Hi Guys!

Well I think it's getting close in time the momen to first run my NIB tower 75... I was wondering if a scimitar 11x7 would be too small for breaking in the engine? I have an 11x7 and an 12x6 there, but I was thinking running it with the smaller one because I can rev it up more, and do the breaking in procedure that Dar Zeelon sugested...

Another fact is that I'm going to run it with zero nitro, plain castor oil.... Does this engine have more than one head shim that I can remove or should I leave it the way it is?.

Also I pushed tight the carb until I heard a click and was fully seated, opened the backplate to search por metal shards, none found.
It comes with a no brand glow plug, but I suspect it is the same super tigre glow plug..and heard that it will burn out at the end of breaking in....

Take a loot at the plane I'm building...it's not finished yet, but there are few things left plus covering...!! And I have to get a bubble cabin.... or make it, because I cannot get a molded one!! any suggestions?

Thanks a lot, Jorge

As long as you do not over rev the engine it will be fine

If you have a heat gun for your covering work, you can heat the engine before the first
start up. You noticed how tight the engine is ? When you start the engine it will knock for
several seconds because it is tight. If you heat it up first, that knocking can be eliminated.

FBD.

I second the heatgun to warm the engine on startup. Don't overrev the engine it doesn't like to turn the high rpms.

Yeahhh it¡s very tight, without a propeller I cannot turn it by hand...
Acctually, I don't have a heat gun, only my mom's hair dryer hehe, I expect I can order an Iron/heat gun combo soon...

Which is then the rpm limit that I should run on the engine while the breaking in with the 11x7?

Thanks for the replys

Refrain from turning the engine by hand....dry. Do not flip the engine over with a prop, dry.
Open the exhaust and drip a few drops of oil into the back of the cylinder wall. Run the piston
up a bit and put a few drops of oil on the side of the piston, so that it in turn will get some oil
on that side of the cylinder wall.

The hair dryer will help put some heat in the engine, although not as good as a heat gun.

The engine is rated at 17,000 RPM....you will be turning it at right about 15,000 with the 11-7
prop, so you don't need to worry.

FBD.

Jorge - Just last week, I ran-in a new TH75. Just some observations for ya .....

I used an APC11x6, 15% fuel (18% oil), tower plug that came with the motor, and a pitts style exhaust. Per the manual, I had the HS needle at 4.5 turns out. Put alittle after-run oil around/on top of the piston, and it fired right up. Ran it WOT for the first and second tank. I did lean the HS needle a half-turn or so during the first tank .... it was 4-strokin abit. RPM was upper-12K's for those first 2 tanks.

The 3rd tank, I put an APC 12x6 on it, and again ran it at WOT taking note of head temp as I leaned the HS abit more. RPM's were low-mid 12K's.

I did run one more half tank or so, working on a decent transition so it would be flyable. I should mention that I did let the engine cool completely between each tank.

I've now got about 1.5 gallons of fuel through it, and its getting better and stronger with every flight. After each flight up to this point, I've made small changes to both the HS and LS needles, and also paying attention to head temp. I've also changed to an OS#8 plug. At this stage, I've found that a Zinger 12x8 prop is best .... but that is sure to change as I make needle adjustments. I should mention that I'm not looking for speed ..... I want power and pull for the Big Stick 60 its mounted on. I tried a couple of props in the 13" diameter range, but didn't like them. I'm still alittle more than 3 turns out on the HS needle so its still on the rich side ..... but its smooth, has an improving idle and a nice stream of smoke.

