combatpigg

My Feedback: (3)

With a sport timed engine you can get away with that strategy and the engine will respond with lack luster RPM and no harm done if you don't over heat it.
With the pipe timed engines that I've prematurely ruined, the props chosen loaded the engines enough to create enough heat to cause who knows how many different ways to have an engine fail.
Detempered wrist pin circlips wedged between piston and liner
Melted silicone pipe seals causing high speed lean out when fuel pressure drops
Expanded, gouged pistons, blistering hot crank cases charring hard maple wood mounts
Spun bearing in case.
Head bolts stretched
Glow plug elements wedged between piston and liner
Heavily pitted piston and combustion chamber instead of nice covering of carbon / varnish.
These engines should be treated just like you would a diesel, you FIRST try to run them undercompressed, then gradually increase the compression until they just begin to "sing". Every time you go up in nitro or prop load the compression needs to be backed way off, then through patient testing you subtract shims and take notes of what you have done.
A quick clearance check can be done with fine [small diameter] solder. send some of it through the glow plug hole, then carefully rotate the engine past TDC to crush the solder. now just measure the thickness of the crushed solder and you know your head clearance. Every prop and fuel combo will have a head clearance range that works best.
The combat engines with open exhaust aren't nearly as finicky or critical, but it's still good practice to start out undercompressed and then gradually increase compression until you start blowing [obliterating] plugs, then back off.

MJD

My Feedback: (1)

Gotcha. I don't like the sound of your piped GZ experiences!

I've been trying to get my hands on the piped speed version of the Profi .049, but I've been told getting stuff out of Ukraine has been a challenge for some months. Probably good that I don't.

combatpigg

My Feedback: (3)

The combat engines are so much more fun for the dollar and still capable of 150 mph with open exhaust. They allow you to forget about being an "Engine Man" and simply concentrate on all the other stuff that makes a successful RC speed plane work.
If the circumstances were just right, I'd try another piped 1/2A engine someday but I'm thinking it would be best to steer away from the G&Z and adapt a combat engine to do the job.

MJD

My Feedback: (1)

Agreed - the Profi .061 and .049 I have are no more difficult to handle than a TD, maybe less so, as long as you get along with pressure fuel systems. This project will be a good indicator of what kind of speeds may be possible on an open exhaust .049, even if another 10-20 is possible with a dedicated design. No matter what, it ought to be fun.

joebahl

My Feedback: (2)

Here are a couple plans for some 049's ,The ACE Pacer is tiled and the GLH-11 is not . joe

MJD

My Feedback: (1)

I have a Pacer kit, and a few of the other popular 1/2A models of that era. - Mach None, Upstart, etc. They are great sport models but not really candidates for speed flying unless you're using a .15. The Boomerang is probably capable of 50% more top speed with the same power. I had an ACE Simple 400 (a bit smaller than the Pacer, same wings no center section) that I flew lekkie, running maybe 325 watts (that's strong .15 territory). Best I saw on that was a bit over 120mph. Not bad at all, but on a TD that peaks out at about 80 watts you'd be stuck in the double digits.

My goal is 150mph on an .049. I'll be happy if this model makes 140, but I hope to be surprised. I believe a dedicated speed design for this or an equivalent engine is capable of 160-165 or somewhere around there. Nobody really knows yet. I flew a 25" span thin winged racer on the Profi .061 and it went like a raped ape. No clocking on the speed yet, but it was noticably faster than the Simple 400. And it was nowhere as clean as this model will be. So I am "cautiously optimistic".

aspeed

I got one flight out of my Simple 400 and Norvel .061 as the last flight in the fall. A bit rich but at the 1 minute mark I had it full throttle and wanted more speed. I think a leaner run and it will be fine. It got a little far away to see, and I almost didn't get it back. I have to watch that. I can't use the Fora because of the muffler rule and a weak sphincter muscle. I think a throttle would be ok so I could gradually pour it on, but it won't allow for that. A flying buddy had a GLH with a TD .09 that he though was pretty good. I think I will copy that plan just in case I feel industrious. The GLH looks like a candidate for a 1/4" balsa wing replacement with a spar. Sheet Wing Racer.

