GregP
Major
Laxitivly explained at last, Eureka! There might be some BENDING involved somewhere ... but I digress.
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MW-50 Bf 109s Vs Fw 190 A
- Thread starter Jenisch
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But didn't GregP just say 1800 hp on a prop is like a maximum of 3307 pounds of static thrust at the peak relevant speed? 2000 hp on a Spitfire would be over 3600 lbs of static thrust while sustaining turns, vs 3000 lbs on the Vampire...
This is obviously confirmed, you would think, by the heavier weight of the Spitfire climbing faster, from likely a much lower peak sustained climbing speed, than the Vampire...
If a heavier much more draggy aircraft, with a higher wingloading, climbs faster than a lighter sleeker aircraft, and this means the heavier aircraft has less thrust at the relevant peak climb speeds (which are also likely pretty close to peak turn speeds at full power), you'll have to run that one by me in detail...
And if the difference in wingloading between the Vampire and Spitfire (33 lbs vs 35 lbs, of which what is made of it is just laughable) amounts to around 6%, how does that confirm a proven gaining of 25% per turn to reverse a tailing Spitfire position in four turns? This means the Spit XIV, probably going at 20 seconds for each 360° turn, is hugely slower-turning than the Vampire, which for its part was inevitably completing them in around 15 seconds to gain one full 360° turn in only four full 360° turns...
And all of you failed to mention that the most significant discrepancy between the two was likely the drag, not the thrust, especially the engine cooling drag, which is why a pusher prop fighter would have been a much more relevant comparison... Let me chalk you up with a big fat fail on that while I am at it...
Gaston
And where did you get the grotesque idea the Spitfire could sustain its tightest possible turns at 400 knots?:
Quote: ""Turning Circles: The Vampire I is superior to the Spitfire XIV at all heights. The two aircraft were flown in line astern formation. The Spitfire was positioned on the Vampire's tail. Both aircraft tightened up to the minimum turning circle with maximum power. It became apparent that the Vampire was able to keep inside the Spitfire's turning circles. After four or five turns the Vampire was able to position itself on the Spitfire's tail so that the deflection shot was possible."
Besides, from lower speeds, with more weight, a higher wingloading and much more drag, the Spitfire is acknowledged to climb faster: Surely your great science can tell me how that means less total thrust?
Besides, if you HAD looked it up, you would know there is no straightforward answer: Here is an interesting post that shows the effect of speed, the 270 mph of the Lancaster being the more relevant speed to the Spitfire/Vampire turn contest at minimum radius:
Propeller Thrust Figures [Archive] - PPRuNe Forums
Quote: "Okay so you're talking about thrust-to-weight, thrust-to-drag, and lift-to-drag figuresNo, thrust versus horse power.
For example, the Mosquito I is quoted as having a maximum speed in the order of 370MPH, and the Lancaster I about 270MPH, both using the same engine giving 1,280 horse power. Given the paucity of exact figures these are ball park and will do for illustration.
Using the formula thrust=horse power*375/velocity
Mosquito thrust=1280*375/370 = 1,297 pounds/engine
Lancaster thrust=1280*375/270 = 1,778 pounds/engine"
Since it is not 1280 hp on the Spitfire Mk XIV going in circles at 270 mph or less, but more like 2000 hp or more post-war, if not more, the figure is around 3000 lbs, close to what GregP mentionned...
And again a big fat fail on the issue of drag, obviously more relevant....
Gaston
GregP
Major
Gaston, at this time nobody cares what you post, nor will they argue with you anymore until you BUY AN AERODYNAMICS TEXT and READ IT.
When you do, please come back and talk with us.
Hope I didn't overstep my bounds there ... FlyboyJ. If I did, mea culpa and I'll refrian from posting to our buddy Gaston entirely going forward.
FlyboyJ, the Chino airshow is May 5-6. Will you make it? If so, can we get together on Friday, May 4?
When you do, please come back and talk with us.
Hope I didn't overstep my bounds there ... FlyboyJ. If I did, mea culpa and I'll refrian from posting to our buddy Gaston entirely going forward.
FlyboyJ, the Chino airshow is May 5-6. Will you make it? If so, can we get together on Friday, May 4?
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Jabberwocky
Staff Sergeant
A Griffon 65 had a hair under/over 2000 hp, depending on conditions. Going by the figures you provided (thrust=horse power*375/velocity), then the Spitfire XIV has 2000*375/448 = 1,674 pounds/engine.... can you tell me, is this figure less or more than 3,000 lbs static thrust?
Of course, for a supercharged internal combustion aero engine, power depends on greatly on altitude. At 0 feet the Griffon made 1850 hp and at 18,000 ft it made 1650 hp. Those are pretty big variations in thrust.
All other sorts of things come into account when considering rate of climb. Like, specific excess thrust, L/D and prop reduction ratios. Look at this: http://www.spitfireperformance.com/spit14climb-level.jpg. Different reduction ratios produced a minimal difference in speed, but a 10-12% difference in rate of climb.
The Lancaster/Mosquito I example you bring up also completely ignores the fact that the Lancaster I reached its top speed at about 17,000 ft in early versions (Merlin 22 at +9 lbs) and about 11,500 feet with the later versions (Merlin 224 at +16 lbs). At similar boost levels, the Mosquito Mk IV reached its top speed at about 22,500 ft (Merlin 21 at +9 lbs) and about 16,500-17,000 ft when the Merlin 21 was cleared for +14 and +16 lbs boost.
Do you think that makes a difference?
Of course, for a supercharged internal combustion aero engine, power depends on greatly on altitude. At 0 feet the Griffon made 1850 hp and at 18,000 ft it made 1650 hp. Those are pretty big variations in thrust.
All other sorts of things come into account when considering rate of climb. Like, specific excess thrust, L/D and prop reduction ratios. Look at this: http://www.spitfireperformance.com/spit14climb-level.jpg. Different reduction ratios produced a minimal difference in speed, but a 10-12% difference in rate of climb.
The Lancaster/Mosquito I example you bring up also completely ignores the fact that the Lancaster I reached its top speed at about 17,000 ft in early versions (Merlin 22 at +9 lbs) and about 11,500 feet with the later versions (Merlin 224 at +16 lbs). At similar boost levels, the Mosquito Mk IV reached its top speed at about 22,500 ft (Merlin 21 at +9 lbs) and about 16,500-17,000 ft when the Merlin 21 was cleared for +14 and +16 lbs boost.
Do you think that makes a difference?
FLYBOYJ
"THE GREAT GAZOO"
No worries Greg! No, not planning on making Chino although I will be in California. If the opportunity presents itself? Let's keep in touch!
FLYBOYJ
"THE GREAT GAZOO"
And this is defined and measured how?
kettbo
Senior Airman
I am away from some of my books
What was the weight penalty for a MW-50 set-up?
Weight of a mid 1943 Bf-109G6 compared to an August 1944 Bf-109G14 should work
What was the weight penalty for a MW-50 set-up?
Weight of a mid 1943 Bf-109G6 compared to an August 1944 Bf-109G14 should work
