La-7 vs ??? (attn Franek)

[Franek Grabowski]

I do not know what was the source of Gordon and Khazanov and how they described the data, however already mentioned report states that series La-7 achieved 556 km/h or 596 km/h with a booster at 0m, 653 km/h at 6000m and max speed 655 km/h at 6100m.
For a comparison, Me 109K-4 that appeared at more-less same time, had following speeds: 515/0, 580/0 [MW50], 710/7500 [MW50], 645/8400, 670/9000 according to Janda/Poruba.
It is also worthy to mention that Me 109 had a high level of automatics that reduced pilot's activity to a single lever. Quite to the contrary Soviet aircraft had almost no automatics and speeds mentioned were rather hard to achieve during the actual dog-fight.

[Jukka Juutinen]

Originally Posted by Franek Grabowski

I am not sure if I should post a separate reply but I think it would be clearer.
Great there is a separate board but woul it be possible to have some storage area for photos and drawings?

Finally something technical. The main difference between Soviet and Western aircraft was that they largely consisted of wood. Wood allows to make very aerodynamic shapes but it takes volume and weight to achieve same endurance. That was the main reason the world moved to metal designs and still continues the way.

Not so simple. First, we have to determine whther we use wood as such or as laminated structures. In general it is true that wooden structure of same strength takes up more space but necessarily weight. With wings this could be problem (e.g. dH Hornet) but usually less so with fuselages. Wood does have one excellent characteristics: very good fatigue strength (Finnish aircraft desgner Arvo Ylinen wrote several articles on this for Finnish trade journal "Aero").

Another Soviet difference was that they often had steel wing spars (spar booms) if the spars were of metal. This mayn sound awkward, but it is not so. If we assume alloy steel treated to provide an ultimate strength of 1400 N/sq.mm, we get approx the same weight for the same strength if we use high quality Al-alloy (600 N/sq.mm max) with steel having better fatigue characteristics.

So, if I were to design an aircraft employing maximum amount of wood, I´d probably do an all wood monocogue fuselage with a segment of the fuselage built integrally with an all wood wing centre section and outer wings with two steel truss spars with plywood covering.

[Franek Grabowski]

Originally Posted by Jukka Juutinen

Not so simple. First, we have to determine whther we use wood as such or as laminated structures. In general it is true that wooden structure of same strength takes up more space but necessarily weight. With wings this could be problem (e.g. dH Hornet) but usually less so with fuselages. Wood does have one excellent characteristics: very good fatigue strength (Finnish aircraft desgner Arvo Ylinen wrote several articles on this for Finnish trade journal "Aero").

No doubt wood or plywood is very nice material but it went away not without reason. Apart of rather complicated treatment that must be done by a skilled labour it is very prone for atmospheric condition. They are also much harder in servicing, quite simple in the metal aircraft.
Technically, as noted, wood (in any form) takes precious volume - due to aerodynamic/mechanic rules (especially fighter) aircraft must be as cramped as possible - comparing to a metal aircraft there is much less space for internal fittings, eg. fuel tanks. This must cause increase of dimensions and subsequently weight.
If you look at Mosquito, it was quite a heavy aircraft comparing to similar metal ones. It was not so important as it was to fly straight and level and wood allowed to make very clean aerodynamic lines. I do not want to discuss Hornet, I simply do not know anything about the design but I am awared it was in use for quite a period.
Anyway, I think Soviets would have make better use of resources making Pe-2 of wood and La-7 of metal.

Another Soviet difference was that they often had steel wing spars (spar booms) if the spars were of metal. This may sound awkward, but it is not so. If we assume alloy steel treated to provide an ultimate strength of 1400 N/sq.mm, we get approx the same weight for the same strength if we use high quality Al-alloy (600 N/sq.mm max) with steel having better fatigue characteristics.

Well, I learned that steel spar had less deflection and it was a major reason for use. I know P-39 had steel wingspar but I do not recall any such Soviet fighter, any samples please?

So, if I were to design an aircraft employing maximum amount of wood, I´d probably do an all wood monocogue fuselage with a segment of the fuselage built integrally with an all wood wing centre section and outer wings with two steel truss spars with plywood covering.

I am not sure of joint of the spar with the centre section. Perhaps a tubular steel centre section would be a better sollution? Just wondering, I have no experience.

[Jukka Juutinen]

Doesn´t La-7 have steel spar caps (booms)?

Tubular centre section sounds OK to me.

[Franek Grabowski]

Originally Posted by Jukka Juutinen

Doesn´t La-7 have steel spar caps (books)?

You have surprised me. I always thought it was alluminium spar but frankly I cannot find anything on my shelf.

[Jukka Juutinen]

I think e.g. Pilawskii´s book and Gunston´s Encyc...Russian Aircraft refer to "chromansil" caps (booms) which I interprete to mean HGSA steel (or HMA, don´t remember which is which). I think the Czech MBI book by Milos Vestsik refers to the same.

[Jukka Juutinen]

I checked Gunston. He describes La-7 spars as having D-17T webs (Al-alloy) with spar booms of Chromansil steel rolled to an ultimate tensile strength of 130 kg/sq.cm (about 1300 N/sq.mm). Despite terse prose, Gunston´s Encyclopedia has lots of interesting snippets, like this. Polikarpov´s I-185 had also steel spars.

[Franek Grabowski]

Hmm, I cannot find anything at the moment but I take it - sounds convincing. It is a mixed alluminium and steel spar though.
By the way, do you have anything on temperatures in cockpits? La-7 was a little bit warm and I know there were some troubles in early 190s but I do not know what temperatures were in series aircraft.