RCU Forums

RCU Forums (https://www.rcuniverse.com/forum/)
-   "1/2 A" & "1/8 A" airplanes (https://www.rcuniverse.com/forum/1-2-1-8-airplanes-70/)
-   -   .020 size GLH (https://www.rcuniverse.com/forum/1-2-1-8-airplanes-70/11589607-020-size-glh.html)

hllywdb 11-07-2013 02:32 PM

.020 size GLH
Has anyone done one of these yet? Seems like a natural choice for a TD 020. Reasons are simple. My 020 wee stick is fun, kind of like a radio control nat. But at 6oz if a cow farts on the other side of the field it gets a bit squirley. My GLH, on the other hand (the one with the 1/4" thick wing) will fly through a tropical storm. So I've got a GLH drawn up with an 18" span and an under 1/4" wing, still built up (Hey, I like working with toothpiks). Anyone have any idea what prop might work well? Thinking maybe something around 4X2.5 or 3.5X3? Probably have to cut something down.

hllywdb 11-20-2013 04:46 PM

2 Attachment(s)
Ok, Printed the plans, at a 16" wingspan, drew up the cut files and had the balsa cut. Once I started building the fuselage it became apparent that I went a bit small. There was no way to get an elevator servo inside the fuselage. Even a 6gram servo was too tall once I put the arm on it. So I cut an access hole in the bottom and mounted it from the bottom up. Had to cover it first as it would have been a pain afterward. Then figured might as well mount the engine too. http://www.rcuniverse.com/forum/atta...mentid=1940914http://www.rcuniverse.com/forum/atta...mentid=1940915Pictured next to the wee stick you can see how small the fuselage is.

skaliwag 11-20-2013 06:37 PM

The Cox # 856 4.5 X 2 works just fine on the TD .020. Your picture shows the stiff Grey prop that was meant for it. The paperwork that came with this engine says 19.5K on it. I have one that does 22K.

Not worth trying to reinvent the wheel by cutting down heavier pieces of composite with a big hole you have to plug up with more aggro, time to make and weight.

hllywdb 11-20-2013 08:12 PM

I know but that's only about 40mph on a 2" pitch. My 1/2a GLH is doing 27k with a 4" pitch. That's why I was thinking if I could at least get to a 3" with something.........

combatpigg 11-20-2013 09:12 PM

Interesting project..!
I can only hazard a guess how to approach a project like this because I've never owned a good running .020.
For the best chance of success with a 3,5 x 3 or a 3 x 3, I'd build it like C/L Speed plane.
Make the wing and everything else as small and skinny as possible.
This gives the engine / prop combo it's best opportunity to "come to the party" when you shift into high gear with less diameter and more pitch than what is considered normal.
I'd also expect to spend time with an Xacto knife scraping and shaping prop blades to eliminate excess material that is there more for safety factor than it is for performance.
After building the "most minimal" airplane and spending at least a certain amount of time to find the best working prop the limiting factor becomes how much air you can get into that engine and possibly even shaving the piston. Shaving the piston not only increases RPM, but it also moves up the "Red Line" for ball socket longevity.
I've never had a good .020 specimen to play with though, so this is just late Autumn bench race talk from deep in the woods......

hllywdb 11-21-2013 06:59 PM

1 Attachment(s)
Kind of what I was thinking CP. I was able to scrounge up some 1/8 X 1/16 spars and cut the ribs with less than 1/16 between the spars. (Yes I cut extra as I knew I would break a few) So with 1/32 caps it puts the wing at right under 1/4". Nice and slippery. The prop is another issue. A 5X3 cox is too chunky to whittle down. I'm thinging starting with an APC with a 3" pitch and dealing with the moster hole issues in the middle.http://www.rcuniverse.com/forum/atta...mentid=1941105

combatpigg 11-21-2013 09:04 PM

That looks really good..!

Funny thing about making little planes go fast. When I first got into the hobby I used to ask all the Old Timers about what they knew about going fast and 90% of the feedback was,"It doesn't take any skill to go fast, ANYBODY can do that...just stick a big engine on a little plane"........
Well, that never seemed like a very satisfatory or a very FUN answer. It takes more work to build extremely fast, extremely manueverable, extremely 3D, etc. It's the physical challenges that drive the creativity, as much if not more than just the aesthetics.
As for the prop...I think you are on the right path by adapting APC's small electric props in the 3 pitch to suit that engine

hllywdb 11-22-2013 09:46 AM

Given the practical realities of dealing with a TD 020 I don't think the plane design will be the limiting factor in speed. The plane is more than slippery enough, it is a matter of the correct prop. While I have been playing with 1/2a engines for over 45 years, I just started playing with the 020 size this year just to make sure I wasn't missing out on anything. While there are tons of ways to make 1/2a motors go faster, the practicality of doing it with the 020 is outside the budget of most of us now that a replacement piston/liner set involves buying a good pee wee and canablizing it. Backplate pressure isn't practical and there never was much in the way of fine thread needles. Prop selection is slim at best. Most designs and kits for this size were of the FF, Old timer, or high wing slightly better than trainer variety. I suspect any real attempts at "speed: were done in the CL circles. So in the real world my best bet is to build the GLH style and find a prop cutting combination that works for the motor.

