Mosquito VI initial climb rate seems to be too low

[Karnak]

I have been putting the new version of the Mosquito VI through its paces and it is very good, I do have one concern about its performance.  While some people have expressed concerns about its MIL speed performance I can't find anything that indicates a problem there.  The climb rate on the other hand seems to be a bit low.

I tested the AH v2.19 Mosquito at full fuel and overload ammo, weight of 19,547lbs in the E6B and at +18lbs boost starting from 170mph I reached an initial climb rate of 3,025fpm.  With 25% fuel and no ammunition at a weight of 16,484lbs I obtained an initial climb rate of 3,785fpm.


The only document that I have found relevant Merlin 25 Mosquito VI climb rate data in is in the addendum to report 74, Tactical Trials for Mosquito VI.  The entire report, including the addendum, is here:
http://www.wwiiaircraftperformance.org/mosquito/Mosquito-VI-tactical.pdf
 
The addendum is not as detailed in layout, but it states that the Merlin 25 Mosquito VI was tested in the same configuration as the Merlin 23 Mosquito VI was.  The lightest configuration for the Merlin 23 Mosquito VI was the long range fighter at 19,941lbs, carrying a 113 gallon long range tank in its bomb bay.  I used the 100% fuel and overload ammunition to approximate this weight, assuming a short flight before trials began.

In section 6 of the addendum it states "Near the ground the rate was approximately 3,800 ft. per minute in a steady climb."  If the RAF test was accurate, it would seem that the initial climb rate of the Mosquito VI in AH is about 700-800fpm too low.

I don't have any other data, of any kind, referring to the Merlin 25 Mosquito VI's climb rate at +18lbs boost, so there may be better information in HTC's possession.  I also must admit that having been given something I'd been requesting for nine years I feel a bit awkward making this post, but I figure now is the best time to bring it up when the new version is still being actively worked on.


In every other way, the new Mosquito meets or exceeds all of my hopes and I am still somewhat stunned that the remodeling of it happened as it did.

[Krusty]

I think 3800fpm is a zoom from cruise speeds, going by the wording in another thread. Also, avgas weighs 6 pounds per gallon. You may be better off testing with bombs onboard instead of overflow ammo, since that really doesn't weigh enough for the comparison.

Other than that it also says the Mossie is 700 fpm worse than the Fw190 near the deck, and more than 1000 fpm worse than a 109G2. Add to that the fact the RAF underestimated the LW aircraft performances most of the time, and you can see the 3800 fpm is just impossible. 190a5 does about 4000 fpm in-game on the deck, G2 about 4200 fpm.

It's not like the mossie was ever going to compete with a 109 or spitty in climb rate.

[Karnak]

Krusty, I think you are reading the Merlin 23 section to get that.  Only the addendum is about the Merlin 25 and there are no mentions of Fw190s or Bf109s.

Also, the "steady climb" part of that does not sound like a zoom climb.  3,800fpm isn't much of a zoom climb unless it is from a cruise, as it states "The climb has also improved considerably at full power so that the Mosquito can pull up from low level into a cloud 2,000 ft. above it in less than 30 seconds from fast cruising.".  Fast cruise being referenced elsewhere as 250mph.  I think it is pretty clear that the 3,800fpm is the initial sustained climb rate at low altitude and +18lbs boost.

As to competing with Spitfires, Fw190s and Bf109s, the addendum was typed on 4 August, 1943, at a time when the Spitfire Mk IX powered by the Merlin 66 was in service with an initial climb rate like that of our Spitfire Mk VIII and Spitfire Mk XVI.  The Bf109 was likewise superior.  I am less familiar with the Fw190s climbing at that time.

I could be wrong on this of course, but if I didn't have confidence in my position I wouldn't have posted it at all.

[Krusty]

The "steady rate" was immediately after talking about zoom climbing into some clouds 2000 ft above in only 30 seconds (that's about 4000fpm, pretty close to 3800, eh?). Regardless, I don't honestly think the mossie with Merline 25s could climb that well as compared to the speed and climb rate of the Merlin 23 model. If it could climb that well, it's level speed would also be through the roof. This is a very heavy plane, with only so much wing area. To get that performance in a climb from a mossie airframe you'd have to double the horsepower without increasing weight. Just not realistic IMO.

[Karnak]

Says less than 30 seconds, which 3,800ft would not produce for a cloud layer 2,000ft above.

It is similar, but it does not match.  It also would be a redundant statement.  It notes again in section 8 that the Merlin 25 Mosquito VI has good climb at full power.

[RTHolmes]

its pretty clear to me that it means 3800fpm steady state climb. are there any other sources for mossie climbrates?

the maneuverability section sounds alot more like our new mossie than the old one

[MiloMorai]

[Scherf]

That chart is +9 boost, and the heavier weight is near as dammit full fuel & ammo, and 4x500lb bombs.

[Pyro]

I don't know what weight they were at when they recorded 3800 fpm, it doesn't specifically say in the report, but I can say that it couldn't have been 19941 lbs.  1 HP = 33000 ft-lbs/minute.  Therefore to climb a 19941 lb airplane 3800 feet in one minute would require 2296 excess thrust horsepower above the power required for steady flight at climb speed.  Assuming a propeller efficiency of .8 and it would require your engines to produce 2870 excess brake horsepower or 1435 BHP per engine above the power required to fly a 19941 lb plane at 170 mph.  That just doesn't pass the smell test.  They'd probably need like 2000 HP engines to hit that performance at that weight.  My guess is that it was done at a lower weight.

[Karnak]

That makes sense Pyro.  I pretty much hit that climb rate in AH en a Mosquito with 25% fuel and no ammo.  At 50% fuel and overload ammo, 17,920lbs, the AH Mosquito hits about 3400fpm.

[Mace2004]

I think 3800fpm is a zoom from cruise speeds, going by the wording in another thread.

Climb rates are measured as stead-state, zoom is meaningless.  Take any aircraft going 250mph and pull straight vertical and the initial "zoom" climb rate would be over 20,000 FPM.  Not really a meaningful number.