A Radial Engined Fighter for the Australians to build (and maybe the Chinese and Indians)

[FLYBOYJ]

I think they have some actual studies or estimates on the open wheel well issue, for the Spitfire and a couple other planes (Wildcat?) I'm not sure where to find those though.

And that is probably true and that is where the design negotiation comes down between the aerodynamicists and systems engineers of how much is lost in performance vs. an easy system function.

Drag is hard to calculate but small things (radio masts for example) seem to sometimes make a big difference.

They do but is also depends where on the aircraft they are located. When I crewed an aircraft at the Reno Air Races we removed as much "stuff" from the airstream as possible and also taped up seams and fairings. IIRC everything forward of the Mean Aerodynamic Chord (MAC) was the most critical.

 

[Shortround6]

proves that the more conventional landing gear (with fully covered wheels) was certainly possible.

It may be "possible", it it worth the cost? and there are a lot of costs.

And I'm not saying the P-40 was a flying brick either, by any means, but it certainly could be improved. In terms of drag, there is a lot of difference between these two P-40s

How much difference between those two P-40s? Unless you have wind tunnel results everything is a guess. Since the short nose P-40 moved the prop hub up 6 inches compared to the long nose the radiator/oil cooler area didn't actually change that much. The distance from the top of the cowl to the bottom of the cowl/duct changed very little if at all.

In one test a P-40B (that is a P-40C in the picture) did the following in comparison to a P-40D (Picture is a long tail P-40F or L with Merlin which did a have bit bigger scoop)
P-40B.................15,000ft....................352mph................1090hp/3000rpm
P-40B..................15,000ft...................310mph.................720hp/2280rpm
P-40D.................15,175ft...................354mph.................1085hp/3000rpm
P-40D.................15,175ft...................307.5mph...............725hp/2280rpm

That certainly looks like within under 2% difference to me
Now please note that the power is estimates based off the rpm and boost pressure and the atmosphere (temperature and pressure).
Many radial engines had torque meters and they could actual measure the power in flight, the V-12s could not do that.

Drag is hard to calculate but small things (radio masts for example) seem to sometimes make a big difference.

They do, the difference is speed is not expressed well when you are using mph unless the planes are flying at about the same speed at about the same altitude. Saying change Q on Spitfire is worth 6mph flying 375mph at 20,000ft is the same as change Q adding 6mph to a P-40 flying at 330mph at 10,000ft has got two variables thrown in.

An Ozhawk with a two speed supercharger might be a little slow, but if it's still producing say 1,100 hp at 20,000 ft, before 1943, that could fit into a niche that the Allies did not have very well covered except by the P-38 and Corsair which were in small numbers and still dealing with teething problems. A Ozhawk with a two stage R-1830 could of course be even better.

If the Ozhawk making was 1100hp at 20,000ft with just a two speed supercharger would be a miracle worthy of witnessing by the Pope and every other religious leader of the time.
A P & W R-1830 with a two speed supercharger was good for 1050hp at 2700rpm at 13,100ft. You are going to loose approximately 2% for every 1000ftof altitude so expect about 900hp at 20,000ft.
That was the whole reason for using the two stage supercharge in the first place. And there were some limits to the two stage supercharger as used in the F4F.
P & W seems never to have rated the engine at "Military power" That was the Navy's doing.
P & W rated the -86 engine at 1200hp at 2700rpm for take-off.
they also rated it "normal" max continuous at

1100hp/2550rpm at 3500ft
1050hp/2550rpm at 11,000ft
1000hp/2550rpm at 19,000ft.

The supercharger on the regular R-1830 was running out of breath. The engine that gave 1050hp at 2700rpm at 13,1000ft was good for 1000hp at 2550rpm at 12,500ft.
In other words you weren't going to get much extra power out of it by winding the snot out out of the engine.

Conversely, with the availability of higher octane fuel, an "Ozhawk' with a low altitude but extra 'peppy' 1350 hp R-1830-65 like the FM-2 could make for a very nice interceptor and low altitude fighter I think.

Ok This is total confusion. The difference between the FM-1 Wildcat and the FN-2 Wildcat had very little to do with the octane of the fuel.

