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How to get the best MPG with a plane?

The best MPG you get :



The elephant is the circulation
ENVA ENOP ENMO, Norway

On a second thought. This is better:

The elephant is the circulation
ENVA ENOP ENMO, Norway

Malibuflyer wrote:

Actual terrain, however, is always so much uneven, that you loose more energy by correcting to keep the right altitude than you save due to ground effect.

You can fly along ridges, not sure if they count as 1000ft agl ground effect on windy days
Yes practically it’s only doable over water but not sure how long one can last without getting tired or exposed to some malfunction?

I recall while doing low flying in Turbulents D31, I only needed about 2000rpm power (vs max 3000rpm) to hit VNE in ground or water effect, it was not intuitive as on takeoffs you tend to accelerate slowly if you set 2000rpm and you may not get past VS0 speed with that power but once you are past some min drag speeds that tiny 300rpm excess of power (it only need about 1700rpm to stay level) will just get things crazy toward VNE in ground effect, I imagine it can be a long 4h flight that is highly efficient even on high power setting and I think the only way to exceed VNE on full power on level flight in the typical SEP is to fly at 2ft agl…

The idea is not new: the only way to reach max range with lot of headwinds (then land beyond crosswinds limits) is to fly faster speed or lower altitude (or both )

It seems some did use this in practice !

Edits: funny LeSving shared the same video at the same time :)

“Ekranoplanes” but they were hard to fly as hand flown all the time


“Camels on final”, this was really a stretch of gliding to max range and max speed !


Last Edited by Ibra at 26 Nov 15:27
Paris/Essex, France/UK, United Kingdom

Malibuflyer wrote:

I’d argue it is very theoretic as the only surface that is “level” enough to actually do this is water w/o any significant waves

I do it regularly in my flying boat when crossing the lake, or in my 150 over the ice in the winter. It is vital though, that the surface have texture, so you can know your height. Unbroken snow, or glassy water is not safely possible. I also have done it over the tundra of the arctic, when MPG was vital, though I agree, control inputs must be kept to a minimum.

Home runway, in central Ontario, Canada, Canada

I think I’ve seen this or a similar article before, but I guess the very important part is this one:

Vmax endurance = Best Glide Speed/1.316

Vmax range = Best Glide Speed

Voptimum cruise = (Best Glide Speed) * 1.316

Ok, we are talking IAS here, that is important.

So if I look at it using the Vbg of my plane of 93 KIAS I’d get:

Vmax endurance = Best Glide Speed/1.316 = 70 KIAS

Vmax range = Best Glide Speed = 93 KIAS

Voptimum cruise = (Best Glide Speed) * 1.316 = 122 KIAS

So obviously the question arises, what is that in TAS at altitude for Vmax range and V optimum cruise? (it’s hardly relevant for max endurance)

With ISA conditions, I’d get the following for IAS/KTAS 7000 ft / KTAS 10’000 ft / KTAS 15000 ft

Vmax range = 93 KIAS / 104 KTAS / 109 KTAS / 118 KTAS

Voptimum cruise = 122 KIAS / 135 KTAS / 142 KTAS / 154 KTAS

The obvious question will be, if you can actually achieve V optimum cruise in a non turbocharged airplane at 15000 ft. Otherwise, 135 kt at 7000 and 142 kt at 10’000 ft sounds quite familiar for long range cruise and 65% cruise respectively. Maximum cruise at 15000 ft however would be 140 KTAS.

Max range corresponds to an 1800 RPM long range cruise I’ve never tried before, but which yields indeed the best range at exactly the speeds calculated above.

I’d have to try max endurance once to figure out what kind of fuel flow that would yield and consequently how long the plane could stay airborne.

Interesting calculations anyhow.

LSZH(work) LSZF (GA base), Switzerland

The good thing about Vopt cruise is the resulting MPG will be higher and not very sensitive to the altitude you choose to cruise at or your climb/descent profile: anyway you will need a high power setting in climb to maintain it, low power setting in descent and medium power setting in cruise

This is more “MPG optimal” than climbing at slow speed, cruise at faster speed and descend at high speed, when people say you need to climb to 15kft to get a good TAS & MPG they forget that if flying a 50NM leg it’s not possible, so you need to keep one speed and manage altitude & power…

On 500NM, going for steep climbs to high altitudes on slow speeds is not “MPG efficient”, in theory, if you want best MPG: you have to climb at Vopt on WOT & max RPM power, then keep WOT & low RPM level when ROC is close to zero to keep flying Vopt (maybe it’s about 60% power in NA), then plan to fly descent on zero power at Vopt

I don’t think many of us will do exactly as above, unless they are renting DRY for fuel and paying for TACH hours

Last Edited by Ibra at 26 Nov 22:29
Paris/Essex, France/UK, United Kingdom

SD has this “calculator” where you can find best altitude (along with several other), both with respect to time and fuel. It requires a good input of the data of your plane, garbage in = garbage out. It seems to take into account climb and descent, maybe also wind, but haven’t studied in that detail.

The elephant is the circulation
ENVA ENOP ENMO, Norway

@Mooney_Driver

What is Vopt cruise, as a practical definition?

Vmax range at best glide speed (or slightly faster, since the prop is useful rather than adding drag as in a glide) would appear to be Vopt cruise if the definition of optimum cruise were best MPG.

How are you establishing Vopt cruise as best glide x 1.316? What is optimum about it? As I understand it, the only practical reason to ever fly faster than best glide (or best glide plus a tiny bit) is because you want to get there quicker, and of couse how much quicker one wants to get there is subjective, not quantifiable, and therefore how can you create a defined speed for it?

Same as in our cars, we all ‘cruise’ at 70-80mph because it is a nice compromise between speed and efficiency, rather than at ~50mph which gives best efficiency. This doesn’t mean the 70-80mph is objectively optimum for anything, it’s just a measure of our appetite for burning more fuel than is strictly necessary in order to save time.

One could perhaps attempt to define some point on the efficiency curve where MPG really starts to get poor (perhaps as a proportion of optimum MPG?) but it may look quite different for different conveyances.

EGLM & EGTN

Carson speed Vopt is the on that maximise “Speed*MPG” = “the least wasteful way of wasting fuel”

All efficient speeds one can fly can be optimised as “MPG*V^x” wher x goes from -1 to +2:
- MPG*V^-1 is max endurance and max time achieved at VMS min sink just few kts above stall VS
- MPG*V^0 is max range which gives best MPG and max distance achieved at VBG
- MPG*V^1 is Carson speed which gives best MPG for each extra unit of speed achieved at Vopt
- MPG*V^2 is max level flight cruise speed (drag to maintain level on given MPG goes quadratic) somewhere above VMaxCruise for max structural cruise

One can also argue why not “MPG*V^1.43213” ? Anything x from 0 to 2 is “speed & mpg” efficient…

If one use quadratic curves for drag & fuel flow there will be an appt image 1.3 factor that comes with any x+1 exponent in these speed, VMS= VS+5kts, VBG = 1.3*VMS, VOpt= 1.3*VBG, VMaxCruise=1.3*Vopt

Last Edited by Ibra at 27 Nov 10:14
Paris/Essex, France/UK, United Kingdom

Carson speed is not the best MPG, however. Best MPG should be Vbg but in reality it is higher due to engine efficiency falling at the low power levels involved in Vbg flight.

Administrator
Shoreham EGKA, United Kingdom
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