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What Exactly Is, "Flying On The Step"?  
User currently offlineMsllsmith From United States of America, joined Feb 2004, 396 posts, RR: 9
Posted (10 years 8 months 1 week 6 days 8 hours ago) and read 10508 times:

This question was prompted when reading a response from SlamClik to a query about B757 cruise speeds.....

"Climb may be performed anywhere down to about L/DMAX but it takes quite a while to climb back up "on the step" after getting the speed so low at altitude."

Is 'flying on the step' max cruise speed/fuel burn efficiency? What?

I am trying to finish up my Flight Dispatch certificate,.... and this made me realize, that although I have heard this phrase forever.... I probably do not understand it.

On one hand, in my ASA test prep there is a question,

"What are the characteristics of an airplane loaded with the CG at the aft limit?"... the answer is, "Lowest stall speed, highest cruise speed, and least stability".... (plus I remember once asking a B747 Cpt. why, when looking at the artificial horizon indicator, it was nose high at cruise altitude.... and he indicated that it was routine to fly 1 or so degrees nose high as it was 'more efficient'...[remember this was when I was a FA and had nothing but time to stand around during long flights and ask questions]....)

On the other hand, I recently came across this quote from an Ernest Gann novel (The Aviator....pub. 1981) , about an airmail pilot flying a Stearman set in 1928....

"...The Kollman altimeter announced he was holding the aircraft steady at 8,000 feet. There was a rate-of-climb instrument with a needle hovering a hair below horizontal. An indication of constant decent. The instrument was lying, provoked by his personal habit of trimming the Stearman slightly nose-heavy and thus gaining a minute advantage in cruising speed."

Granted, comparing a Stearman and a modern jet transport is under the comparing "Apples and chimpanzee" category..... but are both of these scenarios an example of "flying on the step".... and if so, why one nose up and the other nose down?

Thanks,
LLSmith

PS...I've searched the archives here and couldn't find an answer.... hope it's not too redundant.



There's nothing more beautiful than flying into the dawn.
20 replies: All unread, jump to last
 
User currently offlineB747skipper From , joined Dec 1969, posts, RR:
Reply 1, posted (10 years 8 months 1 week 6 days 7 hours ago) and read 10467 times:

Hola LLsmith -
xxx
Aft CG means better fuel savings -
In a 747, we try to achieve a 28-31% CG load, the best for low drag...
Nose heavy, we have to compensate with "trim tail up" = more drag.
Adds up to what the wing has to "carry"...
xxx
Wish I had a classroom board to show you, with the basics 4 forces..
Lift, weight, thrust, drag... takes 90 seconds to enlighten your deficient brains.
xxx
Anyone has an idea about how to explain ('splain) to LLSmith here?
Never done that on the web...
How in hell do you get a WEB INSTRUCTOR certification anyway...
xxx
Time for my Campari - Chao.
Happy contrails -
(s) Skipper


User currently offlineMsllsmith From United States of America, joined Feb 2004, 396 posts, RR: 9
Reply 2, posted (10 years 8 months 1 week 6 days 7 hours ago) and read 10457 times:

Hey, Skipper,

I think I get the drift. When is there a blackboard when you really need it? Its tough being stupid.....so I have to work at it constantly.....

So what is "flying on the step"?

Best,

LLSMith



There's nothing more beautiful than flying into the dawn.
User currently offlineRalgha From United States of America, joined Nov 1999, 1614 posts, RR: 6
Reply 3, posted (10 years 8 months 1 week 6 days 7 hours ago) and read 10449 times:

Wow. I won't have time to write a complete response, but I'm sure others will fill in the holes.

First, the worst, that Stearman thing. The pitch attitude of the airplane has ZERO to do with what the VSI (vertical speed indicator) reads. The VSI in that airplane was reading a hair low because it wasn't calibrated correctly.

Trimming nose-heavy won't give you any advantage in cruise, it will just make the pilot hold the nose up and get tired faster, the horizontal stab. is still producing the same amount of lift. There may or may not be an imperceptable change in drag from the position of the trim tab, this depends on the airplane and configuration.

