PZL P-11g Kobuz

[Graham Boak]

What is the latest/best history available for this variant?  I gather that there are no photos - or at least none that were available a few years ago.  There was a story that at least one saw combat, but this has also been described as commandeered export P-24(s).  I'd quite like to modify one of my P-24s to one of these, but what did it look like?  My assumption for the best PZL could produce, in the circumstances, would be a P-24 airframe with a Blenheim-type cowling (i.e. with cooling gills) and a 3-blade variable pitch propeller.  However, this may be logical enough but is not necessarily what actually happened.

[JWM]

Hi,

On Polish IPMS web page one can observe result of conversion of Mirage 1/48 P 24 F/G into Kobuz

http://ipms-warszawa.pl/pzl-p-11g-kobuz/

It is said that it containes all what is currently known about this variant including scheme and marking (white 1).

Text is in Polish but with help of google translator you can get main ideas. Since she was as prototype still in factory the unarmed machine was evacualted in some steps  to eastern part of country. Then four MG were installed and she went into fights late, on 14 September and saw action in two days when pilot Lt. Henryk Szczęsny got two victories over He 111> However the second battle made serious damage in P 11 G. It is not know if was repared and evacuated to Romania or left on airfield. 

@MitchK was constructing PZL P 11G - with WIP thread. There were some discussion or advices on details about conversion 

Regards

J-W

P.S.

Edited November 29, 2017 by JWM
added PS

[Graham Boak]

Thank you, very interesting.  It isn't clear to me why the exhausts should come out on each side of the fuselage, whereas on the Blenheim and Gladiator they are grouped close together underneath.  Presumably this is because the 9/3 o'clock positions were used on earlier versions, but does this imply the same engine version as on earlier P-11s  rather than a later one?  Not a modeller's problem, of course, but interesting.  I do have Jerzy Cynk's comments in his Putnam book on Polish Aircraft, but I was previously avoiding  this as it may be superseded by better information.  However, he does write that the engine was to be the Mercury VIII as in the P-50, which is logical enough..    

[JWM]

Regarding  exhaust and cowling - here is photo pf PZL P 50 Jastrząb (first prototype).

 

So it clear that at least from this side exhaust was at half of height of fuselage. 

The photo of second prototype showes other side

The rest is based on info that engine of Kobuz came from Jastrzab

Cheers

J-W

 

 

[Graham Boak]

Thanks for those, I don't think I'd seen them.  The starboard view is a little confusing - there appears to be something going on slightly below half-way yet there's no gap in the gills.   I do have a very basic P.50 kit somewhere, but I'll bet it lacks all such detail!

 

Of course, just because the P.11g had the same engine as the P.50 doesn't necessarily imply the same cowling, but  in this case I think it a very safe bet.

[neilh]

That stbd view looks to be an exhaust stub coming from the collector ring but much shorter than the picture of the port side ( which looks similar to a Blenheim exhaust ), and seems to exit outwards at 90 degrees with an oval exhaust outlet.

[Graham Boak]

Which perhaps was a revised installation for both sides on the 2nd prototype?  In which case it would also apply to the P-11g.  Fuel for a Poland 1940 modelling theme?

[Troy Smith]

11 hours ago, JWM said:

@MitchK was constructing PZL P 11G - with WIP thread. There were some discussion or advices on details about conversion 

 

[Graham Boak]

This thread above states that the second of JWM's photos does not show the 2nd Prototype but the first pre-production example intended for a Gnome Rhone engine.  So an aft exhaust would be more appropriate and we are not looking at a collector ring on the front.

[303sqn]

The fuselage of the second prototype was abandoned at the PZL factory hanger.

[JWM]

There was discussion on Polish historical aviation fora and journals what exactly is on this photo which I gave here as "second photo" from my post. This photo (and few more) was  found few years ago in some private archive. The machine on it is different not only in cowling from what is known about shapes of first prototype of P 50. It has long fairing behind canopy.  It is usually named (considered) a photo of second prototype - how I named it here. There is no eveidence for existing of P50 with GR engine - at least I do not remember such info.  I am not sure if it can be GR engine (14 cyliders) - it does not look much longer than cowling of first prototype. However - a lack of gill is clear.  

Cheers

J-W

 

[KRK4m]

As the only French engine considered for the P.50 was a 14-cylinder GR14N as used by P.24F/G/H/J there should be no collector ring - in all GR14 exhaust valves were faced rearwards, contrary to the Mercury with its rear inlet/forward exhaust design. Thus the aircraft on the 2nd photo also features some Bristol 9-cylinder radial. The only difference between the cowlings on the 1st and 2nd pictures seems to be shortened exhaust pipe (with oval outlet flush to the cowling side) that doesn't protrude into cooling gills area. Thanks to that the gill design could be simplified with no need for the reduced-size gills surrounding the longer pipe of  the 1st prototype. We can argue about the 9 blisters for Mercury cylinder heads (as in Blenheim or Gladiator) that are visible on the 1st photo and that are less evident on the 2nd one - either the cowling was totally new (with some 30-40mm increased diameter) or the rumours about fitting the sleeve-valve Perseus aren't so close to the S-F as most of us do think. We have to remember that PZL 49 development of PZL 37 bomber would feature Hercules engines, so the sleeve-valve technology could also enter the world of  9-cylinder radials in the Polish Air Force.

