Early Mustangs-performance/experience?

tomo pauk · Dec 20, 2017

Yeah, let's not miss a chance to trash Merlins, even if the figures don't exactly prove the point.

EKB said:
Re: Rolls Royce Merlin XX / Merlin 45 / Packard V-1650-1 / Allison V-1710-81/85

A P-40F with a Packard Merlin XX engine was heavy, at about 8,500 lbs. for take-off. The Kittyhawk II with British spec changes weighed about 9,000 lbs. with a normal service load. Either way the rate of climb was poor and service ceiling was below 35,000 feet during U.S. and U.K. government trials.

Basic weights (includes radios and 6 guns, but no ammo, pilot, fuel and oil), 'clean' A/C, data from 'America's hundred thousand', lbs:
-P-40F: 7089
-P-40K: 6880;
So the -F is ~3% heavier empty.
Engine power at 20000 ft, no ram: 840 HP for the -K, 1060 for the -F. The -F has ~25% more power there, it's power is better from 6000 ft above.

That does not read like a missed opportunity.

In any case a Mustang with a Merlin XX would have been heavier still, and would not have climbed higher than a P-39N, P-40N or P-51A.

Cram 180 gals of fuel on the P-39N and P-40N, full ammo, additional oil, and then see how good they will climb. The engine installed on the P-51A, P-39N and P-40N will have power deficit of 150 HP at 20000 ft vs. Merlin 20/28/V-1650-1, and was running late vs. V-1650 by almost a year. Any vs. Merlin XX by two and half years.

The supposed performance gain of the Merlin XX was brought into question after the A&AEE used a Hurricane for trial installation with the Merlin 45 engine. This airplane easily out-climbed a standard production model with a Merlin XX. Hurricane P3157 (Merlin 45) climbed to 20,000 feet in 7.1 minutes, compared to a best time of 8.5 minutes by Hurricane Z3564 (Merlin XX). The take-off weights were 6,685 lbs. (P3157) and 7,397 lbs. (Z3564).

The Merlin 45 weighed less, consumed less fuel, had fewer moving parts, and returned a lower build and maintenance cost than the Merlin XX. It's no surprise that the RAF made the Merlin 40 series standard for Spitfires until the 60 series was available.

Merlin 45 for the Americans is the moot point - they don't have it in production.
The decison to use Merlin 45 on Spitfires have had much to do with realities of war-time production (Merlin 20 series went to bombers in huge quantities, plus at the Hurricane), as well as timing, since Hurricane needed any help it can get to cancel the performance gap vs Bf 109E in 1940. Thus Spitfire got Merlin XII, and later 40 series.

The Allison engine held a big advantage at forward airstrips because of the down draft carburetor, with the air scoop being on top of the engine nacelle. The RAF Desert Air Force and USAAF reported that the V-1710 ran dependably with the air cleaner removed, for the purpose of increasing power.

The Merlin used an updraft carburetor setup that ingested dirt and sand like a vacuum cleaner. Taking out the air cleaner was attempted, but doing so ruined the Merlin quickly. The engine nacelles of many RAF planes were retrofitted with tropical air intakes but the Kittyhawk II was not one of them.

The Merlin Mustangs need to be deployed in Britain. Allison Mustangs don't have the altitude performance to challenge Luftwaffe avbove 15000 ft, until the 2-stage engine is available.

added:
Merlin 45: 1385 lbs,
V-1650-1 (= Merlin 28): 1520 lbs

EKB · Dec 20, 2017

tomo pauk said:
Yeah, let's not miss a chance to trash Merlins, even if the figures don't exactly prove the point.

Basic weights (includes radios and 6 guns, but no ammo, pilot, fuel and oil), 'clean' A/C, data from 'America's hundred thousand', lbs:
-P-40F: 7089
-P-40K: 6880;
So the -F is ~3% heavier empty.
Engine power at 20000 ft, no ram: 840 HP for the -K, 1060 for the -F. The -F has ~25% more power there, it's power is better from 6000 ft above.

Except that the P-40K was not equipped with the V-1710-81. A better comparison would be a Merlin 32 Seafire or Merlin 50M Spitfire with same take-off weight as P-40K.

