cmbaviator

Not enough "nose heay" during flare ?

Recommended Posts

Hi Guys,

 

I haven't been flying the 747v3 for months and restart flying since the -800. I messed up my flare as i Floated way too much even though it was within the LZ. But I notice that even when I released the yoke, the pitch was decreasing very very slowly. 

As far as i understand ground effet, it has mainly two effects :

1) as you approach closer to the ground, the vertcial speed will increase due to more lift

2) as you approach closer to the ground, the aircraft is subject to a negative ( nose down) torque.

the 1) seems to be spot on but however I still reserved on 2), it seems that the decrease of pitch is due to the lost of speed after retarding the throttle.

I own the 737/777/747 and all have the same issue with 2) unless i'm completely wrong.

Before i was flying with the IXEG B737-300, and you can really feel the nose down effect after passing 60 feets, you needed to hold a bit more back pressureto maintain your ROD until flare.

Also do you need to retard earlier ? here is a video of my landing

 

 

 

Edited by cmbaviator

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

8 minutes ago, cmbaviator said:

-800

8. There is no such thing as an 800.

8 minutes ago, cmbaviator said:

Also do you need to retard earlier ?

For not knowing the proper landing technique enough to know when to retard the throttles, among other things, I find the thread title a little inappropriate, honestly.

Share this post


Link to post
Share on other sites

I mostly fly A320 or B737-300 on Xplane, you usually retard at 20-30 feets, i was wondering if its the same for the 747 or you should retard between 30-40 fts ?

innapropriate ?

 

This topic is about the negative torque induced by ground effect and if the 747 should be affected or not because currently it doesn't feel at all

 

It gets better: All of these effects are reversed when landing. In other words, when we least want a reduced indicated airspeed, a nose-down moment, or a decrease in drag and thrust, that’s what we get. It’s no wonder primary students can have trouble with their landings.

 

source : http://www.aviationsafetymagazine.com/issues/35_10/features/Using-Ground-Effect_11069-1.html

Share this post


Link to post
Share on other sites
4 minutes ago, cmbaviator said:

I mostly fly A320 or B737-300 on Xplane, you usually retard at 20-30 feets, i was wondering if its the same for the 747 or you should retard between 30-40 fts ?

innapropriate ?

Yes, inappropriate. Granted, English may not be your primary language, so I will grant that you might not have intended it, but the thread title comes across as "your plane is incorrect," while your post itself contains many questions that show that your experience does not match up with the claim of the thread title.

To me, it is inappropriate to make an assertion from the point of limited experience. I don't fly helicopters. I'm not going to open a thread about a helo simulation and question its accuracy for something this specific. Moreover, I'm not going to cite generic sources (and yours was written for single-engine GA pilots, largely).

Try using the information you have cited to land the MD-11, for example. Aircraft all follow the basic laws of aviation, but to lump them all into this idea that "a plane is a plane, and they'll all follow this random article I've quoted" goes against the laws of physics, and the facts of the situation. Why, for example, might one have to get a type rating for different types of aircraft? The answer is not only related to how the systems are set up, or the buttons on the flight deck - it's because planes have different flight characteristics, as well.

If you were to quote an article about mastering stalls in aircraft, and then go up in a 747 to attempt to use that same knowledge, you'd find yourself having a bad day, very quickly.

Share this post


Link to post
Share on other sites

i'm not asserting, I'm just asking if it's normal or not to not feel the nose down effect in 747 heavy during flare, it's a question and i'm just expecting developpers or real pilot to confirm it or not.

 

 

 

Share this post


Link to post
Share on other sites

In a General aviation single engine prop (C172 for example) you flare by holding the airplane a few inches off the ground and basically let it stall.

You can‘t do that with a 200 tons airliner. 