MJD

My Feedback: (1)

The GLH could indeed use something else for the wing. Especially with the featherweight gear we have these days, all that camber would just slow you down.

Progress on the nose of the Boomerang - I roughed out the nose top half in cross-grained balsa, then skim coated it in epoxy filler, then shaped and sanded. Now one more touch up cycle with a bit more epoxy filler (lightweight stuff). I have added very little weight here so far, maybe 2 grams. I'll tie this back to the fuse with 3/4oz cloth, and fill/wet sand everything back into harmony again. I'll hit the nose with epoxy primer before mounting the engine again and beginning on the cowl plug. Glad it's winter..

MJD

My Feedback: (1)

The engine bay so far. I have to blank off the opening to the fuse, I have a piece of 1/4" balsa cut and sanded to shape for that. Gives something to aim for with cowl screws. I guess I'll try the plasticine plug method to pull a cowling mold. I'll cut some profile plates for the cylinder cowl from thin ply, and build up to those while sculpting more freehand elsewhere as needed. That's the theory anyhow, apparently others have done it. What could go wrong.. go wrong.. go wrong..

If anyone has any better ideas, I'm all ears. I want it to look like a slick ukie speed cowl. I'm going to have to get at the fuel line for fueling and pinch-off. With the pressure from a bladder, why couldn't I just access the fuel line for fueling and pinch-off from the cooling/exhaust outlet at the rear of the cowl, if I use silicone extensions from the bladder?

I have some paper/phenolic tubing just the right ID for the exhaust tunnel, so I just have to grind an elliptical notch for the angled tube in a thin-wall Kevlar fuse.. that would be setting "10" on the Dremel with the diamond cutter I think. Tough stuff even this thin.

MJD

My Feedback: (1)

I measured the wing thickness at the root at 0.343", and the chord at 4.5" - 7.62%.

Mr Cox

Thanks for the data. I will compare with a few planes I have at home...

Regarding the conversion of the boomerang, I'm just wondering how you decided on the engine position?
A little further back could possibly help with the balancing, and also enable a spinner to go flush with the old nose (as it would on electric)?

MJD

My Feedback: (1)

I hate spinners on small high rpm IC engines, maybe for no good reason but I avoid them. I did look at the Brodak 1" Al spinner and thought I might shape the nose to match that, but instead I chose to go with the tapered nose and spinner nut approach used on a some of the F3 speed designs (see pic). So I moved the engine back just far enough to put the mounting lugs behind the electric motor nose ring. As to balance, it is working out okay. With the battery and elevator servo roughly in place, the fuselage balances very close to the desired CG position. Only the top cowl left to go up front, and the fuel bladder will be as close to the CG as I can get it.

Lifer

My Feedback: (1)

That is one awesome looking flying machine. Back in the day, I always wondered what an rc version of a CL Speed plane would look like. Now I know.

joebahl

My Feedback: (2)

I see your realy into speed MJD and thats a good looking one to do it with. I use to fly pylon in my youth ,40 size birds .I still have a HP40 pylon racing motor and tuned pipe around here somewhere. I got the plans for alot of 049 planes here http://my.pclink.com/~dfritzke/ and since i build scale birds now and electrict i blew the 049 shrike up for a future build. My 049's are sold off along with my nitro and gas motors but i still like to watch others mount them on their birds and fly them. joe

Mr Cox

I like the aluminium spinners from MP Jet. I've never had any problems with them, but i have not gone past 25krpm (yet).

