Performance at higher altitude airports

[Lindenberg]

How does a Flight Design perform when flying to higher altitude airports like Bryce Canyon? My in-laws have a cabin at Panguitch Utah which is about 14 miles to the West of Bryce Canyon airport and I live in Southern California.

[Roger Fane]

Many of us have been in and out of Bryce Canyon without issue. As long as the prop is pitched to make decent rpm at higher altitudes, you just use more runway, and the climb rate is cut in half. My two times at Bryce, takeoffs were at 9,500' density altitude, two good sized guys and 15 gallons of fuel on board.

[CT4ME]

Take a look at some of JosJunkers posts... or Charlie Tango's... the CT is a very capable bird. Just keep your weight down, if possible, and expect about 1/2 the climbing performance. I've done Bryce, and Flagstaff at 9300 with no problems.

Tim

[Runtoeat]

Many of us have been in and out of Bryce Canyon without issue. As long as the prop is pitched to make decent rpm at higher altitudes, you just use more runway, and the climb rate is cut in half. My two times at Bryce, takeoffs were at 9,500' density altitude, two good sized guys and 15 gallons of fuel on board.

 

Roger, what is a "decent RPM" that you are wanting to see for higher altitude performance?

[Roger Lee]

Hi Dick,

 

That question is hard to answer. We should set our prop pitch to to the altitude we normally cruise. I normally cruise at around 4500-4500. That is where mine is set for 5500-5550 WOT. I just went to Flagstaff, AZ and was up at 9500 so I lost a little performance and rpm will not go up to 5500 WOT at that altitude. Don't get me wrong the plane will perform just fine. I can tell you that at 7100' field elevation and at 1450-1470 lbs the CT will take off and perform just fine. Climb is a little slower, but so what. It will take off and climb to 10K with no problem. If you fly out of an airport all the time at that altitude then set the prop pitch for the higher cruise altitudes. I can see a 400 rpm WOT drop when I'm at 10K verses my 4500, but I fly down there 95% of the time.

[Runtoeat]

Hi Roger. I'm finding that my WOT rpm's in cold weather is 5750 and in the hot weather the WOT rpm's are about 5850. Since Rotax doesn't want us to run over 5800 for more than a few minutes and you recommend running about 5500 to 5550 rpm, I'm going to re-pitch at the next inspection. We discussed this last winter when I was seeing 5750 rpm and you estimated about a 1.25 to 1.50 degree pitch increase. Would you still say this is still a good start point when I re-pitch?

[Roger Lee]

Hi Dick,

Yes you do need a re-pitch. You are loosing a lot of performance. You have great climb, but that's it. If you can see 5800+ then use

1.75-2 degrees more pitch.

[johngpilot]

How does a Flight Design perform when flying to higher altitude airports like Bryce Canyon? My in-laws have a cabin at Panguitch Utah which is about 14 miles to the West of Bryce Canyon airport and I live in Southern California.

I have the performance charts for altitudes above 5000 for T/O and OBS available on the FD web site:

HERE

 

http://flightdesignusa.com/wp-content/uploads/2009/12/TO-above-5000-50FT-obstacle.jpg

 

http://flightdesignusa.com/wp-content/uploads/2009/12/TO-above-5000.jpg

[Douglas Bohnert]

10,000 ft at Leadville, CO in a CTLS, Rotax 912, no problems at all. Prop was re-pitched max RPM was 5400. We were also using bigger tires (600-6), no wheel pants.

[Roger Lee]

Hi Doug,

 

At that elevation I would add another 150 rpm which is about .75 - 1 degree less pitch. Your plane would perform even better in all aspects.

[Douglas Bohnert]

Hi Doug,

 

At that elevation I would add another 150 rpm which is about .75 - 1 degree less pitch. Your plane would perform even better in all aspects.

