Help for my First Spaceplane [landing/design]

[GuyWithGlasses]

Hello everybody,

I've been working around in a Mk3-based-parts ship for interplanetary flybys (and to meet several contruction-station / turism contracts). I've managed to construct a ship with aorund 65Tn with 3 nervs and aorund 7,5kdV, with a total 20 of crew capability ( this is why I used Mk3 parts). It has 0,3TWR full loaded; it has a reasonable time-burns and docks quite well with a litltle monop..

The design has evoluted (adding more mass) adding surface control parts (and wings and landing gears) with the objetive the ship can plane to the KSC (I haven't added any turbojet engine to maximice the deltaV in space).

I try landing near to the KSC in a similar way I do with rokets; In the dessert gulf (from a 80x80Km aprox. orbit) I burn retrogade to meet de trayectory of the island near KSC and after this, I use mechjebs Smart ASS to a 25º ptich angle.

The result, the ship flyes well until the thicker slices of the atmosphere (around 20Km), the nose goes from 0º to -5º and a few seconds after that, the ships starts flipping in yaw and pitch.. and I don't Know what I have to add/remove to solve it :-S

 

A few images to the design.. 

https://imgur.com/OtukXVk

https://imgur.com/rOgx4xm

https://imgur.com/6Lzed0p

https://imgur.com/GxV2IY9

Cheers!

 

[FancyMouse]

Putting Nerv engines at the back is pretty challenging for spaceplanes because they easily pull CoM backwards, making it harder to adjust CoM and CoL. I guess your case is simply CoL gets in front of CoM. In thinner atmo, other stuff can still overcome aerodynamics, but when air gets thicker, you will lose control. In some sense, I think the plane isn't really properly designed for horizontal flight.

[ARS]

Judging from your claim, your plane has low stability in level flight, which usually caused by the imbalanced center of mass. Nuclear rocket is heavy, so placing it on the rear shifts center of mass to the rear of the craft. While this can be remedied by redesigning the craft to achieve balance between center of mass and center of lift, the fuel can also be the source of your problem. On departure, your  plane might look stable, but when you returned, usually there's a very little fuel left since the majority of it has been used during the trip, and since mk3 parts are among the heaviest parts available (especially fuel tanks), having lost a majority of fuel means your plane won't be balanced anymore. On vacuum, this isn't a problem, but when you enter the atmosphere, aerodynamic effect kicks in. I suggest to adjust the setting of fuel consumption priority on the fuel tanks, which one being drained first and which one being drained last in SPH (try to test drain the tanks in SPH and see how it affect the balance of CoM and CoL, make sure the last tank being consumed still allows a balance between those 2 aspects)

[GoSlash27]

Guy,
 Too much drag in the nose. You have a compact, aerodynamic mass behind the wings, but a big, light, balloon out front.

 Best,
-Slashy

[AeroGav]

At high angle of attack yaw stability decreases,  that is why fighters like F-15 have twin tails.    The forward fuselage is catching a lot more of the air than it will in normal flight.

The main tail fin is not very far behind your CoM, so it doesn't have much leverage - it won't be as effective.

Also,  you have two sets of AV-R8 winglets mounted with 4 way radial symmetry ahead of the main wing.  

You need to reattach these immediately with mirror symmetry if you change nothing else about your design -  the vertically mounted winglets on the top and bottom will be ahead of your craft's CG,  and will actually be working to reduce yaw stability not increase it.

BTW,  those two rows of winglets are weird.     For controlling pitch, you want the forward pair as far forward as possible so they have leverage.   For controlling roll,  you'd be better off attaching them to the wingtips so they are far outboard.

Have you gone into game settings and enabled "Advanced tweakables"?  You should right click on each surface and disable the control functions you don't want.  Eg. The tail fins should not attempt to control roll, only yaw  etc.

Finally,  try coming in at a less extreme re-entry angle.    In KSP aerodynamics,  25 degrees is quite extreme and i don't think your craft has the agility to hold that.   There is no real need to.     Try setting 10 degrees instead,  and burn retrograde to intersect the ground a little earlier (like the desert) because drag will be less.     If it starts looking like you're overshooting,   raise the pitch a few degrees more for extra drag.    If it starts undershooting, lower the nose closer to 5 degrees , which is the best glide angle.     

BTW your method of attaching engines looks like it will create huge drag.    KSP aerodynamics hates it when you mate parts of differing diameter together without using an adapter.  It also hates empty attachment nodes, if you are not using all the points on an engine mount you need to put a cone.  Performance is  a different subject though,   this is about loss of control. 

