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bouncing off the runway



 
 
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  #21  
Old June 27th 08, 01:02 AM posted to rec.aviation.piloting
Bertie the Bunyip[_24_]
external usenet poster
 
Posts: 2,969
Default bouncing off the runway

"Robert M. Gary" wrote in news:249fc31e-dca1-4ea9-a824-
:

On Jun 26, 11:14*am, "Ol Shy & Bashful" wrote:
On Jun 26, 11:49*am, "Robert M. Gary" wrote:

On Jun 26, 7:25*am, E Z Peaces wrote:


Doesn't a three-point landing occur at stall speed? *


That is one of the biggest myths in aviation. I've flown a lot of
taildraggers (GA) and few of them had the stall angle and the 3 pt
angle in alignment. As an example the Globe Swift stalls with the tail
about 2 feet off the ground while the Decathlon/Citabria stalls with
the tail on the ground and the mains still several feet in the air,
its very, very much still flying in the 3pt position. The hard part of
landing a Citabria is not to crush the mains after landing the tail.


-Robert, CFII


Bull****!


I'll be happy to provide you a tailwheel checkout.

-Robert


Hopefully not in a Swift!


Bertie
Ads
  #22  
Old June 27th 08, 01:05 AM posted to rec.aviation.piloting
E Z Peaces
external usenet poster
 
Posts: 8
Default bouncing off the runway

Ol Shy & Bashful wrote:
On Jun 25, 10:00 pm, E Z Peaces wrote:
Yesterday I chatted with a retired man flying a model airplane. He said
he'd taken lessons in a plane with conventional gear in the 1950s. On
his third lesson, the instructor had him land. It was perfect.

After that, every time he landed he would bounce and float above the
runway. His instructor didn't know what caused it. A senior instructor
went up with him and observed that when he touched down, he didn't
continue to hold the stick back. That caused the tail to rise and the
plane to lift off.

That doesn't make sense to me. I've always understood that with
conventional gear, excess speed is the cause of bouncing and floating.
With the main wheels forward of the center of mass, your angle of attack
will increase when you touch down, and the plane will rise if you still
have flying speed.

If a pilot touches down too fast, I've understood that he needs to keep
the tail up and use the brakes without nosing over.

If the instructor had told him he was touching down too fast because he
wasn't holding the stick back far enough during descent, that would make
sense to me because a higher angle of attack induces more drag.

The man said the problem was that he had failed to keep the stick back
after touchdown. Does his recollection make sense?


Are you kidding? After nearly 60 years the recollections of a 3 hour
student have any validity? The VAST majority of botched landings are
due to flawed airspeed control and it doesn't matter what kind of
airplane. Many instructors fail to recognize that, or, fail to do
anything about it, especially when instructing. I see it all the time,
harp about it daily,and continue to mentor less experienced pilots on
this.
In the case of taildraggers specifically, if the airspeed and vertical
speed are not controlled, it will nearly guarantee a bounce with
predictable control problems. For a three point to be executed
properly, the airspeed MUST be near stall as in within Vso+ 5 mph or
less. Anything in excess of that must be dissapated during the flare/
roundout or touchdown and will result in an unpredictable touchdown
point.
Now, are you talking about a full stop landing? Then the touchdown
speed should be as low as possible. Are you talking about a gusty
cross wind? Then you have a different set of conditons to deal with.
Not to be a pushy butthead but I've got at least 6-7000 hours in
tailwheel aircraft crop dusting in a broad variety of aircraft
including twin engined and a lot of time instructing in them (couple
of thousand hrs..?)
taking a deep breath and just sitting back now .....
Ol S&B
p.s. I realize you were asking and not postulating so please don't
feel I was being gruff towards you personally?


Thank you very much! I was postulating. From what I knew, a perfect
landing with conventional gear means stalling so low that the wheels
touch down gently, and you can't rise again unless you're going too
fast. I lacked the experience to know if there was any way his
recollection of the cause of his problem could be correct.

I've never had a flying lesson. About second grade I began reading
books about the mechanics of aircraft. Through my teens I often held
papers at arm's length, curved for rigidity, to get a feel for the
relationship between speed, angle of attack, lift, and drag. I studied
pilot manuals for the Thunderbolt and the Mustang and and cockpit photos
of other aircraft. I liked to pedal to the airport and watch the
mechanic work.

