The K8J project

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Hot Wings

Grumpy Cynic
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Sad news for the K8J:

My test flight alerted the EASA, which consequently contacted the french aviation authorithy about it. They have decided to revoke the K8J permit to fly.
There is a reason the English voted for Brexit ;)

Your turboprop plans may end the same way. We have an expression here in the US "It is often easier to get forgiveness than permission". It didn't work for you the first time around. :depressed
If you can afford the time and money to build the turboprop version, knowing that you may meet the same end, it may be the best option?
 

Arfang

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A Part 103 jet ultralight pilot does not need any endorsement. But a K8 does not qualify under Part 103 because of weight.
That was my point. It's the same here, UL pilots don't need endorsement for turbine/jet engines.

Look at Jbiplanes Wankel
A google search took me to the REAA forum and to a page with CAD renderings but I found no Wankels on this website, what exactly should I look for?

There is a reason the English voted for Brexit
I would also like the bureaucracy to bureaucrexit.

Your turboprop plans may end the same way. We have an expression here in the US "It is often easier to get forgiveness than permission". It didn't work for you the first time around.
If you can afford the time and money to build the turboprop version, knowing that you may meet the same end, it may be the best option?
Are you suggesting putting the turboprop without telling anyone? There might be no need to do that, some measures have been taken but I can't give more details for now.
 

Hot Wings

Grumpy Cynic
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Are you suggesting putting the turboprop without telling anyone? .
No. If the path looks to be reasonable according to the French regulations*, AND you can afford to ultimately be rejected, then build without consulting the EASA for their opinion. Getting permission or approval from the EASA may be a long and expensive project.



*or some other path that you may already have found but don't care to share right now - which is completely understandable.
 

ypsilon

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Mar 1, 2016
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There is a reason the English voted for Brexit ;)
option?
In all fairness. This time it isn't the EASAs (EUs) fault. They just told the french authorities, that this machine isn't EASA business, which it clearly isn't under regulation 2018/1139. It's the french authorities that messed up here. Sometimes the EU is more reasonable than our national governments.
 

BJC

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The jet powered Mitchel wing was operated under USA FAR 103 but was limited to 5 gallons of fuel. It was barely enough for two short circuits of the ultralight strip at Sun-n-Fun.
It didn't go far, but it arrived in style.


BJC
 

Arfang

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Unfortunately, no answer from the aviation authorities or even from the ultralight federation. The K8J will not fly again. However, the engine supplier accepted to replace the turbojet with a turboprop transforming the K8J into a K8T.

It's a KingTech K-100TP producing 13kW, spinning a 4 bladed 26x22 propeller.

20190308_170336.jpg

The engine will be mounted in the nose. Above the nose actually. The pitot tube will have to be moved under the propeller arc, where the tow hook is currently located.

Here's a rough idea of the engine installation:

K100TPmount080319_1.jpg K100TPcowling080319.jpg

It would be made out of steel sheet and welded to the fuselage. The idea is to use the engine mount as part of the cowling. It's still work in progress at this point.
 

Arfang

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As you wrote, the structure is designed to react to 'tow' loads. However I can only get an estimate for thrust since no propeller data is available.

Using formulas from Simplified Aircraft Design for Homebuilders, I was able to estimate a thrust force of 112lbf at 32kts, taking into account a 10% power loss due to cooling drag. 120lbf without power loss. Eta P was 0.75, Advance Ratio was 0.569 and the Power coefficient was 0.078 in both cases.

Using J.C. Debreyer formulas I got an Eta P value of 0.57 at a max cruising speed of 75kts. Using that value of 0.57 the thrust goes down to 88lbf at 32kts. Those numbers could be off though, I'm still at the beginning of the learning curve. I'm thinking about using the highest thrust result to calculate the thrust loads on the structure and the lowest result to calculate the flight performances.
 

Grelly

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Aug 27, 2010
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Surrey, UK
Somehow I am very late to this thread, but had to chip in. I have many happy memories of flying the K family back in the late 70's, early 80's. I learnt to fly in K13's and K7's and graduated to K8's, K6's and K18's. I lost interest in gliding when the club I belonged to sold the last of their rag-and-tube gliders and went all K21's and K23's. For me, the glass machines didn't have soul the way that the earlier gliders did.

Good luck with your project.
 

Arfang

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Quick update on the project:

The engine mount design is done, the engine will be located over the main spar instead of the tractor configuration presented earlier. The reason for that is to be able to remove the mount in the case I want to install another engine or operate it as a 'normal' glider. Also, it's a tried setup used previously on another motorized K8:



Here's my design without the cowl and fairings for comparison:



Also, the airplane has been re-registered as a K8T by the authorities, thus allowing me to perform flight tests.
 

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bmcj

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Given the high exhaust speed compared to the flight speed, would a thrust augmenter tube give you more overall thrust?
 
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Arfang

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Why not, although I didn't find anything about thrust augmentation on turboprops. Do you have more information on the subject?

What I could do is add curved exhaust pipes to direct the exhaust flow backwards.
 

Arfang

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The powerplant unit is now complete with fairings and air intake, all 3D printed. The intake alone took 72 hours.

20190725_223914.jpg
 
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