Warbird Information Exchange

Hello Rich and All,

I have been refered here by Dudley Henriques for a couple of bits of information. By way of introduction, I am a low hours pilot but the majority of my flying has been aerobatics. My only "warbird" time is a little on the Nanchang and Tiger Moth but I also have aerobatic time on the Super Decathlon, Extra 300L, C152 and Fuji (the latter two being marginal aerobatic aircraft at best, in my opinion...but you take what you can get).

I have long had a love for Spitfires and have recently finished a 2 1/2 year project to build a full scale cockpit section linked to MS Flight Simulator and fully functional as to controls and instruments (within the limitations of FSX).

Anyway, to the questions at last:

1. I have film of the Spitfire flaps coming down at a million miles an hour on the ground and I know the mechanics of that but when airborne, do they also deploy at that rate or is it more slowly / how slowly.

2. I believe from a maintenance manual, which I have, that they are held down by a spring arrangement and will begin to retract by themselves if left extended at anything above 120 mph. Could you confirm this? If so, does this do damage to the mechanism?

3. Retraction is reported (in the performance trials done by the RAF) to take 6-8 seconds does this occur more slowly on the ground?

3. The early marques (I to V - I believe) used a boost cutout override operated by a red thumb switch forward on the throttle quadrant. This switch being wired against inadvertant use (and its use was a reportable event in the aircraft's maintenance log). However the Mk II is listed as 9lb Rated boost, 12 1/2 lb Takeoff Boost and 12lb "emergency boost".
So it would appear that every takeoff would "break the wire", clearly making the wire pointless in the first place.
So, did the engine somehow deliver 12 1/2 boost at sea level (or near it) without "breaking" the wire or was Takeoff Boost synonimous with Emergency Power and Rated Boost the actual "normal" Takeoff Boost?

Thanks in advance for any help you can offer.


Darryl

I'll answer what I can. Must of what I know is ground based MX stuff and really only on the Mk XVIII. And that is based on my 2008-10 timeframe.
Maybe Jim or Bill can chime in on flying and Merlin powered info.

1. I have film of the Spitfire flaps coming down at a million miles an hour on the ground and I know the mechanics of that but when airborne, do they also deploy at that rate or is it more slowly / how slowly.
2. I believe from a maintenance manual, which I have, that they are held down by a spring arrangement and will begin to retract by themselves if left extended at anything above 120 mph. Could you confirm this? If so, does this do damage to the mechanism?

The flaps are air powered to extend and held up by a spring which also acts to pull the flaps up when up is selected. Selector is a lever on the inst panel. Down allows air pressure to reach the actuators. Up shuts off the air pressure and vents the actuators to the atmosphere. The springs pull and air loads push the flaps up. They deploy at a 85 degree angle, all down or up, no other settings in between. On the ground they do extend with a bang.
I know Jim tries to keep within the flap and gear speeds. We haven't had an overspeed. I imagine overspeeding when selecting the flaps will slow their deployment more so than ripping them off. Since there isn't a maneuvering feature or partial flaps available it would be rare to use them in any other situation other than slowing down during a landing approach. That basically involves bleeding energy and speed to decrease speed. At your flap speed you deploy the flaps. They do pitch you down fairly good as told by Jim.

3. Retraction is reported (in the performance trials done by the RAF) to take 6-8 seconds does this occur more slowly on the ground?

The retraction time on the ground is influenced by the friction of the seals in the actuator. There is an orifice that the air escapes through when Up is selected on the lever. They will only retract so fast due to that orifice, even in the air. On the ground one side will retract faster than the other due to the friction of the seals in the actuators being different. In flight air loads equalize so they come up together.

4. The early marques (I to V - I believe) used a boost cutout override operated by a red thumb switch forward on the throttle quadrant. This switch being wired against inadvertant use (and its use was a reportable event in the aircraft's maintenance log). However the Mk II is listed as 9lb Rated boost, 12 1/2 lb Takeoff Boost and 12lb "emergency boost".
So it would appear that every takeoff would "break the wire", clearly making the wire pointless in the first place.
So, did the engine somehow deliver 12 1/2 boost at sea level (or near it) without "breaking" the wire or was Takeoff Boost synonimous with Emergency Power and Rated Boost the actual "normal" Takeoff Boost?

I really don't have any experience on these early aircraft. Maybe Bill or Bent Wing Bomber, aka Fred, who works on a Mk V can fill us in on this. At least with the Mk XVIII we use significantly less boost on take off than we can use in the air.

Hope this helps.

_________________
Rich Palmer

Remember an Injured Youth
benstear.org
#64- Stay Strong and Keep the Faith

BOOM BOOM, ROUND ROUND, PROPELLER GO

Don't Be A Dilbert!

Thank you Rich,

The MK II pilot's notes mention that the flaps will partially retract if 120mph is exceeded and contemplate if left down "through serious ommission of drill" on go around they MUST NOT be retracted until 120mph is reached.

I had seen flaps retract at different rates for each and wondered if that happened in the air...thanks for that.

Hopefully some one will know about the "boost", that one has me scratching my head.

Thank you sir, most helpful!!



Darryl

Realized today while running the Spit that the flap speed is 140 knots as placarded on the panel.
Reads along the lines of "Do Not Extend Flaps or Leave Flaps extended Above 140 Knots".

_________________
Rich Palmer

Remember an Injured Youth
benstear.org
#64- Stay Strong and Keep the Faith

BOOM BOOM, ROUND ROUND, PROPELLER GO

Don't Be A Dilbert!

Thanks Rich,

Yes I am aware that "modern" aircraft say 140knots. Interestingly, the wartime aircraft (at least Mks 1-IX) were placarded at 160mph DESPITE the pilot's notes being very specific about 120mph in three or four separate places.

I suspect that the 160mph/140knt is the aerodynamic limit of the flaps whereas the 120mph is the operational requirement, probably, as the Mk II PN's explain because...."the flaps can not be lowered to increase drag above 120mph ASI because they affect the flow of air to the radiator, and cause the engine temperature to rise above the limit". Therefore it seems to be the throttle setting required to maintain a speed higher than 120mph that causes the problem rather than a physical problem with the flaps themselves (although it is noted that they will partially retract at above 120).

Oh I do envy you your work!!!

Thanks again,

Darryl