Couple of things to watch out for .... both carb related. At some point during the second tank of breakin, the carb barrel stop screw backed out. Since the engine cylinder is mounted horizontal ... this allowed the carb barrel to pretty much drop out. Didn't notice it until after the engine burned the whole tank of fuel .... how long it was like that, I dont know. That screw, as well as the carb hold-down nut has a generous amount of thread lock now. The carb body itself is the second part to watch out for. For most of a gallon of fuel, I was having trouble shutting off the engine with the Tx throttle-cut. I knew there was an air leak somewhere, and had covered all the bases of culprits .... including reading ALOT of posts about defective carbs on the TH75. I'd already had the carb off a couple of times and was sure I had pushed it down into its mount sufficiently....and then tightened the nut. On saturday, I decided to try it one more time ..... with the engine warm. Loosened the nut, and pushed the carb down for all I was worth .... ..... tightened the nut, and Ba-Da-Bing!! No more air leak! And the engine shuts down everytime now.

I flew the plane about 10 times on sunday ... and the TH75 is fantastic!, and getting better all the time!

Your mileage may vary, but I hope my very recent experience is of some help to ya!

FlySafe! Larry (Larrys4227)

Wow larry that's great info...!!


I can't wait to run the engine..but Have few things left to do in the plane, so I think I'll have to wait a month or so to get it finished... I'll take your suggestions...also i'm going to threadlock the large bolt of the muffler and all the junctions to get it sealed....

So, I will break-in the engine with 11x7 propeller...and then I'll switch to 12x6...Is all I have here by now.... I'm looking for kind of speed, but the plane is a little big...let's see when I finish it.

Thank you

Jorge

I had some muffler troubles with my TH75.. couldn't keep the dang thing on! Final solution was to throw out the through bolt that goes through the muffler.. Went to the hardware store and bought a piece of threaded rod.. Put that through the muffler and used double jam nuts on each end with red locktite.. Oh, also used red RTV high temp silicone on the 3 main sections to keep them together.. the RTV has enough flex that it doesn't vibrate into pieces.. That sucka hasn't moved since..

Jorge - There is alot of vibration when breaking in the engine. I've noticed recently that the more fuel I put through it, the better its getting. Since I have the pitts style exhaust, I dont have the through-bolt, but I did thread lock the mounting bolts. Have not had any problems with it. I also thread locked everything else .... eventually getting to the carb. Dont know why I skipped that at first ... dummy me. LOL! Also, make sure your prop is balanced.

What kind of plane are you putting the TH75 on? Dont recall you mentioning that ... maybe you did. [8D]

FlySafe! Larry (Larrys4227)

Jorge,

This is a good time to run the engine on a test stand before your model is finished.

Larry the first post has pictures of the plane I'm building, it's my own design...

And about the test stand, it would be great...the thing is that I don't have a test stand and I think if I run the engine here in the apartment everybody is gonna get rid of me!!!....but anyway, I think it's a good idea to put the engine in a stand...

Thank you for the replys.

Jorge

LOL! Serves me right for not looking back at the 5 pictures you posted. Nice looking plane! The TH75 should pull it around nicely.

Engine breakin + Apartment = Eviction Notice

Yup, I'd come up with another plan .....

Keep us posted!

FlySafe! Larry (Larrys4227)

Some people run their new engines at the field when they go out to fly. That's what I would do.

The Tower 75 will run with the bes of them including OS and will probally last longer.

Can you mail order from Sig?

http://www.sigmfg.com/cgi-bin/dpsmar..._02Canopies_01

David

wowa..thanks David, I really don't know if I can order from them, but I give it a try... THank you!

Jorge

Well, This is an update...I'm really happy indeed...I bought 3 rolls of Monokote (I haven't covered with monokote since like 5 years ago...due to $$, I used vinyl that cost about the whole material to cover the plane half the price a roll of monokote here) and covered the plane...I fitted the Tower 75 with a 11x7 scimitar prop, and also I'v sealed the muffler with rtv (I found that the center and front parts of the muffler already came with RTV), also sealed the junction with the block.

Just some aileron hingin' and aileron servos installation and I'm done.....well also balance...it is nose heave (note long nose moment)

I removed a one of the two head shims that came (the thiker one) because I use 0 nitro.

I hope I can break in the engine soon and let you how it goes.