The extra "peppy" 1350hp engine in the FM-2 was not a P & W engine, it was a Wright R-1820-56W Cyclone 9 cylinder engine that used water injection.
Trying to manufacture Wright Cyclone 9s on machinery that made P & W 14 cylinder Twin Wasps was going to take a bit of doing.
Before anybody gets a bright ideas of using the Wright Cyclone 9 for Australian production instead of the R-1830 Wasp the 1300-1350 Cyclones 9s used in the FM-2 were a totally new engine that shared just about zero parts with the 1200hp Cyclone 9 that came before it. New cylinders, new cylinder heads, new crankcase, new crankshaft and so on.

P & W did come out with a Peppy 1350hp version of the R-1830 in 1944 but it did require a number of things to be changed and not just pouring different fuel in the tank.
One thing they did was copy the cylinder construction method used for the R-2800C (from the P-47M) for better cooling. There were other changes.

 

[Farky]

Getting back to the "Ozhawk" - while I agree it wouldn't be as fast as a Tomahawk or a Kittyhawk, I think the potential of a two speed or a two stage engine R-1830 could bring some very welcome capability to the Allied forces in the Pacific in particular, assuming (and this is of course, a big if) they could get it working soon enough. When did they have them in Beauforts exactly?

Right from the start of production because at some point first 90 Beauforts were supposed to be for RAF with R-1830 S3C4G (two speed supercharger, import from overseas), next 90 for RAAF with R-1830 S1C3G (single speed supercharger, engine produced in Australia). Anyway, first Beaufort with Twin Wasp (two speed supercharger) was delivered to RAAF in September 1941. If I remember well, in January 1942 when they were discusions about Boomerang some 90-ish Twin Wasps with two speed supercharger were in Australia and at least 300 more ordered for delivery.

P & W did come out with a Peppy 1350hp version of the R-1830 in 1944 but it did require a number of things to be changed and not just pouring different fuel in the tank.
One thing they did was copy the cylinder construction method used for the R-2800C (from the P-47M) for better cooling. There were other changes.

Interesting, do you please have more details about those changes?

USAAF cleared regular R-1830 S3C4G (aka R-1830-90B) for 1350 hp in 1944, Boomerang was tested with this War Emergency Power rating. It didn't work on Boomerang because of cooling issues.

 

[Shortround6]

Right from the start of production because at some point first 90 Beauforts were supposed to be for RAF with R-1830 S3C4G (two speed supercharger, import from overseas), next 90 for RAAF with R-1830 S1C3G (single speed supercharger, engine produced in Australia). Anyway, first Beaufort with Twin Wasp (two speed supercharger) was delivered to RAAF in September 1941. If I remeber well, in January 1942 when they were discusions about Boomerang some 90-ish Twin Wasps with two speed supercharger were in Australia and at least 300 more ordered for delivery.


Interesting, do you please have more details about those changes?

USAAF cleared regular R-1830 S3C4G (aka R-1830-90B) for 1350 hp in 1944, Boomerang was tested with this War Emergency Power rating. It didn't work on Boomerang because of cooling issues.

I am going by the list of R-1830 engines on Enginehistory.org.
There are not a lot of details.
One of the earliest non-turbo 1350hp engines was for the Convair 39

A number were used on assorted cargo/passenger versions of the PB4Y-2 with different designations and few other aircraft.
They were allowed to run at 2800rpm instead of 2700hp.
the very brief notes may be missing punctuation.
It says "improved: Accessories Section Supercharger Cooling Fin & Muff Arrangement."

Some of the engines got an automatic spark advance system.

Please note that the weight of the engine went up to 1573lbs compared to the 1490lbs for the -90B engines.

There was a turbo version for the YB24-K and the planned B-24N all but one canceled at the end of the war.

 

[Wild_Bill_Kelso]

It may be "possible", it it worth the cost? and there are a lot of costs.

How much difference between those two P-40s? Unless you have wind tunnel results everything is a guess. Since the short nose P-40 moved the prop hub up 6 inches compared to the long nose the radiator/oil cooler area didn't actually change that much. The distance from the top of the cowl to the bottom of the cowl/duct changed very little if at all.

