R40-C: How would you do it?

[wuzak]

In 1939 the USAAC was looking for new aircraft which would provide a quantum leap in performance over existing types.

In order to get this aircraft in production as quickly as possible the standard process was abandoned in favour of a "streamlined" process called "Request for Data R40-C" (40 represening Fiscal Year 1940).

The goals were high. Initially a top speed of 525mph was requested, but this was later revised down to 450mph and then 425mph (remember the P-38, P-39 and P-40 hadn't yet made production, none of which could match that performance). It was to be a single engine, single seat fighter with heavy aarmament, which could include anything from the .30 LMG to the 37mm cannon. Unconventional layouts would not be looked upon unfavourably.

The choice of engine included those under development at the time, and included: the Allison V-1710 V-3420, Continental IV-1430, Wright R-2160 Tornado, Pratt Whitney X-1800 and R-2800 and the Lycoming O-1230/H-2470 (not sure when the latter began).

It was expected that the prototype would be built and tested during FY41, with production coming on line in FY42 (ie by June 1942).

Historically 3 types were selected for further development, 3 of them flying. Vultee had the XP-54, Curtiss the XP-55 and Northrop the XP-55. The XP-55 was to use the IV-1430 and the others the X-1800. The XP-55 ended up with the V-1710, the Xp-54 the H-2470 and the XP-56 with an R-2800.

All three were pusher aircraft, of different configurations - the Vultee was a twin boom aircraft, the Curtiss a tail first design and the Northrop a flying wing.

http://www.fantastic-plastic.com/VulteeXP-54AnigrandPhoto.jpg

http://www.aviastar.org/pictures/usa/vultee_xp-54.gif

http://farm4.static.flickr.com/3199/4555977591_8eed842e62.jpg

http://kikakuya.files.wordpress.com/2008/07/ascender.gif

http://jpcolliat.free.fr/north/images/xp-56_3.jpg

http://www.aviastar.org/pictures/usa/northrop_xp-56.gif

I believe that the Bell XP-52 and XP-59 also came from R40-C. McDonnell proposed its Type 1, which interested the USAAC sufficiently that a contract for development of the Type 2 (XP-67) was awarded.

So, what configuration, engine, etc, would you choose?

 

[davebender]

prototype would be built and tested during FY41, with production coming on line in FY42

That's a very ambitious production schedule!

If you want a fast aircraft in production by mid 1942 I recommend the Mustang. Early models would be powered by the Packard built Merlin engine. Later models would be powered by a Packard or Ford built Griffon engine. The Mustang has plenty of room under the hood for the larger engine. Purchase Hs.404 20mm cannon from Britain (so they will work properly) and put two in each wing.

 

[wuzak]

This project predates the Mustang by the best part of a year.

The performance they were asking for exceeded the P-51A's performance, and the aircraft was to be, no doubt, powered by US engines. And I don't think US manufacture of the Merlin was yet on the table.

The production schedule is ambitious, overly so as it turned out, but is the USAAF's, not mine.

 

[tomo pauk]

I'd like to see a two-stage R-2800 in a slightly (10% for all of 3 dimensions - cca 20% up for area, or 1/3rd up for volume) scaled-up P-51 airframe.

A P-47 seems to fit the bill here generally.

 

[davebender]

US Warplanes
618 Mustang Mk.I produced during 1941.
The Mustang airframe exceeds the 1942 production goal by a full year. In addition to availability I selected the Mustang airframe because it meets the specification objective for high speed.

The Rolls-Royce Packard V-1650 "Merlin" Engine

The first two Packard-built Merlins to be completed were demonstrated on test stands at a special ceremony at the Packard plant in Detroit on August 2, 1941. Full production began in 1942

Nothing prevents the U.S.A.A.C. from further developing the Allison engine as a Mustang powerplant. However the Packard built Merlin engine also meets the mid-1942 production goal. Having two engine options for the Mustang airframe is a good thing.

An American built Griffon engine would offer a third option for the future. Perhaps in 1944.

 

[tomo pauk]

The data from the uswarplanes.net needs to be carefully interpreted - it was the 1st example of Mustang Is produced in 1941, not the whole order (618 pcs). The US hundred thousands give a number of 138 P-51s produced (= mostly/all as Mustang I for RAF) in whole 1941.

The Packard Merlin that can propel P-51 to 425 mph is the two-stage (V-1650-3 or later) two-speed variant; the single-stage V-1650-1 wont cut it here.

 

[krieghund]

US Warplanes
618 Mustang Mk.I produced during 1941.
The Mustang airframe exceeds the 1942 production goal by a full year. In addition to availability I selected the Mustang airframe because it meets the specification objective for high speed.

The Rolls-Royce Packard V-1650 "Merlin" Engine


Nothing prevents the U.S.A.A.C. from further developing the Allison engine as a Mustang powerplant. However the Packard built Merlin engine also meets the mid-1942 production goal. Having two engine options for the Mustang airframe is a good thing.

An American built Griffon engine would offer a third option for the future. Perhaps in 1944.

