Spit 1a

[Welshman]

also seems to have the 2 speed prop not the rotol , i tried the rotol hurry for a very quick test and held 280 easy , the 2 speed hurri was stuck at 250 .

[ATAG_Dutch]

According to the graph on the link I gave, the Spit1a with +6.25lbs boost should be 285mph @ zero ft, with 355ish @ about 19.000ft. But it does state @ 3000rpm, and with a Rotol prop.

The +12lb graph shows higher performance all round. I couldn't find a two-speed prop performance graph, but will have a hunt around.

Edit: The only reference I could find to DeHavilland 2-speed prop performance was in Alfred Price 'The Spitfire Story', but no figures are present for max speed at sea level. Max @ 18,600ft is 367, ceiling 34,400.

It does state that the original fixed pitch 2-bladed prop had max speed @ 2000ft (lowest shown) of 295mph. The 2-speed prop was much heavier, inhibiting the rate of climb, but you'd expect performance in coarse pitch to be similar to the fixed pitch.

[furbs]

Just used the FMB to start with a Spit 1a at 18,000 ft @ 300MPH

The spit then started at 200 MPH and wouldn't go any quicker.

Can someone else please test the same?

[Welshman]

spit IIa has the rotol prop and i just held 310 , without full trimming etc at sea level

so i guess we just need the rotol spit 1 not the 1938/9 version

[Plt Off JRB Meaker]

furbs,will check my settings properly tonight and get back to you,I'm sure I've had my Mk1a over 250mph.

Will confirm this later if I get the chance.

[furbs]

Welshman, well im sure the spit 2 should be quicker than that.

[ATAG_Dutch]

Originally Posted by furbs

Can someone else please test the same?

Just done it.

Entered 500kph @ 6000m in FMB, and once the 'plane was trimmed out for straight and level, with boost through the gate and coarse pitch, after a bit of a wait and some re-trimming the airspeed indicator read 240mph, which allowing for IAS/TAS calculations, put the speed at about 350mph.

This looks about right to me. Unless my maths is wrong, I had to convert to metric and back also.

Which begs the question, when you enter speed in FMB, are you entering IAS or TAS? Does FMB calculate the difference?

Interestingly, she really wanted to climb so lots of down trim was needed. Might test the altitude again to see if anything has changed.

[Welshman]

starts loosing boost above 18000 too

[Welshman]

yes i know but no good for top speed

[Plt Off JRB Meaker]

Originally Posted by Dutch_851

Just done it.

Entered 500kph @ 6000m in FMB, and once the 'plane was trimmed out for straight and level, with boost through the gate and coarse pitch, after a bit of a wait and some re-trimming the airspeed indicator read 240mph, which allowing for IAS/TAS calculations, put the speed at about 350mph.

This looks about right to me. Unless my maths is wrong, I had to convert to metric and back also.

Which begs the question, when you enter speed in FMB, are you entering IAS or TAS? Does FMB calculate the difference?

Interestingly, she really wanted to climb so lots of down trim was needed. Might test the altitude again to see if anything has changed.

Well done Dutch,got there before me,top job