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Why Can The 737-200 Shorter Runways Than 737 NGs?  
User currently offlineMozart From Luxembourg, joined Aug 2003, 2152 posts, RR: 13
Posted (10 years 3 months 1 week 5 days 22 hours ago) and read 7775 times:

I read in several posts that the 737-200 has a better performance on short runways. AS uses it to do "difficult" airports like Dutch Harbour.

Not knowing Dutch Harbour or any circumstances that make an airport require a 737-200, I was wondering what it is that makes the 737-200 better suited?

THanks to anyone who has the patience to explain this to me in "simple terms" (not a pilot myself).

Cheers

28 replies: All unread, showing first 25:
 
User currently offlineQantasA332 From Australia, joined Dec 2003, 1500 posts, RR: 26
Reply 1, posted (10 years 3 months 1 week 5 days 22 hours ago) and read 7723 times:

I believe the 732's better performance on short runways is due to it being much lighter than any 737NGs...less weight, less inertia...simple as that, I think...

qantasA332


User currently offlineAloges From Germany, joined Jan 2006, 8617 posts, RR: 43
Reply 2, posted (10 years 3 months 1 week 5 days 18 hours ago) and read 7640 times:

One important bit is landing performance.

The 737-200 is better suited for landing on short runways because all of the air that flows through its engines can be reversed by its bucket-type reversers. The cascade reversers on the 737NG engines can only reverse bypass/fan air, so their performance may be inferior enough to keep the aircraft from landing and stopping safely at places like DUT.



Walk together, talk together all ye peoples of the earth. Then, and only then, shall ye have peace.
User currently offlineSllevin From United States of America, joined Jan 2002, 3376 posts, RR: 6
Reply 3, posted (10 years 3 months 1 week 5 days 17 hours ago) and read 7609 times:

Good point about the buckets, but that can't be the reason, because you must always assume that the reversers don't work when determining landing distances. Just like you always assume a V1 engine failure for takeoff.

I suspect it's the lighter weight.

Steve


User currently offlineSlamclick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 4, posted (10 years 3 months 1 week 5 days 16 hours ago) and read 7580 times:

If Alaska Airlines' use of the 200 at Dutch Harbor is your evidence that it is more capable on short runways you have perhaps drawn the wrong conclusion from that.

AS uses the 732 in a Combi configuration. They also have the gravel runway kit with vortex interrupters on the engine intakes. Their 732 fleet is ANC based (where MD-80s and the rest of the 737s may be SEA or LAX based) and operates rather like an airline-within-an-airline. I don't know the entire reason they dedicated their remaining 732 fleet to this type of service but I suspect that the gravel runway mods may not be available for the CFM-engined airplanes. Whatever the history there, you may be sure it is not performance-driven.

The CFM engined 737s outperform even the B-737-200 with JT8D-17AR engines. The NG aircraft are even better. They have 18 FEET longer wings, with greater chord. Even at greater gross weight they have light wing loading which, along with thrust loading are the real issues.

And the performance issue is always takeoff. It is never landing length. Any jetliner I've ever flown would land and stop on a runway one third the length it would then require to take off again. Ask yourself, what would be the sense of taking your airplane into an island airport where it could not take off again. What are you going to do, barge it out?

I have taught 737 performance and created 737 performance lessons for 737-300/400 and -700/900. The takeoff and landing performance of the NG aircraft is nothing short of fabulous. The highest density-altitude airport in the AS system is RNO. A 737-700 can land at RNO at maximum certificated landing gross weight (meaning performance issues were not a factor) on the hottest day in RNO history, and do a quick-turn at maximum certificated takeoff gross weight, meaning that brake energy is not an issue for a departure 15 minutes after landing. I don't know another airplane that could do that. Certainly the 732 can not.

Aloha can meet the noise requirements at SNA with an NG and fly to HNL from there. Try that in a 732.

No, performance is certainly not the issue. Believe that it is still the gravel runway mods on the 732 that they keep for the Red Dog Mine strip.






Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineInnocuousFox From United States of America, joined Dec 2003, 2805 posts, RR: 15
Reply 5, posted (10 years 3 months 1 week 5 days 15 hours ago) and read 7542 times:

Damn, dude! I can't add you to my respected user list once you are already there! Sheesh! (Good info, btw!)


Dave Mark - Intrinsic Algorithm - Reducing the world to mathematical equations!
User currently offlineSlamclick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 6, posted (10 years 3 months 1 week 5 days 15 hours ago) and read 7538 times:

Thanks I-fox. I tried to add myself to my own respected user list and was informed that we are not allowed to do that. Hey! Respect yourself!




Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineN243NW From United States of America, joined Jul 2003, 1609 posts, RR: 20
Reply 7, posted (10 years 3 months 1 week 5 days 14 hours ago) and read 7521 times:

Slamclick,
So I am not the only one who has tried that before! Cheers,
-N243NW Big grin



B-52s don't take off. They scare the ground away.
User currently offlineAloges From Germany, joined Jan 2006, 8617 posts, RR: 43
Reply 8, posted (10 years 3 months 1 week 5 days 14 hours ago) and read 7498 times:

Thanks SlamClick, I guess you corrected that little bit of knowledge I had acquired here! What you said makes a lot of sense.

AFAIK, the gravel kits are only available on the 737-200 and the -100*. My guess is that ground clearance is the reason for this, since the vortex dissipators protrude somewhat deeper than the rest of the nacelle, as you can see here:

View Large View Medium
Click here for bigger photo!

Photo © Aaron Hall


* I didn't know about that until I looked it up in the database, here's an example (maybe the only one):

View Large View Medium
Click here for bigger photo!

Photo © Juan Carlos Guerra Aviation Photography of Mexico
View Large View Medium
Click here for bigger photo!

Photo © Jorge Rocafort




Walk together, talk together all ye peoples of the earth. Then, and only then, shall ye have peace.
User currently offlineThrust From United States of America, joined Sep 2003, 2686 posts, RR: 10
Reply 9, posted (10 years 3 months 1 week 5 days 13 hours ago) and read 7487 times:

The 737-200 is better on shorter runways than 737NGs because it is a much lighter aircraft. The PW engines don't weigh as much as the CFM56 engines on the 737NGs. Therefore, since they are lighter aircraft, they can get off the ground much quicker than the 737NGs. Also, the NGs carry heavier loads of fuel, adding further weight to the aircraft. Finally, the majority of the 737NGs carry more passengers than the 737-200s. It's simply just the weight.


Fly one thing; Fly it well
User currently offlineSlamclick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 10, posted (10 years 3 months 1 week 5 days 10 hours ago) and read 7462 times:

Thrust

With only 8 replies before yours, you really should have read them all. The question was already answered with supportable facts. In your reply you made six declarative statements. Five of the six are wrong, the one that is correct leads to an incorrect assumtion.

We were speaking of the Alaska Airlines operation at Dutch Harbor AK.

You Said:

The 737-200 is better on shorter runways than 737NGs because it is a much lighter aircraft.

The F-15 is lighter than the C-130. Does that make it use less runway? There are other factors. (I may say that again.)

The PW engines don't weigh as much as the CFM56 engines on the 737NGs.

True statement. The P&W JT8D weighs a bit over 4500 pounds. The CFM-56-7 weighs about 5200 pounds. That means that if weight was the only issue, the P&W powered airplane could carry seven hundred pounds per engine more than the CFM or a whopping 1400 pounds. But this completely ignores the greater thrust of the CFM, along with a host of other factors.

Therefore, since they are lighter aircraft, they can get off the ground much quicker than the 737NGs.

Getting off the ground "quicker" is not necessarily even desirable with VMCconsiderations. With the same rudder, at lighter weights VMC is generally lower. Again, there are many more factors at work here. The usual takeoff weight limiter is one of the climb gradients required in FAR 25. On a short segment, landing weight plus burnoff to destination often establishes takeoff weight.

