Questions re Polikarpov-fighters.

[Kari Lumppio]

Originally Posted by Arsenal VG-33

...there is no interest in the “modern” or “obsolete” definition, but only on the strenth vs weight ratio. The highly stesses stainless steel 30Kh GSA used on the I-18 airframe (120-140 kg/mm²) was very effective on that way. “Modernity” is a kind of industrial problem, and technically not always the best. In 1939, light alloys were giving 40 kg/mm² resistance, at best.

Hello!

I am sitting on the fence on the topic of this thread. But about the materials. With the values you give steel with strength 120 kg/mm2 has less than 4% better strength/weight ratio than "light alloys".

But can you make whole airframe out of steel? No! Usually steel is used only to make the load carrying members like fuselage tubular frame which has to be covered to get the aerodynamic form. Many times it was aluminum "roof" and fabric covering below that. Steel fuselage frames most often were statically determined meaning there was no alternative load paths if the frame tubes were damaged. I do not know if this was generally taken in account in design.
BTW the delta wood was similar to steel in the use - it was used only where high strength was needed (spars, stringers). Not for whole airframe.

For light alloys the design is usually totally different. The whole "cover" was load carrying element which was supported by frames and stringers against buckling/collapsing (some reversible buckling of panels is usually allowed for). Conservatively designed stiffened structure usually had redundancy and provided multiple load paths even when damaged ("fail safe"). Curtiss design is a good example.

In the real light structures stability is usually of more concern than material strength. Even in tubular frames. If so, then the much higher density of steel becomes literally a burden. There is no use for the extra strength of steel over light alloys then.

Plus. Was the "30Kh GSA" steel really stainless? Was it weldable, and how easily?

As far as I know steel frames usually were of chromolybdene (spelling) steel like AISI 4130 (good weldability). It rusts easily, the high-strength version (4130N) rusts like hell. I have right now one test series in environmental chamber downstairs, a work project. It was covered with rust spots within hour when in 60 degrees Celsius/95% relative humidity. Aluminum 7075 - both clad and bare - have got only some oxidation spots after couple of weeks. Another thing to ponder in design.

Regards,
Kari

[Arsenal VG-33]

Hello

The problem I have with the relative performance of the pre-production series I-180 relative to the third prototype isn´t about the expected fall in performance with mass-produced aircrafts versus hand-crafted prototypes, as Franek Grabowski deduced.

On that point, Franek is right, but pre-production and the very first serial aircrafts are usually better in USSR, than the mass-produced ones.

The pre-production aircrafts are less developed than the third prototype. They have the same powerplant, (M-88R), but are heavier, and are without the aerodynamic "improvements" of the third prototype. Yet, they are supposed to be faster, and with a higher rate of climb.
Are you saying that the difference is due to the pre-series having larger propellers?

According to Youri Gouglya, the I 180-3 had many defaults noticed during state acceptance trials reports (may 40)

-lack of the plexiglass canopy
-unsatisfactory work of the tail weel retraction system
-unsatisfactory propeller
-rough surfaces in general (high rugosity)

-and from Polikarpov letter, wrecked (twisted) fuselage...

But it was considered, once those small problems resolved the plane would easily reach 600 km/h. In other worlds, virtually this contractual speed was attained and aircraft officialy accepted for production.
Heavier? But at 2429 kg the I-180S had only 4 kg more that the I-180-3.
Look at http://articles.gourt.com/en/Polikarpov%20I-180

So, in order to reassure Franek, the serial aircraft did lost some performance...

The alternative explanation is that performance measurements are in some way "doctored", as is alleged that Yakovlev did for the Yak-1, and as Bloch did for the MB-152. (I bought a rather expensive book; Joanne´s Le Bloch MB 152, mainly in order to find out the details of that story, but although superbly detailed in almost every respect relating to the MB-150 series, he just mentions it in passing, confirming that the test figures were indeed faked, and then goes on to other subjects.)

I will exchange you with great pleasure some scans from Googlya and Maslov books about i 180 against your4S MB 152 by PM. It’s rather expensive even for me...

I disagree with you about there being nothing wrong with the MB 152. As the late Gaston Botquin argued 30 years ago, the Curtiss H 75 was a far more effective fighter.