In one test a P-40B (that is a P-40C in the picture) did the following in comparison to a P-40D (Picture is a long tail P-40F or L with Merlin which did a have bit bigger scoop)
P-40B.................15,000ft....................352mph................1090hp/3000rpm
P-40B..................15,000ft...................310mph.................720hp/2280rpm
P-40D.................15,175ft...................354mph.................1085hp/3000rpm
P-40D.................15,175ft...................307.5mph...............725hp/2280rpm

That certainly looks like within under 2% difference to me

Even in what you are suggesting, you'd be wrong, but you made a mistake, look at those two aircraft in the photo again.

Now please note that the power is estimates based off the rpm and boost pressure and the atmosphere (temperature and pressure).
Many radial engines had torque meters and they could actual measure the power in flight, the V-12s could not do that.

They do, the difference is speed is not expressed well when you are using mph unless the planes are flying at about the same speed at about the same altitude. Saying change Q on Spitfire is worth 6mph flying 375mph at 20,000ft is the same as change Q adding 6mph to a P-40 flying at 330mph at 10,000ft has got two variables thrown in.

The aircraft in that image did 370 mph at 20,000 ft. If we are talking about 1942-1943 production P-40s, most of them could do about that much.

If the Ozhawk making was 1100hp at 20,000ft with just a two speed supercharger would be a miracle worthy of witnessing by the Pope and every other religious leader of the time.
A P & W R-1830 with a two speed supercharger was good for 1050hp at 2700rpm at 13,100ft. You are going to loose approximately 2% for every 1000ftof altitude so expect about 900hp at 20,000ft.
That was the whole reason for using the two stage supercharge in the first place. And there were some limits to the two stage supercharger as used in the F4F.
P & W seems never to have rated the engine at "Military power" That was the Navy's doing.
P & W rated the -86 engine at 1200hp at 2700rpm for take-off.
they also rated it "normal" max continuous at

1100hp/2550rpm at 3500ft
1050hp/2550rpm at 11,000ft
1000hp/2550rpm at 19,000ft.

1,000 hp at 19,000 ft, even if that really is the best they could get out of it (I'm not sure I buy that), is still actually pretty good. It's about what the two early P-40s you listed above were getting at 5 km lower. That much power at 19 or 20,000 feet means probably pretty good speed at that altitude. That would be pretty helpful. For example in the kind of situation they faced when Darwin was being bombed.

Ok This is total confusion. The difference between the FM-1 Wildcat and the FN-2 Wildcat had very little to do with the octane of the fuel.

The extra "peppy" 1350hp engine in the FM-2 was not a P & W engine, it was a Wright R-1820-56W Cyclone 9 cylinder engine that used water injection.
Trying to manufacture Wright Cyclone 9s on machinery that made P & W 14 cylinder Twin Wasps was going to take a bit of doing.
Before anybody gets a bright ideas of using the Wright Cyclone 9 for Australian production instead of the R-1830 Wasp the 1300-1350 Cyclones 9s used in the FM-2 were a totally new engine that shared just about zero parts with the 1200hp Cyclone 9 that came before it. New cylinders, new cylinder heads, new crankcase, new crankshaft and so on.

P & W did come out with a Peppy 1350hp version of the R-1830 in 1944 but it did require a number of things to be changed and not just pouring different fuel in the tank.
One thing they did was copy the cylinder construction method used for the R-2800C (from the P-47M) for better cooling. There were other changes.

I'll take your word for it. But 1) by 1943 Australia is starting to produce two stage engines for the Beauforts, right? And 2) by that time shipping engines to Australia wasn't so hard or perilous any more.

But that said, good point about the FM-2 using the R-1820, I forgot about that. I still say if you were using the best available R-1830 you'd start seeing a pretty nice fighter plane at some point.

 

[Admiral Beez]

If the RAN obtained an aircraft carrier, say HMS Hermes in 1939, given to Australia as a means of keeping Imperial carrier aviation active in the Indo-Pacific but on someone else's dime, could the RAN have made their radial fighter work as a combo with the RAAF? If the wingspan can be kept narrow like the Brewster Buffalo, folding wings aren't necessary.

