Westland Wapiti IIA - Engine Variant Question (See attached image)

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Profile picture for user Jagan

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The other Wapiti thread got me interested in posting this. I am putting together a 'technical guide' on the Wapiti variants something that will be of use to modellers and other wop fans. I have a question on the engine variations on the Wapiti IIA.

As per the existing Litterature , the Wapiti IIAs were all equipped with the Jupiter VIII engines, but visually there are differences between the examples produced. Please see the attached Image

I have included two images of each type.

Type A seems to have served in Iraq and India . Jupiter VIII engine with that conical fairing on the front part, no massive exhaust collector ring. Some of the aircraft appeared to have been modified to the Type B seen below

Type B: The "Classic" Wapiti IIA - what we see or imagine it to be. Engine Exhaust collector ring that pipes the exhaust along two long pipes below the front fuselage.

Type C: Now this variant has a 'Flatter' profile in front of the engine. the Conical exhaust collector is replaced by a flatter exhaust ring. And perhaps unusally this type of engine profile is seen only on variants that served in the UK - with the aux squadrons like 601,602,603 etc.. I have not see this profile in the ME or in India.

My question is

1. What are these different variations / Mods described as?
2. if they are all not the same type of engine VIII.. then what are they?
3. Are there any archival data / litterature that explains these differences? I went over all the published articles and books on the Wop and could not find a satisfactory explanation..

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Bristol Jupiter publication

Hi Jagan,

I'm on holidays and away from my books, but the Bristol Bulldog manual had a little (and I emphasize "little") blurb on the Jupiter engine and exhaust system.

If you're not in a hurry, I can have a look through it when I get back, and see if there's any specific data about exhaust development that might prove applicable to the later Jupiter engines on the Wapiti.

Alternately, and perhaps it might shed more info, there is the engine manual noted below in (via google-search):
Bristol Jupiter Series Viii 8 & ix 9 Aero Engines Air publication 1371 1st edition July 1929.

Don't have a copy, unfortunately, so can't tell you what's specifically in it.

Good luck.
...geoff

Profile picture for user Jagan

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I'm on holidays and away from my books, but the Bristol Bulldog manual had a little (and I emphasize "little") blurb on the Jupiter engine and exhaust system.

If you're not in a hurry, I can have a look through it when I get back, and see if there's any specific data about exhaust development that might prove applicable to the later Jupiter engines on the Wapiti.

That would be great Geoff. I can wait till after the holidays. so take your time.

I have the Wapiti IIA Manual from 1929 as well as the Jupiter VIII manual but both of them dont cover the details I was looking for, leading me to suspect these were modifications that were not covered in the original manuals..

Profile picture for user John Aeroclub

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Hi Jagan

I have business to attend too this morning. but I will come back to this fascinating thread later. J9724 was the last of the batch built as a IIA, J9725 was the first of the batch (J9725 to J9759) built as Mk V.'s. We need pictures of the a/c post J9725.

Back earlier than I thought.

Type A are fitted with geared Jupiter VIII's and with direct exhaust ports (these must have been pretty noisy and smelly). Type B have the later exhausts with the larger collector ring chamber developed for the (longer gearbox) geared Jupiter's (VIII and VIII.F) However to confuse some Mk II.A's were also produced with the ungeared Jupiter VI ( group C) and these had the smaller diameter props and thinner bifurcated exhaust collectors required by the lesser 'prop to crankcase' clearance. The Mk V Wapiti seems to be quite camera shy and if we can find some good side on shots it will be easy to see any length difference.

Regards

John

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Type A are fitted with geared Jupiter VIII's and with direct exhaust ports (these must have been pretty noisy and smelly). Type B have the later exhausts with the larger collector ring chamber developed for the (longer gearbox) geared Jupiter's (VIII and VIII.F) However to confuse some Mk II.A's were also produced with the ungeared Jupiter VI ( group C) and these had the smaller diameter props and thinner bifurcated exhaust collectors required by the lesser 'prop to crankcase' clearance. The Mk V Wapiti seems to be quite camera shy and if we can find some good side on shots it will be easy to see any length difference.

John this is awesome information.. I could never understand why in spite of being the same engine the A and B type of aircraft looks so different.

To add a bit of additional twist, I have photographs of the same numbered aircraft with both the TypeA and Type B looks.. so assuming that at some point the Type A got converted to Type B

Reg TypeC that they were Jupiter VIs.. I suspected but had no proof. it gets confusing because the UK squadrons had a mixed bag of Wapitis - J series, K series etc and they all had the thin profiled engine.. So we will have to assume the UK ones were all VIs and the overseas ones were all Jupiter VIIIs

Reg different photos of Mark V, I got a ton of them here http://www.rafcommands.com/galleries/Aircraft-Database/Westland-Wapiti/MkV-J9725-J9759

I am trying to put together a database of "1 of every number" at this location

http://www.rafcommands.com/galleries/Aircraft-Database/Westland-Wapiti, dividing them by Contract Number, block number and ofcourse Mark Number..
(Photo Credits belong to multiple sources - but all for common good of research). You will see the 'Type C' engine on the Mark VI

lastly I re-checked my copy of the Jupiter VIII, VIIIF and XI manual and it does talk about the 'B' type Exhaust Collector ring and its fitment.. That manual IIRC was dated 1931 and after so it fits well with the expectation that the exhaust collector ring over the geared Jupiter VIIIF is a later mod.