In the high-school library I found a 1948 book by an instructor named
Lang, I think. It explained concepts learned from experience rather
than laymen's theory. Throttle for vertical speed, elevator for
airspeed. Ailerons for direction, rudder to center the ball. If you
want to know where you're going, watch the way the scenery shifts
against the windshield.

As a CAP cadet, I was assigned to the simulator room at an Air Force
base the summer I was 17. Those simulators had frosted windshields and
no video. Other cadets tried and failed with the F-106. I was the only
one to try the B-25. I wasn't familiar with bomber cockpits, but the
individual instruments and controls were familiar. I toured Boston by
radar, returned to the base, set the flaps, guessed a reasonable descent
speed, and followed the instruments in, using the elevator for airspeed
and the throttle for descent.

In view of my awe of flight, it was disappointingly easy. The sergeant
in the control booth played with me on my second flight. I had various
problems including an engine fire and loss of hydraulics. Books had
told me how to respond to such emergencies, and I made another adequate
landing. Then a pilot came in to log some training time.

The following October a parent in the squadron invited me flying. His
invitation was very brief. I hadn't known he had a plane because he'd
never spoken to me before. It was a Cessna 310.

At the airport, he told the other three to sit in back and me in front,
on the left. That was the second time he'd spoken to me. I figured he
wanted me in front because I was taller.

At 3,000 feet he told me, "Take over." I thought he intended to let me
guide it a minute or so, but he didn't speak again, so I spent twenty
minutes touring. I would have liked to hedgehop but refrained because I
didn't have permission.

Eventually he told me to find the airport. I knew the terrain and had a
compass, and before long the airport was in sight. When we were almost
there he said, "Traffic pattern is to the left." I'd forgotten that. I
steered right and began circling left.

Then he said, "Runway 1." That would mean a complete circle. I brought
him around to a point far enough out that I thought he'd have a
reasonable glide path. Instead of taking over, he cut the throttle to a
whisper, dropped the gear, and set the flaps. He told me the descent
speed. That was the fifth thing he'd said to me since taking off. I
think he was the last thing he ever said to me. From a couple of miles
out I could see we were overshooting the end of the runway, so I reduced
our speed slightly by raising the nose.

As we got closer, I saw a gusty crosswind on the sock. The other runway
would have been better but he said nothing. He'd know how to handle the
crosswind. He'd also know how to flare. I didn't know our rate of
descent but figured we'd crash into the runway if he didn't flare or if
he flared too soon.

We were down around treetop level when I realized there was no longer
time for him to take over. How could I flare safely without knowing our
stall speed or how the aircraft would respond? In climbing aboard I
hadn't noted the height of the window above the wheels. It seemed only
realistic to predict that in two more seconds we would be a ball of
flame. Still, I wouldn't have missed this opportunity for the world.
At least I had tricycle gear, which tolerates landing too fast and
crosswinds.

As I flared, the sock showed a big gust from the left. Would we be
drifting right when we touched down? I knew a responsible pilot would
have let the gear absorb the stress, but I was a perfectionist novice.
I dipped the left wing while kicking right rudder to stay aligned with
the runway, then picked the wing back up. That was to skid into the
crosswind. It seemed risky because I didn't know how well the airplane
would respond at that speed and with the mass of the tanks on the wingtips.

I expected a vertical bump and a lateral lurch. Instead, tire vibration
was the only clue that we had contacted the runway. I didn't need
brakes. When it was clear that we would need throttle to make it to the
parking area, the pilot took over without a word.

Beginner's luck: that deadstick landing in a crosswind was my first and
last opportunity to fly an airplane.
  #23  
Old June 27th 08, 01:56 AM posted to rec.aviation.piloting
Bertie the Bunyip[_24_]
external usenet poster
 
Posts: 2,969
Default bouncing off the runway

E Z Peaces wrote in
:

Ol Shy & Bashful wrote:
On Jun 25, 10:00 pm, E Z Peaces wrote:
Yesterday I chatted with a retired man flying a model airplane. He
said he'd taken lessons in a plane with conventional gear in the
1950s. On his third lesson, the instructor had him land. It was
perfect.

After that, every time he landed he would bounce and float above the
runway. His instructor didn't know what caused it. A senior
instructor
went up with him and observed that when he touched down, he didn't
continue to hold the stick back. That caused the tail to rise and
the plane to lift off.

That doesn't make sense to me. I've always understood that with
conventional gear, excess speed is the cause of bouncing and
floating. With the main wheels forward of the center of mass, your
angle of attack will increase when you touch down, and the plane
will rise if you still have flying speed.

