Spitfire Mk I Undercarriage Unit

Is anyone interested in the GA of the round type undercarriage unit?

Cheers Steve
I think the Anson also used a similar pump arrangement as well but not entirely sure. I may have that Pilot’s Manual buried away somewhere.

I’ll have to have a detailed look at the “round” type U/C unit GA’s that I have but I think you are correct..they worked on one “circuit”. The system is listed as “having to pressurize”, the reason that the lever was to be held out of the gate for a second and then brought back “in one smooth movement” or similar.

The indicator window should show “idle” , I believe, anytime the gear is not in transit. IIRC the fluid idles (is redirected) through the system until the lever “pressurizes” at which point the flow to the wheels is opened and the necessary pressure is excerted.

Been a while since I looked at it, so I may be off on a couple of details ,

Darryl

In the later, powered unit (ie. virtually all Spitfires & Seafires) there is of course only one operating jack per side,

I recall the early manual pump arrangement used the same hardware as the Walrus, thats the last time I saw one.

i will check Tony. It may well be a ‘closed loop’ hydraulic system’ as your chap refers to, in which case gravity would provide little help as he says!
I will see if the pump design is double cylinder…this would make both the forward and aft movements ‘pressure’ movements hence suggesting both add

Cheers Tony,

Yes, if that is the case then the “Raise / Lower lever” would serve two functions… to unlock the pins and to close/open the hydraulic line for the appropriate pump action. Then the pump could move as normal and use both the forward and back stroke to generate pressure.

If the cylinders are the same then I should probably be right about the “stroke” “movement” but I hate it when you have to put an interpretation on things..you are never quite sure you are right. Far better that the cylinders turn out to be different and the manual can be read at face value!

Having said that, there are numerous examples of ambiguos, unclear and even conflicting information being put in Pilots Notes.

regards

Darryl

i will check Tony. It may well be a ‘closed loop’ hydraulic system’ as your chap refers to, in which case gravity would provide little help as he says!
I will see if the pump design is double cylinder…this would make both the forward and aft movements ‘pressure’ movements hence suggesting both add

From my Fluid Dynamics expert:

“I can confirm that hydraulics work on positive displacement principles which are a constant, variances only occur with heat and degradation of the hydraulic fluid.

Gravity would have no effect on the number of strokes as pistons within the pump will move the exact same amount of fluid each stroke. This volume is fixed by the area of the cylinder bore and the length of the stroke. For instance – If each stroke moves 30ml of fluid and it requires 600ml to achieve full stroke of the landing gear legs, then 20 cycles will be required.

Gravity may however have an effect on the effort(power) required to complete the number of strokes. If the weight of the wheels and struts is not countering the driving force to pump it down then the effort will be less.

If it takes more strokes to drive the gear down than up then the up and down pistons are of differing sizes. Looking at the LG unit it does appear to contain two pistons in an under and over arrangement. My thinking is that with more strokes you will have more power/force and it is more important to force the gear down than to force it up agreed? Especially if you have a ME109 cannon shell sticking out of your right elbow at 45 degrees. “

So it would appear that the system may have been desgined to allow for twice the number of cycles each at half the effort. Much more important to get the gear down if you are tired, wounded, etc etc

Of course my alternative view is still possible… so Tony, can you see inside your unit and tell us whether the two cylinders are the same or is one twice the size of the other?

These things just get harder by the minute!

Thanks guys!!!!

PM’s on the way,

Mike..I’m NOT suggesting you have misread them for one minute, but the Pilot’s Notes seem odd..then again, it is interesting that the two terms are used…30 “full strokes” and 15 “full movements”

Are the entries concurrent or are they separated by other sections… It is strange, as Tony mentioned, that it takes more to lower than to raise…
However one reading of “stroke” would be a single push forward OR pull back….and of “movement” one full cycle..ie back and forward. So 15 “movements”
would equate to 30 “stroke” on that reading. The context may be very important. If the entries are in the same paragraph, one after the other, this is less likely..but if one is in a “taking off” section and theother in a separtae “landing” section..then my alternative reading is much more likely.

This would be closer to what Bob Doe describes (20) and the difference may just be that things never quite work as advertised??

I would have thought that 1 pump of the handle would move 1 “unit” of fluid which would move the gear 1 “unit” of travel. If the system allowed slack, then I see how the gear might come DOWN with less pumps, but up? Strange. I do know that some of the old manuals are contradictory in some places, (say as to Radiator temp allowed) so I suspect my alternative reading MAY be the right one….can you get any sense of context?
Enquiring minds need to know!! *G*

cheers

ROCKETEER…….you have a FLAP GAUGE!!!!!!!:eek:
Please pm me !
Kind Regards Mike:

fascinating…more pumps to lower than raise….you would have thought that once the uplocks are released, gravity would help greatly.

