Stealth Pilot wrote in
:

On Thu, 10 Jul 2008 07:54:50 +0000 (UTC), Bertie the Bunyip
wrote:

wrote in
news:801c3098-d23a-4d31-a72c-9b93ad4e5339
@m45g2000hsb.googlegroups.com:

On Jul 9, 1:24 pm, Bertie the Bunyip wrote:

I still don't see it shortening the landing roll. Can't see the
physics that would make a wheel landing shorter. I'll just have to
try it!

Here are the physics:

The trike, to get maximum weight on its mains for braking
traction, has to keep its weight off the nose. We can use full up-
elevator, but the presence of the nosewheel assures us that it will
take some of the weight and that we cannot get the wing's AOA low
enough to stop it lifting. The only advantage we have in the trike
is
the elevator's downforce added to the airplane's weight. Electric
flas
make it worse, since we can't retract them instantly to dump their
lift.

The taildragger can get its tail way up high. If you sit in
the
airplane while its tail is on a jack or some other support so that
the
airplane is in level attitude, you will be astounded at how nose-low
it feels. Observe the propeller clearance in this position, too, and
make some allowance for bouncing that might lower the prop closer to
the runway. I used to do this with students who were afraid to raise
the tail to level attitude, and they always amazed at the picture
out
the front.
A taildragger with long legs, like a 185, can get its tail even
higher than level. I've seen a shot of a Helio Courier with its tail
up so that the fuselage was pointed downward at 5 or 10 degrees, and
the pilot was braking hard. No lift at all in that scenario, and
manual flaps can be retracted quickly to get even more weight on the
wheels. Most taildraggers will have the main axles 15 degrees ahead
of
the airplane's CG, meaning that if you pick up the tail you can
raise
it until the airplane is at that 15 degree nose-low attitude and it
will be balanced there. You'd better have lots of skill if you're
going to try this in the rollout. Pilots of another humanitarian
outfit that operated Helios did this all the time, since the Helio's
short-field takeoff capabilities are of no use if you can't get into
that short little strip and get stopped in the first place.


Oh, I can do it, but I don't see it giving you any more braking. Quite
the contrary. A given braking force will apply a rotational force
around
the airplane's gear. In the three point attitude, you've got more of
the
airpane sitting behind the gear, so more braking should be available.
Also, if you touch down in the same spot three point as opposed to
doing
a wheel landing, you should have touched down with less airspeed.
Therefore less energy to kill.
For the sake of argument, let's say that you touched down at the same
speed, though, and that you are now tail high. It would want to be
very
high indeed to contribute the same amount of aerodynamic drag as the
three point attitude. OK, your Cf is a bit better because of the extra
weight on the wheels, but since the limiting factor is nosing the
airplane over as opposed to achieving max Cf that's irrelevant.


Bertie

the wings stop an aircraft more effectively than tiny brake pucks.
thats why 3 pointing it achieves the shortest landing.
the actual landing speed is lower and the wing is generating lotsa
induced drag on the backside of the performance curve.

I dont believe that getting rid of flaps shortens the landing.

Yeah, generally I agree. Depends on the airpalne, probably, but I can't
think of anything that would stop more quickly with the flaps up.
One of the things I found alarming in at least one old private pilot
course that was out there, I think it was the Jeppeson one, was advising
the pilot to push forward on the stick in a trike in order to shorten
the landing distance. The reasining was that it put more weight on the
wheels and allowed harder braking. In my experinece, if you are braking
that hard, the nosewheel is already pretty firmly on the ground and you
have enough braking already! Pushing would only put more weight on the
nosewheel at the expense of weight on the mains...
I've seen a lot of airline pilots do this, even though the Boeing
manuals specifically state to only relax up elevator enough to allow
good enough nosewheel contact in order to allow good steering.

Bertie