Also, the NGs carry heavier loads of fuel, adding further weight to the aircraft.

Dead wrong. In the first place no airline carries more fuel on any given flight than is necessary for the completion of the flight, considering traffic, weather and alternate/reserves. That is; burnoff to destination, plus fuel to alternate if required, plus 45 minutes reserve for domestic flights. Exception would be tankering fuel through a place where fuel was scarce or expensive. No one tankers out of Dutch Harbor. Then the CFM burns a lot less fuel than the JT8D and therefore for the same segment, will require less fuel, not more.

Finally, the majority of the 737NGs carry more passengers than the 737-200s.

The passenger load is the passenger load. The number of people buying tickets out of Dutch Harbor is what drives the passenger load. There may be more seats installed on an NG but (as I said before) there are other factors.

It's simply just the weight.

It is never "just the weight." On a Cessna 150 the weight carried affects the performance. So does the density altitude. So does runway slope. So does runway surface. So does wind. It is never "just the weight"

Don't mean to pick on you here but this forum is generally for people outside of, or new to, the industry to get correct answers to technical questions. The Civil Aviation forum seems to be more tolerant of unsupported or unqualified opinion.







Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineNormalSpeed From , joined Dec 1969, posts, RR:
Reply 11, posted (10 years 3 months 1 week 5 days 9 hours ago) and read 7439 times:

One simple reason: The -200 is cooler.

-Normal


User currently offlineSlamclick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 12, posted (10 years 3 months 1 week 5 days 9 hours ago) and read 7443 times:

NormalSpeed

No argument there. If I flew for AS I believe I'd bid a year or two of that. It is about the last place you can find fun in this profession. And you gotta love the roar of that old Pratt & Whitney.




Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineSkymonster From , joined Dec 1969, posts, RR:
Reply 13, posted (10 years 3 months 1 week 5 days 7 hours ago) and read 7397 times:

Performance is governed by a huge range of factors. For many years, I worked for an airline that operated DC-9s - 10 series and 30 series. The UK CAA insisted that our wet runway stopping distances were calculated without the use of reversers (this meant that performance was still valid with the reversers inoperative, which in some ways wasn't a bad thing). End result of that though was that the -10 series was often more restricted than the much larger and heavier -30 series. The -30 series had leading edge slats and uprated brakes, meaning it was slower over the threshold and its stopping distances were less than the -10 series which had no slats and less efficient brakes. Therefore, we could often operate the -30 into shorter airfields than we could the -10 series. The -10, being a bit of a pocket rocket, was sometimes less restricted outbound, but even that could be an issue due to the "no reversers" aborted takeoff requirement the CAA imposed - the -30 would also on some shorter runways carry a weigh restriction outbound, but usually that wasn't a problem because the sectors involved meant we weren't looking for high fuel loads.

Whilst I appreciate this discussion is about 737s, the above should illustrate why size and weight aren't always the be-all and end-all of aircraft performance.

Andy


User currently offlineMozart From Luxembourg, joined Aug 2003, 2152 posts, RR: 13
Reply 14, posted (10 years 3 months 1 week 5 days 6 hours ago) and read 7380 times:

WOW!!! I am impressed, I really learned something here. Slamclick and Andy, welcome on my list.

Allow to add one more "dummy" question: what EXACTLY does the gravel kit do? And what do the vortex interrupters exactly do?

Thanks guys


User currently offlineSlamclick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 15, posted (10 years 3 months 1 week 5 days 4 hours ago) and read 7351 times:

Mozart

I never flew the 737 with the "off-road" kit. I only know a couple of things about it.

They can use lower-pressure tires with a slightly wider tread and lower sidewall, hence smaller diameter. I don't know if Alaska uses these or not but they are an option and Wein used them, at least some times. These tires do not fully seal the main gearwell and protrude a little bit into the slipstream and I imagine that there is a small climb and cruise penalty for the drag. There is also a gravel/spray deflector for the nose gear.

