Why turboprop?

[Keith Lane]

I was sitting in the North Bay, Ontario airport waiting on a CRJ ride to Toronto last week and chatting with the aircrew of a RCAF C-130 who were waiting on a release time to arrive on station for an exercise.
After the crew went out and "kicked the tires and lit the fires", my boss asked me what the advantages of a turbo prop over a jet for the C-130 were. I was at a loss as to the correct answer.
Any thoughts? What answer should I have had in my head for this one?

 

[Skip Miller]

I was sitting in the North Bay, Ontario airport waiting on a CRJ ride to Toronto last week and chatting with the aircrew of a RCAF C-130 who were waiting on a release time to arrive on station for an exercise.
After the crew went out and "kicked the tires and lit the fires", my boss asked me what the advantages of a turbo prop over a jet for the C-130 were. I was at a loss as to the correct answer.
Any thoughts? What answer should I have had in my head for this one?

I bet short field performance is high on the list. Also the HerkyBird was certified back in the 1950s (first flight in 1954) when jet efficiency still sucked, so I bet that draggy airframe had better range with props than with jets of the time.

-Skip

 

[Ken Ibold]

As Skip mentioned, short field performance is typically better for a turboprop than a jet. Add to the mix the fact that the engines are "backwards" in turboprops compared to jets -- that is, the air inlet is in the back -- so FOD is less of a concern.

Also, turboprops are more fuel efficient, with the efficiency delta being greater at lower altitudes. So plan in such things as maximizing payload, typical mission length, expected altitudes and you come up with a lot of ways turboprops make more sense than jets, even today.

 

[ScottM]

Add to the mix the fact that the engines are "backwards" in turboprops compared to jets -- that is, the air inlet is in the back -- so FOD is less of a concern.

I am almost certain that the intake is in the front on the c130 engine.

 

[KennyFlys]

I am almost certain that the intake is in the front on the c130 engine.

I believe you are correct! I'm glad you're finally right about something.

 

[Ken Ibold]

I am almost certain that the intake is in the front on the c130 engine.

Which engine is it? Some are "backwards," some are not.

 

[KennyFlys]

Which engine is it? Some are "backwards," some are not.

Allison T-56 on the J Model. I'm not sure how it varies going back to earlier designs.

 

[ScottM]

Allison T-56 on the J Model. I'm not sure how it varies going back to earlier designs.

I remember when the unit I was assigned to went from C130A to C130H. The engine may have changed but the nacelle did not and they had the intake on the front. But that does not mean there was ducting in there to deliver it to the back of the nacelle. That is why I am not sure.

 

[gkainz]

E-2A, B and C (all using some variant of the T-56 I believe) and the P-3 ? all have the intake on the front, if I'm not mistaken ...

The Orion boys did manage to hang the engine upside down, but I don't think I've seen one backwards.

 

[Trapper John]

I remember when the unit I was assigned to went from C130A to C130H. The engine may have changed but the nacelle did not and they had the intake on the front. But that does not mean there was ducting in there to deliver it to the back of the nacelle. That is why I am not sure.

Looks like intake in the front...

Trapper John

 

[Steve]

The P&W PT-6 variants have the intake located aft of the exhaust.

 

[CJones]

The P&W PT-6 variants have the intake located aft of the exhaust.

Yup. And IIRC, Garrets have a front intake.

Edit: Garret Turboprop conversion on Ag-Cat (intake makes it look like it's smiling)

PT-6A on Air Tractor 802F:

 

[Steve]

I guess there are a few exceptions, the Beech Starship and Piaggio Avanti come to mind. Of course in those examples they mounted the engines backward.

The P&W PT-6 variants have the intake located aft of the exhaust.

 

[sba55]

Why turboprop? Because owning one is sort of affordable, or, at the very least, possible. In a year or so, a TBM 700 is going to look really attractive!

-Felix

 

[AWACSEng]

Turboprops also produce nearly instantanious power. The engine runs at 100%, the blade angle varies to produce the thrust.

 

[Teller1900]

The P&W PT-6 variants have the intake located aft of the exhaust.

Indeed. Eg: the 1900 uses the PT-6. Our nacelle scoop is in the front, but when the air comes into the scoop it simply fills the engine nacelle and is sucked in through a wire mesh grating at the back of the engine. The air then travels forward through the compressor section, is turned 180 degrees into the burner can, then another 180 degrees to go forward through the power section before getting blown out the stacks at the front of the engine. It's what's called a reverse flow turbine. This allows there to be "inertial separators" or ice vanes just inside the intake scoop that, when deployed, force all solids and liquids to fall out the bottom of the nacelle without making it to the back of the engine where the actual intake is. You lose a little bit of power with the reverse flow design, but it's MUCH smaller physically and does a really good job of preventing, or at least reducing FOD ingestion into the engine itself.