Improve That Design: How Aircraft Could Have Been Made Better

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bulid the demon and the skyraider wouldnt have happened
 
wuzak said:
I'd guess better metering of fuel to each cylinder.
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Okay, that makes sense. As for the R-3350's switching to direct-fuel injection, was this during the war?
No more than any X-engine, though balancing could be an issue.
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So, it's preferable to have 90-degrees for an X and 60-degrees for a V?
So the master rod is the bigger one?
The twin crank solution adds weight, and requires gears to join the crankshafts together, but simplified other parts of the engine, such as using the same blocks, heads and intake manifolds as the base Vee engine.
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I'm confused why the horsepower would be different, you basically have two V-1710's -- one upright, the other upside down. I don't quite grasp why you would have less than twice the horsepower.
The downside to master and slave rods is that the pistons don't have the same stroke, so extra tuning may be required
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Wait, all the pistons don't go up and down the same amount? I thought they were all the same...
The Vulture had master and slave rods, with the big end bearing on the master rod causing a lot of problems
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Why did it cause so many problems?
How early would the Army have fully committed to the V-3420? That is the real question, since Allison was not big enough or willing to develop engines without the prospect of sales.
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The US Army was the one that wanted the engine built. That's what lead Allison to design it. So, that's not the issue.

I can see the following advantages for the W-3420 (as it was): It was lighter, and simpler; and the following disadvantages: It was very wide and would make it difficult to fit in some fighter designs.
 
I remember something being said about medic's having a cross on their helmet, which they said enemy snipers were using to aim at them better. This might have been during the course of the Vietnam war.
 
Zipper730 said:
Okay, that makes sense. As for the R-3350's switching to direct-fuel injection, was this during the war?
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I believe that happened just before the end of the war.


Zipper730 said:
So, it's preferable to have 90-degrees for an X and 60-degrees for a V?
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I would think that equal spacing of the banks is preferable on an X engine.

Engines with that arrangement include the Rolls-Royce Vulture, Exe, Pennine and Eagle XVI, the Allison X-4520 and the Daimler Benz DB 604. All were X-24s, except for the Eagle XVI, which was an X-16.

The Napier Cub engine of 1919 was an X-16 with the outer pairs of banks separated by 90°, with the upper banks separated by 52.5°.

Both the X-3420 and V-3420 had 60° between the outer banks. So both could share the cylinder blocks, heads, intakes with the V-1710.

The X-3420 had 90° between the upper banks, which meant that the lower banks were 150° apart, and pointing down 15° from the horizontal. This would require adding a system to return the oil to the sump from the cylinder heads/cam covers.

The V-3420 had 90° between the centrelines of the outer banks. Which meant that the upper banks were 30° apart, but also spaced by 12 3/4in separation between the cranlshafts.


Zipper730 said:
So the master rod is the bigger one?
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Yes.


Zipper730 said:
I'm confused why the horsepower would be different, you basically have two V-1710's -- one upright, the other upside down. I don't quite grasp why you would have less than twice the horsepower.
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Allison estimated 1,600hp for the X-3420 and 2,300hp for the V-3420 (ie double what the V-1710 had, or was projected to have, at the time).

Allison did not have much, if any, experience with master and slave rod engines. The X-4520 mentioned above had each pair of banks connected to the crankshaft with fork and blade rods, with one pair of banks offset from the other (the same was the case for the Eagle XVI).

They estimated a maximum of 2,400rpm for the X-3420, which is why the power estimate is lower.


Zipper730 said:
Wait, all the pistons don't go up and down the same amount? I thought they were all the same...
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They can't be with master and slave rods. The master rod is connected to the crankshaft, and the slave rods to it. So the slave rods are shorter and do not centre on the crank pin, so they have different motion from the master rod. This means they either have shorter or longer stroke than the master rod (I can't recall which).

Engines with fork and blade rods have the same stroke across all cylinders.


Zipper730 said:
Why did it cause so many problems?
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The designs they had never did get sufficient clamping force on the bearing for it to work effectively.


Zipper730 said:
The US Army was the one that wanted the engine built. That's what lead Allison to design it. So, that's not the issue.
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They did. And then they didn't. Then they did. And then they didn't.

It also did not help Allison that the Army wanted the engine but did not give firm orders for production models.


