Landing gear door operation

[Elliot Wilen]

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

[Larry]

Sparky's got it correct on those two birds (EA-6B Prowler & A-6E Intruder).
I spent about half my career keeping those turds fixed so he could go
flying. I QA'd lots of late night "drop checks" at the Rock and afloat
making sure those gear doors worked as required.

> 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?
I can't speak for the others, but in the case of the Prowler, I understand
it was to address a low speed performance issue (as it was explained to a
groundpounder).

> Is this due to Navy
> "culture" or somehow related to a safety/reliability issue for
> carrier-based operation?
Actually my gut tells me that due to the very demanding nature of carrier
landings (high angle of attack, high rate of descent, critical application
of power, etc, etc) I'd say that the pilot must have absolute control of the
aircraft and research has shown that closing the gear doors (whenever
possible) can contribute to smoother airflow and thus better
controllability. What a mouthfull. You got the idea.


> the Prowler had a provision for
> the forward gear doors to be opened on deck by the plane captain.
Gotta make sure there are no hydraulic leaks before you go off the pointy
end there Sparky. We want you all to make it a round trip you know!

Interesting looking back for a moment.

Larry
AECS (AW/SW/MTS)
Disabled Combat Veteran
USN Retired

20 years of Navy in my rear view mirror
and getting further away every day ;-)







"Elmshoot" > wrote in message
...
> Elliot,
> On the A-6 Intruder the forward gear doors stayed open when the gear was
down.
> On the EA-6B the forward gear door was only open while the gear was in
transit
> then it closed. When the gear was extended via the emergency gear
extention the
> forward gear doors stayed open with a note in the Natops manual about
added
> drag from the doors being open and higher fuel burn. The Prowler had
better
> throttle response than the Intruder. However on speed was slightly on the
back
> side of the power curve so the reducton of drag was felt to be warneted.
> Now before you get your knickers in a twist, the Prowler had a provision
for
> the forward gear doors to be opened on deck by the plane captain. So
almost all
> pictures of the Prowler on deck will show the gear doors open. 1400 hrs in
the
> A-6 and 2200 in the Prowler are my reference for the above.
> I don't know of and have never heard of any conspierency for some standard
> configuration for the gear doors. Frankly I have never even though about
the
> question.
> Sparky
>
>
>
> >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
> >
> >
> >
> >
> >
> >
>
>

[Mary Shafer]

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

[Lynn Coffelt]

"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

[Robert Moore]

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)

[Ed Rasimus]

"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

[Dudley Henriques]

"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

[Lynn Coffelt]

"Pechs1" > wrote > Or USAF...I don't know of any US military
fighter that had doors that closed
> after the LG were down, ala an airliner..F-15, Century series fighters,
etc.
>
> No reason to...to close some doors..maybe some airline puque can say why
some
> airliners DO have some dorrs that close-to save fuel???
>
> P. C. Chisholm
> CDR, USN(ret.)
> Old Phart Phormer Phantom, Turkey, Viper, Scooter and Combat Buckeye
Phlyer

Hmmmm, Didn't some (or maybe all) F-86 series retract the nose gear
door after the nose gear extended? The reason, I believe, was that the huge
door was an aerodynamic hindarance to "slipping" and a liability during
crosswind landings. Kind of like a big fin on the pointy end.
Seem to remember we "dirty fingernailed" having to hit a switch or
position a valve before the engine "spooled down" or restart the engine to
get the door down. (for postflight inspection, etc)
Old Chief Lynn

[W. D. Allen Sr.]

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

[Paul Hirose]

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 >

[Urban Fredriksson]

In article >,
Elliot Wilen > wrote:

> 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?

Apart from what's already been mentioned I can add that
the gear bay can contain things which you want to access
during normal handling on the ground. On Draken for
example the ground crew data entry panel is in the nose
gear bay. That's why they open almost 180 deg.

And speaking of air brakes, Gripen's front nose gear door
doubles as one -- but only on the single seat version.
--
Urban Fredriksson http://www.canit.se/%7Egriffon/
1) What is happening will continue to happen
2) Consider the obvious seriously
3) Consider the consequences - Asimov's "Three Laws of Futurics", F&SF, Oct 74

[Frank Minich]

The RA-5C's doors (nose and main) closed after gear extension.

The system was pretty nice in that on hydraulic failure all the gear would
free-fall after manual release, since all of the gear extended to the rear
(of course, the doors wouldn't close in this case). If I remember
correctly, it was a PMCF check to drop the gear manually (the non-essential
systems had hydraulic power removed when the the cockpit "hydraulic" switch
was in "flight" position) and then switch to "land" position and retract
them, just to verify operation.

Don't know why North American went to the trouble of retracting them - might
have had something to do with the airflow around the control surfaces, or
reducing drag for single-engine operation. The main gear doors were pretty
big - maybe they stood a chance of damage on landing - but the nose gear
door?

Frank

"Elliot Wilen" > wrote in message
om...
> 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