I wrote more on drag here -

BTW,  when you graduate from Spaceplane on a stick type launchers,  here's a type of two stage to orbit jet boosted design to consider -

https://kerbalx.com/AeroGav/Learstar-A2

It's actually based on the stock VAB Learstar, I converted it to jet boosters instead of rocket -

stock version - 

 

[GuyWithGlasses]

Thanks for your answers..

 

On 4/12/2017 at 4:27 PM, FancyMouse said:

Putting Nerv engines at the back is pretty challenging for spaceplanes because they easily pull CoM backwards, making it harder to adjust CoM and CoL. I guess your case is simply CoL gets in front of CoM. In thinner atmo, other stuff can still overcome aerodynamics, but when air gets thicker, you will lose control. In some sense, I think the plane isn't really properly designed for horizontal flight.

 

On 4/12/2017 at 4:45 PM, ARS said:

Judging from your claim, your plane has low stability in level flight, which usually caused by the imbalanced center of mass. Nuclear rocket is heavy, so placing it on the rear shifts center of mass to the rear of the craft. While this can be remedied by redesigning the craft to achieve balance between center of mass and center of lift, the fuel can also be the source of your problem. On departure, your  plane might look stable, but when you returned, usually there's a very little fuel left since the majority of it has been used during the trip, and since mk3 parts are among the heaviest parts available (especially fuel tanks), having lost a majority of fuel means your plane won't be balanced anymore. On vacuum, this isn't a problem, but when you enter the atmosphere, aerodynamic effect kicks in. I suggest to adjust the setting of fuel consumption priority on the fuel tanks, which one being drained first and which one being drained last in SPH (try to test drain the tanks in SPH and see how it affect the balance of CoM and CoL, make sure the last tank being consumed still allows a balance between those 2 aspects)

Yesterday I redesigned the model, trying to put COM upwards.. I removed the central NERV, moving the central tanks upward and moving backward the passengers cabin... It flyes deeper in the atmosphere..

But I think the problem wasn't there...

 

20 hours ago, AeroGav said:

At high angle of attack yaw stability decreases,  that is why fighters like F-15 have twin tails.    The forward fuselage is catching a lot more of the air than it will in normal flight.

The main tail fin is not very far behind your CoM, so it doesn't have much leverage - it won't be as effective.

Also,  you have two sets of AV-R8 winglets mounted with 4 way radial symmetry ahead of the main wing.  

You need to reattach these immediately with mirror symmetry if you change nothing else about your design -  the vertically mounted winglets on the top and bottom will be ahead of your craft's CG,  and will actually be working to reduce yaw stability not increase it.

BTW,  those two rows of winglets are weird.     For controlling pitch, you want the forward pair as far forward as possible so they have leverage.   For controlling roll,  you'd be better off attaching them to the wingtips so they are far outboard.

Have you gone into game settings and enabled "Advanced tweakables"?  You should right click on each surface and disable the control functions you don't want.  Eg. The tail fins should not attempt to control roll, only yaw  etc.

Finally,  try coming in at a less extreme re-entry angle.    In KSP aerodynamics,  25 degrees is quite extreme and i don't think your craft has the agility to hold that.   There is no real need to.     Try setting 10 degrees instead,  and burn retrograde to intersect the ground a little earlier (like the desert) because drag will be less.     If it starts looking like you're overshooting,   raise the pitch a few degrees more for extra drag.    If it starts undershooting, lower the nose closer to 5 degrees , which is the best glide angle.     

BTW your method of attaching engines looks like it will create huge drag.    KSP aerodynamics hates it when you mate parts of differing diameter together without using an adapter.  It also hates empty attachment nodes, if you are not using all the points on an engine mount you need to put a cone.  Performance is  a different subject though,   this is about loss of control. 

I wrote more on drag here -

BTW,  when you graduate from Spaceplane on a stick type launchers,  here's a type of two stage to orbit jet boosted design to consider -

https://kerbalx.com/AeroGav/Learstar-A2

It's actually based on the stock VAB Learstar, I converted it to jet boosters instead of rocket -

stock version - 

 

 

..it seems to be something related AeroGav said... with the new model, If I try landing with the control surfaces off (in the first model), it doesn't flip in any direction... (but its pitch is below 0º with smart ASS configured in 10º).

