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Wings. Who needs em? (Serious question.)


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So before I start off I need to preface this by saying that this is a serious question, inspired by all the really awesome new parts in 0.25. I am not trolling and I am not doing that Socratic method thing where you ask stupid questions in order to guide someone else. Furthermore I have hundreds of hours logged and have put all kinds of crazy junk into orbit and beyond. Serious question:

What are wings for?

No really. Why would I want something adding more drag and mass only to convert some of my always useful forward velocity into not always useful radial-out velocity? Mass which is always slowing me down (unless I jettison the wings when I reach space, which makes sense, but then why not jettison them on the launch pad? And that radial-out is a best case scenario, assuming you've perfectly aligned your CoL with your CoM. Otherwise it turns into unwanted rotation. Did I mention that your CoM is constantly moving due to fuel consumption?)

So, why wings?

The smartass answer is, of course, that you need lift in order to not smash into the ground. And maybe for Orville and Wilbur Wright, this was the case. But I have access to reaction wheels and more thrust than the Wrights could have dreamed of. Consider this 'spaceplane':

NuNiCf7.jpg

Has airbreathing engines and also vacuum engines, can fly in atmosphere, can fly in space. I just did it, stable orbit with fuel to spare. What I can do, that Wilbur couldn't, is freely adjust my angle of attack. This ugly beast 'flies' at a 30-45 degree angle, easily shrugging off the forces of gravity that would have required wings in the past.

Now have a look at this thing. Be careful, looking directly at it may cause nausea.

qP0AJWN.jpg

I especially like the mis-rotated ram intakes. Classy.

This is how I put pretty much all my heavy cargo into orbit. Airbreathers get it up to about 30km, then detachable SRBs get it the rest of the way. There's nineteen turbojets on here, and zero wings. Lands with parachutes, gets recovered about 50km from KSC at a 95% refund.

I'd like to improve my designs. People seem to like wings. Help me understand why. Pictures and graphs might help, I guess I'm stupid because this is not obvious to me at all.

Edited by Riph
edit: setting to 'answered', many helpful posts were made, see especially Kerikbalm on pg 3
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Gameplay.

There is no payload you can lift with a spaceplane that couldn't be put in orbit faster and with a lower part count with a vertically launched vehicle. There is no spaceship which wouldn't have a lot more delta-v if it didn't jettison its wings once atmospheric flight is over.

Yes, spaceplanes can be recovered for more than 95% their value. But there are rockets which can also be recovered for 95% their value.

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As Sirine said, they provide maneuverability in the atmosphere, letting you glide/fly to your target without having to do a an ultra precise landing.

They also let you reach orbit with a weaker TWR than a rocket would allow...

Practical use : you can put smaller engines on planes and save on weight what you lose to wing drag.

But, this is an excellent question : people don't always realize that with a TWR big enough (> ~1.5), wings actually make it harder to reach orbit because of the added drag.

Edited by el_coyoto
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It is roleplay in current KSP. People want to build and fly realistic like vessels, although they would not necessarily like if there were realistic aerodynamics (which mean that thin fuel tank would be destroyed immediately at 45 deg angle of attack), realistic thrusts of jet engines (much less than current) and realistic cost ratio between rocket engines and jets. On the other hand, realistic limitations would exclude spaceplanes completely like in the real world.

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Practical use : you can put smaller engines on planes and save on weight what you lose to wing drag.

Can you explain this in better detail? My (totally uneducated) assumption was that an engine with 100 thrust units, with wings, pointed horizontally east, is generating something like 90 acceleration units east (due to wing drag), and 10 acceleration units up (due to lift). Acceleration can't magically come from nowhere, so it'd have to be converted from horizontal to vertical. Right?

Since I can simply point my nose upward at a 9 degree angle (9 is 10% of 90 degrees), I can achieve the same effect (90 east, 10 up).

I'm sure someone can poke a massive hole in my assumptions here, and that's what I want. I want to know how this stuff works.

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Propulsion in the real world of spaceplanes:

All spaceplanes to date have used rocket engines with chemical fuels. Due to the orbital insertion burn necessarily being done in space, orbital spaceplanes require rocket engines for at least that portion of the flight.

A difference between rocket based and air-breathing aerospace plane launch systems is that aerospace plane designs typically include minimal oxidizer storage for propulsion. Air-breathing aerospace plane designs include engine inlets so they can use atmospheric oxygen for combustion. Since the mass of the oxidizer is, at takeoff, the single largest mass of most rocket designs (the Space Shuttle's liquid oxygen tank weighs 629,340 kg, more than one of its solid rocket boosters), this provides a huge potential weight savings benefit. However, air breathing engines are usually very much heavier than rocket engines and the empty weight of the oxidiser tank, and since, unlike oxidiser, this extra weight (which is not expended to add kinetic energy to the vessel, as is propellant mass) must be carried into space it may offset the overall system performance.