I think the 1942 production goal is just out of reach but this is my selection to meet the criteria

 

[davebender]

Neither will any other aircraft engine in service during 1941. If the U.S.A.A.C. are serious about this specification then they will spend money for engine development.

 

[tomo pauk]

The turboed R-2800 will and did; here is for XP-47B, from Wiki:

An engineering prototype P-47B was delivered in December 1941, with a production prototype following in March 1942, and the first production model provided in May.

I do agree that pouring some dollars in engine development in late 1930s would've reaped handsome dividends within a short period of time.

 

[davebender]

What was the service life of that engine during 1941?

 

[tomo pauk]

Enough for service in 1st prototype.

 

[wuzak]

US Warplanes
618 Mustang Mk.I produced during 1941.
The Mustang airframe exceeds the 1942 production goal by a full year. In addition to availability I selected the Mustang airframe because it meets the specification objective for high speed.

The Rolls-Royce Packard V-1650 "Merlin" Engine

Nothing prevents the U.S.A.A.C. from further developing the Allison engine as a Mustang powerplant. However the Packard built Merlin engine also meets the mid-1942 production goal. Having two engine options for the Mustang airframe is a good thing.

An American built Griffon engine would offer a third option for the future. Perhaps in 1944.

The P-51 project didn't commence until 1940 - so didn't exist at the inception of R-40C. Nor did US production of Merlins.

 

[Shortround6]

Neither will any other aircraft engine in service during 1941. If the U.S.A.A.C. are serious about this specification then they will spend money for engine development.

They were spending money, not enough when it counted and spread a bit to thin too. Spending money in 1940-41 for engine development is 2-4 years too late for a usable engine or major revision for use in 1942
Please remember that work on the R-2800 STARTED in 1936 as a 18 cylinder 2600cu in engine and by April of 1937 they were releasing early specifications.
The Continental IV-1430 was ONE of the Army's favorites at the time.
The Lycoming was doubled to become the power plant for the XP-54 and was proposed for other aircraft.
The Wright Tornado was another money pit that went nowhere.
A number of prototype aircraft were given Allison's or P&W R-2800s when these "wonder" engines crapped out.
But let's not kid ourselves that it was due only to a "lack of money".

 

[davebender]

That engine should fit nicely into the Mustang airframe.

 

[Shortround6]

And it would have done what?

The Wiki article has a number of serious errors. For one the 1600hp level needed 15.5lbs of boost at sea level. The engine used a single stage supercharger and had one speed, being an Army favorite it needed a turbocharger for altitude performance.

 

[gjs238]

How about scaling up the V-1710 with greater displacement, ala DB600 series?
I thought the DB's didn't need as much boost as the Merlin V-1710.

 

[Shortround6]

They don't but "scaling" up doesn't really save a lot of development time and effort. The different dimensions mean the the crankshaft, camshafts and other parts will have different vibration characteristics and those were a major headache in sorting out high power aircraft engines. Even changing the RPM an existing engine ran at could run into overlapping harmonic vibration problems. This is one reason the the Merlin ran at 3000rpm max rpm from first to last.

 

[wuzak]

And it would have done what?

The Wiki article has a number of serious errors. For one the 1600hp level needed 15.5lbs of boost at sea level. The engine used a single stage supercharger and had one speed, being an Army favorite it needed a turbocharger for altitude performance.

When the IV-1430 flew in the XP-67 and XP-49 it was reckoned to be making no more than 1050hp. It was said to have done a dyno test late in the war at 2100hp, but by then it was clear it wasn't going to go into production.

The problem with the IV-1430 was that Continental wasn't willing, or had insufficient funds, to put money into development themselves. Therefore they had to rely on USAAC funding. They also insisted on contracts for all engineering changes, no matter how small. The result was that while the IV-1430 program began 2-3 years before the PV12/Merlin it was still undergoing single cylinder testing after the Merlin had gone into service.

 

[wuzak]

How about scaling up the V-1710 with greater displacement, ala DB600 series?
I thought the DB's didn't need as much boost as the Merlin V-1710.

They don't but "scaling" up doesn't really save a lot of development time and effort. The different dimensions mean the the crankshaft, camshafts and other parts will have different vibration characteristics and those were a major headache in sorting out high power aircraft engines. Even changing the RPM an existing engine ran at could run into overlapping harmonic vibration problems. This is one reason the the Merlin ran at 3000rpm max rpm from first to last.

Not sure how much a V-1710 could be overbored - but it couldn't have been much.

The problem is to get a much bigger bore requires a wider bore spacing - the Merlin had 6.175" between bore centres, the Griffon 6.9". The Merlin bore was 5.4" and teh Griffon's 6.0". The V-1710 had a bore spacing of 6.3" (IIRC) and a bore of 5.5".

Getting a significantly larger bore would require new blocks and heads. Not simple.

The easier way to increase capacity was to stroke the engine. In other words, put in a longer throw crank. That requires new rods, a new crank and associated parts. It probably also means new big end and main bearings, could require new gears for prop reduction and accessory and supercharger drives. A lot of effort.

 

[gjs238]

Yes, I'm thinking of something analogous to the DB603.