And what country can preserve its liberties if their rulers are not warned from time to time that their people preserve the spirit of resistance? Let them take arms. The remedy is to set them right as to facts, pardon and pacify them. What signify a few lives lost in a century or two? The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants.
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.
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.
ReplyDelete