EKB · Dec 20, 2017

tomo pauk said:
The Merlin Mustangs need to be deployed in Britain. Allison Mustangs don't have the altitude performance to challenge Luftwaffe avbove 15000 ft.

But they would not be better off with Merlin XX Mustangs, a plane that would not climb higher but would most definitely use more fuel and weigh more than a P-51A.

tomo pauk · Dec 20, 2017

EKB said:
Except that the P-40K was not equipped with the V-1710-81. A better comparison would be a Merlin 32 Seafire or Merlin 50M Spitfire with same take-off weight as P-40K.

Choice between V-1710-81 or -73 does not chage anything weight-wise.
Comparing any Spitfire with any P-40 does not add anything to this thread IMO.

EKB said:
But they would not be better off with Merlin XX Mustangs, a plane that would not climb higher but would most definitely use more fuel and weigh more than a P-51A.

Let's see.
For max cruise setting, auto lean mixture: V-1650-1 used 53 gph at 16000 ft, auto-lean, making 758 HP; the V-1710-81 used 63 gph at 16600 ft, 760 HP. Or, the V-1710-81 will use almost 20% more fuel for same gain.
Military power, auto-rich: V-1650-1 used 120 gph for 1120 HP at 18500 ft; the V-1710-81 used 135 gph for 1125 HP at 15000 ft.

Granted, the Mustang with V-1650-1 would've been heavier than the P-51A, but it would've also be faster above 10000 ft, would've offered superior range, while being available many months earlier.

Greyman · Dec 20, 2017

Shortround6 said:
Well something doesn't smell right about this.
According to most sources the difference in weight between the Merlin 45 and the Merlin XX was about 25-30lbs not 700lbs. Hurricane Z3564 was used for a number of tests but it was a IIb with 12 machineguns.
Was Hurricane P3157 similarly equipped? (roughly 200lbs for the extra 4 guns and ammo over a MK IIa)
One book claims a 490lb difference between a IIa and IIb just at empty weight (tare) without guns installed and both would have Merlin XX engines.

In Fact Hurricane P3157 seems to be a Hurricane I from Gloster's first production block of 500 aircraft. Not saying it wasn't later used for test purposes but
something seems a bit dodgy comparing these two aircraft.

I have a copy of the test in question and P3157 appears to be a standard Mk.I (Rotol prop).

"The supposed performance gain of the Merlin XX was brought into question after the A&AEE used a Hurricane for trial installation ..."

Brought into question by who, would be my question. The A&AEE would know how much weight would effect the Hurrie's climb:

Hurrie I L.2026 (Merlin III, Rotol) - 6,315 lb - 20,000 feet in 8.35 min
Hurrie I L.2026 (Merlin III, Rotol) - 6,750 lb - 20,000 feet in 9.75 min

EKB · Dec 20, 2017

Shortround6 said:
Well something doesn't smell right about this.
According to most sources the difference in weight between the Merlin 45 and the Merlin XX was about 25-30lbs not 700lbs. Hurricane Z3564 was used for a number of tests but it was a IIb with 12 machineguns.
Was Hurricane P3157 similarly equipped? (roughly 200lbs for the extra 4 guns and ammo over a MK IIa)
One book claims a 490lb difference between a IIa and IIb just at empty weight (tare) without guns installed and both would have Merlin XX engines.

P3157 was not a Hurricane II.

EKB · Dec 20, 2017

tomo pauk said:
Let's see.
For max cruise setting, auto lean mixture: V-1650-1 used 53 gph at 16000 ft, auto-lean, making 758 HP; the V-1710-81 used 63 gph at 16600 ft, 760 HP. Or, the V-1710-81 will use almost 20% more fuel for same gain.

Military power, auto-rich: V-1650-1 used 120 gph for 1120 HP at 18500 ft; the V-1710-81 used 135 gph for 1125 HP at 15000 ft.

Granted, the Mustang with V-1650-1 would've been heavier than the P-51A, but it would've also be faster above 10000 ft, would've offered superior range, while being available many months earlier.

