Improve That Design: How Aircraft Could Have Been Made Better

[wuzak]

I figure used in an aircraft for a starting point.

I'm sure it flew in a test bed before it made its way into the XB-19A.

I would have figured they'd have just built another factory to be honest.

A factory was built for the IV-1430, but that never went into production.

Instead, other engines were built there - a radial (not sure which one) and then the V1-650 Merlin.

If needs must, that factory could have been converted to production of the V-1710 and V-3420.

the original idea was to simply use 2 x V-1710 blocks, and it started out as an X-cylinder engine, but for one reason, it ended up as a W.

Why was this?

The original scheme was for the X-3420, which was an X engine, using four V-1710 cylinder banks and heads on a crankcase that had a single crankshaft. Each bank had 6 cylinders. The angles between the banks were not 90° like the Vulture, but I can't recall what the angle were.

The X-3420 was also to be direct injected, as was the goal at the time for the V-1710 as well.

Allison produced a mock-up of the engine, but I don't think they built a running example.

It may have been due to a change in personnel that saw Allison counter-propose the V-3420. The reasoning was that using twin crankshafts, and 60° between two banks either side there were more components that could be carried over from the V-1710. It was also though that more power would be available, due to stronger crankshafts and connection rods - which would be the master and slave type for the X-3420. The projected power output was, simply, twice the output of the V-1710 at the time. Which meant 2,000hp for the V-3420 at that time, as compared to 1,600hp estimated for the X-3420.

The V-3420 was expected to be cheaper and easier to build, and be available for production sooner, due to the higher number of shared components.

 

[Conslaw]

I don't know about the technical details of the V-3420. Based on the performance of the prototype engines, which did pretty well, I think there were likely two related reasons it didn't go forward. First the R-3350 was a bit ahead in development and (2) without an earmarked plant by 1942, there was no place to build it. As it turns out, it wasn't needed and the powers that be made the right call.

 

[pbehn]

Re: He 177 Grief

Hang on, I thought the drag was the installation (carburetor intake, radiator, oil-cooler) not the propeller? Is a larger propeller similar in effect to a wing with higher aspect ratio?

Regardless, I would have figured that higher drag would be beneficial in the dive phase as it acts like a brake a little bit. I'd have figured the problem would be during the cruise phase.

I have no idea, the world of propellers is lost on me, it is a science in itself. I do know that an engine that is shut down with an un feathered prop causes massive drag. But that is my limit of "expertise".

 

[XBe02Drvr]

I do know that an engine that is shut down with an un feathered prop causes massive drag.

Commonly known as "windmilling". Akin to using engine braking to slow a motor vehicle. A similar phenomenon exists when an airplane wants to go faster (perhaps in a dive) than the speed its propeller governed at redline and full throttle would naturally pull it. Now the tail is wagging the dog and the prop is creating lots of drag and abusing the reverse thrust bearing in the engine, which in engines not designed for reversible props is often much less robust than the main thrust bearing, if it exists at all.
That's why planes like that are required to carry power in the dive, and if steep dive bombing, need some variety of aerodynamic speed limiting.
Now imagine an 80-90 thousand pound four engine bomber engaging in such antics and "diminishing returns" comes to mind, doesn't it?

 

[pbehn]

Commonly known as "windmilling". Akin to using engine braking to slow a motor vehicle. A similar phenomenon exists when an airplane wants to go faster (perhaps in a dive) than the speed its propeller governed at redline and full throttle would naturally pull it. Now the tail is wagging the dog and the prop is creating lots of drag and abusing the reverse thrust bearing in the engine, which in engines not designed for reversible props is often much less robust than the main thrust bearing, if it exists at all.
That's why planes like that are required to carry power in the dive, and if steep dive bombing, need some variety of aerodynamic speed limiting.
Now imagine an 80-90 thousand pound four engine bomber engaging in such antics and "diminishing returns" comes to mind, doesn't it?

That bit I understand, its when it comes to how a constant speed prop behaves when overspeeding in a dive I havnt a clue. The proposition is that two large props are better than 4 small ones. I understand the logic of the argument having that braking effect close to the centre of gravity (and all the other centres too) is beneficial. But if some learned fellow were to propose that it was advantageous to have this breaking effect spread by four props along the wing, I would have to agree with that too because I just dont know.

