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Relationship between P-11g and P-24


Graham Boak

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Looking at the profiles for the forthcoming P-11g Kobuz (https://www.72news.eu/2019/09/ibg-models-pzl-p11g-kobuz-markings.html), it does seem to be a combination of the P-24 and a Mercury engine.  Whereas this has often been assumed in the past when information was severely lacking, is this still considered as a fair assumption?  I have more P-24 kits than I need, and spare (ex-Frog Blenheim) Mercury engines and cowlings.  Is it known what, if any, other details should be considered?

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Rather P11c with Mercure, although with closed cockpit... Despite apparent layout similarities of PZL fighters  there was several very important construction differences between P24 and P11c (as well as between P11c and former P11a or P7): the main was which part of fuselage was monocock and which were based on steel truss inside. So the pannel lines goes differently.

There are better specialists then me on BM like @GrzeM or @KRK4m to explain details...

Regards

J-W

 

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There is big problem with Kobuz, as the only existing example was the prototype, made of various parts of the existing airplanes rather than from scratch. And - that prototype was different than the final, production version. Unfortunately the documentation has been lost, and even the accounts are scarce and contradictory (they seem mix data of the prototype and the production version). There is no photo of this plane.

 

In general idea of Kobuz was to mix P.11c fuselage with the P.24 wing and PZL P.50 Jastrząb engine (Polish produced Bristol-PZL Mercury VIII). But it was production version, never realised. The prototype was for sure different. From scarce accounts one can assume that the series produced P.11c fuselage was used, with series Jastrząb engine most probably with Jastrząb cover and propeller, and it had 4 machine guns. Nobody knows if the P.24 wing was used or P.11c one (both were ready available in factory at that time). Romanian sources give information that Henryk Szczęsny (who for sure flew Kobuz operationally in September 1939) flew to Romania on "P11" with 8.129 airplane serial number and non-standard engine number 8004 (typical for P.11c PZL-Bristol Mercury V had numbers in 4xxx range). But what it means it is still not precise. 8.129 before the war was non-standard PZL P.11c with stronger Mercury VI engine, personal airplane of General Ludomił Rayski, commander of Polish Air Forces from 1926 till March 1939. After Rayski's dimission in March 1939 his plane was no longer needed and most probably it was modified to become Kobuz prototype (timing is correct). But what was the scale of modification? It is possible that only the engine was changed for Mercury VIII, and the cockpit was covered (there is pilot's account that the cockpit was covered with canopy, but it didn't fit to the turtledeck so there were big apertures behind the pilot's head - I assume that P.24 broader canopy was fitted on narrower P.11 turtledeck, which explains the apertures). Was the P.24 wing used in prototype? Nobody knows. I belive it was not necessary, but possible. Number of machine guns used in combat is 4, what may suggest typical P.11 two in fuselage and two in wings (what suggests rather normal P.11c wing) or 4 mg's in wings (worse for airplane performance - heavier wing armament was disliked by the pilots, but may be explained with lack of synchronisation gear for three-bladed propeller).

Engine was Polish-produced Mercury VIII (there were over 100 ready for P.50 Jastrząb). I belive that engine cover must have been smooth, like in series produced Jastrząb (Jastrząb prototype had bulged cover, but it's engine remained on the Jastrząb prototype in September 1939, so was not used on Kobuz.

Smooth engine cover on production Jastrząb:

spacer.png

 

Bulged engine cover on Jastrząb prototype:

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Propeller should be Hamilton-Standard. I don't belive French propeller used on Gnome-Rhone P.24 engines fit the Bristol.

Wheel-spats - nobody knows, if these were applied on the prototype or planned for production airplane.

That's it.

Edited by GrzeM
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One interesting statement there is that the P50-2 and production aircraft were to have Gnome-Rhones not Mercuries, so it is just as well that I haven't removed the blisters … yet.

 

I'd like to know a little more about the longer fuselage on the P-50-2, having a short stubby P-50-1 kit one and potentially a spare Gnome-Rhone from a P-24 kit.

