Why propellers of P-38 Lightning rotate outwards?

[drgondog]

simply stated - if a rotor or prop turns (top to bottom) one way, the fuselage holding the sucker wants to rotate the other way ... so aileron and rudder (or tail rotor thrust) needed to 'counteract' that nasty 'ol prop.

Of couse in case of Helo, some tail rotors 'pull' into fuse and others 'thrust'. An imbedded tail rotor simplifies the aerodynamics of the tail rotor. 'lose a tail rotor and you can kiss your ass goodbye if you have any altitude at all. Very bad 'thing'. It has been a very long time but I believe the King Cobra at Bell had a rotor system delivering 600,000+ foot pound of torque.

Joe dead on on reducing power on TO for a lost fan on a 38... because as he explained it the asymmetrical thrust for live engine (and lift on live wing) turns everything to dead engine - a very bad thing. Of couse it has to be done slowly..

SoD correct about the actual design reasons for 38 prop rotation scheme due to effect on centerbody/wing area..

[drgondog]

Originally Posted by drgondog

simply stated - if a rotor or prop turns (top to bottom) one way, the fuselage holding the sucker wants to rotate the other way ... so aileron and rudder (or tail rotor thrust) needed to 'counteract' that nasty 'ol prop.

Of couse in case of Helo, some tail rotors 'pull' into fuse and others 'thrust'. An imbedded tail rotor simplifies the aerodynamics of the tail rotor. 'lose a tail rotor and you can kiss your ass goodbye if you have any altitude at all. Very bad 'thing'. It has been a very long time but I believe the King Cobra at Bell had a huge (4 bladed -two engine) rotor system delivering 600,000(??) pounds of torque. (Don't hold me to the very big number - my memory is not reliable here)

Joe dead on on reducing power on TO for a lost fan on a 38... because as he explained it the asymmetrical thrust for live engine (and lift on live wing) turns everything to dead engine - a very bad thing. Of couse it has to be done slowly..

SoD correct about the actual design reasons for 38 prop rotation scheme due to effect on centerbody/wing area..

For what is worth I'm trying to research my notes of nearly 40 years afo on the whopping torque number

[kool kitty89]

Originally Posted by mkloby

Counter rotating props is termed when you have props turning opposite directions from each other - it is not related to the direction of rotation of a single propeller. We term contra-rotating props two props rotating in opposite directions on the same axis.

In the US, at least for mil aircraft, props generally rotate clockwise. In our helos the rotors generally spin CCW.

That's what I thought, but GaryMcl seems to be saying that counter-rotating means counter-clockwise-rotating...


I've also heard that, in addition to improving airflow characteristics over the wings/booms, the outward (from the top) rotating props made for a more stable gun platform.

One other interesting thing is that the Allison V-1710 was a big part of what made this counter-rotation practical as:
"Another feature of the V-1710 design was its ability to turn the output shaft either clockwise or counter-clockwise by assembling the engine with the crankshaft turned end-for-end, by installing an idler gear in the drive train to the supercharger and accessories and by installing a starter turning the proper direction. So, there was no need to re-arrange the ignition wiring and firing order, nor the oil and Glycol circuits to accommodate the direction of rotation."
It would be much harder (and more expensive) if the engines didn't offer this feature. (one reason for not using Merlins; the Contenental I-1430 may have been a problem to in the XP-49, unreliabillity aside)

[GaryMcL]

Originally Posted by kool kitty89

That's what I thought, but GaryMcl seems to be saying that counter-rotating means counter-clockwise-rotating...

Your confusion is no doubt my fault because I had the clockwise/counter-clockwise references backwards in my original post. I realized that and posted the error correction later.

A counter-rotating prop, i.e. rotating opposite from normal, will spin counter-clockwise as viewed from behind the engine. A normally rotating prop rotates clockwise as viewed from behind.

Viewed from in front of the aircraft, normal rotation is counter-clockwise.