 

[wuzak]

I'll take your word for it. But 1) by 1943 Australia is starting to produce two stage engines for the Beauforts, right?

I'm not sure if they were being produced in Australia by that time, but if they were they would be two speed engines.

 

[wuzak]

Even in what you are suggesting, you'd be wrong, but you made a mistake, look at those two aircraft in the photo again.

What mistake did he make?

 

[wuzak]

...is for sure reflecting a 'heavy' laden aircraft flown at low boost, probably continuous rated power, maybe with a belly tank?. The other very thorough Australian test I posted a couple of posts back shows far better performance, starting at 300 mph at Sea level and going up to 348 mph at 12,300. And this is a heavily laden plane at (8600 lbs) and flying at only military power (44" Hg). It also started climbing with 2000 fpm which rate continued until 9,500 ft. (this was at only 39" Hg power setting). The fact that the ROC remained the same up to that height is a good indicator more power was available.

More power should be available as it climbed towards its critical altitude.

 

[Farky]

I'll take your word for it. But 1) by 1943 Australia is starting to produce two stage engines for the Beauforts, right?

No, altough nearly 1000 Twin Wasps were made in Australia, they never produced R-1830 with two stage or two speed supercharger. Australia was only building version R-1830 S1C3G with single speed single stage supercharger in two variants - engines serial Nos.1 to 581 inclusive were originaly fitted with coupled (rigid) reduction gear drives (US designation for this variant was R-1830-82), engine serial No. 582 and subsequent were fitted with de-coupled (splined) reduction gear drives (US designation R-1830-90).

 

[Shortround6]

Here is a link to the P & W R-1830 engine index.

https://www.enginehistory.org/Piston/P&W/R-1830/R-1830Index.pdf

It should cover all the versions of the R-1830 made by P & W and their licensees.
Not sure about Swedish engines as they were licensed after the fact.
Please read the notes as some of them were planed or proposed engines or tested but not manufactured/sold.

Like any list this big there may be the occasional typo/misprint.

 

[Wild_Bill_Kelso]

What mistake did he make?

The more modern looking one is a P-40F. Three feet longer, no nose gun farings, no nose scoop, and a lot of minor improvements.

 

[Wild_Bill_Kelso]

No, altough nearly 1000 Twin Wasps were made in Australia, they never produced R-1830 with two stage or two speed supercharger. Australia was only building version R-1830 S1C3G with single speed single stage supercharger in two variants - engines serial Nos.1 to 581 inclusive were originaly fitted with coupled (rigid) reduction gear drives (US designation for this variant was R-1830-82), engine serial No. 582 and subsequent were fitted with de-coupled (splined) reduction gear drives (US designation R-1830-90).

Ah ok, so they imported the 2 speed or 2 stage engines for the Beauforts?

 

[Farky]

Ah ok, so they imported the 2 speed or 2 stage engines for the Beauforts?

Engines with two speed superchargers were imported, namely R-1830 S3C4G .

Here is a link to the P & W R-1830 engine index.

https://www.enginehistory.org/Piston/P&W/R-1830/R-1830Index.pdf

It should cover all the versions of the R-1830 made by P & W and their licensees.
Not sure about Swedish engines as they were licensed after the fact.
Please read the notes as some of them were planed or proposed engines or tested but not manufactured/sold.

Like any list this big there may be the occasional typo/misprint.

Basically same thing (engine index) but for all USAF engines is here - USAF Engine Models

It is interesting that there is a difference in those documents in case of engines we were talking about, "P & W index" got R-1830-75 at 1350 hp@2800 rpm, the other index got 1350 hp@2700 rpm for the same engine.

Edit: from US to USAF

 

[Shortround6]

Neither index has all the information we might like but the USAF engine models

Is just that, USAF engine models.

No navy engines and no commercial engines.

I could be wrong but I believe all the 1350hp engines in the P & W list are listed at 2800rpm.

The USAF list has quite a number of discrepancies.

 

[Shortround6]

The more modern looking one is a P-40F. Three feet longer, no nose gun farings, no nose scoop, and a lot of minor improvements.