30 ft is ok to „close the throttle“ respectively retard the thrust levers. But don‘t wait the airspeed to slow down, it won‘t do that enough. This airplane is sluggish. You will run out of runway before it sits down by itself.

rather fly it on the ground. To flare an airliner means you don‘t stall it but you simply reduce the decent rate. Check your speed being at Vref moments before touch down when you close the throttles, then lift the nose a bit, however, fly it onto the runway, when touched down, your spoilers will deploy, your autobrakes will kick in, your lift is destroyed, now fly the nose down to the ground. Push. Thats all.

 

happy landings

Share this post


Link to post
Share on other sites

The 747 is a very different beast to to the 737 in terms of flying characteristics -- the Jumbo is, by and large, extremely stable and surprisingly responsive for an aeroplane of its size. When it comes to control inputs less, generally, is more, particularly in the roll axis.

The one area I think may be lacking a little in the PMDG model is the thrust-pitch couple -- my understanding of the real thing is that there is quite a strong coupling (i.e. if you reduce thrust the nose should pitch down quite positively and vice versa) which isn't really replicated well in FS as a whole.

However, that said if you are asking why you floated, the answer is quite simple: not so much a late reduction of thrust as too much flare. The pitch change in the flare in the 747 is really quite tiny -- only about two degrees at the most, which is just barely enough to determine that the pitch has changed at all (i.e. the exact moment you see the horizon move down relative to the top of the glareshield -- that's about two degrees and you should stop there!). In your video, if you look at the ADI you will see your pitch change is closer to 4 degrees -- i.e. nearly double the recommended amount.

The FCTM contains full details of the recommended technique.

  • Like 2

Share this post


Link to post
Share on other sites
8 minutes ago, skelsey said:

is the thrust-pitch couple -- my understanding of the real thing is that there is quite a strong coupling (i.e. if you reduce thrust the nose should pitch down quite positively

Isn‘t that obsolete with the fly by wire in the -8 and 777/787?

Share this post


Link to post
Share on other sites
1 minute ago, Ephedrin said:

Isn‘t that obsolete with the fly by wire in the -8 and 777/787?

Probably! Sorry, I always forget that this forum includes questions about the -8 -- comments above reference the -400 :).

Share this post


Link to post
Share on other sites
5 minutes ago, Ephedrin said:

Isn‘t that obsolete with the fly by wire in the -8 and 777/787?

The -8 isn't FBW...

Share this post


Link to post
Share on other sites

Thank you for your inputs.

I may  have over pitched up as i thought i may need to hold more back pressure to counteract the pitch down moment (main subject of this topic)  normally induced during ground effect

Share this post


Link to post
Share on other sites
1 hour ago, scandinavian13 said:

The -8 isn't FBW...

I‘ve just read about the 748. I was pretty wrong about it, I really thought it was fbw, brought to the standard of the 777... so basically it has the same flight controls as the 744... I wonder why it feels so different from the 744. since I thought it was fbw I flew it just like the 777 and there wasn‘t much difference. I didn‘t notice a change of the pitch and bank when I didn‘t touch the yoke. Is it just that stable? 

Share this post


Link to post
Share on other sites
3 minutes ago, Ephedrin said:

Is it just that stable? 

Different wing. Different engines. Longer.

Keep in mind that the 748 was aimed at keeping the type certificate the same. Entirely redesigning the flight control system wouldn't exactly be a good idea for maintaining that kind of commonality. This includes the bleed-based ECS, despite using the GEnx engine developed for the 787, which was designed to be bleedless, but a variant was developed for the 748 - again, commonality.

  • Upvote 1

Share this post


Link to post
Share on other sites
2 minutes ago, Ephedrin said:

I‘ve just read about the 748. I was pretty wrong about it, I really thought it was fbw, brought to the standard of the 777... so basically it has the same flight controls as the 744... I wonder why it feels so different from the 744. since I thought it was fbw I flew it just like the 777 and there wasn‘t much difference. I didn‘t notice a change of the pitch and bank when I didn‘t touch the yoke. Is it just that stable? 

