Speed graphs for Spitfire and Hurricane

[fruitbat]

Originally Posted by Buchon

28mph is a lot of speed, yes, but that´s with Boost.

The performance line posted by B6 is the base performance line, meaning without Boost.

That base performing line B6 posted is 28mph slower at sea level than it should be for a spit running on 87 octane fuel at max power ie 6 1/4 Lbs, there is no 'boost' to add to it with that fuel, let alone the extra 25 mph at sea level that running 100 octane fuel and 12Lbs boost would get you.

[Buchon]

Originally Posted by fruitbat

That base performing line B6 posted is 28mph slower at sea level than it should be for a spit running on 87 octane fuel at max power ie 6 1/4 Lbs, there is no 'boost' to add to it with that fuel, let alone the extra 25 mph at sea level that running 100 octane fuel and 12Lbs boost would get you.

As I said you are comparing a base performance line and Boosted performance line,which is wrong.

Here a really good graph posted by Kwiatek where we can see a base performance line and Boost performance lines, pls watch it :



The red line is base performance line, without Boost, I know that is max weak mix and calculated but its a good reference, the real speed should be a slight better then.

So we have a 246mph of sea level without Boost and 283mph with Boost.

Now we can extrapolate that data to the graph made by Klem which contain the B6 data :



Obviously he is comparing base performance line with Boost line but that don't mean that its not a interesting graph because we have here the sea level speed of the base performance line posted by B6.

As you can see the B6 graph data shows a sea level speed of 255mph without Boost, considering that the 246mph mark of Kwiatek graph is weak mix calculated I can say that it´s pretty accurate.

So, what is wrong with the B6 graph ?

I can say nothing but we need the freaking Boost modeled

[Kwiatek]

Originally Posted by Buchon

So, what is wrong with the B6 graph ?

I can say nothing but we need the freaking Boost modeled

Beacuse it show maximum speed for Spitfire MK1 which mean for 87 octan - +6 1/2 mainfold pressure (boost) - so not red but blue line from RAE charts.

Red line is for maxium continous weak mixture power which mean +2 1/2 mainfold pressure ( boost) for economical flying.

[klem]

Originally Posted by Buchon

As I said you are comparing a base performance line and Boosted performance line,which is wrong.

Here a really good graph posted by Kwiatek where we can see a base performance line and Boost performance lines, pls watch it :



The red line is base performance line, without Boost, I know that is max weak mix and calculated but its a good reference, the real speed should be a slight better then.

So we have a 246mph of sea level without Boost and 283mph with Boost.

Now we can extrapolate that data to the graph made by Klem which contain the B6 data :



Obviously he is comparing base performance line with Boost line but that don't mean that its not a interesting graph because we have here the sea level speed of the base performance line posted by B6.

As you can see the B6 graph data shows a sea level speed of 255mph without Boost, considering that the 246mph mark of Kwiatek graph is weak mix calculated I can say that it´s pretty accurate.

So, what is wrong with the B6 graph ?

I can say nothing but we need the freaking Boost modeled

I'm not sure who is misunderstanding who but all the curves on the chart I posted, excluding the curve I overlaid from B6's data, are original data from tests made at the time and the first line (lowest speeds in pale blue) are for the boost at +6 1/4lbs Merlin III with 87 octane and a three bladed constant speed propeller. The higher boost curve at +12lbs with 100 octane is the next one listed and in a deeper blue.

My curve takes B6s data (orange line, which only went down to 3000m), projected down to 0 feet (yellow line). The projection may turn out to be not strictly accurate but is a fair basis for the question.

If you look at Kwiatek's chart you will see along the line that starts at 283mph @ 0 feet the words +6 1/4 lbs boost, i.e. the max with 87 octane. The red line is when running 'Max Weak mix' which would of course yield less power and the boost pressure is not given but the pilots notes state that at the weakest setting the max permitted are +2 1/4lbs boost and 2.600 rpm. These are probably the settings reptresented by the red line.