Moreover one should remember that - although very similar externally - the fuselages of the P.11c/f/g/h and all the production P.24s are totally different structurally. And it is not only the case of the enclosed cockpit and wider dorsal fairing behind it - in all the P.11s the monococque part starts behind the pilot seat while in all the P.24s in also does include the whole cockpit area (so it's a good 4 feet longer forward).    

 

 

As the manufacturing jigs for both fuselages were ready in the PZL Okecie factory it would be a total waste of time to produce a third one, combining the P.24 canopy and rear fairing with the Mercury engine bearers and side-mounted synchronized MGs from the P.11 (in twin-row GR-powered P.24s all the guns - two or four depending on variant - were located only inside or under the wings). Then if the Kobuz (P.11g or P.11h as the latest data shows) was to use the P.24 monococque cokpit part and canopy it would be called the P.24 (with some suffix letter) and if it was called P.11 it had to feature the standard P.11c airframe fitted with the P.50 Mercury VIII power-egg (i.e. complete with 3-bladed propeller and cowling).

Maybe the wheels were spatted, probably the cockpit was enclosed (but using the P.24 canopy looks unrealistic, as it would need the P.24 dorsal fairing to be implemented to the already existing P.11 rear fuselage of different geometry) and surely the plane was 4-gunned. But I'm not sure whether PZL have utilized the 4-gun P.24 wings or the late P.11 2-gun wings PLUS 2 guns on the fuselage sides (considering that complete P.11c fuselage was used).

In his 2014 book "Polish Aircraft in Romania 1933-47" by Stratus, Dan Antoniu states that the sole P.11g (c/n 8.129, fin serial 8004) had been flown in September 1939 to Romania by por. (F/O) Henryk Szczesny. The aircraft, bearing Romanian side numer #316, has been damaged beyond repair od 5th March 1942. 

The other thing is whether should we believe it...

Cheers

Michael

Edited December 2, 2017 by KRK4m
misprint observed

[Graham Boak]

Very interesting.  In view of the number of serviceable Polish aircraft that did fly to Romania, it should be no surprise that a serviceable Kobuz would do the same.

 

I wasn't aware about the structural differences between the P.11 and the P.24, but can make a few points. 

First, it seems to me that there'd be no more work modifying the P.11 headrest (and cockpit sides) to take the P.24 enclosed canopy than to design an entirely new canopy.  So I don't see this as a discriminator.  I agree that there would have been reason enough modify the P.11 to an enclosed cockpit.

Second, although I now understand the engineering differences between the two a little better, I suspect that a new aircraft for the Polish AF with a Mercury would have been called a P.11 variant for political reasons, whatever the origins of the fuselage. 

Third, I suspect that it would be easier (if not very) to fit a Mercury VIII onto a P.11 airframe than a P.24 one.

Fourth, would the P-50 installation permit the fuselage-mounted guns of the P.11c?  I think that this would be the driver between the choice of a 2-gun P-11 wing and a 4-gun P-24 wing.  The possibility of a 6-gun Kobuz may have been considered, but weight grounds would possibly have ruled it out.

Fifth, would there have been any engineering pressure to adopt the P.24 fuselage anyway, as it was presumably superior in some way to that of the P.11?

Six, given the desperate need for more fighters, would it not have been desirable to use both the P.11 and P.24 jigs?  Whether this would mean two versions of the Kobuz or Gnome-Rhone P.24s in Polish service, I won't make a guess.  However, either case would suggest a Kobuz based on the P.11c was most likely.

 

[KRK4m]

There is plenty of written material about the Kobuz prototype in the Gen. Sikorski Polish Institute archives in London SW7 (20, Prince's Gate). They include statements of both F/O Szczesny and the chief engineer of PZL Okecie. And there's nothing there about any parts of the P.24 to be used. Both gentlemen do state that P.11g prototype utilized production P.11c airframe, i.e. with girder framed cockpit part and standard P.11c wings with ailerons (the P.24 used flaperons like early Polikarpov I-16 variants). Both do remember 4 MGs and the enclosed canopy with open rear vents for good rear visibility (something like Macchi 202, thus no P.24 canopy), which in my opinion suggests staying with the narrow P.11 dorsal fairing. There's nothing said about the wheel spats, although Szczesny says that from some distance the Kobuz looked like a production P.24, which in turn suggests spatted wheels and the 3-bladed prop. Six MG armament was planned for the production Kobuz and MAYBE then the P.24 wing could be used, but as the prototype had 4 guns using P.11c wings and fuselage the only possible (for me) layout followed the late P.11c - two MGs in wings and two on fuselage sides.

Of course we can only follow such a deduction or not - the truth remains undisclosed

Cheers

Michael

 

[GrzeM]

On 2.12.2017 at 1:25 PM, Graham Boak said:

the P.24 fuselage anyway, as it was presumably superior in some way to that of the P.11?

In fact the P.24 fuselage was somewhat inferior to the P.11c one - as the P.24 was just strengthened and longer P.7 fuselage (1932 design), while the P.11c was later desingn, developed from P.11a in 1934 and had modified front area, including lowering enigne in order to improve visibility (and all that structural differences excellently described by KRK4m). 

8.129 was general Rayski's personal aircraft, "normal" P.11c but with stronger Mercury VI engine. I'm not sure it has any relation with Kobuz.

Some historians state that Kobuz was in general P.11c fuselage with P.24 wing (that made sense as P.24 had four guns in the wings).