The pitch attitude of an airplane in level cruise flight is dependent on the type of airplane, the airspeed, the weight, and other things. There is one pitch attitude that will give you level flight at a given airspeed, weight, and configuration. It so happens that the most efficient airspeed to cruise at in the 747 results in a positive pitch attitude.

Flying "on the step" is one of the many myths of aviation. The common argument is that by climbing above the intended cruise altitude, and then diving back down to it, you can cruise at a higher airspeed than if you just leveled out, thus being "on the step". This is complete BS. Rather than delve into a detailed explaination of why this is not true is something I don't have time for right now, but I'll be happy to go into it later if someone else doesn't beat me to it.

Anywho, gotta run now.  Big thumbs up



09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
User currently offlineRalgha From United States of America, joined Nov 1999, 1614 posts, RR: 6
Reply 4, posted (10 years 8 months 1 week 6 days 7 hours ago) and read 10448 times:

One other quick remark. Basically an aft CG results in less fuel burn because your overall induced drag is decreased. The horizontal stabalizer must produce "inverted lift" (lift in the downward direction) to balance the airplane. The further aft the CG is located, the lower the magnitude of this downward lift. This means two things. All lift produces induced drag, so less downward lift means less induced drag from the horizontal stab. Also, any downward lift from the horizontal stab. must be balanced by upward lift from the wing. So, less downward lift means less upward lift, which means less induced drag from the main wing.

Hard to explain only in text, but that's the jist.



09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
User currently offlineJetguy From , joined Dec 1969, posts, RR:
Reply 5, posted (10 years 8 months 1 week 6 days 6 hours ago) and read 10381 times:

"Flying "on the step" is one of the many myths of aviation."

I'm going to play the Devil's advocate here. I fully expect to be shot down by at least one of you "technotypes" out there; but hey, that's never stopped me before. Big grin

There was a time when I told my students that there was no such thing as a "step" - where the airplane performed better, ie cruised faster at a given power setting. Then I flew a Lear (3,000 hours in type). Lears definitely have a "step". Since I last flew a Lear I have accumulated just under 3,500 hours in Gulfstream G100s and I've noticed the same thing and even to a greater degree.

Being from the school of "there ain't no such thing as "the step", I had to try and reconcile what I was seeing with what I had been taught and believed. For what's it's worth, this is the way I explained it to myself...

We all know that for any given power setting, you can maintain two speeds - one lower, the other higher - depending upon which side of the power curve you happen to be on. It's a function of the angle of attack. The same principle applies to large aircraft as well. At altitude, in the "cruise mode" - near the apex of the polar chart - the difference between the two speeds that any given power setting will maintain becomes minimal - but it still exists. It is very visible on the angle or attack indicator.

Granted, we don't climb a few hundred feet above our assigned cruise altitude and dive down to pick up our speed - ATC would take a dim view of the resulting altitude bust. What we do do is maintain climb power until the aircraft has accelerated to the planned cruising Mach or maybe even a scosh faster before pulling the power back to cruise. This has the same effect as climbing above and descending back to the assigned altitude. In the Lear this technique produced a consistent 3 to 5 knot increased TAS, the G100 seems to increase slightly more. The effect is even more evident in the AoA indications.



User currently offlineThirtyEcho From United States of America, joined Dec 2001, 1656 posts, RR: 1
Reply 6, posted (10 years 8 months 1 week 6 days 5 hours ago) and read 10359 times:

Flying "on the step" is a bit like seeing a UFO, you won't believe it, and you'll think it is impossible, until you actually see it. I'm with Jetguy on this because I've seen it many times (and deliberately induced it).

I was taught how to do this by a retired American captain; bear in mind that this guy retired in 1959, so you can see how far back into the dim prehistory of airline flying he went. "Diving" back to altitude is an exaggeration and you don't need to go "a few hundred feet" above your assigned to induce the "step" effect. Bear in mind that this was a routine practice before airliners did much IFR flying (there were whole airlines that were not authorized for IFR, even into the 1950s) and there was no way for radar or a transponder to bust you, anyhow.

I'll grant that Jetguy's practice probably works well with jets, with the big power loading, but propliners and GA singles and twins need a bit of help to get on the step. This is done by climbing slightly above the cruise altitude, holding climb power, and descending back to the cruise altitude before power reduction. The airplane will accelerate above crusing speed and, after the power is reduced, hold about 1/3 of that increase for the rest of the flight. An especially slick airplane might hold half of it.

