Help with King 150 AP usage

LuvFlying

LuvFlying

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LuvFlying
Hello everyone. I beleive this is my first post here. AdamZ keeps nudging me to come on over and say hello. (I typically hang out on the Purple board and occasionally and cautiously dip my toe into the red board).

I've recently purchased a really loaded Mooney J. It has a King 150 with an altitude pre-select.

While in cruise, with altitude hold on, if ATC instructs me for lower, it seems like I should be able to turn off ALT and pull the throttle back for a nice even paced descent. But that's not what happens. I turn off ALT, pull the throttle.. and I just go slower (ALT is maintained).

The ALT pre-select is not in any active (armed or capt) mode.

I know I can do my descent via the pre-select, but that's way more button pushing and twisting (many more steps) than the procedure I just described.

I've been through the manual a dozen times. Can anyone shed some light?

Thanks.
 
Welcome to POA Bob! :D

Do you have an up/down vertical trim control button like I do on my 150?
I don't have the altitude pre-select, so maybe it's slightly different???

What I typically do, is to disengage ALT hold, then hit the vertical trim up or down a few times to establish a climb or decent.
 
AdamB said:
Welcome to POA Bob! :D

Do you have an up/down vertical trim control button like I do on my 150?
I don't have the altitude pre-select, so maybe it's slightly different???

What I typically do, is to disengage ALT hold, then hit the vertical trim up or down a few times to establish a climb or decent.
Click to expand...
Thanks for da welcome.

I do have that rocker.
I have not tried it in that combo.

I was trying the rocker today to get a better understanding of it's opps, it would seem that I would not have to turn off ALT for lower using the rocker. With ALT on, for as long as I'm pushing Down, I get a 500'/min descent untill I let go. Nice for small trimming, but not practical for long descents, esp in turb.

Does it act differently when I turn off ALT?
 
Yeah, when not in ALT hold mode, I usually press it several times (probably around 8 to 10 in my plane)
to establish a 500-700 ft/min descent without having to hold it.

Although now that I think about it, maybe I should hold it until I reach the descent rate I desire, then let go. (something to try next time I fly).

then I just monitor it. If the descent rate slows, I'll press it a couple more times, etc...
You get the idea.

My manual says, When not in ALT mode, adjusts pitch attitude at a rate of 0.7 deg/sec.
 
Looking at the manual AGAIN it says...
"The ALT mode is canceled by automatic glideslope capture or by depressing the "ALT" button"

So if I turn off ALT, and pull the throttle, it should not try to hold the altitude.
 
Hey Bob WELCOME to POA. good seeing you today. I told ya someone here would have information on this. I can also vouch for your beautiful Mooney being " loaded" what a great panel!
 
Hmmm...

ALT ON: Pressing the rocker points the plane down or up at a constant rate of 500'/min. Then holds the altitude where released

ALT OFF: Depressing the rocker increases the pitch (up or down) and continues that path after releasing the rocker. (Holding the rocker down for several seconds increases the rate -> TBD)

Ok, that makes a bit more sense.
 
AdamZ said:
Hey Bob WELCOME to POA. good seeing you today. I told ya someone here would have information on this. I can also vouch for your beautiful Mooney being " loaded" what a great panel!
Click to expand...


Me too!

I was able to take a peek at Alton Bay a couple of weeks ago.
Sweet airplane!!!
 
Thanks Adam(Z). It's a double reward to mix business with pleasure!
 
Ok, so I'm kinda getting my head around this but then I run into this..
Again the manual "The ALT mode is canceled by automatic glideslope capture or by depressing the "ALT" button"

So I disengage the ALT, what's supposed to happen? Shouldn't I lose altitude if I reduce power. It still tries to maintain alt.grrr... just when I thought I had it figured out.:mad2:
 
AdamB- Next time you are flying The Jet, turn off ALT and pull the throttle. Let me know what happens.
 
LuvFlying said:
Ok, so I'm kinda getting my head around this but then I run into this..
Again the manual "The ALT mode is canceled by automatic glideslope capture or by depressing the "ALT" button"

So I disengage the ALT, what's supposed to happen? Shouldn't I lose altitude if I reduce power. It still tries to maintain alt.grrr... just when I thought I had it figured out.:mad2:
Click to expand...


Wouldn't glideslope capture be for just an approach? does it have an approach mode?

If ya can't get it figured out by May A2 ( thats what we call him here if were both on I'm A1) Will be at the Flybq you can fly with him and he'll show ya. A2 you don't mind me volunteering your plane right:D
 
Howdy, Bob. Welcome to PoA - don't be a stranger. You know we are an inclusive community, because we even like Adam! (chuckle)

---

I believe that your autopilot, when you depress the "Alt" button and take it out of altitude-hold, is reverting to Attitude Hold mode. Hence, assuming you were properly-trimmed when the alt hold was engaged, when you disconnect Alt hold, your altitude should vary very little. That's why the up/down rocker switch is there - so you can select the pitch you like.

Now, hearkening back to my younger years, when I had the mental energy to remember things like flight dynamics and the relationship between pitch, power and airspeed, if you leave the attitude-hold in, and reduce power, you'll eventually go down, but the A/P will maintain the same pitch, so you'll have to lose some airspeed first. But I am dopey this morning.

In my plane (S-Tec 30 autopilot), disconnecting altitude hold removes the pitch control servo from the equation completely, since the 30 has no attitude control logic in it. Hence, when I do that, if I reduce power, I will (after the plane gives up some of its kinetic energy) settle into a stable descent at approximately the same airspeed I was trimmed-out for before. You have to use your pitch rocker to do that.

