Two interview questions
10-08-2007, 05:39 PM
#3
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Joined APC: Jan 2006
Position: Engines Turn Or People Swim
Posts: 39,289
Originally Posted by flyingfalcon401
I need some help with a couple of questions:
1. When will a compressor stall most likely occur?
2. What determines the most desirable cruise altitude for jet aircraft?
1. When will a compressor stall most likely occur?
2. What determines the most desirable cruise altitude for jet aircraft?
2) Generally you want less-dense air (less drag), which always means higher altitudes. But the tradeoff is that it at takes a lot of gas to climb to higher altitude, so on a shorter flight it may not be economical to burn the gas to get to F390 only to have to immediately start your descent. Also high-altitude winds play an important role. You may better of at F290 with a 30 kt headwind than that at F390 with a 130 Kt headwind.
These are typical CRJ altitudes (westbound, no unusual wind):
15 min flight: 16,000
30 min flight: F240
1 hour flight: F320
> 1 hour flight: F380
10-08-2007, 05:44 PM
#4
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Joined APC: Jan 2006
Position: Spartan
Posts: 3,652
Originally Posted by rickair7777
1) In addition to what Joe said, a strong X-wind can be a factor.
2) Generally you want less-dense air (less drag), which always means higher altitudes. But the tradeoff is that it at takes a lot of gas to climb to higher altitude, so on a shorter flight it may not be economical to burn the gas to get to F390 only to have to immediately start your descent. Also high-altitude winds play an important role. You may better of at F290 with a 30 kt headwind than that at F390 with a 130 Kt headwind.
These are typical CRJ altitudes (westbound, no unusual wind):
15 min flight: 16,000
30 min flight: F240
1 hour flight: F320
> 1 hour flight: F380
2) Generally you want less-dense air (less drag), which always means higher altitudes. But the tradeoff is that it at takes a lot of gas to climb to higher altitude, so on a shorter flight it may not be economical to burn the gas to get to F390 only to have to immediately start your descent. Also high-altitude winds play an important role. You may better of at F290 with a 30 kt headwind than that at F390 with a 130 Kt headwind.
These are typical CRJ altitudes (westbound, no unusual wind):
15 min flight: 16,000
30 min flight: F240
1 hour flight: F320
> 1 hour flight: F380
10-09-2007, 08:13 AM
#5
Prime Minister/Moderator
Joined APC: Jan 2006
Position: Engines Turn Or People Swim
Posts: 39,289
Originally Posted by Slice
I know you're not talking about the -200 in the last two...especially 380.
10-09-2007, 08:35 AM
#6
Gets Weekends Off
Joined APC: Jan 2006
Position: Spartan
Posts: 3,652
Originally Posted by rickair7777
Getting filed at 320 -340 is not too unusual in the 200...sometimes you make it, sometimes you don't. 350+ is pretty much 700/900.
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