Twin boom question

[kool kitty89]

Stich, the original specification behind the P-38 was for a small order of interceptors. As such the original P-38 design (ie that used for the XP-38 ) was not designed for large scale production. When this philosophy changed, significant changes had to be made to make it suitable for mass production. (the YP-38 and all subsequent aircraft)

Despite the inherant delay this would have caused in development, the crash of the XP-38 (which would still have been fairly representative for testing) delayed the whole program by over a year. (until the first YP-38 was ready)


And Marcel,

If you notice, pretty much all my posts are tied to the twin boom configuration's various advantages, layouts, and characteristics. (in fact I brought up the specific point you noted in my response to Bill -drgondog- in post #10)

 

[Marcel]

Hi KK,

You're right, I was more aiming at these poste:

Also with all your guns in central locations they pack a greater punch then say a mustang that has to offset there guns to a certain range or distance to bring all guns into play to hit the target at the same time.

Also has advantages of range, don't forget!

Which are both statements true for any twin engined fighter.

 

[kool kitty89]

Interesting the one looks like a ME110...

I like the looks of that one in particular. Reminds me more of a cross between a P-80 and a De Havilland Albatross though.

On another though on the P-38, bulky nacelles could have been avoided if the landing gear has been carried in the inboard portion of the wings. (with additional fuel being carried in the fuselage) Though this may bring into question the placement of the bomb/drop-tank pylons. (depending on how the gear is arranged)

On advantage of the P-38's central pylon configuration was the ability to carry asymmetric loads. (the Corsair had this too) Additionally it put the stress on a very strong part of the airplane, with less structural limitations than outboard wing mountings.

Again this may still have been possible in the "conventional" twin engine configuration, sepending on how the gear could be placed.



Marcel,

Thanks, but if you note Micdrow's statement would apply to any a/c witout a tractor propeller. (including a single engine pusher -not to mention jets-)

 

[FLYBOYJ]

On another though on the P-38, bulky nacelles could have been avoided if the landing gear has been carried in the inboard portion of the wings. (with additional fuel being carried in the fuselage) Though this may bring into question the placement of the bomb/drop-tank pylons. (depending on how the gear is arranged)

And where would the turbo charger and ducting go?

 

[Velius]

I spent 73 seconds on it... I wast designing a new aircraft,,, just a quick sketch..
copy and paste

oh . I thought it was an actual concept.

And it remains an active concept in Homebuilts. The latest(?) being The New Horizons design. In their words, eliminating visibility problems...

I think the twin boom concept was chosen for this reason on the FW-189 for it's reconnaissance role. And indeed, the fuselage section was constructed almost entirely with glazed glass windows to get an unobstructed view in just about every direction. A small note- it's usefulness for recon roles earned it the nickname "flying eye"

 

[Marcel]

oh . I thought it was an actual concept.



I think the twin boom concept was chosen for this reason on the FW-189 for it's reconnaissance role. And indeed, the fuselage section was constructed almost entirely with glazed glass windows to get an unobstructed view in just about every direction. A small note- it's usefulness for recon roles earned it the nickname "flying eye"

Correct and suprise suprise, look at the amount of glass on the G.1

 

[Waynos]

And on the same theme over 30 years later............

 

[SoD Stitch]

On another though on the P-38, bulky nacelles could have been avoided if the landing gear has been carried in the inboard portion of the wings. (with additional fuel being carried in the fuselage) Though this may bring into question the placement of the bomb/drop-tank pylons. (depending on how the gear is arranged)

I could be wrong (have before), but I believe this would have made the wings too thick on their inboard portion, not to mention what you've already said about losing the inner-wing pylons AND internal tankage.

 

[kool kitty89]

FLYBOYJ,

The turbochargers/ducting would be in the same location, the turbochargers didn't add any real "bulk" to the nacelles. Then again, the landing gear wouldn't add a lot either. (adding to length, but that wouldn't have a significant effect on drag)

And after I thought about it, I think the gear were best where they were. (booms or no booms) Hence why pretty much all twin engined piston engined aircraft of the war had them located in the nacelles.

