mmattockx

Some speed engine rookie questions... I bought one the super cheap MDS FIRE 61's mentioned by Kmot in this thread:

http://www.rcuniverse.com/forum/m_70...tm.htm#7044171

Since it comes with nothing resembling instructions, I am looking for a bit of guidance on running this in on a stand. I have run my share of glow engines, but nothing like this before. This is also the first time I have run the FIRE configuration if that matters, all others have been side exhaust. So here we go...

1) What is a reasonable prop to start with, APC 11x6, 11x7, 10x9? Something with lower load than that, or more load?

2) I have never run a full length tuned pipe before, where can I find info on setting the initial pipe length? I am looking for the formula(s) that will give a ballpark length given a target rpm range and exhaust timing. Or should I look at a Jett short pipe, if they will make one for me? Bob, any thoughts? I realize it's not perfect, but how about an MCP? Simple, light, easy to make. Maybe not full power potential, but decent (in my mind, anyway).

3) To run in, do I just use the typical ABC engine technique of: open needle valve 3 turns, start, peak and then back off 500rpm, let run through several tanks?

4) If I can't find a pipe, is it OK to run it on open exhaust if I elevate my test stand tank a few inches to ensure adequate fuel flow? My neighbors might be pissed, though...

Any other tips, experiences welcome.

Thanks,
Mark

rmenke

My Feedback: (13)

Guys:

Started to put my 2Cents in and then considered the principals and their reactions, then chicked out. Glad all is well in the end. Had several MDS engines, 48 & 58 & 68. Never had a problem with any of them. The 58 a real screamer, stronger than most 60's around. Same guys who always have engine problems with anything hated them. Loose carb barrels were a problem until you had several carbs in the shop, then you could hand lap a good fit, problem went away. They always went bang after I sold them back, wonder why.

daven

My Feedback: (1)

I'll answer what I can, although I'm shooting in the dark with this thing also.

1) What is a reasonable prop to start with, APC 11x6, 11x7, 10x9? Something with lower load than that, or more load?

I've always believed that it is best to break in a high performance motor at a rich setting and at a higher rpm. I was going to use a 11x6 APC for break in on mine.

2) I have never run a full length tuned pipe before, where can I find info on setting the initial pipe length? I am looking for the formula(s) that will give a ballpark length given a target rpm range and exhaust timing. Or should I look at a Jett short pipe, if they will make one for me? Bob, any thoughts? I realize it's not perfect, but how about an MCP? Simple, light, easy to make. Maybe not full power potential, but decent (in my mind, anyway).

There is a lot of great info on the MACS website, I'm still undecided on a pipe also at this point.

3) To run in, do I just use the typical ABC engine technique of: open needle valve 3 turns, start, peak and then back off 500rpm, let run through several tanks?

With a standard .61 sized prop, that would make sense. Running a smaller prop like I intend, I will be closer to 800 off peak, and pinch the line every 10-15 seconds to warm things up.

4) If I can't find a pipe, is it OK to run it on open exhaust if I elevate my test stand tank a few inches to ensure adequate fuel flow? My neighbors might be pissed, though...

It will be loud, but it is ok to run them that way. I will do all of my initial runs without a pipe to get some baseline numbers that you can compare to afterwards when you add the pipe. Try to find a remote location.

mmattockx

Thanks, Dave. 11x6 it is, 800rpm off peak and perhaps open exhaust.

I was also thinking that open exhaust would be a good baseline to see where it wants to run before I try to figure out a starting pipe length.


Mark

combatpigg

My Feedback: (3)

If the engine is of questionable quality like some have mentioned, the first el-cheapo parts to suspect would be the bearings. I would break the engine down and see what it has before running it. Macs should be able to fix you right up with an exhaust system, the engine needs some sort of tank pressure to keep up with fuel demand if it is a racing engine. To break it in without the hassle of a full pipe, I would run it with open exhaust and use a "combat style" latex bladder for a tank, running the engine in 2 ounce bursts.

MJD

My Feedback: (1)

The MDS FIRE .60 isn't AFAIK I know any kind of racing engine, but a pattern engine. I've never yet run either of mine. But at the time we were bringing them in we were told they were for aerobatics use, i.e. they were a 1980's design pattern engine. Still, none of us know the whole story on timing etc. so I'm anxious to hear some test stand numbers. I guess some results from one of the folks who just got them will tell the story.

MJD

mmattockx

That is actually better for me, I have several classic pattern planes in the build line and a 61 FIRE will suit a couple of them perfectly. I will try to get mine out once it warms up, but that is at least 4-6 weeks away yet.

Edit - I forgot about the Bolly Book for pipe tuning info. It has a wealth of information in a lot of detail.

http://www.bolly.com.au/book/content.html


Mark

MJD

My Feedback: (1)

You're north of me but it's bad enough here.. I gave up winter model flying activities YEARS ago.. it ain't worth it, better to spend the time fixing/building/armchair-ace.

As I recall what we were told was that these engines were intended for F3A, FAI aerobatics. So I would, from the age of them, guess they are set up to pull hard on typical pattern prop sizes for that era which - correct me if I am out here, were 11-7, 11-7.5, 11-8, maybe some 11.5-ish sizes - and would likely run what, 14+K? I'm not a pattern guy myself so bow to the specs from other's memory.

MJD

Kmot

My Feedback: (24)

Hey MJD, do tell us all you remember about these engines! This is good info!

