Lifting the Mk3 planes

[storm_soldier2377]

I've been trying to make Mk3 spaceplanes the past while and encountering problems keeping the planes in the sky. I have no problem getting them into space, as that can be solved with the classic KSP solution — just add more thrust. The problem though comes when I am trying to glide back to KSC, as without a lot of thrust they fall like a stone. I am mainly talking Big-S delta wing here, as it seems to have trouble lifting even the smallest Mk3 planes despite appearing to be suited for them. The FAT-455 Wing fares a bit better, but not too much.

[Temstar]

What's the dry weight of you spaceplane? Can you post a screenshot?

[ineon]

One important thing that I always try before sending a space plane to space is seeing how it acts as a plane. I will empty all the rocket fuel out (anything that contains LF&O) and and empty 90% of the remaining LF. At that point I want to simulate landing it from space to stop me wasting my time by orbiting something that will not re-enter. I'll try a couple of things:

• Does it turn?
• How slowly can it go without dropping out of the sky?
• Can I land it? And can I reliably point it at the runway?

As many will tell you designing (and flying) a space plane is hard, and without a picture it might be hard to tell you exactly what is wrong. However, here are some general thoughts:

• Have you angled the attack of wings up by a few degrees? This gives the plane a small amount of natural lift.
• How far are the control surfaces from the centre of mass? If the dry CoM is near the front, then elevator (on the tail) will provide you with the best control. If it is at the back then canards (at the front) will give you better control.
• More wings!!! (although you might have already mentioned you tried this)
• Have you tried running your engines at 10-25% to give you a little more speed? Landing slowly is important, but the approach doesn't need to be so slow.
• You've not got airbrakes on have you? Probably obvious, but I thought that I would ask.

[storm_soldier2377]

7 hours ago, ineon said:

One important thing that I always try before sending a space plane to space is seeing how it acts as a plane. I will empty all the rocket fuel out (anything that contains LF&O) and and empty 90% of the remaining LF. At that point I want to simulate landing it from space to stop me wasting my time by orbiting something that will not re-enter. I'll try a couple of things:

• Does it turn?
• How slowly can it go without dropping out of the sky?
• Can I land it? And can I reliably point it at the runway?

As many will tell you designing (and flying) a space plane is hard, and without a picture it might be hard to tell you exactly what is wrong. However, here are some general thoughts:

• Have you angled the attack of wings up by a few degrees? This gives the plane a small amount of natural lift.
• How far are the control surfaces from the centre of mass? If the dry CoM is near the front, then elevator (on the tail) will provide you with the best control. If it is at the back then canards (at the front) will give you better control.
• More wings!!! (although you might have already mentioned you tried this)
• Have you tried running your engines at 10-25% to give you a little more speed? Landing slowly is important, but the approach doesn't need to be so slow.
• You've not got airbrakes on have you? Probably obvious, but I thought that I would ask.

With the Mk2 parts I have no problem building a spaceplane. I even built one with the panther engines. Its mostly the Mk3 parts I have issue with. Here's a screenshot of it without fuel.

 

 

As you can see, I haven't angled the wings, I should give that a shot. I don't have airbrakes on, as I am perfectly capable of gliding back to KSC without them, provided my plane generates enough lift of course.

Edited February 8, 2016 by storm_soldier2377

[WhiteKnuckle]

Congratulations, you've built a shuttle. And just like the real thing, it has the glide characteristics of a brick.

 

Seriously though, it's big so it has a lot of drag, but once it's out of fuel/payload it doesn't weigh much. So there may be a limited amount you can do design-wise. Have you tried a very steep approach with a big flare at the end? You'll touch down with a lot of speed (again, like the real shuttle) so you may need drag chutes or airbakes.

[moogoob]

31 minutes ago, WhiteKnuckle said:

Congratulations, you've built a shuttle. And just like the real thing, it has the glide characteristics of a brick.

 

Seriously though, it's big so it has a lot of drag, but once it's out of fuel/payload it doesn't weigh much. So there may be a limited amount you can do design-wise. Have you tried a very steep approach with a big flare at the end? You'll touch down with a lot of speed (again, like the real shuttle) so you may need drag chutes or airbakes.

It might be that. I've done some shuttle designs with both Mk 2 and Mk 3 parts, and the Mk2 parts always glide better, and have less drag. It may have something to do with the Mk2 parts' body giving lift, or with the Mk3 parts being just plain big and stubby rather than sleek.

With my (so far only experimental) Mk3 designs, I chalk "runway landings" as a best-case scenario, with parachute ditchings being the primary method of recovery.

Edited February 8, 2016 by moogoob
adding more text

[Evanitis]

2 hours ago, storm_soldier2377 said:

Its mostly the Mk3 parts I have issue with.

Had some brainstorming in another thread with a fellow who had similar issues. Turned out that empty Mk3 cargobays generate lift that doesn't appear in the VAB/SPH. Try balancing the CoM-CoL accordingly... just imagine some wings to the center of the 'bay.

[Vegetal]

When you say it falls like a stone, do you mean they go nose down into the earth? Because with that little pitch authority you have and hugely offset CoL to the rear, that's my guess......

[storm_soldier2377]

Remember this is an SSTO, not a shuttle. It just looks like one because the Mk 3 parts are designed to resemble shuttles.  I am using Mk3 fuselages to lift probes in orbit that won't fit in Mk 2 cargo bays. 