I am thinking that in the current state of the hobby any real speed at this size is going to be achieved by burning electrons, not fuel molecules. Probably even at the 1/2a size. And while I could go faster with electric, without the dopler effect of a screaming, unmuffled nitro motor going by it just wouldn't be any FUN. I doubt NASCAR could fill the stands to watch a pack of 40 Teslas go whirring by no matter what the speed. It's just not beer drinking music. But I digress....

So my "adjusted for reality" goal is that it should be fairly simple work to get double the speed of my wee stick\pee wee combination with a design that flies in a respectable manner with less of an issue with wind. I prefer planes that carve their way through the sky rather than flutter.

combatpigg 11-22-2013 12:25 PM

I'll bet there's room to install a 1/16" brass tube somewhere on that little sucker...? I've drilled into a TD .049 case through one of the mounting lugs, THEN cross drilled the first hole to intersect with the first hole that was drilled. The cross drilled hole enters the top side of the lug and it is sized for a press fit nipple..or you could tap threads. The first hole that was drilled needs a plug pressed in to seal off this operation and now you have a custom crankcase pressure tap that will be the envy of the whole neighborhood and a great conversation starter when you're at a cocktail party, too....
Anyway, having the pressure tap facing straight up right there at the mounting lug is the most handy place to have it instead of in the backplate.

skaliwag 11-22-2013 10:39 PM

I wonder at what RPM a TD .020 will go Super Nova?

MJD 11-23-2013 06:51 AM

Hp peak is at about 23k, so in rough numbers yer looking at 46mph tops on 2" pitch and 69mph on 3" pitch. Or 56-57 on 2.5" pitch.

That Cox 3.125 x 2.5" 3 blade is about the only off the shelf glow prop with more than 2" pitch for this engine. Ugly looking POS though, can't imagine it is one of the more efficient choices, but ??

What are the chances of success repitching a 4.5x2 then trimming it down, I wonder..?

Think you got problems? I found an old post in another forum - someone was complaining about the lack of choices of pusher props for electric motors.. okay then.. :p

hllywdb 11-23-2013 04:30 PM

Think you got problems? I found an old post in another forum - someone was complaining about the lack of choices of pusher props for electric motors.. okay then.. :p
Realy???? Put the prop on backwards and switch 2 wires, the motor reverses direction. Kind of like an over-prime in our world but it actually runs good.

I'm thinking cutting down an apc is my best bet. They tend to be thin anyway. I looked at the 3 blade, but thick blades and they have the famouse Cox "2 speed slush box tourque converter" effect being so soft. Not sure the auto feather is what I need for this.

combatpigg 11-23-2013 04:35 PM

I think a 4.2 x 4 would be interesting to work with. It might be possible to heat it with a heat gun and lay the blades into a jig that is set for a 3 pitch. If there is a will, there is a way. I have absolutely no idea what is available in electric props, but I would call APC and ask them if that mess of a web site proved to be too.....convoluted.........to figure out what they got that might be in the ball park.
They have an amazing selection of props that are just about perfect for every application that I've ever needed help with but this .020 speed plane project might be pushing it.
To answer Skaliwag's question, I've talked to at least one guy who ran a TD .049 with just a 4 inch popsickle stick on it because he just wanted a high tach reading to look at. So, there has undoubtedly been guys who have performed totally sick experiments in their dungeons on .020s, too.

hllywdb 11-23-2013 04:42 PM

I thought about the 4.2 too, even cutting it down to 3" and leaving it 4" pitch. The plane is light enough to get a good launch on a 3" thrust and it just might come up on pipe in a dive. Don't know unless you try. I know they say no electric props on glow but they have some small speed props made for 31k motors and I can't see where a 020 is realy going to rip it limb from limb. The electric motors have instant tourque which I think would be much harder on the prop.

MJD 11-23-2013 04:53 PM

2 Attachment(s)
I was wondering if a cox 4.5x2 could be repitched with heat, then trimmed.
Actually some of those 1/2A combat props have pretty thin, light blades. Check this out:


This is somewhere around a 4.75x2.75 or 4.9x2.7 or something like that, I forgot the specs.. anyhow they came from Larry Driskill. Blades are very light and thin and that hub ain't too bad compared to many other options.

Here's one, but no mention of actual pitch. Figure between 2.5 and 3. They should know.


combatpigg 11-23-2013 05:47 PM

Cox put some effort into arriving at 4.5 x 2 as a well matched load for the .020..so deviating from that with more pitch means that the load factor needs to remain close to what COX arrived at for a good match to the engine.
I think removing micrograms of weight from inside the piston is a good first move to enable the engine to respond the most to slight reductions in load. I would practice first on SureStarts to get the feel for it.

