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Old Nov 05, 2014, 12:31 PM
DNZ
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Guide for selecting a glow fuel engine

Has anyone seen a good guide as to how to select the right size glow fuel engine for a plane. That might have like c.c. /pound per flying capabilities? Is there something similar to the electric motor charts that show watts/pound ratio per flying capabilities?
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Old Nov 06, 2014, 12:42 AM
"Experimental"
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United States, NY, Elbridge
Joined Feb 2013
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Welcome to RCG.

I'd have thought somebody would have given you an asnwer by now.

Ok, I'll bite. Here is my thinking. As you will find, opinions vary.

Most engine manufacturers list recommended props for their engines, and how fast they will turn them. That's a good place to start.

Search online for the old Bolly propeller manual/guide. It's a tad dated, but is a "must have" for any serious builders library. Bolly is sadly out of business (I guard my Bolly collection jealously), but the book has a wealth of information on everything from theory to ignitions to tuned pipes, how to set them up and what works with what. And it's free to download. If you can't find it, go to Flyingiants and look up my Super Chipmunk build thread, there's a link in the 1st couple of pages.

Another way to get an idea what size engine will be a good fit is to look through the hobby shop sites and see what engines are used in planes similar to the one you are building. Most kit/ARFs these days recommend motors/engines. If it's an electric plane kit that doesn't spec an engine size/type, then it may be designed for electric only and if you want to run fuel in it, it may need modifications such as firewall strengthening, shifting internals to put the fuel tank on the CG, servo upgrades etc. These mods are best done after you've got a few planes under your belt, unless you have an experienced pilot/builder helping.

I did see a rough guide put out by OS a while back, but I can't seem to find it right now. It took the type of plane/intended use into consideration which is required. 1 cubic cetimeter of displacement is not equal in diferent engines, or engine types.
A 2 stroke fires twice as often as a 4 stroke, thus requires more displacement to make the same power. Even then, the powerband is lower on the 4 stroke, not a bad thing if you want to pull a heavy plane around, or like the "scale" sound. Nitro/Methanol makes more power per cc than gasoline, but is less fuel efficient and the oil it exhausts is messy (but the smell, at least for me brings back irreplaceable memories). Gasoline 2 strokes are powerful, cheap to operate, easy to care for, and clean. They generally are found in the larger sizes, but most mfrs are making replacements for .60 glow now (7-9cc gas). 4 stroke gas has a great sound, are super torquey, but tend to be heavy for their displacement. These are just the general characteristics to give you an idea. The merits/drawbacks of each type has been debated ad infitinum, some poeple get hung up on a particular type as "best". They all have advantages/disadvantages. If you pick one that is MATCHED to your application, and learn to operate/care for it properly, you'll be happy with it. READ! After you have some experience, you'll have a feel for what engines work with particular size/style plane. If you don't have access to them in real life, watch people start and run the different engines on utube, and see how each flys. Seeing helps quantify ambigous terms like "scale sound" etc. It's all about learning. (and who doesn't love to watch planes fly - not bad homework - huh?)

I personally like to have thrust levels at 80-120% the planes weight, but the plane type and purpose very much affect that decision, a slow workhorse like a Telemaster will work great on the low side, where your Corsair needs some grunt, as it was designed to kill things, and doesn't like to be flown too gently. Warplanes, Acro and 3D planes love to be overpowered... you can't hang on the prop @ 80 percent power/weight.

If you like to do math, you can convert watts to HP and play with those numbers - there are good online converters to save you the math. There used to be "dream wheels" which were 'wanna be' slide rule type devices - basically a mechanical look up table to match engines to planes, props to engines etc. They called them "dream" wheels for a reason, they can't do what a human can... take all factors into account.

If you're relatively new to this sport (welcome), I'd personally recommend sticking with a model specifically designed for fuel power (if your heart is set on fuel power), preferably a high wing trainer. Run the recommended motor, toward the high end if several are listed, that way when you get better at flying, you'll have power on tap for some aerobatics. Well powered models allow you to "power out" of bad situations as well.

If you are indeed just getting into this sport, consider an electric RTF. The Apprentice is a great plane, and has a "bail out" switch which levels out the plane in the event of a loss of control. Electric doesn't have the romance and some would say realism of fuel, but I have to admit, I like electric. While it willl never replace fuel, it has some advantges you just can't deny. Try it, you'll like it. I personally fly both, and if asked to give up one, I really have to say I'd keep the electric. Why? Simple - I love to fly, and you can fly a wider variety of planes in more places, easier than you can fly fuel. If I chose "fuel" in my hypothetical desert island example, I'd have to give up - Indoor flying, Foamboard flyers, Flying at the park/school, Helis, multi-rotors, the list is long. I enjoy grabbing my Ember 2 and flying around the yard, coffee in hand in the morning calm as the sun comes up. That has a lot of appeal, just as does the 1/4 scale 32cc aerobatic Chipmunk. That being said, I'm NOT giving up either. My point is not to be unduly prejudiced against electric. I really believe it's the perfect beginner setup. Once you get the crashing mostly over (someday I'll be there), you can build a gas trainer and learn the ropes of fuel. Remember, in this era of sueing over hot coffee, you're best off flying fuel at an AMA sanctioned field, with AMA insurance in full effect. Besides, that way, you meet other people who love to fly.

It's hard enough to learn to fly without trying to de-bug a new plane/engine at the same time. I spend my winters flying almost any plane/powerplant I want. Invest in a good SIM, I like Realflight, but Phoenix is highly regarded too. Flying different plane/powerplants on the sim will let you "try out" electric vs gas vs nitro, etc. Realflight is true to life enough you can really get an idea of how each airframe/power system behave. I've built planes because of how they fly on RF, and havn't been disappointed when I flew them IRL.