The new model:

https://superki82.imgur.com/all/

https://imgur.com/QGBMknd

 

I've added a small MK3 cargo bay instead the 2,5m cargo bay, to put the central tail backwards. I've moved the solar panels in it, and now I'm trying with different configurations of the position of the big S wings...

But, What is CG?  and is there a better way to put the Nerv engines radially to a spaceplane? (without part clipping).

 

Edit: I forgot two questions... yes, I had advanced tweakeables On, and my configuration is:

- Central trail and upward winglet: Yaw

- Elevons: Pitch

- DeltaDeluxe winglet: Roll

 

On the other hand, I used 20º of pitch cause I read an old post that people recommended 40º degrees.. lol

 

 

 

 

 

Edited December 5, 2017 by GuyWithGlasses

[AeroGav]

14 minutes ago, GuyWithGlasses said:

The new model:

I've added a small MK3 cargo bay instead the 2,5m cargo bay, to put the central tail backwards. I've moved the solar panels in it, and now I'm trying with different configurations of the position of the big S wings...

 

 

But, What is CG?   -   Centre of Gravity  = same thing as Centre of Mass = The Yellow ball in the VAB

16 minutes ago, GuyWithGlasses said:

  and is there a better way to put the Nerv engines radially to a spaceplane? (without part clipping).

I like that method.

There are still some problems with the control layout.

Why have you got a tail fin at the front, attached to the roof of the cockpit?  Vertical surfaces passively increase stability when they are behind CoM,   even without being actively steered, aero forces on the fin push the tail back into line.  Conversely, aero surfaces ahead of CoM make stability worse, when they catch the air they will try to push the nose further out of line.  Get rid of it !!

Also, why have you got a pair of vertically orientated fins on the wingtips?     They are close to your centre of mass, so they have little leverage to control yaw.   Get rid of them, or if you want extra wingspan or roll authority, use the rotate tool to turn them horizontal.

 

21 minutes ago, GuyWithGlasses said:

with the new model, If I try landing with the control surfaces off (in the first model), it doesn't flip in any direction... (but its pitch is below 0º with smart ASS configured in 10º).

 

The blue ball seems to be a long way behind the yellow, so the good news is it is very stable in pitch, but it looks like it will be very nose heavy.  It will be very hard to hold the nose up on this design.   The only surfaces that can do so are the elevons you attached to the trailing edge of the wing,  as they are behind your centre of mass, they can get the nose up by pushing the tail down, so the nose pivots up like a see-saw.

 

But, they are pretty close to the centre of mass so won't be very effective as there is not much leverage.

Try attaching a pair of canards either side of the cockpit, use the offset tool to slide them as far forward as possible.

Remember, stability is not the same thing as control.   Stability comes first, then you add enough control to make the plane do what you want.

29 minutes ago, GuyWithGlasses said:

and now I'm trying with different configurations of the position of the big S wings...

The plane will glide more efficiently when the distance between yellow and blue balls is not so huge,   but obviously you still want to be stable.   You can safely use designs where  the blue ball is less far aft when the centre of mass doesn't shift much in your craft.     For example, imagine a space plane with heavy engines right at the back and a light cockpit up front.   It is balanced by fuel and cargo bays up front, but when returning from orbit empty,  the centre of mass will move way aft and become aerodynamically unstable.     A good basic layout has cargo bays right in the middle over centre of mass,  so it doesn't change Centre of mass whether loaded or not,     and distributes fuel ahead and behind the cargo bay in such a way that fuel burnoff does not change balance either.    Then you arrange the components that are always there - engines, cockpits , crew cabins  - to make the plane balance when empty.     Your design is pretty good already from what i can tell -  you have 6 tons of nerv engines fairly close to CoM,   and these are balanced by a 4 ton cockpit which is lighter than the nervs, but has more leverage due to being further away from it.

 

[GuyWithGlasses]

Hello!

I added the winglets in the main wing cause I've readen thats was the way to control roll... There is no need to have control surfaces to control roll?

The lastet plane with your suggestions.. https://imgur.com/xIeUDxZ

It flyes! xDDDDDDDDDDD at about 26k starts gliding well (loosing velocity slowly) but about around 10k the pitch falls below 0º degrees, I'd been able to try landing at about 100metres of the runaway at about 50m/s, I've lost the main wings..

Regards!

[GoSlash27]

GuyWithGlasses,

 The new design looks a lot more promising. Good job! I'd recommend getting rid of the winglets forward and at the wingtips.
 If you need more pitch authority, I recommend adding a pair of elevators to the vertical tail.

