Originally posted by PanzerIV
whoops, didn't notice that the La7 and La5 use the same engine, howd they get the extra horsepower, fuel? The cowling was completely new over the La5
did it have superchargers or something to add horsepower.
The La7 has no extra HP over the La5FN............the engines were identical. Later La7's had "coupled control" of throttle and mixture.............
The La7 had a new anti flap prop but this was also added to some late La5FN's.
The La7 had lighter wings due to a final design on a metal spar over the earlier wooden ones but infact the bulk of the La5FN's also had metal sparred wings based on a design developed for the La5F (and used on some L5F's)
The only reason that La5FN's continued in production between May and October 44 was the massive number of La5FN wings in stock during May 1944.
Relocation of the oil cooler and redesign of the engine cowling (and wheel well cowling)brought the bulk of the savings in drag enjoyed by the La7 over the La5FN. This also cured some poor engine cooling "effects" that dogged the La5FN limiting its performance in key areas. It's highly probable that the La5FN could not maintain WEP for periods as long as the La7 and particularly not at low airspeeds eg under sustained climb.......... due to the requirements of engine temperature management.
Some drag was reduced on the La7 by more efficient wing roots although this does not seem to have added to lift or turn.............. infact the reverse if the oft purported (but not evidenced) better turn capability of the La5FN is true then the wing root change seems the only area where it may stem from due to some change in lift from this usually turbulent area.
WEP on the ASH 82FN was simply increasing the rpm from 2400 to 2500 however top line performance under WEP for both the La7 and the La5FN was achieved by also trimming the engine cowling and exhaust cowling air control vanes for minimum drag this trimming alone made a differenceof some km/hr (cant rem the exact figure but think it was 15km/hr).
Such trimming was at the sacrifice to less efficient engine cooling. Lavochkins were faster for longer in winter!
Having said all that re the engine cowling it is now clear that the so called onion cowling of the La5F was dropped quite quickly on the La5FN indeed probably from mid 43 onwards (if it was ever properly used). The La5FN has shorter cowling covers than the La7 but they were (like the La7)cylindrical and not bulged as often depicted.
