erazz

Hello All,

I've just completed building my Wren MW54 almost from scratch. (bought the turbine, diffuser, compressor and the combustor)

I'm planning to install it on a JHH Kfir fuselage and I have a couple of questions I hope you can help me with.

1) Where should the C.G. be? (I'm hoping that I can mount the engine in the back and save the trouble of an exhaust pipe)

2) Should I use flaperons or split elevators/ailerons?
pros and cons as I see them:
- flaperons have more drag.
- flaperons need less servos (2 instead of 4 - and no, I'm not going to use 3 or 2 and use long push rods for split )
- if I lose a servo with flaperons... well...

3) Should I add the rudder or just glue it on (a Friend told me I won't use it at all)

4) Should I mount the antenna on a whip?
I'm using the flightworks fuel pump which is really well suppressed and I really don't like the look of whips.


I'd really appreciate any input you can give me on this plane.

erazz

BTW if anyone is interested I have some pictures of the building process (of the engine).

SJN

I would like to se more pictures...

Does anyone know how high the temps are at the diffuser and intake area ?


SJ.

L Turner

My Feedback: (3)

I recommend you refer your questions to Larry at www.jethangar.com. Check out the Kfir FD3/67 turbine conversion pictures at his web site.
He has been always been very helpful to me, both with DF engine problems and in suggestions for my RAM 500 Cougar conversion, now almost ready to go.

Doc_Dyer

My Feedback: (4)

I thought that I read somewhere that the turbine model had to have brakes and a rudder? is that written somewhere? AMA rules maybe??

Bradley

Gordon Mc

My Feedback: (11)

Since the originator of the thread is in Israel, he probably doesn't care about the AMA rules ... but yes, AMA does require a rudder on turbine models, and requires brakes if the aircraft will not remain motionless when the engine is running at idle.

Erazz - we'd love to see some pics of how you built the engine - either here in the jets forum, or over in the "User product Reviews" forum (http://www.rcuniverse.com/forumdispl...s=&forumid=142) would be great.

Gordon

erazz

Just been to JHH's site. I guess since they're stocking Wren engines now they'd know

Luckily I don't have to deal with the AMA... On the other hand finding a place to fly here is not that easy, especially with jets.



O.k., about the engine. I'm copying stuff from my log, basically the things that seem most interesting (to me )

Picture #1:
This is the combustion chamber (combustor). You're basically looking up the tailpipe here. The fuel is injected through the curved tubes there it vaporizers. Combustion occurs near the front of the chamber and progresses back to the annular aperture where the turbine is located.

This whole thing is only than 3" across.

MMallory

My Feedback: (1)

Erazz,

Check out this thread.

http://www.rcuniverse.com/showthread...420&forumid=26]

erazz

Picture #2:

Shaft tunnel being turned here. Though some of these parts look simple, they are in fact extremely hard to make because of the accuracy required.

erazz

Thanks MMallory,

If he can fit THAT into the tail then I'm home free (my engine weighs a lot less)

Picture #3:
Being impatient and out of 3.5" dia. mild steel rod I decided to make the rear case out of a large (20x30x5mm) square piece of steel.

Ever see a 1 ton lathe dance? Scary...

erazz

Picture #4:
The finished part (case rear) being drilled for the case screws.

erazz

Picture #5:

Brazing the fuel ring.
Difficult difficult impossible. Basically I burnt through so many of them I just gave up and ordered one from Wren. I still don't understand how they do it but after seeing their work I'm glad I bought one.

erazz

Picture #6:
Even though I didn't use it, this is the most complete ring I managed. (right before I discovered a loose needle and blew another hole)

This is the mandatory flame test. Mandatory because of the neat picture.

erazz

Picture #7:
All the parts ready for assembly.

erazz

Picture #8:

Balancing.

The idea here it that the rotating parts are mounted inside a tube (I used the shaft tunnel) and rocked back and forth. Needless to say that this is a long proccess and that the bearings need to be COMPLETELY clean.

After 4 hours I thought I was done. Later (while running) I discovered that I the balance is still not good enough. I'm going to steal a friend's dynamic balancer and redo this step.

erazz

Picture #9:

The completed engine after 6 months and lots of $$$$$.

Way worth it in my mind. I didn't save any money over the kit that Wren produce (the tools cost a lot) but I had a lot of fun and I know how to service my engine (basically don't touch it until it makes strange noises ).

ajcoholic

My Feedback: (10)

Thats very excellent work! I built a Wren MW54 from their kit last year (flying in a Mick Reeves Super Reaper) and just last evening finished my first "scratch built" engine, a KJ66. I too bought the same parts as you did (diffuser, combustion chamber, turbine wheel and compressor) and did the rest myself. Its sure neat, and I will hopefylly get a chance to test run it as soon as I get the GB Hobbies TCU hooked up and programmed.

Are you planning to build another engine? I think I will try another one in the future.

Regards from Canada,
Andrew Coholic

PS see the detailed building with pics of my engine at: http://www.rccanada.ca/bb/viewtopic.php?t=2018&start=80

DaFatha

erazz,

Saw your post about the Mirage. Here are a few comments I hope will be helpful to you and others:

1) Highly recommend incorporation and use of rudder on your Mirage. Without it you will lack control in cross-wind situations. Actually, all airplanes fly better with all the flying surfaces functioning--afterall, the real one has a rudder for a reason!
2) I recommend using elevons and with today's radio technology, it's simple. In the "early days" we didn't have the luxury of mixing on the transmitter.
3) In order to give you CG information we need to know the
a) wing span (there are 3 different wing for the Mirage) and
b) whether or not it has canards.

Best regards,
Larry Wolfe
[email protected]

erazz

Thanks Larry!

Saved me an e-mail there .

My Mirage has the sport wing (I bought the cores from you a few months ago) and I probably won't use canards.

My main concern with the rudder is that at first I thought to put the engine right below it. Right now it looks like I'll mount the batteries in the nose (2 6v batteris - one for the radio and one for the pump) so hopefully I'll be able to put the engine behind the rudder and solve that problem.

Reply to ajcoholic:
Thanks! Saw the link and I can only sympathize. I also work on an Imperial lathe. Thankfully I had a gear ratio that gave me exactly 1mm pitch so I was o.k. there.

I think I spent about 3 times as much time making tools and fixtures and about 5 times as much time measuring. Not to mention all the parts I had to redo .

I am planning another engine. I'm collaborating with a few people to make an engine with a 34mm compressor and a 31mm turbine. Projected speed: 215,000 rpm. It's all very preliminary so don't stay up late waiting for updates... (I'm not even sure it will run)

ajcoholic

My Feedback: (10)

Good luck with that new engine! Are you a member of the GTBA? If not, you should get the back issues of the newsletter on CD and read all of it, there is tons of valuable information and also makes a very complete history of the progress of the micro turbine engine to date.

Regards,
Andrew