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cmbaviator

Too easy to makes greasers? Questions on the ground effect

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Hi guys.

 

Normally the ground effect has mainly 2 effects:

 

* huge amount of lift created, therefore killing some vertical speed. I'm not used to heavy aircraft, been flying mainly the a320 and 737cl, it looks like this effect takes place around 200 feets agl (for the b747) until touch down.

 

* negative torque. As the aircraft comes closer to the ground, a negative torque is applied on the aircraft, well, after 6-7 landing I haven't been able to feel that pitch decreasing, it only decreases when I retard the throttle between 30-40 fts agl.

For me the first effect is greatly implemented but is the second effect implemented ? Or maybe it has marginal effect on a heavy aircraft like the b747??

 

With the IXEG 737cl on Xplane, you can really feel the need to maintain more back pressure to maintain your attitude when you are < 20 fts

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FSX and X-plane has flawed ground effect. FSX has too much while Xplane has too little. As you stated, ground effect will cause a gradual decrease of sink rate about 200 to 300ft per minute loss. An aircraft enters ground effect at a height of half the wing span. Another effect you mentioned is that ground effect will cause the nose to drop. The aircraft when flown properly will be trimmed at REF+5 on approach. Losing the 5 knots as you cross the threshold along with ground effect and speed lost in the flare requires some back pressure to maintain the flare pitch. The IXEG 737 you mentioned had the ground effect issue of xplane engineered out. On another note, the 747 is known to have a cushion effect due to its wing design. My buddies who flew the E-4B said you could grease it with ease.

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FSX and X-plane has flawed ground effect. FSX has too much while Xplane has too little. As you stated, ground effect will cause a gradual decrease of sink rate about 200 to 300ft per minute loss. An aircraft enters ground effect at a height of half the wing span. Another effect you mentioned is that ground effect will cause the nose to drop. The aircraft when flown properly will be trimmed at REF+5 on approach. Losing the 5 knots as you cross the threshold along with ground effect and speed lost in the flare requires some back pressure to maintain the flare pitch. The IXEG 737 you mentioned had the ground effect issue of xplane engineered out. On another note, the 747 is known to have a cushion effect due to its wing design. My buddies who flew the E-4B said you could grease it with ease.

IXEG has tweaked the xplane ground effect model so it should be pretty accurate.

 

 

you can see that when i flare to the correct attitude (5°), the vertical speed is cut rapidly but then i need to hold some back pressure to try maintainning that attitude which is not the case in the B747 in my opinion, currently the B747 behaves the same but without the need to hold some back pressure (in order to maintain that pitch attitude).

 

So i  want to know form PMDG devs if they have modelled that negative torque or not and if not if they plan to do so.

 

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I have never heard anyone complain that an airplane is too easy to land. Theres a first for everything i guess...

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FSX and X-plane has flawed ground effect. FSX has too much while Xplane has too little.

Ground effect in FSX can be modified in the air file, you can make it zero if you want. The problem in FSX is that ground effect is simplified. It only affects lift. There is no pitching moment effect (the " negative torque" Camille refers to). Nor is there a reduction in induced drag. So unless PMDG has added ground effects outside the air file then the pitch effect can't be present in the 747v3.

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I have never heard anyone complain that an airplane is too easy to land. Theres a first for everything i guess...

I didn't said that it is in really life but the way the ground effect has been modelled with the B747 is very easy to land, at 100-50 fts, put yoke at neutral, the ground effect will reduce the V/S to -550-500 and you juste need to retard slowly the throttle at 30 fts and start pitching up slowly and here comes a greaser. For me itsd much harder to land the ixeg B737Cl than the B747, you can see that the pitch is less stable when entering into ground effect compared to a very stable pitch on the B747.

Ground effect in FSX can be modified in the air file, you can make it zero if you want. The problem in FSX is that ground effect is simplified. It only affects lift. There is no pitching moment effect (the " negative torque" Camille refers to). Nor is there a reduction in induced drag. So unless PMDG has added ground effects outside the air file then the pitch effect can't be present in the 747v3.

