What is the best speed for aircraft to fly in terms of fuel economy ?

Answer 1

Parked on the runway with the engines off.

Answer 2

This is a simple question that has created a lot of crazy answers above. There are two terms to become familiar with when speaking of fuel economy and airplanes: Maximum Range and Maximum Endurance. Max Range is simply the most distance for a given amount of fuel. Max Endurance is the most time for a given amount of fuel. Max Range is always faster than Max Endurance. Max Endurance is always at a higher AoA, than Max Range. Both of these speeds decrease with weight and generally increase with altitude. Hope this helps.

Answer 3

I cannot believe that out of 13 answers above, no one even came close to answering your question properly and most answers were based on guessing and assumptions.

Okay lets assume it's a perfect, standard day with no wind.
I assume you are not a pilot so I will explain briefly two things. You have two types of drag affecting the aircraft.
1) Parasite drag, increases with airspeed (thats the one generally caused by the shape of the aircraft)
2) Lift induced drag, decreases with airspeed (that is the one caused by the wings when they produce lift)

If it doesn't make sense to you, how Lift induced drag can actually decrease with increasing airspeed, well consider that to maintain level flight at a lower speed you have to pitch the nose up and maintain a higher angle of attack, which introduces a larger area of the wing and that causes more drag. Similarly the faster you go the smaller the angle of attack, hence less Lift Induced drag.

Now, if you add both Parasite Drag and Lift Induced Drag, and you plot them on a "Total Drag vs Airspeed" graph, you will have high total drag at low airspeeds (due to Lift Induced Drag), then it will decrease as speed is gained to a minimum value (lowest point) and then start to increase again (this time due to Parasite Drag). At that lowest point you will find the Vmd, or Minumum Drag Speed. Theoratically that speed should give you the best range, but in reality the best range speed is slightly higher than that. Right after the Vmd for a small increase of speed the Fuel Flow increases with a proportional value, so that would give you a the Vmr, or Maximum Range Speed. Maximum range also equals best fuel consumption, which answers your question.

So in summary the best speed for fuel economy is slightly higher than the minimum drag speed. It is not usually published in light aircraft manuals, but in largeer planes and airliners it is published as Vmr. Also note that of course the higher you go the higher Vmr will become, therefore it will give you even better range.

Your question is very good, but very difficult to answer. During pilot training, all these issues are mostly explained with the exclusive use of many graphs, which make it easier to understand. So it was very hard for me to put it into words, without showing you all the graphs, but I hope you get it.

There is unfortunately no simple unswer to your question. This is the only way to explain it and not many people above me got even close. Somebody even mentioned Vy.....thats the best climb speed and has less than nothing to do with cruise speeds. I hope this all helps. Read it a couple of times till it makes sense. Good luck!!!

Answer 4

Best fuel economy is usually much slower than normal cruise speeds. Typically it's near the best glide speed for the aircraft or if you have an AOA it's around .35 Yes flying higher will give you better economy so you have to pick an altitude first but once you've determined what altitude to fly at slowing until your indicated airspeed is near best glide will usually give the best SFC (specific fuel consumption in miles/pound of fuel). In the airplane I fly best cruise speed is obtained around 33,000 feet where I can get about 390KTAS with an SFC of about .37 nm/lb. If I slow to about 280KTAS I'll get an SFC of about .47 nm/lb. That's a significant improvement if I'm not in a hurry. Unfortunately Max cruise and Max range are 2 very diffent speeds.

Answer 5

I fly a sailplane so I therefore get excellent fuel economy. I can fly for several hours on a good day with only a couple of gallons expended in the tow.

Answer 6

Interesting question. Most commercial jets operate near the coffin corner, not far above their minimum clean air speed, not far below their maximum mach number and on high power. The engines burn less fuel in the cold thin air at high altitude and the ground speed is higher for a given air speed. 250KIAS at 45,000 feet is something like M0.9 and 500kts ground speed. Most jets cruise at M0.8-0.9, some a little slower and few a little higher.

Answer 7

Hmmm, interesting. Well from my experience on MS-FlightSim, I get very good mileage from my Learjet-45 and B737-400 by flying them the following ways:

B737-400:
This airplane -they say- is supposed to cruise between 35,000-37,000ft @ Mach 0.74 but I fly mine at 40,000ft@Mach 0.76
This allows me to enjoy fuel flows in the range of 250lbs/hr and below. I reckon that if I want to fly as high as 45,000ft+, I'd have to fly faster or the thinner air at Mach 0.76 would'nt give my wings the support they need to allow me to cruise with a nose pitch of 1-degree angle-of-attack...what I'm convinced is the best possible for good mileage without over-tasking "altitude-hold" by the MCP.

Learjet-45:
I go for 47,000ft @ Mach 0.78 on long flights, trying to secure 51,000ft isn't easy. I've only managed getting there twice or thrice and noticed that anything slower than Mach 0.77 gets my nose higher or sees me loosing altitude in a sneaky way.

Bottom line:
On your IAS dial, avoid the "barber pole". Flying on it raises your SFC as the air starts getting too thick for your plane to fly through. On the other hand, flying too far "under" the barber pole either leaves your nose pitched too high or your plane on a sneaky loss of altitude. Outside all the math, you should go for a speed which is furthest beneath the "barber pole" that allows your plane's nose to maintain 1-degree AoA.

Answer 8

There are 4 cases.....Jet and Prop, Range and Endurance.
If you want to travel for example from Paris to New York you are interested to the max range speed, if you want to stay in flight for example for 1 hour(consuming the less fuel possible)you are interested to fly at max endurance speed.
Prop and Jet planes are different because jet engines produce thrust while prop engines produce power.
JET PROP
max.endurance min. drag speed min. power required speed
max.range min. (drag/speed) speed min. drag speed

max range speed for props is the same condition of max endurance for jets....this because power required/speed is equal to drag.
max endurance speeds are slower than max range speeds...
and the fact that max range for props is equal to max endurance for jets shows you that props are better to fly slow and jets are better to fly faster...
To know these speeds for an actual airplane you need to know the drag vs speed or power required vs speed diagrams....or you can obtain these knowing the polar and with a lot of calculations...

Answer 9

It depends on the winds aloft, if you are fighting a head wind, higher power settings and faster speeds. If you are enjoying a tailwind, then lower power settings and slower speeds give you the best range

Answer 10

Obviously you know NOTHING about flying a plane.

You fly fast enough to get the plane "on the step" then adjust the mixture back to just before the engine(s) quit. Speed is relative... you are not driving a CAR... you are flying a PLANE and they are not the same when it comes to economy.

Answer 11

It depends on the aircraft. The most economical speed is often indicated as an aircraft's "cruising speed" relative to a "cruising altitude".