# How much energy is used for lift and for thrust in various aircraft?

1. Aug 27, 2013

### Bararontok

Can somebody post a table of the average lift energy/thrust energy ratios or percentages of various types of aircraft?

2. Aug 27, 2013

### Aero_UoP

lift energy and thrust energy? with units of Joule ? Lift and thrust are forces...

3. Aug 27, 2013

### Bararontok

What I am asking for specifically is the percentage of the power/energy expended by the engine to generate lift and the percentage of the power/energy used to generate thrust for various types of aircraft.

4. Aug 27, 2013

### Aero_UoP

I'm afraid that unlike the wing, engines don't generate lift. They only produce thrust.
Now as for the energy, I think that what you need is the Specific Fuel Consumption. Maybe you can find the sfc for various engines on the internet.

5. Aug 27, 2013

### Bararontok

Of course the engine does not directly generate lift. When it propels an airplane forward, the wings move against the wind and generate a constant difference in air pressure where the pressure underneath the wing is higher than the pressure above it. In the case of a helicopter, the rotating rotor blades basically act like a vertically positioned fan that blows air downwards to generate lift. Forcing the wing to move against the wind to generate the difference in air pressure in an airplane or blowing air downwards with rotor blades in a helicopter both require energy from the engines and what I am asking for is an average percentage of the energy used in the process of lifting the aircraft up and the amount used to produce the forward thrust.

6. Aug 27, 2013

### Aero_UoP

7. Aug 27, 2013

### Bararontok

This might be the information I need in determining the percentage of energy used by the engine to force the wing to overcome drag and generate a constant pressure difference.

http://en.wikipedia.org/wiki/Lift_to_drag_ratio

The tables show the lift already divided by the drag. Now all I need to do is calculate the percentage of energy that the drag and process of creating a constant pressure difference uses up when the engine produces thrust in the case of an airplane and use the same principle in the lift processes of other types of aircraft in addition to factoring in the thrust-weight, thrust-drag, volumetric and specific power density values of various aircraft configurations and get the average of each aircraft then come up with a table comparing the % energy used to produce thrust and the % energy used to generate lift of various aircraft configurations though it would help if such a table is already available.

8. Aug 27, 2013

### Aero_UoP

6 lines, 1 single sentence. What am I supposed to understand from that? This post is quite incomprehensible to me.

9. Aug 27, 2013

### Staff: Mentor

I don't see why l/d ratio isn't already the answer you are looking for...

.....minus the already explained caveat that the question is meaningless as worded.

10. Aug 27, 2013

### Bararontok

It is the answer I am looking for, I just wanted the values expressed as a percentage of the total power/energy used for lift versus the percentage used for forward thrust.

11. Aug 27, 2013

### Aero_UoP

12. Aug 27, 2013

### Bararontok

Yes, I understand now. This value takes into consideration the energy used to overcome drag and the energy required to lift an aircraft of a specific weight to a specific altitude and accelerate it to a specific velocity. Thank you for the information.

The following is a list of links for all of the relevant values:

http://en.wikipedia.org/wiki/Thrust_specific_fuel_consumption
http://en.wikipedia.org/wiki/Thrust-to-weight_ratio
http://en.wikipedia.org/wiki/Lift_to_drag_ratio
http://www.grc.nasa.gov/WWW/k-12/airplane/sfc.html

13. Aug 27, 2013

### Aero_UoP

No prob. You're welcome :)

14. Aug 28, 2013

### Staff: Mentor

Just a little more:
L/D ratio is a percentage. As far as the engine knows, 100% of the energy/force generated goes to countering drag. But a certain percentage of that drag causes lift (yeah, a little sloppily conceived, but basically right...). That's the L/D ratio.

Also, just so we're clear: there is no energy or power consumed by lift in level flight. The force is perpendicular to the direction of motion. But if you find it useful for some reason, you can still use the SFC times L/D in that way.

15. Sep 29, 2013

### skindo

Well, just to be precise, a certain percentage of the thrust would go to countering gravity (when having a downward component) or to accelerating the aircraft downwards (when having an upward component). This includes situations in which the flight is "level" but due to e.g. a large angle of attack during a slow approach, the aircraft maintains a constant altitude but the thrust has a non-negligible vertical component.

16. Oct 7, 2013

### The Jericho

I'm sure It's power to weight ratio that he wants... Weight = lift in straight and steady flight. Find the aircraft mass and max thrust and you get a ballpark figure.

If you want to get a more accurate figure you can find the NACA specs and get the coefficient of lift and by using the lift equation, find v when L = mg and this will tell you the velocity required to create lift equal to the aircraft mass. You can then use the thrust equation for to find calculate the required amount of thrust to maintain that velocity. Is that what you wanted?

Cheers,

The Jericho.

Last edited: Oct 7, 2013
17. Oct 8, 2013

### Bararontok

Yes, the equations you listed here and the previous set of formulas relating lift and thrust are what I wanted. Thank you for this extra information.

18. Jan 5, 2014

### Bararontok

Additionally, is it also possible to divide the lift by the weight to get a lift-to-weight ratio?

19. Jan 5, 2014

### SteamKing

Staff Emeritus
L/W >= 1.0, at least for flying aircraft. If it's the other way, the aircraft won't be flying for long.

20. Jan 5, 2014

### etudiant

Thrust to weight has often been used as a simple metric to rate the agility of fighter aircraft. Over the years, this has crept up, from 0.2 for the early jets to over 1.0 for current designs. Of course, the measure is often inflated by the afterburner contribution, which yields great results for airshows, where fuel is not an issue.
Commercial jets usually run around 0.1-0.2, again overstated because take off thrust is only used for a minute or two and cruise thrust is usually only about 20% of that.