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Can't Launch Space Plane


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So, considering I have Aviation (by accidental purchase), I decided I was going to try and build/launch a space plane.  That should give me the ability to fly over different areas of Kerbin and do some research and get some Science.  Sound idea, but for some reason I cannot get off the ground.  The build (spoilered to not clutter up the rest of the post):

Spoiler

 

Main

  1. Mk1 Cockpit
  2. Mk1 Crew Cabin
  3. Structural Fuselage
  4. Aerodynamic Nose Cone

Tail

  1. Tail Fin
  2. AV-T1 Winglet

Wings

  1. Structural Wing Type C
  2. Elevon 1

Engines

  1. Mk0 Liquid Fuel Fuselage
  2. J-20 “Juno” Basic Jet Engine
  3. Small Circular Intake

Ground

  1. LY-05 Steerable Landing Gear
  2. LY-01 Fixed Landing Gear

Science

  1. 2HOT Thermometer
  2. PresMat Barometer
  3. Mystery Goo Containment Unit

Crew

  1. Jebediah Kerman (Pilot)
  2. Bob Kerman (Scientist)
  3. Bill Kerman (Engineer)

 

So I get this built, and everything where I believe it should be, and I go from the space plane hangar to launch.  I throttle up to max, turn SAS on, stage the engines...and watch the thing roll down the runway until it explodes.  Yes, I am trying to pitch up using S.  And W.  Without and without SAS turned on.  With and without the Elevons deployed.  With the Elevons deployed both normal and not.  Nothing I do gets this craft off the ground, and I'm at a total loss as to why.

I looked around, but the only tutorial I found talked about Center of Lift...without giving a single build guide to go from nothing to basic liftoff.  Yes, the technical information was great, but I learn through practical example far better than just reading up on it.  So I now find myself having to ask what I did wrong, and why I can't get off the ground here.  Can someone please help me understand what I did wrong, and how to correct it both now for my first flight AND in the future so I don't have to ask again?

Imagery.

3iGeyFo.jpg

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17 minutes ago, Popestar said:

So, considering I have Aviation (by accidental purchase), I decided I was going to try and build/launch a space plane.  That should give me the ability to fly over different areas of Kerbin and do some research and get some Science.  Sound idea, but for some reason I cannot get off the ground.

First of all nice clean plane, good job.

Your back wheels need to be just behind the center of mass to achieve lift off.

You can check this forum post, is extremely well made.

You can also check this video, there are many out there, i timed it when he speaks for wheels but the rest of the video is useful as well.

 

Edited by Boyster
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Another thing, you seem to have little to no pitch control.  To fix this, you need control surfaces far from the center of mass (CoM).  The winglets you have as elevators won't work because they are fixed.  Try replacing them with the tail fin you have as the tail.

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You have no pitch control on that plane, so it's not surprising that you can't get off the ground. Your rear wings are fixed (never a good idea) and the elevons on your main wings are right on top of the centres of mass and lift so have pretty much zero effect on pitch, assuming they'll even deploy at all.

Swap the rear wings for tail fins or winglets with control surfaces (AV-R8 or delta-deluxe) and you should have no trouble at all getting off the ground; at that stage the real trick will be getting back on the ground again in one piece.

I think your wheels should be OK, or possibly moved back a bit depending on how much fuel you have in that rear tank- moving the gear further back also increases the angle you can pitch up before you hit the back of the plane's body against the ground, which is a good thing if you want your plane to stay intact when taking off and landing. One other thing- unless you want to carry more than one Kerbal, passenger cabins are a waste of space and you'd be better off with either a Mk1 fuel tank for more range or a structural fuselage for reduced weight.

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The back wheels have a trick too, they must alow the plane to pivot upwards. If they are too far in the bottom it won't work, if too close to the front the plane will fall backwards to the ground. The perfect spot is right below the center of lift.

The front wheel also has something to add, make it taller than the rear ones so the plane starts in the runway facing up in an angle (10º or so)

 

wind---> \ wing of the plane

this is called by the way Angle of attack.

 

Off topic: making the first plane is hard, but satisfying AF once you fly it!

