RAF Chipmunks

[CoffmanStarter]

GR4T ...

Welcome !

If the Chipmunk was equipped to 'aero tow' then a mirror was fitted on the top of the front cockpit windshield frame looking aft

Can't help you with running costs etc. Dora-9 might be your best bet

[Wander00]

I42 - thanks for the encouragement - I too am a sailor of sorts and my last paid employment was as paid Secretary of one of the UK's three premier Yacht Clubs. That was some privilege too

[smujsmith]

GR4 Techie,

The Chipmunk with the unusual engine cowling, used for aerotow at Bicester was probably the "Supermunk" that had been modified by replaced the gypsy major engine with a rather big Lycoming ISTR. I got an aerotow from it one breezy day, whilst Flying Bicesters ASK18 (light glider), after the usual "up slack". All out was signalled, the throttle was opened and I took off in his propwash. Grit my teeth and hang on was all I could do. Hope that helps. It wouldn't surprise me if Coff has a photograph for you!

Smudge

PS GR4, this could be the super Chippie you saw. I believe it saw service with the RAFGSA at Bicester;



Credits as on image

Smudge

[Dora-9]

GR4:

PM sent re costs (though, having had two top overhauls in two years, possibly I'm not the person to ask).

[Dora-9]

Chipmunk W&B - some thoughts

As a Chipmunk owner/operator, W&B has always been of interest. There seems to be a dearth of data regarding "balance", just a lot of myths.

I thought I had both diagrams recently posted, although on closer comparison my diagram is actually for a Mk.20 (the export T.10) whereas Coff's drawing is for a Mk.21 (the quite rare Chipmunk certified "from the ground up" as a civil aircraft). Given that the airframes are identical, the data shown (in particular the Moment Arms) here won't change for a T.10/T.20/Mk.21/Mk.22.



As part of my Chipmunk restoration, I purchased from DHSL at Duxford (at not inconsiderable expense; I only have one book at home that cost more, and that's a collector's item) an Approved Flight Manual (AFM) for a Mk.22. Now I could have registered it as a T.10 (permissible in Australia) but at the time the paperwork path of least resistance was to register it as a Mk.22.

But a Mk.22 is identical to a T.10 apart from some placards. I went to great lengths to keep the aircraft as it came out of the RAF in 1994, i.e. a "late" Chipmunk with the "Canadian" heater/exhaust, strakes and the broad-chord rudder. The following changes occurred:

1. Slick magnetos replaced the original BTH items - not only infinitely better but allegedly slightly lighter (I don't have the actual weights).
2. Metal 24 gallon tanks - again allegedly slightly lighter than the bag tanks but again I have no precise figures.
3. Radios comprised a King KY96 VHF Comm, a KT-76 Xpdr and an altitude encoder - total weight with rack 11 lbs (17 lbs lighter than the STR9X).
4. Dual Concorde RG25-XC 12V batteries at a total weight of 47 lbs, which I'm told is slightly lighter than the Hawker "two batteries contained in a single box" kit that the RAF fitted.

Back to the AFM - Section III Limitations:

Much as Coff described (I'm always left wondering how, unless you're carrying lead ingots, you're ever going to squeeze 40 lbs into the locker). However while the MAUW is quoted at 2100 lbs, it then says that flight at 2200 lbs is permissible provided that aerobatics are not flown and the aircraft not engaged in either "...public transport or aerial work". My Chipmunk has an empty weight of 1478 lbs (perhaps a little lighter than the standard RAF T.10) but with full fuel (24 gals), 2 X 200 lbs occupants and the mythical 40 lbs in the locker I gross out at 2091 lbs. Overloading then is very unlikely, without having to use the higher weight limit. This section also confirms the Moment Arm for both the rear seat occupant (max 250 lbs) and the locker are the same as in the diagrams. Note however, the permissible CofG range is defined as 6.8 to 0.77 inches forward of the datum which is what Coff's Mk.21 diagram states but NOT what's on the T.20 sheet.