Chin mounted radiators would make the nacelles bulkier and add drag. (though, having them grouped with the engine and oil cooler reduces vulnerability)

Mounting the radiators (probably along with oil coolers and intercoolers) in extended inboard wing sections (ie Mossie or Whirlwind) may have been a possibility. (the resulting increase inchord may have also delayed compressibility) This may have had other issues though.

So, for the "conventional P-38," compact, low drag, outer-wing mounted radiators were probably the best choice. (like on the Bf 110)

 

[FLYBOYJ]

FLYBOYJ,

The turbochargers/ducting would be in the same location, the turbochargers didn't add any real "bulk" to the nacelles. Then again, the landing gear wouldn't add a lot either. (adding to length, but that wouldn't have a significant effect on drag)

And after I thought about it, I think the gear were best where they were. (booms or no booms) Hence why pretty much all twin engined piston engined aircraft of the war had them located in the nacelles.

Chin mounted radiators would make the nacelles bulkier and add drag. (though, having them grouped with the engine and oil cooler reduces vulnerability)

Mounting the radiators (probably along with oil coolers and intercoolers) in extended inboard wing sections (ie Mossie or Whirlwind) may have been a possibility. (the resulting increase inchord may have also delayed compressibility) This may have had other issues though.

So, for the "conventional P-38," compact, low drag, outer-wing mounted radiators were probably the best choice. (like on the Bf 110)

You forget one thing - the set up of the turbo chargers are based on the size and length of the ducting running from the intakes to the turbocharger and on to the engine. If the ducting is shortened or lengthened it will effect the turbo charger performance. Remember, it was decided to build an interceptor that could climb and with the "tools" available a turbocharged twin seemed to be the way to go - what was available was the Allison so by adding the turbo charger everything "worked." I think in the end this is the reason why Johnson decided on a twin boom configuration.

BTW Johnson was also very "into" twin tail (H tail) configurations. His college thesis actually gave critical critique of the Electra's first windshield configuration and actually

 

[Graeme]

Johnson explains the reasoning behind the long nacelle/boom...

 

[kool kitty89]

Yes, the twin boom configuration was naturally the most practical solution, my argument was more or less academic. (I do think the airfoil chosen for the P-38 was it's main development limitation -and not just due to compressibility, but that's not the nature of this discussion)

The coment that the turbochargers had to be used because they "had a long engine." ??? That makes no sense to me at all.

The turbochargers had to be used to obtain good high altitude performance. (the V-1710 being equipped with a relatively small supercharger, though compared to the early Merlins and DB-601 it's critical altitude wasn't much lower, all being rated for "medium altitudes")



Everyone but the US was using single-stage supercharging on their engines, up until the Merlin 60 series came out. Though single stage two-speed (though never Used on the Allison) or variable speed (DB engines) were faily commonly used.
The only country using 2-stage superchargers operationally in the early stages of the war was in fact the US, with the good old F4F's P&W R-1830-76/86 featuring a 2-stage 3-speed (including neutral) supercharger with intercooler. (some models, particulalr for foreign use, featured engines -Wright 1820 or P&W 1830- with simpler single stage 2-speed units, and the FM-2 with it's Wright engine featured one such as well -resulting in slightly poorer altitude performance)
The Corsair's R-2800 featured a similar 2-stage supercharger.(along with a more powerful one in the F4U-4)
Had Allison focused on such developments, thy too probably could have had a decent 2-stage supercharger available fairly early on. (though USAAC policy focused on turbocharging -technically all the engine companyies had to do was make sure the engine would be suitable for a turbocharger installation, the R-2600 being an example of an engine with poor turbocharging qualities)

Then of course came the 2-stage Merlins.

But no operational German engines ever featured 2-stage superchargers or intercoolers (inless the rare use of turbocharging). However, due to the larger displacement of the DB-605 (at similar size and weight to the Merlin) it was still able to compete for performance at high altitude. (particularly with the larger DB-603 supercharger of the AS and D models, and of course, GM-1 provided further high altitude booting possibilities for German engines)

And turbocharging in pretty much any case on a WWII aircraft was actually 2-stage, with the turbocharger (after passing through the intercooler) feeding into an "integral" "engine supercharger."



