Be easy on me, This is my first post..... Ever,

 

I have a landing/take off distance question. I own the 737 NGX and the 777-200. The 737 NGX uses more runway for Landing and Take off than the 777. The 777 can land less than 4000 feet. Is there something wrong with my install for the 777? I am only assuming being that if it is a heavy the landing distance should be at least double that length.

 

Next question, I was thinking of buying the 747. Is the landing distance more than the 777? When I land I want to feel like it took some effort to stop and I can land the 777 shorter than my friends in a 737.

 

Thanks for any help or manual adjustments that will help.

 

Doug Benware

 

 

I have a landing/take off distance question. I own the 737 NGX and the 777-200. The 737 NGX uses more runway for Landing and Take off than the 777. The 777 can land less than 4000 feet. Is there something wrong with my install for the 777? I am only assuming being that if it is a heavy the landing distance should be at least double that length.

 

Hi, Doug,

 

Welcome to the Avsim and PMDG forums!

 

Your question is very interesting!  I've never directly compared the two landing and takeoff distances.  However, it's not easy to answer because both distances depend upon a number of factors.  I doubt that a fully loaded (max takeoff weight) 777-300ER will take off using less runway than a fully loaded NGX of any type.  Have you compared both fully loaded? 

 

But that assumes everything else being equal.  For example, if either aircraft (same load) takes off w/ a strong headwind it will use up less runway than with no headwind since w/ a headwind it will reach takeoff airspeed sooner.   Likewise, w/ a strong headwind, the landing roll will be shorter due to a slower ground speed at touchdown.

 

If I get a chance, I'll take a look at the performance tables that come w/ both aircraft -- you might want to do the same.

 

Just some things to think about.

 

Mike

 

 

e easy on me, This is my first post..... Ever,

 

Hey Doug - welcome to the forum.

 

This is a good question, but one a lot more complex than one might first assume. Sure the 777 is a larger, and much heavier aircraft, but you have to look a lot deeper than the surface:

 

It's worth mentioning that the 737 has brakes on four wheels (two on each of the mains) to slow it down.  The 777 has three times as much, with twelve.  Sure, it's much larger and heavier, but with twelve wheels with stopping power, you have a lot of energy absorption potential.

 

It's all broken down to the basic F = m * a.  Increases in m result in a larger F to be absorbed.  The 737's autobrake level two gets you about 5 ft/s² of deceleration.  At MLW (-700), that's an absorbed F of 670000 lbf/s².  Assuming four brakes share this load equally, that's 167500 lbf/s² per brake.

 

For the 777, assuming the same 5 ft/s² of deceleration, at MLW (-200LR) that's an absorbed F of 2460000 lbf/s².  Assuming twelve brakes share this load equally, that's 205000 lbf/s² per brake.

 

In the end, the difference is "only" about 37500 lbf/s².  Solving for the equivalent mass, that's only about 7500 pounds of difference per brake.  So, despite the 737 and 777 themselves being 358000 lbs apart (MLWs of 134000 lbs and 492000 lbs, respectively), the individual brakes only see them as 7500 lbs apart.

 

Add to this fact that the 777 brakes have an extra disc compared to the 737 (5 and 4, respectively), you could break it down like this: 737 is 41875 lbf/s² per disc, and the 777 is 41000 lbf/s² per disc.  Since the rim diameter is only about an inch different between the two planes, you could assume the brake disc size is relatively similar enough to dismiss surface area differences.  That 875 lbf/s² difference amounts to an equivalent mass of 175 pounds of difference per pad...or just about the weight of myself.  Not too different when you brake (har har) it all down.

 

 

 

The inverse is true for takeoff performance. Remember that, despite the 777 being significantly heavier, its two GE90s are each the size of the 737's fuselage (in diameter). They put out significantly more thrust, as well.

Excellent Answers.

I guess I shouldn't assume unless I give it a little deeper thought. Thanks for the detailed information, This is why I have bought PMDG software so I can learn and with the added perusing of the forums I am getting what I paid for.

 

Thanks again guys.

 

Doug Benware

The inverse is true for takeoff performance. Remember that, despite the 777 being significantly heavier, its two GE90s are each the size of the 737's fuselage (in diameter). They put out significantly more thrust, as well.

Kyle has given an excellent explanation of braking and takeoff capabilities of the two aircraft. Now I will give you some actual figures. VHHH-KLAX in 777F, 100 tons of cargo, 257000 lbs. of fuel, flaps 5, assumed temperature of 37C, takeoff used about 10000 ft. of 12500 ft. runway. At KLAX I plan on landing on 25L and exiting the runway at taxiway N about two-thirds down an 11000 ft. runway. Amazing takeoff and stopping power.

