Correct procedure to capture altitude

[Samaritano 305]

Hello.

 

I am enjoying this MU2 and so far I have been able to do 3 full flights. My question comes regarding the ALT SEL mode. According to the manual you need to use in conjunction with IAS or VS. I haven't been able to capture the altitude selected on  Sperry ALT SEL unit. I establish a climb of around 700 fpm and then select VS first followed by ALT SEL and the aircraft immediately pitches up. It keeps trimming up and airspeed starts bleeding off. When I try the same but this time with IAS, after establishing a speed of around 200 kts. the aircraft behaves similar and just pitches up without me being able to correct the pitch with the trim.

 

Can somebody how this works and what is the correct way of using the autopilot vertical navigation mode?

 

Thanks.

 

Ed 

[atulumello 0]

I always select ALT ARM, followed by VS or IAS.

[raymie 81]

Here is what I do and so far it works for me

 

--Dial in your desired cruise altitude on the "Alt Set" under the VSI

--Click on "Alt Sel" Mode

--Click on "VS" Mode

--On the main Auto Pilot control head adjust the "Pitch Trim" wheel for your desired rate of climb.

Once airborne power up the auto pilot and select Yaw Damper. You should be good to go. Auto pilot should capture your desired alt. automatically.

 

Hope this helps

[andresico 0]

I do as Raimie and it works.

But, the ias mode doesnt always hold the speed that the AC had when pressing the button.

 

Also appr is a bit so so. I´ve done some 10 autopilot approaches so far and its by far the most stable experience. It tends to wobble up and down to much and sometimes I have to disable it. I thought it was me going to fast, but no, its much more general.

In general, compared to good quality jet addons and even the Carenado B1900 the autopilot on the MU is not really up to the same level. Its not a big issue because the AC is a nice handflyer.

[Samaritano 305]

Thank you guys. I'll try today when I get home. I like the airplane a lot. Like Andres said, it's a nice hand flyer.

[louisdecoolste 12]

IAS should function as a pitch mode - there is no autothrottle on the aircraft so it should adjust pitch to maintain the IAS at the moment of application.

 

In practice this is still a very `loose` mode for climbing as it seems to work to +5/-20 KIAS of selected airspeed. Not workable at the higher end of the speed range as you can go overspeed without careful attention to the Power Levers.

 

It does work better coming down when you preselect the altitude, activate ALT SEL, activate IAS mode and then carefully pull back on the power levers to around 40%, resulting in a pretty reasonable and consistent mode and rate of descent.

 

Unfortunately this is opposite to the normal use of Pitch hold vs. IAS hold in the real world - where IAS is used for climb and Pitch for descent. IAS on climb prevents inadvertent AOA divergence and stall from lack of attention to airspeed, whereas pitch mode is used to establish a consistent rate of descent that keeps ATC happier, with PL's retarded to keep IAS at the nominal value.

 

At present (v1.7) there is still far too much variation in power with altitude - the real TPE profile sees the percentage stay pretty much where it is put from 0-16,000 feet or so, after which PL advance is needed to offset reducing power setting and maintain a consistent power - subject to ITT limits.

 

This has been discussed before things went quiet here, so one can hope that the pair of developers are actually working on this. 

 

I haven't seen the pitch response described above under APR, but the Moo is noted as a `slippery` aircraft, reluctant to slow down and you really need 150 KIAS or less to enable suitable pitchover to G/S capture. In practice I tend to hold 40% power all the way through descent-to-level at Procedure Altitude, giving 180-170 kts, then deploy first stage flap to drop airspeed below 150. Once G/S capture is assured drop the gear and that will give a suitable approach speed to short final, when the 2nd stage flap is deployed aiming for 120-110 over the fence. The ONLY time I adjust the PL's through all this is to retard for landing and reverse.

 

Try that and see if it works better.

[atulumello 0]

I do as Raimie and it works.

But, the ias mode doesnt always hold the speed that the AC had when pressing the button.

 

Also appr is a bit so so. I´ve done some 10 autopilot approaches so far and its by far the most stable experience. It tends to wobble up and down to much and sometimes I have to disable it. I thought it was me going to fast, but no, its much more general.

In general, compared to good quality jet addons and even the Carenado B1900 the autopilot on the MU is not really up to the same level. Its not a big issue because the AC is a nice handflyer.

 

I've never had a problem with the IAS hold. I engage it once I reach my desired speed... Then the aircraft proceeds to lower its AOA, then shoots back up, and holds IAS. 

[capceo 117]

 

 

--Click on "VS" Mode
--On the main Auto Pilot control head adjust the "Pitch Trim" wheel for your desired rate of climb.

 

louisdecoolste is on the money. Generally speaking, we use IAS hold for climb, and VS mode for descent in real life. 

 

Bear in mind for what it's worth though, that 120-110 is a bit fast over the fence. 100-110 is a better figure, and 105 generally works perfectly. Rounding the airplane off and trying to flare at 120 will only result in an excessive float, greatly increasing the runway required.

 

Another aviation quote from an anonymous pilot: "You can't use runway that's behind you." In real life, it is for this reason that I always square the airplane off when entering the runway for takeoff as opposed to following the yellow taxiway line up to the centerline. Why leave 100 feet of runway behind you?

 

Same concept on approach. On a visual approach, I'll fly down the VASI/PAPI, red over white. Once I know that I have the runway made (with an engine out), I'll dip below the VASI and aim to touch down as soon as safely possible. You can't use runway thats behind you...

[louisdecoolste 12]

The old anonymous pilot.