I first did this in a lowly C172 and went on to make it a practice in Beechcraft and Cessna twins (the Beech 18 did it especially well) and many other airplanes. I no longer do things that way because, as you know, I would never deliberately bust an altitude by even an inch.


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 7, posted (10 years 8 months 1 week 6 days 4 hours ago) and read 10334 times:

First, let me apologize for starting this by the use of that phrase. It is just a thing that you will observe and the explanations may fall short. What you will experience in a swept wing jet will be rather different from what will be done in a straight wing recip transport. Ernie Gann was a great writer but did not log any meaninful jet time. I think that Jetguy and ThirtyEcho did a fine job of explaining it in the two posts above.

As to the forward/aft CG effect on cruise. I will undertake a partial explanation of that. First, we don't simply trim to this condition. We must load for it. We trim for zero net elevator force or hands-off flight.

Let us say we are flying a small jetliner at a weight of 150,000 pounds in cruise flight. We are flying dead level, so how much net lift is being generated by the wings? Well, an amount exactly equal to our weight. Now, move some weight aft. Shift the CG aft by dragging some cargo back or sending all your first class passengers to the back of the plane. (don't try this at home, I am a professional)

The weight being moved aft will make the plane tail heavy. You will have to compensate by trimming the nose down. Well, you can't actually trim the nose down, we don't have canards, so you must trim the tail UP. That means that the 150,000 lbs is being divided between the wings and the horizontal stabilizer. Let's for sake of argument say that the split is 145,000 being carried by the wings and 5,000 lbs being carried by the tail.

Now let's move the weight forward. Upgrade people starting at the rear and fill up first class and get everyone else as far forward as possible.

Now the plane is nose heavy. We will have to trim the nose up. That means we have to trim the tail DOWN. Let's say we got the same amount of shift so we have to develop 5,000 lbs of downforce on the horizontal stabilizer. Guess what? The wings now have to carry their original 150,000 lbs PLUS that five thousand pounds of down force for a total of 155,000 pounds of lift. How do we produce that lift? By increasing the angle of attack all the way across the wing, tip to tip. That has the additional effect of increasing body angle and parasitic drag.

More lift equals more drag. Lift is just drag in an upwards direction.

As Skipper says, it is easier with a board.

I'll leave the explanation of the effect on stability for someone else.






Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineRalgha From United States of America, joined Nov 1999, 1614 posts, RR: 6
Reply 8, posted (10 years 8 months 1 week 6 days 4 hours ago) and read 10317 times:

ThirtyEcho, I'm going to have to disagree with you on that. Jetguy's explaination does hold water and things are different up high. However, I've never seen that effect in light aircraft, high or low altitude. It appears to have a speed boost by diving down to your altitude, but the same airplane with the same power setting eventually reached that same speed without diving. It just takes a long time.

I leave the power at climb power until reaching approximatly cruise speed, then back off to cruise power, but the times that I've immediatly set cruise power, it still reaches the same speed, it just takes forever. Same thing goes for when I've done the dive bit.

There was an article somewhere written about this, but I have no idea where I saw it. If I find it I'll post it.



09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
User currently offlineFlyboySMF2GFK From United States of America, joined Mar 2004, 193 posts, RR: 0
Reply 9, posted (10 years 8 months 1 week 6 days 3 hours ago) and read 10289 times:

One time way back I asked my instructor if we could tilt the seats back and set them to their rear stops during cruise to get a few more knots. Leave any smart remarks at the door  Insane

I'm a fairly heavy guy (too many tacos, no wait, Mom says I'm big-boned) and the instructor wasn't a featherweight but I kid you negative that we got 2 knots on our groundspeed. WHOOOPEEE!!! Sit back up, re-trim and the 2 knots went away. CG plays a big part, but that much displacement on a Warrior makes a lot more difference than if I sat a row back in a 757.


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 10, posted (10 years 8 months 1 week 6 days 2 hours ago) and read 10249 times:

Interesting experiment, but two knots on groundspeed is not significant unless we know what your wind factor was throughout the flight. I sit there and watch the wind fluctuate as much as ten knots from minute to minute on my ND.