Edited by Graham Boak
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Monografie Lotnicze 36 PZL P.11 part 1.

In the summer of 1937, in the construction office of the PZL No. 1 Aircraft Factory at Okęcie-Paluch, P.11c performance calculations were made for the PZL-Bristol Mercury VIII engine with a power of 625 KW (850 HP), which was then produced by the PZL Engine Factory No. 1, Warsaw. This project was abandoned because it turned out that despite the significant power increase, the speed of the aircraft would not reach 400 kph due to the large diameter of the engine, increasing the aerodynamic resistance.

When, in April 1939, the production of the PZL 50 Jastrząb fighter aircraft was halted due to its low performance and unsatisfactory properties, they began to look for the possibility of quickly developing another fighter design.The Aviation Command rejected the proposal for the production of P.24 aircraft with French Gnome-Rhone engines, both because of their unreliability and long lead time for the order in France. Since 150 Mercury VIII engines, made for Jastrząb I, were immediately available, the decision was made to start production of the P.11c with these engines. At the PZL No. 1 plant in Warsaw, a project for such a modification was started. The new P.11c version was designated PZL P.11g Kobuz.. In the summer of 1939, one P.11c was turned into a P.11g prototype at the PZL-WP No. 1 plant. In comparison with the P11c it received a modified engine cover, a new propeller and a covered cabin as with the PZL P.24. The prototype Kabuz flew at Okęce in the middle of August 1939 piloted by Kazimierz Kula. The aircraft reached a maximum speed of 390 kph in the trials.

The production of 90 Kabuz was commissioned to Podlaska Wytwórnia Samalotów (PWS) in Biała Podlaska, where the wings were manufactured for the P.24 as spare parts for export. The tailplane was to be made by Lubelska Wytwórnia Samolotów (LWS), which produced them for the P.24. Production was to start in September 1939, and deliveries of the first aircraft in the first quarter of 1940. In the first days of September 1939, the Kobuz prototype was evacuated by factory pilots to Lwow and then to Gródek Jagielloński. From there, Ing. Pil. Jerzy Widawski moved it to Wielicka near Kowel. In Wieliczka, the plane was taken over by military forces and armed with 4 guns. On 14 and 15 September it shot down two German bombers. Damaged Kobuz was destroyed at this airfield a few days later (according to one report it flew to Romania).

Monografie Lotnicze 36 PZL P.11 part 2.

Apart from the eleven from III/3 Dyon, on September 14, another P.11 fighter took part in the operation - the prototype of the P.11g Kobuz aircraft. Kobuz, which at the outbreak of the war was at the Institute of Aviation Technology in Warsaw, was evacuated to Lwow on 5 September and then to Gródek Jagielloński. September 13, Ing. Pil. Jerzy Widawski brought the plane to the airfield at Wieliczka (40 km southeast of Kowel), where at that time were the 2 Dyon Łoś from the Bomber Brigade. After a review by mechanics and the installation of weapons (4 guns), P.11g was given to the defenders of Wieliczka, an improvised fighter squadron consisting of pilots of the Advanced Fighter School, which had so far only a few P.7a aircraft. On September 14, on the beginning of the afternoon, the WSM instructor, Lieutenant Henryk Szczęsny, attacked a group of He 111 Bombers with the Kubuz and shot down one aircraft that crashed near Kowel.

[15 september]

Defending airfield Wielicku Fighter Squadron pilots WSP alerted several time when German aircraft appeared. Around 17.30 Henryk Szczęsny with the P.11g intercepted a group of 5 He 111. One of the bombers struck by Polish fire, caught fire in the air and fell to the swamp near Kowel. During this fight, the pilot was injured in the leg and his plane - P.11g – badly damaged. Most probably, the Kobuz did not return to service. One of the reports from Romania reported that the aircraft was evacuated there, but this information has not yet been confirmed.

