Slick9

losing altitude during sharp turns...

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good morning all - looking for some expert help or opinions on my T7.  I just moved from FSX to P3Dv4 and everything is working like it did in FSX except during sharper turns.  I was flying the pattern and doing touch and goes a few days ago.  during each of the 90 degree turns around the pattern, the aircraft would transition from +/- 50FPM vertical speed to dropping to +/- 1000FPM.   I was hand flying with the autothrottle armed and VNAV mode active, so in anticipation of the altitude loss in the turn, I would pull back on the yoke and trim nose up as I started the turn, this helped but then resulted in the aircraft starting to climb as soon as the turn was completed.  I don't recall this being an issue for me in FSX, but then, I also was not doing a lot of pattern flying, I was doing line flying.  Another thing I tried was to fly the pattern with the AT disconnected, then as I approached the turns, I would manually add thrust, this alleviates the loss of altitude in the turn, i noticed when flying with the A/T, there was no increase of thrust during turns.  Anything stand out to the experts here? Am i missing something?  thnx for any help.

Richard

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This is physics and normal for how every airplane behaves..

Imagine the airplane from behind: when you fly straight ahead you have 100% lift area: your wings. 

As soon as you bank into a turn the direction of the lift isn‘t 90 degrees upwards anymore and so the area which creates lift is reduced to a percentage, depending on how steep you fly your turn. So the airplane will go into a dive. You counter this when you increase your pitch (lift up your nose). So the wings create more lift during the turn to keep your altitude.

absolutely normal behaviour. Maybe your realism settings in FSX weren‘t set correctly or what ever... 

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Hi Marc,

I agree that from a physics standpoint the behavior is expected. I should have added - I thought (and I could be wrong) that the T7 with it's fly by wire systems had a way to compensate for the loss of altitude in a turn.

 

Richard

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As mentioned above:

The 777 is, fundamentally, an aeroplane. It may be a very advanced aeroplane with a lot of electronic assistance for the pilot, but it is still ultimately an aeroplane and aeroplanes must obey the laws of physics.

This means that in a level turn, assuming constant airspeed the angle of attack must be increased in order to maintain level flight for the reasons explained above. 

This increase in lift also results in a small increase in drag which may require a small increase in thrust to counter but at normal (<30 degrees) bank angles this increase in drag is normally considered negligible and thus no thrust increase is usually necessary. 

Now, I am sure that the 777 advertises (as in Boeing advertise - not PMDG) pitch compensation in turns. However, such features are often imperfect in real life (that is certainly the case with the A320) and in practice some pilot input may be required. A sink of 1000fpm does seem excessive though. 

What I would suggest is that:

- It is generally considered poor technique to trim in turns or other transient manoeuvres for the reason you experienced - you will very quickly find yourself back out of trim again when you roll out

- What mode was the autothrottle in? Whilst it may sound pedantic, it is really important to be precise with language when describing the autoflight system (or any aircraft system): "Armed" means "Not active but will become active when certain conditions are met". Were you really flying with the A/T *armed* (in which case one wouldn't expect it to do anything) or did you really mean *active* (in which case how the A/T behaves will depend upon the mode it is in and the selections you have made on the MCP).

In SPEED mode the the A/T will adjust thrust to maintain the airspeed target you have set in the MCP. If the speed does not reduce there is no reason it should increase thrust.

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even airbuses lose altitude in turns as they hold the attitude, not the altitude... fbw is not a magic system, it just is a replacement of old steel wires going through the plane.. and although there are several computers actually flying a 777 or an airbus, it is still a plane and a plane needs to be flown. Either by the autopilot or by you. 