-Slashy

Edited December 6, 2017 by GoSlash27

[AeroGav]

12 hours ago, GuyWithGlasses said:

I added the winglets in the main wing cause I've readen thats was the way to control roll... There is no need to have control surfaces to control roll?

A vertical surface can never control roll or pitch,  it can only generate Yaw, because it can only deflect airflow left or right.    You need horizontal surfaces that lift up or push down parts of the plane.    They either lift the nose up or push the tail down to control pitch, or they lift one wing up and push the other down, to generate roll.      Real airplanes do have winglets but they are passive (no actively steering surfaces).   They reduce wingtip vortexes which cause drag and make turbulence for airplanes landing after them,  but KSP does not simulate wingtip vortexes.

12 hours ago, GuyWithGlasses said:

at about 26k starts gliding well (loosing velocity slowly) but about around 10k the pitch falls below 0º degrees, I'd been able to try landing at about 100metres of the runaway at about 50m/s, I've lost the main wings.

The thing is, in gliding flight, you have no engine power to maintain forward velocity,  so you counteract drag by flying "downhill".   During re-entry you want to lose speed ,  and stay out of the thicker parts of the atmosphere until your speed is reasonable.    But by the time you are subsonic (under 240 m/s)  you need to maintain speed at a reasonable value.

So, on the final 1000m altitude down to 100m altitude,  set pitch so the nose is pointing no more than 3 degrees above prograde.      On the final 50m above ground level, start increasing pitch to reduce the rate of descent to something your landing gear can handle.    You will no longer be getting enough velocity from flying "downhill" and your speed will start to decrease,  but hopefully you will have enough airspeed in the bank to maintain this low descent rate all the way to touchdown, without stalling.

Honestly,  you might be best off hand flying the actual landing.  Mechjeb is great for precise control on ascent for max delta V,   but in a rapidly changing situation like this it's gonna be tough.

Try to get used to thinking about "angle of attack" and not "pitch".   "Angle of attack" is the difference between where the nose is pointing and where the plane is actually going.    When angle of attack increases, lift increases, enabling you to fly more slowly.   However most of the increase in lift is from 0-10 degrees.   After 10 degrees there is not much more lift to be had, and at 30 degrees the wing stalls and lift actually starts decreasing.      Drag increases rapidly with increasing AoA, and goes up even faster after you stall.

I suspect you were telling mechjeb to maintain a flight path that didn't maintain your airspeed.    You got very slow,  and the nose might have been pointing at close to zero pitch,  but the airplane was dropping like a brick with the prograde vector in a 20 degree descent.   Thus your angle of attack was +20,   with high drag, and a high rate of descent needed to stop airspeed falling even further.      As a result you landed at high rate of descent which broke the wings.      

Note, this can be a problem when you attach the landing gear to the wings of heavy airplanes in KSP.   Sometimes it is best to attach them to the body, use the rotate tool to make them point straight down,  then use the offset tool to space them outwards.

11 hours ago, GoSlash27 said:

I recommend adding a pair of elevators to the vertical tail

Also known as a T tail 

Use the offset tool to move them to the top of the tail fin.  Because the tail fin is swept, this means it can be as far back as possible (far from CoM, so plenty of leverage) and also means it is well clear of engine exhaust.        I think he can keep his canards though,  as he is not having problem with excessively forward CG.  Also remember the rear mounted tail gets the nose up by pushing down,  so if you're having a problem with excessive descent rate on touchdown it's probably better to get the pitch you need from lifting the nose "up", if possible.

@GoSlash27 I do use tail elevators on my current designs as well though.   

Normal pitch control is via the canards at the front, but during the speedrun I "deploy" the rear elevators with an action group, which lifts the tail slightly , pushing the nose down a couple of degrees.   This stops the plane climbing above flameout altitude till i've wrung every bit of speed i can from the air breathers.   Then reset to neutral trim for the NERV-powered part of the climb.

 

Edited December 6, 2017 by AeroGav

[fourfa]

What a great thread! The help found in this forum for difficult spaceplanes in KSP is amazing

[GuyWithGlasses]

On 6/12/2017 at 8:40 AM, AeroGav said:

A vertical surface can never control roll or pitch,  it can only generate Yaw, because it can only deflect airflow left or right.    You need horizontal surfaces that lift up or push down parts of the plane.    They either lift the nose up or push the tail down to control pitch, or they lift one wing up and push the other down, to generate roll.      Real airplanes do have winglets but they are passive (no actively steering surfaces).   They reduce wingtip vortexes which cause drag and make turbulence for airplanes landing after them,  but KSP does not simulate wingtip vortexes.