I wouldn’t say that, the Hawk was much more reliable in terms of MTTF and MTBR (mid time to fault)/ (mid time to repear) and the Bloch a kind of “hangar queen”. But this latter point was progressevely improved...
Both of them were underpowered and slower than the Me 109E but could outfight it in a turning circles dogfight.

The rest for tomorrow...

VG

[Franek Grabowski]

Originally Posted by Kari Lumppio

But can you make whole airframe out of steel? No! Usually steel is used only to make the load carrying members like fuselage tubular frame which has to be covered to get the aerodynamic form.

Steel was often used for spars, in order to increase stiffness.

Plus. Was the "30Kh GSA" steel really stainless? Was it weldable, and how easily?

I presume you know the answer, as you would not ask not knowing it, would you?

Originally Posted by Arsenal VG-33

I would be very cautious in my turn about your knowledge in the catastrophic situation in the french industry in 1936. We were desesperatly trying to resolve problems, by different ways. I personnaly think that the Polikarpov I-17 produced in the USSR with licensed tree-bladed Ratier prop and hispano engine could have been a good temporary solution.

Another good temporary solution would have been to establish Gulag archipelago across the Europe and to send there people's enemies. Certainly it could substantially improve the French industry.

Oh, really? You see that...
Well read my post again...about 1940, thin tubes, chromansils end etc...

Yes, I have read, and I stand by my comment, that steel is still heavier than aluminum. Feel free to think otherwise, if you want.

Stap'me! Did you find it by yourself once more, without any help?
Thank you for all this "Lapalissades"* (*trivial evidencies from Lapalisse a french Phylosoph from the Rennaissance aera).
But read Shavrov, Kosminkov: sometimes it was the opposite.

I do not know what has Shavrov or Kosminkov or even Lapalisse to the question of Birgir.

Are you still kidding? I-180, was no more overstressed, understressed either hyperstressed than the others soviet fighters of its time. It was just responding to the soviet specification standarts of the year (7,5-8G, i thing). Maybe more, but NOT LESS.

I am not sure if this was the correct word, but I have no better one. Nonetheless I see you are confusing things. One thing is to withstand specifications, say that 8G, and completely another a safety margin, size, etc. allowing for installation of more powerful engine, heavier armament and equipment, additional fuel, etc. The best case of such development is Spitfire which started as 1000 hp powered bird with 8 mgs, and ended as a 2000 hp beast with 4 cannons and ordnance racks, this without any major structural changes of the basic airframe. If any modification of I-180 required to redesign the aircraft, then it was absolutely justified to cancel it.

Furthermore before building a plane you have to send a complete file of calculations to the state acceptance commission, and theorycally wait for a positive answer.

What calculations?!

But you might be very youg, ask to your older poles what was it to be leaving under soviet (heavy) administration. Even Kafka, would have not enough imagination...

I am old enough. But even they did not manage to turn a carrot into a fruit nor to consider curvature of banana.

[Arsenal VG-33]

Sorry Birgir,

I have missed your post here:

The translation is not very clear, but it seems to indicate that unresolved issues regarding debugging the prototype were rather minor. So compared with the other russian fighters, it was a mature design. (Lamp in cabin, cleaning tailwheel? real problems or mistranslations?)

The real translation is lack of the bulkhead, non retracting tailwheel

Now considering the same plane with

satisfactory prop ( + ? km/h)
enlosed canopy (+ 15/20 km/h)
retracted tailwheel ( + 5 km/h)
highly polished with accurate fuselage lines (+ 10 km/h)

I would say YES, the plane would be faster than 600 km/h!

Also the production programme is not unreasonable, in view of the fact that the factory changed over to producing Laggs, using totally different technology, and still produced several hundred machines in the first half of 1941.

The Lagg was a technological "beast" since it could reach 515 km/h at SL with only 1020 hp. But a kind of industral disaster too, cause resins used to make the Delta D were travelling from the USA to USSR through germany.

This allowed the Luftwaffe to change over to 109E in a short period in 1939. It seems that the M-88 was only in hiatus for 4-5 months in 1940.

AFAIK, problems with M 88 occured when soviets were trying to put in production a new M-88 with 200 hours (300h?) overhall, instead of the old one (100) (150?). I don't remember original values exactly... No production was stopped, only deliveries and flights with the new modernized engine, during state investigation tests in summer 1940. Planes with the old engine versions were still flying...