It is important to note that mass fraction is an important concept in the engineering of a rocket. However, mass fraction may have little to do with the costs of a rocket, as the costs of fuel are very small when compared to the costs of the engineering program as a whole. As a result, a cheap rocket with a poor mass fraction may be able to deliver more payload to orbit with a given amount of money than a more complicated, more efficient rocket.

Propulsion in KSP world of spaceplanes:

Off the shelf is the KSP way, this strategy is known as the "big dumb booster" approach and is considered cheap as developement cost are marginal even in the new 0.25 hard mode of career.

Wings will give you life and manouverability but the savings of spaceplanes are marginal dispite the fact that fuel cost in KSP are one of the biggest cost you'll face there is always plenty of money around.

EDIT:

Planes can't fly without wings. In KSP is easy to get out the atmosphere on jet engines alone (with or without wings.); but, you have to circularise with chemical bi-propelant rockets.

Edited by peter1981
responce to Riph below
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Peter1981 just gave an awesome and factual answer to why we should use air-breathing engines. It was a good read and I honestly feel bad saying this but uh.. what about the wings? The question was about wings. Nobody's arguing that air engines aren't awesome, I use them all the time. My "big dumb boosters" are air breathing.

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Do you mean why wings are used in real spaceplanes? Because in real life there are risks on parachuted landings and splashing to water, especially with higher masses than small return capsule have. There are both safety risks and also military risks. Soldiers want that their secret data and things land on their own airports. As far as I know there are (or have been) not many winged orbiters and all of them are at least partially military vehicles. And any of them does not benefit of their wings during ascent.

There are also plans to make to build more advanced air breathing spaceplanes with some kind of hybrid engines, which can possible be more economical than "big dumb boosters", but they need long and expensive research and product developing phase before any realization. They need wings also to overcome low TWR. Normal jet aircraft have TWR of less than 0.5.

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IRL, and with mods like far, they are use to allow you to lift much heavier payloads than a given engine would otherwise be capable of lifting.

Its more efficient to have wings with a few degre AoA, than a rocket engine at 45 degrees, where you loose roughly 30% of your dV to gravity drag.

Sure in KSP, you can get to near orbital velocity quite fast, but you can't do that IRL, and with NEAR/FAR, you top out at about 1,700 m's, and still need lift.

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Can you explain this in better detail? My (totally uneducated) assumption was that an engine with 100 thrust units, with wings, pointed horizontally east, is generating something like 90 acceleration units east (due to wing drag), and 10 acceleration units up (due to lift). Acceleration can't magically come from nowhere, so it'd have to be converted from horizontal to vertical. Right?

That's physics 101, but it can't be all of it.

Just looking out of the window at what seems to be a cargo plane with two turboprop engines. I sincerely doubt that it has TWR>1, so a vertical liftoff would be out of the question. Yet the wings somehow turn that underwhelming thrust into sufficient lift. Small forces moving big things isn't unheard of (think of a lever), but I have no idea how wings do it. I am, however, pretty certain that this wouldn't fly in KSP fizzics.

I, too, hope that someone will give a good answer.

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Do you mean why wings are used in real spaceplanes? Because in real life there are risks on parachuted landings and splashing to water, especially with higher masses than small return capsule have. There are both safety risks and also military risks. Soldiers want that their secret data and things land on their own airports. As far as I know there are (or have been) not many winged orbiters and all of them are at least partially military vehicles. And any of them does not benefit of their wings during ascent.

There are also plans to make to build more advanced air breathing spaceplanes with some kind of hybrid engines, which can possible be more economical than "big dumb boosters", but they need long and expensive research and product developing phase before any realization. They need wings also to overcome low TWR. Normal jet aircraft have TWR of less than 0.5.

There are no real spaceplanes. The closest are the Shuttle/Buran, which used the wings (and it's gliding ratio comparable to a brick) to land; the VentureStar, which didn't work; Skylon, which doesn't yet exist; the X-37, which can't take off on its own; SpaceShip One, which is suborbital and is air-launched.

EDIT: In other words, even in the real world, while wings are the way to fly atmospheric aircraft, they aren't used for orbital injection. Maybe Skylon will change that and, even then, check how small its wings are supposed to be.