The thing is, in gliding flight, you have no engine power to maintain forward velocity,  so you counteract drag by flying "downhill".   During re-entry you want to lose speed ,  and stay out of the thicker parts of the atmosphere until your speed is reasonable.    But by the time you are subsonic (under 240 m/s)  you need to maintain speed at a reasonable value.

So, on the final 1000m altitude down to 100m altitude,  set pitch so the nose is pointing no more than 3 degrees above prograde.      On the final 50m above ground level, start increasing pitch to reduce the rate of descent to something your landing gear can handle.    You will no longer be getting enough velocity from flying "downhill" and your speed will start to decrease,  but hopefully you will have enough airspeed in the bank to maintain this low descent rate all the way to touchdown, without stalling.

Honestly,  you might be best off hand flying the actual landing.  Mechjeb is great for precise control on ascent for max delta V,   but in a rapidly changing situation like this it's gonna be tough.

Try to get used to thinking about "angle of attack" and not "pitch".   "Angle of attack" is the difference between where the nose is pointing and where the plane is actually going.    When angle of attack increases, lift increases, enabling you to fly more slowly.   However most of the increase in lift is from 0-10 degrees.   After 10 degrees there is not much more lift to be had, and at 30 degrees the wing stalls and lift actually starts decreasing.      Drag increases rapidly with increasing AoA, and goes up even faster after you stall.

I suspect you were telling mechjeb to maintain a flight path that didn't maintain your airspeed.    You got very slow,  and the nose might have been pointing at close to zero pitch,  but the airplane was dropping like a brick with the prograde vector in a 20 degree descent.   Thus your angle of attack was +20,   with high drag, and a high rate of descent needed to stop airspeed falling even further.      As a result you landed at high rate of descent which broke the wings.      

Note, this can be a problem when you attach the landing gear to the wings of heavy airplanes in KSP.   Sometimes it is best to attach them to the body, use the rotate tool to make them point straight down,  then use the offset tool to space them outwards.

Also known as a T tail 

Use the offset tool to move them to the top of the tail fin.  Because the tail fin is swept, this means it can be as far back as possible (far from CoM, so plenty of leverage) and also means it is well clear of engine exhaust.        I think he can keep his canards though,  as he is not having problem with excessively forward CG.  Also remember the rear mounted tail gets the nose up by pushing down,  so if you're having a problem with excessive descent rate on touchdown it's probably better to get the pitch you need from lifting the nose "up", if possible.

@GoSlash27 I do use tail elevators on my current designs as well though.   

Normal pitch control is via the canards at the front, but during the speedrun I "deploy" the rear elevators with an action group, which lifts the tail slightly , pushing the nose down a couple of degrees.   This stops the plane climbing above flameout altitude till i've wrung every bit of speed i can from the air breathers.   Then reset to neutral trim for the NERV-powered part of the climb.

 

 

I hadn't too much time last days.. but thx for all your advices!

The last design I did last week was this: https://imgur.com/BxdS0j8

I toke the ship to a 80x80Km orbit and save the game, and I've tried around 5-10 times to land without much success xD

The last two-third times I've tried as AeroGav said, putting the nose 3º upper prograde, but around 10-15km, when I down the nose with smart ASS, the ship starts moving the nose up and down (to be around 7-10 of angle of attack), it's nearly imposible to control, but at around 2-3km the ship stabilices again, and almost allways I achieve to land... without one wing, normally xD

Some crashed pics xD

https://imgur.com/31USzoa

https://imgur.com/j5cl8bk

 

Regards!

 

 

[AeroGav]

7 minutes ago, GuyWithGlasses said:

 

I hadn't too much time last days.. but thx for all your advices!

The last design I did last week was this: https://imgur.com/BxdS0j8

I toke the ship to a 80x80Km orbit and save the game, and I've tried around 5-10 times to land without much success xD

The last two-third times I've tried as AeroGav said, putting the nose 3º upper prograde, but around 10-15km, when I down the nose with smart ASS, the ship starts moving the nose up and down (to be around 7-10 of angle of attack), it's nearly imposible to control, but at around 2-3km the ship stabilices again, and almost allways I achieve to land... without one wing, normally xD

Some crashed pics xD

https://imgur.com/31USzoa

https://imgur.com/j5cl8bk

 

Regards!

