P-40 with Griffon engine

[Dash119]

The P-51 had even less of a bump, if it was there at all.

There are no humps/bumps/blisters on the P-51 for either the Allison of the Merlin. In all the pictures I have seen of "Precious Metal", I am not seeing any either.

In looking back at the Griffon powered Spitfire, it looks to me like the blisters are to accommodate the height rather than the width of the new engine.

 

[wuzak]

You know, I never fully understood the term "H.P. / Hr.".
I can understand "lbs./hr.", in the fuel consumption rating, but ".../H.P. / Hr."?
Can someone please explain?

It's brake specific fuel consumption (BSFC).

The BSFC measures the thermal efficiency of the engine.

Efficiency can be calculated as the ratio of the power generated to the potential power in the fuel. That is, if you have 30kW generated and the fuel youuse has a potential power of 100kW, your efficiency is 30%.

lb (fuel)/hour is a different way of expressing the fuel power. HP is the power generated.

Let's take the figure of 0.5lb/hp/hr.

The fuel flow rate is 0.5lb/hr per hp

Convert that to metric (cos it's easier) the fuel flow rate is 0.2268kg/hr or 0.000063kg/s.

The energy content of petrol is approximately 45MJ/kg

Multiplying the energy content and fuel flow rate gives the potential power in the fuel.
0.000063kg/s × 45MJ/kg = 2.835kJ/s = 2.835kW

The output is 1hp = 0.7457kW.

The efficiency is 0.7457kW/2.835kW = 26.3%

BSFC of 0.53lb/hp/hr = 24.8%

 

[Dash119]

A little more from the layman...

Fuel Economy would likely be measured in miles per gallon which is different than how much horsepower we produce per gallon. How far we travel per each gallon of fuel we burn is a function of both engine and aerodynamic efficiency.

A Cessna 182 burns about 13 Gallons Per Hour at 75% power, and a speed of 165 MPH. 165 Miles / 13 Gallons = 12.692 Miles Per Gallon.

A Boeing 787-900 burns about 2300 Gallons Per Hour at a cruise speed of 560 MPH. 560 Miles / 2300 Gallons = 0.243 Miles Per Gallon.

So the Cessna 182 is wildly more fuel efficient than the Boeing 747...

The comparison is really apples to oranges, so they added one more measurement, Seat Miles Per Gallon.

Cessna 182 - 4 seats x 12.692 MPG = 50.768 SMPG

Boeing 787-900 - 360 seats x 0.243 MPG = 85.05 SMPG

So load carrying also plays a role in some of these numbers when discussing efficiency.

 

[Reluctant Poster]

 

[Reluctant Poster]

There are no humps/bumps/blisters on the P-51 for either the Allison of the Merlin. In all the pictures I have seen of "Precious Metal", I am not seeing any either.

In looking back at the Griffon powered Spitfire, it looks to me like the blisters are to accommodate the height rather than the width of the new engine.

Note that the thrust line of the Griffon is lower than the Merlin in the Spitfire

 

[GregP]

Hey Reluctant Poster, what document is that out of?

I tried searching for SC-SP-209 without any luck.

Thanks!

 

[Reluctant Poster]

Hey Reluctant Poster, what document is that out of?

I tried searching for SC-SP-209 without any luck.



Thanks!

I downloaded it 13 years ago!

There was only the 4 pages. It was copied from a paper source.

 

[GregP]

Thank you. Appreciate it.

Is the report 3415-37B, 512.6501, or EO 11653? I'm not sure how to try to find it.

Anyway, thanks again
for posting it.