If a pilot touches down too fast, I've understood that he needs to
keep the tail up and use the brakes without nosing over.

If the instructor had told him he was touching down too fast because
he wasn't holding the stick back far enough during descent, that
would make sense to me because a higher angle of attack induces more
drag.

The man said the problem was that he had failed to keep the stick
back after touchdown. Does his recollection make sense?


Are you kidding? After nearly 60 years the recollections of a 3 hour
student have any validity? The VAST majority of botched landings are
due to flawed airspeed control and it doesn't matter what kind of
airplane. Many instructors fail to recognize that, or, fail to do
anything about it, especially when instructing. I see it all the
time, harp about it daily,and continue to mentor less experienced
pilots on this.
In the case of taildraggers specifically, if the airspeed and
vertical speed are not controlled, it will nearly guarantee a bounce
with predictable control problems. For a three point to be executed
properly, the airspeed MUST be near stall as in within Vso+ 5 mph or
less. Anything in excess of that must be dissapated during the flare/
roundout or touchdown and will result in an unpredictable touchdown
point.
Now, are you talking about a full stop landing? Then the touchdown
speed should be as low as possible. Are you talking about a gusty
cross wind? Then you have a different set of conditons to deal with.
Not to be a pushy butthead but I've got at least 6-7000 hours in
tailwheel aircraft crop dusting in a broad variety of aircraft
including twin engined and a lot of time instructing in them (couple
of thousand hrs..?)
taking a deep breath and just sitting back now .....
Ol S&B
p.s. I realize you were asking and not postulating so please don't
feel I was being gruff towards you personally?


Thank you very much! I was postulating. From what I knew, a perfect
landing with conventional gear means stalling so low that the wheels
touch down gently, and you can't rise again unless you're going too
fast. I lacked the experience to know if there was any way his
recollection of the cause of his problem could be correct.

I've never had a flying lesson. About second grade I began reading
books about the mechanics of aircraft. Through my teens I often held
papers at arm's length, curved for rigidity, to get a feel for the
relationship between speed, angle of attack, lift, and drag. I
studied pilot manuals for the Thunderbolt and the Mustang and and
cockpit photos of other aircraft. I liked to pedal to the airport and
watch the mechanic work.

In the high-school library I found a 1948 book by an instructor named
Lang, I think. It explained concepts learned from experience rather
than laymen's theory. Throttle for vertical speed, elevator for
airspeed. Ailerons for direction, rudder to center the ball. If you
want to know where you're going, watch the way the scenery shifts
against the windshield.

As a CAP cadet, I was assigned to the simulator room at an Air Force
base the summer I was 17. Those simulators had frosted windshields
and no video. Other cadets tried and failed with the F-106. I was
the only one to try the B-25. I wasn't familiar with bomber cockpits,
but the individual instruments and controls were familiar. I toured
Boston by radar, returned to the base, set the flaps, guessed a
reasonable descent speed, and followed the instruments in, using the
elevator for airspeed and the throttle for descent.

In view of my awe of flight, it was disappointingly easy. The
sergeant in the control booth played with me on my second flight. I
had various problems including an engine fire and loss of hydraulics.
Books had told me how to respond to such emergencies, and I made
another adequate landing. Then a pilot came in to log some training
time.

The following October a parent in the squadron invited me flying. His
invitation was very brief. I hadn't known he had a plane because he'd
never spoken to me before. It was a Cessna 310.

At the airport, he told the other three to sit in back and me in
front, on the left. That was the second time he'd spoken to me. I
figured he wanted me in front because I was taller.

At 3,000 feet he told me, "Take over." I thought he intended to let
me guide it a minute or so, but he didn't speak again, so I spent
twenty minutes touring. I would have liked to hedgehop but refrained
because I didn't have permission.

Eventually he told me to find the airport. I knew the terrain and had
a compass, and before long the airport was in sight. When we were
almost there he said, "Traffic pattern is to the left." I'd forgotten
that. I steered right and began circling left.

Then he said, "Runway 1." That would mean a complete circle. I
brought him around to a point far enough out that I thought he'd have
a reasonable glide path. Instead of taking over, he cut the throttle
to a whisper, dropped the gear, and set the flaps. He told me the
descent speed. That was the fifth thing he'd said to me since taking
off. I think he was the last thing he ever said to me. From a couple
of miles out I could see we were overshooting the end of the runway,
so I reduced our speed slightly by raising the nose.

