Improve That Design: How Aircraft Could Have Been Made Better

[TheMadPenguin]

B-29: Give it a new wing (ok, 2 new wings) mounting 3 R2800s (as found in the P-47 with super and turbo) each instead of 2 3350s
The R3350 improved over time, so did the R2800 in the P-47.

 

[Koopernic]

The Planes of Fame flies a Flugwerk Fw 190 repolica with an R-2800 in it and a cut down prop from a C-47 Glider Tug wide-chord unit. There are small oil coolers all over the inside of the cowling, similar to the German approach. Not surprisingly, it got hot on its first flight. The solution was to add two oil coolers, one under each wing, with very small inlets that do not detract from the looks or aerodynamics.

Today, it flies without cooling problems and John Maloney hearded it around Reno in the Bronze Race in 2010 at 283 mph. The bronze winner was a Yak-3 at 317 mph, so it wasn't exactly slow but also wasn't exactly run very hard either since it was just a fun fly arond the pylons.

No real point here except that cooling was and IS an issue with the Fw 190 and all radials. Some handle it better than others. Basically, running an air-cooled radial at WEP means running it at high power until the oil gets to the upper limit of temperature. Then you either reduce power or have a forced landing when the radial throws a scrap iron fit up front and drips all over the windscreen.

Did anyone ever try an engine driven cooling fan on the R-2800?

 

[MiTasol]

Did they have inertial shoulder straps in WW2 era aircraft ?

Yes and no
They had retractable shoulder harness but not inertia reels. The pilot had to lean back, wait about a second for the spring mechanism to pull the harness tight and then manually lock it in that position.

P-40 seat -- the circular item is the belt tensioner - the shaft across the front connects to the locked/free handle. The tension cable runs through the conduit to part way up the back of the seat then connects to the shoulder straps. On the P-40 there are also side adjusters for the lap straps that are quick adjust.

 

[wuzak]

Did anyone ever try an engine driven cooling fan on the R-2800?

There was one on the XP-56

 

[P-39 Expert]

P39 - can I ask for your views on this

The driveshaft weighed 10lbs according to Larry Bell in an interview once. I'll try and look it up when I get home. The center bearing that connected the two 5ft shafts was indeed securely mounted on the base of the very robust "canoe" that held the engine, pilot, nose armament, nose landing gear and remote reduction gear which drove the propeller. The "canoe" assembly was mounted on the wing which gave the whole thing a very sturdy construction.

 

[P-39 Expert]

Larry Bell and boys sure screwed up when they went to all the trouble to design and build the P-63 when all they had to do was tweak the P-39 (take the armor out of the nose and move the radio),

What I'm saying is Bell/AAF should have put the -93 two stage Allison into the P-39 while they were waiting for the first P-63 to get finished. The -93 was in production in April 1943 but the first P-63 wasn't available until October. Seven wasted months, but then again I think the AAF was intentionally delaying the whole thing because it was just going to the Russians anyway.

 

[TheMadPenguin]

The driveshaft weighed 10lbs according to Larry Bell

I'm inclined to think this might be the truth in a strange (to us today) way. Armor plate (STS for example) was referenced in pounds, to tell the thickness, but that was pounds per square foot.
The drive shaft given as 10 pounds per linear foot makes good sense to me: two 50 pound sections making a 100 pound, 10 foot shaft.

 

[swampyankee]

Did anyone ever try an engine driven cooling fan on the R-2800?

All the helicopter installations used cooling fans. A well-designed airplane installation won't need one.

 

[GregP]

Hi XBe02Drvr,

Wish I could claim that wording, but it's a phrase Joe Yancey uses when an engine commits suicide. That's when he gets to repair them.

One Allison user had a unit run out of fuel (another person trying to fly with air in the gas tanks), and when they "pickled" the engine for transport for repair after the "ground strike," they removed all the spark plugs, put paper towels in the coolant openings, but left the spark plug holes open to the elements! So, when Joe got it, I was working there at the time, there was sand all in the cylinders, but the cooling jacket was pristine! Go figure! After complete disassembly, it needed to have all 12 cylinders honed. Other than that, it was good to go. Whoever took charge of the cleanup and aircraft retrieval wasn't exactly having his sharpest day that day.

Most of the scrap iron fits I have seen with Allisons were caused by the hand on the throttle / mixture levers. I have only seen two where the Allison failed.