 

Polskie Lotnictwo Myśliwskie w Boju Wrześniowym, Jerzy B Cynk

September 13, two days after the departure of most of the Radziechów school staff to Kuty - a concentration of supernumerary flying and ground personnel from aviation units and schools - P.7 unit, commanded by Lt.. Henryk Szczęsny and the cadet pilot students and a group of mechanics moved from Radziechów to the Wielick airfield, where the Łos of the Bomber Brigade were stationed. The team was subordinated to Cpt. Łaguna, responsible for the OPL airfield.

On the same day, prototypes arrived at Wieliczka: P.46/II Sum II, from Lwów, piloted by engineer Stanisław Riessa, and P.11g Kubuz, piloted by Jerzy Widawski. Kubuz, evacuated from Okęcie to Lwow on 5 September and then moved to the airfield in the area of Grógek Jagielloński, breaking his stabilizer.

Kubuz, evacuated from Okęcie to Lwow on 5 September and then moved to the airfield in the area of Grógek Jagielloński. He caught in landing the empennage of the Sum, breaking his stabilizer. The slightly damaged Kubuz was repaired and ready for combat use the same day and Capt. Łaguna gave it to Lt. Szczęsny.

Beginning on September 14, the squadron of Lt. Szczęsny, strengthened with the Kubuz, was the defence of the airfield, which was supposed to defend the Wielicka area and ensure the take-off and landing of Łoś. This was the first time the Bomber Brigade had any airfield defence since the beginning of hostilities.

September 14 the squadron aircraft patrolled several times. In the south, Lt. Szczęsny, flying the Kubuz, allegedly shot down one He 111 in the Kowel area, which is not confirmed in the Luftwaffe documentation.

 

Footnote 820.

According to the reports of Capt. Cwynar, IPMS Lot AII.23/1a-6, -7, -8. Despite some reliable information about the use and successes of Kobuz in the defense of Wielicka, contained in the London documents and September studies in the archives of IPMS, in Poland the fate of Kubuz remained unknown until recently; the most common was the erroneous message about the prototype's destruction during the Okęcie bombing. At the same time, the legend was established, finding its source in Henryk Szczęsny's statements that in Wieliczka he flew a P.24. Kubuz had a closed P.24 cabin and, apart from the Mercury VIII engine, it was very similar to the P.24. One can only surmise, Lt. Szczęny did not realize what plane he fought with. The message about the evacuation of the Kobuz to Wielicka and handing it over to Lt. Szczęsny was also confirmed by Jerzy Widawski. None of the surviving original documents indicating the equipment of the Pilot School mentions a P.24.

In addition to the fighter dyon of the Poznań Army, the ad hoc squadron of Lt. Szczęsny, consisting of pilots of the Advanced Fighter Pilot School, whose task it was to defend the Łoś bombers' airfield in Wieliczka, also conducted a much more effective operation.

The squadron was scrambled several times. During one of the flights, Szczęsny, flying the faster Kobuz, fought alone a formation of Heinkels and shot down one of them. Szczesny was injured and his plane was hit.

The operation records of the KG 55 confirms the loss of He 111P z.1 squadron I./KG 55 (probably as a result of the fight with Szczęsny), whose crew, under the direction of Fritz, died in the Dubno-Chyrów area and was buried in the Polish territory.

The ad hoc squadron of the Advance Pilot School, deprived of its commander, Lieutenant Szczęsny, injured the previous day, made a few flights in the morning, protecting the airfield during the departure of the Łoś dyon. These activities closed a short period of its combat work. What happened to it is difficult to determine. It must be assumed that the damaged Kubuz was destroyed when the squadron was evacuated.

 

According to Romanian records it was evacuated to Romania, pilot Henryk Szczęsny, original (Polish) serial 8.129, engine number 8004, given Romanian number 316, SOC 5/3/1942, reason, accident.

 

 

 

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20 hours ago, Graham Boak said:

One interesting statement there is that the P50-2 and production aircraft were to have Gnome-Rhones not Mercuries, so it is just as well that I haven't removed the blisters … yet.

