Choosing the Right Turboprop Engine for Light Aircraft

[Sunige]

Hi,

I'm a third year student studying mechanical engineering under going a third year dissertation.

My individual project consists of designing a light aircraft, however I have ran into a few issues. I want to import a turboprop engines for my 4 person light aircraft. Following that I am very interested in the Pt6a turboprop engine however there are various models with different shp. I am fully aware that the shp will be low because of the nature of the aircraft but I can not find any equation to relate shp, velocity and can not decide which one to go for !

Would you guys have any tips or sources that would be helpful to help me choose between individual engines?

Thanks

source: http://www.pwc.ca/en/engines/pt6a-21

 

[etudiant]

The PT6 is a family of engines, rather than a single model, with power from 600-1500sHp.
This is really too big for a light 4 seater, you would be better served by the RollsRoyce/Allison 250.
More generally, you might look at existing 4 seat aircraft to get a sense for how much power is needed for a given performance. Do note turbine engines are rarely used, because they are so expensive relative to a200-300hp piston powerplant.
Older designs such as the Cessna 210 might need 300 hp to get the same performance that a Mooney achieves with 240 hp. Speed is not as much a function of power as it is of aerodynamic design, with power more a tool to provide more payload/climb. You first size your people box and then wrap the airplane around that.

 

[Sunige]

Hi,

Thank you for your reply that has really helped me out !

I was basing my models on the Cessna super cargomaster, the epic Escape, Epic Lt, Piper Meridian and Socata TMBM850 with maximum sHp of 675-1000. The reason why I want to use a turboprop is because of the increase of range and the reduction in service maintenance of the engine.

Following your advice I will most likely go for a Rolls Royce Turboprop.

Thank you

 

[etudiant]

Do keep in mind that turboprops are much more expensive than piston engines, it probably doubles the price for a 4 seater. That is why they have not become more widespread in private aviation, the cost is too high.
The aircraft you mentioned for the PT6 are all relatively big, designed for cargo or for high speed high end private/corporate travel. The RR/Allison has found applications in helicopters mostly, can't think of any airplanes that use it offhand, but there are surely a couple.
A light aircraft by my lights is something that grosses out at maybe 2500 pounds. The Meridian is twice that.
I think that the FAA has a specification for Light Sports Aircraft that maxes out at about 1200 pounds.
There are wonderful resources available to help in aviation, not just from NASA, but also from the industry associations such as GAMA, the General Aviation Manufacturers Association. Embry Riddle is an aviation oriented university, they have lots of study courses rich with insights.
Good luck with your design!