Best regards

[Arsenal VG-33]

Hello Kari

[quote]

Originally Posted by Kari Lumppio

Hello!

I am sitting on the fence on the topic of this thread. But about the materials. With the values you give steel with strength 120 kg/mm2 has less than 4% better strength/weight ratio than "light alloys".

But 120 kg force is an exceptionnal value for mid 30ies! In France we use 80-95 kgf/mm² even in mid 40ies.
38-42 kg is usual for dural, anywere.

The same for delta D. with 27,4 kg/mm². French "hardened woods" were weaker, even with the same density.

For light alloys the design is usually totally different. The whole "cover" was load carrying element which was supported by frames and stringers against buckling/collapsing (some reversible buckling of panels is usually allowed for).

The best repartition "load" for cover is obtained in a monocoque structure, wich is even better in that way that the Vickers "Geodetic one". It's why a wood plane could be lighter (Arsenal VG against Dewoitine 520) or equivalent to à dural one, even with the disastrous weight/resistance ratio of wood materials. Cf Mosquito. Even with oregon pine or balsa.

If Dural is a superior material by itself and you have a lot or very strong plane parts only attached by rivets one to each other. Don't forget the whole plane balance (in 1938 of course) count also the weakness lines due to holes for rivets, and the advantages of the glue and welding techneakes.

Plus. Was the "30Kh GSA" steel really stainless? Was it weldable, and how easily?

two links:

http://www.viam.ru/index.php?section=169&language=2

http://www.metaltrade.ru/abc/x/2257.htm


AFAIK 140 kg/mm² is a value fo clean metal, 120 for the welded one.
Stainless is a translation from the dear Green-Swanborough-Dexter Gordon books.
Haw stainless it was, how was it weldable? Better wright or mail to the VIAM. I only know that this metal Chromansil was used in thin welded tubes in I-153/i-16, 18; Yak airframes.

As far as I know steel frames usually were of chromolybdene (spelling) steel like AISI 4130 (good weldability). It rusts easily, the high-strength version (4130N) rusts like hell. I have right now one test series in environmental chamber downstairs, a work project. It was covered with rust spots within hour when in 60 degrees Celsius/95% relative humidity. Aluminum 7075 - both clad and bare - have got only some oxidation spots after couple of weeks. Another thing to ponder in design.

I'm not fluent in AISI standards, i'm using french XC ones. But i'v got a friend of mine working at L'Institut Français de la Soudure, as an inspector. If problems persits, he will tell you what to do.

Best regards

[Franek Grabowski]

The Lagg was a technological "beast" since it could reach 515 km/h at SL with only 1020 hp. But a kind of industral disaster too, cause resins used to make the Delta D were travelling from the USA to USSR through germany.

Smooth aerodynamics does not make a perfect fighter alone. Otherwise I am not sure what are you trying to prove.

But 120 kg force is an exceptionnal value for mid 30ies! In France we use 80-95 kgf/mm² even in mid 40ies.
38-42 kg is usual for dural, anywere.
The same for delta D. with 27,4 kg/mm². French "hardened woods" were weaker, even with the same density.

May I ask again, what resistance are you comparing?

The best repartition "load" for cover is obtained in a monocoque structure, wich is even better in that way that the Vickers "Geodetic one". It's why a wood plane could be lighter (Arsenal VG against Dewoitine 520) or equivalent to à dural one, even with the disastrous weight/resistance ratio of wood materials. Cf Mosquito. Even with oregon pine or balsa.

Wooden aircraft will never be lighter than a metal one. IIRC Mosquito was about 1,5 ton heavier than a contemporary metal aircraft, though better aerodynamics was certainly a gain.

If Dural is a superior material by itself and you have a lot or very strong plane parts only attached by rivets one to each other. Don't forget the whole plane balance (in 1938 of course) count also the weakness lines due to holes for rivets, and the advantages of the glue and welding techneakes.

It is superior, and that is why we are doing metal aircraft, not wooden ones.

AFAIK 140 kg/mm² is a value fo clean metal, 120 for the welded one.
Stainless is a translation from the dear Green-Swanborough-Dexter Gordon books.
Haw stainless it was, how was it weldable? Better wright or mail to the VIAM. I only know that this metal Chromansil was used in thin welded tubes in I-153/i-16, 18; Yak airframes.

