OT- WWII fighter planes - why so heavy?

GregSY · Mar 15, 2017

I was watching some YouTube video's on the P-51 Mustang vs a German F-W fighter and the specs on each kinda surprised me....they each weighed over 9,200lbs.

I know the engines were heavy...but given that these are planes and all.... why are they so heavy? I mean...you needed to carry one pilot, some machine guns, and that's all. Is it just a case of the technology and materials of the day warranted that sort of weight? If the planes were produced today, wouldn't they be lighter? Or does the weight add other benefits in terms of handling, stability, etc.?

SAG 180 · Mar 15, 2017

They were long range, big planes, a person standing beside one shows the size which was comparable to a 4 seater twin engined plane. They also carried 269 gallons of fuel internally, had a liquid cooled motor with coolant to a radiator as well as armaments.

GregSY said:
I was watching some YouTube video's on the P-51 Mustang vs a German F-W fighter and the specs on each kinda surprised me....they each weighed over 9,200lbs.

I know the engines were heavy...but given that these are planes and all.... why are they so heavy? I mean...you needed to carry one pilot, some machine guns, and that's all. Is it just a case of the technology and materials of the day warranted that sort of weight? If the planes were produced today, wouldn't they be lighter? Or does the weight add other benefits in terms of handling, stability, etc.?

daryl bane · Mar 15, 2017

No expert here, I think radios and armor plate would contribute to that weight..

johnoder · Mar 15, 2017

They had to (hopefully) take the aerodynamic flight loads of 500+ mph pull outs from power dives - without the wings going away.

Not a requirement in your puddle jumper

Not lightly built by any means

Our 2700 HP ADs were 12,000 empty - a fair sized truck of a single engine plane - and the fastest in a dive I was ever on board was but 320

Eric M · Mar 15, 2017

I believe they were also built to be able to take a lot of damage, and still be able to fly. Heavier structural members, redundant control systems, etc. Aerial refueling didn't really exist; all fuel had to be carried internally, or in external drop tanks.

dgfoster · Mar 15, 2017

Engine and fuel alone (without drop tanks) was 3200 pounds. Add "industrial design" for hard landings, guns, armor, retractable gear, oxygen, supercharger---not your average Cessna 172.

Reputedly a very complex plane to fly. Amazing for its time and still today.

D

DDoug · Mar 15, 2017

if you read any accounts from the designers, it was all a rush job.
Going into ww2 they still had "rag & tube" planes, ...at the end, Jet engines,
forged aluminum landing gears, aluminum monocoque construction, hydraulics,
etc.

Especially enlightening, concerning the "rush to develop" is the rotary engine.
http://www.enginehistory.org/engines.shtml
Scroll down to this article:
"No Short Days:
The Struggle to Develop the R-2800
"Double Wasp" Crankshaft"
To understand some of the "rush"

And this one:
http://www.enginehistory.org/Wright/Wright R-3350.pdf

And this one too:
http://www.enginehistory.org/References/WWII Eng Production.pdf

There wasn't much time to test, rebuild, test again, optimize for weight etc.

lucky7 · Mar 15, 2017

Guy down the street from me rebuilt a Mustang dug out of a Bolivian swamp. Impressed me just how big and heavy a Merlin engine is. And as johnoder said, to be able to take the dynamic dog fighting demands (consider 6-7 g's!) on an airframe that carries the horses of a Merlin is a tall order. And the sound... Only thing better than a Merlin powered Mustang is a Lancaster...

Lucky7

moonlight machine · Mar 15, 2017

800 lbs of machine guns + ammo and enough structure in the wings to handle the recoil. A Rolls-Royce Merlin weighs 1600 lbs. Think about what it takes to keep it from falling off when pulling out of a dive. I am amazed they were so light considering the total lack of exotic metals and composites in use in WW2.

Limy Sami · Mar 15, 2017

lucky7 said:
And the sound... Only thing better than a Merlin powered Mustang is a Lancaster...

Lucky7

Or a Mosquito ?

moonlight machine · Mar 15, 2017

lucky7 said:
Guy down the street from me rebuilt a Mustang dug out of a Bolivian swamp. Impressed me just how big and heavy a Merlin engine is. And as johnoder said, to be able to take the dynamic dog fighting demands (consider 6-7 g's!) on an airframe that carries the horses of a Merlin is a tall order. And the sound... Only thing better than a Merlin powered Mustang is a Lancaster...

