Zoom climb

[Shortround6]

Once again from Zeno's.

The P-38 cannot fly longer than the P-51 at high speed (380mph or so) although it can do it (Fly 380mph) while staying within max continuous power power setting at some point between 25,000 and 30,000ft. Like the Mustang, backing off a bit on the speed adds quite a bit to the range as getting down to where they could switch to the lean mixture meant they were burning 54% of the fuel and still getting 88% of the speed.

Please note that this is with tank supports only and the P-38 is NOT going to do 380mph with any size under wing fuel tank/s. The late P-38s were a big improvement on the early ones but were not going to match the P-51.

 

[pbehn]

There are enough tales of lancasters returning from Germany to prove that a merlin can cruise at any speed it has fuel for. The idea that it can travel as far at 380MPH as it can at 220MPH defies what I know about engines and drag resistance.

 

[Shortround6]

Who is saying it can go as far at 380mph as it can at 220mph?

And again, we have to be very careful about specifying the other conditions at which the plane is "cruising". One chart shows a P-51D with a pair of 75 gallon tanks doing 202mph at sea level using 1600rpm and 32in and burning 42 gallons an hour. It will also cruise at 25,000ft with engine settings of 2100rpm and wide open throttle (engine limited by prop setting?) at 305mph and use 60 gallons an hour. Range is just about the same for planning purposes. The ability to "cruise" at 25,000ft or better where the air is thin can screw up basic drag calculations if comparing to planes that are cruising thousands of feet lower.

The Mustang could "cruise" at 380mph with a pair of 75 gallon drop tanks (390 gallons available after basic allowance for starting, warm up and take-off). It was also supposed to be hit 370mph at 25,000 using max continuous power with a pair of 110 gallon tanks. (440 gallons total after basic allowance) so we also have to be sure we are comparing the same amount of fuel.

 

[GregP]

Its not me who is missing the point Bill, it is you. This is tiresome, but one more shot at it, futile though it may be.

My dash 5 doesn't have one single entry in the mission planning charts for 380 mph. The highest you can plan for is 375 mph. If you do plan for that speed, you certainly won't be escorting anyone and you had better be flying a mission radius of 350 miles or less if you want to have some reserve in case of bad weather when you get home.

You once took me to task for arguing pointlessly when the facts were against me. You're there. Go plan an escort flight, London to Berlin, and come back and tell me you'd be cruising at 380 mph. You can't, and that was my point, and it is true, needling and sarcasm aside.

Perhaps you might want to attend our program in July 4 entitled "Little Friends" where we will have a presentation on escorting bombers with the P-51D in the PTO. If you Google Planes of Fame and the events calendar, you can check it out. We will even have a WWII P-51 crew chief in addition to covering the flying, who will detail it from their perspective.

I will grant you can fly the P-51D pretty fast (365 – 375 mph) for shorter mission where there are only other fighters in the formation, but that didn't happen a large percentage of the time, and they weren't going all that far if they did. Several hundred miles. Possible after we had airstrips on the continent. It wasn't happening in 1943 and most of 1944. DID happen in late 1944 – 1945. By the time April 1945 rolled around, they could probably hit Berlin at WER speeds and still make it back. But that is NOT what won the war in the air.

 

[drgondog]

Its not me who is missing the point Bill, it is you. This is tiresome, but one more shot at it, futile though it may be.

My dash 5 doesn't have one single entry in the mission planning charts for 380 mph. The highest you can plan for is 375 mph. If you do plan for that speed, you certainly won't be escorting anyone and you had better be flying a mission radius of 350 miles or less if you want to have some reserve in case of bad weather when you get home.

Greg - SO WHAT? in the context of could the P-51D cruise continuously at 380mph, it doesn't matter if a 'mission planning chart doesn't contemplate the Need. But I'll give you as you seem lost. How about a ring defense drawing from Alaska and Washington in 1946 which detects USSR TU-4s inbound from 800 miles out from Anchorage? Wouldn't it be nice to put on just 75 gallon tanks, climb to 25,000 feet and cruise to a radar directed intercept 300 miles offshore?