The best altitude performance the single stage V-1710 managed was with the supercharger gear ratio increaded from 8.8:1 to 9.6:1 on engines like the the V-1710-81/99/85/83, which increased WEP to 1,480 hp at 10,500 ft. (mil 1,125 at 17,500 ft). But due to increased charge heating max boost was limited to 57," the older engines (-39, 35, 73 etc) had a WEP limit of 60" with ~1,570 hp, but only at ~5,000 ft with mil of 1,150 hp at ~14,000 ft. (all figures with ram air -high speed level flight, w/out ram -low-peed/climb figures are all 2,000 ft lower)

This performance was almost as good as Merlin 45 (single-stage single speed as well), but max power is still a bit short as well as critical altitude. But not bad with all things considered.


Also note that with the 8.8:1 blower, the actual boost (MAP) limit was above 70" Hg, but this results in almost 1,800 hp, well above the 1,600 hp rating for the reduction gearing (not to mention other structural areas) and in any case this would only be atainable at SL with full ram. (or over-rev to 3,200 rpm)

http://www.raafwarbirds.org.au/targetvraaf/p40_archive/pdfs/Allison 1710-39 abuse.pdf

 

[kool kitty89]

You forget one thing - the set up of the turbo chargers are based on the size and length of the ducting running from the intakes to the turbocharger and on to the engine. If the ducting is shortened or lengthened it will effect the turbo charger performance. Remember, it was decided to build an interceptor that could climb and with the "tools" available a turbocharged twin seemed to be the way to go - what was available was the Allison so by adding the turbo charger everything "worked." I think in the end this is the reason why Johnson decided on a twin boom configuration.

I agree this is the best overall layout. As I put in my last post, I was just discussing how the P-38 might have been arrange in a "conventional" layout.

However, I didn't say anything about movint the turbocharger, so I'm not sure why you made the first comment. The P-38 had a pretty compact location for the turbocharger, almost back to back with the engine with relatively short ducting (except for the original intercoolers in the wing LE) generally similar to that on a B-17 or B-24, opposed to the much longer ducting of the P-47 with its ventral turbocharger.

BTW Johnson was also very "into" twin tail (H tail) configurations. His college thesis actually gave critical critique of the Electra's first windshield configuration and actually

Did you forget to finish that last sentence?

 

[FLYBOYJ]

Did you forget to finish that last sentence?

Yes, the kids started crying

 

[FLYBOYJ]

However, I didn't say anything about movint the turbocharger, so I'm not sure why you made the first comment. The P-38 had a pretty compact location for the turbocharger, almost back to back with the engine with relatively short ducting (except for the original intercoolers in the wing LE) generally similar to that on a B-17 or B-24, opposed to the much longer ducting of the P-47 with its ventral turbocharger.

OK I see your point - I thought the turbocharger was further back than it actually was.

 

[kool kitty89]

Yes, the kids started crying

Sorry, what was the rest of that though?

Were you just going to mention how he influenced the L-10 design? (twin tail, wing fillet, altered windshield/nose)

And the preference to twin-fin tails is demonstrated on the sketch of a "conventional" P-38 as well.

 

[FLYBOYJ]

Sorry, what was the rest of that though?

Were you just going to mention how he influenced the L-10 design? (twin tail, wing fillet, altered windshield/nose)

And the preference to twin-fin tails is demonstrated on the sketch of a "conventional" P-38 as well.

Well because of his paper he eventually got hired at Lockhhed. He convinced Lockheed to go with an "H" tail and to drop the "motorboat" inward canted windscreen.

 

[kool kitty89]

Right.

They also tested a T-33/T2V experimentally with a twin-tail very similar to the Super Electra/Lodestar/Ventura/Hudson. (the biggest difference is the tailplane not extending past the fins)

 

[AMCKen]

One of my 'fantasy' aircraft was to build one with the P-38 basic layout but with just a single Allison T-56 in the nose.

 

[SoD Stitch]

One of my 'fantasy' aircraft was to build one with the P-38 basic layout but with just a single Allison T-56 in the nose.

Is that a turboprop? I'm guessing the one turboprop probably had about as much power as the twin Allisons, if not more. This is essentially what they did to the Mustang when they developed it into the Enforcer.