It has a very different wing.  Note how much more fuel the Main 2 & 3 now hold compared to B744.  I would say it has the same controls as the B744, although similar for type rating the outboard ailerons are electronically controlled.. this only affects low speed flight.  The new wing and the longer body no wonder it handles differently.  Kyle beat me.

The OP question about torque effecting a nose down moment due to aerodynamics sounds reminiscent of a discussion I've read here before that is always initiated by someone from the XPlane audience.  Seems to be a thing in that crowd.  It doesn't apply to the B747.

  • Like 1

Share this post


Link to post
Share on other sites
5 minutes ago, downscc said:

The outboard ailerons are electronically controlled..

Then I think that‘s what I read and substituted to the whole airplane.

Share this post


Link to post
Share on other sites

Welcome to my world. I've been writing about this for years. It's not just the 747, it's all aircraft models that use the internal ESP (FSX & P3D) flight model. Flight dynamics during thrust changes and in ground effect are almost non-existent. OEI dynamics are obviously wrong too. Some developers have used external flight model to overcome this. Some others use FBW laws to induce pitch down during the flare

Share this post


Link to post
Share on other sites

It is sometimes easy to forget when engrossed in operating the PMDG B744v3 that it is only a simulation and a pretty good one at that!  Even full sized zero flight time simulators cannot accurately model the exact handling characteristics of a real aircraft.  Very large aircraft like the B747 and Airbus A380 have a lot of inertia and so it takes them longer to respond to any change of thrust, pitch etc than it would for a smaller aircraft such, as a Cessna 172 or B737.  And has already been said, any decent aircraft addon like PMDG's QOTS B744 and their latest -8 are bound to be affected by the limitations of the actual simulator platforms themselves.   

When carrying out a manual landing in the QOTS B744 the flare should be initiated at approximately 30ft above the runway; increasing the pitch attitude slightly by approx 2 degrees and then smoothly reducing the thrust to idle whilst holding the pitch attitude constant to counteract the simulated nose-down pitch tendency.  The aircraft should be flown onto the runway and not allowed to float, so don't raise the nose any further or change the trim in any way and simply allow the nosewheel to slowly settle as soon as the mainwheels touch down and the automatic spoilers deploy (don't forget to arm them on the approach!).  If you are having difficulty with the landing technique then try carrying out an automatic landing on the same (CAT III) runway, listen to the Radio Altimeter callouts and watch carefully what happens to the aircraft pitch attitude from 50ft down to the nosewheel touchdown.  It is all a question of numbers, really!

Share this post


Link to post
Share on other sites
20 minutes ago, berts said:

The aircraft should be flown onto the runway and not allowed to float, so don't raise the nose any further or change the trim in any way and simply allow the nosewheel to slowly settle as soon as the mainwheels touch down and the automatic spoilers deploy

My very first Level D experience over 20 years ago was in the 744 (in the “Eddie Allen” for those that know it).  At the time I had around 250 hours TT but in nothing bigger than a Cessna 210. There were many takeaways on that day, but the one that stands out the most was the instructor telling me to get the nose down on the first few landings. For me coming from light aircraft where you want to keep the nose off as long as you can it took conscious effort in the 744 to fly the nose down.

Share this post


Link to post
Share on other sites
1 hour ago, BrianW said:

My very first Level D experience over 20 years ago was in the 744 (in the “Eddie Allen” for those that know it).  At the time I had around 250 hours TT but in nothing bigger than a Cessna 210. There were many takeaways on that day, but the one that stands out the most was the instructor telling me to get the nose down on the first few landings. For me coming from light aircraft where you want to keep the nose off as long as you can it took conscious effort in the 744 to fly the nose down.

Haha - sounds familiar, but the inverse.

I always landed pretty flat in the Chickenhawk. Was nice when I finally moved to the 'nole, 310, and later the Slowtation. No excessive flare. Just kinda set the thing down.

...when I was in the 744 sim, though, I was asked if I was going to flare at all, but I think that was more the fact that I wasn't used the the sight picture of being that high up - oops.

