R-2600 table

[tomo pauk]

After some looking, I've found the table of R-2600-13. The 'emergency maximum' (military rating) is stated as 1700 HP both for low and high blower, ie. @ 4.5kft and 12kft altitude respectively. Was that true?
(I do know that 12kft was not that high altitude anyway, but it beats contemporary V-1710 by some 50%)

 

[Shortround6]

I don't think so. Most likely it is a misprint and the MAX EMERGENCY rating should be 1450hp 12,000ft.
Unless you believe a supercharger in high gear that should take double the power to drive takes NO more power than low gear, unlike every other 2 speed engine in the world. Or that you can make 1700hp in high gear at 12,000ft using almost 10% less fuel than the same engine could make at 4,500ft in low gear.

See: http://www.zenoswarbirdvideos.com/Images/TBF/TBFEDOLC.pdf

26% more power than the Allison but unless you use the cowling techniques of the FW-190 you may have 30% more drag and you certainly have more weight.

 

[tomo pauk]

I don't think so. Most likely it is a misprint and the MAX EMERGENCY rating should be 1450hp 12,000ft.
Unless you believe a supercharger in high gear that should take double the power to drive takes NO more power than low gear, unlike every other 2 speed engine in the world. Or that you can make 1700hp in high gear at 12,000ft using almost 10% less fuel than the same engine could make at 4,500ft in low gear.

See: http://www.zenoswarbirdvideos.com/Images/TBF/TBFEDOLC.pdf

Glad to know I was right to question those 1700 @ 12kft. Thanks for the link, BTW

26% more power than the Allison but unless you use the cowling techniques of the FW-190 you may have 30% more drag and you certainly have more weight.

The engine-caused drag takes between 11.5% (Firefly) to 27% (Typhon) of total drag; Firebrand was at 14.4%. I have mostly the data about British planes, plus FW-190 (21.5%) P-51.
So if we use 20% as a number for engine-caused drag for P-40 and increase that value by 30%, resulting plane has it's total drag increased by 6%.

As for the weight, engine section + engine + accessories + cooling weights 2050 lbs for P-40E; P-40F/L weights another 220lbs more for those parts. We can delete one pair of guns, too (another 160lbs) and their ammo (140 lbs). Don't have non-Wikipedia data for R-2600, but I don't see that such engine would've been heavier than regular P-40. The deleted guns can save another 2% on drag, too, so we have 4% draggier plane, of same weight, that can muster 1/4 more HP than V-1710s on 12k and above. Of course, its 50% more HP at 4,5K and down.

 

[davebender]

Air cooled radial engines require additional weight for cooling also. It just isn't as apparent. The engine cowl must be larger and you need additional space between the engine and firewall.

Look at Fw-190 development. Early models had engine failures caused by over heating. The problem was solved by moving the engine forward 15cm.

 

[tomo pauk]

Perhaps radials need some additional space, but not that much? I'd like to see a drawing that can substantiate that (US) radials needed much of that space, unoccupied by engine accesories.

FW-190 featured a tightly cowled engine, much tighter than contemporaries. So it's a matter of installation, rather than of engine being of radial type.

 

[Shortround6]

I don't have the original source but there is a comment in the combined volume of "The development of aircraft engines" by Robert Schlaifer and "Development of Aviation Fuels" by S.D. Heron that the XP-40 had 22% less drag than an R-1830 engined Curtiss Hawk in 1939, not 30% so you have my apologizes for the mistake.This difference was computed from flight tests of the time. (pages 683-684). This is drag of the aircraft not just engine caused drag. This can be seen by comparing the performance of the P-36/Hawks to the XP-40 and early P-40s.


After much work P&W managed to get the difference down to 8% greater drag by some time in 1942. Of course by that time the installation of the V-12 engines was a bit better too.

Of course the R-2600 has 16 sq ft of frontal area compared to the R-1830s 12.6 so we can safely assume that the R-2600 will have bit worse streamlining even if it is not the 27% increase the difference in frontal area suggests.
Perhaps a better "drag model" is the Hawk A-4 with a Cyclone engine. 1000hp at 14,200-15,000ft. speed 323 at 15,100ft at 5750lbs. The P-40E is supposed to go 362mph at the same altitude using 1080hp (or less, 1030?) at 8400lbs?

