not a rigid body from a physics point of view, so the
CG can change, maybe not by much but I dont know enough about the
tailwheel to know if it moves just a little bit forward which may be
all it takes to make it "more" stable. Basic 101 piloting may not
always be enough to answer every question.

Well, the CG doesn't change, (disregarding fuel burn and such) but
it's position in relation to things like the Cl and the point where
the wheels touch the ground can change depending on what you're
doing. The example of the aircraft in a level attitude as opposed to
three point is one such case, but in general, it's not really
significant to the way you control the aircraft. It's worth knowing
about, but not getting excited about.


Bertie

On 25 Sep, 20:28, wrote:
On Sep 25, 8:05 am, Bertie the Bunyip wrote:





Little Endian wrote in news:1190700037.145345.27050
@y42g2000hsy.googlegroups.com:

This weekend I began my tailwheel endorsement endeavor and had a
lesson in a shiny 160 hp Citabria. It was great fun but the stick and
rudder forces seemed pretty heavy compared to the C-150 I am used to.
The trim was in an unfamiliar position and I didn't get used to using
it enough on the first flight perhaps. However are there tailwheels
that are lighter to handle than the citabria?
The other issue I was wondering about: does the position of the CG
shift when the tail is raised? So is the tailwheel more stable while
taxing at a higher speed on the two front wheels? In other words, I am
wondering if a tailwheel taxing with the tail raised has a similar CG
position to a tricycle gear airplane.

Not really, and I'd be surprised if you could taxi a Citabria with the
tailwheel raised anyway. Easy in a cub, though.

The problem with the Citabria is it's a bit too easy for tailwheel
conversion. You'll get the basics, but if you try a cub afterwards you'll
find it significantly more difficult, wheras the other way around would be
a piece of cake. Citabria is a good airplane, but it's not the best
tailwheel trainer for that reason. However, it will certainly do in a
pinch!
The CG doesn't change significantly when the tail is raised, though, to
answer your question, and fast taxiing is something best left to someone
with a LOT of tailwhel time. Taxiing on the mains is something best left to
airshow pilots or guys that can afford to replace props as easily as they
would buy a cup of coffee.
Now ask me how I know this.

Bertie

It's not that hard at all. I've taxied down the runway on one main.

Yeah, I know you can do it but it takes an outrageous amount of brake
and power to do it in a Citabria. Or a 180 for that matter.
It's a lot easier in a cub but in any case it's a sure way for a
student to bend a prop..
Not only that you wear the brakes quickly and suck half the airport up
through your prop.





I've taught students that if they're having trouble waking their feet
up or can't seem to get the cross-control set up for a crosswind. I've
brought both the Citabria and 185 pretty much to a halt with the
brakes before setting the tail down. I've done tail-high/nose-low
braking, using a tiny bit of power for elevator authority, to get
weight on the mains and stop really short. You have to realize that
you are flying a taildragger ALL the time, not just when it's in the
air.

Yep,


Bertie

On Sep 25, 3:11 pm, Bertie the Bunyip
wrote:

Yes, sounds like you got the idea. An awful lot of airplanes end up on
their nose (particularly Supercubs for some reason) because the pilot
turns downwind quickley using a bit of brake at the same time.

Bertie

Some quick ways to get a taildragger up on its nose:
-Using lots of brake in the rollout without using elevator to maintain
attitude. And holding the brakes on hard even when the speed is gone.
-Taxiing too fast downwind and either losing control (no airflow over
the surfaces; got to fly a taildragger all the time, remember?) and
initiating a groundloop, or turning too quickly out of a tailwind. The
wind against the side of the fuselage, under the upwind wing and under
the stab combines with centrifugal force to lift a wheel, whereupon
the downwind wing drags on the surface, and now that more wind can get
at the wing and stab, there's more lift, the tail comes up, and
inertia through the CG and against the dragging wing does the rest.
-With CG forward (nobody in the back), doing a runup without holding
the elevator back will lift the tail of many taildraggers. As the tail
comes up, the angle between the CG and the locked mains decreases so
that the tail gets even lighter, and over she goes. Happens if the
pilot has his head in the cockpit and isn't paying attention to what's
going on outside. Can happen, too, if the pilot is trying to taxi
through deep snow or gooey mud.

