The K8J project

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Arfang

Well-Known Member
Joined
Aug 10, 2014
Messages
93
Location
Switzerland
Good day all,

I think it's time to finally present my project. It's a jet conversion of a Ka8B glider.

The goal from the get-go was to make a jet-powered conversion as inexpensive and simple as possible while being compliant with the french ultralight regulations. Also important was keeping the number of unknown factors down, focusing on having a flying airplane, improvements can always be added later.

The requirements for a single-seat ultralight were:

MTOM: 300 kg (661 lbs)
Vstall max: 65 kph (35 kts)
max engine power: 80hp

My personnal additional requirements were:

A minimum climb rate of 1.5 m/s (295 fpm) and enough fuel to gain approximately 3000 ft AGL in order to have enough altitude to switch to ''soaring mode'' before the engine runs out of fuel.

The choice of a glider airframe was motivated by the relatively high LD and low weight of this aircraft type, allowing good enough performance with only a small engine, reducing the cost. That and the fact that there are plenty of airworthy old gliders for sale at reasonable prices.

So I ran some numbers, compared several types of gliders and bought a Ka8B.

IMG-20180511-WA0001.jpg

Now to the ''build log'', note that not everything is mounted in place yet, I still need to do the engine installation and wiring, probably this week-end.

Added a nosewheel on the bottom of the skid, like on the Turbine 1-26. http://csanders2775.wixsite.com/turbineschweizer126
Chad Sanders was very helpful and provided more information about his nosewheel installation than I could ask for.

20180902_170302.jpg

Replaced the cockpit floor and seat, replaced the instrument panel with a custom one to accomodate the ''throttle'' and FADEC display.

20180914_193828.jpg20180903_200340.jpg20180903_200326.jpg

Designed an engine mount to install a 310N thrust engine on it. It's not retractable to keep the installation as simple as possible. The mount also holds the fuel pump and FADEC. The triangular structure on the left drawing is located on the left in the last image.

20180914_200136.jpg20180914_193647.jpg20180708_163003.jpg

3D printed fairings will slide over the mounts to cover the cables and fuel line.

20180914_194827.jpg

A 2.5 US gal fuel tank is located beneath the engine mount. I still consider making a custom one and I'd like to thank the HBA members who helped me but for now the goal is to keep it simple.

Removed several unnecessary elements like the second vertical speed indicator, second thermos bottle and tow hooks. The airframe ended up at the same weight as before the engine installation.

The airplane has now received a temporary permit to fly, if I'm not mistaken it will be the first 3-axis jet-powered ultralight under french UL regulations. It's also probably the cheapest private jet in the world.

First test flight will take place hopefully before the end of the month.
 

Arfang

Well-Known Member
Joined
Aug 10, 2014
Messages
93
Location
Switzerland
Update on the K8J: The test flight had to be postponed due to me not being able to find a suitable trailer. Fortunately, I found one for sale last week, so everything is now ready.

I decided to use those two weeks to make some improvements, I replaced the engine mount fairings with a lighter version and added an aluminium plate to better support the fuel tank straps.

20181010_182034.jpg20181010_182045.jpg20181010_182058.jpg20181010_182237.jpg

Also added some thermal protection to the top fuselage and tail:

20181010_182510.jpg

I noticed that a small portion of the fabric is slightly loose under the tail section, maybe someone more qualified than me could give me some advice on that.

20181010_183411.jpg
 

Chilton

Well-Known Member
Joined
Jun 28, 2014
Messages
98
Location
Jersey, channel islands
Loose fabric generally means something underneath has moved, possibly just fairing strips but may be structural, can you get at the inside for a look in any way?

I once rebuilt a PA15 which had a very similar start to that, but the owner decided to just shrink the fabric down, result went from one cracked longeron to both, plus the upper longerons bent when he landed!
 

Arfang

Well-Known Member
Joined
Aug 10, 2014
Messages
93
Location
Switzerland
Thank you, I'll see tomorow if I can see something from the inside. Is there something specific I should look for? I slid a block of foam under that area a couple of days ago to better distribute the weight, maybe it has something to do with my issue.
 

Chilton

Well-Known Member
Joined
Jun 28, 2014
Messages
98
Location
Jersey, channel islands
As it is probably 20 years since I last okkked at a K8 I cant remember if there is wooden fairing structure there or just the main longeron, if there is fairing theere it has probably pushed something out of position or cracked a strip, in which case not a biggie, if a longeron it is a bigger issue but mainly what you are looking for is anything which has moved.

To be honest if the fabric which has slackened is aagainst the main structure I think you will have to cut it open to check what has caused the movement but if it is only fairing pieces you should be able to make sure it does not interfere with controls and be good.

Fingers crossed it is fairing!
 

cluttonfred

Well-Known Member
HBA Supporter
Joined
Feb 13, 2010
Messages
7,306
Location
World traveler
No comments to offer except that this is a very cool project and thanks very much for sharing. I hope to see pics and video of your K8J in flight sometime soon!
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
You've probably already thought of this, but if not, it might be a good idea to use a bunch of temperature sensors while taxi testing to make sure you're not overheating anything on the fuselage that's downwind of the jet.
 

Arfang

Well-Known Member
Joined
Aug 10, 2014
Messages
93
Location
Switzerland
I have bad news, the structure underneath the fabric is in fact a longeron and it is bent.