 

My instructor (a wizened veteran of WWII) often challenged received wisdom, He scoffed at that remark with a simple: "More pilots have been killed landing short than were ever killed landing long."

 

Your truism is certainly true for take-off, but landing? A fast landing that is recognizably too far down the runway converts to a go-around far more easily than trying to reclaim lost airspeed at excessive AoA when `draggy` on short finals and below the g/s.

 

Either way, short field technique and full flaps notwithstanding, speed at PL ground idle in this model bleeds faster than a chewed neck at a Dracula convention. If you're not using full flap (not recommended for anything other than that proverbial short field landing) then the normal landing flap and reverse once wheels are firmly down gets you stopped plenty pronto. Even more so when the brakes are used with vigour. Most Moos will happily get into places they can't get out of.

 

If you are going short field, then you might trade off that extra 5-10 knots for a shorter, slower rollout but for normal flying in a reverse-equipped t/p carrying the extra speed gives greater lateral control to the spoilerons. These are all fractions, so perhaps the best summary is to say that Moo pilots should master all of this, and much else besides.

[Samaritano 305]

Well it still does not work for me. The airplane is all over the place pitchwise. I first select the ALT SEL  then establish a climb of around 500 ft/min. and then proceed to press IAS and the airplane start to climb all the way from 0 ft./min to maybe 100 ft./min sometimes doesn't even climb.

 

I also have problems with factory GPS ( no addon GPS here), when I press on PROC and then ENTER to select an approach the ENTER button does nothing, either on VC or Pop up 2D GPS. 

[Samaritano 305]

It is working now. I had to uninstall the MU2 and do a reinstall. Everything seems find. I was able to use the AP for climb using ALT SEL and IAS. For descent it was a little bit more challenging and could not get it to work. When I select ALT SEL and then VS it would level off. I won't let me trim.

[N405GJ 36]

Happy to hear you got most of your issues with the MU corrected.

 

It is working now. I had to uninstall the MU2 and do a reinstall. Everything seems find. I was able to use the AP for climb using ALT SEL and IAS. For descent it was a little bit more challenging and could not get it to work. When I select ALT SEL and then VS it would level off. I won't let me trim.

What I typically do for decent, is basically the same as for climb. I use the GTN750's built in vcalc tool to tell me when to start my decent. For a typical decent I would do the following.

 

Typically I am at FL26-FL28 in cruise, ALT and Nav modes on.

First I set the desired altitude into the altitude window.

Then dial in the altitude I am descending too, click the VS button on the AP panel.

Lastly, I go down to the AP master panel and dial in the the desired VS.

 

For me this is usually -1500 FPM, power levers back to 40% torque. This keeps the speed up where you want it.

From what I can see from your post the only thing you are missing to use the VS mode for decent is to dial in the VS on the lower AP panel.

 

Hope this helps and brings you even more enjoyment of the MU. She is a great bird to fly around, and awfully damn fast for a turboprop. I love getting ground speeds of 320-330, all the while burning only 500-600lbs of fuel per hour.

[Samaritano 305]

 

From what I can see from your post the only thing you are missing to use the VS mode for decent is to dial in the VS on the lower AP panel.

 

Hope this helps and brings you even more enjoyment of the MU. She is a great bird to fly around, and awfully damn fast for a turboprop. I love getting ground speeds of 320-330, all the while burning only 500-600lbs of fuel per hour.

 

This is the part that I'm not doing. Thank you for sharing that bit of knowledge. 

 

Ed

[N405GJ 36]

This is the part that I'm not doing. Thank you for sharing that bit of knowledge. 

 

Ed

It's my pleasure.

[capceo 117]

 

 

My instructor (a wizened veteran of WWII) often challenged received wisdom, He scoffed at that remark with a simple: "More pilots have been killed landing short than were ever killed landing long."
 
Your truism is certainly true for take-off, but landing? A fast landing that is recognizably too far down the runway converts to a go-around far more easily than trying to reclaim lost airspeed at excessive AoA when `draggy` on short finals and below the g/s.

 

I've also heard that quote myself. It usually refers to the technique smart pilots flying single engine airplanes use when they're trying to make the field engine out. But when you're flying a high performance twin like my airplane in real life, coming over the fence below the VASI at 1.3Vso is perfectly safe. It is not a technique that I would advise in a piston single unless you are very familiar with both the airplane, and the airport. I'll use it in a single occasionally if the runway is short, but you really have to make sure that when you commit to dipping down below the VASI, you absolutely positively have the runway made if you lose the engine. So in an airplane like a Cessna 172, doing it with anything more than 30 degrees of flaps would be a mistake. 

 

In my 414A, we come over the fence at around 95 to 100 knots indicated. If you were to lose an engine on short final, it wouldnt matter how far below the VASI you were (for the most part). The airplane has so much forward momentum and is so far above a stall, that the 325hp you're still getting from the good engine if you need it would be more than enough to carry the airplane to the runway, or even execute a go-around.

 

The bottom line is that following the PAPI/VASI all the way down will ultimately (depending on the field configuration) land you 1/3 of the way down the runway. So on a 3000 foot runway, it will put you just under 1000 feet down the runway. In an airplane like my 414A, 3000 foot runways are comfortably useable, but not if you touch down with 2000 feet remaining. Then it gets a little tight. If the runway is available, use it!

 

It's also important to note that I am not referring to dipping below the glideslope on a precision approach. Anyone who dips the GS is a fool. In fact, most ILS approach plates will remark that the GS path is no coincident with with the VASI. This is because they are designed to put you in two different places on the runway. The VASI will put you 1/3 of the way down, the GS will put you in the touchdown zones.