 

[Greg Boeser]

Pilots in the Aleutians learned to use the braking power of their propellers to decrease their landing rolls in B-26s. They would cut the engines on touchdown, then restart them when they needed the power to taxi. This got a few pilots in trouble when they rotated back to the States, where such unorthodox methods were frowned upon. They also found that while the technique worked on the Pratt and Whitney equipped B-26s, it didn't work so well on the Wright equipped B-25s.

 

[XBe02Drvr]

while the technique worked on the Pratt and Whitney equipped B-26s, it didn't work so well on the Wright equipped B-25s.

Wright engines weren't famous for their strong reverse thrust bearings.

Pilots in the Aleutians learned to use the braking power of their propellers to decrease their landing rolls in B-26s. They would cut the engines on touchdown, then restart them when they needed the power to taxi. This got a few pilots in trouble when they rotated back to the States, where such unorthodox methods were frowned upon.

No wonder! That's a great way to shock cool engines and crack cylinders.

 

[XBe02Drvr]

But if some learned fellow were to propose that it was advantageous to have this breaking effect spread by four props along the wing, I would have to agree with that too because I just dont know.

(Another restating the obvious!) If you have your braking effect props spread out, they become more susceptible to a slight imbalance in drag, especially in the outboard ones, making aircraft control and thus, bombing accuracy, difficult.
Otherwise it's just comparative pi r□'s of the propeller disks.

 

[pbehn]

(Another restating the obvious!) If you have your braking effect props spread out, they become more susceptible to a slight imbalance in drag, especially in the outboard ones, making aircraft control and thus, bombing accuracy, difficult.
Otherwise it's just comparative pi r□'s of the propeller disks.

Thats easy for you to say because you know what you are talking about, flaps and other devices are frequently spread along the wings, so if some fellow of letters was to say "four engines are advantageous in dive bombing due to the spanwise spreading of loads and limiting of maximum beam stresses" (or some other BS) I couldnt say that its wrong. Like the stuff you just posted about bearing loads and shock cooling, its all very complicated lols.

 

[Zipper730]

Commonly known as "windmilling". Akin to using engine braking to slow a motor vehicle. A similar phenomenon exists when an airplane wants to go faster (perhaps in a dive) than the speed its propeller governed at redline and full throttle would naturally pull it. Now the tail is wagging the dog and the prop is creating lots of drag and abusing the reverse thrust bearing in the engine, which in engines not designed for reversible props is often much less robust than the main thrust bearing, if it exists at all.

So the matter is that the windmilling effect would produce higher drag in dives, which normally is good, but it would put excessive stress on the engine?

Still, with a drag difference of 3%, would it be that serious? The He 177 already had dive-brakes, and they weren't all that big compared to the Ju 88.

Now imagine an 80-90 thousand pound four engine bomber engaging in such antics and "diminishing returns" comes to mind, doesn't it?

Truthfully the dive-requirement was added only after the aircraft had passed the mockup. Early on the plane was configured to perform some degree of glide-bombing (the Germans called it light to moderate angle dive-bombing), which I'm unclear on the exact number (though 40-50 degrees was a figure I heard once).

The dive-bombing requirement was added (supposedly) after the plane had been evaluated at a mock-up. Supposedly after the mock-up went okay: Udet told Heinkel the plane wouldn't be needed! Despite this, Udet said he was okay with the plane being used for other roles, including maritime patrol, but it'd require dive-bombing capability. Heinkel flat-out told Udet that the aircraft would never be capable of the 60-degree dive-requirement.

From what I remember reading, the idea to demand dive-bombing for all bomber aircraft seemed to have come out of the Spanish Civil War: The idea was that a dive-bomber could heap more bombs on target than level-bombing. Interestingly, the Germans didn't seem to devote much effort to bombsights early on.

If you have your braking effect props spread out, they become more susceptible to a slight imbalance in drag, especially in the outboard ones, making aircraft control and thus, bombing accuracy, difficult.