The R-2600 will have just over 1300hp at 15,000ft. So that "extra" 300hp needs to haul an extra 2,650lbs 39mph faster than the Cyclone in the A-4 Hawk managed to equal the P-40E.
The R-2600 will have a higher cooling drag than either the R-1820 or the V-1710.
The R-2600 weighs about 1980lbs dry and without a number of accessories, like exhaust system, starter and the larger propeller needed to effectively us it's "extra" power. It does weigh 370lbs more than the Allison and the radiators/cooling liquid. ALL forward of the CG.

Lets assume that your deletion of guns cancels ALL the extra weight of the bigger engine and you can rearrange everything else to balance. You wind up with a plane with 1/3 less firepower with marginally (if any) improved speed at altitude.

Allowing the V-1710 to use WER of 1470hp at sea level goes a long way into cutting into (or eliminating) whatever supposed advantage the R-2600 has down low.

 

[davebender]

U.S. Fighter Aircraft Empty Weight.
Data from the below web site.
Welcome To the Warbirds Resource Group - Naval Aviation Resource Center
6,200 lbs. P40. V12 engine.
7,125 lbs. P51. V12 engine.
8,982 lbs. F4U. R2800 radial engine.
9,042 lbs. F6F. R2800 radial engine.
9,950 lbs. P47. R2800 radial engine.

Why were U.S. radial engine fighter aircraft so large and heavy compared to U.S. V12 powered fighter aircraft?

 

[tomo pauk]

I don't have the original source but there is a comment in the combined volume of "The development of aircraft engines" by Robert Schlaifer and "Development of Aviation Fuels" by S.D. Heron that the XP-40 had 22% less drag than an R-1830 engined Curtiss Hawk in 1939, not 30% so you have my apologizes for the mistake.This difference was computed from flight tests of the time. (pages 683-684). This is drag of the aircraft not just engine caused drag. This can be seen by comparing the performance of the P-36/Hawks to the XP-40 and early P-40s.


After much work P&W managed to get the difference down to 8% greater drag by some time in 1942. Of course by that time the installation of the V-12 engines was a bit better too.

Of course the R-2600 has 16 sq ft of frontal area compared to the R-1830s 12.6 so we can safely assume that the R-2600 will have bit worse streamlining even if it is not the 27% increase the difference in frontal area suggests.
Perhaps a better "drag model" is the Hawk A-4 with a Cyclone engine. 1000hp at 14,200-15,000ft. speed 323 at 15,100ft at 5750lbs. The P-40E is supposed to go 362mph at the same altitude using 1080hp (or less, 1030?) at 8400lbs?

The R-2600 will have just over 1300hp at 15,000ft. So that "extra" 300hp needs to haul an extra 2,650lbs 39mph faster than the Cyclone in the A-4 Hawk managed to equal the P-40E.
The R-2600 will have a higher cooling drag than either the R-1820 or the V-1710.
The R-2600 weighs about 1980lbs dry and without a number of accessories, like exhaust system, starter and the larger propeller needed to effectively us it's "extra" power. It does weigh 370lbs more than the Allison and the radiators/cooling liquid. ALL forward of the CG.

Lets assume that your deletion of guns cancels ALL the extra weight of the bigger engine and you can rearrange everything else to balance. You wind up with a plane with 1/3 less firepower with marginally (if any) improved speed at altitude.

Allowing the V-1710 to use WER of 1470hp at sea level goes a long way into cutting into (or eliminating) whatever supposed advantage the R-2600 has down low.

To toss in in some stuff:
If we develop P-36 (one with 9 cyl) into a plane with R-2600 (having 4 HMGs 'stead of 4-6 LMGs), the new P-XY would've been hardly 2500 lbs heavier. I can agree with 1000-1500lbs more, but not with 2500.
Let's speak about climb rate. My proposal has better power-to-weight ratio than P-36/40, so it beats them.

added: So far we've talked about effects of 'bomber' engine strapped into a fighter hull as-is. Wright was delivering its Cyclon 9s (R-1820) with FTH at 14-17kft for hight blower, in 1939-40. The R-2600 with similar supercharger gearing was very much feasible in 1940/41, making a better 'fighter' engine.

 

[tomo pauk]

U.S. Fighter Aircraft Empty Weight.
Data from the below web site.
Welcome To the Warbirds Resource Group - Naval Aviation Resource Center
6,200 lbs. P40. V12 engine.
7,125 lbs. P51. V12 engine.
8,982 lbs. F4U. R2800 radial engine.
9,042 lbs. F6F. R2800 radial engine.
9,950 lbs. P47. R2800 radial engine.