Edited by juanml82
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Can you explain this in better detail? My (totally uneducated) assumption was that an engine with 100 thrust units, with wings, pointed horizontally east, is generating something like 90 acceleration units east (due to wing drag), and 10 acceleration units up (due to lift). Acceleration can't magically come from nowhere, so it'd have to be converted from horizontal to vertical. Right?

Since I can simply point my nose upward at a 9 degree angle (9 is 10% of 90 degrees), I can achieve the same effect (90 east, 10 up).

I'm sure someone can poke a massive hole in my assumptions here, and that's what I want. I want to know how this stuff works.

I think you're right on the principle, and the upward acceleration from lift doesn't appear magically : it costs you drag.

Lift helps fight gravity because it pulls your aircraft up. Doing the same without wings would require you to tilt the craft more so that the engine also fights gravity. So part of the engine TWR is "wasted" to keep your vertical speed positive.

Thus a wingless plane/rocket/thingie will need a good TWR (2) to fight both gravity AND drag, while a winged designed will use some of its lift to fight gravity, meaning you can select engines with less TWR.

Such engines are usually lighter, which is more or less the point of using wings : less engines required.

It's a choice : either you try to spend as little time in the atmosphere with a wingless design, treating it as a hostile parameter and trying to escape it as fast as possible, or you try to use it to your advantage thanks to the lift provided by a winged design.

The engine on a winged design will also spend less thrust fighting gravity (because of a more horizontal attitude), BUT as you've said, there's no free lunch and this "magic" upward acceleration coming from your wings has a price : more drag than a wingless design.

Hope it was a bit clearer, it's sometimes hard for me to be concise and accurate in English... :blush:

Edited by el_coyoto
clarifications
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It is economic optimization, not just delta-v, thrust or any single technical parameter. Airplanes needs insane amounts of delta-v to work against drag, but it is not so bad for overall economy, because they have huge ISP values. Boeing 747 (one version) have 4*260 kN = 1040 kN thrust. I do not know, but if I assume that it needs half of that during a cruise flight, it uses about 6 km/s dv per hour of flight (I assumed mass of 300 t, about half between empty mass and maximum takeoff mass). Intercontinental flight takes easily more dv than return trip to any planet in the Solar system.

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Wings will have L/D ratios well over 1:1, some above 20:1, but for a spaceplane, its probably going to be more like 5:1

That means for every 5 kN of lift they generate, they'd generate 1 kN of drag. Obviously in this case, you can reduce your gravity drag losses by a substantial amount without much additional drag losses.

Its not just about allowing lower TWR engines.. its about more efficient ascents.

Its already been shown that optimal ascent (although this is assuming a vertical launch) occurs when gravity drag losses = atmospheric drag losses, ie at terminal velocity.

With wings, this skews it to a different speed - reducing total losses, and keeping the conditions to those that air breathers can use longer.

But IRL, or with far, terminal velocity is quite high... but also IRL, if you travel at those speeds, Q is going to be high and your structure will have to be stronger and heavier.

Wings allow you to efficiently ascend at much slower speeds, allowing the structure to be lighter (at least for the parts that won't have to deal with reentry).

But at the most basic level, they blunt your losses to gravity drag, which is particularly important if you want to ascend through the thick atmosphere slowly, before the dash to orbital speed.

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So before I start off I need to preface this by saying that this is a serious question, inspired by all the really awesome new parts in 0.25. I am not trolling and I am not doing that Socratic method thing where you ask stupid questions in order to guide someone else. Furthermore I have hundreds of hours logged and have put all kinds of crazy junk into orbit and beyond. Serious question:

What are wings for?

No really. Why would I want something adding more drag and mass only to convert some of my always useful forward velocity into not always useful radial-out velocity? Mass which is always slowing me down (unless I jettison the wings when I reach space, which makes sense, but then why not jettison them on the launch pad? And that radial-out is a best case scenario, assuming you've perfectly aligned your CoL with your CoM. Otherwise it turns into unwanted rotation. Did I mention that your CoM is constantly moving due to fuel consumption?)

So, why wings?

The smartass answer is, of course, that you need lift in order to not smash into the ground. And maybe for Orville and Wilbur Wright, this was the case. But I have access to reaction wheels and more thrust than the Wrights could have dreamed of. Consider this 'spaceplane':

http://i.imgur.com/NuNiCf7.jpg

Has airbreathing engines and also vacuum engines, can fly in atmosphere, can fly in space. I just did it, stable orbit with fuel to spare. What I can do, that Wilbur couldn't, is freely adjust my angle of attack. This ugly beast 'flies' at a 30-45 degree angle, easily shrugging off the forces of gravity that would have required wings in the past.