The other thing, the obvious thing is the vortex interruptor. It appears as a small strut extending below the intake of each engine.

If you ever have the opportunity to see a 737 (or any wing-mounted engine) idling on a wet ramp you will see it generate whirling vortices on the surface of the water and suck it up into the engine. It sort of goes away when the plane starts to move, but at very low speeds or stationary the suction gets pretty strong. Well it is there in the dry too, sucking up gravel and loose debris. This mod uses a bleed-air spray to break up the vortex.

I don't know if there are any other differences with the kit.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineLiamksa From Australia, joined Oct 2001, 308 posts, RR: 0
Reply 16, posted (10 years 3 months 1 week 5 days 3 hours ago) and read 7338 times:

G'day Slamclick

Sorry not related to the original topic but a quick quesiton:

With the same rudder, at lighter weights VMC is generally lower

Is this just due to using de-rates at lighter weights therfore less assymetric thrust to coutner with rudder?

Thanks, Rob.


User currently offlineSllevin From United States of America, joined Jan 2002, 3376 posts, RR: 6
Reply 17, posted (10 years 3 months 1 week 4 days 18 hours ago) and read 7255 times:

Is this just due to using de-rates at lighter weights therfore less assymetric thrust to coutner with rudder?

Not quite sure what your asking, but I'll jump back in...

Vmc is lower at lightler weights because when something weighs less, it's easier to displace. It's the old "an object in motion tends to remain in motion."

Something big and heavy, you lose thrust on one side, it will yaw slowly and ponderously.

Something that's lightweight...well, it reacts much faster to changes and yaws quicker.

Steve


User currently offlineSlamclick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 18, posted (10 years 3 months 1 week 4 days 16 hours ago) and read 7238 times:

Stone the crows! Sllevin beat me to it, fair dinkum.

Liamksa

My responses are usually kept general and aimed at people who are not professional pilots, dispatchers or mechanics. So I did not even mention that the 737 NG also have a vertical fin nearly six feet higher than the classic, with a rudder proportionally longer.

Now I was a marginal student in "bonehead math" but the VMC issue can be understood with geometry. I like to think of a triangle with one point at the Center of Gravity, one at the operative engine and the third at the rudder. Where the CG is a fulcrum on this triangle you put the thrust of the one remaining engine as a force at that point on the triangle and the resistance (due to airload) of the rudder at its point on the triangle and you can see what is at work in the VMC issue.

So you put an engine way out on the wing, like number 1 or 6 on the old B-47 and you have a lot of asymmetry to overcome with the rudder. Add thrust and the de-stabilizing force increases, reduce thrust and it decreases. (I sure wish a lot more light twin pilots could visualize this.) Increase rudder size and more force is available at that corner. Apply rudder trim to remove the load on your leg and you effectively make the rudder smaller and less effective. We can do this because if you increase forward speed you increase airload on the rudder making it more effective.

This triangle model also helps explain the difference between the engine-out characteristics of the MD-80 vs. the 737. It is kind of fun to play with this idea on the board with students. Anyway, I believe that your understanding of the answer to the question you posed lies in that little geometry problem.

regards

Slam



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineTimz From United States of America, joined Sep 1999, 6708 posts, RR: 7
Reply 19, posted (10 years 3 months 1 week 4 days 8 hours ago) and read 7192 times:

Do we have some confusion here on Vmc?

A lower Vmc means control is less of a problem, right? Sllevin makes it sound like lighter aircraft have more trouble staying straight. It's the other way round, isn't it?

Still doesn't explain why, tho.


User currently offlineLiamksa From Australia, joined Oct 2001, 308 posts, RR: 0
Reply 20, posted (10 years 3 months 1 week 4 days 7 hours ago) and read 7174 times:

Thanks to the amount of info out there on the web i'm now more confused than i was to begin with.