Why were U.S. radial engine fighter aircraft so large and heavy compared to U.S. V12 powered fighter aircraft?

You know why as good as I do
P-47 was designed from inside out, supercharger installation dictating bulk and therefore weight; the hefty armament, ammo fuel load dictated further weight increase.
Naval fighters have had big fuel load, generous wings to increase low speed handling, in the same time being stressed for harsh carrier landings.

We can toss in F8F here: US built, radial engined, carrier capable, but still lightweight.

 

[Shortround6]

To toss in in some stuff:
If we develop P-36 (one with 9 cyl) into a plane with R-2600 (having 4 HMGs 'stead of 4-6 LMGs), the new P-XY would've been hardly 2500 lbs heavier. I can agree with 1000-1500lbs more, but not with 2500.


added: So far we've talked about effects of 'bomber' engine strapped into a fighter hull as-is. Wright was delivering its Cyclon 9s (R-1820) with FTH at 14-17kft for hight blower, in 1939-40. The R-2600 with similar supercharger gearing was very much feasible in 1940/41, making a better 'fighter' engine.

The P-36/ 75 Hawk was basically the same plane as a P-40 for everything except the cockpit forward. Please see your copy of Dean's "AHT" for the weight growth of the P-40. The only way you can keep the weight growth down to even 1500lbs heavier is leave out things like armor and self sealing tanks. Please notice the weight change in the wings and a few other areas.
Curtiss had put out a "manual/sales brochure" on the Hawk. It stated that the "G" loads were 8 normal and 12 ultimate with the Cyclone engine. Changing to the twin wasp (R-1830) increase the weight and lowered (I don't have it in front of me on this computer to about 11.75 "G"s ultimate. EDIT> 11.5 Gs< Curtiss stated in the brochure that the Twin Wasp version could be supplied at 12 "G"s ultimate for additional cost and weight. Increasing the gross weight of the Hawk by 1500lbs would lower it's Ultimate "G" loading to about 9.75 and it's normal or service "G" load to 6.34. Now the US Army may have let a few planes slide a little bit as the war went on from model to model but there was no way they would accept this kind of change. More weight in a stronger structure to get the "G" limit back up. There was also a landing "G" limit, The plane was to be built to stand up to certain "G" loads in landing.

Edit> here is the link to the manual/brochure: http://www.ww2aircraft.net/forum/other-mechanical-systems-tech/h75a-flight-manual-23226.html <

You are in a rough spot. You want a radial engine and must take the radial engine drag penalty AND you want the armament/armor/protection of a P-40D so you must take the weights of the P-40D/E (minus the engine) You also want an even heavier engine installation and an engine that can (and will) use more fuel.

Aside from a pair of .50 cal guns what are you willing to give up? Armor? self sealing tanks. Structural strength or the ability to turn? Please remember that in a nominal 2 "G" 180 degree 10 second turn it is quite possible to touch 5-6 "G"s for a fraction of a second.

Changing the "gearing" on the R-2600 isn't going to do much. It is already running 10.0 gears in high blower. Changing to even 11.0 gears will take an additional 21% power to drive. Take another look at the charts. At the same rpm and manifold pressure the engine drops from 1700hp to 1450hp when the supercharger changes from 7.0 (or close) to 10.0 gears. The supercharger takes double the power to drive with the 10.0 gears and heats the air more for a less dense charge. Heat the air too much and you have to use less manifold pressure to avoid detonation.
Please note that supercharger ratios cannot be compared from engine to engine. Knowing the diameter of the impeller helps figure out tip speed but there are other variables that throw things off.

 

[Shortround6]

Why were U.S. radial engine fighter aircraft so large and heavy compared to U.S. V12 powered fighter aircraft?

Were they? Try figuring the weight of the fighters in comparison to their powerplant weights.

Using the same fuel you are not going to get a 2000lb engine for the weight of an 1100-1300hp engine. throw in everything else you need for a 2000hp engine (bigger prop, cowling, starter, exhaust, oil system,etc) and there is no way that a 2000hp plane can be built to the same weight as a 1100-1300hp plane.

 

[tomo pauk]

This table should be accurate (taken from B-25 manual)?
Gives approx (MIL rating):
-1300 @ 17,7kft,
-1150 @ 22 kft
-1000 @ 26 kft?
...or 1/3 more than V-1710s of pre-P-40M; 1/4 more than -M/N.