Dan

On Sep 25, 12:39 pm, wrote:
Not really, and I'd be surprised if you could taxi a Citabria with the
tailwheel raised anyway. Easy in a cub, though.

Firstly this isnt a troll and if somebody feels it is, they simply
need to ignore it, thats how usenet works. Anyways, the question was
based more on what I saw on the takeoff run where we raise the tail as
airspeed increases. It just felt more stable and more like a
conventional gear takeoff run in that phase, so I was just wondering.
The intent of the question wasn't about how to taxi at a high speed.

The problem with the Citabria is it's a bit too easy for tailwheel
conversion. You'll get the basics, but if you try a cub afterwards you'll
find it significantly more difficult, wheras the other way around would be
a piece of cake. Citabria is a good airplane, but it's not the best
tailwheel trainer for that reason. However, it will certainly do in a
pinch!

Thanks for the tip, I have been looking to find a place to learn in a
cub but the closest one is about 70 miles away, so that may have to
wait.

The CG doesn't change significantly when the tail is raised, though, to
answer your question, and fast taxiing is something best left to someone
with a LOT of tailwhel time. Taxiing on the mains is something best left to
airshow pilots or guys that can afford to replace props as easily as they
would buy a cup of coffee.

What my instructor seemed to imply (and things didn't really sink in
till about a day after the flying) was that the takeoff roll is more
stable when the tail is up. So I was wondering if the CG shifts
forward when the tail is raised because this is a more stable
configuration than when the CG is behind the main wheels.

OK, I'm just a student pilot, and not a taildragger student either.
But I know a little physics. The CG is still behind the mains even
with the tail up. It is possible that the airplane would feel more
stable in yaw when it is accelerating, however. Since the center of
gravity is being pulled along behind the propeller, I would think the
airplane would tend to stay in line. This ignores other influences
like crosswinds and the torque effects of the prop which would tend to
counter this. And it won't help you in taxiing when you are moving at
a constant speed.

OK, I'm just a student pilot, and not a taildragger student either.
But I know a little physics. The CG is still behind the mains even
with the tail up. It is possible that the airplane would feel more
stable in yaw when it is accelerating, however. Since the center of
gravity is being pulled along behind the propeller, I would think the
airplane would tend to stay in line. This ignores other influences
like crosswinds and the torque effects of the prop which would tend to
counter this. And it won't help you in taxiing when you are moving at
a constant speed.

Yes, you are right about the CG not changing, I was probably
mistakenly thinking that the CG moves forward relative to the ground
as the airplane nose is "lowered" but I think that's not correct. The
stability in a level attitude while taxing probably also comes from
the fact that the P-factor is gone and there is no turning tendency
any more.

On Sep 25, 11:37 pm, wrote:
OK, I'm just a student pilot, and not a taildragger student either.
But I know a little physics. The CG is still behind the mains even
with the tail up. It is possible that the airplane would feel more
stable in yaw when it is accelerating, however. Since the center of
gravity is being pulled along behind the propeller, I would think the
airplane would tend to stay in line. This ignores other influences
like crosswinds and the torque effects of the prop which would tend to
counter this. And it won't help you in taxiing when you are moving at
a constant speed.

Yes, you are right about the CG not changing, I was probably
mistakenly thinking that the CG moves forward relative to the ground
as the airplane nose is "lowered" but I think that's not correct. The
stability in a level attitude while taxing probably also comes from
the fact that the P-factor is gone and there is no turning tendency
any more.

Thrust acts along the centerline whether the airplane is
tracking straight or not, whether the CG is behind the mains or in
front. The only time thrust is a little off is when the AOA is high
(tail low) and the downgoing blade has more pull (P-factor). The
airplane will still want to pull left with the tail up due to the
swirl of the prop slipstream striking the left side of the fin, and a
small amount caused by more pressure on the left main due to engine
torque reaction. Raising the tail will make the nose swerve left, a
gyroscopic precession caused by the prop's rotating mass.
Whatever the airplane tries to do, you have to be ready for it
and not afraid to use ALL the controls rather aggressively to show it
who's boss. It won't fly itself.

Dan