Level speed of Mosquito FB VI with Merlin 25s?

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Staff Sergeant
Jul 24, 2005
I have recently downloaded the 1950 operating manual for a Mk VI Mosquito. It is operating Merlin 25s with a maximum boost pressure of +18lbs at 3000 rpm

The speed figures in clean configuration are given in KNOTS and are as follows:

Sea level to 10,000 feet 370 knts
10,000 feet to 15,000 feet 350 knts
15,000 feet to 20,000 feet 320 knts
20,000 feet to 25,000 feet 295 knts
25,000 feet to 30,000 feet 260 knts
30,000 feet to 40,000 feet 235 knts

A knot is approximately 1.151 miles.

So by my reconing the maxiumum speed for a Mk VI with Merlin 25s would be around 425 mph. That is phenomenal, particularly at 18 lbs boost. The most commonly quoted wartime figures for a FB VI is around 380 miles per hour at 13,000 and about 335 mph at sea level. The A&AEE tests seem to confirm that. Is it just a typo or did post war Mossies really have that much performance?

Can anyone help?
Here's a site that has a TAS calculator calculatorhttp://www.csgnetwork.com/tasinfocalc.html

Another way to do it is to read your indicated airspeed (IAS) on your airspeed indicator. Read your altitude above Mean Sea Level (MSL) on your altimeter, based on the proper altimeter setting (pressure altitude). Mathematically increase your indicated airspeed (IAS) by 2% per thousand feet of altitude to obtain the true airspeed (TAS).

This is in no wind condition at a standard lapse rate - 59 degreesF at sea level

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