 

that's why i just want to here a statement from a PMDG Devs. I flied the NGX a lot before the 737CL wnad it was the same thing, looks like there was no negative torque applied to the aircraft. If it's not implemented, it will be nice to have it ^^

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I didn't said that it is in really life but the way the ground effect has been modelled with the B747 is very easy to land, at 100-50 fts, put yoke at neutral, the ground effect will reduce the V/S to -550-500 and you juste need to retard slowly the throttle at 30 fts and start pitching up slowly and here comes a greaser. For me itsd much harder to land the ixeg B737Cl than the B747, you can see that the pitch is less stable when entering into ground effect compared to a very stable pitch on the B747.

 

that's why i just want to here a statement from a PMDG Devs. I flied the NGX a lot before the 737CL wnad it was the same thing, looks like there was no negative torque applied to the aircraft. If it's not implemented, it will be nice to have it ^^

You're comparing to very different airplanes. you're also comparing tow very different simulators.

Saying one plane is easier to land than another and then saying it's modelled wrong doesn't make much sense.

 

The CRJ 200 is much much easier to land than the CRJ 900. They are two different airplanes just like the 747 and 737 which means they will have different techniques.

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Comparing the B737 with a B744?? Pitch and negative torque?  Man, I want some of what you are smoking.

 

Torque is twisting force..., what negative twisting are you talking about?  If the aircraft is demanding slightly more back pressure to hold a pitch while landing it is likely due to the movement of the center of lift vector as ground effect comes into play...so I guess it is a stretch but you could call a pitch axis moment a torque, I guess.

 

To be honest, I don't measure how many degrees of pitch I am holding in a flare and I usually only end up holding a constant pitch angle when i've messed up the landing.  I flare, i land, no holding flare.

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You're comparing to very different airplanes. you're also comparing tow very different simulators.

Saying one plane is easier to land than another and then saying it's modelled wrong doesn't make much sense.

The CRJ 200 is much much easier to land than the CRJ 900. They are two different airplanes just like the 747 and 737 which means they will have different techniques.

I do know that the ground effect affects the planes the same way, there is in my opinion something wrong with the ground effect of the B747 making it easier to land.

 

I only used the comparaison to show the negative torque of the ground effect which is obviously modeled in the IXEG, I'm updating another video of a greaser with the b747, i only had to make very small input to flare, i almost feel like I had to push forward the yoke to avoid floating too much.

 

Anyway I'm just waiting for dev's answer

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I've got a DVD of Cargolux receiving their first 747-400 as it's landing in Luxembourg. Believe me, you won't see it any softer than that, and it didn't look like that was a fluke. I suspect this airplane is very easy to land for quite a number of reasons.

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Anyway I'm just waiting for dev's answer

 

You realize this is a users forum?  For direct contact with PMDG please visit the PMDG Product Support portal at their web site.

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You realize this is a users forum?  For direct contact with PMDG please visit the PMDG Product Support portal at their web site.

Ah okay, thanks for the info

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negative torque

It's a nose down pitching moment. Calling it "negative torque" confuses things.

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Well a former real pilot of the 744 has made a series of tutorials  on youtube for the Aerowinx 744 precision simulator, and one of those videos is a landing tutorial,  and he indeed talks about the reduction in vertical speed below 200ft RA,  but a pitching down moment due to ground effect is not mentioned nor is it visible in the live presentation of the running simulator, the only down pitching moment is due to thrust reduction.

 

Marcel van Santen

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In ground effect the downwash from the wing is reduced. That increases the angle of incidence, and therefore the upward lift, of the stabiliser, which in turn causes a nose down pitching moment. It's all happening dynamically during flare. Speed, pitch and height are all changing. If you need to apply more elevator to flare as the aircraft gets nearer to touchdown it may not be that obvious to the pilot what contributes to what. However the correlation between thrust change and pitch certainly will be.

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