rhbelter
11-18-2015, 03:42 PM
Needed: A twin: The Engines.
Ahoy, EAA Engineers, Designers, Builders:
There are a lot of new/small/powerful/lightweight engines out there -- serious candidates for flight. Many are suitable for development on this airframe. Appropriately 'beefed/sized' to handle a LOT of soup, this general airplane configuration would accommodate such as the Cadillac 2.0 T @272 HP, or Ford 2.3R @315 + HP. A pair of these -w- PSRU/prop is serious economical power, for a VERY fast airplane.
A certificated airplane engine produces about one half horsepower per cubic inch displacement, and is very reliable and simple. The above engines (are able to) crank out more than FOUR TIMES that power density! They include many sensors, computer(s) and thousands of lines of computer code. They are very reliable at normal automotive output levels -- 10% to 20% of max. Airplane engines run at higher power levels. If this high power output in an airplane induces a fault in this (auto) engine, the power is reduced to defend the engine (get-home/limp-home mode) to less than the power which is needed for flight.
If you manage to subvert this 'defensive' mode in order to maintain flight, the engine may well retaliate by exploding! If you 'de-rate' the engine, and develop acceptable reliability, it will likely have far less power, and it won't be cheap.
Because of the above factors, I have no knowledge of a way to make a modern very high output automobile engine acceptable as a single propulsion engine for an airplane, except for a very slow landing speed version (or a racer, with their risks). So: Use a PAIR.
These VERY highly stressed modern engines are so very long-lived and reliable, (at automobile output levels) that the drivers are smashing far more cars than there is a demand for engines. Excellent engines -w- controls/'gozintas' -- are relatively cheap, and should not need very much 'optimization' to be OK for flight __ as a twin. Like: Don't mess with the 'get-home' mode, because your second engine is your 'get-home' mode. With two of them aboard, one can comfortably establish how much reliable continuous power you can take from them. Fuel burn alone ( -- Like 50+ gal/hr) will keep you from running them very hard for very long, and at somewhat lower power, they are very efficient, and likely to survive quite well, and still 'go-fast'.
Every one of these engines will need a PSRU, and here is a rather formal discussion of PSRU's: (edited by a guy who builds good ones).
PSRU -- A Propeller Speed Reduction Unit is a mechanism which drives the propeller at a lower speed (RPM) than the engine crankshaft is turning, by means of gears, belts, or chains. That is necessary when the engine develops the required power at a crankshaft speed which is higher than the speed at which a propeller can safely or efficiently operate. There are many PSRU's available in the marketplace. Some are very good, but others have demonstrated very inconsistent reliability.
There are PSRU's which have been directly copied from problematic previous designs, and which demonstrate exactly the same problems as did their predecessors. Suffice it to say that a PSRU done by an enthusiast with a good fabrication shop, but 'unlettered' in his ability to calculate and then measure the dynamic behavior of his construct can be quite dangerous. Make sure that you know whose work you have, and that the person has a demonstrated grasp of the engineering principles involved.
So: Why all this talk about PSRU's???? While there are many issues about alternative engines, the most consistent and dangerous problem is with the PSRU. While the 'get-home' mode can let you down, an exploded PSRU (or engine) can KNOCK you down!
Enjoy /s/ Bob
Robert H. Belter
rhbelter@comast.net
EAA # 8444, EAA TC # 4561, EAA CH 204,
Ahoy, EAA Engineers, Designers, Builders:
There are a lot of new/small/powerful/lightweight engines out there -- serious candidates for flight. Many are suitable for development on this airframe. Appropriately 'beefed/sized' to handle a LOT of soup, this general airplane configuration would accommodate such as the Cadillac 2.0 T @272 HP, or Ford 2.3R @315 + HP. A pair of these -w- PSRU/prop is serious economical power, for a VERY fast airplane.
A certificated airplane engine produces about one half horsepower per cubic inch displacement, and is very reliable and simple. The above engines (are able to) crank out more than FOUR TIMES that power density! They include many sensors, computer(s) and thousands of lines of computer code. They are very reliable at normal automotive output levels -- 10% to 20% of max. Airplane engines run at higher power levels. If this high power output in an airplane induces a fault in this (auto) engine, the power is reduced to defend the engine (get-home/limp-home mode) to less than the power which is needed for flight.
If you manage to subvert this 'defensive' mode in order to maintain flight, the engine may well retaliate by exploding! If you 'de-rate' the engine, and develop acceptable reliability, it will likely have far less power, and it won't be cheap.
Because of the above factors, I have no knowledge of a way to make a modern very high output automobile engine acceptable as a single propulsion engine for an airplane, except for a very slow landing speed version (or a racer, with their risks). So: Use a PAIR.
These VERY highly stressed modern engines are so very long-lived and reliable, (at automobile output levels) that the drivers are smashing far more cars than there is a demand for engines. Excellent engines -w- controls/'gozintas' -- are relatively cheap, and should not need very much 'optimization' to be OK for flight __ as a twin. Like: Don't mess with the 'get-home' mode, because your second engine is your 'get-home' mode. With two of them aboard, one can comfortably establish how much reliable continuous power you can take from them. Fuel burn alone ( -- Like 50+ gal/hr) will keep you from running them very hard for very long, and at somewhat lower power, they are very efficient, and likely to survive quite well, and still 'go-fast'.
Every one of these engines will need a PSRU, and here is a rather formal discussion of PSRU's: (edited by a guy who builds good ones).
PSRU -- A Propeller Speed Reduction Unit is a mechanism which drives the propeller at a lower speed (RPM) than the engine crankshaft is turning, by means of gears, belts, or chains. That is necessary when the engine develops the required power at a crankshaft speed which is higher than the speed at which a propeller can safely or efficiently operate. There are many PSRU's available in the marketplace. Some are very good, but others have demonstrated very inconsistent reliability.
There are PSRU's which have been directly copied from problematic previous designs, and which demonstrate exactly the same problems as did their predecessors. Suffice it to say that a PSRU done by an enthusiast with a good fabrication shop, but 'unlettered' in his ability to calculate and then measure the dynamic behavior of his construct can be quite dangerous. Make sure that you know whose work you have, and that the person has a demonstrated grasp of the engineering principles involved.
So: Why all this talk about PSRU's???? While there are many issues about alternative engines, the most consistent and dangerous problem is with the PSRU. While the 'get-home' mode can let you down, an exploded PSRU (or engine) can KNOCK you down!
Enjoy /s/ Bob
Robert H. Belter
rhbelter@comast.net
EAA # 8444, EAA TC # 4561, EAA CH 204,