Landing gear door operation

In another online forum, it has been claimed that on the F-18, F-14,
F-4, and possibly F-8, A-7, A-6, and A-4, all the landing gear doors
stay open when the gear are extended. While typically (or at least in
most other military jets), some of the landing gear doors open only
during extension/retraction, and are closed while the gear are
extended.

Can anyone comment on the extent to which this is true? If so, there's
an obvious pattern of this characteristic appearing in fighter/attack
jets which were originally designed for the Navy. Is this due to Navy
"culture" or somehow related to a safety/reliability issue for
carrier-based operation? Or generally, is there some reason that some
jets are designed with gear doors that stay open, while others have
doors that close after the gear are extended? (The only reasons I've
seen that make sense are simplicity versus air drag and, in some
cases, ground clearance.)

Many thanks in advance.

--Elliot Wilen

On Sat, 05 Jul 2003 03:54:46 GMT, "Lynn Coffelt"
wrote:

very early T-38's used hydraulic powered "ailerons" on the main landing gear
doors to help retract the main gear in flight. The wing was so thin that
there wasn't much room for conventional retraction mechanism. Seemed to work
OK, but later models found room for conventional mechanism. Did it use a
shrink scheme to retract the oleo strut while the gear retracted??? Been a
while!

JSC, which flies T-38Bs, used the part of the MLG door on the gear to
increase the drag so they could chase the Orbiter. It had a spring
normally or something and they fixed it in place. If I knew where my
SETP proceedings were, I'd dig it out. The paper was by John McBride
and Dick Grey. It was probably given in about '79 or so.

Mary

--
Mary Shafer Retired aerospace research engineer

"Turn to kill, not to engage." LCDR Willie Driscoll, USN

"Mary Shafer" wrote in message
...
On 4 Jul 2003 19:05:44 -0700, (Elliot Wilen) wrote:

In another online forum, it has been claimed that on the F-18, F-14,
F-4, and possibly F-8, A-7, A-6, and A-4, all the landing gear doors
stay open when the gear are extended. While typically (or at least in
most other military jets), some of the landing gear doors open only
during extension/retraction, and are closed while the gear are
extended.

The F-111 MLG doors open, the gear extends, and the doors shut.
Mostly because otherwise these huge doors would be hanging out being
speedbrakes.

F-4 doors stay open. So do F-15 and F-16 and B-52 doors. Ditto
YF-12, SR-71, T-33, F-104, X-15, F-18, CV-990, A-7, F-8, KingAir,
B-747, B-1, B-2, F-117, B-57, and U-2. Also Lear 24 and 25. And the
Orbiter. These are just the ones I've seen and can remember.

I'd say it's not most, military or otherwise.

--
Mary Shafer Retired aerospace research engineer


stay open: also F-84, F-89, B-47
nose gear door closes: on some models F-86

Old Chief Lynn

From an RAF perspective - the Harrier and Jaguar doors are re-cycle and close
after the undercarriage is down. Tornado doesn't.

The main difference is that both Harrier and Jaguar were designed to operate
out of rough or semi prepared airfields, and this would certainly cut down on
muck in the bays

Ian

"IanDTurner" wrote in message
...
From an RAF perspective - the Harrier and Jaguar doors are re-cycle and
close
after the undercarriage is down. Tornado doesn't.

The main difference is that both Harrier and Jaguar were designed to
operate
out of rough or semi prepared airfields, and this would certainly cut down
on
muck in the bays

Ian

HH-53C (Super Jolly Green) specialized in rough or unprepared airfields, and
with it's wide open bays, muck in the bays was certainly a problem. Once
IIRC we had a "Jolly" return with no gear in one main landing gear bay.
Seems it was left on a stump or something at an unprepared field. Some of
you may remember the "Coasty" (absolutely, positively no disrespect) (USCG)
who flew as an exchange pilot with 37th ARRS, Danang Airfield.

Old Chief Lynn

Mary Shafer wrote
These are just the ones I've seen and can remember.

Perhaps you mis-remember about the B-747?

Bob Moore
PanAm (retired)

"Lynn Coffelt" wrote:

very early T-38's used hydraulic powered "ailerons" on the main landing gear
doors to help retract the main gear in flight. The wing was so thin that
there wasn't much room for conventional retraction mechanism. Seemed to work
OK, but later models found room for conventional mechanism. Did it use a
shrink scheme to retract the oleo strut while the gear retracted??? Been a
while!

Old Chief Lynn

Must have been very early. The airplane came into the inventory in '62
and I flew it in early '65 at Williams AFB. There were no "ailerons"
or movable parts on the MLG doors at that time. There was a
conventional compression strut and a 45 degree "drag link" that pushed
and pulled for extension/retraction hydraulically. The wing had no
bulges, such as on the F-4, to assist in housing the gear when
retracted. The gear strut fit in the wing thickness and the wheel/tire
assembly retracted into the underside of the fuselage.

We had an incident in my pilot training class in which one of the
German student (fully one-third of each UPT class at Willy was
German's enroute to the F-104 across town at Luke), apparently trying
some BFM tactics he had heard about, extended the gear at high speed
and high G load in a turn. The resultant over-stress of the assembly
sheared both MLG drag links leaving both gear unsupported and
braced--swinging freely back and forth in the bay.

