XP-65/F7F Development

[Shortround6]

By 1937 or 1938 weren't we aware what the Germans were doing at all?

There was a lot of secrecy before WWII, for example the Germans did display a DB 600 engine at the 1938 Paris airshow. even though it was months after the fuel injected DB 601 set a number of records. The Fuel injection was NOT put on display and even photographs were not published in common magazines. A number of German aircraft were not publicized much, if at all, until they had been in production for a while.

Infamous?

Yep, over complicated and requiring more than it's fair share of maintenance.
1.1"/75 caliber gun - Wikipedia

40mm would have been better as I think it had a higher muzzle velocity...

Army 37mm AA gun. MV 2600fps with 1lb 5oz projectile.

40mm Bofors gun MV 2870fps with 2lb projectile. The Bofors was better, both fired at about 120rpm.

Wait, I can't speak for the R-2600 but the R-2800 could do around 23,800...

Not with a single stage supercharger. Navy engines with 2 stage superchargers could make 1650hp at 22,500ft no ram and no water injection but were B series engines.

 

[Zipper730]

There was a lot of secrecy before WWII, for example the Germans did display a DB 600 engine at the 1938 Paris airshow. even though it was months after the fuel injected DB 601 set a number of records. The Fuel injection was NOT put on display and even photographs were not published in common magazines. A number of German aircraft were not publicized much, if at all, until they had been in production for a while.

I thought the Ju-87, Ju-88, and He-111 were common knowledge in basic shape

Army 37mm AA gun. MV 2600fps with 1lb 5oz projectile.

40mm Bofors gun MV 2870fps with 2lb projectile. The Bofors was better, both fired at about 120rpm.

The 40mm sounds like a better choice if you're going to push for a heavier gun (at this point in time, had we procured any Bofors equipment? I ask because they're Swedish...)

Navy engines with 2 stage superchargers could make 1650hp at 22,500ft no ram and no water injection but were B series engines.

I don't know how the B's differed from earlier set-ups.

 

[wuzak]

To be clear though: The P-40 used the 0.50 calibur ammo it did because the P-36 did and it was a P-36 with inline, and the P-47 was based on limited wartime experience, correct?

0.30" and 0.50" on early models being replaced by all 0.50"s on later models - because they were the standard guns the USAAC/F used.

 

[Shortround6]

I thought the Ju-87, Ju-88, and He-111 were common knowledge in basic shape

That is true but how much did the US know about the Do 19 or Ju 89? Or what was supposed to replace them?
The USAAC was worried about planes that could reach the US, not planes that had trouble flying past one European country. The Russians had flown 6 and eight engine aircraft in the early/mid 30s and the French had flown 6 engine monoplane flying boats in the Mid 30s. Very large planes were possible even if very expensive. The USAAC was trying to plan ahead.

40mm seems a better choice if you're going to go huge.

it was but then the 40mm bofors didn't exist when work started on the 37mm AA gun. Some countries tended to "stick" with certain sizes of cannon barrels because some of the barrel making machinery and ammo making machinery carries over. The US 37mm AA gun used the same size ammo as the 37mm AT gun even if some of the projectiles weren't exactly interchangeable. Please note the 37mm aircraft gun used different ammo.

To be clear though: The P-40 used the 0.50 calibur ammo it did because the P-36 did and it was a P-36 with inline, and the P-47 was based on limited wartime experience, correct?

The .30 cal ammo was the standard rifle ammo and the .50cal was a standard caliber and gun for the Army and navy. It was quite possible to convert a water cooled AA .50 gun to an aircraft machine gun with the proper barrel, barrel jacket and buffer assembly. The US had been putting .50 cal guns in fighter planes since the 1920s. Or had least had the option. One of the cowl guns cold always have been a .50 even if not always installed. Standerdizing ont eh .50 allowed for a considerable savings in logistics over using different guns for different purposes even if the .50 was not ideal in some situations.

I don't know how the B's differed from earlier set-ups.

P & W engines were described by a letter designation as to the model of the power section ( crankcase, crankshaft, cylinders, etc) Reduction gears and superchargers could vary on the same series engines. B series engines included single speed superchargers used in conjunction with turbos in P-47s, two speed single stage supercharges used in B-26 bombers and others, and single speed speed superchargers with the "two" speed auxiliary supercharger used in the F4U, F6F and P-61. The A series were only massed produced with the 2 speed supercharger. Experimental "A" series engines used other supercharger set ups but none saw service use. The later "C" series engines (NO common parts with the "B") also had multiple supercharger set ups, pretty much the same ones as teh "B" although details changed.

