World War Two Aircraft Exhaust Pipe Design

It's so enlightening stumbling onto answers to questions it never occurred to me to ask.

This channel is such a treasure. It goes into the finest details to give you an even more intimate appreciation of the engineering.

Good video Greg. Let me expand on the A6M5 Zero and it's exhaust pipes. The A6M5 had 4 exhaust pipes on each side of the cowling. The engine was a 14 cylinder twin row radial, so 3 of the 4 pipes were collecting exhaust from two cylinders. This arrangement as you said did provide some "thrust augmentation". This was not the only Japanese aircraft that used this arrangement. The Japanese Army Air Force Nakajima Ki-43 Hayabusa (Oscar) used this version in it's last model, the Ki-43-III (the -I and -II used a single exhaust), arranged in a pattern of 2-3-2 (2 pipes together, then three etc.). It had the same engine as the Zero, so it was able to use a single pipe for each cylinder. The follow on Nakajima Ki-84 Hayate (Frank) used a similar arrangement for its 18 cylinder radial in a 2-4-1 setup, so the exhaust on the bottom of the cowl was for 2 cylinders. Other Japanese aircraft that had multi-exhaust radials were: Navy Mistusbishi J2M Raiden (Jack) fighter, Kawanishi N1K-J Shiden (George) fighter (same engine as the Ki-84) P1Y Ginga (Frances) twin engine bomber (same engine as the Ki-84) later models of the Mitsubishi G4M twin engine bomber (Betty) Army Mitsubishi Ki-67 (Peggy) twin engine bomber Kawasaki Ki-45 (Nick) twin engine fighter Kawasaki Ki-100 (no code name) fighter (the individual exhausts were hidden behind cowl flaps) Kawasaki Ki-102 (Randy) twin engine fighter

Re the Spitfire exhausts, the prototype had individual pipes that exited flush with the cowling. The first production versions (Mks 1-6 inclusive) had the three-per-side arrangement you see on the tropicalized Mk Vb in your vid. From the next production version (Mk IX) onward, the Merlin powered Spitfires had six-per-side 'fishtail' exhausts. In tests done at Farnborough in 1943, the fishtail exhausts were found to increase top speed at full throttle height by 7 mph, due to better thrust. (Price, Spitfire Story, 2003, p. 140). So you're probably right about the exhaust on the A6M5 being designed to maximize thrust. The A6M5 Model 52 had the same engine as the A6M3 and nearly identical airframe, but was about 15 mph faster. Exhaust thrust.

There was also two other exceptions I can think of for why engines didn't have individual short stacks. 1. Night fighter variants often used a collector in a flame damper such as a porcupine design on the Beaufighter and Boomerang 2. Some aircraft usually multi crew (And some small aircraft to this day) provided cockpit heat by passing air through a tube that an exhaust collector ran through. Works great until the collector gets rotten through and then you are providing lovely CO laden exhaust to the pilot to breath >.>

Nice explanation - really interesting; I'd always noticed the individual pipes, but never really considered why they were designed that way.

Most educational video I've seen in a while, thumbs up to you sir!

Thanks to your video I learned something new today about how superchargers eliminate the need for tuned exhaust systems. Thank you!

I'm with you on drag-car looks dude. Great channel.

Fabulous channel you created . A wealth of information . Thank you. NJ , USA

One thing to mention about that Spitfire, because the exhaust extends past the leading edge of the wing, during night flight you could see little to no exhaust flash from the ground. “You can hit what you can’t see” in theory.

I read awhile ago that the Roots type supercharger used on, usually V-8 engines since the 1950s were called blowers because they actually were blowers from different sized GMC 2 stroke Diesel engines commonly seen in buses. Sizes 2-71, 4-71, 6-71, etc. depending on engine size. They were used to scavenge the exhaust in the 2 stoke Diesel to improve efficiency but not to increase cylinder pressure. So it took a few years of hotrodding experimentation to get them to work properly. Roots blowers do not do compression in the “blower” itself but in the intake manifold if directly mounted adding lots of heat to the intake charge. A twin-screw type supercharger does compression between the screws delivering a cooler intake charge and requiring less HP/boost than a Roots.

Cars have bigger exhaust systems to get the exhaust to clear the body. Plus car engines operate over a varying speed range while an aircraft engine is pretty much a constant speed engine. The cowling is tight against the engine and for space and weight issues the less the better. The P-38 and P-47 both had turbocharger installed away from the engine. The P-47 had it installed in the fuselage behind the cockpit with ductwork taking the exhaust gas back and the compressed induction air forward. The turbos of the day were added to those engines after initial design and the turbos of the day were too big to mount up behind the engine. They also needed considerable service so for maintenance it was why they were mounted where they were.

Man, I'm so glad you talked about this. I've been studying, working on, and now building internal combustion reciprocating piston engines as a hobby for the last 20 years and embarrassingly wondered why these planes, like log manifolds on two stroke boats, ran individual pipes instead of long tube headers with proper collectors. Once you reminded me that all of these planes had at least one stage of mechanically driver centrifugal compressors pushing serious manifold pressure and showed a funny car, it clicked. Love this channel Greg! Don't be afraid to go deep on the technical stuff, it's why I'm here!

British radials like the Bristol Mercury and Pegasus ran the exhausts forwards to a large ring collector that shaped the aerodynamic front of the engine cowling. Early models were naturally aspirated but the collector remained when they went to two stage supercharging. During WW2 Rolls Royce started development of a 26 litre V 12 sleeve valve TWO-STROKE engine called the Crecy. The cylinder sleeves and crank were oil lubricated the same same as a four stroke using basically Merlin engine parts. The test bed Crecy was incredibly noisy. There was so much exhaust energy from the bare engine that at high speed 40% OF THE POWER WOULD HAVE BEEN EXHAUST THRUST. Turbo compounding was planned and RR even had prototype mid engine plane based on the Mustang. It was modeled by RR to full size. Tests by Ricardo on single cylinder and V twin test bed units suggested the all up turbo compound power would have been 5000 bhp from a production spec V12 engine. At that time a late model Merlin was making 1750bhp. It all got cancelled in 1945 because better power could be achieved more easily with gas turbines. Source "Rolls Royce Crecy" (Nahum, Forester-Pegg, Birch) https://www.amazon.co.uk/Rolls-Royce-Crecy-Historical-Andrew-Nahum/dp/1872922058

,,, there's supposedly info somewhere that says the P-51 rearward facing stacks were worth about 150 horse worth of thrust .

Installations of the Bristol Centaurus in the Blackburn Firebrand, Hawker Fury, and Hawker Tempest II show individual exhaust pipes discharging through an opening in the cheek of the cowling. I believe this opening acts as an eductor, i.e. the engine is cooled by air flow that enters at the front of the cowling and is accelerated out this opening by a motive effect of the exhaust gasses.

Good point about the decline of funny cars.

Those short stacks on the V12's were also known for warping exhaust valves, when a hot engine was abruptly shut down in cold weather. Also check out the Douglas A-20 Havoc, with Wright 2600 engines, some variants had half collector ring and half short stacks on the engines.

Great video, wouldn't have thought twice about the different exhaust designs without your insight.