 

 

Thanks for the advice Roger, we actually added about 1.25 degrees to the pitch about a month ago. I may take your advice and go with higher rpm and less pitch. The acft is currently at Purdue University where disabled people are learning to fly it as we put the hand control rudder system in it! A Flight Design first!!! Anyway, I have yet to fly it myself since the pitch adjustment, we will next month.

[207WF]

I am pitched to 5500 rpm at about 6,000 feet. I came back from Santa Fe last week, airport is 6400 feet, and stopped in Sedona on the way back, leaving at Density altitude about 9,000. In both cases my rpm on the takeoff roll was very similar to what I see at sea level back home: about 5100 rpm at 60 knots and flaps 15. WF

[207WF]

I had a strange high alititude performance experience on the last trip. Coming back from New Mexico at 8500 feet and density altitude 12,000, the XM weather was earning its keep as we steered around thunderstorms. Full throttle was only giving me 5200 rpm, whereas it would normally deliver 5400 or better under these conditions and it would normally take about 70% throttle to achieve 5200 rpm. I was getting worried about the engine when we cleared the storms and crossed the border into Ca. Suddenly, everything returned to normal and I was only using 70% throttle again for my 5200 rpm! As the full throttle situation lasted for almost two hours, I doubt it could be explained by a large area of subsidence associated with the storms. Could the humidity alone make that much difference, or does my plane just really like California? WF

[sandpiper]

Were you in Roswell? Maybe you picked up a passenger you didn't know about and he/she/it was messing with the motor!

[chanik]

That sounds about right if you were at 80%RH or so and 90F. The mass ratio would be ~3% which means volumetrically about 5% of the air is now water so there would be 5% less O2 in the intake manifold. Water content is an exponential function of temperature. It's directly proportional to partial pressure, p = 611*exp({T/(T+238)}*17.3)

where T is the temperature in Celsius, in case you're curious.

[Ed Cesnalis]

I had a strange high alititude performance experience on the last trip. Coming back from New Mexico at 8500 feet and density altitude 12,000, the XM weather was earning its keep as we steered around thunderstorms. Full throttle was only giving me 5200 rpm, whereas it would normally deliver 5400 or better under these conditions and it would normally take about 70% throttle to achieve 5200 rpm. I was getting worried about the engine when we cleared the storms and crossed the border into Ca. Suddenly, everything returned to normal and I was only using 70% throttle again for my 5200 rpm! As the full throttle situation lasted for almost two hours, I doubt it could be explained by a large area of subsidence associated with the storms. Could the humidity alone make that much difference, or does my plane just really like California? WF

 

sounds like the da to me. 12,000' 5,200 wot isn't a bad prop setting. your hp is down in the 50's. i bet you found lower da when your performace came back.

 

 

 

[Roger Lee]

Hi Ed,

 

Glad your back in the fray. We missed you!

I know you know this, but this will help others. remember the first time we had a discussion and you reset your prop to a flatter pitch.

Quote: " Woodstock comes alive!"

 

I remember our first year at the Grand Canyon. You had you prop set for your high altitude normal flying and at 11,500 you could get almost 5500 and because I was a low lander and had my prop set at 5500 for at 4000'. You and I were flying side by side. We went full throttle and I could only get 5150 WOT and you were getting 5400+ and you just walked away from me. So having a prop set to get 5500 WOT at an altitude of 10K-12K is more advantageous than one set much lower. It helps unload the engine and allows the prop to turn easier and allows you to save even more fuel, get better performance even at 65hp or 65% of your rated hp.

Now here is the down side. You live at the higher altitudes so your prop setting the other 90% of the time was still good to go, but if I had my prop set for 5500 at 12K then when I cam back to my home field at 2400' and my normal flying at around 3500' I would get close to 5800 and maybe more and loose all my performance except for a good climb prop.

This is the biggest and most important reason to set your prop pitch for your normal everyday cruise and live with the differences when you may be exceptioally lower or higher than normal. This is the loss we accept when using a ground adjustable prop.