What is your source for all these numbers?

tomo pauk · Dec 20, 2017

EKB said:
P3157 was not a Hurricane II.

It could be much better if you'd post more data about that particular Hurricane, eg. state of protection installed, guns, ammo, prop etc.

EKB said:
What is your source for all these numbers?

EKB · Dec 20, 2017

tomo pauk said:
It could be much better if you'd post more data about that particular Hurricane, eg. state of protection installed, guns, ammo, prop etc.

A&AEE test aircraft were converted from one version to another on a regular basis. Knowing the engine type and take-off weight is more useful, along with drag items attached.

I get your point about avgas economy at certain max settings, but the operators manuals that you posted also states that minimum specific fuel consumption is lower for the Allison engine.

tomo pauk · Dec 20, 2017

EKB said:
A&AEE test aircraft were converted from one version to another on a regular basis. Knowing the engine type and take-off weight is more useful, along with drag items attached.

Knowing the number & type of guns, ammo or ballast for it, protection is important, so we can level the playing field in regard with rate of climb. Aircarft A that has 8 guns will climb faster than otherwise similar aircraft B that has 12 guns.

I get your point about avgas economy at certain max settings, but the operators manuals that you posted also states that minimum specific fuel consumption is lower for the Allison engine.

I must 1st correct myself, the V-1650-1 used as much fuel as the V-1710-81 on max cruise AL setting - 63 gph (52 imp gals per hour).
As for the lower spec consumption of the V-1710 in low power regimes - yes, sounds great, but I dont't think any Allied aircraft will be using 500 HP when flying over German-held Europe in 1942-44.

EKB · Dec 20, 2017

tomo pauk said:
I must 1st correct myself, the V-1650-1 used as much fuel as the V-1710-81 on max cruise AL setting - 63 gph (52 imp gals per hour).
As for the lower spec consumption of the V-1710 in low power regimes - yes, sounds great, but I dont't think any Allied aircraft will be using 500 HP when flying over German-held Europe in 1942-44.

If the plane was low on fuel then throttling back to reach home base seems like a better alternative vs. taking a bath in the North Sea or parachuting into the arms of Stalag guards.

tomo pauk · Dec 20, 2017

EKB said:
If the plane was low on fuel then throttling back to reach home base seems like a better alternative vs. taking a bath in the North Sea or parachuting into the arms of Stalag guards.

There was a thing called 'mission planing' that was supposed to account for abilities and limitations of a particular piece of military hardware. The planing can tailor bombing raids for targets that are within the combat radius of the escort force. Planning cannot improve aircraft's altitude performance.
The P-51B-K, much heavier, with even thirstier Merlin aboard was good for 460 miles of radius with internal 180 gals + two 75 gal tanks (and 700 miles with fuselage tank filled), with reserves and accounted for climb, with fuel for 20 min of combat. All while cruising at 300+ mph true at 25000 ft. 460 miles from East Anglia = Rostock-Brunswick-Stuttgart line = plenty of German factories to bomb.

pbehn · Dec 20, 2017

tomo pauk said:
There was a thing called 'mission planing' that was supposed to account for abilities and limitations of a particular piece of military hardware. The planing can tailor bombing raids for targets that are within the combat radius of the escort force. Planning cannot improve aircraft's altitude performance.
The P-51B-K, much heavier, with even thirstier Merlin aboard was good for 460 miles of radius with internal 180 gals + two 75 gal tanks (and 700 miles with fuselage tank filled), with reserves and accounted for climb, with fuel for 20 min of combat. All while cruising at 300+ mph true at 25000 ft. 460 miles from East Anglia = Rostock-Brunswick-Stuttgart line = plenty of German factories to bomb.

Planning is based on estimates, if anything was estimated incorrectly or things changed mid operation then the contingency may be insufficient. Within the planning was (for example) 15 minutes combat but LW pilots didn't give a cheery wave after 15 minutes.

tomo pauk · Dec 20, 2017

pbehn said:
Planning is based on estimates, if anything was estimated incorrectly or things changed mid operation then the contingency may be insufficient. Within the planning was (for example) 15 minutes combat but LW pilots didn't give a cheery wave after 15 minutes.