MJD 11-23-2013 06:31 PM

I'm sure those combat props would have to be trimmed to 3.5" or less. Of course they could always be narrowed and depitched a bit too.

hllywdb 11-23-2013 08:22 PM

APC does list both a 4.5x3.5 and a 4.6x3 but both are slightly heavier hubs than the 4.2x4. I would think that at this size you don't need to drop as much in diameter to go up in pitch because the hub takes up a larger percentage of the prop as compared to going from say a 12x6 to a 11x7. So a 3x4 may be fine. I am a little hesitant to start cutting up pistons not only due to availability but also because mine seems to be prone to blowing glow heads (at $10 a pop) if I get just a bit lean. So I think I will start with just prop work rather than trying to get a few extra thousand rpm. Then if I can score a couple extra tds fairly reasonable I may start looking into some of the aluminum backplate/venturi combinations I have seen on the bay as it looks like I am going to have an open front bay for a tank. Right now it looks like the battery will be going in the aft part of the main bay to balance. Then I may start playing with pistons and crankcase pressure.

combatpigg 11-23-2013 09:12 PM

I noticed that glow plugs are $10 now. See if you can order extra head shims. Use the least amount of compression that allows easy starting and running. To know what that point is, you must first start out UNDERcompressed, then slowly work your way upwards.
Just the same as handling a diesel, but often taken for granted that the factory setting is good enough.
At really high RPM, high power achieved, short glow plug life is just part of reality...but with .020s I would have guessed that they are naturally easier on plugs than a .049 running in the same RPM range.

MJD 11-23-2013 10:24 PM

If TD .020's are anywhere as touchy on needle settings as Pee Wees can be at times (usually improved if perhaps not eliminated with the old trick of silicone tubing on the needle to seal air leaks), I could see plug life being a roller coaster ride. I've owned several Pee Wees and generally I find TD .010's easier to start and needle. I've never owned a TD .020, though some years back I started and flew a buddy's many times (on was it a Micro Star? A small parasol wing thing on infernally unreliable Cannon micro gear.. Pilot kit maybe?). As I recall it was a pretty sweet engine to run as long as it was treated it well and in accordance with the golden rule of small engines, keep it clean and feed it good quality clean fuel. Oh yeah, and if you have an adjustable glow panel, take care to set it at minimum and work up to a nice glow setting by watching a plug outside of the engine and out of the sun or bright light. They're expensive little buggers to burn out. And if you disassemble a Pee Wee, be really careful how much you torque the backplate bolts. Sausage fingers on screwdrivers can crack the hub in the backplate, and good luck fixing that leak. That one grounded my .020's more than once at a young age due to a lack of sense for small fastener torque.

Something tells me 3" pitch just may be too much for the engine, or at least at a useful prop diameter that lets you get it up to peak power if you want to boogie along. But I could be all wet, it's just a gut feel. I tend towards the 2-1/2" to maybe 2-3/4" range. 23k at 2.5" = pitch speed approx. 57mph, 2.75" 63mph, neither of which ain't slow for an .020. The combat props come in a variety of pitches around those numbers.

But whatever - it will be fun and hopefully not frustrating experimenting with the limited choices.

I saw one fly in a small low wing thing with ailerons. It used a small balloon tank immediately behind the firewall, and seemed to run steadily enough through maneuvers.

hllywdb 11-24-2013 06:34 AM

CP I wish they made a Galbreath head for the 020 I use them on all my TDs and AMEs that are modified to scream. I added shims after burning out 2 in 20 sec. The first one came with the motor so I thought it could have been softt.

MJD the 020 needles like any TD which is to say much better than anything with a backplate. A 2.5 or 2.75 may be a good place to start so I may call the shop in Canada this week. otherwise I'll work with an apc. I don't think I need a lot of thrust as the anemic pee wee has good vertical and the GLH is the same weight or less.

hllywdb 11-24-2013 06:40 AM

Speaking of reedies of all the ones I've owned for some weird reason my black widows have always been the most consistent. Maybe just the luck of the draw but none have ever given me any trouble.

WINANS 11-25-2013 03:53 PM

I've run a pile of TD .020's over the years, and they are probably my favorite Cox engine. They needle well, and are worlds apart in consistency as compared to the PeeWee - totally different animals. The TD .020 is the sweet spot engine of the cox group, IF you like that size of stuff. I probably have a dozen of them sitting around.


hllywdb 11-25-2013 04:53 PM

Hi Scot,
Any you can't live without?

WINANS 11-26-2013 10:23 AM

If it would get a project going for you, and actually get used, then yes, I could part with one. I also have a trove of .020 parts, props, etc. So much stuff is boxed up - woudl need to sort through.

All times are GMT -8. The time now is 05:15 AM.

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.