I have learnt to fly on sail planes (ASK 13 and ASH 25). What I was taught before circling in the thermals was to pull the plane up a few degrees before banking into the turn. This prevents exessive g forces when you have to „pull your VSI back from the negative part“. Of course an airliner is flown „slightly“ different from a sail plane, but the theory is the same. Try to combine your pitch with the bank angle. Train this and you will get used to it. :)

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Thanks for the answers gents!!  Simon you are correct I have to go back through the flight and take note of the annunciations so I can know exactly which modes were active.  I'll report back after i do another run around the pattern.  Unfortunately I won't be able to do it till the weekend. But I shall return. :) thnx

 

Richard

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2 hours ago, Slick9 said:

Thanks for the answers gents!!  Simon you are correct I have to go back through the flight and take note of the annunciations so I can know exactly which modes were active.  I'll report back after i do another run around the pattern.  Unfortunately I won't be able to do it till the weekend. But I shall return. :) thnx

 

Richard

PMDG asks that we sign our full names here Richard.

I believe you will find the section on high bank angle maneuvers in the FCTM pg 7.12 instructive. I believe that your use of trim in the turn was behind the loss of altitude, the AFDS should compensate for increase angle of attack in a turn up to 30 deg bank and your use of trim was working against the AFDS. The trim in the simulation may be thought of as speed trim rather than pitch trim because our yokes/joysticks cannot simulate what a pilot actually senses in the real aircraft. I recommend turning on the Show FBW Trim speed option (Introduction pg 91) to overcome this limitation in the simulation.

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17 hours ago, Ephedrin said:

even airbuses lose altitude in turns as they hold the attitude, not the altitude... fbw is not a magic system, it just is a replacement of old steel wires going through the plane.. and although there are several computers actually flying a 777 or an airbus, it is still a plane and a plane needs to be flown. Either by the autopilot or by you. 

I have learnt to fly on sail planes (ASK 13 and ASH 25). What I was taught before circling in the thermals was to pull the plane up a few degrees before banking into the turn. This prevents exessive g forces when you have to „pull your VSI back from the negative part“. Of course an airliner is flown „slightly“ different from a sail plane, but the theory is the same. Try to combine your pitch with the bank angle. Train this and you will get used to it. :)

Airbus do not lose altitude in turns up to 30 deg bank. No pitch input is necessary if you are straight and level to begin with. They aren’t maintains attitude, it’s vertical acceleration which is maintained. This assumes completely calm conditions. In real life this is unlikely so some pitch correction may be necessary.  

The same applies to the 777. It’s nose should not drop in a normal turn and no pitch input should be necessary. The problem comes in trying to demonstrate this in FSX and P3D with hobby level flight controls. A pure roll input is required to avoid any pitch input and this is very hard to achieve. Ironically, you stand more chance of seeing this work using keyboard commands. 

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1 hour ago, kevinh said:

Airbus do not lose altitude in turns up to 30 deg bank. No pitch input is necessary if you are straight and level to begin with. They aren’t maintains attitude, it’s vertical acceleration which is maintained.

Thanks for the clarification!

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1 hour ago, kevinh said:

Airbus do not lose altitude in turns up to 30 deg bank. No pitch input is necessary if you are straight and level to begin with. They aren’t maintains attitude, it’s vertical acceleration which is maintained. This assumes completely calm conditions. In real life this is unlikely so some pitch correction may be necessary.  

The same applies to the 777. It’s nose should not drop in a normal turn and no pitch input should be necessary. The problem comes in trying to demonstrate this in FSX and P3D with hobby level flight controls. A pure roll input is required to avoid any pitch input and this is very hard to achieve. Ironically, you stand more chance of seeing this work using keyboard commands. 

back to zero: it does lose altitute. I have leveled off at 6000ft at 270kt which gave me a pitch of 2,5°. then I just banked to 15° left and achieved a decent rate of 2-300ft/min, banked to 30° and had -400ft/min. the pitch remained at 2,5°. This was the airbus, I have no time to check the 777 now as I have to leave for work. And I haven't dived into the 777 FBW system that much.. :D But I expect it to behave very similar. 

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1 minute ago, Ephedrin said:

back to zero: it does lose altitute. I have leveled off at 6000ft at 270kt which gave me a pitch of 2,5°. then I just banked to 15° left and achieved a decent rate of 2-300ft/min, banked to 30° and had -400ft/min. the pitch remained at 2,5°. This was the airbus, I have no time to check the 777 now as I have to leave for work. And I haven't dived into the 777 FBW system that much.. :D But I expect it to behave very similar. 