 

[XBe02Drvr]

I think I understand, you could make an airplane with a wildly varying CG...

"Couldn't keep the pipper on target! Soon as I touched the trigger, pipper rose sharply off target." At GE, we got complaints like this as soon as the first cannon equipped F-4Es were tested. The cannon (and ammo drum) were WAY out in front of everything except the radar dish, and at 100 rds/sec, the CG was shifting faster than the pilot could compensate. (Didn't have today's fly-by-wire active-stability computers then!)
Solution: redesign the feed mechanism and drum to capture the spent brass and feed it back into the vacated portion of the drum. ("Elbows and a__holes" on the production floor trying to incorporate the design changes without slowing production.) Unfortunately this changed some parameter having to do with vibration modes or resonant frequencies or something like that, such that once the cannon was fired, the radar was OTS UFN.

 

[Niceoldguy58]

Shortround6, unfortunately that drawing is NOT of the Martin XB-16, but rather of the Materiel Division Model 319. The attribution of many designs in the 1934-1938 range are woefully inaccurate. This and more will be finally cleared up in 2018.

The AAC had a nearly obscene love for the 37mm gun, planning to fit it to nearly everything from fighters to bomber gun turrets. I even have official drawings of a wing redesign on the P-51/A-36 to fit an internally-mounted 37mm. Pretty much every Attack aircraft from at least the A-26 on through the A-41 had multiple 37mm's fitted in at least the design process if not the prototypes.

I've been attempting to put together the story of the 37mm for a long time. Despite anything said about hitting power, etc., my gut feeling is that there is an unstated "not invented here" underlying attitude by the Army/Army Air Corps that negatively impacted the 20mm. The 20mm WAS discussed, up to and including being fitted to the P-40 (separate consideration from the Madsen 23mm externally mounted). In WWII, only the Navy fitted 20mm to its aircraft, with the USAF lagging until the 1950s.

As for the weapons mounting in the F7F/XP-65, I surmise that the streamlining of the nose of the aircraft made it impossible to mount weapons around the nose wheel. The wings were certainly large and deep enough to mount numerous .50cals or a smaller number of 20mms. I don't know too much about the XP-65, but that is one where I don't know of any interest in mounting 37mms. Then again, the AAC wasn't involved in the XP-65 long enough to look at that mounting seriously.

Regarding engines, I recommend people obtain the Kilner Board Reports which resulted in the R-40A and R-40B programs. One of the key items in those reports was concern that the AAC was relying too much on one engine type in its Specifications and the designs submitted, specifically the Allison inline. This resulted in two different directions of design, one being the universally unsuccessful "X" engines and the other greatly expanded development of radial engines mentioned earlier in this thread. Fortunately, Pratt and Whitney had plunged into radial technology with both feet, resulting in the R-2800 and eventually the R-4360. Wright had also done so with the R-2600 and the trouble-prone R-3350.

The Navy, of course, had turned to radial engines exclusively earlier in the 1930s, which frankly makes many of the entries for the eventual F7F project a bit peculiar. I recommend your looking at the section on this program found in American Secret Projects by Tony Buttler and Alan Griffith (me) which goes into some length about all the entries and includes 3-views.

I hope this is useful.

AlanG

 

[tomo pauk]

Hello, Alan,

The 20mm WAS discussed, up to and including being fitted to the P-40 (separate consideration from the Madsen 23mm externally mounted). In WWII, only the Navy fitted 20mm to its aircraft, with the USAF lagging until the 1950s.

The USAF was installing the 20mm on P-38, P-51 (four per aircraft), P-400 (version of P-39), P-61 and A-20 (four in the nose).

 

[Shortround6]

First, hank you for the correction on eh XB-16. But is does show the USAAC was interested in very large aircraft at the time. Wither for offence or for planning for defense against.

Chinn's "The Machine gun" volume 3 pages 31-39 and pages 351-380 had a history and technical details of the US 37mm automatic cannon, but few, if any, mentions of policy or thinking behind requirements, or much for test results except for broken parts or malfunctions (on the 37mm those mentions are few or non-existent).
Quite a bit of work was done on developing disintegrating link belt feeds and feeding from left or right of the gun/s as opposed to the AIrcobra style feed.
There were three basic guns with a host of modifications/prototypes. Basically the M4 as used in the Aircobra. The M9 which was an aircraft version of the M1A1 37mm AA gun (using the same ammo as the AA gun) and the M10 which was basically a fast firing M4 (up to 165 rpm but using the same ammo as the M4). How many of the M9 and M10 were actually installed in service aircraft might be in dispute as apparently development took longer than expected and the M4 had to be used in some cases.