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So, I changed up the tail fins and made sure the wheels weren't too far forward or too far back...and I still can't get off the ground.  I've included all of the tail fins I have access to, and none of these say whether or not they are fixed or not, so I'm not sure what ones I'm supposed to use.

Any chance someone else can build this on their end and test to find out why I can't get off the ground?  Please?  Because at this point, it feels like this tech tree component is nearly useless.

8A5afnx.jpg

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21 minutes ago, Echo__3 said:

Your second attempt looks much better. Here is a tutorial that may help you better understand building planes.

 

I'll watch that...but I can't build that plane; I don't have the parts available, nor is my runway upgraded to allow for that wingspan.  And it doesn't tell me which tail fin to use to achieve lift, which is my big problem right now.

Again, I feel like this tech tree upgrade is a complete waste at this point.  I'm not just frustrated - I'm ready to skip space planes altogether and just focus on rocketry.

 

EDIT:  I started watching this, and he literally states right off the bat that this is not going to be a basics video.  So this will be no help at all.

Edited by Popestar
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2 hours ago, Popestar said:

So, I changed up the tail fins and made sure the wheels weren't too far forward or too far back...and I still can't get off the ground.  I've included all of the tail fins I have access to, and none of these say whether or not they are fixed or not, so I'm not sure what ones I'm supposed to use.

Any chance someone else can build this on their end and test to find out why I can't get off the ground?  Please?  Because at this point, it feels like this tech tree component is nearly useless.

Can you give it more wing area? How fast is it going when you try to lift off? 

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Just now, Vanamonde said:

Can you give it more wing area? How fast is it going when you try to lift off? 

Not sure on the wing area; I know the span can't be longer than that as my runway isn't upgraded at all.

As far as speed goes, I start trying to pitch up (S) at 50 m/s, and I can hold the S key down from that point on with zero effect.  Eventually the plane just crashed and burns.

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12 minutes ago, Popestar said:

Not sure on the wing area; I know the span can't be longer than that as my runway isn't upgraded at all.

As far as speed goes, I start trying to pitch up (S) at 50 m/s, and I can hold the S key down from that point on with zero effect.  Eventually the plane just crashed and burns.

Without pictures, I am just guessing wildly. Have you checked your center of lift in relation to your center of mass? When I have these issues (and I still do from time to time) it is often because I have built the thing so heavy that it uses too much fuel achieving flight. Also, start small. Try building small space planes that can achieve orbit. Once you can get small ones up, begin the process of building a bit larger with equal success. Keep doing this cycle and eventually you might get to the size of the craft you want.

OR...

Do what I have done on occasion - go to KerbalX and find one that resembles what you have in mind. Download it and study it. Learn how other forum members overcame the same issues you are having now.

As a side note -

I have discovered that a traditional rocket has more raw lifting power than a space plane. As a big fan of the Space Transportation System (STS - NASA's Space Shuttle Program), it was retired because it was inefficient as a heavy cargo lifter. The amount of cargo it could carry was limited to the dimensions of the shuttle's cargo bay area. Essentially, the space shuttle proved itself as a concept, but became nothing more than a pickup truck in the American space program.

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Planes are hard. You need to understand the basics of aerodynamics just to get into the air: centre of mass, centre of lift, landing gear placement, angle of incidence, control surface placement, that sort of thing. Expect to do a fair bit of work to get a feel for the basics. Do read the Basic Aircraft Design - Explained Simply tutorial and/or watch some of the videos.

I tried recreating this and it flies just fine, main difficulty is that the tail is a bit long and the gear is a bit low so you have to be very careful when rotating for take-off and flaring for landing, or you'll get a tail strike. You could easily address that by swapping out the (empty) fuel tank and nose cone for a Tail Connector B which allows more ground clearance. Even so this is very good for a first attempt -- it's got all the right pieces in more or less the right configuration, you just need to move them around a bit to get it to work. Use the centre of mass and centre of lift indicators, they'll help a lot.