This is correct.

As Kevin says, the Airbus maintains neither attitude nor altitude but a 1g load factor. The manuals will tell you that no pitch input is required for turns up to 33 degrees AoB, but as Kevin says in practice the system is good but not that good and thus a few hundred fpm sink is quite normal on the real aeroplane if no pitch input is made - this is modelled in the FSL bus.

I imagine the same is true on the 777 but as I say, the 1000 fpm described by the OP seems excessive and more akin to a conventional aircraft.

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FSL, PMDG, Majestics, A2A, Leonardo... We are in sim's heaven ^^

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19 hours ago, kevinh said:

Airbus do not lose altitude in turns up to 30 deg bank. No pitch input is necessary if you are straight and level to begin with. They aren’t maintains attitude, it’s vertical acceleration which is maintained. This assumes completely calm conditions. In real life this is unlikely so some pitch correction may be necessary.  

The same applies to the 777. It’s nose should not drop in a normal turn and no pitch input should be necessary. The problem comes in trying to demonstrate this in FSX and P3D with hobby level flight controls. A pure roll input is required to avoid any pitch input and this is very hard to achieve. Ironically, you stand more chance of seeing this work using keyboard commands. 

You are right. 

The nose wouldn’t drop in both airbus and 777 because of the FBW system, but you still need to pitch up slightly in turn to maintain altitude like a conventional airplane, all the FBW does is it maintain a stable attitude in turn so that pilots do not need to apply constant back pressure on the yoke or side stick. If you simply roll airplane without any pitch input the airplane would deccent at about 100fpm depends on AOB. 

 

The PMDG 777 in for some reason does require a much larger pitch change than the real airplane in turn especially with AOB >20deg. 

 

For example a level turn with F5 out 180kts you will need almost 10deg nose up to maintain level flight without losin altitude. In contrast a normal straight and level flight for the same pitch and speed is about 5-6deg nose up. 

On the real airplane for any turn with AOB below 30deg all you need is ~ 1 deg pitch up at max. With N1 incense by 5% most of the time. 

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On 05/01/2018 at 1:27 PM, Ephedrin said:

back to zero: it does lose altitute. I have leveled off at 6000ft at 270kt which gave me a pitch of 2,5°. then I just banked to 15° left and achieved a decent rate of 2-300ft/min, banked to 30° and had -400ft/min. the pitch remained at 2,5°. This was the airbus, I have no time to check the 777 now as I have to leave for work. And I haven't dived into the 777 FBW system that much.. :D But I expect it to behave very similar. 

The 777 FCOM, Vol 2, page 9.20.10, mentions that no additional back pressure is required to maintain altitude in turns with bank angles up to 30 deg.

The A320 FCOM says a similar thing:

Quote

In normal turns (up to 33 ° of bank) the pilot does not have to make any pitch corrections once the turn is established.

So it ought to work in the sim and it seems to me that it is.

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On 4 January 2018 at 4:45 PM, Slick9 said:

good morning all - looking for some expert help or opinions on my T7.  I just moved from FSX to P3Dv4 and everything is working like it did in FSX except during sharper turns.  I was flying the pattern and doing touch and goes a few days ago.  during each of the 90 degree turns around the pattern, the aircraft would transition from +/- 50FPM vertical speed to dropping to +/- 1000FPM.   I was hand flying with the autothrottle armed and VNAV mode active, so in anticipation of the altitude loss in the turn, I would pull back on the yoke and trim nose up as I started the turn, this helped but then resulted in the aircraft starting to climb as soon as the turn was completed.  I don't recall this being an issue for me in FSX, but then, I also was not doing a lot of pattern flying, I was doing line flying.  Another thing I tried was to fly the pattern with the AT disconnected, then as I approached the turns, I would manually add thrust, this alleviates the loss of altitude in the turn, i noticed when flying with the A/T, there was no increase of thrust during turns.  Anything stand out to the experts here? Am i missing something?  thnx for any help.

Richard

Just to add to what Kevin and Simon have said;

Patterns are generally flown with VNAV off, AP disconnect and A/T On. What are you speeds for the various pattern segments? If you're flying slightly slow then the FBW is going to be coordinating the turns to preclude the risk of dropping airspeed - hence pitching down, etc - maybe something of the behaviour you're seeing.