Share this post


Link to post
Share on other sites
22 minutes ago, scandinavian13 said:

...when I was in the 744 sim, though, I was asked if I was going to flare at all, but I think that was more the fact that I wasn't used the the sight picture of being that high up - oops

Kyle, how embarrassing for you! 

To be perfectly honest, I bet every pilot has been there and misjudged the flare at one time or another.  And when it happens it certainly doesn't need a member of the cabin crew to come onto the Flight Deck with a watering can saying "Now you've planted it you might as well water it"  to tell you so!

Edited by berts

Share this post


Link to post
Share on other sites

I watched the entire video and the reason that he floated down the runway was due to some of the inherent design features along with the way the aircraft performance data is certified. Basically, all transport category aircraft are designed to be at 50' at Vref with the power at idle in order to land within the touchdown zone ( -250'/+500' of the aiming points ). Any effort to increase the amount of flare is undesirable...A good technique would suggest that at 100' RADALT begin to slowly and smoothly reduce thrust to idle ( Or let the ATS do it's job ) and hold the attitude you flew during the approach with a very slight increase in back pressure to arrest any slight sink developed as a result of the thrust being reduced...This should yield good CONSISTENT results WITHOUT highly undesirable /floatingballooning A BIG NO_NO in a large airplane in particular...Which is the case of the 747-800 like depicted here, SHOULD any ballooning/floating occur an immediate GO-AROUND should be initiated...Also, any thought toward "padding" your speeds is a BIG no-no, because the amount speed increase above the computed Vref/Vac creates an exponentially longer runway length to stop. Large airplanes are designed to be flown "by the numbers" for a reason...It's all about predicted performance and consistent results by the average line pilot. 

Share this post


Link to post
Share on other sites

-8 has a supercritical wing, one of the reasons it has such long-range and can fly at high Mach numbers...

Share this post


Link to post
Share on other sites
28 minutes ago, BE19Pilot said:

-8 has a supercritical wing, one of the reasons it has such long-range and can fly at high Mach numbers...

Welcome to the PMDG forums, please note their rules ask us to sign our full name on all posts.

Is the supercriticality a thing when the wing is in landing configuration?

Share this post


Link to post
Share on other sites
1 hour ago, BE19Pilot said:

at 100' RADALT begin to slowly and smoothly reduce thrust to idle

😨

I can think of quite a lot of (in fact, most) transport category aeroplanes where bringing the thrust to idle at 100R would result in the main gear struts being punched through the wings.

The FCTM guidance, oddly enough, provides consistent results. If you can find a Boeing (or Airbus) manual, or a rated trainer, suggesting retarding the thrust levers at 100R I'd love to see it.

  • Upvote 1

Share this post


Link to post
Share on other sites

Landing a large aircraft like the B744 is not as straightforward as BE19 suggests. Some of his points are no doubt valid for smaller aircraft, but I am reminded of the old saying that “there are as many ways of flying an aircraft as there are instructors”!

What I described earlier is a small part of the recommended landing technique adopted by most, if not all, B744 operators that I know of. There is a large difference between the B744’s wheel base and the increased cockpit height; in fact it is almost double that of the earlier generation of longhaul passenger jet aircraft such as the DC8 and B707. This means that the B744’s main gear will not touch down at the selected visual aiming point and during a typical approach its wheels will cross the runway threshold at about 50ft for all normal glidepath angles. Therefore, in order to ensure a safe threshold clearance the recommended touchdown point for the main gear should be at least 1,000ft down the runway.

As well as remembering to allow for this large difference between the gear height and the pilot’s eye path height, the aircraft’s inertia must also be taken into account on every approach; especially during the commencement of the flare. Reducing the thrust to idle at 100ft RA for a normal, stabilised approach is NOT recommended on the B744. The aircraft could easily end up landing hard as Simon suggests, or even worse landing short with the pilots kissing goodbye to the main gears (and probably their careers) as the wheels and legs depart the aircraft after hitting the runway threshold.

Edited by berts
  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now