You keep harping on an ETO mission, and I have forgotten more about both Mission Segment Weight Fractions in preliminary design than you know, as well as studied the development of the Combat Radius Charts for AAF for more than 30 years. I was the guy that kept shooting your crazy assumptions down regarding your 'notions' of how the F4U and F6F could have been useful as long range escort - simply because you didn't understand the theory of Mission Profiles or the supplementary Mission Segment Weight Fractions.




You once took me to task for arguing pointlessly when the facts were against me. You're there. Go plan an escort flight, London to Berlin, and come back and tell me you'd be cruising at 380 mph. You can't, and that was my point, and it is true, needling and sarcasm aside.

Shortround, can you help me out? How many times have we separated the concept of "continuous cruise at 380mph without burning engine up" from the concept of a 'typical' 8th AF Escort mission profile for Mustangs during WWII?

Perhaps you might want to attend our program in July 4 entitled "Little Friends" where we will have a presentation on escorting bombers with the P-51D in the PTO. If you Google Planes of Fame and the events calendar, you can check it out. We will even have a WWII P-51 crew chief in addition to covering the flying, who will detail it from their perspective.

Interestingly, the Iwo to Tokyo Mission Profile is totally different as the P-51s are flying at optimal cruise or near it, in near formation with the B-29s using them for navigation bell cows. With 160 gallon tanks, a different set of cruise data had to be developed - and I have not seen it. But the PTO profile basically deleted the 'fast cruise to R/V' segment of ETO SOP and inserted ' form up with B-29 and stick with him'

I will grant you can fly the P-51D pretty fast (365 – 375 mph) for shorter mission where there are only other fighters in the formation, but that didn't happen a large percentage of the time, and they weren't going all that far if they did.

Thank you - after three straight replies trying to get THAT point across. Yes 375 or 404mph with external tanks or clean with racks and full internal fuel at 2700RPM/46" MAP until fuel runs out in less than 5 hours.

Several hundred miles. Possible after we had airstrips on the continent. It wasn't happening in 1943 and most of 1944. DID happen in late 1944 – 1945. By the time April 1945 rolled around, they could probably hit Berlin at WER speeds and still make it back. But that is NOT what won the war in the air.

Bless you Greg - may we conclude that a.) you know that at 2700RPM/46'MAP and 100gph burn rate that a P-51D can cruise (initially - but faster as the weight of the fuel is burned away) at 375mph TAS at 25,000 feet with two 110 gallon external tanks, and b.) that absent tanks and operating at 2700RPM/46" MAP it can cruise initially at 404mph at 100gph - but faster as internal fuel is burned away, and that c.) that is Not a practical 8th AF long range escort Mission Profile

 

[l'Omnivore Sobriquet]

I always thought that the P-51D escorts (ETO) were carried in two waves.
Each one cruising most of the time at the Mustang's own 'best speed' for long range, that is, much faster than the biggies. Neither of those waves accompanied the Big Friends the whole way.

First 1/3rd of the bombers' path would be covered by short range escort (Spitfires, P47...), then the 1st wave of Mustangs, having departed late, and cruised their own economical 'fast' speed, joined the biggies, loitered with them a bit (doing S) for the 2nd 1/3rd of the path, then upon being relieved by the 2nd wave Mustangs, went on free fighting for a while, away from the bombers, causing havoc.

A small portion of the escort P-51D could be dedicated to accompany the Big Friends the whole way, at close range, but that's just a small portion. The main P-51 force being, most of the time 'fast' either for range economy or of course fight. [and quite away from the bombers.]

I suppose you all know this, or is it simplistic, or a myth ?

I always thought that to achieve long range the P-51D needed to cruise high and fast (best distance covered for the fuel consumed, thanks to very clean airframe and potent altitude engine+compressor package.)

I'm afraid Greg and Drdondog are chasing different cats here... But I 'd sure like to know the real numbers, and this is an interesting read.