Slamclick - I understand everything you wrote

Where i am confused is the effect of weight on Vmc. There are two schools of thought:

1. Vmc increases with an increase in weight
2. Vmc decreases with an increase in weight.

For 1. The factor here seems to be the aircraft's inertia as mentioned by Sllevin. I don't really understand how a change in the weight alone could affect the speed below which directional control cannot be maintained. I think i'm missing something obvious?

For 2. The thoughts out there seem to be that the component of weight used to remove the slip when applying 'five to the live' is greater at higher weights, therefore less work counteracting the assymmetric thrust/drag to be done by the rudder alone. I understand this theory.

Any ideas?  Confused


User currently offlineSlamclick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 21, posted (10 years 3 months 1 week 4 days 6 hours ago) and read 7163 times:

Liamksa

You've got me scratching my head. I do not have immediate access to the performance charts that I need to give your question the answer it deserves. I am going to have to generalize and I do not want to get it wrong. And I hope it was not something I wrote that has me confused.

I am not clear on the role (if any) of gross weight in VMCG or VMCA except for this: The issue, as I understand it is in having V1, VR, and V2 reduced by low gross weight until they are near or below VMC And the problem is in continuing a takeoff after an engine failure with such a low V1, not in rejecting it.

Now to give you more than that I would have to go back and read what I've already written here and I hate to read my own writing.

Does that come close to the answer you were looking for?



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineLiamksa From Australia, joined Oct 2001, 308 posts, RR: 0
Reply 22, posted (10 years 3 months 1 week 1 day ago) and read 7001 times:

Slamclick

As you mention the reduction in V1, Vr and V2 at lighter weights becomes an issue when V1 approaches Vmcg and Vr approaches Vmca.

For certification purposes Vmc is calculated with the "most unfavourable weight". After finding some comments in other forums and articles the consensus seems to be that Vmc increases with a reduction in weight. Reason being the greater horizontal component available with a higher weight when limited to 5 degrees of bank (mentioned above).

Therefore a lighter weight is used for Vmc calculation as it is a control rather than performance issue.

Even still i'd imagine the difference is minimal. When i'm hearing pops and bangs near Vr i'll take the lighter weight any day  Big thumbs up

Rob.


User currently offlineIsmangun From Indonesia, joined Jan 2001, 117 posts, RR: 9
Reply 23, posted (10 years 3 months 1 week 21 hours ago) and read 6990 times:

Back to the -200s on short runways:

If the 737-500s considered as 737-NGs, they can serve -200s roles.
-500s is quite a -400 with shorter fuselage, almost as long as -200s, or you can say -500s are -200s wih CFM56 engines (+improved wings, etc, etc).

Working on limited runway length involved several considerations, including ASD (Accelerate-Stop Distance) and BFL (Balanced-Field Length) which somehow if should you abort T/O you will be able to stop by the end of the runway. These figures interrelates with weight. So I guess there are relationships between -200s (and -500s) weight and short runways.

Cheers,



If it's an Airbus, I'll take the bus...
User currently offlineFilterboy From United Kingdom, joined Dec 2003, 81 posts, RR: 0
Reply 24, posted (10 years 3 months 1 week 20 hours ago) and read 6985 times:

Slamclick

Thank you for your general answers that all us non professional pilots can understand. I will adding you to my respected users list

Anyways I found a photo of an engine test that shows the vortices you were talking about.

View Large View Medium
Click here for bigger photo!

Photo © Pedro



25 Shark : I work for AS. Slamclicks got it right. The main reason for using the -200 in Dutch Harbor and some of the other places in Alaska is the fact that its
26 Pilotpip : I've read that some -200s have screens just ahead of the IGVs, is this true? To add to this discussion, I never really thought that FOD was all that i
27 SlamClick : Filterboy Thanks, that picture is SO cool! And it looks like the ramp is dry so that is just air and the little bit of moisture being whipped out of i
28 MD-90 : As far as Vmc goes, for much smaller aircraft, like your typical Cessna or Piper light or medium twin, Vmc isn't a problem at all at higher weights be
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