Well - not exactly. PZL P.50/I prototype really flew, while the P/50/II was almost finished, but without the engine. And while the P.50A (Mercury VIII) production has been started in 1939 (see the photo of the partially completed airframe with German soldiers) the G-R engined P.50B was only a project without even a flying prototype, moreover, there is no confirmation that any proper G-R engine ever reached Poland. 150 PZL-produced Bristol Mercury VIII engines for production P.50A planes were ready before the war (some were later sold by Germans to Finland AFAIK). Fact of use of the Mercury VIII on the Kobuz and first production P.50A is undisputable.

What the cover of the G-R engine on P.50 looked like is a mystery.

 

18 hours ago, 303sqn said:

 airfield at Wieliczka (40 km southeast of Kowel)

 

Not "Wielicka" but "Wielick".

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I just now saw this discussion, and it is very interesting, indeed! I have always liked the looks of the P.7, P.11, and P.24, but this prototype is the bee's knees! Thank you all for your posts on a very interesting and little-known topic! A 1/72 kit would be so nice!

Mike

Edited by 72modeler
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If I build the existing Kobuz prototype (which was used operationally above Wielick by Henryk Szczęsny - two Heinkels shot down) I'd take productional P.11c (Rayski's 8.129), change the engine with Mercury VIII in smooth cover from the production P.50 and three-blade constant speed Hamilton-Standard prop. And add the closed canopy. Maybe I'd add the wheel spats. Nothing more. But it's an educated guess. I think there are no primary sources or accounts contradicting any detail of that version. But also P.24 wing is possible, while not confirmed.

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  • 2 weeks later...

I'd like to know a little bit more about differences between the P-11c and the P-24, as my references on these aircraft are somewhat dated, and tend to assume that differences are minor.   In recent postings there has been a vague comment about differences between a true monocoque fuselage (P-24?) and a framed structure (P-11c?).  And hence some panel changes, but what?  There is a difference in the extra support cables for the undercarriage, in that the P-11c's meet on the centreline whereas the P-24's cross over.  The P-24 is said to have a wider canopy/cockpit/headrest fairing.  I followed the discussion about the lack of fuselage guns but would point out that there was a synchronising mechanism for three-bladed props on the Mercury, witness the Gladiator Mk.II.  So there is not a technical reason to remove these guns to the wing, which would indeed render the aircraft slightly more clumsy but would had a greater rate of fire.  Also, what was the difference between P-11c and P-24 wings?  Was there also a difference in engine coolers?

 

Transferring this to the P-11G, it would seem more sensible to me for PZL to base a new variant on the later, improved, fuselage of the P-24 rather than that of the P-11c.  Fitting the (presumably slightly modified) engine mounting of the newer Mercury would cause little problem to the forward fuselage structure (bulkhead?), and would be needed on both types, compared to the changes in designing/fitting a new closed canopy to a P-11c cockpit.  Why make backward changes when the more modern type is available on the production line?

 

I have Azur's P-11E and P-24, plus an Encore P-24F/G.  I'd like to be able to use one of the P-24 kits as a basis for a P-11g conversion although I don't wish to lose the P-11F, though I can use it to check against the P-24s for access panel differences on the fuselage.  Assuming Azur has noticed these,  I suspect the kits also include Mercury engines and cowlings from other variant boxings, but I do have spare Frog Blenheim cowlings and engines.  However if the P-11g was to use smooth cowlings, the blisters would have to be removed from these.  I would point out that the blisters are circular in cross-section, rather than the flattened shapes seen on the new P-11g kit, and I think the Frog parts give a better representation of these.  If you are going to remove them from the IBG kit anyway then this won't matter.  Any difference in the oil coolers is still an open question that would need sorting.

 

But then I'll probably need transfers, so maybe I should just buy the Kobuz kit anyway.  And then argue the toss.