F3A, FAI Aerobatics. What else?

mmattockx

I think bigger prop loads and quieter set ups were just coming in then. The number stamped on mine is 03-91-1450, which sounds like March 1991, serial #1450 to me. Turnaround came in for the 92 season I believe, so this is just before that. Would putting a degree wheel on it to check exhaust timing shed any light on it's likely rev range? Any other dimensions/timing that might help with that?

Edit - Kmot, what solvent did you use to clean out the storage goop? I have laquer thinner and varsol handy, any other better choices?


Mark

daven

My Feedback: (1)

A can of brake cleaner worked for me.

Kmot

My Feedback: (24)

I used McKay's #50241 carb cleaner. Go to the thread in Glow Engines. Some of the guys are using acetone, brake cleaner, and other stuff.

http://www.airosol.com/McKay/parts_dip_products.htm

mmattockx

Brake cleaner is handy, too. Any thoughts on the timing?

Mark

Kmot

My Feedback: (24)

If you have a degree wheel small enough the timing would tell all.

HaveBlue

if you want a small degree wheel, go get one of those 360 degree protractor like students use at school(or use to anyway)

MJD

My Feedback: (1)

I'm afraid the feeble amount of info I've offered up to date is all I ever had. Having never run mine beyond that I have not confirmed any suspicions one way or the other, so I am quite interested to hear people's findings - it sounds like we'll something soon.

Yeah, the date range of the engines I have encountered - mid '80's to early '90's - is certainly hanging off the caboose of the ballistic era. But I would suspect the design details hark to the mid or earlier '80's. A degree wheel would certainly tell a tale of it's intentions.

MJD

mmattockx

Just exhaust timing or transfers and intake as well? I will try to get it going this coming weekend, I will be swamped with work and family stuff until then.

Mark

Kmot

My Feedback: (24)

Mark, according to this info posted on the Bolly Book you referenced, the exhaust timing should be sufficient I would think:

Racing engines commonly have exhaust timings of say 175 to 195 degrees.

Other high performance engines (ducted fans or free flight etc), have timings of say 160 to 175 degrees.

‘Normal’ engines have timings of 145 to 160 degrees.

MJD

My Feedback: (1)

http://www.rcgroups.com/forums/showthread.php?t=316163

has a little bit of discussion about this engine. I don't think this link has already been posted but if so, well here it is again. Seems the carbs are hit or miss, some work alright, some don't, and there is mention of fitting Perry carbs to them and liking the results. But the word apparently is that they are strong runners, which is not unheard of with MDS engines if nothing else.. i.e. the designers knew what they were doing, but the execution in production results in a few roughs in the diamonds or whatever the appropriate metaphor is.

So it seems there may be some purpose to this madness!

MJD

mmattockx

I got to printing a degree wheel off and checking exhaust timing tonight. Exhaust duration measures at 167 degrees (+/- 1 degree or less), which would put it into the high performance, but not racing category.

It looks like I got a FIRE pattern engine instead, which is fine with me. Now I hope the carb cooperates and lets it perform properly.


Mark

Kmot

My Feedback: (24)

A high performance pattern engine is A-OK with me too! Thanks for checking! [sm=thumbup.gif]

mmattockx

A couple more questions on this engine. I am planning on bench running it with open exhaust in the next couple of weekends if the weather holds and I need a bit more guidance...

1) Does anyone know how much nitro these things like? I am planning on using 10% or 15% unless otherwise informed.
2) Glow plugs - hot, cold, in between, what?
3) Break in prop - APC 11x6 a reaonable choice? Less load, more load?
4) How many turns out on the needle? I am planning on starting at 3.5-4 if know one knows better.

Thanks,
Mark

daven

My Feedback: (1)

1. Probably likes less nitro as most non-North American countries do. If you use 10 or 15%, you would want to add at least two extra of the provied head shims, and maybe all 3.

2. For higher revving motors, I tend to the cold side.

3. APC 11x6 sounds good to me.

4. I'd start about 5 turns out. Your probably be plenty rich, but I'd rather bring it slowly up than to start to close to lean right out of the chute. I normally start everything full throttle, so that probably sways how I do things.

VERY curious to hear your results, especially without muffler. Remember your ear plugs

mmattockx

Dave,

1) What will happen if I use all 3 shims and don't need them? Just less power? How do I tell if I need them or not, just pull one at a time and see how it responds?
2) Define cold? I have always just used sport engines and boring old Fox "sport" plugs. Should I be looking at OS #8 or something else?
3) Well, at least I got one thing right...
4) Seems fair to me. At least rich won't hurt anything like lean will.

I will post results when I get a chance at it.

Edit - I forgot to add I have it all apart now to clean out the storage gunk and might as well add the shims now. BTW, Varsol didn't touch the goop, it took brake cleaner and several applications to get the crank turning freely. I am also contemplating cleaning up the ports as shown in a hop up article posted here a while back. The ports are actually pretty nice, angled more than typical sport engines and looking more like the finished item in the hop up article than the "before" pics. Worth it or not?

Mark

Kmot

My Feedback: (24)

I cleaned the ports up on mine with a needle file. But I did not modify their size.

I ran my engine with a muffler and 0% FAI fuel, and for the first start initially had the HSN open 3.5 turns and the throttle wide open. It would not start, too rich. I ended up closing the throttle to idle, and leaning the HSN. It started at idle, and when I opened the throttle it died. Too rich. I leaned the HSN again and started it at idle, and slowly opened the throttle and it ran rich but ran. I was then able to lean the needle to peak power and then richened it slightly for break-in.

Have you seen the vids?

http://media.putfile.com/MAC-10cc-Russian-FIRE

http://media.putfile.com/Russian-MAC-10cc-Part-2