range, endurance and headwinds

[angelorange]

One argument/rule of thumb as to the best speed (IAS) to fly for best range states:

" fly faster into a headwind and slower with a tailwind"

The logic goes something like this:

If an aeroplane (engine/wing combination) is most efficient at say 300 kts IAS and you encounter (yes OK totally unlikely) a 300 kt headwind then to make any progress at all you need to fly faster - so best range is achieved above the optimum IAS.

Of course for endurance it's another matter.

I was just wondering if this was always true? Most Pilot's Handbooks contain test flight data or theortical information for the best power setting to use in the cruise for a given weight, Altitude and ISA+/- Atmospheric conditions. However the ones I've looked at did not consider wind as a factor.

Then there are differences in how you fly a turboprop compared with a jet.

Any ideas say for a realworld headwind of say 70kts at FL260 in a Turboprop?

Cheers

[411A]

A general rule of thumb is to...

Turboprop, fly a higher airspeed INTO the wind.

With a jet, maintain the relevant LRC mach number, consistant with the inputed (or calculated) enroute winds in the FMS/FMC.

Others may disagree, of course.
And, most likely will.:E

[extreme P]

Keep in mind LRC does not take winds into account. It is always 99% of best still air range. ECON takes winds into consideration and flies faster into a headwind and slower in a tailwind. A book called Aircraft Performance Theory will detail it.

[Piltdown Man]

For a turbo-prop (F50 in my case), I recon that once above about FL140, carry on climbing if the tailwind increases by 6kts per thousand (or more) but stop climbing if the headwind increases by 4kts per thousand (or more). So far I have only ever seen the fuel burn of any flight be directly related to the time spent in the air, not the level I flown (but I have only flown little turbo-props, not big ones - I'm sure an Electra would give different results). However, in most turboprops, you are generally flying flat out anyway - the levers are in the cruise position (or EGT's are set etc.) and you fly at what ever speed the plane gives you. So you don't have the option of going faster, only slower!

The Jets I have flown however, yield different values. Generally, you have to get to a sensible level (say where Vno = Vmo) and then select a level that will optimise specific fuel consumption. If you are stuck at a level, fly faster in a headwind and slower in a tailwind. You can prove this on a graph - but we are only talking of a change of a few knots of airspeed. But as 411A says, the silicon brain is best used for this maths.

[angelorange]

Thanks guys

According to some text books efficient flying (cruise) is based on:
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1. The Airframe Attitude (for a given IAS) independant of aLtitude - (Min Drag Alpha for most wings about 4 degrees). Approx. best IAS for Props is Vmd and for Jets is usually 1.3 Vmd in climb and 1.2 Vmd in cruise. Obviously fuel burn weight reduction affects attitude required / drag and power over time spent in cruise.

2. The Powerplant (differences between Prop and Jet) based on work done and hence TAS. For max range height flown is less important to Props (so F140 to F280 sounds sensible for TPs) but higher the better for Jets.

3. Prevailing Wind - G/S more to do with point 2 above.
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a starting point at least!

[Phil Squares]

Have 0 experience in turboprops so can't even make a guess on that one.

However, with turbofans, as stated flying faster into a headwind and slower in a tailwind is the objective of ECON Cruise. The increase or decrease will be a function of CI.

If you're flying at LRC then headwinds will have no effect on crusie speed. In LRC speed is a function of altitude and weight only.

[Confucius]

On Hercs we would look at the groundspeed/fuel burn equation (on average ~16lb/nm) and then see what would happen to this figure if we climbed, or descended. Unless the change in wind velocity was significant it was pretty much guaranteed climbing, even into a h/w, to cruise or service ceiling was more economical, but bloody slow. I've found it better to descend on more than one occasion, but it was certainly a rare occurrence. Max TAS was about 16K, min fuel burn got better the highewr one went.

Is grinder Charlton still with us?

[bookworm]

I was just wondering if this was always true?

It's always true if you're genuinely looking for maximum range. If you've found the still-air optimum endurance speed, and consider flying the same speed in a headwind, then an infinitesimal increase in speed will always make an infinitesimal increase in range. Increase your infinitesimals until you find the new optimum...

However, the magnitude of the effect may turn out to be very small, both in terms of the speed increase required, and in particularly in terms of the practical increase in range. So the value of making this an operational policy is questionable.

[747dieseldude]

Since I don't have FMS with ECON in my diesel, the rule of thumb we use,
is for every 10 kt add/reduce 0.001M.