Performance Chart

cocolos

cocolos

Pre-takeoff checklist
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cocolos
How would you read out the power output above 11,000ft on this chart?
qasy4azu.jpg
 
By the way sorry for the orientation. Well lets say I want to go to 13,000ft at 2450 RPM does that round to 55% power? Do I just extend the lines and interpolate?
 
Yes, to a point. The problem is that the power side of that chart doesn't have a limit line like the speed side to show the limiting altitude above which you can no longer pull that much power due to the reduced air density. You can see that the 75% and 65% lines end at 8000 and 10000, respectively, but you can't quite see where the 60% and 55% lines end. So, while the straight lines can be interpolated upwards, there will be a point where you can't get the engine to turn that RPM, and I'm not sure you can actually pull 55% power at 13000 feet. However, if you could, then a linear interpolation to about 2525 RPM would be correct.
 
It can't make over 75% power above 8000 anyway, so just leave the throttle wide open and lean until rough/enrich until smooth
 
dell30rb said:
It can't make over 75% power above 8000 anyway, so just leave the throttle wide open and lean until rough/enrich until smooth
Click to expand...

Agreed. Why do you care if it's 55% or 65% power? The engine is fine at any setting up there. If you're worried about whether it can get up there for terrain clearance, stay at least 10% below max gross and give yourself at least 2000 feet margin during climb. Don't go with winds above 20 knots at the summit (whether stable or unstable). Cherokees (even with 180 HP) are very sluggish climbers above 10,000 feet.

It starts to be a strong function of temperature up there, as well.
 
MAKG1 said:
Agreed. Why do you care if it's 55% or 65% power? The engine is fine at any setting up there. If you're worried about whether it can get up there for terrain clearance, stay at least 10% below max gross and give yourself at least 2000 feet margin during climb. Don't go with winds above 20 knots at the summit (whether stable or unstable). Cherokees (even with 180 HP) are very sluggish climbers above 10,000 feet.

It starts to be a strong function of temperature up there, as well.
Click to expand...

Thanks yea I was mostly concerned with clearance. I guess at gross it's better to just avoid high terrain area. I am thinking of taking a mountain checkout. anyone know how long they usually are?
 
My "checkout" was a 2 hour round trip to Big Bear from Lancaster -- in a Warrior (it's possible, but you have to be aware of the limitations, especially how Vy is lower in IAS at 8000 feet than at sea level, and you DO NOT take off full rich). That's a minimum. There are all-day courses available that make landings on several high and eastern Sierra airports. That may be tough this time of year, as IMC (and ice) is common even when the weather is clear down below.

Read Sparky Imeson's book to start. There is a TON of good stuff in there.

And keep in mind that Lake Tahoe is well below 10,000 feet. Squawk Peak (the highest point around there) is just a bit above. Clearing Donner Pass or Echo Summit (which is slightly higher) with 2000 feet of clearance isn't too hard in Cherokee as long as the winds aren't high. Trying to get to Mammoth over Yosemite, with its 2000 AGL clearance (it's a national park) over a 10,000 foot pass, is another story. You won't get there at all on a warm day.

The main thing is, keep an out in case things don't go how you want.

I'd encourage you to contact a local flight instructor with signficant mountain experience. They aren't rare so near the Sierra, but they aren't every CFI either.
 
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cocolos said:
By the way sorry for the orientation. Well lets say I want to go to 13,000ft at 2450 RPM does that round to 55% power? Do I just extend the lines and interpolate?
Click to expand...

It looks like at 2450 rpm, you could do 10K at 55%. To do 13K, you would need to run 2510 rpm for 55%. Your chart does show it would be 124 MPH at 13K at 55%.
 
MAKG1 said:
My "checkout" was a 2 hour round trip to Big Bear from Lancaster -- in a Warrior (it's possible, but you have to be aware of the limitations, especially how Vy is lower in IAS at 8000 feet than at sea level, and you DO NOT take off full rich). That's a minimum. There are all-day courses available that make landings on several high and eastern Sierra airports. That may be tough this time of year, as IMC (and ice) is common even when the weather is clear down below.

Read Sparky Imeson's book to start. There is a TON of good stuff in there.

And keep in mind that Lake Tahoe is well below 10,000 feet. Squawk Peak (the highest point around there) is just a bit above. Clearing Donner Pass or Echo Summit (which is slightly higher) with 2000 feet of clearance isn't too hard in Cherokee as long as the winds aren't high. Trying to get to Mammoth over Yosemite, with its 2000 AGL clearance (it's a national park) over a 10,000 foot pass, is another story. You won't get there at all on a warm day.

The main thing is, keep an out in case things don't go how you want.

I'd encourage you to contact a local flight instructor with signficant mountain experience. They aren't rare so near the Sierra, but they aren't every CFI either.
Click to expand...

Okay that right there I had a question about (Vy at altitude) I thought that Vy IAS will always be the same because you still need the same amount of pressure over the wings...but in writing this I realized you will have less power at altitude.

So how do you figure Vy at altitude then?
 
MAKG1 said:
Cherokees (even with 180 HP) are very sluggish climbers above 10,000 feet.
Click to expand...

And Arrows (Cherokee with folding gear) with 200 HP aren't any better, at least not on a warm summer day. BTDT.
 
cocolos said:
Okay that right there I had a question about (Vy at altitude) I thought that Vy IAS will always be the same because you still need the same amount of pressure over the wings...but in writing this I realized you will have less power at altitude.

So how do you figure Vy at altitude then?
Click to expand...

An approximation is that it approaches Vx at the service limit, presumed linearly. Vx actually goes up a bit with altitude (in IAS), but it's a smaller effect than Vy.

I hear some POHs have Vy against altitude tables, but I haven't flown an aircraft that has one of those.
 
I guess a good approximate would be to just linearly interpolate between the Vx and Vy and the service limit.
 
cocolos said:
is running WOT at altitude bad of the engine?
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Not just no, hell no. As long as the RPM is not over redline.

In many respects, flying at high altitude is like shortening the throttle knob (and lengthening the mixture).

If you have a manifold pressure gauge, there is usually a maximum MP for continuous operation. Above a certain altitude (it's like 5000 feet in a 182), full throttle won't exceed that. If your aircraft is turbocharged, that altitude might be high.
 
MAKG1 said:
Not just no, hell no. As long as the RPM is not over redline.

In many respects, flying at high altitude is like shortening the throttle knob (and lengthening the mixture).

If you have a manifold pressure gauge, there is usually a maximum MP for continuous operation. Above a certain altitude (it's like 5000 feet in a 182), full throttle won't exceed that. If your aircraft is turbocharged, that altitude might be high.
Click to expand...

That makes sense. it's not turbocharged its a cherokee 180.
 
FYI, if you want to try out your aircraft at high altitude without going into mountainous terrain, there is nothing keeping you from flying at 10,000+ AGL over KSAC. I tried each of the models I fly over the Central Valley prior to taking it into the mountains, to feel out its performance. Be careful, drink enough, and watch for signs of hypoxia.

When I checked out in the 182, for some odd reason, the CFI wanted me to try some really high altitude stalls. We took it up to 10,500 near Hollister (not directly over it -- KSJC traffic doesn't like that) and promptly demonstrated that stalls there look a lot like they do at much lower altitude....
 
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