9) Spaceplane trial and error

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Building a spaceplane in KSP isn’t easy, it takes a whole different approach and skillset to building rockets. I’ve never built one before so this is my attempt. My objective is to make a SSTO spaceplane that can dock at the KSS and then return to the landing strip at KSC.

 

Rather than go straight for it, I decided to get the basics of flight ironed out with a simple little plane:

 

Flight 10: Basic Jet

This short little guy was my first attempt
This short little guy was my first attempt

The first plane was simply a couple of jet fuel tanks with a basic jet engine on the back and a couple of wings for lift.

And it actually managed to fly!
And it actually managed to fly!
Pretty stable too!
Pretty stable too!

The first flight was a sucess so far! It got itself up into the air without a problem and was very stable in flight. There was only one real problem with it…

This problem
This problem

After a quick flight around the KSC I decided to try and land. And this I simply could not do. I could line up to the runway and with some trial and error (and many dead Kerbals, no ejector seat on this baby!) I could get it to touch down at a reasonable angle. But as soon as I applied the brakes or it slowed down to some critical speed, the nose would pitch downwards and slam itself into the ground. At the time I couldn’t figure out what was wrong but in hindsight I found that the front landing gear has to be placed on the capsule itself, not just behind it as I had done. I fiddled around with some other none-spaceworthy designs for a while to get a better feel for things….

Some were too back heavy and ended up flipping
Some were too back heavy and ended up flipping
Some had too much lift at the front and... also ended up flipping
Some had too much lift at the front and… also ended up flipping
Some were just too fat and ended up not having enough lift to get airborne....
Some were just too fat and ended up not having enough lift to get airborne….
This is what happens to planes that don't have enough lift!
This is what happens to planes that don’t have enough lift!
But some were just right!
But some were just right!

Over time I learnt what worked and what made stuff crash or fail in other unspeakable ways. I learnt that:

The centre of lift needs to be behind the centre of mass.

There needs to be enough of it to lift the weight of the craft.

You need enough control surfaces to be able to force the nose to point up when in thick atmosphere (it tends to point towards the direction of travel which is straight ahead just after takeoff).

Basic jet engines have waaaaay more thrust than turbo jets at low altitudes.

You need enough thrust to gain speed but too much will make you flip.

The plane needs to be slightly back-heavy or the nose will tend to pull downwards.

But if it is too back heavy the plane will flip.

Flipping is both hilarious and frustrating.

No matter how many Kerbals die, more will always want their chance to get into space.

 

So, after all that messing around with basic flight, it was time to get into space!

Flight 11: Spaceplanes in space!

My first spaceplane design
My first spaceplane design

My first attempt at this used rocket fuel for the central fuselage and two jet fuel fuselages on the wings, equipped with turbo jets. Two more basic jet engines and a LV-T45 rocket engine on the back provide extra thrust at low altitudes and non-atmospheric propulsion respectively.

The plane flew well and actually managed to get to space!
The plane flew well and actually managed to get to space!
But didn't stay there for long.
But didn’t stay there for long.

The plane was able to get to space but not establish orbit. One of the main problems was a lack of air from the intakes. Jet engines need atmospheric oxygen to run and all 4 of mine had their own air intakes for this purpose. However, once it got to around 17000m, the basic jet engines were almost useless (their thrust plummets at high altitudes) and the intakes weren’t pulling enough air in to run the ramjets efficiently. That meant I had to start the rocket engine earlier than I would have liked and it used up it’s fuel before it could get into orbit. So, modifications were made…

Take 2
Take 2

This time, more control surfaces were added and ram air intakes were added to the turbo jets. These are far more effective at grabbing air at high velocities and altitudes. It still retained the basic jets for thrust at low altitudes. However, the plane wasn’t able to gain any altitude.

Correct end not pointed to space
Correct end not pointed to space

No matter what I did with this plane the nose just refused to rise and I couldn’t get above 1000m. Luckily, I had by this time learnt how to land!

Not the runway but the wheels seem rugged enough to take a grassy landing!
Not the runway but the wheels seem rugged enough to take a grassy landing!

The problem this time was that the control surfaces at the front weren’t providing much lift so the centre of lift was too close to the rear of the plane.

So, more trial and error time!

Jeb was happy that an escape mechanism had been installed for this round of 'trial and error'
Jeb was happy that an escape mechanism had been installed for this round of ‘trial and error’

After an hour or so of re-jiggering spaceplanes I finally came up with a design that worked:

May I present:  A working SSTO spaceplane!
May I present: A working SSTO spaceplane!

The basic jets were scrapped, I found that the turbo jets produced enough thrust as long as there were enough lift surfaces. The turbo’s managed to stay on up to 26000m and kicked the plane up to a speed of 1100m/s. The aerospike engine then fired and carried the plane into orbit.

Jeb was so excited and confident about this one that he even did an EVA selfie once orbit was achieved.

HAI GUYZ!
HAI GUYZ!

Once orbit was achieved, another burn took the spaceplane straight to the KSS for a docking maneuver.

The spaceplane comes in to dock
The spaceplane comes in to dock
And manages to grab ahold of the KSS
And manages to grab ahold of the KSS

After swapping some science and admiring the RIS docked to the other end, Jeb undocks and begins his return journey, aiming for the KSC.

Re-entry was dramatic as always.
Re-entry was dramatic as always.

A quick burn of the jets brought the plane on a course for the KSC. A few kilometres away the engines were cut and the plane glided towards the runway for a smooth nightime landing.

Ta-da!
Ta-da!

A very proud moment for me! Not only had I created an SSTO plane, I had also learned to fly it, docked with a spacestation and returned for a textbook landing on the runway. Happy days!

 

Pfft, its easy really. Not sure what all the fuss was about.
Pfft, its easy really. Not sure what all the fuss was about.
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