If you stand in front of the aircraft and look at the prop you'll find the leading edge of the prop blade to the left on a normally rotating engine which means that it will rotate counter-clockwise as viewed from the front.

Sorry about the original error.

[kool kitty89]

But what I always thought counter-rotating propellers, as mkloby seems to be saying too, is when you have 2 propellers on 2 separate engines rotating in opposite directions, not a single propeller rotating the opposite from normal.

Originally Posted by mkloby

Counter rotating props is termed when you have props turning opposite directions from each other - it is not related to the direction of rotation of a single propeller. We term contra-rotating props two props rotating in opposite directions on the same axis.

In the US, at least for mil aircraft, props generally rotate clockwise. In our helos the rotors generally spin CCW.

Wikipedia says likewise too: Counter-rotating propellers - Wikipedia, the free encyclopedia

Thus the XP-38 hat counter-rotating props rotating inward from the top (left-prop CW, right-prop CCW when viewed from behind/from the cockpit) while the production models used the opposite rotation with both outwardly rotating from the top. (which as previously stated was to improve air-flow and platform stability)

Ergo, the Wright flyer also used counter-rotating propellers.

[GaryMcL]

Originally Posted by kool kitty89

But what I always thought counter-rotating propellers, as mkloby seems to be saying too, is when you have 2 propellers on 2 separate engines rotating in opposite directions, not a single propeller rotating the opposite from normal.

That is right. What I was trying to do was describe the two engines rotating in opposite directions individually because to accomplish this you have one engine rotating normally and one rotating in the opposite direction and each will have differing torque and p-factor effects.

The confusion is probably my use of the word counter to describe the engine in the pair that is operating the reverse of normal, i.e. counter to normal. I should have use something like reverse or opposite but I used counter the same as would be used to describe something running the reverse direction of a clock, i.e. counter-clockwise. And the clock references probably confused things more by throwing in more counters. Just too many counters.

Made the whole discussion kinda counter-intuitive.

Does this help any?

[ThunderThud]

Did you also Know that the initial batch of P-38's Destin for the RAF Had no superchargers installed as the U.S. Deemed them to be a secret part of the aircraft.This made the P-38 a slug compared to its US counterpart.

[FLYBOYJ]

Originally Posted by ThunderThud

Did you also Know that the initial batch of P-38's Destin for the RAF Had no superchargers installed as the U.S. Deemed them to be a secret part of the aircraft.This made the P-38 a slug compared to its US counterpart.

That's incorrect.

It was on the British order specification to omit the superchargers. The British P-38s were slugs and as a result deemed not suitable for RAF. That situation did help Lockheed and the USAAF because at the time of that order there was an upcoming production gap. That situation allowed the production line to remain in tact with no interruptions.

I believe Martin Cadin mentioned that in his book "Forked Tailed Devil." I also heard this from a number of old Lockheed folks when I worked there in the 1980s.

[kool kitty89]

You mean turbochargers, the integral superchargers of the allisons were retained iirc. The british planes also didn't use counter-rotation so the trops would be interchangable with their P-40s'.

Another note is that the P-38 w/out turbos performed even worse than a P-39 w/out a turbo! Though performance with both craft w/turbos goes to the 38, except possibly in medium-high speed maneuvering and terminal dive control.

[FLYBOYJ]

Originally Posted by kool kitty89

You mean turbochargers.

Yep - to a maintainer we know they're different but in the end we also know the end result.

[kool kitty89]

I wonder how a Brit version would've done adapted to merlins; though it wouldn't have been easy to set up counter-rotation, they didn't use that anyway. And assuming the merlin has the improved variable supercharger for altitude performance. Plus they'd have the advantage of using an indigenous engine.

Also those British P-38s performed so badly that they were returned to the US and used as trainers. (with counter-props, but still no turbos)


The P-38 certainly did get one significant thing from this trade though, its name. It was the Brits that came up with Lightning and it stuck, though the birds they got sure weren't fit for the name...

