How does lift effect delta-v?

[Odielthen]

What is the relationship between Lift and ÃŽâ€V? Is there any kind of a relationship? How is it calculated (on Kerbin and other atmospheres)?

The Wiki page lists the Delta Wing as having 1.9 Lift Generated. There are no units or other explanation that I could find!

I am trying to create more efficient space planes, but I'm not able to do much engineering design. It involves too much trial and error for me at the moment.

I run completely stock KSP.

Thanks!

Edit: Thank you all very much for your insight! I truly have learned a lot from this!

Edited February 18, 2014 by Odielthen
My question has been answered!

[UmbralRaptor]

Lift can affect ÃŽâ€V requirements (increasing them outside of infiniglider abuse), but can't be directly included in the rocket equation.

For efficient stock spaceplanes, it's about having lots of intake area, a good TWR, and a wing layout that lets you fly with a low AoA. Beyond that, the lolhuge effective Isp and suspiciously good TWR of the stock turbojet does wonders.

[Jimbimbibble]

To clarify, wings can never directly increase your velocity, but the reason you get so much more dV with spaceplanes is that you can gain a lot of altitude with an air breathing engine before switching to rockets. It's the engine efficiency, not lift that gives you the benefit. Wings add mass and drag, so don't add a bunch of them. Just use what you need to get up to 20-25km and let the rockets take you the rest of the way.

[KerbMav]

On a similar note:

If turning a rocket at the 90° marker "safes" dV because we take the rotation of the planet with us, would taking off with a plane at 270° (from the other side of the runway than planes are deployed normally) gain us airspeed because of the atmosphere rotating towards the plane?

[TheHolm]

Wings can greatly increase deltaV by providing a lift to compensate a gravity pull. For each Newton of drag they generates 1.9 Newtons of lift if placed correctly.The biggest problem is that it very hard to build effective plane and even harder to properly pilot it.

[Claw]

On a similar note:

If turning a rocket at the 90° marker "safes" dV because we take the rotation of the planet with us, would taking off with a plane at 270° (from the other side of the runway than planes are deployed normally) gain us airspeed because of the atmosphere rotating towards the plane?

No. Your surface speed will be faster for a given orbital speed, but you will find it's harder to get orbital velocity with a TurboJet going west than going east. These numbers aren't exact, but if you're going 2200m/s surface speed eastbound, you're going >2300m/s orbital. If you are going 2200m/s surface speed westbound, you're going <2100m/s orbital.

[Claw]

Wings can greatly increase deltaV by providing a lift to compensate a gravity pull. For each Newton of drag they generates 1.9 Newtons of lift if placed correctly.The biggest problem is that it very hard to build effective plane and even harder to properly pilot it.

The concept here is correct, but the numbers aren't. Wings can aid in lowering deltaV requirements because of a variety of things they enable. Such as taking off with a TWR of < 1.0.

However, they do not generate 1 newton of drag for every 1.9 newtons of lift. It isn't a direct correlation like that. The lift equation increases lift produced until about 25 AoA, at which point the lift force generated begins to decrease. The induced drag caused by the wing increases as a cosine which will peak out at 90 AoA.

The raw drag value of the part is also misleading. There is inherent parasite drag due to the part, but KSP's current drag model is a weighted scheme.

[Claw]

What is the relationship between Lift and ÃŽâ€V? Is there any kind of a relationship? How is it calculated (on Kerbin and other atmospheres)?

The Wiki page lists the Delta Wing as having 1.9 Lift Generated. There are no units or other explanation that I could find!

I am trying to create more efficient space planes, but I'm not able to do much engineering design. It involves too much trial and error for me at the moment.

I run completely stock KSP.

Thanks!

Lift is generated primarily as a function of airspeed, air density, and Angle of Attack (the angle between your prograde marker and the yellow "V" line). To say a wing has 1.9 lift rating is somewhat useful, but doesn't tell you how much weight it can carry because it depends on a lot of things. I could spam you with the lift and drag equations, but it doesn't feel like that will answer your question.

I feel like your real question is something along the lines of "How much wing do I need for my plane?" If that's the case, then typically around 0.5 to 1.0 lift rating per ton of craft works as a starting point for space planes. If you have a high TWR (more than about 1 on takeoff), then you don't need as much wing. If you have a low TWR (0.7-1.0 on takeoff), then you'll want more wing. If you have a higher TWR (2 or higher), then you almost don't need any wing at all, except enough to get off the ground if taking off horizontally.