In one, a distributor shaft broke cleanly. Luckily, the pilot was making a fast low pass down the runway at the time, traded airspeed for altitude, and landed without incident. The repair was simple and quick ... a new shaft and he was good to go. But, Joe didn't know that until the engine got to the shop and was examined, so it still had to be pulled and transported. I don't work there anymore, but we are still good friends.

The other one was a cylinder liner failure on Galcier Girl's attempt to recreate Operation Bolero. That was preventable in hindsight.

I'm not too sure how familiar with Allisons most in here are, but the pistons have four ring slots. Three up high (a compression ring and two oil rings), and one at the bottom of the piston skirt (an oil ring). The bottom ring prevents the piston from slapping in the bore when it is running. After WWII, they started using Allisons and Merlins for hydroplane racing, and those boys were nothing if not lazy when it came to going by the book for overhauls. One of their "tricks" was to chuck the pistons up in a lathe and remove the bottom ring groove. If they did that, they could remove and install the cylinder banks without cracking the engine cases. But, that leaves the piston no bottom support and it can slap back and forth in the bore. It will do that for about 100 - 250 hours and then crack the liner, which leaks coolant into the cylinder. The pilot can see the failure because coolant leaves a smoke trail. Some of the guys even drilled lightening holes in the piston skirt. I have a pair of those (only 3 rings and skirt holes) that used to be in Guy Lombardo's championship-winning hydroplane.

As it happens, the engines in Glacier Girl at the time had pistons with the bottom ring removed. That is no longer the case, and she is running very well these days. I hope she does so for a long time to come.

 

[XBe02Drvr]

The bottom ring repvents the piston from slapping in the bore when it is running.

Is that why Allisons could handle high MP, ultralow RPM cruise more gracefully than some of their contemporaries?

 

[GregP]

Generally, Allison components are beefier and less numerous than Merlin components, including bolts. Merlins have about 13,000 parts in them, give or take a few. Allisons have about 7,000 parts in basically the same size package. Beefier parts generally mean less breakage at normal stress levels. Actually, they'd have the same dispalcement except the Allison has 0.1 inches more bore. Both have 6-inch stroke. The Merlin has a 5.4-inch bore while the Allison has a 5.5-inch bore. 1649 cubic inches versus 1710 all due to 0.1" of bore.

Not too sure if bottom piston rings are a real reason; Merlin pistons also have four rings with one at the bottom of the skirt. But, Allison rods will handle a LOT more power than Merlin rods. Merlin rods will give up and fail somewhere around 2500 hp. Allison rods will take more and the G-series rods will take over 4000 hp, so they use them in the racing "Merlins" at Reno that really have very little "Merlin" left in them. Yes, they have Merlin cases and crankshafts, but they generally run Allison G-series rods, aftermarket pistons and wrist pins, aftermarket valves and fuel systems, and a host of other mods.

Basically, Racing Merlins are a "power system" composed of a lot parts that start with a Merlin engine case and cylinder bank set. Also, Allison bearings were the best at the time. The War Department made Allison share their bearing technlogy with Rolls Royce during the war. Otherwise, the TBO of the Merlin would never have been as good as it was.

It would not have changed the way the Merlin ran; it ran great. But it DID change the time between overhaul, which helped during the war. Methinks the crew chiefs were busy anyway during the war. They'd have been even MORE busy had not Rolls Royce implemented the 0.020"silver over 0.040" lead over steel bearings that Allison shared.

As far ultra low rpm cruising, low rpm is more stressful to the rods and bearings than high rpm, assuming the "high rpm" is within book limits (basically 3,000 rpm). Once you get to 3,600 rpm, then the high rpm is more stressful to the engine as a whole. Nobody much thinks about it, but the bearings take a beating at and around idle since ignition basically pushes the pistons and rods down against the bearing surface while the engine is turning over very slowly. Both Allisons and Merlin bearings (and all inlines) are less stressed at 1800 rpm than they are at 900 rpm. Let's recall that one Allison cylinder, assuming WER of 1,600 hp, can produce 125 hp. That's a pretty big hit on the bearing.

Anyway, Allisons and Merlins were both good engines. If you were going to 25,000 feet and didn't have a turbocharger, then the 2-stage Merlin was the way to go. The Merlin was one of the great engines of the war, for sure, regardless of any other stories or intrigue behind the engine. It worked when it needed to work and went as high as was needed easily. The Allison could, too, but not without the high-altitude boost system affored by the turbocharger setup. I'd like to have seen a complete Merlin 2-stage supercharger adapted to an Allison power section. Maybe somebody did one but, if so, I have not seen it or heard of it.