Edited by Graham Boak
Typo corrected, plus some minor improvements.
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The P.24 wing was designed to accommodate heavier armament, either two 20.01 mm Oerlikon cannons mounted at the strut support, two or four machine guns, or two cannon and two machine guns. The P.11c wing could only accommodate two machine guns. It was intended that the Kubuz would have four improved KM Wz 36 guns in the wings so the P.11c wing could not be used.

 

There were no P.11d or P.11e so I presume you mean the P.11f. The ‘d’ and ‘e’ are a bit of a mystery but one of them was almost certainly a navalized version of the 11c. In 1933-34 the KMW intended to build up a land based force of 24 fighters similar to the P.11c but adapted for naval needs. These plans were later abandoned.

 

The Azur P.11 kits are bit of a dogs breakfast and cannot be relied on. For example the fuselage is about 3 mm too long. Basically they are the P.24 kit with a different fuselage. However, they forgot to include a modified bulkhead (behind the seat and which did not exist on the real thing) and cockpit floor. So you have to file down the existing parts to fit in the fuselage. The bulkhead does not serve any use so I cut of the headrest and discarded it. The seat blocks off the resulting ‘hole’. I had to file off a fair bit of the cockpit floor sides to get that to fit. There is nothing that joins the cylinder heads to the exhaust ring.

 

They used the same wings as the P.24 kits which have different panels, not very noticeable but the ‘wedge’ in front of the windscreen is missing.

 

With the P.11f the exhausts are supplied as resin castings. One review claimed they were too short or too long, cannot remember which. I don’t think so, they do fit, but I had to do a lot of fiddling to get them in the correct place. I do have an issue with them. In the kit they are a tube, round in section, and constant diameter. Looking at photographs they appear to me to taper and oval in section. Kinda like a long flattened cone.

 

It seems that IBG are intent on kitting all the P.11s and P.24s. Lets hope they do a better job than Azur.

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Thanks for the response.  I did mean the P-11F, and have now corrected this typo (and modified slightly the text around it) in the above posting. 

 

Where is the error in the P-11f?  Was the P-24 fuselage actually longer than that of the P-11c, or is this a kit problem with both?

 

I have also answered by own question about the oil coolers, although this does perhaps raise a question about the coolers for the later Mercury.  Given this, the enclosed canopy and the use of a P-24 wing with four guns, then the use of the P-24 fuselage for the Kobuz would seem to be the obvious engineering answer, and the use of a P-11c fuselage perverse.  Whether the use of an early P-24 fuselage or a later one (with two coolers on each side of the fuselage) may still be uncertain, the engineering changes would seem to be slight - and there may have been a different solution again for the Mercury.  

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I think the lenght of rear parts of fuselages (not talking on total lenght, since there were different engines making total lenght differences) are the same for P11c and P24 despite the differences in technology quoted previously. BTW I 've bumped today on interesting photo of destroyed (or not completed)  in Sept 39 in Warsaw P 24 prepared for Bulgaria.  It is from very interesting but difficult to go through it Polish forum Odkrywcy. Photos of airplanes from 1939 are in 34 separate threads, each one with at least dozens of pages....https://forum.odkrywca.pl/topic/758714-zdjęcie-naszego-samolotu---część-31/page/7/#comments

sl1600_2_copy98.jpg&x=800

cheers

J-W

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I think a/c 313 is one of the escaped Polish P.11c, hence the different cowling.  They seem to have had 300-series numbers (e.g. 315).  The P-11b certainly seems a little odd.

 

I'm inclined to believe you about the same size fuselage (without engine) but aerodynamically I would have expected a need to balance the longer nose with either a longer fuselage or (more likely) a larger tail.

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To compensate for changes in the CoG the a 45 cm section was inserted in the fuselage between the wing mountings and the cockpit.

 

The P.11b was a P.11a with a GN engine. Because the Romanian order had a higher priority the P.11bs were built before the P.11as, following the production of the P.7. The first 20 were fitted with a short chord cowling ring with no exhaust collector ring, individual exhausts exiting in the rear. Similar to the P.7. After that they had a longer chord cowling with a collector ring, similar to the P.11a and c. The were numbered 1 to 50 in Romanian service.