EDIT: Also, if you start to place wings with funny angles, it reduces their effective lift rating and can increase induced drag.

If that doesn't answer your question let me know.

Edited February 17, 2014 by Claw

[TheHolm]

I could spam you with the lift and drag equations, but it doesn't feel like that will answer your question.

Could you please do it? Or just point on Wiki page or other docs where lift mechanic described.

[Armchair Rocket Scientist]

What is the relationship between Lift and ÃŽâ€V? Is there any kind of a relationship? How is it calculated (on Kerbin and other atmospheres)?

The Wiki page lists the Delta Wing as having 1.9 Lift Generated. There are no units or other explanation that I could find!

I am trying to create more efficient space planes, but I'm not able to do much engineering design. It involves too much trial and error for me at the moment.

I run completely stock KSP.

Thanks!

Basically, wings decrease your dV slightly (because they make the vehicle heavier). When you're flying close to horizontal, they can hugely decrease your gravity losses at the expense of increased drag. On a rocket, they're just dead weight because you want to get out of the atmosphere as fast as possible. On an airbreather, you WANT to be flying horizontally in atmo. Wings make it so you can put almost all your thrust into building up speed instead of fighting gravity, which lets you use your jet engines more efficiently.

Short answer: wings are like the Oberth effect. They don't affect your actual dV, but if used right they let you do more with the dV you have.

[Rusty6899]

Basically, the delta-v of your rocket is governed by the Tsiolkovsky rocket equation alone. What can change is the delta-v requirements for a certain maneuver, depending on how efficiently it is carried out. For example, if you have a rocket with 10,000m/s of delta-v, but a TWR of 1.1, you probably won't get into orbit, as the delta-v requirement would be much higher than for an efficient launch (~4550m/s) due to the significant gravity losses caused by the low thrust/slow ascent.

I can't say I am aware exactly how this applies for drag/lift, but my guess would be that it would negate friction losses rather than gravity losses, although I could be wrong.

[nhnifong]

And another person converts to FAR....

[Claw]

Could you please do it? Or just point on Wiki page or other docs where lift mechanic described.

Lift equation for Control Surfaces: sin(AoA)*pressure*speed*lift

Lift equation for Wings: sin(AoA)*(1-|sin(AoA)|)*cos(AoA)*pressure*speed*lift

[Claw]

On an airbreather, you WANT to be flying horizontally in atmo. Wings make it so you can put almost all your thrust into building up speed instead of fighting gravity, which lets you use your jet engines more efficiently.

Short answer: wings are like the Oberth effect. They don't affect your actual dV, but if used right they let you do more with the dV you have.

Yes and no. You can use wings to get a craft airborne that otherwise would not have been able to. (i.e. TWR less than 1) So in one regard they do let you get more use out of the dV you have, but that shouldn't be confused with needing less dV.

[arq]

Wings do *not* increase dV. If you get a dV-tracker and watch dV into orbit, it can easily reach 6000m/s or much more. What they *do* do is make fighting gravity more efficient, essentially reducing gravity losses in exchange for increased drag loss. But drag loss is small at high altitude, so that's a good trade.

The reason SSTOs are so efficient is the massive ISP of airbreathing engines. Oxidizer is heavy, so using jets as long as possible is advantageous. They are MASS-efficient, not DELTA-V-efficient.

[TheHolm]

Do you know drag equation for wings? It is different from normal drag. Is it also linear proportional to speed? I would expect see ^2 there.

[Claw]

Do you know drag equation for wings? It is different from normal drag. Is it also linear proportional to speed? I would expect see ^2 there.

Induced drag from wings is (AFAIK) the cosine version of the lift equation. The stock KSP parasite drag model is a weighted function so I can't just give you a number for the wings, and I don't remember the weighting function off hand.

The control surfaces are bugged such that the lift will continue to increase all the way till 90 deg AoA. This isn't usually a problem unless you build an airplane that only uses a canard for pitch control, or you build a craft that only uses control surfaces for lift generation. If you build a balanced design it isn't usually a problem.