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Wednesday, October 16, 2024
Interesting exhaust ports. There must be an aerodynamic reason they look like that.
Looked it up and found this.... By: antoni - 7th October 2007 at 00:25 - Edited 1st January 1970 at 01:00
Spitfire Mk Vb EN946 was tested at Boscombe Down in late 1943. It was found that replacing the exhausts with fishtail units increased the speed by 7 mph. The hot gases leaving the exhausts can act like small rockets. Highly tuned engines used in the Reno Races make use of this. At the very high boost pressures used there is a decrease in the horse power output because more hp is needed to drive the supercharger. It is the jet effect of the exhausts that gives an increase in air speed.
One aspect of relatively very short primary exhaust devices is they need to be long enough to inhibit colder air from hitting the very hot exhaust valves during the dwell cycle, aka reversion, in concert with inhibiting the atmospheric pressure pulse reversion wave between cylinder firing. They employ these very short exhaust pipes because of wieght and available space, just not enough space behind the engine cowling for a proper performance enhancing tuned exhaust system, and the nose fairing is a critical shape and area in regards airflow along the fuselage, lot of factors, its always a question of balances, what do you where do you sacrifice, what power weight or speed do you play with? Any bit which adds to performance and reliability, ease of repair or maintenance, cost too, the design and engineering is thick soup.
They did, it was called the P40-F. The engine they used was a Merlin 28 with a single-stage supercharger, which was less powerful at high altitude than the P51s two-stage supercharger engine. The problem was that Merlins were in such demand for Lancasters, Mosquitoes, Hurricanes and Spitfires that the three factories in Britain couldn't keep up with demand and the Packard Merlins were needed for P51s. Al_in_Ottawa
The hot exhaust gases can provide a small amount of thrust. In the '30s the exhaust stacks were flush with the cowling surface in an effort to minimize drag, look at Spitfire K5054, but testing revealed that a bit more speed could be squeezed out with a properly designed exhaust. They also wanted to reduce the exhaust flames that ruined the pilot's night vision and made it easier for the enemy to spot them at night. Al_in_Ottawa
Probably, but also adds to the overall aggressive look
ReplyDeleteLooked it up and found this.... By: antoni - 7th October 2007 at 00:25 - Edited 1st January 1970 at 01:00
ReplyDeleteSpitfire Mk Vb EN946 was tested at Boscombe Down in late 1943. It was found that replacing the exhausts with fishtail units increased the speed by 7 mph. The hot gases leaving the exhausts can act like small rockets. Highly tuned engines used in the Reno Races make use of this. At the very high boost pressures used there is a decrease in the horse power output because more hp is needed to drive the supercharger. It is the jet effect of the exhausts that gives an increase in air speed.
Wow, thanks!
DeleteSource for the comment above and some additional images - https://www.key.aero/forum/historic-aviation/76753-hurricane-early-spitfire-exhaust
ReplyDeleteConvergent duct as I recall.
ReplyDeleteOne aspect of relatively very short primary exhaust devices is they need to be long enough to inhibit colder air from hitting the very hot exhaust valves during the dwell cycle, aka reversion, in concert with inhibiting the atmospheric pressure pulse reversion wave between cylinder firing.
ReplyDeleteThey employ these very short exhaust pipes because of wieght and available space, just not enough space behind the engine cowling for a proper performance enhancing tuned exhaust system, and the nose fairing is a critical shape and area in regards airflow along the fuselage, lot of factors, its always a question of balances, what do you where do you sacrifice, what power weight or speed do you play with? Any bit which adds to performance and reliability, ease of repair or maintenance, cost too, the design and engineering is thick soup.
It might also manage back pressure.
ReplyDeleteSo has somebody dropped a RollsRoyce into a P-40….??… instead of the stock Allison…a la kinda like dropping a 427 in where a 350 had come stock…
ReplyDeleteP-40F and P-40L odels were built with Packard Merlins.
DeleteLater Allison V1710s also had these type exhaust stacks, though.
DeleteThey did, it was called the P40-F. The engine they used was a Merlin 28 with a single-stage supercharger, which was less powerful at high altitude than the P51s two-stage supercharger engine. The problem was that Merlins were in such demand for Lancasters, Mosquitoes, Hurricanes and Spitfires that the three factories in Britain couldn't keep up with demand and the Packard Merlins were needed for P51s.
DeleteAl_in_Ottawa
The hot exhaust gases can provide a small amount of thrust. In the '30s the exhaust stacks were flush with the cowling surface in an effort to minimize drag, look at Spitfire K5054, but testing revealed that a bit more speed could be squeezed out with a properly designed exhaust. They also wanted to reduce the exhaust flames that ruined the pilot's night vision and made it easier for the enemy to spot them at night.
ReplyDeleteAl_in_Ottawa