I haven't had much time to play recently but i remember haßdving trouble gliding even the smallest planes with the Mk3 parts. I have considered using parachutes and I will try steep descents next time I play.

One question. Does parachutes/drogue chutes work at helping your plane slow down on the runway like an Su-25. Never actually tried it.

[Evanitis]

9 minutes ago, storm_soldier2377 said:

Remember this is an SSTO, not a shuttle.

Different lifting methods, but basically the same thing once on orbit and on the way down.

I'm no expert on parachutes - never needed one on a plane. If a craft can pitch up, it will slow down without any extra help. If it can't pitch down, it's a design problem. Or an explosive one.

[storm_soldier2377]

Okay so I've found a way to land it. Basically point prograde when you've slowed down to about 1400 m/s and do a big flare at 1000m altitude. I did have to add airbrakes and make my ailerons work on the pitch axis though. However now I have to figure out how to land it at KSC. With a Mk2 fuselage plane this is rather easily done regardless from where you deorbitted. This is quite a bit different though.

[RizzoTheRat]

Drag has two components, form drag which is mainly about the size of the aircraft pushing through the air, and induced drag which is about the generation of lift. 

The point where the drag, weight and lift vectors cancel each out will tell you your glide ratio (angle of descent), however the faster you go the lower the induced drag gets, but the higher the form drag gets, so there will be an optimum speed at which you'll get your best glide slope angle.  The bigger the aircraft the more form drag, and the heavier the aircraft the more induced drag, so generally speaking a big heavy aircraft will fall out of the sky quicker than a small light one.

Modern gliders can have a glide ratio above 50, ie for every 50 meters horizontal travel they'll lose 1 meter altitude (apparently Seagulls have a similar glide ratio but always overtook me in thermals, so pilot skill makes a difference too :D), by comparison the space shuttle was about 4.5, which is around half what a Paraglider can manage and only slightly better than a steerable parachute.

Moral of the story: don't be surprised that your Mk3 gliders come down fast. 

 

[AlphaMensae]

On 2/9/2016 at 10:57 AM, storm_soldier2377 said:

I did have to...make my ailerons work on the pitch axis though. 

That was a big part of your problem, those things are actually elevons, a combo elevator+aileron, and need to have pitch control enabled.

[storm_soldier2377]

5 hours ago, Laguna said:

That was a big part of your problem, those things are actually elevons, a combo elevator+aileron, and need to have pitch control enabled.

I am aware of that, but they were functioning as ailerons as I usually turn my pitch off in those make the pitch axis a bit less sensitive as to not accidentally pitch up too much during the ascent and inducing too much drag.

Anyway I made a new plane where I managed to squeezed some more wings and canards and it's working much better now. 

[KerikBalm]

is it possible that he's a cargobay glitch, and the wings are counted as occluded, and all he has is body lift?

[luizopiloto]

Press F12 to see the aero forces... helps a lot...

[Araym]

I did a lot of costruction of "spaceshuttles" with Mk3 spaceplane parts, using a reference Inigma's one (link on my sign, if you hover above the engineer patch), so I provide you some ideas:

1. Shuttle-like designs (like yours, even if it has not external tank and booster, referring to the orbiter itself when it reenters from space) have very poor lifting capability. I generally compensate it building "double layered wings" (basically another shuttle-like wings, clipped on the one you already have, maybe slightly angled to have more lift)
2. Engine/tail/rear section tends to be the heavier portion of the plane, if you put there your tanks: it could develop (mostly in the landing phase) the issue to drag you down like a standard, balistic landed, capsule, with your back pointing down. In that case, you generally cannot recover, as in KSP "inverted control surfaces" go nuts. (My issues with my shuttles were the weight of my engines, umbalancing the CoM to the rear too much)
3. Split your fuel load both forward and back the central cargobay: both for better payload weight management and to resolve orbiter weight balance as well, try to have you center of mass at the center of your cargobay(s)
4. Check if you have the wings "empty" o "fully fueled"... you might have deadweights on you plane
5. We cannot fully design wings properties, to fullfill the role you need, plenty: generally, on the drawing board, we replicate some plane designs, but pratically KSP handle then lifting factor not really realistically. FAR does it, so then you could design a (space)plane with all the needed characteristcs...
   ... or stock, you can "cheat" it using clipped lifting surfaces. In my shuttles, adjusted the "weight to the rear" problem on my own way (like Inigma's one, I used 3x Skipper as SSME, then switched to the new KS-25 "Vector" just for looks, but they were way too powerful, and squad balance "thrust" with "dead weight" on the engine, so I made a edit for a new engine using the Vector model, but weigth and thrust of a Skipper ) I found my orbiter nose-heavy.
   I resolved the issue putting a square wing CLIPPED INSIDE the cockpit, slightly angled up, to provide the needed lift to the nose on the unpowered-gliding phase. If it's not a design choice (I was looking to a clean shuttle-like design, unlike you, designig it more feeely) you can add some externa canards on the nose, to balance the lift, leaving them outside/not clipped, to help yourself to have some autoriti to raise the nose of your planes.
   I generally found any conventional design based on mk3 in the needs of some lift/control surface on the nose. Almost always. So the 2 options: clipped inside the cockpit or outside, they always work and generally are welcomed by any design.