As we got closer, I saw a gusty crosswind on the sock. The other
runway would have been better but he said nothing. He'd know how to
handle the crosswind. He'd also know how to flare. I didn't know our
rate of descent but figured we'd crash into the runway if he didn't
flare or if he flared too soon.

We were down around treetop level when I realized there was no longer
time for him to take over. How could I flare safely without knowing
our stall speed or how the aircraft would respond? In climbing aboard
I hadn't noted the height of the window above the wheels. It seemed
only realistic to predict that in two more seconds we would be a ball
of flame. Still, I wouldn't have missed this opportunity for the
world. At least I had tricycle gear, which tolerates landing too fast
and crosswinds.

As I flared, the sock showed a big gust from the left. Would we be
drifting right when we touched down? I knew a responsible pilot would
have let the gear absorb the stress, but I was a perfectionist novice.
I dipped the left wing while kicking right rudder to stay aligned with
the runway, then picked the wing back up. That was to skid into the
crosswind. It seemed risky because I didn't know how well the
airplane would respond at that speed and with the mass of the tanks on
the wingtips.

I expected a vertical bump and a lateral lurch. Instead, tire
vibration
was the only clue that we had contacted the runway. I didn't need
brakes. When it was clear that we would need throttle to make it to
the parking area, the pilot took over without a word.

Beginner's luck: that deadstick landing in a crosswind was my first
and last opportunity to fly an airplane.


Sniff. Anyone smell a sock?

Bertie
  #24  
Old June 27th 08, 02:17 AM posted to rec.aviation.piloting
E Z Peaces
external usenet poster
 
Posts: 8
Default bouncing off the runway

Bertie the Bunyip wrote:
E Z Peaces wrote in
:


I've read about oleo aircraft struts at least as early as the 1920s.


Theyre not dampers, they're oleos and provide no damping. Shock
absorbers are something different and have a different function, though
tey're misnamed in any case, since its the springs that absorb and the
shicks, as they;'re called, prevent the energy stored in the spring from
rebounding the wheel off the road. Airplanes don't have shock absorbers.


Here's an example:
http://www.hangar9aeroworks.com/Aero...oncastrut.html
  #25  
Old June 27th 08, 03:10 AM posted to rec.aviation.piloting
Bertie the Bunyip[_24_]
external usenet poster
 
Posts: 2,969
Default bouncing off the runway

E Z Peaces wrote in
:

Bertie the Bunyip wrote:
E Z Peaces wrote in
:


I've read about oleo aircraft struts at least as early as the 1920s.


Theyre not dampers, they're oleos and provide no damping. Shock
absorbers are something different and have a different function,
though tey're misnamed in any case, since its the springs that absorb
and the shicks, as they;'re called, prevent the energy stored in the
spring from rebounding the wheel off the road. Airplanes don't have
shock absorbers.


Here's an example:
http://www.hangar9aeroworks.com/Aero...oncastrut.html


Yeah, I know,. I was flying one a couple of days ago and I've had them
apart, too.
It does little or nothing to stop a bounce in spite of it's name. I can
also stater that categorically since I was training two ab-initio tailwheel
pilots in it.




Bertie
  #26  
Old June 28th 08, 12:27 AM posted to rec.aviation.piloting
E Z Peaces
external usenet poster
 
Posts: 8
Default bouncing off the runway

Bertie the Bunyip wrote:
E Z Peaces wrote in
:

Bertie the Bunyip wrote:
E Z Peaces wrote in
:

I've read about oleo aircraft struts at least as early as the 1920s.
Theyre not dampers, they're oleos and provide no damping. Shock
absorbers are something different and have a different function,
though tey're misnamed in any case, since its the springs that absorb
and the shicks, as they;'re called, prevent the energy stored in the
spring from rebounding the wheel off the road. Airplanes don't have
shock absorbers.

Here's an example:
http://www.hangar9aeroworks.com/Aero...oncastrut.html


Yeah, I know,. I was flying one a couple of days ago and I've had them
apart, too.
It does little or nothing to stop a bounce in spite of it's name. I can
also stater that categorically since I was training two ab-initio tailwheel
pilots in it.

Have you stood by the wing tip and rocked the wing like a seesaw? If
you can get it to rock higher and higher and it keeps rocking after you
let go, then I guess the landing gear doesn't have effective shock
absorbers.

I remember touchdown bounces from my days with balsa, tissue and dope.
None of my models would have bounced even slightly from a stationary
drop because all had rigid landing gear.