We can take a look on that from German side.
It is Spring/early Summer of 1943 in the ETO. WAllies have 3 short ranged fighter (mostly Spitfires, some P-47s), 1 long ranged (P-51 with Merlin), and two 4-engined bomber for each fighter LW can muster west from Berlin, and between Pyrenees and Norway. Stripping the escorts from bombers is out of question west from Ardennes due to Spitfires and P-47s. After that, LW can decide:
-all against escorts?
-all against bombers?
-a combination?
Either of 3 cases has drawbacks. Case 1 means both fighter forces trade losses, while bombers remain unmolested. Case 2 means that interceptors might be hacked by escorts. Case 3 represents dividing of forces, ie. it is against the 'concentration of forces' mantra. The 15-20 min duration of combat is equaly applicable to LW.
We might also look at the inability of fighters based in France to effectively contribute vs, bombing raid incoming over the North Sea, or inability of fighters located in Norway, Denmark and Northern Germany vs. the raid incoming over France - further problems for the LW.

pbehn · Dec 20, 2017

I was just stating reasons a plane may be short on fuel,

EKB · Dec 29, 2017

Lost in this discussion is that the Merlin 20 series was not regarded as a high altitude engine in the RAF.

That is why Mosquito bombers with Merlin 21/25s were ultimately consigned to low altitude air strikes. The engines simply did not give enough performance for high altitude missions, during which the loss rate was higher than acceptable.

With a normal combat load the service ceiling of a Mosquito IV or Mosquito VI was about 30,000 feet, or about the same as a Whirlwind I or Mustang I used by the RAF Army Co-operation Command.

tomo pauk · Dec 29, 2017

EKB said:
Lost in this discussion is that the Merlin 20 series was not regarded as a high altitude engine in the RAF.

That is why Mosquito bombers with Merlin 21/25s were ultimately consigned to low altitude air strikes. The engines simply did not give enough performance for high altitude missions, during which the loss rate was higher than acceptable.

With a normal combat load the service ceiling of a Mosquito IV or Mosquito VI was about 30,000 feet, or about the same as a Whirlwind I or Mustang I used by the RAF Army Co-operation Command.

Still on the anti-Merlin crusade??
RAF couldn't wait to install Merlin 20 in the Hurricane in order to cancel out Bf 109E performance advantage. Spitfire III was the best-performing of the line until Mk.VII/VIII/IX emerged.
And why stating out faulty data? Service ceiling of Mossies with 20s series Merlins was 33000 ft at max weight (includes the 4000 cookie on board), and 34000 ft on mean weight. Reason to why Mosquitoes were better used in low level bombing has everything to do with bombing accuracy.
Service ceiling of the Hurricane I was in the ballpark of 33000 ft, vs. 37000 ft for the Hurricane IIa (8 .303s).

pbehn · Dec 29, 2017

I thought bomber cruising height was also governed by the height vapour trails form and persist.

GregP · Dec 29, 2017

I show a Merlin XX at 1,280 HP for takeoff and 1,480 HP/3000/6,000 ft and 12,250 ft.
I show the Merlin 45 at 1,480 HP at 12,250 ft.

The only difference I see is the Merlin XX had a single-stage, 2-speed S/C and the Merlin 45 had a single-stage, 1-speed S/C. They SHOULD have been very close in performance up until the single-speed unit started losing a bit before the 2-speed unit. Not sure what altitude that would be, but they cannot be 700 pounds apart due to addition/deletion of a couple of gears.

In fact, the Merlin 45 was a version of the Merlin XX. I believe they used the same block, but could be mistaken there as I haven't seen it definitively stated other than that the 45 was a version of the XX, implying same basic engine.

tomo pauk · Dec 29, 2017

Very roughly, the Merlin 45 is kinda Merlin XX with deleted 'items' (low supercharger gear and necessary clutch & gear changing mechanism). Benefit is lower weight (10%, give or take) and shorter length, plus it is easier to produce. Shortcoming is less power between Sl and 5000-10000 (depending on ram effect available), along with being available some 6 months later than the Merlin 20.

Early Mustangs-performance/experience?

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