 

[GregP]

They did take turns escorting bombers, l'Omnivore Sobriquet. I made a statement about cruise speed when escorting bombers and Bill jumped on it just like that cat you mentioned. Predictable. In WWII, after things got going, one group or more would escort outbound and another group would take over inbound, having cruised there quite efficiently so they'd have the fuel to escort all the way back home. It sort of depended on what targets were on for the day and how much enemy fighter resistance was expected enroute.

Unfortunately, the guys who there there don't support that they flew fast over the bombers they escorted. They cruised to save fuel and only got fast when they got jumped, expect engagement, or saw enemy planes in the distance closing. The idea was to stay with the bombers as long as possible.

If they were alone (just with other fighters) then they had no constraints and were free to plan their flights as they so chose. I never made the claim that all the P-51 mission were escort missions. But, once again, if you aren't escorting bombers, then unless you are just trolling along looking for enemy fighters to shoot down, what are you doing there?

If you are providing ground support, you had a couple of bombs under the wings and weren't cruising at 380 mph. If you DID happen to be on a fighter sweep, then you also weren't that fast until you got to indian country ... anywhere you expected flak or enemy planes be. They didn't usually fly "blind." The unit S-2 could tell them mostly where the flak was and where they could expect enemy fighters. Messerschmitts weren't exactly "long range" planes, so you knew about where they might be from where they were based.

If they were in a fighter-only formation only, I'd expect them to be above 300 mph when they entered that area and to decelerate back to good fuel economy speed when they were in areas where no contact was expected.

Here is one page on the web: P-51 Mustang Specifications - MustangsMustangs.com

You don't see any 380 mph cruise speeds, do you? Look at the range. The P-51B could get to Berlin and back with drop tanks at 290 mph @ 20,000 feet. There is no single entry anywhere for cruise speeds above 300 mph except for the P-51H that didn't ctually fight in combat in WWII, and the 300 mph cruise was the Allison-powered P-51A.

Now we all KNOW the P-51B/C/D/K could easily get to 380 mph and faster, but they didn't cruise there normally. Cruising there would be over the max continuous power setting in all of my pilot manuals for the aircraft, which you could DO ... but there was really no point in doing it unless you had a reason to do so. If they were alone (just fighters), I'd expect them to cruise between 290 and 365 mph TAS at 25,000 feet. Anything faster would be a photo run over a defended target, an attack run-in, or something like that. And that fits in very nicely with what the real WWII veteran pilots said in many presentations at the museum.

As I said above, we're having another one in two weeks about escorting bombers with the P-51D in the PTO ... seemingly a related subject to the discussion at hand. It isn't like we haven't had this subject come up before.

 

[pbehn]

Sorry guys you have lost me. It may be possible to hit 380MPH with whatever external tanks and call that "cruising" at whatever altitude but that isnt cruising. My car is restricted to 155MPH, it does
45 MPG at any continuous speed between 60 and 110 MPH above that consumption plummets to between 8 and 10MPG at 140 MPH. Being a restricted engine I could hold it with my foot on the floor on a German autobahn without it blowing apart but that isnt "cruising".

Can someone tell me how many gallons per hour a merlin consumes at the maximum because I clearly remember reading about BoB pilots returning to base after short engagements low on fuel and ammunition having flown nowhere but being on maximum power for a comparatively short time climbing and in combat. There is a very real reason that "combat range" includes 15 minutes at maximum, it consumes massive volumes of fuel.

 

[GregP]

For a P-51D, at max continuous power, which is 46" MAP @ 2,700 rpm, it uses 98 GPH at 25,000 feet. At the same altitude and full throttle and 2,100 rpm, it uses 60 GPH, or a gallon a minute.

If you are down at 10,000 feet and cruising at 34" MAP and only 1,650 rpm, you can reduce to 49 GPH. But the government was paying for the overhauls back then. Most people today who fly one plan on 60 GPH and don't try to lean it out quite so far. There is almost nobody today who can run one at full power, much less WER ... because we don't have the fuel to get best performance out of a Merlin. We're stuck with 100LL petrol ... unless you happen to be racing at Reno.