The Hyper engine/s started in 1932 with Continental working essentially as the Army's machineshop. Lycoming joined in around 1935/36 (with a few ex Continental engineers), P & W started the X-1800 in 1938 (?) In 1938 Allison built a total of 14 engines.

 

[Niceoldguy58]

Tomo, you are quite correct about the fighters/attack ac sporting the 20mm. I had totally forgotten about them and was writing in a hurry. My apologies.

Shortround6, I will bow to your recitation of the dates for commencement on the Hyper-engines. I took some time to actually look back into my notes instead of relying on an aging memory filled with DH-4 info today and looked at the number of single and multi-engine designs that were originally intended for one of these engines. There were quite a few.

Many thanks for the corrections.

AlanG

 

[Shortround6]

You are bringing much information to the table also. Much appreciated.

Now in fairness I would note that while Continental and Lycoming started in those year progress was near glacial in speed and for a number of years the only hardware was one and two cylinder test rigs. Complete 12 cylinder engines only being assembled in 1939 or 1940 so the Allison did sort of become the defacto liquid cooled engine for a number of projects. Or filled in for prototypes while the "wonder" engines were still being worked on in the shops.
As you are well aware, what was planned or hoped for often fell well short of being accomplished in a timely fashion which makes trying to sort out intentions or policy a bit difficult.

 

[Zipper730]

Regarding the engines, the project timing probably didn't allow consideration of the R-2800.

According to this, the project started in 1939. At which point the R-2800 was still relatively early in development, while the R-2600 was in production.

The XF6F also used an R-2600.

Had the USN or USAAF procured an aircraft with a new engine before this time? Regardless, as the F6F evolved, the R-2600 was replaced with the R-2800...

It is right on topic guys. He was asking why some things happened the way they did and what I wrote is exactly on-topic. I'm amused that Tomo is ttelling me it's mis-information. That's funny. It's like me telling him why things happened the way they did in Poland. Thanks for a good one, Tomo.

And I didn't say nobody experimented with 2-stage superchargers, I said I didn't known why they didn't pursue it MORE, and still don't. I was taking about U.S. manufacturers, not British manufacturers. And nobody in here can tell me unless they were there. Perhaps the ones that were developed were pretty good for the radials, but I've never been happy with the auxiliary supercharger that Allison used. It worked, but the unit on the Merlin is much better designed. There was considerable room for improvement.

Allison's main beef was sharing bearings and we've had threads on it before. Valves that wear longer were important, and made their way around to everyone. It was inevitable, and even Allison knew it.

 

[wuzak]

I'm not sure I understood the rationale behind the Hyper-engine development. I get that they wanted a horsepower for every cubic inch of displacement, but I'm curious why they developed so many engine proposals when they had so little money to fund them (particularly after the early 1930's when there was little demand for inline engines outside of airships and military designs).

You are missing another part of the equation - the aim was also to get 1hp per pound of weight.

As for funding, the hyper program was funded by the USAAC Materiel Division. The basic cylinder was developed by Sam Heron at Wright Field, Ohio.

Who did you think funded them?

As to why there were so many developments (well, there were the Continental and Lycoming engines, and the Chrysler one came later) is probably because those developments were substantially or wholly funded by the US Army.

This funding model may have delayed progress. Because each new development had to be approved by the Army, thus there was a lot of bureaucracy.

The Continental hyper engine program started before the Rolls-Royce PV-12, yet Continental were still doing single engine development when the Merlin went into service with the RAF in the Hurricane.

Also, there was no purpose to their design beyond military use.

 

[MiTasol]

In WWII, only the Navy fitted 20mm to its aircraft, with the USAF lagging until the 1950s.
AlanG

P-38 all models and P-39D-1 had 20mm cannon

 

[tomo pauk]

So did the P-61s and P-51s/Mustang II. Plus a batch of A-20s that Soviets received.

 

[pbehn]

20mm cannon were the RAFs preferred armament on fighters from around 1939/40, Hurricane Typhoon Tempest Whirlwind and Spitfire all had cannon, various reasons why they weren't universal but it was a policy.

 

[Zipper730]

You are missing another part of the equation - the aim was also to get 1hp per pound of weight.

