Last year, I began to question the amazing flight performance of the Yak-9U in AH. I didn't know anything in detail about Yaks but it just seemed a bit uber to me. I was assured, however, by some folks purportedly more knowledgeable that it flies in AH at least as well as it did in real life. I still didn't buy it, so have spent the time since then trying to learn more about Yaks in general and the 9U specifically, as well as doing some controlled tests in AH.
I have come to the following conclusions:
- That the 9U's level speed in AH is very close to that of the stats I can find. So no room for complaint there.
- That the 9U's climb in AH is a bit worse than the stats I can find, but is probably about right all things considered.
- That the 9U's turn performance in AH is a bit better than the stats I can find, but that's probably because I can pull more Gs than were possible in real life.
- That the 9U's dive performance in AH is WAY better than it was in real life, so should be considered seriously bugged.
I got my real-life data from Red Star series #5,
Yakovlev's Piston-Engined Fighters, by Yefim Gordon and Dmitriy Khazanov, translated by Sergey Komissarov, published in 2002. It uses Russian primary sources exclusively and has a lot of detail in how various real-world test data were obtained, so that I could duplicate the procedures in AH. So I think these numbers are probably about as good as any you can find on this plane (and other Yaks, for that matter).
ENGINEThe Yak-9U was powered by the VK-107A engine. This engine was rushed into production long before it was ready, so had a lot of SERIOUS problems in service. When it worked, it was great, but it often didn't. Of course, most of this reliability stuff can be ignored in AH, like it is for other historically unreliable planes.
HOWEVER, one of the problems the VK-107 had was constant overheating at the intended max setting of 3200rpm. Thus, in service they had to limit it to 3000rpm to reduce this problem as much as possible, while keeping as much power as possible. This was a fleet-wide thing, not a quirk of some individual or dogged-out planes. And in AH, the 9U's max RPM is in fact limited to 3000 to relfect this.
The book says that the reduced RPM lowered level speed and ROC a bit but doesn't say how much. And from reading the book, the best interpretation is that its stats for the 9U are at 3200rpm. Thus, in AH it shouldn't go quite as fast and should take a little longer to climb. And as far as I can tell that's the case. I figure if HTC set the RPM to 3000, they took it's effects into account. So keep that in mind in what follows.
LEVEL MAX SPEEDThe book has 2 sets of stats for the 9U: that of the prototype and that of a standard production machine from 1944. The production planes were heavier than and not as smooth as the prototype so had lower performance. But I figure that's what we have in the game (especially because the RPM is 3000) so I compare AH data to the production machine data.
Book (1944 production machine, apparently at 3200rpm):
- Sea Level: 357.2 mph
- At 16,500': 417.5 mph
AH (at 3000rpm):
- Sea level: 354 mph TAS
- At 16,500': 412 mph TAS
So in AH the 9U is a tiny bit slower. You'd expect that from the lower RPM, but is it enough slower? I have no way of telling, but I'll give HTC the benefit of the doubt there. So levevl max speed looks right.
RATE OF CLIMBBook (1944 production machine, apparently at 3200rpm, apparently full tanks)
- Time to 16,400': 5.0 minutes
AH (at 3000rpm, full tanks)
- Time to 16,400': 5 minutes 28 seconds from start of roll
Again, the AH 9U has slightly worse performance, as expected. And again, I have no way of knowing if it's worse by the right amount, but I'm not going to complain.
TURN PERFORMANCEThe book says the test was to make a flat 360^ circle as hard as possible at 1000m (3280'). The production 9U could do this in 20 seconds, but it doesn't say at what G level. In AH, I could do this in about 18 seconds at 5-6 Gs the whole time. Again, this seems close enough not to worry about.
DIVE PERFORMANCEHere is where things go bad for AH's 9U. In the game, the 9U is almost magically immune to the effects of compression and doesn't break up at high speeds. This enables it to run down all other prop planes, because it can reach a higher speed and still maneuver while everything else either locks up or falls apart at lower speeds.
In the thread last year, several people with more aerodynamic knowledge than me explained why the 9U might have had a higher critical mach number than other planes, such as the P51D. You can also see the results of some tests I did comparing how compression affected various planes, including the 9U.
Here's that thread.OK, I still don't know much about transsonic aerodynamics, but I do know this: the 9U was made of WOOD for the most part, and this was a light as possible. It had metal wing spars and some metal ribs, but the skin was plywood that was glued on. And this meant that it simply could not handle extremely high speeds and their associated G loads without breaking up. The book mentions a number of Yaks of various models breaking up from excessive speed and/or G.
After WW2, they built the Yak-9P. This was just an all-metal 9U (at first only the wings were changed). The all-metal wings increased the strength of the plane, and the book says the following, in comparing the 9P to the 9U: "... the indicated airspeed in a dive could be increased from 404 mph to 447 mph, and the maximum G load in recovery from a dive was brought up to 8.0 instead of 6.5".
The 9U in AH greatly exceeds the numbers even for the 9P without injury. It does not begin to even buffet until it gets about 550 TAS, is capable of exceeding 600 TAS and recover from a 45^ dive, and certainly never breaks just from high speed. And once it gets buffeting, it's impossible to pull more than 2-4 Gs (depending on speed) anyway, so the G redline can't be exceeded.
I have managed, during MANY test dives, to pull both wings off just once, but I've been unable to repeat that. It happened at total blackout Gs so I don't really know what I did anyway
. But it must have been something very strange because that's the only time I've ever broken a 9U. Total blackout happens about 7.5 Gs, which is possible at speeds just before the plane starts buffeting, but don't break the plane. I've pulled enough Gs pulling screaming 9Us out of dives to remain totally blacked out for at least 5 seconds after releasing the stick, but with this 1 exception I've never even lost a control surface.
So as far as I can tell, the 9U's dive is WAY too good. While it
might have been able to do this from an aerodynamic point of view alone, it wasn't strong enough structurally to survive the attempt. If somebody can show me that it WAS strong enough, then I'd feel a lot better. But until then, I've got to believe that the 9U's pretty uber-porked in this area.