 

 

I think you'll have to share the craft file on Dropbox or KerbalX or similar so we can download it and find out what the problem is.    

On final approach to landing,  what are your 

1. speed (eg. 80 m/s)
2. pitch angle  (eg. Prograde Vector 15 degrees below horizon)
3. angle of attack (difference between where nose is pointing and prograde)

On touchdown, what are your forward speed, rate of descent and angle of attack like?  Is the plane stalling, or running out of ability to generate nose-up force?

I just reinstalled mechjeb myself,  it doesn't let you apply your own inputs when it is controlling the plane.  What happens if you disable mechjeb below 200 m/s  and just try hand flying it to touchdown? Unless there is something wrong with the airplane,  it shouldn't be hard to do.

 

[GuyWithGlasses]

20 hours ago, AeroGav said:

I think you'll have to share the craft file on Dropbox or KerbalX or similar so we can download it and find out what the problem is.    

On final approach to landing,  what are your 

1. speed (eg. 80 m/s)
2. pitch angle  (eg. Prograde Vector 15 degrees below horizon)
3. angle of attack (difference between where nose is pointing and prograde)

On touchdown, what are your forward speed, rate of descent and angle of attack like?  Is the plane stalling, or running out of ability to generate nose-up force?

I just reinstalled mechjeb myself,  it doesn't let you apply your own inputs when it is controlling the plane.  What happens if you disable mechjeb below 200 m/s  and just try hand flying it to touchdown? Unless there is something wrong with the airplane,  it shouldn't be hard to do.

 

 

I've done another try without smartASS, only keyboard; The plane has flown like a plane with a drunked-pilot aboard, , I hadn't be able to control the plane properly (the ship tends to roll) but.. the landing has been softer than previous landings xD (but the same result,  a funny crush, I'm an awfull pilot xD ).

 

The answers, if had readen well..

1. Between 40-50 m/s.

2. The prograde vector normally is beetween 15-25 degrees.

3. Around 10-15 degrees, even a few more in a few cases.

 

I think I need way mooooooore practice.

 

If I have done well, the file: https://www.dropbox.com/s/66swlmgdyxobmvr/SpacePlane15.craft?dl=0

 

[AeroGav]

2 hours ago, GuyWithGlasses said:

 

I've done another try without smartASS, only keyboard; The plane has flown like a plane with a drunked-pilot aboard, , I hadn't be able to control the plane properly (the ship tends to roll) but.. the landing has been softer than previous landings xD (but the same result,  a funny crush, I'm an awfull pilot xD ).

 

The answers, if had readen well..

1. Between 40-50 m/s.

2. The prograde vector normally is beetween 15-25 degrees.

3. Around 10-15 degrees, even a few more in a few cases.

 

I think I need way mooooooore practice.

 

If I have done well, the file: https://www.dropbox.com/s/66swlmgdyxobmvr/SpacePlane15.craft?dl=0

 

Thanks for the craft file.  

I could never design a rocket lifter that can fly with a monster like that on top of it,  your rocket is actually rather graceful.

To save time though, i used the cheat menu to put us in orbit then flew a quick re-entry.

You really need to fly this plane manually.    It's handling qualities are OK, but it is very draggy and glides like a brick.

Final approach speed should be about 110 m/s.   This gives a nose above prograde angle of about 5 degrees.    This means you have a little bit of kinetic energy in the bank for the touchdown.   Stall seems to be about 65m/s.    When you get to about 300m above ground level, start reducing rate of descent,  you'll have about 20 seconds to land before your speed bleeds off and you stall.

Manually flying your plane -

It's actually perfectly ok with mechjeb and SAS off,  it always wants to go straight.       Hold down ALT and tap the S key a few times to add a little bit of nose up trim.  It should settle into a glide with the nose about 5 degrees above prograde.    In the bottom left of the screen are the pitch./roll/yaw indicators, you will see the indicator on the first notch on the nose up control input scale.

400m above ground,  do another ALT S to add more nose up trim and it gradually rounds out for a landing flare pretty much by itself.   ALT  W decreases nose up trim.  Alt X resets trim to neutral.

NExt time you're 1000m above ground quick save so you can practice manual landings.

BTW I made a sucessful water ditching first try with no damage, but I landed short of the shoreline because i wasn't used to an airplane that has such a bad gliding angle.

Note, there is one major screwup in the craft that will affect controllability - the ailerons on the trailing edge of the wing are set to control pitch and nothing else.   They should only be set to control roll.

 

Edited December 12, 2017 by AeroGav