I was reading in AOPA, not a very reliable source of BC info I seen, this article:
http://www.aopa.org/aircraft/articles/2009/090323questkodiak.html

...its [Quest Kodiak] exhaust pipes aim backward, rather than down, to avoid setting tall grasses on fire.

Is this true and really a big problem in tall grass from the exhaust pipe alone?

I do live in Arizona and don't have much experience with tall grass.

How ironic. In the old days of fabric skin, radial engines and backfires, exhaust was aimed down, not back, to avoid setting the dope and oil impregnated fuselage on fire.

I don't have any details, but as I understand, that exhaust of a turboprop in a constant blast, something to the tune of 1000 degrees. I also read somewhere that Jay leno melted the front bumper of a car that got too close at a stoplight with his turbine powered motorcycle. (yes it does exist!) I would bet that the reason for the exhaust pointing back has more to do with aerodynamics than fire prevention, but I suppose there is a risk otherwise. Anyone have turboprop time to verify that anything I say has merit?

KB

When I was in AF primary flight training in the new T-6, our flight manual stated that the exhaust ports pointing backwards actually accounted for a slight amount of thrust, as opposed to them pointing down, which would provide nothing whatsoever. The quest uses a similar setup to that aircraft. I am wondering if this is a case of an engineer doing something smart, and then someone in the PA department saying something dumb. Happens a lot.

I believe last summer a Porter left Smiley Creek and it burned the grass where he started up and taxied out on the runway.

TrevDog wrote:I was reading in AOPA, not a very reliable source of BC info I seen, this article:
http://www.aopa.org/aircraft/articles/2009/090323questkodiak.html

...its [Quest Kodiak] exhaust pipes aim backward, rather than down, to avoid setting tall grasses on fire.

Is this true and really a big problem in tall grass from the exhaust pipe alone?

I do live in Arizona and don't have much experience with tall grass.

Sounds like a little bit of marketing hype to me. The quest is powered by a PT6-34, the exhaust location just lends itself to those stacks, virtually every PT-6 installation I have ever seen ( I am not a turbo prop guru ) looks like that.
We have a few -34 conversions and the stacks on those point straight out. The one I am currently flying was rebuilt a while back and the stacks were replaced with new Airtractor styled ones that sweep back just like the Quest ones. It was reported that there was some advantage at certain power setting, but since it was a major airframe / prop / powerplant, restoration, I don't think anyone here could confirm that... Turbines are just giant air compressors, so the least amount of bends (restrictions) for the escaping exhaust the better, I believe the sweep back just lends itself to scavenging.

Flying in the dark I have never seen flame coming from the stacks of a PT-6, this would probably be a bad thing. (heat yes, flame,no...) On the other hand the first early morning (dark) departure I made with an R1340 had me thinking the entire airplane was on fire, hence the heatshields on the right side flying wires of a cat...With a shorty stack, on take off that cat would routinely show better than 2' of flame half a foot round...
kinda like a giant torch

Can anyone else think of a PT-6 install with downward stacks? Does that mean the opposing one points at the sky

Take care, Rob


There have been a few different flavors of turbo porters. I wonder which one the fire starting porter was?

The Kodiak has been designed for a specific purpose. That is to support missionaries in Africa. Tall grass can be a problem there.

The only PT-6 installation that I've seen that comes with a different style of stack is on the Cessna Caravan, which has a very large, long exhaust stack that goes under the belly and aft. I was told that Cessna chose that specially designed exhaust for the Caravan to keep exhaust gases as far away from doors and windows as possible, to help prevent extensive use of sic sacks by passengers. Fly a turbine beaver sometime, and you'll see what I mean. Not horrible jet fuel fumes, but they're there, and some pax are pretty sensitive to exhaust fumes from a turbine.

I suspect the Quest folks chose the "standard" PT 6 style exhaust because thats what's available, not to prevent fires.

The US Fish & Wildlife Service has ordered several Kodiak aircraft for waterfowl survey work. They required a Caravan-like exhaust, to keep the exhaust streams away from the viewing angle of the observers. You don't want to try to count ducks through the exhaust of a turbine.

MTV