Improve That Design: How Aircraft Could Have Been Made Better

[P-39 Expert]

No turbo for the P-39, best thing that ever happened to it was deleting the turbo. To improve performance just delete some non-essential equipment to make them lighter (.30 cal wing guns and nose armor plate) until the mechanical second stage was in production in April '43.
The internal supercharger step-up gears could accommodate ratios from 6:1 up to 11.6:1 by simply changing the number of teeth in the drive gear and the driven gear. The two stage engines (turbo and mechanical) used lower ratios (6.44, 7.48 and 8.1) since the second stage was supplying sea level air to the internal stage. Single stage engines used the 8.8 and 9.6 gears and it was hoped that the 9.6 gears could be introduced in late '41 to increase critical altitude from 12000' to 15000' and provide about 100 additional horsepower above about 9000' as compared to the 8.8 gears. The 9.6 gears proved unable to take the increased manifold pressure and could not complete the standard (for the U.S) 150 hour test. Possibly because port backfire screens were still in use (until mid '42) that reduced the manifold pressure at the port into the cylinder. Had these backfire screens been deleted the unrestricted flow from the supercharger to the intake ports may have reduced the load on the gears enough for them to pass the test. But the backfire screens were not eliminated until mid'42 while Allison was in the middle of redesigning the gear housing to accommodate wider gears to handle the increased pressure. The wider gears were in production from August '42 and were in production P-39Ms from November '42. So about a year was lost fixing the 9.6 gear problems.

 

[XBe02Drvr]

One mock up put the turbo and intercooler in pod on the centerline replacing the drop tank or bomb.
It is a mock up so they never fitted the intended exhaust manifolds/pipes.

Hey it's a P39J (J for jet boosted)! They stole one of the XP59's engines to make a V1 killer out of a 'cobra!

 

[pinsog]

Hey it's a P39J (J for jet boosted)! They stole one of the XP59's engines to make a V1 killer out of a 'cobra!

I sure like your idea better than the one they came up with! (As long as I don't have to fly it)

 

[Zipper730]

When you're dealing with a compressible fluid such as air, just about all parameters are going to be exponential in nature. That's never been a secret. Now a precise determination of the strength and likely breaking point of those gears may have required more calculating power than was available in those pre-computer days.

So you think they miscalculated, or in some way, got careless?

Yes.

Did they miscalculate how much the shaft and gears could take, or did they get careless?

There is this drawing from Flight of a Merlin fitted with turbos.

I have the image here

[/quote]Did Allison ever think of that kind of thing?

The B-29 had two turbochargers, one either side of the nacelle, behind the engine.

I thought the turbines were pointed either down or aft at an angle...

 

[wuzak]

Did Allison ever think of that kind of thing?

I doubt it.

Firstly because a single B-series turbo was sufficient for the V-1710 and, secondly, the exhaust and turbo installation wasn't in their scope, instead falling to the airframe manufacturer.

 

[swampyankee]

I doubt it.

Firstly because a single B-series turbo was sufficient for the V-1710 and, secondly, the exhaust and turbo installation wasn't in their scope, instead falling to the airframe manufacturer.

Why the turbo installation fell to the airframe manufacturer, not the engine company is one of the mysteries of WWII-era procurement.

 

[Big Jake]

Very few bombers could carry the same weight of "small" bombs as large ones. Small being under 250lbs. even an He 111 dropped from 4400lbs carrying eight 250kg bombs to 3520lbs carrying thirty two 50kg bombs and they managed to stuff four 50kg bombs in each 250kg bomb cell.

Hanging them on individual racks really sucks up room. In part due to the needs of hoisting bombs into position and the needs of the armorers to work around the bombs fitting fuses and safety wires.

AIrplanes have two CG or perhaps weight distribution problems is a better way of saying it. The first is flying and most of us are familiar with that. The second is landing and/or ground handling. Once a number of planes were modified with extra armament or operational equipment they managed to keep the flying CG pretty much in place but the ever increasing loads often strained the landing gear or made ground handling difficult. Pilots manual for even the B-25C/D prohibits pivot turns, notes that on soft surfaces the nose wheel can dig in a reverse itself (turn 180 degrees) if the tire sinks more than 2 inches into the soil. It suggests having a crew man walk in front of the plane monitoring the wheel if the ground is soft.

On some planes it was a trade off between more effective armament (or more effective placement) and increase ground accidents/ even if repairable.

On the B-26 they added tons of equipment/consumables to the original design. Moving the turret forward (to behind the pilots? ) would seem doable, but they were adding a single fixed .50 in the nose and the four cheek guns, Perhaps they needed the turret to stay where it was?
Of course they added more/bigger lower waist guns and an extra crewman? so perhaps moving the turret would help with that? B-26 went through a lot of weight shifts.