We used to do something similar but for a different purpose. When a friend was flying under the hood in a Baron we'd lean forward to watch. When he got it all trimmed out for this, and got distracted by finding an approach plate or something we would slide our seats aft and recline them. Usually good for a good 200 foot altitude gain before he would catch it.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineMsllsmith From United States of America, joined Feb 2004, 396 posts, RR: 9
Reply 11, posted (10 years 8 months 1 week 6 days 1 hour ago) and read 10226 times:

Thanks everybody..... I always figure, if you have a question, ask it.... otherwise you'll never get an answer.

But SlamClick, I've got to tell you, I really loved yours. (the apology really should come from me for starting this) THis is partially tongue in cheek, ..... but it was spoken like a pilot who's had way too many FAs hang around in the Flight Deck and ask those pesky, "How come....?" questions when you'ld rather be reading your latest Formula One magazine. Also, it prompted a stream of consciousness fantasy of, as a FA, trying to casually coerce all the "Big Boned" in the plane to relocate to the aft..... "Excuse me Sir, the Cpt. has requested that you and your extremely fat family move to the rear of plane....you'll be closer to the aft galley..."

But, it was also answered like a former Flight Dispatch teacher. In simple language....with easy to understand analogies.

One of things I like about this site is that the 'heavy hitters' and the 'bright PPs' will jump in and give it a go to answer, regardless of how difficult or stupid the question (I used to have a reliable and non-judgmental aerospace engineer/pilot type to take seemingly simple questions to.... but as he has recently died... and is no longer answering his phone, these questions go to you folks. Congratulations.)

There is still that equally pesky question about the Stearman,....yes, Gann was a terrific writer.... but jet time aside, could there be some reason a Stearman would get better performance out of a nose heavy configuration? From the few hours I've spent in the forward seat of a Stearman, I can see visibility (?)... or could it be the configuration of the wings on a tailwheel a/c (?).... or.... also since the airmail carried their load (even when they were not shipping bricks first class to fool the feds... for extra cash) forward of the pilot, would that effect the trimming of it? It would seem to do the reverse? (as an aside....I know there were two versions of the Stearman....but had always thought of it as a Military trainer.... and thought it was designed in the early thirties...)

Perhaps, one of you antique plane guys with bi-plane time could chew in this a while.

Thanks again,
LLSmith



There's nothing more beautiful than flying into the dawn.
User currently offlineFlyboySMF2GFK From United States of America, joined Mar 2004, 193 posts, RR: 0
Reply 12, posted (10 years 8 months 1 week 5 days 22 hours ago) and read 10166 times:

Slam,

You're right! I probably looked at the IAS and noticed the increase there, too, but I only specifically remember the GS readout. Something about big orange numbers...



User currently offlineB747skipper From , joined Dec 1969, posts, RR:
Reply 13, posted (10 years 8 months 1 week 5 days 17 hours ago) and read 10122 times:

Dear SlamClick -
xxx
Thanks a bunch for providing a written explanation of forward/aft CG and effect on drag, I could not figure a way to explain it as well as you did, as a matter of fact I printed your text, I will probably use it in the future if I am required to write a text with my little diagram of arrows on a classroom board.
xxx
Now as to stability... I take my turn for the explanation.
xxx
Aft CG or forward CG, difference in stability.
In simple words, visualize your CG moving forward (nose heavy airplane).
First consequence, more "weight on the wing" = HIGHER STALL SPEED...
Second consequence, longer arm to tail fin from CG (where the YAW AXIS is) = LOWER VMCA speed.
Third consequence, in stall, may recover better (nose heavy) = nose falls down first.
Fourth consequence, more induced drag (weight on wings) = higher fuel flow.
But shall we say the main consequence is "MORE STABILITY" -
xxx
Now move the CG aft (tail heavy airplane).
First consequence, less induced drag = fuel economy.
Second consequence, shorter arm from CG to tail fin (higher VMCA - not good).
Third consequence, less weight on the wing = LOWER STALL SPEED...
Fourth consequence, in stall, tail heavy, does not help nose to fall and recover airspeed.
xxx
Notice that in FAR 25, certification of airplanes -
Flight tests for demonstration of VMCA speed is done with AFT CG (the most detrimental CG).
Flight tests for demonstration of stall speeds is done with FORWARD CG (gives you higher stall speed).
xxx
Our friends studying, even PPL exams, should know the above theory.
And know the explanations of why this and why that.
xxx
Happy contrails - Thanks for the assistance of the Tech.Ops "Team"...
(s) Skipper