Now have a look at this thing. Be careful, looking directly at it may cause nausea.

http://i.imgur.com/qP0AJWN.jpg

I especially like the mis-rotated ram intakes. Classy.

This is how I put pretty much all my heavy cargo into orbit. Airbreathers get it up to about 30km, then detachable SRBs get it the rest of the way. There's nineteen turbojets on here, and zero wings. Lands with parachutes, gets recovered about 50km from KSC at a 95% refund.

I'd like to improve my designs. People seem to like wings. Help me understand why. Pictures and graphs might help, I guess I'm stupid because this is not obvious to me at all.

These designs are nice and all but, take either one of them and go land at the island runway to "pick something up" or drop off or whatever. Then take off again, get into orbit, deliver a payload, return and land at KSC, and then go back to the island runway, all in one go.

Then try it with wings. You'll see that you used much less fuel and were actually able to pull it off.

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My 2 main reasons for using wings in KSP are:

1. It's fun and challenging. IMO it's much easier stack up some rockets and blast a payload into space.

2. Cost. I rarely transmit science in my Career games (So far only sending science from Eve's surface). SSTO spaceplanes are the back bone of my fleet. I can deliver 30 tons to a 100k orbit with my Super Guppy spaceplane. After landing and recovering my spaceplane, the only costs to get that cargo to orbit is fuel. I so far have been unsuccessful with SSTO rockets packing more than simple probes. Not to say it can't be done, but I haven't been successful yet.

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These designs are nice and all but, take either one of them and go land at the island runway to "pick something up" or drop off or whatever. Then take off again, get into orbit, deliver a payload, return and land at KSC, and then go back to the island runway, all in one go.

This assumes that OP needs to consider this use case, which they probably don't.

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These designs are nice and all but, take either one of them and go land at the island runway to "pick something up" or drop off or whatever. Then take off again, get into orbit, deliver a payload, return and land at KSC, and then go back to the island runway, all in one go.

Actually you can do so quite easily by flying over your target, deploying chutes, and powered landing carefully to guide your fall. :wink:

This design assumes zero wind (which KSP has.. for now..) and also a kerbal nearby who can magically 'repack' those chutes with zero complications from this act. (Which KSP has. For now.)

That means for every 5 kN of lift they generate, they'd generate 1 kN of drag. Obviously in this case, you can reduce your gravity drag losses by a substantial amount without much additional drag losses.

This... seems like magic to me, but I'm no rocket scientist. Thank you for actually answering the question :D

However, now I have to ask, is this in real world physics only? Or does this work in KSP as well? So far my experiments with wings tend to end in less efficient flights, but this could because I'm doing it wrong.

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Can you explain this in better detail? My (totally uneducated) assumption was that an engine with 100 thrust units, with wings, pointed horizontally east, is generating something like 90 acceleration units east (due to wing drag), and 10 acceleration units up (due to lift). Acceleration can't magically come from nowhere, so it'd have to be converted from horizontal to vertical. Right?
Wrong. A good wing can generate 10 or 20 times as much lift as it does drag. I shan't claim to know why that's the case but it is. (The lift-to-drag ratio of a plane is equal to its constant-speed glide ratio, by the way).
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Even in KSP? I think the issue in game (vs RL) is that the atmosphere is… not good, plus, jets are flatly ridiculous in game. Serious spaceplane designs were not SSTOs (there eight be some exceptions talked about, I'm sure), they usually had 2 stages, even if both were aircraft.

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It's nice to know I'm not the only person who asks this question.

While I occassionally like to play around with spaceplanes they always seem to be the hardest way to get to space. Wings are fine for plain old 'planes that don't need to reach orbit and, in KSP, they do at least work but taking them to other bodies (except Laythe) is just daft. It might be daft fun, which is fine, but there's no other reason.

Having said that ...

My next tutorial is intended to be "World of SSTO" written in collaboration with Wanderfound, who is a spaceplane enthusiast (and therefore uses FAR). We're still finalising the structure but are intending to have this very debate, presenting our alternative rocket, JATO and spaceplane solutions and critiquing each other. The hope is that from that people can take whichever designs they like (if any) with a fuller understanding of the pros and cons on both sides.

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I feel it's several elements of the following which constitute the reason ksp players need/use wings.

-They give significant upward lift for SSTO's, allowing them to carry much larger payloads.

-(some) Roleplay

-In-air control

and finally, the challenge and allure of a nice looking wing design. They certainly evade me!

-Caveman.

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