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Author Topic: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?  (Read 1018 times)

Offline Henry McClusky

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Is there a chart or some other data that gives guidelines for picking the correct engine?

Maybe something based on plane weight and drag?

I'm wanting to design and build a plane around an old Torpedo 35 glow plug engine I currently have that was my grandfathers, that I flew CL with back in the 1970's.

I've got quite an assortment of old engines.. everything from some Thimble Drones to the Torpedo 35.

Thanks,


Online Dave_Trible

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Re: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?
« Reply #1 on: December 03, 2018, 07:02:49 PM »
Hello Henry.   Firstly take the time to attempt running those old engines on a test stand.  I have bought and collected many over the years and I must tell you there could be a good chance some of those have internal corrosion and may sort of melt down on the first tank of fuel.  You don’t want to build a new plane and find the engine is junk.
Once you have that known just pick known designs for whatever engine you have and basically duplicate general areas and moments to start.  An example might be a Ringmaster for that Stallion .35.  Don’t try going much larger,  just too much load on that old engine.  Also know there may be no parts to be found for these older engines.  If you have a good runner use plenty of oil in the fuel and run it with TLC.  If you would like to fly quite a bit it may serve you better to acquire newer equipment that will stand up better and you could find parts and replacement engines.   I have a good bunch of golden oldies but don’t run them hard or often and in most cases have several like copies for backup. 
Good luck and don’t be afraid to copy from other good airplanes.  I like it when someone likes to put in some extra effort to be creative and try to be different.

Dave
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Offline Tim Wescott

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Re: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?
« Reply #2 on: December 03, 2018, 07:03:13 PM »
That's a hugely complicated question, made complicated-er by the fact that motors of different eras are, well, different, and by the fact that there's a lot of mediocre pilots out there with strong opinions (like -- me!!).

My rules for listening to advise on this forum are to pay attention to who actually flies, and to pay attention to what's actually been done.  So if someone whose won at the Vintage Stunt Champs tells you what size plane works with a Torp -- believe them.  Or if someone can name a plane that placed in the Nats with a Torp -- believe them.

I've never seen a Torp in person (so you know how much to believe ME).  I'm going to guess that it will be happy with roughly the same airplane as a Fox 35, or a bit less.  So, something Ringmaster sized is probably about right.  Lose the nylon prop, though -- even new those things would throw blades.  Use a modern glass-filled nylon prop (like APC), or use a nice old-looking wooden prop.  Or, a plane the same general size as the ones that flew well with it back in the day.

The Babe-Bee is probably good for one of those all-sheet 1/2-A jobs like a Sig Skyray (not 35).  A Golden Bee would be better -- the Babe-Bee is made for free flight, and the pickup is fixed at the bottom of the tank.  There are dodges for making them work, but I don't know 'em!  With a Golden Bee you can rearrange the pickup tube.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Dave Hull

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Re: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?
« Reply #3 on: December 03, 2018, 07:50:03 PM »
I agree with Tim on the Baby Skyray for the Baby Bee.  However, I am puzzled by his statement that these have a fixed fuel pickup at the bottom of the tank. I've never seen that but if someone has one, I would like to see it and learn something new. As far as I know, they all have a plastic fuel pickup line that connects to a nipple on the inside of the backplate that feeds the needle valve. For control line, just make sure the tube is cut off at an angle and then stuff it into the pocket at the edge of the backplate right above the lower outboard tank screw. The Baby Skyray works even better without the landing gear if you can fly over grass. You can always increase your flight time by substituting the larger 8cc tank (and bolts) and reuse everything else in your photo. These parts are still available new, if you want them. Your engine may or may not have the stock, single bypass cylinder porting. If it has a #2 stamped on the port, it would be a single port engine with good power. A later dual bypass engine will make more power, and you can design something a little bigger if you'd like.

A few other considerations for the older Torp 35:  they do not have provisions for a muffler, so this may affect what you can do, or where you can fly. Note that the exhaust port is on the opposite side from most other engines, which you may find annoying in a classic profile arrangement. They are light, so a "modern design" would likely end up tail heavy. There seem to have been a lot made, and they still show up frequently on auction sites. If you see any corrosion, clean the engine thoroughly before you run it to avoid excessive wear.
« Last Edit: December 04, 2018, 12:47:53 AM by Dave Hull »

Offline Henry McClusky

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Re: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?
« Reply #4 on: December 03, 2018, 08:11:31 PM »
Thanks Dave, Tim and Dave.

Would you suggest new glow plugs?

What fuel would you recommend for a bench test?

Is there something I should do to prep the engines before running them, like soak them in WD-40 or ?

I'm pretty good with small block V-8 Chevy's and Ford's... but these one lungers , not so much.

Offline Dane Martin

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Re: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?
« Reply #5 on: December 03, 2018, 08:42:40 PM »
Thanks Dave, Tim and Dave.

Would you suggest new glow plugs?

What fuel would you recommend for a bench test?

Is there something I should do to prep the engines before running them, like soak them in WD-40 or ?