Then they supply good fuel ... most of the time.

I know 3 or 4 people who cruise them square ... that is, 25 - 25, or 25" MAP and 2,500 rpm. Figure a gallon a minute for that after you cut back from takeoff and climb power, and you won't be too far off.

 

[Shortround6]

A lot depends on altitude. It may also depend on which P-51D we are talking about.

According to the post war manual A clean P-51D (racks but no stores) needed 20+ gallons for starting, warming up and take-off. It needed 17 minutes to climb to 25,000ft using 2700rpm and 46in. It used 42 gallons for the climb and could cover 66 miles while climbing Page 105) but lets ignore that as part of forming up in small formation. Greg has specified a 350 mile radius for this example. Chart after allowance for take off says 240 gallons available without external tanks, but we used 42 for the climb so 198 gallons left.
Column III of the "Flight Operation instruction Chart says the plane should do 397mph at 25,000 ft using 2400rpm and 42in (nowhere near max continuous) and 160 gallons should be good for 735 miles. Covers the 350 mile radius with a bit left over like 5 min but then we still have 38 gallons left in the tanks if our plane has not used any higher throttle settings during the flight (combat) and 38 gallons is good for over 50 minutes as most economical at low altitude. BTW, column IV on the chart says 370mph at 25,000ft using 2250rpm and full throttle (whatever boost the engine will give at 25,000ft at 2250 rpm) and at that engine setting 700 miles needs only 140 gallons of gas. Plane could cruise at 380mph using in between settings and use 150 gallons? At 24,000ft , 3000rpm and 61in the fuel use is supposed to be 3.0 gallons a minute.

No figuring in the above for the decent from 25,000ft to near sea level, count that as part of the reserve.

 

[Shortround6]

Sorry guys you have lost me. It may be possible to hit 380MPH with whatever external tanks and call that "cruising" at whatever altitude but that isnt cruising.

Can someone tell me how many gallons per hour a merlin consumes at the maximum because I clearly remember reading about BoB pilots returning to base after short engagements low on fuel and ammunition having flown nowhere but being on maximum power for a comparatively short time climbing and in combat. There is a very real reason that "combat range" includes 15 minutes at maximum, it consumes massive volumes of fuel.

A cruise chart was posted back in post # 16. Post war Manual doesn't give fuel consumption for WER but for Military power it was about 3.0 gals a minute. That is 61in or a bit over 15lbs boost. Mustang carries about 2 1/2 times the Fuel of a Spitfire. Take out 45 gallons from above example for 15 minutes at Military setting. But that was for an aircraft without drop tanks.

 

[pbehn]

3 gallons per minute is 180 per hour a six hour mission uses 1080 gallons.................I think my question is answered.

 

[Greyman]

Mustang Pilot's Notes has:
67 boost, 3000 rpm, 137/165 imp/us gallons per hour
61 boost, 3000 rpm, 112/135 imp/us gallons per hour

 

[pbehn]

Mustang Pilot's Notes has:
67 boost, 3000 rpm, 137/165 imp/us gallons per hour
61 boost, 3000 rpm, 112/135 imp/us gallons per hour

I always understood that the chief difference between the P51 and the P47 was 40 to 50 GPH at cruising speed.

 

[GregP]

There aren't any P-51D charts with a 397 mph TAS at the power levels you suggested, Shortround. At least not in 51-127-5 dated 15 Aug 1945, which is a Pilot Flight Operting Instruction.

Google that number and download it. And since you are quoting a clean airplane, and going so fast, you certainly aren't escorting anybody. Maybe you're using AN 01-60JE-1?

 

[Mike Williams]

Hmmm...

 

[Shortround6]

3 gallons per minute is 180 per hour a six hour mission uses 1080 gallons.................I think my question is answered.

Is it? nobody is claiming the Mustang was cruising at "full throttle" Ie, 3000rpm and 61in (15-16lbs boost).

