JHH-A7 with the new Kingtech K45
 

Starting a conversion on an old JHH-A7 electric to turbine. This will be a Kingtech Demo plane for the all new Kingtech K45. I know some people still have these planes sitting around so the K45 should make a good fit for this aircraft.
http://www.rcuniverse.com/forum/atta...mentid=2100626

http://www.rcuniverse.com/forum/atta...mentid=2100627

First up was to build the cockpit. The cockpit comes with some vacuum formed plastic parts that need to be assembled. Needless to say it was a pain. My goal was to make it look good but also make it easy to remove for access to the batteries. I want this plane to be an everyday flyer and so I am going to try and not get crazy with scale details. I was able to make the cockpit all one piece for easy removal.
http://www.rcuniverse.com/forum/atta...mentid=2100628http://www.rcuniverse.com/forum/atta...mentid=2100629http://www.rcuniverse.com/forum/atta...mentid=2100630http://www.rcuniverse.com/forum/atta...mentid=2100631

The electric set up had the engine mounts behind the gear. I will use the same mounts for the turbine so for CG both receiver packs and ECU packs need to go into the nose. The new smaller Kingtech LIFE batteries fit well for this in front of the cockpit. They come with nice long leads already installed also.

http://www.rcuniverse.com/forum/atta...mentid=2100632http://www.rcuniverse.com/forum/atta...mentid=2100633

I have the pipe on order along with some other odds and ends. I will use regular dubro fuel tanks. The plane already has electric gear from down and locked. Will install a spektrum receiver along with a eagle tree gyro.

Kick a@$ love this jet, nice project!

Very cool project Kris!!

I have been wanting to build Century jet A7 for a while. This thread is pushing me to the edge. ;)

Any idea of weight? I am planning on putting a K45 in a Phoenix Preceptor.

Not sure if you want weight of the plane or just the turbine. Here are the specs of the K45. Weight shows 1 pound. If you need me too I can weigh it. It has a tiny little fuel pump :)
Diameter: 76mm (2.99")
Length: 195mm (7.68")
Weight: 700g (1 lb. 8.6 oz. )
Max. RPM: 162000
Thrust: 4.5 kg @ 15° C ( 9.9 lb @ 15° c )
EGT: 700°C max
Fuel consumption: 155 g / min ( 5.46 oz / min )
Fuel: Diesel, Jet A1, Kerosene
Lubrication: 5%
Maintenance cycle: 25 hr USD300

Sorry to be unclear. I have the engine already. I was curious as to what you thought your all up weight would be.

Im a big fan of small turbine jets. Love the project.

Ahh ok no problem. When I get the pipe and tanks I will stick it all in and weigh it. Hopefully next week it will all show up.

Hi Kris,
My JHI A-7D with a Wren44 (RIP:() weighed a hair over 13lbs dry. This with a 4oz header tank, two 1100mah A123's, and scale cockpit and pilot.
- Mike

I'm looking forward to how you make out with this conversion. I have a Yellow A-4 that I'm going to put a turbine in and I'm deciding between a K-60 or a K-45...

Bob

Is the A-7 kit still available? Love that plane...

Mike that A7 looks great! Sorry to hear that it is not with us still. I hear most of them eat it on a crosswind.

Bob I will keep you updated. I have everything now accept tanks and pipe. I need both of those before I go any further.

Scoles its not made anymore sadly. I hear Global jet club bought the rights to it but nothing is made.

Actually was lost at the AZ Jet Rally 3 years ago.....a 2.4ghz conversion on my Multiplex Evo "worked until it didn't".....sucked.

I'd say that you really have nothing to worry about as far as flight characteristics; very honest and it will waggle the wings if you get too slow. The narrow main gear really don't do well in a crosswind......just like the real one, it has to be flown all the way to taxi speed.
- Mike

I had tons of flights in mine before I sold it and this is what I learned:

Dont use take off flaps, it makes the jet wheel barrel and like to get it in the air before it's ready!

Use very little rudder if any! I like rudder in my jets but the rudder is extremely effective and causes roll!! I had no more than 1/4" of travel in mine and that was still a lot...

Be sure the nose gear is on a separate channel, lots of the crashes were guys leaving the nose and rudder on the same channel, they would trim it in the ground for the nose gear and not realize that they added a tiny bit of rudder trim, when the jet would lift off the rudder would roll it over and then into the ground....

Crosswinds.... I flew mine in crosswinds every so often, it is totally doable but remember the rudder will add lots of roll! The jet will weather vane in the crosswind and some guys would try to compensate with rudder and roll it into the ground. The anehdrial also is a bit of issue with the crosswind but if you keep it in the ground longer it won't have a problem.

The jet definitely likes to shimmy around when getting slow but it never seemed to be a problem.

If Iwere to build another I would put a cortex or 3e on it and I think it would improve the airplane quite abit, but still very minimal rudder!!!!!

I read this with great interest. I had one of these models and considered it to be one of the prettiest scale models at the time. However it was the only plane that I have owned that proved to be unflyable. In the Uk we always fly in winds and normally about 20 mph or over is considered too strong. Most of our ex RAF airfields have been built on a standard pattern with the main runway aligned west east the then prevailing wind direction. It does seem that this has changed in the last 75 years and we just have to be ready to fly in cross winds. Large heavy jets can normally fly in cross winds especially when the wind direction is not exactly 90 degrees to the runway. Sometimes were are lucky to fly on main runways enabling small jets to take off across the runway.

