Twin boom question

[Velius]

Hello everyone,

I was wondering about this the other day- what are the structural/aerodynamic advantages and disadvantages of twin boom aircraft like the P-38, Fokker G.1, FW-189, etc.?

 

[drgondog]

Hello everyone,

I was wondering about this the other day- what are the structural/aerodynamic advantages and disadvantages of twin boom aircraft like the P-38, Fokker G.1, FW-189, etc.?

Can't think offhand of an advantage other than two engines when one lets go (maybe - the bromide about the purpose of the second fan is to carry you safely to the crash site) - and frequently you can not only carry a larger payload but have more room for fuel and also have the potential for more power/wt ratio for acceleration and climb. Armament packaging is more efficient

In general, the cons are -

It is difficult to reduce drag of a twin to anywhere close to a well designed single.

It is heavier

It is bigger and easier to see

It has a higher rolling intertia

It is more expensive

It is more complicated and requires longer training

With twin engines in nacelles you have 'three' fuselages to create parasite drag.

Fuel transfer typically is more complicated

These are not universal truths... but food for thought?

 

[Watanbe]

you can load up the nose with some serious firepower, peace of mind having two engines

 

[comiso90]

I always wondered what the performance of the P-38 would have been if it had a conventional fuselage like the mossie.

.

 

[Velius]

Interesting concept Cosimo. The horizontal stabilizer looks a little too small for the rest of the plane.

 

[comiso90]

Interesting concept Cosimo. The horizontal stabilizer looks a little too small for the rest of the plane.

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

 

[kool kitty89]

In the case of the P-38 the booms may have allowed more internal space than "normal" nacelles. This is significant as turbochargers were installed, and it allowed the radiators to be mounted farther back on the boom. It allowed the use of a larger and higher AR horizontal stabilizer than would normally be practical for a fuselage mounted tail.


A twin boom configuration is also important in cases other than twin-engine a/c. Such as in a pusher configuration with the engine mounted on the rear of the central pod. This provides space for a central (unsynchronised) mounted armament like a twin, but the smaller size of a single engine a/c.

Twin boom push-pull aircraft (Fokker D.XXIII) are also something to be noted, and generally easier to arrange than the configuraton used on the Do 335. (and is occasionally used on modern aircraft)


It's advantageous for jets as well, as in the case of the Vampire (Venom, Sea Vixen) this allows for an aircraft with short intake and exhaust which minimizes thrust loss. (particularly important to early jets with relatively low thrust engines) Although single boom designs like the Me P.1101 gave similar advantages.

 

[SoD Stitch]

In the case of the P-38 the booms may have allowed more internal space than "normal" nacelles. This is significant as turbochargers were installed, and it allowed the radiators to be mounted farther back on the boom. It allowed the use of a larger and higher AR horizontal stabilizer than would normally be practical for a fuselage mounted tail.

kk is quite right. In the case of the P-38, half of the reason for going with the twin-boom configuration was so that there was a place to put the (fairly large) turbo-superchargers; a conventional nacelle would not have worked for the Allison V-1710 engines AND the turbo-superchargers, there simply would not have been enough room. It also incidentally provided a convenient place to house the main landing gear.

 

[kool kitty89]

Comiso, here are some drawings of other P-38 configurations:
it came up in this thread: http://www.ww2aircraft.net/forum/aviation/why-not-jet-driven-p-38-a-9076-2.html

Interestingly, it included the twing boom push-pull arrangement I mentioned earlier.

 

[kool kitty89]

Stich, I think it could have worked, but the nacelles would have had to be long to have space (and proper positioning) for the landing gear. (or switch to a taildragger) The radiator could have gone under the foreward part of the nacelle, like the one on the P-40's nose.

However, with the large nacelles (probably weighing almost as much as the previous booms) and the added weight of the fuselage, the aircraft would probably have been somewhat heavier.


