How do you compare a turboprop and a piston engine?
- Friday Dec 4,2009 11:15 PM
- By diddy
- In Others
I need to know how to compare the power of the two. I tried doing it by looking up specs but I couldn’t figure it out. I’m trying to figure how much power a plane would need to get moving to that which a ship needs. I know it sounds crazy but it’d be awesome if someone could help.
I actually think that I am trying to compare the thrust.
Piston, Piston Engine, Thrust, Turboprop
6 Comments
Piston engines are rated by torque and horsepower, as are turboshaft (turboprop and helicopter, as well as stationary) engines.
When comparing performance however, turbine engines will have the ability to maintain more horsepower at altitude (in less dense air) than their naturally aspirated piston counterparts. This is because they compress air before it enters the combustion chamber.
Turbocharged piston engines will be able to maintain similar at-altitude performance as the turbine, because a turbo-supercharged (ts) or turbo-normalized (tn) engine is actually a hybrid design of the two types. A turbine uses exhaust gasses to compress the air in the intake tract. Ts engines can compress intake air to a pressure greater than normal atmospheric (>29.92 mm/Hg) Tn engines just raise the manifold pressure to normal levels (</= 29.92)
Generally speaking, the turbine has the advantage of greater reliability because of its lack of reciprocating parts, the piston or turbo-piston engine has the advantage of greater fuel economy (higher break horsepower/ specific fuel consumption) mainly because the combustion chamber is sealed during the power stroke.
There are also turbo-compound piston engines, which can be even more efficient…..lots of terms, most folks don’t know they existed anymore. See the Lockheed super-G Constellation for an example of a turbo-compound piston engine driven aircraft.
Finally, to help you with your project, at sea level, where a ship would operate, the horsepower rating of a turbine and a piston engine could be directly compared. Note: some engines are rated in kilowatts, which can be converted to horsepower with a simple formula see http://www.mr2ownersclub.com/converter.htm .
Just another hint to help solve your problem, compare the density of air and water, and calculate how much each vehicle must displace in order to move.
Horsepower always worked for me.
Propeller engines power output is measured in horsepower.
The actual THRUST horsepower is less than the engine output because of the losses in propeller efficiency.
The turbo prop engine is pound for pound more efficient and reliable while the piston is cheaper to operate, and maintain. The Turbo prop has many more hours between inspections and overhauls. example: PT6A about 3500 hours between overhauls, while a piston engine from a twin, runs 1800 hours between overhauls. More parts int he piston engine means more can go wrong. http://www.airliners.net/aviation-forums/tech_ops/read.main/100148/
If you want to compare power needed to get a plane moving versus getting a ship moving that’s a different question. A ship has a lot of mass and sits deep in the water. To get it moving it must overcome the resistance of the water in front of it. A plane on the other hand only has to overcome the friction of it’s wheels on the ground and is relatively free to move. A ship requires a great deal more power.
Hope this helps
The power requirements between planes and ships are pretty similar actually. The ship may be much larger and the drag of water much greater, but it doesn’t need power to support itself in the water and is much slower.
Most modern warships use gas turbine propulsion. Often they will use two smaller turboprop derived engines for cruising (~3000-5000 HP) and use an airliner turbofan core engine for acceleration and sprints (~15000-25000 HP).
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