MJD

My Feedback: (1)

I'm targetting 34-36k in the air, so while I realize a good, small Al spinner has no trouble at those rpm, I just decided I wanted to go spinner nut and keep as much of the prop active as possible. Bad choice? Maybe, I don't know yet..! I clearly understand and appreciate the advice from DD and others to consider a spinner and different engine location. But I am also trying out my own ideas, for better or worse.

p.s. Brodak 1" (25.4mm) spinner, 2-hole: http://brodak.com/brodak-1-spinner-with-2-holes.html

MJD

My Feedback: (1)

They're all over this stuff in Germany, Netherlands and elsewhere in Europe. Google "Dachau speedcup", web and images.

http://www.youtube.com/watch?v=BmQpcjMiExM

(it's not enough to use two MB .40 engines with 6.5" props, he had a LH crankshaft made for one of them too.)

http://www.youtube.com/watch?v=D5jw-LoWnXI

http://www.youtube.com/watch?v=NRvaOhofkQU

from these you'll find a bunch more on the sidebar.

In the 10cc class, imagine modified OPS, Picco, etc. 10cc c/l speed engines running 25-26k in the air on 8x12 props on ~1m span models. Vroom vroom!

Mr Cox

Yes, that's a whole other league they are playing in...

It is a bit funny how they turn, it seems a heavier model has a potential of going faster than a lightweight one, considering how they use gravity to accelerate.

aspeed

I like Control line Speed better. It isn't how you cheat, it is more accurate. They may as well do huge loops, and get a radar reading at the bottom of the loop. An average reading would be more accurate.

MJD

My Feedback: (1)

But don't forget that they are timed over a distance, and have to do it both ways. it's no walk in the park. I think achieving absolute top speed like this is kind of thrilling, why add constraints when you have the whole sky to work with? It's a level playing field, where does the cheating come in? They have to fly level entry and exit paths as well as the timed section, there is an altitude limit.


Both CL and RC speed are cool, I think. These guys are pulling a lot of performance out of some of these modded motors, many equal in dedicated effort to CL speed fliers. F3D who hangs around RCU is a good example, that twin is his. Insane. It is cool to see just how potent those MB .40's are, nipping on the heels of the big block crowd.

MJD

My Feedback: (1)

And to unload the engine enough to get the pipe on the next stage and pull hard in the down line, then they decelerate through the timed course. So smooth flying is essential to make the most of the pass.

combatpigg

My Feedback: (3)

[QUOTE=MJD;11713295]But don't forget that they are timed over a distance, and have to do it both ways. it's no walk in the park. I think achieving absolute top speed like this is kind of thrilling, why add constraints when you have the whole sky to work with? It's a level playing field, where does the cheating come in? They have to fly level entry and exit paths as well as the timed section, there is an altitude limit.
Regardless of the flight pattern or the timing method, numbers are just numbers when you are out there for the sheer thrill of it.
I like the lack of constraint, the ability to roll, zoom straight up a few hundred feet, then send it screeching almost straight down like a falcon that sees dinner, I love the intense sounds and the magic that's involved with having an invisible leash between me and my obedient toy. This mode of model plane flying has taken time away from C/L Combat, RC Pylon, RC 3D...but there's only so much time and not enough to do everything at once.

aspeed

I don't deny that it is a great buzz, but a couple hundred feet dive can fudge the numbers for timing. Strafing runs low to the ground at 200, what could be better?

combatpigg

My Feedback: (3)

They have weight / wing loading limits for competition. The plane must maintain height limitations above the ground at both ends of the level portion of the flight pattern. The forward half of the "level flight zone" is not clocked. The electronic timer begins when the plane reaches the halfway point inside the "level flight" zone.
I think it's a fair and realistic way to see what a .40 - .60 - .90 cubic inch engine can do with a prop bolted to it. As MJD says, without the dive it would not be possible to prop the engines as aggressively as they do...to reach the magic supercharge effect of tuned resonance with a prop that is otherwise an overload. They could fly the whole course with less prop, no dive and less speed.....but this event's rules evolved over many years time with the influence of the guys who are the ones who spend the money and the time to put on this tremendous show of speed and power. I have no idea what all of the speed flyer's opinions are about how this event has been designed, but they have pretty good participation numbers every year.

aspeed

Control line speed outlawed pipes on any motor over a .29, so getting a .90 on a pipe is a good thing to see. I guess the nitro boats can do this, but they don't get the speed that a plane will.