The push-pull twin boom configuration is interesting as it eliminates the extra drag and rotational inertia (though the small booms will still add some) of outboard placed engines, and is significantly simpler than the Do 335's arrangement. (however, only a small armament would be able to be sone mounted, and -except for an engine cannon- would have to be synchronized)


And, Bill, most of what you discussed was common to all twin engined aircraft. I think the question was what was the advantages of the twin boom configuration compared to wing mounted nacelles with a central fuselage. (though, as I introduced, there are many other possibilities for the twin boom arrangement)

 

[Marcel]

In the G.1 the configuration was made like this because the rear observer/gunner got a good view to all side (even under) while still being very close to the pilot, which was preferred by Fokker.

 

[Micdrow]

As a side note after listening to lectures on the P-38 glacier girl and Ruff Stuff another advantage was that with the weapons in the center they where easier to aim. Conventunal fighters with the engine in front are subject to more vibration in the nose making it harder to aim. There is very little if any vibration in the nose of a P-38 when it comes to aiming during battle.

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.

 

[Watanbe]

Also has advantages of range, don't forget!

 

[kool kitty89]

Micdrow,

I noted that already in post #7. The twin-boom (single engine) pusher also allowed this. (the push-pull obviously would not)

Of course, you could still mount nose (or wing root) guns on a/c with a tractor propeller on the nose, but they would have to be synchronized (except for an engine gun) which reduced RoF and excluded weapons not able to be synchronized. The size and number of weapons are also more limited given they all have to fit around the engine and compete for ammo space. (except for wing root guns)

 

[Marcel]

You are all talking about the advantages which are shared between all twin engined fighters. I think the question was why a twin boom construction. I believe in several cases this was because of the visibility for the gunner in the rear. Could the P38 configuration been chosen because of the tricycle gear?

 

[FLYBOYJ]

Could the P38 configuration been chosen because of the tricycle gear?

I believe that Kelly Johnson wanted to build an interceptor that could carry a big gun and could climb extremely well. At the time the P-38 design team thought the only way to achieve the design goals was with a supercharged twin. Using the twin boom alleviated bulky nacelles and lended it self for a nice turbocharger installation. Also remember - those responsible for the design of the P-38 thought that no more then a handful of the aircraft would be produced.

 

[Marcel]

Good point Joe, I forgot about the superchargers. Twin booms was a neat solution indeed.

 

[comiso90]

Comiso, here are some drawings of other P-38 configurations:
it came up in this thread: http://www.ww2aircraft.net/forum/aviation/why-not-jet-driven-p-38-a-9076-2.html

Interestingly, it included the twing boom push-pull arrangement I mentioned earlier.

Interesting the one looks like a ME110...

 

[Graeme]

Couple of illustrative advantages.

In the case of the ANT-23, the booms provided access for the recoilless cannons...



For White Night, it allowed a large payload to be carried...



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

"Our design is a pilot-forward design, keeping the wings and propulsion system aft of the pilot thereby eliminating visibility issues common in the traditional "tractor" designs."

New Horizons Aircraft Inc. | Prototype Aircraft, Light Sport Airplane, Experimental Airplane





Some of their future designs...

 

[SoD Stitch]

I believe that Kelly Johnson wanted to build an interceptor that could carry a big gun and could climb extremely well. At the time the P-38 design team thought the only way to achieve the design goals was with a supercharged twin. Using the twin boom alleviated bulky nacelles and lended it self for a nice turbocharger installation.

Good point, Joe. The requirements the USAAC were looking for virtually ruled out the use of a single engine; at that time (1938 ), there was no single engine (yet) on the market that provided adequate performance, hence the use of twin engines. Since twin engines were required (and also twin turbo-supercharger), Lockheed's airframe options were extremely limited.

Also remember - those responsible for the design of the P-38 thought that no more then a handful of the aircraft would be produced.

And, yes, at that time Lockheed figured they'd be lucky if they got an order for 50 (yes, that's right, I said 50) from the USAAC, instead of the over 5,000 that ended up being produced before War's end; the first models were virtually "hand built" before the institution of the assembly line in 1942.