User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 14, posted (10 years 8 months 1 week 5 days 13 hours ago) and read 10070 times:

B747Skipper thanks for the kind words and the stability explanation. I've always thought about it in terms of skiing. Weight aft - better speed, less stability; weight forward less speed, more control. Of course I knew that it was not for the same reasons and besides I fly like I ski - that "control" thing is overrated and nowhere near as much fun as the speed!

LLSmith you are right about there being two "stearman" aircraft and beyond the superficialities, they are not very much alike. The one everyone knows is actually the Boeing 75 Kaydet that was always called after its designer Lloyd C. Stearman.

Stearman founded his own aircraft company, moved it to Wichita and eventually sold to Boeing. I don't know if he went with it, but he eventually wound up working for Kelly Johnson at Lockheed.

The Boeing 75 was not a great design for carrying loads. It had a fairly symmetrical wing section which made it good as a trainer - it flew pretty well inverted. The cropdusters used them because they were cheap and plentiful. I've heard stories about buying them "by the acre" from boneyards where they stood upended on their firewalls like a formation of air corps cadets.

For dusting they usually changed the wings as soon as they could afford to, with Vern's or Leo Smith Ruleto wings carrying far heavier loads. The Navy's N3N started with a flat-bottom wing. The Stearman had ailerons only on the lower wing.

The original "Stearman" (don't know any model numbers) is quite a different airplane. It has the familiar flat-bottom airfoil, or at least more so than the trainer. The lower wing is quite a bit shorter than the upper and the overall design is not quite so modern as the Boeing 75. I also believe that it has two seats in the forward hole and one in the aft, similar the the Waco.

The Cadillac dealer in Reno has one of the originals. I've been told that it is the very plane he soloed back in the '30s which he bought after he became prosperous. Nice story. It is a beautiful airplane. I want one! Anyway I am pretty sure this is the model Gann would have been describing. I've read all of Gann's books including "The trouble with Lazy Ethel" which I may be the only person to have read. I just don't remember the passage cited.

Airflow issues surrounding a biplane are beyond my meager and much-forgotten education. It's not like designing airplanes was an exact science back then. The VSI reading may have just been the product of improper placement of the static port. The airspeed indications likewise have little more than election-year credibility. The upper wing usually carried more of the load than the lower. The airflow from one likely impinged in some way on the other. Then there is propwash and drag from struts and wires. Sorry, not even going to hazard a guess on this one.






Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 15, posted (10 years 8 months 1 week 5 days 13 hours ago) and read 10048 times:

Having flown DC-3's, DC-6's and Lockheed Constellations in the past, can say that ALL of these aircraft were climbed slightly high (100-200 feet), then descended slowly to the desired cruise altitude, while maintaining climb power.
Once level at altitude, reduce to cruise power (approximately 50% BHP) and adjust mixture to autolean, close cowl flaps and oil shutters as needed...presto, time for coffee.

ANY other method of level off at the desired cruise altitude took MUCH longer to reach the desired cruise speed, simply because these aircraft, as well as many older turboprops (F.27/FH227's for example) did not have excess power at higher altitudes, unlike many turbofan powered aircraft today.


User currently offlineMsllsmith From United States of America, joined Feb 2004, 396 posts, RR: 9
Reply 16, posted (10 years 8 months 1 week 5 days 12 hours ago) and read 10032 times:

Thanks Skipper,

I've really enjoyed watching this unfold. Thanks again to all my on line professors. I figured I pretty much understood this stuff.... and if you believe that, I have a bridge in downtown Manhattan for rent or sale. Made a few diagrams of my own.... It's just so damned interesting!