American max continuous sort of split the difference between British Climb and Max cruise. Americans would allow 2700rpm and 46in (8lbs) as long as the fuel lasted or temperatures remained in limits.
Two stage Merlins used in Spitfires were allowed a "climb" rating of 2850 rpm and 12lbs (54in?) for 30 minutes and 2650rpm and 7lbs boost (44in) max cruise. I sure wouldn't get too exited about 50rpm and 1lb of boost. you can get that kind of variation between two planes sitting next to each other on the flight line n any given day.

The Mustangs fuel capacity helped give it a disproportionate range compared to similar fighters ( not comparing P-47 and P-38s here).
Comparing to Spitfire MK IX they are both going to use up about the same amount of fuel starting up, warming up, taxing and taking off. If you are going to climb to 25,000ft the Mustang sill use a bit more fuel. It is heavier. How much the lower drag helps I don't know.
So lets assume the Spitfire is staring with 103 US gallons and the Mustang is starting with 180 US gallons. They both US 20 gallons from start up to wheel sup. Mustang uses 42 gallons getting to 25,000ft. Spitfire uses less-30-33 gallons? even less? Lets say 20 gals just for illustrations sake. Mustang has used 62 gallon and has 118 gallons left, Spitfire has used 40 gallons and has 63 gallons left. 15 minutes at 3 gallons a minute each for combat =45 gallons. Mustang has 73 gallons left and the Spitfire has 18 gallons. Now we do want some reserve to help find the home field so 10 gallons should give us around 20 minutes at most economical (give or take). Spitfire has 8 gallons to divide up between cruising out and cruising home. Mustang has 63 gallons.
Now throw the rear fuselage tank (85 gallons max, but often restricted to less) in the Mustang, start up, warm up and take-off stay the same, climb to 25,000ft stays pretty much the same, combat allowance stays the same, reserve stays the same (or is increased) but basically the the rear fuselage tank could double the operational radius since you had about twice the fuel for "cruising". change in drag is negligible because we haven't changed the outside of the plane.

The above is simplistic (very) but hopefully gets the point across. we have to be careful that we are comparing apples to apples and just because another aircraft with different drag and vastly different fuel capacity could do something or behaved a certain way does not mean the Mustang is going to have similar restrictions. It may have it's own restrictions/problems though.

 

[Shortround6]

Hmmm...

Hmmm...........Indeed

 

[grampi]

Sorry guys you have lost me. It may be possible to hit 380MPH with whatever external tanks and call that "cruising" at whatever altitude but that isnt cruising. My car is restricted to 155MPH, it does
45 MPG at any continuous speed between 60 and 110 MPH above that consumption plummets to between 8 and 10MPG at 140 MPH. Being a restricted engine I could hold it with my foot on the floor on a German autobahn without it blowing apart but that isnt "cruising".

Can someone tell me how many gallons per hour a merlin consumes at the maximum because I clearly remember reading about BoB pilots returning to base after short engagements low on fuel and ammunition having flown nowhere but being on maximum power for a comparatively short time climbing and in combat. There is a very real reason that "combat range" includes 15 minutes at maximum, it consumes massive volumes of fuel.

I'd like to know about a car that gets 45 MPG at 110 MPH...I didn't even know such a car existed...

 

[pbehn]

I'd like to know about a car that gets 45 MPG at 110 MPH...I didn't even know such a car existed...

3 litre turbo diesel Audi, thats what it shows on the instantaneous and average MPG. The problem is in the "continuous" bit. Even on an autobahn with no speed limit the faster you want to travel the more times you have to brake or at least coast, even in a stream of cars doing 110 MPH you are on and off the gas all the time even if you dont touch the brakes. If you slow down to 100 then to get back to 110 sees you doing about 6 to 8MPG for a while. Below 60 it isnt any more economical either as it starts shifting down the gears 50MPH is 1000RPM in 7th. At 110 it is much more economical than my old 2 litre toyota diesel which was thrashing its innards out. That said, I have never ever got near the claimed figures around town and it has 50000 on the clock now and uses about 10% less than when I bought it.