That makes more sense actually...

As for funding, the hyper program was funded by the USAAC Materiel Division. The basic cylinder was developed by Sam Heron at Wright Field, Ohio.

Who did you think funded them?

Well you said USAAC Material Division...

As for the cylinder-design: Why not just use an off the shelf cylinder while the new one is being developed? It might require restrictions on the engine, but at least the rest of the machinery can be run and ironed out.

As to why there were so many developments (well, there were the Continental and Lycoming engines, and the Chrysler one came later) is probably because those developments were substantially or wholly funded by the US Army.

I understand that they funded them, but if you have budgetary problems -- you either have to throttle back all designs you have (and if you have a lot, all go to a crawl), throttle back some selectively (and risk getting accused of impropriety), or cut some designs and allocate funding to the best.

This funding model may have delayed progress. Because each new development had to be approved by the Army, thus there was a lot of bureaucracy.

So it had to go up a lot of layers to make approval or rejection; then go back down all those layers?

Also, was this a 1-way system (Army tells them what to do, the company does it), or 2-way (Army tells them what to do, Company does it; Company submits ideas of their own/Army listens and tells them yes/no).

The Continental hyper engine program started before the Rolls-Royce PV-12, yet Continental were still doing single engine development when the Merlin went into service with the RAF in the Hurricane.

I'm still surprised it took them so long to realize other engine developments at the time (NACA cowling for starters, improved radiator designs) meant the flat cylinder was unneded.

 

[XBe02Drvr]

As for the cylinder-design: Why not just use an off the shelf cylinder while the new one is being developed? It might require restrictions on the engine, but at least the rest of the machinery can be run and ironed out.

Zipper, some of the things you say stretch the limits of credulity, but this one hits the absurdity button so hard clenched jaws can't keep my mouth shut!
Clearly you've never gotten your hands dirty with any of this stuff. An engine is an integrated system that has to fit and work together, and the cylinder is where it's happening. You can't design a crankcase, crankshaft, con rods, gearbox, accessory case, carburetion system, etc, around a cylinder that doesn't exist yet in any definite form. Sure, you can design around what you imagine it will be, but the development process has a funny way of throwing a monkey wrench into that. Then you have to redesign everything. If you "temporarily" bolt a set of "off the shelf" cylinders (provided you even have suitable substitutes) into this dream engine of yours, you're still going to have to re-engineer everything once you know the final configuration and dynamics of the developed cylinder design. Think you can sell that concept to Material Command in an era of shrinking budgets and isolationist thinking? Good luck!
Cheers,
Wes

 

[Shortround6]

I'm still surprised it took them so long to realize other engine developments at the time (NACA cowling for starters, improved radiator designs) meant the flat cylinder was unneded.

It took more than that. And do try looking up the NACA cowling, it was an ever evolving item all on it's own. It did NOT spring into being in a single month or even year fully done and in final form. The early ones had no internal baffling, Like between the cylinders of the engine, no adjustable slots or flaps on the exit (no adjustment of airflow for speed or power output/actual cooling need) And so on.

 

[pbehn]

What I find interesting reading about engine development is how nothing was or is as simple as it seems. The Vulture should have been a simple development as it used much of the Peregrine design, however it wasn't successful because, well because things are never that simple. Then, as a company gets everything sorted, there is a need for something better. Just when RR got the Merlin to produce 2000 BHP someone said "Hey that's great but can you cut down the frontal area?

 

[XBe02Drvr]

What I find interesting reading about engine development is how nothing was or is as simple as it seems.

Reminds me of the crusty old Chief Avionics Technician who woke us up on the first morning of antennas and transmission lines phase in A School.
"Any you maggots got any clue to what the letters F M stand for?"
(Class hotshot): "Sure, Chief that's Frequency Modulation, where the carrier wave is modu--"
"Wrong, Sailor! You believe that bullpucky? What, you some kinda engineer or somethin? Any right thinkin' tweet knows it stands for f--kin' magic! You think those test rigs them engineers design with all their fancy formulas actually WORK when they build 'em? 'Course not! They tweak this and try that, and finally go back to their drawin' boards in disgust and tell the techs to tear down and dispose of the rig. Well no tech worth his salt tears down a perfectly good rig without first applying a little "FM" just to see what might happen. Sooner or later, word filters up to Engineerin' that the techs have a new toy down in the shop, and it works good. That, son, is F. M.!"
The jump from theory to function can be a big one and seldom goes as planned.
Cheers,
Wes