Climb by AOA autopilot

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FrankBravo

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FrankBravo
I have seen many modes for autopilot, does anyone know of a autopilot that will climb by AOA?
 
Never heard of one that will. What would that buy you over current fielded modes of climb. (FLC, VVI, etc)
 
EvilEagle said:
Never heard of one that will. What would that buy you over current fielded modes of climb. (FLC, VVI, etc)
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Figure above a altitude airspeed changing to Mach changes a little, just setting the thing to climb a .X AOA would be constant as far as demand on the aircraft
 
The autopilot would probably chase a dancing AOA more than you’d want. Unless it’s a calm day. On a turbulent day in many aircraft Pitch mode gets you close and can work better than VS mode.
 
FrankBravo said:
Figure above a altitude airspeed changing to Mach changes a little, just setting the thing to climb a .X AOA would be constant as far as demand on the aircraft
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Would it be the same demand?

I can tell you that you need more pitch at high altitudes with fixed power than lower altitudes, so for me it seems like you would need a higher AOA at high altitudes to result in a climb than you would at low (density) altitude. If you didn't change the AOA that the AP was shooting for you would have too shallow a climb down low or too steep a climb up top. At very high altitudes the effective wind going over the wing is akin to travelling slower at low altitude (thus the low KIAS) so you would need a higher AOA, right? As I understand it, that's the reason behind the switch to mach.

I just did a quick google on the subject and some very smart people have put pen to (digital) paper. The long and short of it is that constant thrust at constant IAS gives constant AOA. Since we don't have constant thrust (decreases with climb) you would have to change AOA to have Vx, Vy or any other best climb profile.
 
No. The closest-ish thing that people will use is IAS

Theoretically if someone had an experimental and were so inclined they could rig up an Arduino and do some trial and error with this...
 
EvilEagle said:
Would it be the same demand?

I can tell you that you need more pitch at high altitudes with fixed power than lower altitudes, so for me it seems like you would need a higher AOA at high altitudes to result in a climb than you would at low (density) altitude. If you didn't change the AOA that the AP was shooting for you would have too shallow a climb down low or too steep a climb up top. At very high altitudes the effective wind going over the wing is akin to travelling slower at low altitude (thus the low KIAS) so you would need a higher AOA, right? As I understand it, that's the reason behind the switch to mach.

I just did a quick google on the subject and some very smart people have put pen to (digital) paper. The long and short of it is that constant thrust at constant IAS gives constant AOA. Since we don't have constant thrust (decreases with climb) you would have to change AOA to have Vx, Vy or any other best climb profile.
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I have climbed at IAS and seen my AOA drop especially past FL300
 
TrueCourse said:
The autopilot would probably chase a dancing AOA more than you’d want. Unless it’s a calm day. On a turbulent day in many aircraft Pitch mode gets you close and can work better than VS mode.
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Climbing in VS is normally only used with a bad AP that can’t smoothly execute IAS
 
Hmm, some common ones don't have an IAS climb mode.
 
FrankBravo said:
Climbing in VS is normally only used with a bad AP that can’t smoothly execute IAS
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Not in the aircraft I used to fly. Excluding no-turbulence conditions, VS mode was smoother than IAS. At high altitudes commanded rate would have to be reduced to avoid getting too slow, but it worked better than IAS mode. And it was a great autopilot.
 
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TrueCourse said:
Not in the aircraft I used to fly. Excluding no-turbulence conditions, VS mode was smoother than IAS. At high altitudes commanded rate would have to be reduced to avoid getting too slow, but it worked better than IAS mode. And it was a great autopilot.
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What autopilot, what aircraft?
 
TrueCourse said:
...Pitch mode gets you close and can work better than VS mode.
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I enjoyed flying with a captain who climbed in pitch mode...said it was better than VS mode because it provides stall protection. He set it at some modest climb rate initially and left it until it reached altitude. I played with it for a while because it was so intriguing but ultimately went back to VS mode...just because I was too old to learn new tricks, I guess.
 