On the coment on the ban on exporting turbos, I think this did occur, just not until after this trade took place. I think the ban was lifted (at least for the British) after we entered the war. Though I don't think the Russians ever got any turbocharged a/c, or did the get some P-47s. I know Britain got some 'Bolts, especialy the P-47M for V-1 interceptions, though it arrived too late to see much use aganst Buzz-Bombs, it was quite effective aganst jets. (Assigned to the 56th Fighter Group, and were responsible for all four of that group's jet shoot-downs.)

[dairwin]

Originally Posted by kool kitty89

It would be much harder (and more expensive) if the engines didn't offer this feature. (one reason for not using Merlins);

.... I wonder how a Brit version would've done adapted to merlins; though it wouldn't have been easy to set up counter-rotation, they didn't use that anyway.

Merlin 131.

[FLYBOYJ]

Originally Posted by kool kitty89

On the coment on the ban on exporting turbos, I think this did occur, just not until after this trade took place. I think the ban was lifted (at least for the British) after we entered the war. Though I don't think the Russians ever got any turbocharged a/c, or did the get some P-47s.

The British got their castrated P-38s in 1941. At the same time they received 20 B-17Cs. Guess that was on those aircraft????

"Four supercharged (turbocharged) 1200 hp Wright GR-1820-65 (G-205A) Cyclones."

They ordered the aircraft in late 1940, they were delivered in the spring of 1941. here's a clip showing their use. In the middle of the clip there's a scene showing the "Supercharger" on the bottom of the engines!!!

YouTube - First operational B-17 mission with the RAF (B-17C)


I don't know where you're getting this turbocharger ban - I did see it mentioned on a P-38 website - I think that writer was a bit delusional or had a great imagination. I worked with guys who were there - building and flying P-38s and I never once heard them talk about a "turbocharger ban."

BTW the Russians received 203 P-47s

3 P-47D-10-RE serials 42-75201 to 42-75203
100 P-47D-22-RE serials 42-2553975201 to 42-25638
50 P-47D-27-RE serials 42-27015 to 42-27064
50 P-47D-27-RE serials 42-27115 to 42-27164

[SoD Stitch]

Originally Posted by FLYBOYJ

The British got their castrated P-38s in 1941. At the same time they received 20 B-17Cs. Guess that was on those aircraft????

"Four supercharged (turbocharged) 1200 hp Wright GR-1820-65 (G-205A) Cyclones."

They ordered the aircraft in late 1940, they were delivered in the spring of 1941. here's a clip showing their use. In the middle of the clip there's a scene showing the "Supercharger" on the bottom of the engines!!!

YouTube - First operational B-17 mission with the RAF (B-17C)


I don't know where you're getting this turbocharger ban - I did see it mentioned on a P-38 website - I think that writer was a bit delusional or had a great imagination. I worked with guys who were there - building and flying P-38s and I never once heard them talk about a "turbocharger ban."

BTW the Russians received 203 P-47s

3 P-47D-10-RE serials 42-75201 to 42-75203
100 P-47D-22-RE serials 42-2553975201 to 42-25638
50 P-47D-27-RE serials 42-27015 to 42-27064
50 P-47D-27-RE serials 42-27115 to 42-27164

Flyboy: I've never heard anything about a "turbocharger ban" either; I know that turbochargers were difficult to manufacture, which is why Lockheed approached General Electric to build the turbochargers for the YP-38 in '38 (GE had a lot of experience bulding high-temp steam turbines at that time), but it's not too hard to figure out how a turbocharger works. The only limitations are materials; the theory behind turbo-superchargers was easy, it was actually manufacturing the high-temp alloys that was the hard (and expensive!) part.

[FLYBOYJ]

Turbochargers were made through-out the 1930s by several nations. I do know that during the war when Lockheed was building the P-38 the turbochargers were "GFE" - Government Furnished Equipment.