A chase aircraft (the wing DO) visually inspected the damage and the
student was directed to make a controlled ejection over the base. We
had a procedure, flying off a CHD TACAN radial a set distance at 10k
MSL then ejecting. Both the student and the airplane landed within the
field boundary.

They could never prove the student error (actually student pilots
cannot make "pilot error" judgements) and he graduated on time and
went on to a Luftwaffe career flying the 104.



Ed Rasimus
Fighter Pilot (ret)
***"When Thunder Rolled:
*** An F-105 Pilot Over N. Vietnam"
*** from Smithsonian Books
ISBN: 1588341038

"Peter Stickney" wrote in message
...
In article ,
Mary Shafer writes:
On 4 Jul 2003 19:05:44 -0700, (Elliot Wilen) wrote:

In another online forum, it has been claimed that on the F-18, F-14,
F-4, and possibly F-8, A-7, A-6, and A-4, all the landing gear doors
stay open when the gear are extended. While typically (or at least in
most other military jets), some of the landing gear doors open only
during extension/retraction, and are closed while the gear are
extended.

The F-111 MLG doors open, the gear extends, and the doors shut.
Mostly because otherwise these huge doors would be hanging out being
speedbrakes.

Well, on the 'Vark, the huge door _is_ the speedbrake. The F-111's
maingear retracting sequence is a wonder to behold.

F-4 doors stay open. So do F-15 and F-16 and B-52 doors. Ditto
YF-12, SR-71, T-33, F-104, X-15, F-18, CV-990, A-7, F-8, KingAir,
B-747, B-1, B-2, F-117, B-57, and U-2. Also Lear 24 and 25. And the
Orbiter. These are just the ones I've seen and can remember.

I'd say it's not most, military or otherwise.

It seems to depend on who's making the airplane. North American
products (P-51,various F-86s/FJs, the F-100, etc. have doors over the
wheel wells that are normally closed except when cycling the gear.
Boeing airliners since the 367-80 are the same way (Except for the
737, no wheel well doors), iirc. Some others may have, as well. I
don't remember about DC-8s & 9s.

--
Pete Stickney

A point of note on the P51 at least, is that when you parked the airplane,
(especially on a hot concrete ramp) you ALWAYS wanted to pull the emergency
fairing door release handle, which eased the pressure in the hydraulic
system and allowed the doors to open and hang. If you ever see a civilian
owned 51 parked on a hot ramp somewhere with the doors up, you will probably
see leaking hydraulic fluid under it ,as well as it's rich but not too
bright pilot walking around with a rather large bill from Aeroquip Hose
Inc., sticking out of his flight suit pocket!!!! :-))))
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/CFI
Retired

One argument for designed gear doors to be open during
landing approach on an aircraft carrier would be that the
aircraft jet engine would run at higher RPM during approach
which reduced spool-up time for a bolter or wave off.

At least, spool-up time was a real concern half a century
ago when we trapped under the mizzen mast sails on the poop
deck.

WDA

end

"Mary Shafer" wrote in message
...
On 4 Jul 2003 19:05:44 -0700, (Elliot
Wilen) wrote:

In another online forum, it has been claimed that on the
F-18, F-14,
F-4, and possibly F-8, A-7, A-6, and A-4, all the
landing gear doors
stay open when the gear are extended. While typically
(or at least in
most other military jets), some of the landing gear
doors open only
during extension/retraction, and are closed while the
gear are
extended.

The F-111 MLG doors open, the gear extends, and the doors
shut.
Mostly because otherwise these huge doors would be hanging
out being
speedbrakes.

F-4 doors stay open. So do F-15 and F-16 and B-52 doors.
Ditto
YF-12, SR-71, T-33, F-104, X-15, F-18, CV-990, A-7, F-8,
KingAir,
B-747, B-1, B-2, F-117, B-57, and U-2. Also Lear 24 and
25. And the
Orbiter. These are just the ones I've seen and can
remember.

I'd say it's not most, military or otherwise.

--
Mary Shafer Retired aerospace research engineer

"Turn to kill, not to engage." LCDR Willie Driscoll, USN

Mary Shafer wrote:

The F-111 MLG doors open, the gear extends, and the doors shut.
Mostly because otherwise these huge doors would be hanging out being
speedbrakes.

F-4 doors stay open. So do F-15 and F-16 and B-52 doors. Ditto
YF-12, SR-71, T-33, F-104, X-15, F-18, CV-990, A-7, F-8, KingAir,
B-747, B-1, B-2, F-117, B-57, and U-2. Also Lear 24 and 25. And the
Orbiter. These are just the ones I've seen and can remember.

Not all the B-1 and B-2 doors remain open.

B-1 main gear doors open to allow the gear to drop, then close after
the gear is extended.

The B-2 nose gear door closes after the gear is down. This is possible
because the door is two pieces. The piece that covers the forward
portion of the nose gear well is rigidly mounted on the nose strut.
The strut's pivot point is at the far forward end of the nose well,
thus the "clamshell" covering the rear can be shut when the strut
assumes a vertical position.

It would be impossible to do this with the B-2 main gear, since each
of those doors is one piece.

At the end of a mission the B-2 nose door is opened before engine
shutdown so maintenance can easily access this area. That's why you
always see it open in ground photos. The door is closed after engine
start on the next mission. The switch that operates the door is on a
control panel attached to the nose gear strut.

--

Paul Hirose