Apparently this phrase
" (Picture is a long tail P-40F or L with Merlin which did a have bit bigger scoop)

isn't enough to explain the difference in between the P-40D that data applied to and P-40 in the picture.

Now was there one error or two in this sentence?
"The more modern looking one is a P-40F. Three feet longer, no nose gun farings, no nose scoop, and a lot of minor improvements."

Or is there 3 errors if you are comparing a P-40D to a P-40F?

 

[Farky]

Neither index has all the information we might like but the USAF engine models

Is just that, USAF engine models.

No navy engines and no commercial engines.

I could be wrong but I believe all the 1350hp engines in the P & W list are listed at 2800rpm.

The USAF list has quite a number of discrepancies.

You are right of course, there are no navy or commercial engines (well, some navy engines are listed), I know this is USAF list. I will edit my post.

Discrepancies may be caused by differences in ratings. Unfortunatelly there is only rpm and no manifold pressure in these documents.

 

[Wild_Bill_Kelso]

Apparently this phrase
" (Picture is a long tail P-40F or L with Merlin which did a have bit bigger scoop)

isn't enough to explain the difference in between the P-40D that data applied to and P-40 in the picture.

Well your performance stats certainly would be misleading to say the least comparing a Tomahaw with a P-40D, when in fact it was a P-40F. Stats for any of the 'long tail' P-40s, F, K, L, M, or N indicate considerably better performance, and certainly lower drag than a P-40C.

Now was there one error or two in this sentence?
"The more modern looking one is a P-40F. Three feet longer, no nose gun farings, no nose scoop, and a lot of minor improvements."

Or is there 3 errors if you are comparing a P-40D to a P-40F?

Ok let me spell it out a bit more.

P-40C / Hawk 81 - two nose-gun farings, air intake on top of the engine, and a bit thicker
P-40F / Hawk 87 (late) - 20" longer than the D, no air intake on top of the engine, no nose gun farings, and narrower fuselage.

More on that, according to "The Curtiss Hawks" (Wolverine press, 1972) Page 212:

"The basic P-40 design was changed for the first time with the model D. Behind these changes was the new Allison V-1710-39 engine with an external, instead of internal, spur reduction gear. This engine modification permitted the P-40D and subsequent models to have a slightly narrower fuselage - which was shortened six inches on the D and E."

The radiator scoop was a bit larger though.

America's Hundred Thousand gets into some more detail on this, on page 228

Aircraft / Maximum fuselage width / Maximum fuselage depth
P-40C / 39.6" / 65.7"
P-40F / 37.2" * / 57.6" **

So just as your eye will tell you if you look at the photo (or others) the P-40F was actually considerably slimmer in fusealge, especially in terms of 'fuselage depth'.

* given as 3.1'
** given as 4.8'

The fact that the early D and E were heavier (empty weight P-40C: 5,812, P-40D: 6,208, E: 6,350) and were initially being flown at low power settings, as in your example, by no means proves that they did not have less drag than the B and C (and export equivalents). Quite to the contrary, even the early 'Kityhawks' did have lower drag.

The F removed the radio aerial wire that had previously run from the wingtips to the tail, the L and later F had the radio mast installed behind the canopy and armor removed from the oil coolant tank.

M and N got the cooling gill on the front of the engine. N had aluminum radiators and oil coolers, smaller lighter (27", magnesium) wheels, and "non metalic" fuel tanks.

The later model F, L, and K, and all the M and N had a 20" lengthened fuselage with the rudder and fin moved back behind the elevator hinge center-line . Total length went from 28' 6" for the P-36A, to 31' 8" for Hawk 81 to 33' 4" on later model Hawk 87.

All of these little thing also made a difference.

 

[Wild_Bill_Kelso]

I believe there was also some changes done to the exhaust stacks too but I don't have time to go look that up and I don't know precisely when the change(se) were made. But you can see a difference here I think

 

[Wild_Bill_Kelso]

Speaking of boomerang / hurricane / Spitfire / kittyhawk, there is an interesting comparison on the last page of this one (the green page)

http://www.p40warhawk.com/Models/Technical/MikeHalbrook/P40s%20compared.pdf