-----------------

BTW this is just about MkIIAs and MkVs.. If I go into Mk1 and MkII there are engine differences too - partially faired Jupiter VIs and open Jupiter VIs on the same aircraft.. with spinners and without spinners! etc etc lots of documentation to be made!

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Here is another interesting collage of photos.

Top two photos show the same aircraft J9486.. first one is circa 1929 i think.. second one is around 1932. Shows before and after Modification of Exhaust System. Incidentally this aircraft was one of the few with dual controls, bucket seat in the rear cockpit so that pilots could get type training. This example went to the IAF and was lost in an accident in September 1933.

Second photograph shows J9505 - a Mk IIA with neither of the exhaust systems! whether I am assuming that this is the 'transition' stage from Type A to Type B :).. and a noisy engine I am sure!

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Profile picture for user John Aeroclub

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Jagan

Well you have raised a 'can of worms'. None of the photos of the supposedly Wapiti V batch, (J9725 to J9759 with the exception of J9728) appear to me to have the revised longer rear fuselage which has been an attributed feature of this RAF version in type histories. I personally think that there has been some confusion with the use of K serialled Wapiti II A fuselages which were used to produce the first production batch of Wallace Mk.1's which had the extended fuselage frames.
I also believe that J9728 should not be described as a long fuselage Wapiti V but rather the sole long fuselage Wapiti V. I also suspect that this aircraft became G-AAWA which was later revamped as the Wapiti VIII which then became the Westland P.6. It then became the prototype Wallace and later G-ACBR (the Houston Everest Westland P.6).

Another feature of the extended fuselage airframes is that they are fitted with tail wheels and brakes. I think that brakes fitted to the short fuselage versions would have seen more airframes sitting on their noses.

John

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Jagan

Well you have raised a 'can of worms'. None of the photos of the supposedly Wapiti V batch, (J9725 to J9759 with the exception of J9728) appear to me to have the revised longer rear fuselage which has been an attributed feature of this RAF version in type histories.

I also believe that J9728 should not be described as a long fuselage Wapiti V but rather the sole long fuselage Wapiti V.

Thanks John. Glad to have your well informed opinion to support my open can of worms :)

I stumbled on this while working with Juanita Franzi on the colour profiles and it was during the various correspondence with her, we settled down to the fact that there is no discernible length difference for MkVs with the exception of J9728.

Ofcourse that gallery has pictures of only 14 of the 34 MkVs produced. so another 20 to go.. But at this point I am certain all the rest will be like these 14!. 9728 is the only one of the MkV batch that wasnt shipped to India. And all the 33 remaining ones ended up being sent to India.

So perhaps MkV was just a convenient way to designate some sort of 'tropicalised' variant? or some feature that was used only in the Indian Subcontinent.

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I'm pleased we agree that the whole batch of Wapiti V's will be the short fuselage types. I think a simple answer to the choice of Jupiter engine types is that the large prop, geared engines were more efficient in India in the hotter temperatures and higher altitudes that the Wapiti encountered there. Glad to help.

John

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http://www.rafcommands.com/galleries/var/resizes/Aircraft-Database/Westland-Wapiti/Mark-IIAs-J9380-J9414/J9385.jpg?m=1427756658

To add yet another "Type" to our discussion .. Wapiti IIA J9385, Built Nov 28 and shipped to India.

This has the exhaust collector ring, but the engine is 'partially faired' with just the cylinders sticking out.. normally we would see this in the "A Type" configuration..

I also just added this second pic of J9385 just now
http://www.rafcommands.com/galleries/var/resizes/Aircraft-Database/Westland-Wapiti/Mark-IIAs-J9380-J9414/J9386.jpg?m=1451800272

This shows it with the Type A engine config.. The chronology of the first pic is uncertain, but it looks pre-delivery or in UK.. it could have been a 'test config' to try out the B style engine and fitting?

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An almost identical cowling arrangement for the geared Jupiter as that on 9385 was tried on the Bristol Boarhound. J9385 might also have trialed this cowling before being reverted back to the contract standard and dispatched to India. The fact that the top photo is of the standard test/ trials format/view I think reinforces this.

The fairing plates at the rear consist of 9 separate plates from what I can see and easily removed. Of interest J9382 was retained by the makers and also used for several trials. I'm sure that in the interwar air force there was the equivalent of 'Red Line Entries' for an aircraft to be flown without damaged panels or items such as the exhaust manifolds needing repair but in short supply, so the earlier direct stubs could be temporarily fitted in lieu.

John