Technically, that could be argued to say that even a twin-engined dive-bomber would have problems in that regard.

Pilots in the Aleutians learned to use the braking power of their propellers to decrease their landing rolls in B-26s. They would cut the engines on touchdown, then restart them when they needed the power to taxi. This got a few pilots in trouble when they rotated back to the States, where such unorthodox methods were frowned upon. They also found that while the technique worked on the Pratt and Whitney equipped B-26s, it didn't work so well on the Wright equipped B-25s.

Were the DB 601 or Jumo 211/213 sturdy in that regard?

 

[XBe02Drvr]

Technically, that could be argued to say that even a twin-engined dive-bomber would have problems in that regard.

True, but the proximity of the engines to aircraft centerline tends to minimize that effect to remain within the corrective ability of the flight controls. Less so with outboard mounted engines.

 

[wuzak]

I don't know about the technical details of the V-3420. Based on the performance of the prototype engines, which did pretty well, I think there were likely two related reasons it didn't go forward. First the R-3350 was a bit ahead in development and (2) without an earmarked plant by 1942, there was no place to build it. As it turns out, it wasn't needed and the powers that be made the right call.

The problem for the V-3420 was that it wasn't always a required engine, so development wasn't continuous. Allison had limited development resources, so they concentrated on the V-1710 and the myriad variations the AAF kept asking for.

On the plus side, developments on the V-1710 were (mostly) applicable to the V-3420.

The biggest hope for production orders for the V-3420 would likely have been a production B-39. When the XB-39 program started the R-3350 wasn't very reliable. But by the time the XB-39 took its first flight most of the issues with the R-3350 were solved. But there were still issues, such as take-off performance at high loads.

The XB-39 program was also to use experimental twin stage turbos, instead of the standard type turbos that the B-29 had. That caused delay, and eventually the XP-39 flew without.

The big problem for the XB-39 was the development of the XP-75. This took Fisher away from building the engine modules for the XB-39, and also required Allison to develop the remote shaft and gearbox system and 2 stage supercharging.

 

[Simon Thomas]

No wonder! That's a great way to shock cool engines and crack cylinders.

For current typical single and twins, the coolests operating CHTs are at touch down. Even taxiing back causes the CHT's to rise again.
I see no reason a similar behaviour would not be seen with the radials.
Shock cooling would be very unlikely in this scenario.

 

[XBe02Drvr]

I see no reason a similar behaviour would not be seen with the radials.
Shock cooling would be very unlikely in this scenario.

Apples and oranges. Modern light aircraft in a temperate climate are not the same as heavy military aircraft operating in Alaska. The "incredible prostitute", aka "Baltimore sewer pipe", with its high wing loading would carry more power on its tightly cowled engines on the approach, and the much greater mass of the R2800 would be storing more heat. They ran hot anyway. Landing speeds were high and OATs were low; recipe for shock cooling if the engines were caged at touchdown. The effect is cumulative with repeated abuses. I've had experience towing gliders (Bird Dogs forever) and operating turbocharged planes at high altitudes in winter, as well as changing cracked cylinders. BTDT.
PS: I guess it wasn't clear above, but to get down to survivable landing speeds on short slippery Aleutian runways the Marauder had to be operated on the backside of the power curve on final, a tricky and power hungry operation. "One a day in Tampa Bay!"
Not the case with today's light aircraft.

 

[Greg Boeser]

73rd BS lost two within minutes touching down late on a rain slick runway at Naknek, AK on 16 Aug 1942. One fatality and several injured. Both aircraft were recovered in the '70s and spent time at Hill AFB in Utah, awaiting restoration. Last I saw they were up for sale in 2018. Haven't seen any new info.

 

[Dcazz7606]

P-39 Airacobra. Give it a ventral radiator similar to Mustang or Ki-61 and use the space in the wings for more fuel tanks.

 

[SaparotRob]

Uh-oh.

 

[Thumpalumpacus]

Yeah, there be a s**tstorm a-brewin'. We'll be removing armor before you know it.

 

[P-39 Expert]

Sorry to disappoint you.

 

[SaparotRob]

You da' MAN!