Another thing would be to fly the pattern work with settings as above and keep the T7 in FBW trim for airspeed using the blue indicator on the speed tape on the PFD.

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Hi Jim - generally I fly the crosswind and downwind @  ~200 kts w/ F1 - just before turning base I slow to 180 and go to F5 and continue from there.

 

Richard Bansa

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3 hours ago, Slick9 said:

Hi Jim - generally I fly the crosswind and downwind @  ~200 kts w/ F1 - just before turning base I slow to 180 and go to F5 and continue from there.

 

Richard Bansa

Ummm, seems a little fast - unless you're deliberately loading normal Pax and Freight.

Do you know of the Chrono 45 second "past the Threshold" pattern Procs?

If not - research.

 

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I've never heard of the Chrono 45 Second procedure Jim, I'll do some digging and learn some more. I'm always looking to learn more about the way "the professionals" do it.  Thanks for the heads up

 

Richard Bansa

 

 

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1 hour ago, Slick9 said:

I've never heard of the Chrono 45 Second procedure Jim, I'll do some digging and learn some more. I'm always looking to learn more about the way "the professionals" do it.  Thanks for the heads up

 

Richard Bansa

 

 

Hi Richard,

 

I have contracted Flu since yesterday so am feeling proper rough.

However, take a look at this resource about Base Training and "bashing" circuits in the airframe of your choice; in our case the mighty T777.

I'm sure Skelsey (who knows much more than I) and others can chime in and do a much better job than I at explaining but the essentials are below in the schematic. It's all about energy control.

 

As a rule; start the chrono at the threshold of your selected RWY as you pass on the downwind leg. Reduce KIAS, etc, throw gear down. Speed down.

1c645.png

Wonderful film here - one of my favourites: (Yes, I know it's an A330 but the principles are identical - but I warrant you'll learn more about bashing base training than any instructor can throw at you just by being in the cockpit with these Swiss Air Captains/ SFO chaps)...plus, it's a lovely film. 

"Fifty"

"Forty"

"Thirty"

"Twenty... Retard"

"Ten"

Clang...

"Stand Throttles Up, Flaps 10"

"GO!"

"TOGA"

"Rotate"

(Rinse and repeat)

 

 

Clear Skies. (and don't get this bloody flu)

 

 

 

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Thanks for this tip Jim, if i recall correctly this diagram, or something like it is in the FCOM.  I will definitely check the video out.  I can see one of the big difference between what I'm doing and what the manual suggests - I'm turning base w/ FLAPS 5, and per the manual, it should be FLAPS 15.  

One thing that confused me was places like San Francisco where ATC routinely keeps the heavies at 1180kts til about 5 or 6 miles out. (per my listening to Live ATC).  I guess one difference could be that the aircraft going into KSFO are loaded, and when flying a pattern the aircraft is generally empty.

Jim make sure you get ample rest man, the flu is scary this year!!!! Feel better soon!!

 

Richard Bansa

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9 minutes ago, Slick9 said:

Thanks for this tip Jim, if i recall correctly this diagram, or something like it is in the FCOM.  I will definitely check the video out.  I can see one of the big difference between what I'm doing and what the manual suggests - I'm turning base w/ FLAPS 5, and per the manual, it should be FLAPS 15.  

One thing that confused me was places like San Francisco where ATC routinely keeps the heavies at 1180kts til about 5 or 6 miles out. (per my listening to Live ATC).  I guess one difference could be that the aircraft going into KSFO are loaded, and when flying a pattern the aircraft is generally empty.

Jim make sure you get ample rest man, the flu is scary this year!!!! Feel better soon!!

 

Richard Bansa

Go here to practice Base Training. LFLX. It's where we all go in Europe. Don't try and practice at a busy airfield, odd, unpredictable METAR, etc.

Base Training feels like a big a deal - it feels like it is but it isn't.