Those are some of my thoughts on engine sizing, fuel type, and the meaning of life. Probably more than you wanted to know. Hope it helps.

Clear Skies, Scott
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Old Nov 06, 2014, 05:55 AM
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This goes back to the early 80's .... and was the rule of thumb for most ...





Treat as 'vintage' ... personally I always upped the power by about 15% over what book said.

Nigel
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Old Nov 06, 2014, 12:49 PM
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United States, NY, Elbridge
Joined Feb 2013
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Nice Chart!
Worthy of a blow-up and place in the reference library (pile next to bed).

Somewhat like the OS one, but a bit more elaborate. Vintage is good, if anything, engines these days are up in hp per cubic centimeter (and down in engine per dollar)

What publication did you find it in?

Scott

PS
This is my Experimental SlowStickX, my most recent guess/calculate shot at engine sizing. I started out with a used but quite fresh ASP .15, and it seemed a little small when I test ran it, It would have flown, but I doubt it would have been very aerobatic. I had some credit at HK, so bought a new ASP .25 and it's a LOT more engine -- partly why it's back in the shop for a stick transplant - the 10mm Carbon Fiber one twisted when I opened it up for climbout, requiring a rapid return to base.
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Old Nov 06, 2014, 02:16 PM
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The charts are from old UK mags and also reprinted in :

Radio Control Scale Aircraft by Gordon Whitehead ...

Unfortunately no ISBN ... but I think copies can be had .........

Nigel
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Old Nov 06, 2014, 03:39 PM
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The images are actually pretty good. Certainly usable.
I just didn't realize you were so far from here. I was thinking they must be from a US publication, but I didn't recognize it... Now I know why. It's nice to be able to talk with people sharing interests, but on the other side of the planet. While I wasn't looking, the world shrunk... or grew. Not sure which, but it's a good thing.

A couple of years ago I helped a fellow on an Island in the South Pacific repair an amplifier. I'm often still surprised when I look and see where someone I'm talking with is. My kids just assume we've always been able to do this, to me it's rather incredible. 20 years ago this conversation would cost as much as a small plane.
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Old Nov 06, 2014, 06:12 PM
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Good to see another Bolly fan, I have several and several Taipan glow plugs. I have mostly the Clubman's but also a few of the black ones and at least two of the gray. This is just a couple of them. My little Saito .30 really shines with the 10.5x5, it turns the 10.5x5 at 10,400 rpm.
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Old Nov 06, 2014, 08:42 PM
"Experimental"
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United States, NY, Elbridge
Joined Feb 2013
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There's something about the props, seems they must have put all the theory in the catalog to some real practical application. Quiet, and pull like everybody's elses 1" bigger. Never seen one that needed a gnats eyelash to balance. We better keep quiet, or we won't be able to afford them any more.
Mine are all the wood ones, in the 16-17 x 6-10 range some. Most with the red logo. Smallish gas sizes. Guess it's because I shop for wood. I'm currently building a telemaster with a VVRC 20cc, and would love to find a Bolly wood 16 x 8. Or a Clubman. None around lately. Think I'm going to spring for a Zinger 15x8 4 blade unless something shows up in the next month or so.
Zingers are nice, but not the same. Zoars are nice, but overpriced, and still not Bolly.
Hear good things about the Clubmans though. Some sort of special plastic according to the catalog.
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Old Nov 07, 2014, 02:27 PM
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I'd like to know what happened to Taipan props ... we used them all the time for Club 20 back years ago ... then they went of the shelves and we used MS ...

Taipan had a unique shape to the blade especially near the boss.

Nigel
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Old Nov 07, 2014, 03:31 PM
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Good observation!

I noticeed that, but hadn't put the pieces together.

I recently got a real good deal on a Dynam GeeBee, and it came with a prop like those (and a spare which I managed to break in short order), it has a very aggressive pitch for the 1st 2" or so, then goes back to the more normal profile. I have some similar in my "box-o-props".

I don't know where they came from. I believe they are a name brand "electric" style. Graupners maybe? They have a nice heavy blade with harder than usual plastic and have a thicker than usual hub.
I like them, but didn't make the connection to the Bollys. They may be copies of the Bolly "black"

I don't know what teh purpose of the very aggresive inner section is. I've always thought that portion of the blade didn't conribute much to the overall thrust profile. It may be intended to help airflow thru cowlings like those on many radial engined planes, thus improve motor/engine cooling.

The GeeBee ones are 12x8 if I recall correctly.

A little research may be in order...

Scott
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Old Nov 07, 2014, 07:32 PM
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wing loading comparison charts like that are pretty much useless unless you're talking about a very narrow range of model size. double the size of a specific model and the wing loading for the same flight characteristics is also doubled.

that chart works for 50"-60" span models but not much else.
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Old Nov 09, 2014, 06:06 PM
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Quote:
Originally Posted by ZAGNUT View Post
wing loading comparison charts like that are pretty much useless unless you're talking about a very narrow range of model size. double the size of a specific model and the wing loading for the same flight characteristics is also doubled.

that chart works for 50"-60" span models but not much else.
I suggest you look again ... because the chart gives different engine sizings which clearly brackets either side of your comment.

The charts are published in leading publications - written and vetted by expert modellers .... I think they would have seen any mistakes if any.

I'm glad that you are not building my models !

Nigel
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