Thanks again,

LLSmith

(edit) Wow! A girl goes out for a cup of coffee and misses so much.... thanks for the Stearman stuff SlamClick.....talk about inexact science, my father had a great story about being put through his paces by a bunch of old aircraft guys when he as a 23 yr old kid and was sent by Grumman in 1942(?) to Spartan in Tulsa .... these old guys stood around and watched him lay out a wing jig with nothing but a string, a pencil and a ruler....basically. He said he never sweated like that again.... kind of an aviation hazing....by the way, my parents flew across country in a Stearman for their honeymoon....talk about the romance of aviation.  Love
again,
LL



[Edited 2004-03-22 16:26:12]


There's nothing more beautiful than flying into the dawn.
User currently offlineLiamksa From Australia, joined Oct 2001, 308 posts, RR: 0
Reply 17, posted (10 years 8 months 1 week 3 days 21 hours ago) and read 9818 times:

As for flying 'on the step', I believe Jetguy's on the money. For a given power setting there will be two speeds available (ie: the two points on the curve where power available = power required). Being 'on the step' is when you're flying at the higher of the two speeds.

On a video today I saw a demonstration of how to get 'off the step'. The scenario was a CX B747-400 simulator with RB211-524H engines. The aircraft was placed at 40,000' and at a weight which gave a margin of approximately 30-40kts between the stall and high speed buffet. At a speed ~ 10kts below the high speed buffet the thrust was reduced, decellerating in level flight until the onset of the pre-stall buffet. By this time the aircraft had gone past the lower speed at which level flight could have been maintained with the initial power setting (ie: the 'off the step speed'), and was so far up the back side of the power required curve that full power was needed to maintain level flight, and stop the IAS from reducing further.

The only solution was to descend, trading a bit of that potential energy to accelerate the aircraft onto the right side of the drag curve, and then recapture the initial altitude (if you wanted to test your luck in coffin corner).

A very interesting demo which certainly highlights one of the major differences between putting around in a Cessna and high altitude jet transports  Big grin


User currently offlineQantasA332 From Australia, joined Dec 2003, 1500 posts, RR: 25
Reply 18, posted (10 years 8 months 1 week 3 days 19 hours ago) and read 9800 times:

Yes, Jetguy's explanation is excellent. Simply picture a thrust-required curve with thrust available plotted...at a given thrust (available) setting, there are two intersections of the curves. The one further along the 'V' (velocity) axis is the one at which you're "on the step." Interestingly (and, I suppose, quite obviously) this is also the maximum level-flight speed possible. Also, as Jetguy pointed out, the velocity difference between the two speeds/intersections decreases as altitude increases. This continues until there is no difference whatsoever, and no "step flying" is possible.

Sorry to be replying late, and repeating things a bit. I'm no pilot so I had no idea what "flying on the step" actually was, but now that I do know, I find myself back in the familiar realm of aircraft performance...everything's related, eh?

Cheers,
QantasA332


User currently offlineMsllsmith From United States of America, joined Feb 2004, 396 posts, RR: 9
Reply 19, posted (10 years 8 months 1 week 3 days 13 hours ago) and read 9760 times:

Hey, SlamClick,

In reference to your post above and relocating pax. Yesterday morning after boarding the first flight out of LGA a real life CG related pax relocation: It was early, I was tired....don't remember what I was on, didn't care, only made note that both wings and engines seemed to be intact, and there were two folks up front and promptly went to sleep.... shortly before time for closing the door.... ramp agent appears at the front and politely requests 4 pax to volunteer to relocate to the aft of the a/c.....followed by a stampede of 'volunteers'.... an eye opener, and I had a chuckle. Thought you might like this.

LLSmith



There's nothing more beautiful than flying into the dawn.
User currently offlineB747skipper From , joined Dec 1969, posts, RR:
Reply 20, posted (10 years 8 months 1 week 3 days 13 hours ago) and read 9758 times:

Funny about 747 passenger a/c and CG...
xxx
Take a passenger aircraft (people)...
If "they fit in the cabin, the CG is all right"...
xxx
We got 390 seats on ours. Suppose we have only 200 of them...
Put the 200 on all the forward seats (and upper deck)...
CG is OK... Move them all to rearmost seats...
CG remains OK... Passengers cannot move 747 out of CG limits.
xxx
Do not try that game with a 747-F cargo plane...
xxx
Happy contrails  Smile
(s) Skipper


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