I do acknowledge appreciate the weight analysis

 

[Shortround6]

I am not sure were you are getting your power at altitude estimated from. They seem about 75-100hp too high. Go to the chart I linked to in my first post in this thread and extend the line for the 1450hp down to the lower right. Even moving the line's start point to 13,500 instead of 12,000ft doesn't give the kind of power you are listing. Please note that the lines should be slightly converging, all lines should meet at 55,000ft. With most of the extra power going to fight the extra drag overall performance doesn't seem worth the effort.

 

[tomo pauk]

Not the same engines.
The last table is for -13 -29 subtypes, while the graph you're provided the link shows output of R-2600-8 (Grumman Avenger?).

As for estimates: The subject engine looses 10% of it's power for each 4200 ft above the FTH (55500ft - 13500 ft = 42000 ft => 100%; 4200ft => 10%). The 'second' FTH is @ 13,5 kft (giving 1450 HP there). With another 4.2kft (=17.7kft) added, we have 1300 HP, then another 4.2kft (= 21.9kft) there is 1150, etc. At 30.3kft, 870 HP is available.
Figures for pre-P-40M allisons:
100% = 55500 - 12000 = 43500; 1% = 435 ( we loose 11.5 hp for each 435ft)
So, @ 17.65 kft we have 1000 HP, @ 21,6 it's 900, @ 30.3 it's 670 HP.

As you've stated in another thread, all power gained added drag. I take it that bonus of 1/3 extra power more than makes for it, even more as the plane climbs up into thinner air.
But let's not stop at speed, when talking performance. The climb rate is also important, and here 'my' plane really shines vs. regular P-40, because of way better power to weight ratio.

 

[Shortround6]

Tomo, just move the line over, instead of 1450hp at 12,000ft make it 1450hp at 13,500ft and run the line parallel to the old one. It should be close enough. For best accuracy the lines should converge at 55,000ft. If your theoretical line diverges from the other lines on the chart something is wrong.

There also seems to be something wrong with your formula. An Allison that makes 1150hp at 12,000ft is actually good for about 800hp at 21,000-22,000ft according to a chart in "Vee's for Victory".
Consider that the Allison was actually making around 1450hp in the cylinders at 12,000ft(say 150hp for friction and pumps and 150hp to drive the supercharger) for it's 1150hp to the propeller. At 32,000ft where the air is 1/2 the density that it is at 12,000ft the engine should make 725hp in the cylinders but it has the same 150hp for friction and pumps and even if the supercharger isn't using the full 150hp in the thinner air it is not 1/2 the power used at 12,000ft. If we say 100hp to the supercharger and not 75 for exactly 1/2 we have 250 hp from 725hp for a net of 475hp to the prop at 32,000ft. Somewhere between 47,000 and 48,000ft the air falls to 1.2 the density that it is at 32,000ft and the Allison should make 362.5hp in the cylinders but still have the 150hp loss for friction and pumps and what is the supercharger taking now?
I admit my estimates can be a bit off, an Allison needed about 9000lbs of air to make about 1500hp in the cylinders (IHP as opposed to BHP) and the supercharger with 8.80 gears needed about 180-190hp to supply it. Adjust as you see fit.

If your radial engine plane has 20-25% more drag than the P-40 even 30% more power isn't going to change the top speed much. The closer the drag and power actually available become the less difference or as actually happened, the V-12 fighter actually out ran radial engined versions with the same or more power. You are right, climb should be better than the Allison but the question is how much better? While the drag at climbing speed is much less than at full speed it is the surplus power left after reaching the lowest drag speed (too low a speed like 120-130mph has a higher drag than 160-180mph) that determines climbing performance.
As an example say the P-40 needed 200hp to do 145mph. it has 950hp left for climbing. At sea level the R-2600hp plane has a tremendous advantage it needs 260hp (30% more drag) of it's 1700hp for 1440hp left for climb. at 12,000ft however the P-40 is pretty much the same (950hp for climbing) while the R-2600 plane now has 1190hp left for climb. a 25% advantage. Now the P-40 was good for about 2000ft/min climb. even a 25% increase on that to 2500ft/min isn't going to be enough to turn the plane into a 109 or Zero beater.

 

[tomo pauk]

I've taken 55500 ft as the altitude where power drops to 0 HP, ie. 0%; the altitude for 100% power (1450 HP in 2600-13 case) is 13500 ft, as shown at latest table. The lines shouldn't be paralel, but set to converge at those 55.5 kft.