Lucky7

I have had a ride in a Mustang, 1 incredible hour I will never forget. The sound of the Merlin running flat out is like nothing else. Loops, rolls, dives. My pilot, Kevin Eldridge had thousands of hours in Mustangs, Corsairs and the like and gave me a hell of a ride. Check out the u tube video "Kevin Eldridge super Corsair accident at the Phoenix Air races" His engine blew up and the plane was a ball of fire when he jumped out. I don't know how he sits to fly these things as he has basket balls! We were out in the L A area for the Long Beach Grand Prix. Some of us went out a day early so we could go to Fighter Rebuilders at Chino airport. We got some of their guys in the pits and they got us reduced price rides. What a day!!!

Clive603 · Mar 15, 2017

Hawker Hurricane and Tempest are a good illustration of the evolution in weights. Using fighter bomber variants as these always come out a bit heavier than pure fighters. Hurricane is around 5,600 lb empty, 8,500 lb max take off weight, 318 mph flat out at sea level. Tempest is around 9,000 lb empty, 13,500 lb maximum take off weight, at least 435 mph flat out at sea level. Tempest is pushing half as fast again as the Hurricane, getting on for twice as heavy and more than double the load. OK some is due to the engine as a Sabre is around 2,200 lb installed as against 1,600 lb odd for a Merlin and rather thirstier. Hurricane makes do with 100 gallons internal fuel, Tempest carries something over 200 gallons internally so there is about 1,300 lb difference due to the engine and fuel.

But the rest goes into structural strength. Remembering that a Tempest can approach transonic in a dive, not supposed to go over 550 mph but ...

Clive

JST · Mar 15, 2017

Whenever you add load weight to an airframe, which might be, fuel, guns, ammo, or external stores like drop tanks or bombs, riockets, etc, you have to add quite a bit of structure and engine/fuel weight to carry the load.

And then you may add a need for a larger more powerful engine. The bigger engine uses more fuel, which adds weight, which needs more engine............ If you need range, you add fuel.......

The ratio of added payload to added structure weight depends on where the payload is. In the fuselage, the added structure weight is less, because that is already a strong area, especially if the load is added near the wing spar, so the added structure may be smaller, but the fuel and engine is still an issue.

So is landing gear. Added weight means higher forces on landing. If the gear is in the fuselage, as with an ME 109 or Spitfire, it isn't so bad, but if the gear is mounted out on the wing, the spar must be reinforced to carry the added weight.

Guns in the nose are one thing, they just need a little structure, plus engine and fuel. Guns in the wings require more wing structure, with even more more fuel and engine. They also reduce the roll rate, and maneuverability, so the ailerons may need to be modified, which adds wing weight, engine and fuel.

You understand this is at the design stage. After that, adding things affected performance, because the engine and fuel capacity were not changed when a field modification was made..

The Zero was extremely light weight, which accounts for its excellent performance. But, for engineering and cultural reasons, it lacked features such as self-sealing fuel tanks, with obvious bad results. And the light structure was not nearly as good at absorbing battle damage.

Aircraft are made up of compromises.

Scottl · Mar 15, 2017

Heavy compared to what?

An F-16 weighs 20,300 lb empty.

Specifications * Lockheed Martin

KilrB · Mar 15, 2017

GregSY said:
I was watching some YouTube video's on the P-51 Mustang vs a German F-W fighter and the specs on each kinda surprised me....they each weighed over 9,200lbs.

I know the engines were heavy...but given that these are planes and all.... why are they so heavy? I mean...you needed to carry one pilot, some machine guns, and that's all. Is it just a case of the technology and materials of the day warranted that sort of weight? If the planes were produced today, wouldn't they be lighter? Or does the weight add other benefits in terms of handling, stability, etc.?

It all depends on what your comparing and what your comparing it to ...

Those are the loaded weights.

The empty weights are: P-51D ... 7,600 lbs, FW-190 A-8 ... 7,000 lbs

Even at a measly 3,700lbs (empty) an A6M2 Zero dwarfs a Piper Cherokee or Cessna 150.

Compared to even early war models the P-51 And FW-190 are heavier.

As demands on performance and abilties grew, so did the weight.

Bigger engines, bigger/more guns, more armor, more fuel, more ammunition, carrier landings = more weight.

Still, compare their weight to:

North American P-47D ... 10,000 lbs

Dornier Do-335 ... 16,300 lbs

The trend continues with more modern aircraft that also "only need to carry one pilot and some machine guns" ...