Zipper730 said:
I can see the following advantages for the W-3420 (as it was): It was lighter, and simpler; and the following disadvantages: It was very wide and would make it difficult to fit in some fighter designs.
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I don't know why you would think that the V-3420 would be lighter than the X-3420, since it had two crankshafts, which is one of the heaviest components of the engine. The X-3420 was estimated to be 2,160lb against 2,300lb for teh V-3420.

The X-3420 would have been more compact.
 
You know, maybe he's got an idea here. Build a mini Skyraider with an R2800, and cancel the the Curtiss Widowmak(oops, I meant)Helldiver. Engine's already supercharged, no turbo needed, he's got his precious 20s, what's not to like? With an R2800, it could probably carry a B17-over-Regensberg size bombload.
 
VA5124 said:
japan wouldnt have a chance againist the sbd-6 aka the douglas demon
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1. There was an SBD-6, 450 built near the end of WW II. The nine cylinder Wright cyclone gave 1350hp in this version.
2. The engine in the real SBD-6 weighed 1333lbs.
3. The engine in the SBD-3 weighed 1315lbs.
4. The P & W R-2800 as used in the F4U weighed 2480lbs and needed a much bigger propeller than the engine used in the SBD.
4. The engine used in the Skyraider AD-1 weighed 2822lbs. Also a much bigger prop.

You can build or imagine hypothetical aircraft. They just have to follow the actual laws of physics. It helps a lot if they follow actual history, like not using 1945 engines in 1942.

You might want to consider the need to actually get a hypothetical plane on and off an aircraft carrier if a naval plane. For take off distance the worst US Navy fighter on land used hundreds of feet less runway than the Best US Army fighter.
 

Not a dive bomber but an R-2800 powered torpedo bomber. Consolidated Seawolf, originally designed by Vought but taken over by Consolidated due to lack of production capacity by Vought. Consolidated did have to build a new factory which delayed things.
 


Only 2,000lb bomb load. Not quite a "B17-over-Regensberg size bombload" (ie 5,000lb).
 
wuzak said:
Only 2,000lb bomb load. Not quite a "B17-over-Regensberg size bombload" (ie 5,000lb).
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Yes but the B17-over-Regensberg size bombload when carried by a single engine plane is at a very short distance.

Could carry four torpedoes with a radius of 215 miles.
Weighed more than an A-20G and even more than an early B-26 at normal gross weight.
Also needed Midway class carrier
 
IIRC, the radials we tore down and rebuilt in mech school had slave conrods individually sized for their position on the master rod. Our instructor said that was an attempt to keep compression ratios constant across all cylinders.
 
Regarding Allison Engines

Shortround6 said:
There is reason to believe that Allison could not have done what it did as far as building the engines it did build if it had spent much more time on side projects or not built the engine in a somewhat modular fashion.
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The numbers of people available makes it easy to understand why they would have had so much difficulty with the V-1710-59's supercharger.

Regarding the X-3420/V-3420

wuzak said:
I believe that happened just before the end of the war.
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So, there were some B-29 variants flying around with those in them?
I would think that equal spacing of the banks is preferable on an X engine.
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It definitely produces good symmetry.
Engines with that arrangement include the Rolls-Royce Vulture, Exe, Pennine and Eagle XVI, the Allison X-4520 and the Daimler Benz DB 604. All were X-24s, except for the Eagle XVI, which was an X-16.
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But 90-degrees would have made the engine radically different from the V-1710?

Regarding the X-4520, I'm amazed with so many rows of cylinders (one behind the other) that they managed to employ a successful cooling system (unless they blew the cooling-air in with sufficient force to carry away the heat as fast as it came up) -- the R-4360 had a hard time with four rows, and they were offset from each other.
Both the X-3420 and V-3420 had 60° between the outer banks. So both could share the cylinder blocks, heads, intakes with the V-1710.
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So each bank would be turned on it's side not one bank upper, one bank lower for the X-3420?
Allison estimated 1,600hp for the X-3420 and 2,300hp for the V-3420 (ie double what the V-1710 had, or was projected to have, at the time).
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And this was due to the lower RPM estimated, and this was due to the inexperience with master/slave rods. I'm guessing once they committed to 2400 RPM, it would take serious work to raise it up to 3000 RPM like the V-1710?
They can't be with master and slave rods.
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I guess fork/blades couldn't handle the forces?
The designs they had never did get sufficient clamping force on the bearing for it to work effectively.
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Would this be a problem with the X-3420?
I don't know why you would think that the V-3420 would be lighter than the X-3420, since it had two crankshafts, which is one of the heaviest components of the engine. The X-3420 was estimated to be 2,160lb against 2,300lb for teh V-3420.
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That is interesting.
The X-3420 would have been more compact.
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Because of the lack of two shafts?
 