TrueCourse said:
Not in the aircraft I used to fly. Excluding no-turbulence conditions, VS mode was smoother than IAS. At high altitudes commanded rate would have to be reduced to avoid getting too slow, but it worked better than IAS mode. And it was a great autopilot.
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That's the danger of VS mode. Left unmonitored, such as the pilot getting distracted, it could fly you right into a stall.
 
noahfong said:
I enjoyed flying with a captain who climbed in pitch mode...said it was better than VS mode because it provides stall protection. He set it at some modest climb rate initially and left it until it reached altitude. I played with it for a while because it was so intriguing but ultimately went back to VS mode...just because I was too old to learn new tricks, I guess.
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I’m not seeing the stall protection there. How is that any different than vertical speed mode from a stall perspective?

if you hold a 8 degree pitch and keep climbing, eventually that will result in a stall, no? Maybe in a turbine or even a it or would work?

maybe it’s a little better than vs mode, since it’s not increasing pitch, but I don’t think you can set it and forget it in a NA piston aircraft.
 
Salty said:
I’m not seeing the stall protection there. How is that any different than vertical speed mode from a stall perspective?

if you hold a 8 degree pitch and keep climbing, eventually that will result in a stall, no? Maybe in a turbine or even a it or would work?

maybe it’s a little better than vs mode, since it’s not increasing pitch, but I don’t think you can set it and forget it in a NA piston aircraft.
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But if you set a more appropriate pitch attitude, it works.

granted, you won’t get an optimum climb profile, but the same is true of most other modes you might “set and forget”.
 
MauleSkinner said:
But if you set a more appropriate pitch attitude, it works.

granted, you won’t get an optimum climb profile, but the same is true of most other modes you might “set and forget”.
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I would think in a NA aircraft you're eventually going to stall. Maybe higher than it matters, but if you run out of power in the engine to keep up forward speed, and you hold in that pitch, you'll eventually exceed critical Aoa, no? Again, maybe that's so high it's not relevant. Dunno.
 
Salty said:
I’m not seeing the stall protection there. How is that any different than vertical speed mode from a stall perspective?

if you hold a 8 degree pitch and keep climbing, eventually that will result in a stall, no? Maybe in a turbine or even a it or would work?

maybe it’s a little better than vs mode, since it’s not increasing pitch, but I don’t think you can set it and forget it in a NA piston aircraft.
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In my NA piston single I can select a high VS that it can maintain for a while but if left alone the airspeed will continue to decrease as the plane struggles to maintain the commanded VS (never happened to me BTW). Eventually airspeed could decay to the point of a stall if corrective action isn't taken. So in theory, by selecting IAS/FLC instead of VS I can ensure the airspeed never drops to a where it would be an issue. Don't know if this holds up for the turbine crowd.
 
tsts4 said:
In my NA piston single I can select a high VS that it can maintain for a while but if left alone the airspeed will continue to decrease as the plane struggles to maintain the commanded VS (never happened to me BTW). Eventually airspeed could decay to the point of a stall if corrective action isn't taken. So in theory, by selecting IAS/FLC instead of VS I can ensure the airspeed never drops to a where it would be an issue. Don't know if this holds up for the turbine crowd.
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My comment was about pitch hold
 
Salty said:
I would think in a NA aircraft you're eventually going to stall. Maybe higher than it matters, but if you run out of power in the engine to keep up forward speed, and you hold in that pitch, you'll eventually exceed critical Aoa, no? Again, maybe that's so high it's not relevant. Dunno.
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select the pitch attitude no higher than what would result in the speed where VX and VY come together at the absolute altitude of the airplane.
 
MauleSkinner said:
select the pitch attitude no higher than what would result in the speed where VX and VY come together at the absolute altitude of the airplane.
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That's pretty much it. I thought it would be obvious but I guess not. I said he initially chose a resulting VS that was modest, meaning somewhere between 500 to 1000 fpm (CRJs cannot climb much above 500 fpm when reaching the 30 thousand; -200 usually can't maintain 500 when reaching the mid-20s). I doubt that was more than 10 deg pitch up. The climb rate will gradually decrease. At some point, if totally left unattended (which we never did, thank goodness) the plane will no longer climb and just "mush" along at 10 deg nose up pitch (or whatever).

Similar to slow flight in a single-engine piston....maintaining altitude with nose high.
 
How about a rutowski climb profile if we are looking at options!
 
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