Echoing Mk5 & Mk12’s comments, the restoration of P9374 is impeccable.

Anyone who criticises restorations and how little of the original is used, should see the lengths they have gone to to make her perfect. They borrowed my flap gauge to replicate it!

I have a uc pump if you need any detailed measurements old chap!

According to my copy of (original)

PILOTS NOTES
THE SPITFIRE 1 AEROPLANE
MERLIN II OR III ENGINE
DATED MAY 1940
..it states….
ABOUT 30 FULL STROKES MAY BE REQUIRED TO LOWER
THE UNDERCARRIAGE.
….then
ABOUT 15 FULL MOVEMENTS OF THE PUMP HANDLE ARE REQUIRED
TO RAISE THE UNDERCARRIAGE.
..hope this helps
Kind Regards Mike

No worries Mark V,

All, thnaks for your help. I couldn’t find it in Sigh for a Merlin but I did find an old interview with Bob Doe……20 strokes of the pump it was.

Thanks everyone

Thank you all!!!

Glad to see that the Mk I will be faithfully rendered in that operating system, cheers Mark. I thought you might have problems getting it registered. I’m not totally sure how you would go here with that.

Ironically today in the UK going down the 100% authentic route is actually the ‘path of least resistance’ in terms of certification. So long as you can 100% confirm to the CAA this aircraft had a manual u/c pump system and the one you are installing in the restoration is the same, generally you will be fine.

PS: Tony I appreciate you were not criticising the project 🙂

Thank you all!!!

Glad to see that the Mk I will be faithfully rendered in that operating system, cheers Mark. I thought you might have problems getting it registered. I’m not totally sure how you would go here with that.

20/21 sounds great just sitting here miming it , that looks pretty close.

Thanks, I have Sigh for a Merlin (in fact on about my third copy!) I will see if I can find it.

I can relate to having seen/put/left something “somewhere”. I have come to believe “somewhere” is an extremely large area!

thanks all

PS, ..no luck on the early DH “flyspray/bike” pump shaped pitch control?

It will be totally functional.

Mark

I think it was 20/21 as well. Sure it was in one of the biographies I read it… :confused:

I disagree – this is a top class restoration and I would be surprised if the gear did not have to be manually pumped up and down as per the original. How else would it be achieved without serious modification (and all the issues that go with that in the UK) and compromised originality?

G’day Mark V,

I’m sure it is top notch.

It was no comment on the class of the job, I was merely questioning whether it would be allowed to be made functional. There are many things that get in the way of a 100% copy (for instance the air/pilot regulating authorities may not be happy with it for some reason).

A case I point out here, CASA will not allow an original, early, Sutton Harness design ..so there is a compromise. It seems obvious to me that once you begin to compromise, anything is fair game…and a “dummy” pump linked to a modeern electric mechanism

If the Spitfire being restored were mine I would want 100% look and feel but would I be prepared (or my insurance company) to risk a pilot CFIT’ing the thing because he got busy with a hand pump?

Any way up though, it is a fantastic project!!

This is frustrating, as a specific number of pumps was mentioned in something I was reading very, very recently – perhaps either ‘Spitfire Women’ or ‘Sigh for a Merlin’ Unfortunately I am at work, so can’t check. However, I think the number was 21. I will check as soon as I get home!

Mark,
Thanks, I think it is that restoration that I have a picture of showing the unit. I suppose that is for show and the gear doesn’t actually have to be PUMPED on her.

I disagree – this is a top class restoration and I would be surprised if the gear did not have to be manually pumped up and down as per the original. How else would it be achieved without serious modification (and all the issues that go with that in the UK) and compromised originality?

I don’t know the answer

Ok, so now I am in trouble!! 🙂

Mark,
Thanks, I think it is that restoration that I have a picture of showing the unit. I suppose that is for show and the gear doesn’t actually have to be PUMPED on her. I can’t wait to see her!. AR213 is a pretty late one and looks more like a Mk II at first glance into the “office”.

I have the GA for the unit and am in the process of organising a working mock up for the simulator. I guess we will just use an educated guess or find another aircraft that still flys with one (Ansons used similar, so did some others I believe ) .

If all else fails we will time some old film and get on a water pump to approximate.

Thank you Sir

I know this is probably a long shot…but can anyone tell me how many pumps of the handle it took to raise/lower the gear with the original two handled unit?

The pumping action was the cause of both the famous “Spitfire Wobble” and “Spitfire Knuckle” but I’ve never seen specifics.

I don’t know the answer but I am looking forward to the first flight of Mk I P9374 from Duxford, maybe next year, and counting them. 🙂

Mark