B-25 - the prohibition on pivot turns has nothing to do with CG. The B-25 has no nose wheel steering and the wheel is free swiveling. You steer the B-25 by differential engine power and very delicate little application of brakes. If you get the nose wheel off of the direction that you are traveling, it will swing to the side and you'll be hard pressed to get it back. If you do a pivot then you'll just have to keep going in circles or have a ground crew member come with a tow bar and get the nose wheel point in the right direction for you. All of the above is on hard surfaces, never mind soft surface.

 

[XBe02Drvr]

You steer the B-25 by differential engine power and very delicate little application of brakes.

Also the T34 and the Be1900 (after the useless, treacherous, maintenance nightmare OEM pneumatic nosewheel steering was consigned to the dustbin where it belonged). The Be99 had direct linkage steering off the rudder pedals, lightplane style, but you could easily overpower it with differential thrust. This can be useful if you find yourself on a slick surface with nil braking action, as sometimes happens when you're flying freight into the back country on the back side of the clock. Beta thrust is a lifesaver.
Cheers,
Wes

 

[Big Jake]

Why the turbo installation fell to the airframe manufacturer, not the engine company is one of the mysteries of WWII-era procurement.

Installation of the turbo fell under the subject of overall aircraft general arrangement and had to do with allocation of space and overall systems arrangement. Different designers adopted different solutions. Some installed the turbo right behind the engine (P-37), some on top of the tail boom (P-38) and some in the tail (P-47). In the B-17 they are behind the engines, in the B-29 on the side.

 

[Big Jake]

Also the T34 and the Be1900 (after the useless, treacherous, maintenance nightmare OEM pneumatic nosewheel steering was consigned to the dustbin where it belonged). The Be99 had direct linkage steering off the rudder pedals, lightplane style, but you could easily overpower it with differential thrust. This can be useful if you find yourself on a slick surface with nil braking action, as sometimes happens when you're flying freight into the back country on the back side of the clock. Beta thrust is a lifesaver.
Cheers,
Wes

And the B-25 does not have Beta

 

[wuzak]

Installation of the turbo fell under the subject of overall aircraft general arrangement and had to do with allocation of space and overall systems arrangement. Different designers adopted different solutions. Some installed the turbo right behind the engine (P-37), some on top of the tail boom (P-38) and some in the tail (P-47). In the B-17 they are behind the engines, in the B-29 on the side.

The turbo on the XP-37 and YP-37 was below the engine, not behind it.

The B-17's turbos were located in the nacelle. It was similar to the P-38 arrangement, except that they were underneath, not on top.

The B-29's turbos are on the sides of the nacelles, not on the sides of the engine.

 

[Shortround6]

So you think they miscalculated, or in some way, got careless?

Did they miscalculate how much the shaft and gears could take, or did they get careless?.

Maybe they never intended the shaft/gears to handle such a load. The Allison was a lot of years in development and fuel (and thus the ability to even use high boost) change considerably in ten years.

In 1935 when Howard Hughes set the world speed record using 100 octane fuel (not 100/30) it cost ten times per gallon what 87 octane fuel did. People knew higher octane fuels were coming but they didn't know when or how widespread they would be ( a few planes had small tanks holing 87 octane for take-off and large tanks for 80 octane for cruise).
Building an engine in 1935-37 that a supercharger, drive shaft and gears sized to handle 200hp or more hp would have meant a heavier engine that needed for the existing fuels, or even the fuels in the immediate future.

 

[Zipper730]

I doubt it. Firstly because a single B-series turbo was sufficient for the V-1710 and, secondly, the exhaust and turbo installation wasn't in their scope, instead falling to the airframe manufacturer.

Understood. What made the B-series the B-series, and so on?

Also, I was curious if the engine guys coordinated with the aircraft industry?

Installation of the turbo fell under the subject of overall aircraft general arrangement and had to do with allocation of space and overall systems arrangement. Different designers adopted different solutions. Some installed the turbo right behind the engine (P-37), some on top of the tail boom (P-38) and some in the tail (P-47). In the B-17 they are behind the engines, in the B-29 on the side.

Fascinating. It does appear to have a double wheel on either side with covering that also seems to serve to turn the exhaust rearwards.

Maybe they never intended the shaft/gears to handle such a load.

It's still kind of strange when you consider that they understood that greater loads were going to be produced by upping the gear-ratio. The only solution is to strengthen things, it appears.

The Allison was a lot of years in development and fuel (and thus the ability to even use high boost) change considerably in ten years.

So the higher boost ratings put more load on the engine as it was?

Building an engine in 1935-37 that a supercharger, drive shaft and gears sized to handle 200hp or more hp would have meant a heavier engine that needed for the existing fuels, or even the fuels in the immediate future.