I bet Kari knows the answer. The question is if you know, what are you writing about.

[Ruy Horta]

Originally Posted by Birgir Thorisson

The wikipedia entry for the Polikarpov I-180, which is well sourced, names a number of projected developments of the I-16, that I have never seen mentioned before. As I understand it, these were attempts to re-engine the basic design with 14 cylinder, two-row radial engines. derived from the Gnome Rhone Mistral-Major (14K I presume). The are called I-161, I-162, I-163, I-164, and I-165.
These seem to be precursors to the second variation of the I-180, (mixed construction), represented by the second prototype. (I-180-2).

A related topic. The wikipedia authors relate M. Maslovs conclusions that the I-180 was cancelled for "irrational" reasons. That, over-awed by the Bf 109, the soviet high command cancelled the radial engined I-180 in favour of in-line engined aircrafts. (Lagg-3, Yak-1).

It is a a reasonable conclusion that the Soviet airforce would have been better off with a fully developed design (I-180), rather than immature designs that were not ready, (MiG, Lagg & Yak), although the expected performance was slightly lower.

Birgir Thorisson

First I didn't follow the complete thread, and second I am not an expert.

Just some random thoughts.

The design philosophy I-180 seemed to have lived on in the I-16x-series you mention, the I-185 and even the MiG-1 (!) and its many derivatives. Even if many of these didn't reach production status, it appears that enough effort was made to do (extensive) research and develop these types.

By the time the I-185 might have been the best Soviet fighters, there were thousands of aicraft of established types rolling off the production lines that had nearly equal performance. Development life of these contemporaries wasn't exactly short and unsuccessful, both Yakovlev and Lavochkin fighters started a (direct) line of high performance piston engine fighters that served until the arrival of the jet.

Polikarpov may just have been unlucky, the loss of Soviet hero Chkalov in the I-180 prototype, his I-16 and I-153 being obsolescent at the start of the second world war, finally the misuse of the MiG-3 (forced to fly under conditions that did not bring out the best it had to offer - high altitude performance).

The radial engine I-180 might just had the bad luck to have been introduced when inline engines were the vogue (and arguably for the right reason). Radials just took a while to catch up again.

[Arsenal VG-33]

May I ask again, what resistance are you comparing?

No need to ask, just read!

Wooden aircraft will never be lighter than a metal one. IIRC Mosquito was about 1,5 ton heavier than a contemporary metal aircraft, though better aerodynamics was certainly a gain.

Give us an example

It is superior, and that is why we are doing metal aircraft, not wooden ones.

About we i don't know. You are certainly doing nothing. I have restored a wooden JoDel wing.

I bet Kari knows the answer. The question is if you know, what are you writing about.

No comment. Just read my posts and links.

[Franek Grabowski]

Originally Posted by Arsenal VG-33

No need to ask, just read!

I am just doing that, and I cannot find what resistance do you mean. You do not know too much about resistance, do you?

Give us an example

Do it yourself, compare such aircraft like Beaufighter, Invader, Ju 88, Me 110, etc. and draw your own conclusions. Or calculate if you can.

About we i don't know. You are certainly doing nothing. I have restored a wooden JoDel wing.

When was Jodel designed and was it a high performance aircraft?

No comment. Just read my posts and links.

I am just doing that, and my impression is that your knowledge on the subject is quite limited.

[Arsenal VG-33]

[quote=Franek Grabowski;79608]

I am just doing that, and I cannot find what resistance do you mean.

And what are you thinking of? That i gave you break limits (Re) for Delta D or Steel and elastic (Rm) one for Dural.

You do not know too much about resistance, do you?

Don't worry for me, be useful just one time, sent us your values.

Do it yourself, compare such aircraft like Beaufighter, Invader, Ju 88, Me 110, etc. and draw your own conclusions. Or calculate if you can.

Can you show me a wooden Beauf, Invader or Ju-88, or a metallic Mosquito?

When was Jodel designed and was it a high performance aircraft?

So what?

I am just doing that, and my impression is that your knowledge on the subject is quite limited.

What is your problem?

I bet Kari knows the answer.

Can you reapeat the question please?