20181012_145651.jpg

I have two options now: either find someone who can repair the structure and the covering or buy a new Ka8 to test the conversion now and repair the first one this winter.

Either way the K8J project is not over. I'll find a solution and keep you informed. Thank you all for your feedback.
 

addicted2climbing

Well-Known Member
Log Member
Joined
Jan 27, 2012
Messages
1,048
Location
Glendale, CA
You have picked my all time favorite sailplane. I have wanted to own one of these for years but at 6'4" and 230lbs I was usually outside the max pilot weight on any but the lightest version without any repair history. I do know I fit if it has the large canopy and not the Ka6 type. Looks like yours has the smaller KA6 type canopy. I will be following your progress.
 

addicted2climbing

Well-Known Member
Log Member
Joined
Jan 27, 2012
Messages
1,048
Location
Glendale, CA
Good day all,

I think it's time to finally present my project. It's a jet conversion of a Ka8B glider.

The goal from the get-go was to make a jet-powered conversion as inexpensive and simple as possible while being compliant with the french ultralight regulations. Also important was keeping the number of unknown factors down, focusing on having a flying airplane, improvements can always be added later.

The requirements for a single-seat ultralight were:

MTOM: 300 kg (661 lbs)
Vstall max: 65 kph (35 kts)
max engine power: 80hp

My personnal additional requirements were:

A minimum climb rate of 1.5 m/s (295 fpm) and enough fuel to gain approximately 3000 ft AGL in order to have enough altitude to switch to ''soaring mode'' before the engine runs out of fuel.

The choice of a glider airframe was motivated by the relatively high LD and low weight of this aircraft type, allowing good enough performance with only a small engine, reducing the cost. That and the fact that there are plenty of airworthy old gliders for sale at reasonable prices.

So I ran some numbers, compared several types of gliders and bought a Ka8B.

View attachment 74198

Now to the ''build log'', note that not everything is mounted in place yet, I still need to do the engine installation and wiring, probably this week-end.

Added a nosewheel on the bottom of the skid, like on the Turbine 1-26. http://csanders2775.wixsite.com/turbineschweizer126
Chad Sanders was very helpful and provided more information about his nosewheel installation than I could ask for.

View attachment 74199

Replaced the cockpit floor and seat, replaced the instrument panel with a custom one to accomodate the ''throttle'' and FADEC display.

View attachment 74192View attachment 74194View attachment 74195

Designed an engine mount to install a 310N thrust engine on it. It's not retractable to keep the installation as simple as possible. The mount also holds the fuel pump and FADEC. The triangular structure on the left drawing is located on the left in the last image.

View attachment 74190View attachment 74193View attachment 74197

3D printed fairings will slide over the mounts to cover the cables and fuel line.

View attachment 74191

A 2.5 US gal fuel tank is located beneath the engine mount. I still consider making a custom one and I'd like to thank the HBA members who helped me but for now the goal is to keep it simple.

Removed several unnecessary elements like the second vertical speed indicator, second thermos bottle and tow hooks. The airframe ended up at the same weight as before the engine installation.

The airplane has now received a temporary permit to fly, if I'm not mistaken it will be the first 3-axis jet-powered ultralight under french UL regulations. It's also probably the cheapest private jet in the world.

First test flight will take place hopefully before the end of the month.
Where in France are you? I have family in the GERS (Samatan) and visit every year. Would be cool to come see you once its flying.
 

Arfang

Well-Known Member
Joined
Aug 10, 2014
Messages
93
Location
Switzerland
That does not seem to be a big deal to repair...where are you?
Where in France are you? I have family in the GERS (Samatan) and visit every year. Would be cool to come see you once its flying.
I live in Switzerland, the airplane is currently there but will be flown and stored in the Doubs.

My next step is to contact Alexander Schleicher for advice and the local vintage glider association to see if they can help me.
 

Arfang

Well-Known Member
Joined
Aug 10, 2014
Messages
93
Location
Switzerland
Regarding the flight:

Takeoff from the concrete runway at 70 kph after approximately 11 seconds, the vertical speed indicator showed 1m/s and reached 1.5m/s when I got up to 90 kph. I felt some turbulences on the crosswind leg due to the Jura mountains nearby. Then finished my climb and set the engine to idle mid-downwind at about 900ft AGL. Landed on the grass runway like a normal glider, touchdown speed was about 60kph. After landing I was met by two police officers who saw ''an airplane going down trailling a lot of smoke'' and came to see if I nedded any assistance.

Takeoff speed and climb rate are close to my predictions.

Regarding the aircraft:

The K8 behaves superbly, I can't wait to fly it next summer in better weather conditions.
Some minor improvements could be made this winter: completely removing the steel plate on the skid to shed some weight and installing a bigger fuel tank. The 2.5 gal I'm using now was almost empty when I landed. And of course I need to find a way to install a camera on board.
 

jedi

Well-Known Member
Joined
Aug 8, 2009
Messages
2,102
Location
Sahuarita Arizona, Renton Washington, USA
Regarding the flight:

........ After landing I was met by two police officers who saw ''an airplane going down trailling a lot of smoke'' and came to see if I nedded any assistance. .........
How do you explain the "Lot of smoke"? I would not have expected it to smoke at idle or if shut down unless there were a fuel source with no fire.
 

Arfang

Well-Known Member
Joined
Aug 10, 2014
Messages
93
Location
Switzerland
There's always some smoke when the engine is running and even more at the start of the cooldown phase, that's probably what they saw.
 
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