 

 

Thanks again guys.

 

You're welcome. And thanks for being one of the few who reads the rules (or incidentally managed to sign your posts without reading them). Either way - I'm pretty sure that's a first for me (to not have to point a new person to the 'rules' thread)...so thanks!

In regards to buying the 747, PMDG are working on a new version of the 747 with all the latest advancements of the 777 which you may want to wait for.

Well done, Kyle! An excellent and fulsome answer.

Well done, Kyle! An excellent and fulsome answer.

 

Thanks Richard!

 

Hey Doug - welcome to the forum.

 

This is a good question, but one a lot more complex than one might first assume. Sure the 777 is a larger, and much heavier aircraft, but you have to look a lot deeper than the surface:

 

It's worth mentioning that the 737 has brakes on four wheels (two on each of the mains) to slow it down.  The 777 has three times as much, with twelve.  Sure, it's much larger and heavier, but with twelve wheels with stopping power, you have a lot of energy absorption potential.

 

It's all broken down to the basic F = m * a.  Increases in m result in a larger F to be absorbed.  The 737's autobrake level two gets you about 5 ft/s² of deceleration.  At MLW (-700), that's an absorbed F of 670000 lbf/s².  Assuming four brakes share this load equally, that's 167500 lbf/s² per brake.

 

For the 777, assuming the same 5 ft/s² of deceleration, at MLW (-200LR) that's an absorbed F of 2460000 lbf/s².  Assuming twelve brakes share this load equally, that's 205000 lbf/s² per brake.

 

In the end, the difference is "only" about 37500 lbf/s².  Solving for the equivalent mass, that's only about 7500 pounds of difference per brake.  So, despite the 737 and 777 themselves being 358000 lbs apart (MLWs of 134000 lbs and 492000 lbs, respectively), the individual brakes only see them as 7500 lbs apart.

 

Add to this fact that the 777 brakes have an extra disc compared to the 737 (5 and 4, respectively), you could break it down like this: 737 is 41875 lbf/s² per disc, and the 777 is 41000 lbf/s² per disc.  Since the rim diameter is only about an inch different between the two planes, you could assume the brake disc size is relatively similar enough to dismiss surface area differences.  That 875 lbf/s² difference amounts to an equivalent mass of 175 pounds of difference per pad...or just about the weight of myself.  Not too different when you brake (har har) it all down.

 

 

 

The inverse is true for takeoff performance. Remember that, despite the 777 being significantly heavier, its two GE90s are each the size of the 737's fuselage (in diameter). They put out significantly more thrust, as well.

 

Reassuring to know there are actually people on this forum that know what they are on about.....you're one of the very few Kyle.

One thing that I once became aware of is that, contrarily to what we think after using airliners like the 777 or the 747-400 in FSX, the reversers have a huge effect but only down to around 60 knots, decaying after around 80 knots, and being practically inefficient at taxi speeds or when the aircraft is stopped. They shouldn't actually be used at such low speeds, even less at high reverse power settings, and... even an empty 744 or 777 will not move back on reverse!

 

Older airliners could do it, not this modern high bypass engines...

Wouldn't like to have you for a line check Kyle

 

Alex Dority

Howdy All

 

Great answer from Kyle.

 

Regarding the reversers - remember that if you're using autobrake 2/3/4, reversers are mostly smoke and noise and give you that feeling of being part of a team - but don't make much difference in stopping distance because the autobrakes work on a deceleration rate. So using reversers shouldn't make a lot of difference to distance, just take some load off the wheel brakes.

 

From my 777 line experience and quite a bit of 737 jumpseat time (I have no operational experience int he 737) - the 777 has great braking. Depending on the 737 (most have steel brakes?) - the Carbon Brakes in the 777 also make a significant difference.

 

I went from the A310-300/A300-600R to the B777 many years ago and stopping performance was one of the big changes we saw. So much better in the 777.

 

Ken

 

 

Great answer from Kyle.

 

Thanks Ken!

 

Really appreciate all the 777 line experience we have in here. I've learned a lot from you and a few others, so thanks for sticking around!

Depending on the 737 (most have steel brakes?) - the Carbon Brakes in the 777 also make a significant difference

 

 

In 737NGX have the option to select from both carbon or steel brakes, but I didn't really notice any significant difference in applying breaking force. The only difference is that the carbon breakes has a much longer life then steel brakes because they support and works better at higher temperature.