Turbine Performance
12-09-2007, 08:13 AM
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Turbine Performance
I have a question about turbine performance that I hope someone can answer.
I learned to fly turbines in Florida earlier this year, and did my learning on a BVM BobCat equipped with a JetCat P-60. I was surprised at how well the P-60 performed. You can't go vertical with it on take-off, but you can do great verticals after building up a little speed.
Then I came back home (to Tennessee) and started flying the jet here. A couple of weeks ago I flew it in Chattanooga, and the jet didn't seem to have as much oomph. It might have been my imagination (maybe I'm just growing used to the jet's speed), but I could swear that the turbine didn't perform as well in Chattanooga as it did in Florida.
Could elevation be the difference? In Florida, I was only a few feet above sea level. In Chattanooga, I was 700 feet above sea level. Can 700 feet make a noticeable difference in a turbine's performance?
One other possibility for the difference in performance is fuel. In Florida, I was burning military-surplus Jet A. In Chattanooga, I was burning civilian Jet A. Is Jet A Jet A, or does the military use a higher grade?
I learned to fly turbines in Florida earlier this year, and did my learning on a BVM BobCat equipped with a JetCat P-60. I was surprised at how well the P-60 performed. You can't go vertical with it on take-off, but you can do great verticals after building up a little speed.
Then I came back home (to Tennessee) and started flying the jet here. A couple of weeks ago I flew it in Chattanooga, and the jet didn't seem to have as much oomph. It might have been my imagination (maybe I'm just growing used to the jet's speed), but I could swear that the turbine didn't perform as well in Chattanooga as it did in Florida.
Could elevation be the difference? In Florida, I was only a few feet above sea level. In Chattanooga, I was 700 feet above sea level. Can 700 feet make a noticeable difference in a turbine's performance?
One other possibility for the difference in performance is fuel. In Florida, I was burning military-surplus Jet A. In Chattanooga, I was burning civilian Jet A. Is Jet A Jet A, or does the military use a higher grade?
12-09-2007, 08:38 AM
#2
RE: Turbine Performance
I wouldn't have thought 700 ft would make any noticeable difference. Jet A is pretty much the same anywhere (although some has FSII and some does not).
Is there a temperature difference between the places you are flying.
I would guess that, either you are getting used to the plane as you say, or you have a different problem. The other thing that I have found affects the feeling of speed is the flying site. If the site is wide open with no restrictions then the model feels slower than flying somewhere where the pattern needs to be kept quite tight.
Is there a temperature difference between the places you are flying.
I would guess that, either you are getting used to the plane as you say, or you have a different problem. The other thing that I have found affects the feeling of speed is the flying site. If the site is wide open with no restrictions then the model feels slower than flying somewhere where the pattern needs to be kept quite tight.
12-09-2007, 10:06 AM
#3
RE: Turbine Performance
You can always plug in the GSU to see if you are getting the full rated RPM and EGT out of the turbine.
If the RPM's and EGT are there then the thrust should be there, unless you fly in sand and have altered the shape of the turbine blades.
Higher altitude will reduce power, I don't know that 700' will make a noticeable difference. Every field that I have ever flown at was between 600 and 675 feet.
OR, Just face it that you are getting good at flying that ship.
If the RPM's and EGT are there then the thrust should be there, unless you fly in sand and have altered the shape of the turbine blades.
Higher altitude will reduce power, I don't know that 700' will make a noticeable difference. Every field that I have ever flown at was between 600 and 675 feet.
OR, Just face it that you are getting good at flying that ship.
12-09-2007, 12:35 PM
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RE: Turbine Performance
It's probably a mixture of things. You are getting used to the speed. Altitude is a factor, although 700 ft should not be a big difference. Temp and humidity also play into performance. I can really tell a difference on those nice cool days, probably 15- 20 mph difference.