Section VI - Weight & Balance:

Now this really piqued my interest as there's only minimal information. I've got a certificate confirming the datum as 1067 mm aft of the firewall (42 inches) and giving an empty weight, Arm and Index Units - and that's it. No other loading/balance information. Oddly, my brother-in-law's Mk.22 AFM has an additional sheet stating something like "provided the aircraft remains in the normal configuration it is unlikely that the balance range will be exceeded", a very sweeping statement indeed. However, working with the T.20 diagram it appears that I am also unlikely to ever exceed the aft CofG limit, which is interesting since changes 1 to 3 as shown earlier would tend to shift my CofG position aft. My "worst-case" scenario is with a 200 lb rear occupant, 40 lbs in the locker and 6 gallons of fuel, the CofG lies at -0.9" (limit is -0.77"). And it's an unlikely situation too, as I was always taught not to have anything in the locker for aerobatics, while 6 gals is close to 45 minute's fixed reserve (you should be landing/have landed by then).

As an aside, since the front seat occupant has no effect on balance it would seem that there is no reason (from the W&B standpoint at least) why the Chipmunk can't be flown solo from the rear seat. Or am I missing something?
.

[India Four Two]

D9,

If it is not prohibited in the Type Certificate or Flight Manual and you are within CG limits, then you can. However, I think you should clear it with your insurance company first and be prepared for some potentially distinctly different handling characteristics, due to the CG being way aft.

I know of some two-seat gliders where it is theoretically possible (with perhaps a few pounds of ballast in the front seat), but is prohibited, usually because some controls are missing from the rear seat. For example, in the case of the Blanik (RIP), there was no rear canopy-jettison lever. In the case of the DG-1000, it is just prohibited with no reason given.

[Dora-9]

I42:

This was meant to be a tongue in cheek comment - for a start in my Chippie I can only transmitt from the front seat.

[India Four Two]

I thought it might! Is the starter in front seat only as well?

The idea of flying the Blanik from the back seat always appealed to me. If the back seater pulls his head back, it is hidden by the wing root and an air to air shot from the 3 o'clock position would make it look like the Marie Celeste of the skies.

[CoffmanStarter]

Morning Gents ...

All good stuff Dora-9. Interestingly I understand the BBMF use the rear seat (but still flown dual) to train pilots new to tail wheel aircraft in getting used to coping with a long nose ready for the Spitfire ... weaving the nose while taxiing.

I certainly don't think you'd want to do any spinning with a well aft CoG if anyone was mad enough to solo from the rear seat

Dora-9 ... Do you still have the RAF 700 for your airframe ?

[CoffmanStarter]

Smudge ...

Nice picture ... But in my book a Chipmunk is only a Chipmunk if it has a Gipsy Major Mk8 engine AND a Coffman Starter ... I'd even draw the line at having a 'Heater' !!!



PS. I'll post a bit on the Tug Mirror fitted to RAF Chipmunks a bit later ...

[Dora-9]

Coff:

I have a huge carton of RAF logbooks etc, I just have to fight off the resident spiders etc to get to it!

And I'm with you: it isn't a real Chipmunk unless it's got a Gipsy. Personally I'd love a cartridge starter too (think of the BANG - "look at me" effect) but I don't think CASA would play ball...

Cheers.

[octavian]

Sadly Coffman, the cost of "your" starter cartridges, the associated storage, routine testing, and problems of expiry dates makes it a non-viable option. Ours has electric start, but you still have the joys of hand and finger priming as well as pulling through; just no satisfying bang or occasional "phut" with all the attendant waiting.

[gpugh]

Hi out of interest do the two Chipmunks with the BBMF and the one with the Navy at Yeovilton still use the Coffman starter

thanks Gordon

[CoffmanStarter]

Hi Gordon ...

I believe both WK518 and WG486 remain as God intended ... No clue about the Navy (Chipmunk) ... Sorry.

Octavian ...

All understood ... Just leg pulling

Dora-9 ...

I wonder if you might be able to help if you've got original RAF Form 700 info. I'd like to try and post examples of the various 700 docs that made up the Blue Ring binder that accompanied each airframe ... For historical purposes. Smudge might also be able to help us as he has a wealth of experience as a RAF Ground Engineer where, amongst venerable service on the Herc, he also looked after AEF Chipmunks a few years ago.