I'm pretty good with small block V-8 Chevy's and Ford's... but these one lungers , not so much.

One thing I've had good luck with regarding wd-40, is to saturate the engine real good. Get it in the venturi and exhaust. Wrap it in a paper towel or two, wet with wd-40 and soak it in a zip lock for a day or two. It frees it up and cleans the rust off your screw heads.

If you need help with the cox engines, send me a PM. Lots of info. Lol

Offline Tim Wescott

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Re: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?
« Reply #6 on: December 03, 2018, 08:49:10 PM »
Oh god I need to stop saying things based on ten year old memories.  (and I need to crock-pot some engines!!)

Backplate on the left (eew!) is a Golden Bee, backplate on the right is a Babe Bee.  What I was remembering about CL is that the tank inputs on the Golden Bee go into the tank itself, and are arranged so they don't spew fuel when you're flying roundy-round.  The Babe Bee runs just fine, but can vent fuel.

Clearly, I was entirely wrong about the pickups.  Ooh, bad Dobby.  Bad Dobby!

AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Dave Hull

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Re: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?
« Reply #7 on: December 04, 2018, 12:41:50 AM »
Basic Cox Cleaning and Rebuilding

You need to get the Cox really clean inside. Little particles of congealed oil will cause fuel metering and reed issues. In particular, corrosion will occur due to the dissimilar metals used in the tank. Steel screws, plated pot metal for the backplate, beryllium copper for the reed (if yours is old enough), aluminum case and tank parts, and so on.

Be careful what you soak your parts in and what you soak in the same container. If you dump all the parts into a cup and pour in the wrong things and leave them sit, when you come back you will have a gooey congealed, dissolved, corroded mess. And will be hitting the swap meets for some more engines. For example, brake cleaner will do damage if used for soaking. Kerosene won't. I haven't used WD-40, but assume that someone recommending it has actually done this without doing damage.

Be very careful when removing the cylinder. You need a Cox wrench. The issue on the older engines is that one tool engages the exhaust ports in order to remove/install. Obviously, distorting the cylinder means your engine may never run right afterwards. Later engines had wrenching flats cut in the top fins of the cylinder.

Once clean, the tuneup should include: new O-ring on the venturi inside the tank, new fuel pickup tubing with anti-collapse spring, new case gasket as a minimum. (0verhaul kit:  49OHKBB)  Be sure the reed is undamaged and will rotate freely when nudged around with the tip of a toothpick. It has to float freely under the retainer clip. All the different style reeds work. Some guys have a preference for one versus the others. There is the star shaped beryllium copper one, a racetrack shaped mylar one, a racetrack shaped stainless steel one, and a racetrack shaped Teflon one. The only one that I think is a bit tricky is the Davis Diesel aftermarket reed made from Teflon. It seems to take a bit of running to seat. I also had a bit more difficulty getting it to float freely under the clip.

Check the needle valve to see if it is straight. If not, it will not give a nice linear rpm change when you turn it. That is annoying and will result in some cooking flights sooner or later. The spring does two things: it keeps the needle from rotating under engine vibration, and; it seems to help reduce air leaks. Air leaks into the tank thru the needle, thru the backplate v-groove seal, thru the case gasket and thru the backplate screws will make the engine harder to set. When you have your engine running, cover up the two tank vents and the engine should lean out and quit. If not, you have a tank leak. They will run ok with a small leak, depending on where it is. If you choose to try the larger tank with the over and under stunt venting that Tim showed, it is really handy to shut down the engine this way. The other way is to flip the plane around so that the pickup comes out of the fuel. Most other “techniques” will wear out or damage the engine. Tim also showed a photo with a standard mod that a lot of guys find effective. Remove the spring on the needle and save it. Install a small flat washer over the pointy end of the needle and then add a short length of medium silicone fuel line over the threads. It takes about a quarter inch or so. Push the needle down to get the threads to engage and start turning. This seals the needle for sure, and will solve many setting and run issues.

Check the glowhead for distorted element, for a frosty look, and for a decent glow with a 1-1/2 volt battery. If you can see it glow it will run. It may run even if you can't see it, but might be hard to start. New glowheads are available, as are tuneup parts from several sources. I have had good service from Cox International in the great white north, eh? See link below. Be sure you have at least one head gasket installed.

These engines use a ball and socket connection between the rod and piston. This will loosen up either during break-in or after some running time. When you have the piston out, check the fit. There should be a little bit of end play but not much. If you feel a clunk-clunk it is too much and continuing to run the engine will start to push the rod up thru the top of the piston. The solution is to reset the rod. There is a standard tool to do this. It takes a bit of feel, but after you've done one you will totally get it. Unless of course, the only tool in your toolbox is a hammer. In that case, just lay all the parts on the bench and use about 4 or 5 good strokes each.

Do not use anything that is abrasive on the piston, cylinder or case. Polish the crank journal and pin if you think they need cleaning up. You are not trying to remove material, rather, you are trying to get any corrosion or semi-permanent gunk off.

On reassembly, do not overtighten the backplate screws. The backplates have a tendency to crack around the bosses. You can get new ones, but they will be plastic. They work, but have different issues.