It's a shame I don't have a test stand, and here in my apartment its complicated...I can't even run the engine here.

Here some pics =)

Jorge

Nice ship Jorge. It looks like it's going to scoot along!

Wellllllllllllllllllllllll PEOPLEEEEEEEEEEEEE TIME TO RUNNNNNNNNNNNNNNNNNTHE ENGINEEEEE HEHE


Hi guys!!, Time has come finally!! I just couldn't wait to test run the engine....and in only a word.... WHAT THE %&!%$"%·/!%· of a an ENGINE!!! awesomeeeeee!!! I'm very excited!!

It was fitted with the original plug, scimitar 11x7 prop and my homebrew 80/20 castor fuel, thicker head shim removed (left the tiny one).

Well, the plane has a 16oz tank, so I don't know if it is too large or its ok for the engine, Filled the tank...don't havy any means to preheat the cylinder so it was a challenge to start the engine for the first time....but once it started it worked all right....
I let it warm and then I went to full throthle...and get it to run at a rich two stroke setting for a coulple of minutes...but noticed the engine wanted a bit more...so i started leaning the engine until I got like 12k rpm....I let it scream at this setting for a couple of munites more (total tun time was about 6-8 min) and then I stopped....refilled the tank, but I don't know how much fuel I got in the tank... started again right away again, and let it run at the same setting for a couple of minutes more, and again it wanted more and more... So I ended at a steady 14600 RPM still rich setting, with plenty of smoke and oil coming from the exhaust....what I can tell is that the engine is LOUDDDDDDDDDDDDD, but I enjoyed that thing screaming.... that was by far the highest RPM I have ever got from an engine... I let it run for the rest of the tank and it was rock solid, but I couldn't get more numbers because it was getting dark already....didn't tached idling as well, because I think it needs more time to get it steady and the transition good enough... now the engine is cold and with very high compression with the nice pinch and with a Very Very Happy owner!!.

So I know it needs more run time, but doing DAR's breaking in procedure and taking into account all the suggestions given....I got a very nice engine!!

THe only problem I found is that the muffler long bolt appear with stripped threads (maybe due to the vibration) and the muffler was coming loose and rotating, I thought it had the front part sealed because it was "glued" to the middle part, so i didn't used RTV, only in the rear part...but after that I noticed that I have to use RTV again jeje.... I'll have to use a security nut, but I have to get it from the hardware store, It was very nice that the engine doesn't leak oil anywhere else where I used RTV.

I hope that the tower 75 will be available soon for all of you that are waiting them...!!! This engine is definately a WINNER!!

Jorge

Anybody there? are good my numbers?? bad?? should I expect more?

Jorge

Jorge,


Those numbers are what I would expect on a low-load prop like that MA Scimitar.

This prop is more effective than the black MA.


Propping it for an even 14K on the ground, using an 11x7.5, perhaps, would make your plane fly better.

Thanks Dar,

Right now I don't have a 11x7.5 prop, I have a scimitar 12x6 and an apc, props I will be trying next time I run the engine and finish the break in.

I was thinking of using the 12x6 for the maiden flight since I think the extra thrust may help in case of problems!

Jorge

Hi Jorge,


Is the plane the engine is mounted in capable of medium speed flight, or is it something that will drop-out, if speed is reduced to below 50 mph?

As long as prop-braking doesn't slow it down to a stall, everything will be OK.

With the 12x6, I would advise you come in for a landing, with 1/4 throttle and chop the throttle as you cross the 'zebra'...

I don't know how the plane will perform....I just designed it with a slim profile but no I don't know actually how the plane is going to perform...I'm just testing and I'm kind empiric designer... so that's why I think would be better to use the 12x6, in case of stall or something...and also the 11x7 looks like a bit small in the nose, but it shouldn't affect the perfomance neither....

So what would be the best prop in that case?

I have yet to try the 12x6

Thanks Again,

Jorge