I think your issue is what Boyster and Fierce Wolf already pointed out, your main gear is too far back and doesn't allow the plane to rotate when you pull up. It's all in the Basic Aircraft Design tutorial, check it out.

yOcks4I.jpg

lpGNz60.png

 

Edited by Brikoleur
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25 minutes ago, Brikoleur said:

Planes are hard. You need to understand the basics of aerodynamics just to get into the air: centre of mass, centre of lift, landing gear placement, angle of incidence, control surface placement, that sort of thing. Expect to do a fair bit of work to get a feel for the basics. Do read the Basic Aircraft Design - Explained Simply tutorial and/or watch some of the videos.

I tried recreating this and it flies just fine, main difficulty is that the tail is a bit long and the gear is a bit low so you have to be very careful when rotating for take-off and flaring for landing, or you'll get a tail strike. You could easily address that by swapping out the (empty) fuel tank and nose cone for a Tail Connector B which allows more ground clearance. Even so this is very good for a first attempt -- it's got all the right pieces in more or less the right configuration, you just need to move them around a bit to get it to work. Use the centre of mass and centre of lift indicators, they'll help a lot.

I think your issue is what Boyster and Fierce Wolf already pointed out, your main gear is too far back and doesn't allow the plane to rotate when you pull up. It's all in the Basic Aircraft Design tutorial, check it out.

yOcks4I.jpg

lpGNz60.png

 

And I asked for the tutorial because I can't find it.  So I still don't know why it won't fly for me when it will for you WITH THE EXACT SAME BUILD.

Again, I'm ready to give up on space planes.  Forget orbit - I can't even get one off the ground.  And the fact that it's an integral part of the game and there is no default tutorial in the game makes zero sense.

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I did it!  I did it!  I got off the ground!

Changed out the passenger cabin for a single empty fuselage, and then I moved the wheels back to just slightly under/behind center of lift.  A little massaging...and I'm airborne!  Unfortunately, I ended up having to revert back to the hangar because, after 10 minutes of flying, I ended up losing control, flipped upside down, and crash-landed in the middle of a field as I tried to turn towards the runway.  But I got up there!

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9 hours ago, Popestar said:

And the fact that it's an integral part of the game and there is no default tutorial in the game makes zero sense.

Planes are far from an integral part of the game.    They are nice and have their uses, but I rarely ever use them other than to mess around.    I find rockets to be far more rewarding.   But to each their own.  If you want to make space planes, all the luck to you! 

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7 hours ago, Popestar said:

Unfortunately, I ended up having to revert back to the hangar because, after 10 minutes of flying, I ended up losing control, flipped upside down, and crash-landed in the middle of a field as I tried to turn towards the runway.

Crashing during 'practice' is fine, we learn with mistakes (sometimes we have the benefit of someone else making the mistakes but more often we need to provide the 'source for experience' ourselves) . However, crashing after a long flight in career is something we'd rather avoid if we have a chance. If you are unsure you can maintain control of your plane during the entire flight (including a safe landing in the end)  including a parachute that you use in such emergencies might be a good idea. In fact you may even make this the standard landing method while you don't get enough practice to land reliably without it.

 

8 hours ago, Brikoleur said:

Planes are hard. You need to understand the basics of aerodynamics just to get into the air: centre of mass, centre of lift, landing gear placement, angle of incidence, control surface placement, that sort of thing. Expect to do a fair bit of work to get a feel for the basics.

Specially when dealing with the limitation of low level facilities and scarce science nodes unlocked, one lack the resources to "brute force" the design to work. If you are ok with mods, there are several that can help (correct CoL, RCS building Aid, Editor Extensions, Precise Editor, ...) but is necessary to understand what option each of those mods bring to the player.

 

9 hours ago, Brikoleur said:

I think your issue is what Boyster and Fierce Wolf already pointed out, your main gear is too far back and doesn't allow the plane to rotate when you pull up.

Is often the case when asking for help that several people will point the same solution. If that solves the issue at hand, great. However, in the long run, try to consider different options, including some that you will figure out from your own experiments. What work best for me may not be what works best for you and what works best for you in some circumstance may be not quite as effective in a different set of circumstances.