One thing to watch is the screw for the prop shaft. The early configurations used a stud that you could bottom out in the crank. This reduced the tendency for the front of the crank to break off at the relief cut for the drive plate knurling. If you use the nice little aluminum spinner and standard screw, you are more likely to pop the crank here. Of course, a heavy wrench hand and hitting the ground has something to do with it too.
Another thing to be aware of is the case bearing. This journal bearing relies on a constant film of oil to avoid damage to the case bore surface. The fuel you choose has a significant impact on the life of this surface. The case is made of an aluminum alloy extrusion that supposedly has bearing properties, but let’s face it, aluminum on steel has low galling resistance. Cox mitigated that with a “special treatment” in their later engines. Anodize for example, helps by increasing hardness but will also wear thru. I’m still not sure what the black coating is on some of the engines I have seen. Sure doesn’t look like anodize and their marketing claims were purposely obfuscated what it was. So knowing this critical wear area, now think about the comment above about polishing the crank. It helps. One way to do this is to put a stud in the crank and chuck the exposed stud up in a drill press. Use something like SemiChrome polish on a towel or just use crocus cloth.

When you go to run it, start out with the needle set at 3-1/2 turns. This should be a little rich. The precision that these engines were made with makes this a pretty certain starting setting. They like to be port primed, usually with each burp until running. To avoid over-priming, close the port and put a drop on the side of the piston. That is enough. Use a good battery. More starting frustration comes from a weak battery than probably anything except trying to run an engine that was put away wet and hasn’t been run or cleaned in months or even years. The non-contacting spring starter will eliminate the problem of repeated starts backwards. You don’t need to wind the thing up, a half turn on the starter is all you need and is safer for your fingers. Half A props cause more minor finger cuts than any other size, it seems. Be careful since blood doesn’t easily come off of a model airplane finish and will remind you each time you see it. Of course, if you are racing your Cox engine, the blood proves you must be going all out to win!

These are amazing little engines, and kept clean, will perform really well.

I hope this helps get you going,

Dave Hull

ref.:    https://coxengines.ca/

          http://mecoa.com/
« Last Edit: December 04, 2018, 01:02:29 AM by Dave Hull »

Offline Henry McClusky

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Re: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?
« Reply #8 on: December 04, 2018, 06:04:35 AM »
Thanks Dane, Tim, TY and Dave,

Much to learn...  I sincerely appreciate your time and tutelage.

I've also got a Fox 0.25 and a 0.19 Torpedo.

4 degree's F here... that's why I was wanting to do some airplane design  /DV.. 

instead of working on the engines in the barn   S?P


Offline Robert Zambelli

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Re: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?
« Reply #9 on: December 04, 2018, 07:28:50 AM »
Henry - I've been running the K&B Green-Head engines since the mid 50s.
The Green-Head series went from .09 all the way up to .45: .09, .15, .19, .23, .29 (sport and racing), .35 (sport and Combat Special), .45 (with and without the internal balancing disc).

They are really good engines and quite reliable.
I run all mine on Brodak 10-23 fuel, 50/50 castor/synthetic. Never had a problem.
The engines are quite tolerant regarding glow plugs. I've run them with OK, K&B, Fox, Champion and others I can't recall.
If I'm not mistaken most if not all the Green-Heads used short-reach plugs but don't quote me.
The early Green-Heads, by the way, had three-bolt backplates. I think they only made them in .29 and .32.
Regarding suitable planes for the 35: For profiles, the Ringmaster, Circus King of for that matter, any of the Brodak 35 size planes will work well. There is also a good line of full-fuselage planes available.
The Fox .25 is also a nice engine. A perfect plane for it is the Sterling Mustang. Built light, it's a very good good performer with the .25.
The Mustang will also fly well with the K&B .19. In the mid-50s, the .19 was highly modified and did quite well in A-Speed.

Bob Z.


Offline Henry McClusky

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Re: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?
« Reply #10 on: December 04, 2018, 08:00:50 AM »
Great information Bob.. thanks for taking the time to help me through this.   H^^ H^^

Offline EddyR

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Re: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?
« Reply #11 on: December 08, 2018, 12:16:48 PM »
It is easy. Just do as the box says.  Some Berkeley kits said to use   .09 -.60 . Super Ringmaster .19-.60
 I am just kidding as the recommendations were  not useful but marketing to the unknowing public.
 Back  when there was many guys out flying CL you found out by looking at what worked. Today I would look on here and see what people are using in models the size you want to build.   
Locust NC 40 miles from the Huntersville field

Offline Tim Wescott

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Re: Engine Sizing... How Do I know What Size Is Best On A Scratch Built Plane?
« Reply #12 on: December 08, 2018, 12:28:36 PM »
Back  when there was many guys out flying CL you found out by looking at what worked. Today I would look on here and see what people are using in models the size you want to build.

I second that.  Just remember that the old engines aren't as powerful as the new ones, and "sport" engines aren't as powerful as the fire-breathing monster ones.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.


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