'Zat help?
 
SCCutler-
ALT off reverts to aTtitude hold... I'm thinking you are on to it. That makes sense because that's the mode it's in when you turn engage the AP and not any other functions.

But then there's Jason's comment. hmmmm...

Jason-
Pushing ALT, light goes out. I can't push the yoke forward/back and it maintains ALT (or maybe it's just trying to maintain pitch) with throttle decrease.

In BOTH your birds, if you turn off ALT, you CAN move yoke?
Do you actually do that in practice or are you thinking strongly that that makes sense - like me?
 
Bob:

My exposure to the 150 is extremely limited; I believe that it always defaults to one pitch mode or another, either altitude or attitude; and (as Jason notes) if the plane is so-equipped (not all are), you select the altitude and VS you want, and it will (within the airplane's dynamic abilities) comply.

I believe that the 150 is much like the Century 2000 in this regard; you always have a pitch mode of some sort engaged, whether it be altitude hold, pitch hold or glideslope capture.

In my plane (S-Tec 30), if altitude hold is not engaged, then I have complete manual control over pitch - the autopilot bows out of the picture completely.
 
LuvFlying said:
Looking at the manual AGAIN it says...
"The ALT mode is canceled by automatic glideslope capture or by depressing the "ALT" button"

So if I turn off ALT, and pull the throttle, it should not try to hold the altitude.
Click to expand...
Do you have the KAP 150 or the KFC 150 with flight director?

In the KFC 150, when you release the ALT hold mode you go back to pitch hold mode. In that case the AP maintains your attitude without respect to altitude. Come to think of it, that might be the same thing in the KAP150 - your modes are either OFF in pitch and roll, or ON in pitch and roll and you have to set the various "goals" with the A/P computer.
 
SCCutler said:
Howdy, Bob. Welcome to PoA - don't be a stranger. You know we are an inclusive community, because we even like Adam! (chuckle)

---

I believe that your autopilot, when you depress the "Alt" button and take it out of altitude-hold, is reverting to Attitude Hold mode. Hence, assuming you were properly-trimmed when the alt hold was engaged, when you disconnect Alt hold, your altitude should vary very little. That's why the up/down rocker switch is there - so you can select the pitch you like.

Now, hearkening back to my younger years, when I had the mental energy to remember things like flight dynamics and the relationship between pitch, power and airspeed, if you leave the attitude-hold in, and reduce power, you'll eventually go down, but the A/P will maintain the same pitch, so you'll have to lose some airspeed first. But I am dopey this morning.

In my plane (S-Tec 30 autopilot), disconnecting altitude hold removes the pitch control servo from the equation completely, since the 30 has no attitude control logic in it. Hence, when I do that, if I reduce power, I will (after the plane gives up some of its kinetic energy) settle into a stable descent at approximately the same airspeed I was trimmed-out for before. You have to use your pitch rocker to do that.

'Zat help?
Click to expand...
+1...
 
The 1984-1998 Malibus and Mirages use the 150 autopilot too. You could find one of the PA46 instructors and get a lot of help on all of the odd problems with this unit. Check out the MMOPA on the web to look for an area instructor.

It would be good to be up on this autopilot since the PA46 will be your next aircraft!

Kevin
 
I did some additional research and now remember that with the KFC150, the autopilot will try to follow the Flight Director, so when the AP is engaged, it will attempt to follow the command bars and the autopilot will attempt to autotrim against control pressures if they last longer than 3 seconds. Therefore, even with ALT not engaged, the autopilot will attempt to maintain the attitude set via the command bars.

The best way to accomplish what you are trying to do would be to reduce power and disengage the autopilot OR manually press DOWN on the vertical rocker switch or use CWS to establish a desired nose down pitch or VS. Alternatively, you can use the altitude preselect to begin a descent.

I removed some of the info I provided earlier which was incorrect to eliminate some confusion.

Hope this helps.

Best,
Jason
 
Last edited:
TMetzinger said:
Do you have the KAP 150 or the KFC 150 with flight director?
Click to expand...
KAP 150. No flight director

kmead said:
It would be good to be up on this autopilot since the PA46 will be your next aircraft!
Click to expand...
:DWho told you I'm eyeing them?

HPNPilot1200 said:
....Therefore, even with ALT not engaged...
Click to expand...

Ok. I think we've come to a consensus.
AP engaged and...
ALT ON:
Altitude is maintained.
Altitude can be adjusted/tweaked (at a rate of aprox 500/min) by pressing and holding the rocker. Altitude is held after releasing.

ALT OFF:
ATtitude is maintained.
ATtitude can be adjusted/tweaked by clicking (each time increasing the rate of change) the rocker. ATtitude is held after releasing.
(Holding the rocker down for several seconds = several clicks => TBD)

That helps me a lot. Makes sense. Thank you all.
Now I can put that to bed. It was really buggin' me.


And Jason summed up my options nicely:
The best way to accomplish what you are trying to do would be to reduce power and disengage the autopilot OR manually press DOWN on the vertical rocker switch or use CWS to establish a desired nose down pitch or VS. Alternatively, you can use the altitude preselect to begin a descent.
 
I think the key thing to understand here is that the KAP 150 always exerts pitch (vertical) control when it's on. You get to chose what the pitch axis is trying to do (hold altitude, hold VS, hold pitch attitude, follow GS, etc) but you cannot get it to just release control of the pitch axis if it's controlling the roll axis.
 
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