Classic British Flight Sim

HI all,

I'd like to put forward some of my theories and experiences for extending range in flights on FS (and possibly in real life?) - and how they compare to the 'real thing'.

Here goes:

I'm aware that generally, we want to be going as high and as (reasonably) fast as we can to get mximum efficiency.
My question was/is - how to go about this?

For the purposes of this exercise of course we must assume total airspace clearance with permission to climb/descend and route at will.

I have tested differing climb techniques, but, I find that for a given fuel load, it is very, very hard to compar like with like. For example, a plane loaded with 20% fuel will reach FL350 much more easily than an A/C with more fuel - so trying to vary the climb technique does not work on light loads.

In ideal conditions, it would appear (to me) that an aircraft correctly flown *should* gain maximum range with slightly *less* than maximum TOW. (We will call TOW fuel load only for this exercise).

The above is on the theory that with less weight to lift, to a given height, once at optimum altitude the plane will have roughly the same load, given it has had less effort to get there.

But, assuming a total load, what do we do to extend?

Despite advice and theory saying 'get to FLXXX' quickly, I have found with numerous flights that I can achive hugely greater ranges with the 'slow climb' technique. I will perform a standard takeoff, and once above FL100 trim the aircraft into a 1500fpm climb. Taking the Super 10, I then take this down 50% at FL200, and another 50% at FL250. Once FL300 is reached I level off, and wait until the fuel is down to 70% load. Then I initiate a climb at 100fpm, and leave this until FL 425 is reached when I level off. I have found no other way to extend range further. I find that while the plane may be a little heavy to sneak above FL300 at that weight, it is countered by the fact that 100fpm is such a slight climb that it does not affect speed, and gives optimum endurance.

The descent is calculated at 800fpm with distance to go vs altitude, to FL100 when I self-impose the 250kt restriction and then adjust descent to needs.

This allows a 'clean' descent with reasonable speed.

Does any of this make any sense? :roll:

Sounds a little extreme!

I tried some long range flights in the Trident 2 a couple of years ago, and the cruise climb seems to work best. Get it up as cheaply as possible, reach climb speed (which should be the most efficient) and select climb power, then select IAS hold to climb gently (and reduce fuel flow) as the weight comes off. Much simpler than the manual way, but don't know if it works as well.

Bear in mind that the optimum altitude will vary with weight, so I can't see any advantage in range by setting off with less than maximum fuel. I think...

James

Max range and efficiency are best found by charts. They will list the optimum cruise altitude for a given weight. Ideally you want to level off at or 1000 feet above the optimum level stated depending on your route of flight and then maintain that altitude until the aircraft's weight reduces sufficiently to climb to the next available flight level.

If you don't have charts, establish yourself in the climb at the specified climb speed and hold that until you cannot maintain at least 500fpm of climb while maintaining maximum climb power and climb speed. Then level off until such at time as you can climb to the next flight level at at least 500fpm without going slower than climb speed.

On piston aircraft, the easy way to figure out when it's time to climb is when your pitch is 0 or your pitch trim is 0. Once this occurs, climb again. As most piston airliners are designed to fly level or slightly nose down, you want to climb each time that you go beyond your normal cruise pitch. Jet aircraft are designed to fly with a slight pitch up, so you need to use the 500fpm climb rule instead.

I would think prbably the best person to answer this as far as the VC10 is concerned would be Tonks. However Chris's statment that there are
charts and tables for this is 100% correct. In my real world - we use a computerised flight planning system that is loaded with the aircraft performance
manual (in our case MD8X, JT8D-219 power). besides taking into consideration the planned load it also considers real time windows aloft,ISA and
routing (This is an oversimplification). And derives a best climb speed (not ROC) to the optimum altitude. One of the biggest problems we have in
flight planning are crews who for whatever reason have had the "get as high as you can as fast you can" docrtrine taught to them early. In truth
the best flight profile for just about any jet aircraft on routes of less than 60 mins is a parabolic arc - powering the aircraft to alitltude then basically
closing the throttles and driting back down to destination. On longer flights obviously this is not practiable, and again as Chris stated the preferred
method for long range flights is a "step climb" - climbing to an altitude where the aircraft's rate of climb slows to less than 500 fpm then leveling off
and burning weight down, then stepping up to the next available flight level as the FMS allows - The principle that worked for the Concorde crossing the Atlantic where to all intents and purposes it was in a continous climb almost the entire journey also works for most airliners today. Our company limits cruise to .75M on the MD80s for fuel conservation (the difference between .75 and .78 being no more than 10 -1 5 minutes on a 3-3.5 hours flight - versus 6000 pph fuel flow at .78 and 4800 pph at .75 - a significant saving). Finally on reaching the required flight level in real life (And with some FS models) its possible to
put the aircraft "on the step" this is done by selecting a specific EPR/mach - then trimming the aircraft very slowly nose down - this will result in seeing the
speed remain constant but the fuel flow will start to get less. obviously as the aircraft burns fuel and the CG moves it will require retrimming - Ive watched
"older" Captains do this literally by resting their palm on the trim wheel and gently moving it back and forth until the required fuel flow is attained.


Hope this didnt muddy the waters - as I said as far as the VC10 goes Tonks is the man to answer these questions

Leif ;-)

Thanks for all that guys. Helps a lot. I don't know why, but I'm always reluctant to use speed hold on any aircraft and prefer to trim it out and use the throttles in small doses to keep things to my liking. (probably because some early FS flights I would stall tha AC etc).

With the '10, basically I use climb speed and power to get to 'stage 1' - just about FL 250, then I get the plane stabilised, and go up to 300 around 500 fpm.

After than, I try to maintain around 470 kts, once it creeps up, I use pitch to climb and hold - once I lose a knot or two I then level until speed comes back, and carry on that way - no more than 1-200fpm, throttles 76/77%.

Using the checklist en-route, (with me anyway) range always looks best this way and increases in a shallower climb but more importantly stays there when levelling off. I have tried higher (500fpm) climb rates to get to given altitudes above FL350, and while *in* the climb, the range goes up very quickly, but strangely comes down more quickly as well - and ends up roughly where it would have been on the slower climb!

Obviously this is all FS related fantasy anyway ;-) - but the principles should work as well in 'weather' - which will be my next challenge... :roll:

I'm actually reasonably pleased to see that with a little thought the range can be extended so much. Just goes to show what watching the figures will gain!

On the subject - for 'idling' descents - what is the general descent rate used? I know that any particular plane will settle into it's own 'groove' - but is there a ballpark figure for generality? No exceeding 800-1000 fpm descent for example?

Thanks for that info Tonks, I've got it ready for my next attempt....

I'm getting a little slouchy getting trimmed into the climb and losing some valuable fuel on some practise climbs I've been doing :-(

Think I'll give it a bash with the power climb next

Tonks wrote:

I try to maintain around 470 kts

:o I hope that is TAS and not IAS.....

Tonks

TAS - I need to have a plane to land at the other end :o