E.g. Instead of moving your rear wheels forward you could use canards instead or changed your wheel base to make your lane sit in the runaway in a slight pitched up position. There are pros and cons to each option. (demonstration: the Fly uses the later solution while the main gear was intentionally placed far behind the CoM, )

 

 

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I tinkered with your design. 

zDELeKM.png 

You can download this version here. https://kerbalx.com/Vanamonde/Bitty-Science-Plane 

I used the offset and rotate tools a fair amount, and it doesn't have all your science parts because I couldn't see where they are in your pics. The main problem with your original seemed to be that the center of mass was far forward of the center of lift, which was holding the nose down when you attempted to take off. The version I made should take off by itself if you turn SAS on and just let it roll down the runway. 

I hope this is helpful. :D 

Oh, and I noticed too late that the dopey landing wheels are facing backwards, but that's just a cosmetic thing and should affect how it works. 

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5 minutes ago, Gargamel said:

Planes are far from an integral part of my game.    

Fixed that for you. Because, while I'm also more of a rocket guy, there are quite a few that prefer to play in a "not so rewarding" way :wink:

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5 minutes ago, Vanamonde said:

I tinkered with your design. 

Those elevon 4 are probably too fancy for someone with Aviation by accidental purchase. Fortunately, elevons 1 would be a fair replacement.

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More is more. Put 3x nacelle+fuel+engine sets under each wing, and watch the beauty rocket off the tarmac!

Seriously, i think you lack both wing area and thrust. Add wing area, and add engines. See what happens.

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On 10/5/2020 at 10:37 PM, Popestar said:

And I asked for the tutorial because I can't find it.  So I still don't know why it won't fly for me when it will for you WITH THE EXACT SAME BUILD.

 

Did you miss @Boyster answer? He linked to a tutorial which was  posted to the forums:

 

Edited by jost
typo
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On 10/4/2020 at 4:47 PM, Boyster said:

Your back wheels need to be just behind the center of mass to achieve lift off.

It slightly miffs me that everyone keeps saying that while forgetting that it's a no-go if your center of mass is in the front half of the plane because you're going to tailstrike if you put the rear wheels too far forward. Not everybody builds Concorde-style rear-wing planes.

For that scenario, put the rear wheel on a Tail Connector part and use the offset tool to nudge the wheel until it's higher up than the front wheels, causing the plane to slightly nose up while standing on the runway. Like this:

7JKaTyw.png

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1 hour ago, Fraktal said:

it's a no-go if your center of mass is in the front half of the plane because you're going to tailstrike

Odd all those real-world aircraft (and pretty much every design, delta or otherwise, I've ever flown in KSP too) manage it then, isn't it?
Avoiding tailstrikes with tricycle gear is simply a matter of ensuring you have sufficient clearance for the AoA you need at your design V1 speed. This is one of the reasons almost all RL aircraft have a raised tail, and exactly what the type-b tail connector is for.

Trading up those fixed gear for something not borderline-unusably-horrible would also help. Between the stumpiness and the janky suspension, I consider those the two most useless and rage-inducing parts in the entire game.

Sure, you could just build a taildragger... But then you are trading a tailstrike problem for a faceplant problem. Thankfully KSP doesn't also have the visibility and passenger comfort problems, which are the real reasons taildraggers are less popular than they once were.


That design you have there could just as easily have tricycle gear and achieve the same AoA without a tailstrike anyway... So long as one isn't completely ham-fisted with the control of course.

Edited by steve_v
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1 hour ago, jost said:

Did you miss @Boyster Auswertung? He linked to a tutorial which was  posted to the forums:

 

My big problem with that tutorial is that while it explains the physics behind how aircraft get off the ground, it doesn't actually do any step-by-step of building one in KSP.  And it's especially frustrating that most of the tutorials I've seen on aircraft and space planes make reference to parts you get well after you first have Aviation available to you.

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8 hours ago, Spricigo said:

Fixed that for you. Because, while I'm also more of a rocket guy, there are quite a few that prefer to play in a "not so rewarding" way :wink:

Good catch!   But yeah, that was my point.   Thanks for the FYP.  :D

 

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