If we can I'd like to capture an example from each of the Sections from the 700. I'll drop you a PM to follow up ...

[smujsmith]

Aircraft F700 Sections

Coff, If I can help, I will try. Here's a list I picked up a while ago on "another site". I don't know what my interest was at the time, but it seems to be what you're looking for now ;

Section 1 - Leading Particulars. What oils and fuels were used, Weight and Moment forms and the register of controlled forms.

Section 2 - Limitations. The Reds, or Acceptable Limitations Log (F703). This is where faults and things that would have an adverse effect on the pilots ability to operate the aircraft were logged but the aircraft could still be operated. (scratch in the canopy etc) This section also had the Blues (F703A) which were mods etc which limited the flying capability and also the whites (703B) which were mods which enhanced the aircrafts ability in some way and were of interest to pilots.

Section 3 - Acceptable Deferred Defects (F704). The greens. This was also known as the Acceptable Deferred Faults log in later life. Stuff that was broken but wasn't going to affect the operation of the aircraft. (Panel holes in non-standard place etc)

Section 4 - Flight Servicing. Contained the F705 Flight Servicing Certificate, F705C Supplementary Flight Servicing Certificate, F725 Fatigue Monitoring log, F737 Oil replenishment log. F706 Weapon state change log, Fuel Uplifts away from base log, and anything else which involved the day to day maintenance required to keep the aircraft flying.

Section 5 - Maintenance. Held the 707A, register of jobcards raised

Section 6 - Scheduled and Out of Phase (OOP) maintenance forecast or short forecast sheet. These were generated by Eng Records using the F700A. Sched maint was primary and minor servicings etc done at set timescales. OOP was done in between or out of phase with the scheduled stuff. The short forecast detailed all the stuff due in the next X amount of days or Y amount of Flying Hours

Section 7 - Miscellaneous. Held things like compass swing data, IN error details, ETI recordings etc.

Credit to original author (unknown by this poster)!

On Transport aircraft for some time there was a duplicate F700 which travelled with the aircraft "down route" numbered the F700RT. Though I'm certain the practice had ended by the time I became a GE on Albert, where we were trusted to carry the original, and hand it back to the relevant Line Servicing Squadron after the debrief on RTB. Hope that helps.

Best

Smudge

[CoffmanStarter]

Well played Smudge ... Many, many thanks

I've been in touch with Dora-9 ... more news hopefully once he's chased the spiders out of his hangar

[CoffmanStarter]

Originally Posted by Dora-9

My "worst-case" scenario is with a 200 lb rear occupant, 40 lbs in the locker and 6 gallons of fuel, the CofG lies at -0.9" (limit is -0.77").

I think I'm right in saying that if the rear seat was occupied the RAF limited the locker load to 18 lb.

[smujsmith]

Coff #310,

I agree, to a point, as a former employee on 6 AEF, the Gypsy Major was the biz. As a former Glider pilot, the supermunk had a lot of whizzbang for the pounds it cost for a launch. As an Airframe fitter, I always respected the airframe for the fact that it could be given such "oomph" and still not suffer the usual exertions of going beyond its designed limitations. Perhaps, even with the Lycoming it never exceeded design parameters, but it sure was a beast to get launched behind. I had an Aerotow at Syreston behind a standard Chippie some years before and know for a fact that 0 - 2000 ft was around twice as long. Horses for courses might be the answer, having worked on the real thing I know that the supermunk would never be an acceptable substitute, except when you need to get under a cumulus cloud in a rush !

Smudge

[India Four Two]

CS,

Good memory. Here's the relevant part of the 3rd Edition Pilots' Notes (1966):



The 1950 Edition makes no mention of any weight limit.

i don't remember the locker being used for anything other than my instructor's hat when on land-away cross countries.

[RNHF_PILOT]

Hi out of interest do the two Chipmunks with the BBMF and the one with the Navy at Yeovilton still use the Coffman starter

thanks Gordon

The Navy Chipmunk WK608 has an electric starter.