 

[wuzak]

The "canoe" assembly was mounted on the wing which gave the whole thing a very sturdy construction.

What a radical concept. The wing connects to the fuselage!

 

[MiTasol]

I'm inclined to think this might be the truth in a strange (to us today) way. Armor plate (STS for example) was referenced in pounds, to tell the thickness, but that was pounds per square foot.
The drive shaft given as 10 pounds per linear foot makes good sense to me: two 50 pound sections making a 100 pound, 10 foot shaft.

Having hoisted P-39 drive shafts hundreds of time I can absolutely gaurantee they did no weigh 50lb though I do think they were weighed more than 10. If I get interested enough I will dig out my microfilm and see what the blueprint says.

 

[GregP]

Hi MiTasol,

My estimate was the heaviest I think it could be based on POH weights, not a guess at actual weight. Think-wall shafts aren't very heavy in general.

I've seen one many times, but always inside the P-39/P-63, never all by itself. I'd guess most people who have seen one have not seen it by itself. They aren't exactly around in large numbers. Out of curiosity, how is it you have hoisted one so many times? Are you working on a P-39 restoration? If so, where? Again, just curious.

 

[Reluctant Poster]

I think the Sterling was designed when the RAF didn't know quite what it wanted. IIRC one of the design parameters was that it could be broken into three and carried by rail, quite why you would want to do that is a total mystery to me.
It did make it quite a good freighter and troop transport

The Lancaster and Halifax were built to the same constraints. Their fuselages were divided into 4 sections.
This was not an unreasonable requirement. It allowed shipping overseas with assembly locally. Packing cases are shown in the following link
Harry Boyle's Tango over Takoradi > Vintage Wings of Canada

It also allowed dispersed construction. An excellent example of dispersed construction was the London Aircraft Production Group
https://www.rchs.org.uk/wp-content/uploads/2017/01/342-London-Aircraft-Production-Group.pdf

The Americans also adopted the idea of dividing the fuselage
"Douglas found it necessary to break the DC-3 down to meet wartime schedules for the military version, the C-47. The fuselage was broken into three, later four, longitudinal sections, each of which could be assembled separately, and then installations were made in each section on a production line basis."

Finally, it should also be noted that the Supermarine 317 was designed to the same specification as the Stirling. The designs could not be more contrasting in terms of their bulk.
The overlay of the three bombers in the wiki article on the Stirling is eye opening
Short Stirling - Wikipedia
There was no reason for the Stirling to be 18 feet longer than a Lancaster.
I would hate to see how bulky Short would have made the Stirling without size constraints.

 

[nuuumannn]

There was no reason for the Stirling to be 18 feet longer than a Lancaster.
I would hate to see how bulky Short would have made the Stirling without size constraints.

The Stirling (and Halifax) have always appeared to me to be over-engineered the more I learn about them and a lot of that, particularly in the Stirling's case comes from Air Ministry interference and attempting to work within the specifics of the written requirements and specs. Short Brothers had experience with large multi engined aircraft (as did Handley page for that matter), yet the Stirling, a massive undertaking at the time fell short of the performance criteria of B.12/36 for numerous reasons and came with built-in obsolescence that could not be worked around without major redesign.

What it does illustrate (along with the Halifax) is that it wasn't easy to put into production large four-engined aircraft built to mid 30s specifications and anticipating whether or not they would be viable going forward. That the Manchester was Avro's very first attempt at a big (ish) all-metal aircraft is impressive (Avro had built Blenheims under licence as their first all-metal type in its workshops) and resulted in a noble but flawed effort, but essentially once the aerodynamic (and equipment) issues were worked out was a very sound design free of the performance constraints of the Stirling and the aerodynamic and overly complicated problems the Halifax suffered. Of course, the Manchester benefitted from the torpedo requirement in P.13/36, giving it that impressively large unobstructed bomb bay, as well as its inherent strength as a result of the catapulting requirement.

 

[swampyankee]

I wonder if the P-39 had been a strictly Soviet product (through licensing or whatever) it would have had a much different reputation.

Sure. Nobody except cognescenti would have heard of it.

 

[nuuumannn]

Nobody except cognescenti would have heard of it.

Well, on this forum we're making damn sure that everybody's heard of the P-39...

 

[GregP]

Nothing really wrong with the P-39, but I think we've had more P-39 discussion than it's merits warrant.

 

[nuuumannn]

Nothing really wrong with the P-39,

Care to elaborate?

but I think we've had more P-39 discussion than it's merits warrant.

Oh, I guess not, then...