 

The P.11f had an exhaust system similar to that of the P.24. The first five were built in Poland the remainder by IAR in Romania. They were numbered 51 to 145.

 

P.11as and P.11cs in Romanian Air Force service were allocated numbers starting from 301. 342 is the highest number I know of. 319 (its not 313) was ex 141 Esk Polish c/n 8.62. Evacuated to Romania by pilot Lech Lachowicki. SOC 25/06/1945, worn out.

Edited by 303sqn
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That fuselage extension makes sense, I've just been staring at the wrong parts of the fuselage in search of anything.  This would also explain the changes in the windscreen.  I still feel that adding a canopy to P-11c would require noteworthy changes to the upper fuselage structure and headrest.  However, the new Mercury may have been heavier than the old one, and the 3-blade prop would have been slightly destabilising, so just perhaps a longer fuselage could have been desirable anyway.  Not enough information (or skills) to judge.

 

In modelling terms it would seem easier to start with a P-24 fuselage and shorten it - just how yet to be defined!  Particularly as a P-24 wing, canopy and (probably) oil coolers are required.  Personally I'd ignore the spats as likely to be more trouble than they are worth.

 

PS 45cm seems a lot.  4.5 cm?

Edited by Graham Boak
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But which book?  I've had a strong denial  (https://www.tapatalk.com/groups/72nd_aircraft/ibg-catalogue-2019-1-72-pzl-p-11-family-t10566.html#p107798) that there was ever any such increase, this story being raised and then repeated because of some misunderstanding of the prototypes.   

 

Be that as it may, in my old Putnam reference Cynk list the P.11c as 7.55m, the P-24A as 7.5m and the later ones as 7.6m.  The difference there appears to be the lack or presence of a spinner.  This appears to be entirely consistent with a 45mm difference, not 45cm.  This is overall, and seems consistent with the longer engine.  It leaves no or very little distance for a longer fuselage, let alone another foot and a half.  I do feel that any such amount would stand out a mile (excuse mixed metrics) when looking at photos.  I'm willing to be convinced by a small fuselage growth, but not this one.

 

So where is the quoted length of a P-24 said to be over 8m?  Glass (PZL P-24, from Wydawnictwo Militaria) quotes the P-24A/B at 7.5m, although he does have the E at 7.83m and the F/G at 7.81m.  His text is Polish: if he explains this difference I can't understand it.  However, it still doesn't allow for 45cm growth, even on the later ones.  

 

I strongly suspect a simple misprint, and possibly a confusion as to just where the growth was.  This does of course read back to criticism of the Azur P-11f fuselage.

Edited by Graham Boak
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I am sure that data from Andrzej Glass book are correct.  Aslo the drawings there (BTW - there is a new, extended edition of P-24 monography:

 

Regards

JWM

 

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I don't think I can justify another book on the subject of the P-24, good though it looks.  A couple of questions about it.

 

1.  Is there any explanation of the different fuselage lengths - the prototypes /I and /II, the E and F/G?  or why there is so little difference on the A/B/C from the P-11?

 

2.  The computer graphics shows a sharply convex curved canopy partly flush with the fuselage and partly faired into the narrow headrest of the P-11.  However I've just been looking at a very good photo of a P-24E where the headrest was much wider as a continuation of the fuselage sides and the canopy sides are effectively straight.  Were there two different standards?  The cg version would perhaps make the fitting of a canopy to a P-11c fuselage much easier.

 

Humph.  Just when I thought I'd sorted these beasties out.

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Here is develpment of canopy of P24 from this newer, extended version of Glass monography:

pzl24_kagero_010.jpg

 

First prototypes of P24 had tail of P11s, with lower fin. This was llike that, bacause p11c is newer then P24, they were developed in paralllel in some way cross kitting design...(a tail for example)

J-W

 

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