North American F-86F ... 11,100 lbs

North American F-100d ... 21,000 lbs

McDonnell Douglas F-4E ... 30,300 lbs

Grumman F-14D ... 43,700 lbs

McDonnell Douglas F-15C ... 28,000 lbs

... well, you get the idea.

moonlight machine · Mar 15, 2017

JST said:
Whenever you add load weight to an airframe, which might be, fuel, guns, ammo, or external stores like drop tanks or bombs, riockets, etc, you have to add quite a bit of structure and engine/fuel weight to carry the load.

And then you may add a need for a larger more powerful engine. The bigger engine uses more fuel, which adds weight, which needs more engine............ If you need range, you add fuel.......

The ratio of added payload to added structure weight depends on where the payload is. In the fuselage, the added structure weight is less, because that is already a strong area, especially if the load is added near the wing spar, so the added structure may be smaller, but the fuel and engine is still an issue.

So is landing gear. Added weight means higher forces on landing. If the gear is in the fuselage, as with an ME 109 or Spitfire, it isn't so bad, but if the gear is mounted out on the wing, the spar must be reinforced to carry the added weight.

Guns in the nose are one thing, they just need a little structure, plus engine and fuel. Guns in the wings require more wing structure, with even more more fuel and engine. They also reduce the roll rate, and maneuverability, so the ailerons may need to be modified, which adds wing weight, engine and fuel.

You understand this is at the design stage. After that, adding things affected performance, because the engine and fuel capacity were not changed when a field modification was made..

The Zero was extremely light weight, which accounts for its excellent performance. But, for engineering and cultural reasons, it lacked features such as self-sealing fuel tanks, with obvious bad results. And the light structure was not nearly as good at absorbing battle damage.

Aircraft are made up of compromises.

That narrow landing gear track width on the ME 109 caused lots of landing accidents. Gear out on the wings with a bit more weight was a better trade off.

WizardOfBoz · Mar 15, 2017

Cessna 172 top speed: 188mph
P-51 top speed: 437mph
And, as John pointed out, the "top speed" in level flight at 25K was exceeded in a dive

Cessna powerplant: Lycoming with ~200hp
P-51D powerplant: Rolls Royce Packard with 1490hp (1720hp for "war emergency")

Cessna Armament capability: Whatever the pilot has in his belt holster
P-51D armament capability: 6 (!) Browning .50 caliber machine guns with 1880 rounds, 2 1000lb lbs, and 10 5" rockets.

Cessna range: 801 miles
P-51D range: 1155 miles (2055 with drop tanks).

The other difference is that the Cessna doesn't have to be combat hardened/high service duty. The P-51D was able to take some abuse and still fly, fight, and return and land. And the P-51Ds were being used every day for long flights.

WizardOfBoz · Mar 15, 2017

johnoder said:
Our 2700 HP ADs were 12,000 empty - a fair sized truck of a single engine plane - and the fastest in a dive I was ever on board was but 320

If I'm grokking this correctly, John, the "AD" is the famous Douglas A-1 (originally "AD") Skyraider. That was a heck of a plane. May I asked when and where you served?

Diving towards the ground at 325mph is something I don't think I'd like.

Kyle Smith · Mar 15, 2017

On a related note there is a decent series on Netflix called Plane Resurrection. Too much talking and not enough technical info, but interesting none the less.

Netflix - instantwatcher - Plane Resurrection

brianweldor · Mar 15, 2017

moonlight machine said:
I have had a ride in a Mustang, 1 incredible hour I will never forget. The sound of the Merlin running flat out is like nothing else. Loops, rolls, dives. My pilot, Kevin Eldridge had thousands of hours in Mustangs, Corsairs and the like and gave me a hell of a ride. Check out the u tube video "Kevin Eldridge super Corsair accident at the Reno Air races" His engine blew up and the plane was a ball of fire when he jumped out. I don't know how he sits to fly these things as he has basket balls! We were out in the L A area for the Long Beach Grand Prix. Some of us went out a day early so we could go to Fighter Rebuilders at Chino airport. We got some of their guys in the pits and they got us reduced price rides. What a day!!!

You should come down to Fayetteville, WV for a ride in a Stearman. I went up with him last summer after trading some welding work, and even let me take the stick for some loops and hammerheads. Open cockpit aerobatics are superb.

OT- WWII fighter planes - why so heavy?

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