Mosquito NF.Mk XIX low altitude performance with N2O boost

[Karnak]

Here is an interesting document that gives the tested speed of the Mosquito NF.XIX at low altitudes with and without nitrous oxide boost.  The NF.XIX used Merlin 25s like the FB.Mk VI Srs 2 that we already have in AH.

The gist of it though is:

377mph at 2,000ft without N2O and 394 with N2O.  Give me this twin engined La-7 killer, please.

394mph with four 20mm Hispano Mk II cannon in the nose.  That would be murderous.

[wetrat]

Yummy.

[hogenbor]

That's indeed murderous... I WANNA!

Where does this data come from? And was it actually used on combat aircraft? I read that together with Tempests, Meteors and Griffon Spits, the Mossie also shot down a large number of V1's. We all know it was fast, but this fast???

Damn, I would love to have this plane (perked of course), what would it take? Drugs, alcohol, sexual favours?

[HoHun]

Hi Karnak,

>Here is an interesting document that gives the tested speed of the Mosquito NF.XIX at low altitudes with and without nitrous oxide boost.  The NF.XIX used Merlin 25s like the FB.Mk VI Srs 2 that we already have in AH.

Alec Harvey Bailey, who worked at Rolls-Royce in WW2, described that N2O was used with 50 Mk XIII aircraft. The power chart for a Merlin 23 engine accompanying the article clearly shows that N2O could only be used above 18000 ft (as stated with your data too), and since the power graph is for static pressure (i. e. without ram effect), that means that the lower limit for N2O application in high-speed flight actually was 23000 ft.

Alec Harvey Bailey comments that N2O gave the Merlin 23 about the same performance as the Merlin 61 at 30000 ft.

The Merlin 25 (which appears to have been used by the Mk XIII too) had the same high-altitude performance as the Merlin 23 and would yield the same results.

As N2O couldn't be employed at low-altitude, the figures you've posted are quite strange. HX802, a Merlin-25-powered V-1 chaser, achieved 354 mph from sea level to 3500 ft, and it had about 1800 HP available using 150 octane fuel. The Merlin 25 would have been good for around 2000 HP, but only with the ram effect from 400 mph - which the Mosquito couldn't achieve at sea level.

Your 377 mph probably are the theoretical speed for a 2000 HP Mosquito, and the 394 mph are the even more theoretical speed for a 2000 HP Mosquito boosted at low level with 250 HP from N2O injection.

Neither the 2000 HP nor the +250 HP were available in practice though.

Regards,

Henning (HoHun)

[Karnak]

Thanks for the info HoHun.

I got that chart from the Mossie VI Merlin 25 data ASAP thread on AGW.

I read over that thread but couldn't really make out a final determination on the correct speeds for the Mosquito Mk VI powered by Merlin 25s.  What were your conclusions?

FYI, the Mosquito Mk VI in AH has a top deck speed of 337mph on WEP.

[Frogm4n]

337 seems a tad slow for a plane the LW couldnt catch for most of the war.

[Neil Stirling1]

AVIA 6/5817.

[Squire]

The Mosquito was hard to catch because by the time the LW scrambled to intercept it, they were on the way home. That doesnt mean a 190 or 109 was actually slower. The Mossie was "fast enough" to be harder to catch as it rtb'd at low level, in comparison to other allied bombers that flew slower, and higher, in protective formations, like the B-26.

[Neil Stirling1]

Rols-Royce Aero Engines, by Bill Gunston.

[Neil Stirling1]

I have just noticed the document posted by Karnack has been crudley doctored, where did you get this from Karnack.
Here is the part where 18000ft is mentioned

[HoHun]

Hi Neil,

Thanks for the complete pages! The additional information confirms my interpretation: The first speed is for +25 lbs boost, the second for the same boost with N2O injection, and they're theoretical only.

The mention of the nozzle of decreased diameter is interesting, too, it confirms that the "present" use of N2O, which probably refers to the high-altitude night fighters, gave more power than 250 HP. (The diagram accompanying the Alec Harvey Bailey article indicates a power gain of 300 HP.)

By the way, does the paper you quoted explain why N2O was only used from 18000 ft up originally? This matches German practice, but I haven't found a good explanation for that either.

Regards,

Henning (HoHun)

[Neil Stirling1]

HoHun, I am visiting the PRO in the morning, I will let you know if I find anything.
During 44 much of ADGB was put on 150 grade and in early 45 the 2TAF as well, those FBV1's fitted with NO2 may well have had 2200hp per engine!
I think Mosquitos shot down more V1's than any other aircraft bar the Tempest, and as you know the Tempest,Spit XIV and P51 were all modified to achieve 390mph +low down.
AVIA 6/5817 gives estimated boosted speeds for the Tempest Spit XIV and P51 at 3000ft, 414mph,410mph and 416mph respectively,  testing AVIA 6/10618 revealed speeds very close to these estimates.

Neil.

[Innominate]

Originally posted by Frogm4n
337 seems a tad slow for a plane the LW couldnt catch for most of the war.

They couldnt catch it because they didnt chase the mossie all the way home to vulch it on landing.

[GRUNHERZ]

The Germans used nitrous boost as well (GM-1), and it too was limited to alts above 18,000 or so.

[HoHun]

Hi Karnak,

>I read over that thread but couldn't really make out a final determination on the correct speeds for the Mosquito Mk VI powered by Merlin 25s.  What were your conclusions?

>FYI, the Mosquito Mk VI in AH has a top deck speed of 337mph on WEP.

That's the value right from the chart posted on AGW for a Mosquito FB 6 with Merlin 25, 3000, +18 lbs, and a manifold exhaust. An FB 6 with a multiple ejector exhaust should be a bit faster.

The HX802 which we thought to be a Merlin 25 Mosquito run at +25 lbs continues to confuse me. I already pointed out that its full throttle height is lowered compared to that of the normal Merlin 25 Mosquito, which didn't appear to make sense.

Well, I just stumbled upon another speed curve that shows similar symptoms: The Seafire LIIC has great performance at low altitude, but then drops off dramatically at quite modest heights.

After seeing that curve, I'd speculate that HX802 had Merlins of some sort with cropped supercharger impellers for improved low-altitude performance. Maybe it didn't even run at +25 lbs (so it didn't need 150 octane fuel), but actually generated more shaft power by diverting less to spin its smaller, more efficient low-altitude supercharger.

I can't find anything like that in my books, but with all the low-level raiding done by Mosquitos, something like an LF 6 might have been tried :-)

Regards,

Henning (HoHun)