The glory of base training is that you'll get better and better at "hand Flying" the 777

You'll get used to the "nod" (porpoising) that the 777 does when heading into a slight head/ side wind on final (she's trying to cross reference  her FBW A/T with ALT)

You'll get familiar with her tendency to "dive" if you ease back pressure on the yoke too early before you've set final Flaps. You'll learn that  you get her under the thumb when you bash the Gear Down.

You'll learn she's "Ground Shy" in the last 400' AGL.

You'll learn to love her. Just flip the A/P off, and trust your feelings..."Pull back stick; cows get smaller, push stick forward; cows get bigger"

She's a Cessna 172 - just bigger.

PMDG have done a truly magnificent job - and it's all there for you to connect with as a pilot.

 

 

 

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The airspace around my home is full of Navy T44 King Air B90s, young Ensigns learning to fly.  The local pattern they fly is similar but there is no base; rather, at the mark past the key point they start a constant radius descending turn from downwind and roll out on final over the lights.  Our coastal bend frisky winds add significant challenge in maintaining the sink rate and bank angles to line up correctly.  I can do it in our C-414 but have not yet figured out how to do it in the PC simulator due to the restricted viewing angles available and lack of the seat of the pants.

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6 hours ago, ganter said:

I'm sure Skelsey (who knows much more than I) and others can chime in and do a much better job than I at explaining

Very kind of you to say so but not much to add really - the only T7 flying I have done was a few hours over a decade ago when the Simfest World Flight sim was a 777 (the Jumbo and more recently the A320 are my 'types') so cannot add much 777-specific advice --  the FCTM diagram and your comments sum it up very well! 

All I would say in general terms is just to be aware that during the touch and go it will not always be possible to stop safely in the event of a problem so go/stop is very much a judgement call (in real life for the Training Captain of course). Also it is wise to stand the thrust levers up reasonably early so as to maintain speed above Vmcg during the 'roll' in case of engine failure.

6 hours ago, Slick9 said:

One thing that confused me was places like San Francisco where ATC routinely keeps the heavies at 1180kts til about 5 or 6 miles out. (per my listening to Live ATC).  I guess one difference could be that the aircraft going into KSFO are loaded, and when flying a pattern the aircraft is generally empty.

Remember that there is a world of difference between operating as a commercial flight in to a busy airport (where ATC will be keen to encourage you to keep the speed up - possibly unreasonably so - in order to maintain high flow rates (the faster you get one aeroplane in the faster you can get the next one in and therefore the more you can land) and operating as a non-revenue training flight at a quieter airfield where you are flying visual circuits and not being packed in to a sequence with dozens of other aircraft.

I spend the vast proportion of my simming time nowadays instructing on our basic flying course at BAV. I find that people have a curious tendency to want to go steaming around the circuit in the C172 at 2400rpm and 110 KIAS and are subsequently perplexed at how difficult it is to fly consistent, stable approaches and get all the checks done etc whilst conforming to the normal circuit dimensions. A small amount of guidance soon has them flying downwind at 80 kt or so, first stage of flap out abeam the threshold, second stage and 70 kt on base and then full flap and 65 kt on final and lo and behold, everything falls in to place nicely with no rush.

Likewise in a jet - there is no need to go haring round the circuit. It's just storing up problems for yourself - you just end up rushed, with a huge amount of energy to bleed off, flying ginormous circuits or all of the above. In the Jumbo IIRC a normal training circuit would be flown at around 165 kt downwind and in the A320 170 kt downwind is about average.

Take your time and give yourself time to think and execute properly - and for what it's worth, don't be afraid to make use of the automatics on downwind for a moment to give yourself thinking space to 'debrief' and consider how the previous approach and landing went and what might be improved this time.

5 hours ago, downscc said:

The local pattern they fly is similar but there is no base; rather, at the mark past the key point they start a constant radius descending turn from downwind and roll out on final over the lights.

The RAF fly oval circuits over here as well; I think it is perhaps easier for spacing when arriving as a formation (after, of course, the customary fast jet 'run in and break' - 420+ kt and 1000 ft at 'initials' then a maximum rate turn to downwind whilst throwing everything out in order to be slowed down and configured before the turn to final).

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