When was the V-1710-59 conceived?

 

[wuzak]

Understood. What made the B-series the B-series, and so on?

The size.

The B-series was rated for 1,000hp to 1,500hp engines, IIRC.

Also, I was curious if the engine guys coordinated with the aircraft industry?

What makes you think they didn't?

Fascinating. It does appear to have a double wheel on either side with covering that also seems to serve to turn the exhaust rearwards.

Which aircraft are you talking about?

It's still kind of strange when you consider that they understood that greater loads were going to be produced by upping the gear-ratio. The only solution is to strengthen things, it appears.

They were constrained by the wheel case designed for the earlier gear set. If they could get away with gears that could fit inside the existing casing then they would save some time.

But they couldn't and it didn't save time.

When was the V-1710-59 conceived?

April 1, 1941, 10.37am.

Seriously, the engine was evolving, as were the aircraft using it.

Problems with the turbo development led to calls for altitude rated engines, which Allison provided. Then, obviously, the engine was lacking altitude performance so they worked towards a solution.

Plus the AAC/F were beating them with the Merlin stick.

 

[Zipper730]

The size. The B-series was rated for 1,000hp to 1,500hp engines, IIRC.

Okay, I thought there was some characteristic about the supercharger layout that made it unique.

What makes you think they didn't?

That's a good enough answer. I was just curious the degree of coordination.

Which aircraft are you talking about?

B-29

They were constrained by the wheel case designed for the earlier gear set. If they could get away with gears that could fit inside the existing casing then they would save some time.

So, they did it under the wishful thinking that they would be able to make it all work and not have to redesign the wheel-case?

Seriously, the engine was evolving, as were the aircraft using it.

I was kind of wondering whether the idea started in 1938, 1940, 1941, etc.

Problems with the turbo development led to calls for altitude rated engines, which Allison provided. Then, obviously, the engine was lacking altitude performance so they worked towards a solution.

Makes sense

 

[P-39 Expert]

Hey it's a P39J (J for jet boosted)! They stole one of the XP59's engines to make a V1 killer out of a 'cobra!

Yes that jet engine was it's Achilles heel tending to catch the tail on fire.

 

[Glider]

Personally I like to keep the changes to a small scale. There were a number of aircraft which would have been far more effective with little changes.
Macchi 202 with 2 x 20mm in the wing instead of 2 x LMG which were hardly worth the effort.
The P51B with the 6 x HMG or even 4 x 20mm that were given to some of the P51A.
Me109F with a couple of HMG in the wing which I believe Galland had installed.
Me109E with drop tanks which I understand were first used in the Spanish Civil War in He51 fighters
The Spitfire with the larger fuel tanks that were in the Mock-up.

People love talking about this engine/turbo instead of that and often ignore and or forget that these are really heavy and will almost certainly really mess with the COG, weightm wingloading and performance and handling. You don't get something for nothing in aviation

 

[gumbyk]

Personally I like to keep the changes to a small scale. There were a number of aircraft which would have been far more effective with little changes.
Macchi 202 with 2 x 20mm in the wing instead of 2 x LMG which were hardly worth the effort.
The P51B with the 6 x HMG or even 4 x 20mm that were given to some of the P51A.
Me109F with a couple of HMG in the wing which I believe Galland had installed.
Me109E with drop tanks which I understand were first used in the Spanish Civil War in He51 fighters
The Spitfire with the larger fuel tanks that were in the Mock-up.

People love talking about this engine/turbo instead of that and often ignore and or forget that these are really heavy and will almost certainly really mess with the COG, weightm wingloading and performance and handling. You don't get something for nothing in aviation

Not to mention that more power=more fuel burn, more fuel capacity required, and more weight...

 

[nuuumannn]

the Be1900 (after the useless, treacherous, maintenance nightmare OEM pneumatic nosewheel steering was consigned to the dustbin where it belonged).

Slightly off topic, but the Beech 1900 appeared to me to be like a small plane trying to be a big one and not pulling it off very successfully. the company I work for used to operate them and thrashed the living cr*p out of them. Ours were the highest houred B1900s around. I never worked on them except overhaulling their props. Our pilots liked them.

On with the wishful thinking...

 

[gumbyk]

Slightly off topic, but the Beech 1900 appeared to me to be like a small plane trying to be a big one and not pulling it off very successfully. the company I work for used to operate them and thrashed the living cr*p out of them. Ours were the highest houred B1900s around. I never worked on them except overhaulling their props. Our pilots liked them.

On with the wishful thinking...

I think that was a combination of an airframe that had been extended to (or beyond) its limits, combined with extremely short routes resulting in higher cycle rates than the manufacturer ever envisaged them doing. I heard that they weren't the highest airframe hours, but certainly fleet leaders in cycles, even though they were the last off the production line