None had a movable elevator. I could climb and dive by changing thrust,
which would move the center of lift by slightly changing the speed. If
I wanted a plane to fly faster, I would move the center of gravity by
weighting the nose so the model would balance at a higher speed.

Without elevator control I couldn't make three-point landings. My
Curtis Hawk had the biggest bounce, but the airspeed was low enough that
it would rise only about five inches before mushing elegantly to the
ground. My Corsair would bounce about two inches.

My Spitfire landed much faster than the others because I weighted the
nose with two flashlight batteries. With that much airspeed, it might
have risen disastrously high if it had bounced on touchdown. It didn't
bounce at all.

The three models were different in the position of the main gear. The
wheels of the Hawk were well forward of the center of gravity;
apparently the Army plane was designed that way to counter the tendency
of a short, high plane to nose over when landing on a rough field at low
speed. When the wheels of my model touched down, the center of mass
would continue to fall, lowering the tail and increasing the angle of
attack. Naturally, it bounced.

The problem wasn't as bad with the Corsair because the wheels weren't so
far forward. The wheels of the Spitfire were farther back, and the
weights brought the center of gravity forward as well as increasing
inertia about the horizontal axis. This way, the tail didn't sink fast
enough for the plane to lift off after touchdown.

With my balsa models, bouncing came from the rapid sinking of the tail
after touchdown. If I'd had elevator control, I might have managed
three-point landings with the Hawk. I don't see how the model could
have bounced in that case. (A neighbor used to fly his father's
Stearman under his brother's instruction. He says he sometimes touched
down tail first.)
  #27  
Old June 28th 08, 01:02 AM posted to rec.aviation.piloting
Bertie the Bunyip[_24_]
external usenet poster
 
Posts: 2,969
Default bouncing off the runway

E Z Peaces wrote in
:

Bertie the Bunyip wrote:
E Z Peaces wrote in
:

Bertie the Bunyip wrote:
E Z Peaces wrote in
:

I've read about oleo aircraft struts at least as early as the
1920s.
Theyre not dampers, they're oleos and provide no damping. Shock
absorbers are something different and have a different function,
though tey're misnamed in any case, since its the springs that
absorb and the shicks, as they;'re called, prevent the energy
stored in the spring from rebounding the wheel off the road.
Airplanes don't have shock absorbers.
Here's an example:
http://www.hangar9aeroworks.com/Aero...oncastrut.html


Yeah, I know,. I was flying one a couple of days ago and I've had
them apart, too.
It does little or nothing to stop a bounce in spite of it's name. I
can also stater that categorically since I was training two ab-initio
tailwheel pilots in it.

Have you stood by the wing tip and rocked the wing like a seesaw? If
you can get it to rock higher and higher and it keeps rocking after
you let go, then I guess the landing gear doesn't have effective shock
absorbers.

I remember touchdown bounces from my days with balsa, tissue and dope.
None of my models would have bounced even slightly from a stationary
drop because all had rigid landing gear.

None had a movable elevator. I could climb and dive by changing
thrust, which would move the center of lift by slightly changing the
speed. If I wanted a plane to fly faster, I would move the center of
gravity by weighting the nose so the model would balance at a higher
speed.

Without elevator control I couldn't make three-point landings. My
Curtis Hawk had the biggest bounce, but the airspeed was low enough
that it would rise only about five inches before mushing elegantly to
the ground. My Corsair would bounce about two inches.

My Spitfire landed much faster than the others because I weighted the
nose with two flashlight batteries. With that much airspeed, it might
have risen disastrously high if it had bounced on touchdown. It
didn't bounce at all.

The three models were different in the position of the main gear. The
wheels of the Hawk were well forward of the center of gravity;
apparently the Army plane was designed that way to counter the
tendency of a short, high plane to nose over when landing on a rough
field at low speed. When the wheels of my model touched down, the
center of mass would continue to fall, lowering the tail and
increasing the angle of attack. Naturally, it bounced.

The problem wasn't as bad with the Corsair because the wheels weren't
so far forward. The wheels of the Spitfire were farther back, and the
weights brought the center of gravity forward as well as increasing
inertia about the horizontal axis. This way, the tail didn't sink
fast enough for the plane to lift off after touchdown.

With my balsa models, bouncing came from the rapid sinking of the tail
after touchdown. If I'd had elevator control, I might have managed
three-point landings with the Hawk. I don't see how the model could
have bounced in that case. (A neighbor used to fly his father's
Stearman under his brother's instruction. He says he sometimes
touched down tail first.)



Wonderful, you should write a book.

Bertie
 




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