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Zipper730 said:
Regarding the X-3420/V-3420
But 90-degrees would have made the engine radically different from the V-1710?
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The intakes would not have fitted. And two cylinder heads and/or rocker covers would have to be redesigned to allow for the oil to be scavenged back to the oil tank.



4 banks of 6 cylinders.

Not dissimilar to air cooled V-12s, such as the de Havilland Gipsy Major/Twelve.

Or for the Napier Dagger - 4 banks of 6 air cooled cylinders mounted in a H style engine (with 2 crankshafts).

I think the offset of the R-4360 made it harder to get cooling right than for an air cooled inline - where the cooling air could be fed into a plenum between the cylinders and forced outwards, or vice versa.


Zipper730 said:
So each bank would be turned on it's side not one bank upper, one bank lower for the X-3420?
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If 0° is vertically upwards from the crank centreline, the X-3420 would have cylinder banks at -105°, -45°, 45° and 105°. The outer two banks were angled below the horizontal (which would be +/-90°).

The V-3420 had cylinder banks at -75°, -15°, +15°, +75°. The outer banks were above horizontal.

I don't know what you mean by "turned on its side".


Zipper730 said:
And this was due to the lower RPM estimated, and this was due to the inexperience with master/slave rods. I'm guessing once they committed to 2400 RPM, it would take serious work to raise it up to 3000 RPM like the V-1710?
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I honestly do not know where they came up with 2,400rpm. Maybe it was the speed of 7 or 9 cylinder radials of the time (1937).

Though, Rolls-Royce were just starting to run the Vulture and would soon run it to its maximum speed of 3,200rpm. The Vulture did have a 5.5 inch stroke, compared to the 6 inch stroke of the V-1710 family.


Zipper730 said:
I guess fork/blades couldn't handle the forces?
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Fork and blade rods could really handle more than 2 cylinders. To run 4 cylinders on a single crankshaft would require two sets of fork and blade rods, side by side. This means that two cylinder banks would be offset along the crankshaft axis with respect to the other banks.

This is actually what the Allison X-4520 did, as was also the case for the Eagle XVI, which was only built as a test engine, and was not flight cleared.

This lengthens the engine, even if not by a lot.

The bigger issue using side by side fork and blade rods was that the crank pin would have to be longer and thus the bore spacing would need to grow.

The crankshaft pins, obviously, were at the same spacing as the bores. And the crankshaft pins had enough room for one set of fork and blade rods. Needing a second set would double the length of the pin.


Zipper730 said:
Would this be a problem with the X-3420?
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Possibly. The angles were different, so they may have been able to find a more suitable clamping solution.

Note that had the Vulture continued Rolls-Royce may have gone for the fork and blade rod solution. The Vulture had a 5 inch bore, like the Peregrine, but a bore spacing almost a half inch longer.

Also note that the later Rolls-Royce Pennine X-24 used single piece master rods and a multiple piece crankshaft, similar to the practice adopted for many radials (like the R-2800).

Pergelator: Master Connecting Rod


Zipper730 said:
Because of the lack of two shafts?
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Yes, and that the two crankshafts were 12 3/4 inches apart.

The X-3420 would have been 12 3/4 inches narrower.
 
Due to the position of the spar, the diameter of the fuselage was too narrow to accept a "tunnel" from the front pressurized compartment to the back. In order to accommodate one the fuselage diameter would have had to increase by about two more feet or so IIRC. I have copies of the original drawings showing this.

AlanG
 
They proposed to use the B-32 as gunships for the invasion of Japan. A friend of mine trained as a gunner for them and was told they would fly low and strafe targets for the invasion of Japan. Some people say this is absurd but they had already been doing that with B-25's in Burma and the distance from Okinawa to the Japanese mainland was a bit far for medium bombers. And for that they did not need pressurization anyway.
 
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