My A7 was powered by a MW44 which was ample thrust. The first flight was in a cross wind and we were flying on a narrow perimeter track. Dave my pilot has flown loads of weird different models some never flown before either as models of full size so was very experienced. He took off and found the plane just such a struggle to fly as it seemed to want to flip over on its own. In the end he landed in long grass wide of the runway and the wing broke in half and the fuselage was badly damaged. I repaired it all and the next time I took it to fly we were on the main runway. This time I had one of the UK's leading display pilots at the sticks. He took off and the plane promptly flipped upside down and smashed itself to pieces on the runway comprehensively destroying itself. We were both a bit shocked as it was so unexpected. I thought at the time I must have assembled the plane with the ailerons reversed and that the pilot had not checked the controls, however unlikely this was.

it seems from your post that this plane has a rudder issue and needs hardly any, and that cross wind flying is not encouraged. That seems a likely explanation of the problems we faced.

The one thing I can say having flown both engines that the Kingtech 45 has more power than needed and is a great engine. The plane is very small and if I was looking for a demo plane I would have gone for something larger to fully utilise the power. Yesterday Dave flew my Swift glider with the Kingtech on it and despite weighing 8 Kg with fuel it was very sprightly.

Good luck with the A7 and do let us know how the maiden goes.

John

I can say there is definitely not a design flaw, it was designed off of wind test models of the full scale. The rudder is just VERY effective and it is not the solution for crosswinds. The key is to keep it on the ground as long as possible and not to use rudder to correct the yaw from the weather vane effect!

The good news about the power setup is the A7 likes to go fast! Mine was flown with EDF with a TJ-100 on 10s,top speed was about 125-140 and it was very locked in at those speeds but at half throttle it liked to move around a lot. Chris Wolfe flew his with a wren 44 and it flew awesome, he now has an12s 9m setup and it moves out real nice and still lands very well at 15lbs.You definitely have to fly it like your in it and no yank and bank, fly it like your in it! Also be prepared to get on the power after you drop the gear, they have a lot of drag. The plane lands awesome but will move around a bit on final and that's normal.

why not use a gyro, would help a lot!!

I still have the video of the first flight and can see where it tried to flip over when banked in a modest turn. All the flying was done level and mostly just doing simple circuits, nothing fancy. It was very windy when we flew it but we would have flown other planes in the same wind. The plane was rocking about and far from stable. I can only think a combination of a strong wind and use of the rudder may have contributed as well as the tall fin. We did have too much aileron travel which didn't help either. The wheels were retracted for most of the flight and it was flown reasonably fast. I am not saying there was a design flaw just pointing out that I have had 31 different jet models and was this was the only one that proved an unsatisfactory flyer and did not survive. As you say on finals it moved about all over the place. I guess you would be ok if it was flown in still conditions only.

John

John

John,

I'm sorry to hear about the A-7. Lots of rudder combined with cross-wind can be a recipe for difficulty. It took me a while to figure that one out myself. However, I've since toned down the rudder considerably on mine (at Brian's recommendation) and the airplane is much more manageable in adverse wind conditions. Also, taking off without flaps has helped improve takeoffs dramatically (also at Brian's recommendation) in these conditions too. I've found that it also helps keep the wing tips from lifting during the takeoff ground run in a crosswind. A few years ago, I converted my original mw-44 powered A-7 to 90mm EDF and she's still going strong! :) Here are a couple shots from our Warbirds and Classics event this past weekend.

http://www.rcuniverse.com/forum/atta...mentid=2101376http://www.rcuniverse.com/forum/atta...mentid=2101377


Kris,

If it's helpful, here's video of my A-7 that was taken around 2008 when it still had the MW-44 in it. At the time, I was using flaps for takeoff and you can see the airplane wheel barrow prior to lift off. As Brian mentioned, the airplane likes to cruise with a decent amount of speed. As it slows down, the wings can wag a bit, but the key is to not try and correct it. If you're using a multi-axis gyro, then I don't expect you will see that at all. CG the airplane by lifting it with your finger tips at the LE sawtooth, that is THE best way to CG the airplane (don't bother with using the measurement shown on the drawing in the instructions). Lastly, regarding rudder throw, I have mine set at about 3/8" travel, I don't recommend any more than that, otherwise elsewhere I'm using all the same recommendations for throws that are in the instructions. Let me know if there's anything I can do to help!

https://www.youtube.com/watch?v=xcXLeOcB00A

Chris

Thanks for your reply.

I had the CG set in the way you describe. From your video looks like you have some flat calm days in the USA. They are few and far between in the UK! I think with the strong winds it just made the landing extremely difficult as it rocked about. At the time we did wonder if the plane might have flown better upside down as it was so keen to flip over. There is no doubt it is a pretty plane especially the white and red NASA scheme so its as all the more upsetting to lose it. It was a long time ago now and I have made many more planes since. The best flying plane I have made so far is a flying wing with no fin and no rudders and just ailerons for control!

John