From the performance graph drawn @ US 100K book, P-40K climbs 2000ft/min @ sl ( MIL rating; R-2600 has ~50% advantage under 7-8K here, so it's 3000 ft/min on paper for such 'P-40'), achieving 2250ft/min @ 10K (2.7-2.8 kft for R-2600?), and then slowing to perhaps 1500 ft/min @ 20K (1900 ft/min for 2600). Good as P-38G under 15K, way better than all P-39 @ MIL, nothing to give to P-47 till 1944, under 15K. Better than Allison Mustangs. Comparable with F-4U prior 1945, F-6Fs, or with light F4F-3 (besting F4F-4, of course).
Such naval planes took 8-10min to climb to 20K; 4-6 min less than P-40K. Quite the difference.

Apart from beating 109/Zero @ climb contest (a very small % out of, perhaps, 170 000 of allied fighters produced between 1939-44 was capable to do that anyway; none before Spit IX arrived?), there is a whole bunch of other applications where a rate of climb can be put to a good use, esp. if it's 25% better than what was available yesterday. Or 50% @ really low level.

edit:
I've taken your advice; the red line shows power for R-2600-13 from 2nd FTH above, blue represents V-1710-39. 900 HP vs. 1200+, at 18.5K for example - it's 1/3rd, not 1/4th bonus. Even the -8 has 25% more power.

 

[Shortround6]

Yes the R-2600 has more power, it also has more drag.
For a reality check try potting the Merlin V-1650-1 as used in the P-40F. 1120hp at 18,200ft.
Please note that at 20,000ft the "F" could be 40mph faster than an "E". If the R-2600 cannot out perform the "F" by a clear margin it has little or no point.
As far as low altitude goes the -39 engine was finally approved for a WER of 1470hp at sea level. I am not sure what some of the squadrons were actually running before "official" approval came through.
P-40Ks started to be delivered in May of 1942 with -73 engines. These were the engines rated at 1325hp for take off and a WER of 1550hp at sea level. Again "official" approval for this rating was delayed. Altitude performance was unchanged but low altitude performance compared to the R-2600 version shouldn't be a lot different.
Most P-40 performance specs are without WER ratings and climb performance at much over 10,000ft are suspect as climb tests were conducted at military power for the first 5 minutes and then the engines were throttled back to 2600rpm and 38.5in ( under 4 1/2lbs boost) manifold pressure for the rest of the climb to altitude test.

"E"s are coming of the production line in Aug, 1941. "F"s in Jan 1942 and "K"s in May of 1942. "F" prototype flew in Nov 1941. When did work actually start (drawing board) on these Versions and when would the decision to use the R-2600 have to be made? Especially since it would require much more redesign.

 

[gjs238]

R-2600 powered Boeing 314 Clippers were criss-crossing the Pacific and Atlantic prior to 12/7/41.
Just can't help but wonder that there was potential for an early-war R-2600 powered fighter.
It wouldn't have been a late-war R-2800 beater, but it could have been an early war R-1820/R-1830 beater.

 

[tomo pauk]

As for 'my' P-40', it would've had R-2600 from day one; meaning: no V-1710s here.

Advantages vs. P-40s you've mentioned:
-vs. F: available 18 months earlier
-vs. WER-capable ones: 1700 HP vs. their 1470/1550; all official documented; available one year before WER for V-1710s

All of that with 'bomber engine' mounted as-is. No tricky cowlings, no WER (yet).

Yes the R-2600 has more power, it also has more drag.

We all know that

 

[Shortround6]

Uh, Tomo, 5th production BA series R-2600 isn't delivered until June of 1941. Hardly 18 months before the P-40F. 443 are delivered in all of 1941, 206 of them in Dec.
The "A" series R-2600 offers 1400hp at 11,500ft. 22% more power than the Allison in an P-40E for over 20% more drag. Performance over the Allison not looking good here.
In 1940 Allison built 1149 engines compared to Wright building 1921 R-2600s. In 1941 the numbers were 6402 Allison's compared to about 7500 R-2600s of both types. The 1700hp BA's were built in a brand new factory in Cincinnati.

The point of the "F" comparison is that if the "F" couldn't do the job needed of air superiority fighter given it's power at altitude, why should we believe the R-2600 version is going to do any better?