"1/2 A" & "1/8 A" airplanes These are the small ones...more popular now than ever.

Cox 049 RPM ???

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Old 11-27-2012, 05:52 PM
  #101
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Default RE: Cox 049 RPM ???

Here's one with a power to weight ratio that makes the Gilbert look like a killer.

I have a homemade marine glow engine that came in a small Chris Craft scale model. It's quaint and funny to me, a half-A with machined brass crankcase and lower cylinder, looks like a Fox .07 cylinder threaded onto a machine shop student's brass hash pipe. Has a flywheel, not a normal thrust washer, so tough to fit a prop for bench running, but maybe I will persevere and try that sometime. Coaxed a few half-hearted pops out of it on the flywheel. Not sure if it is capable of sustained running actually.

I wonder if it is from a plan, maybe an old boat modeller magazine do-it-yourself project? Anyhow I digress from the thread but it is 1/2A.
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Old 11-27-2012, 05:59 PM
  #102
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Default RE: Cox 049 RPM ???

I am amazed that Duke Fox thought it was a good enough idea for him to market.
To place his reputation on.
I suppose it saves quite a bit of labor to produce, but it still needs to be able to pull it's own weight to sell.
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Old 11-27-2012, 07:05 PM
  #103
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Default RE: Cox 049 RPM ???

I'm sure this is a homebuilt project through and through.
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Old 11-27-2012, 08:03 PM
  #104
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Default RE: Cox 049 RPM ???

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ORIGINAL: ffkiwi George-I'm pleased to play fairy godmother this morning [it was either that or get driven mad by all the 'Hobbit' movie premiere hype from all the various media!....yes the world premiere is here today-starting at 7pm. The whole damn city has gone half mad..........]
LOL!

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Anyway-following on from my comments yesterday I've done some test running of the Gilbert 074 this morning (its a lovely spring morning-and no boots or heavy objects have come sailing over the fence yet-so it seems I haven't annoyed the neighbours enough yet....................)

I note for your interest (and anyone else's who may be interested) the following points: (fuel was 15% nitro-20%castor-this mix was chosen so it was as close to your fuel as possible.It was pretty old fuel though-so figures might be improved on a fresh batch!)

(1) The engine starts very easily by hand. Unfortunately-in common with reed valves and other sideports-it starts backwards just as often as forwards. It is noticeably slower backwards-not unexpectedly, as there is no thrust washer or any means of absorbing the crankshaft end loading when running backwards.
Gee, I dunno, Chris. Mine ran both backward and forward, seem to run well either direction. Of course, I've already have at least a half hour's run time, so mine is well broke in. Perhaps I have the later revision, used in Gilbert's last sales attempt as a Parasail pusher?

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(2) My original 'conical' head let me down once again-and would not run without the battery connected-even though the element showed a good healthy glow. It ran a struggling 6000+rpm on the 7x4. I changed to one of the 'truncated trumpet' heads and had no further problems.
Again, I dunno. mine has finally been able to run peak, does quite healthy on a 7x3. Perhaps 7x4 is just a little too much prop pitch? I think my head is the Truncated Trumpet type. Once it starts running steadily, removing the battery has no affect on decreasing RPM.

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(3) Needle setting on the large props I found to be critical-a click either way on the ratchet and revs fell right off. This characteristic disappeared on the 6'' and smaller props.
On mine, the trick was to put a section of silicon fuel line (1/4" or 6 mm long) over the spray bar / threaded needle joint. That stopped an air leak and now I had stable needle valve settings.

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(4) The engine is prone to vibration if there is the slightest prop imbalance or poor prop centre-ing.
My props are reasonably well balanced, no prop shaft wobble during running.

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(5) The engine runs very hot-despite the 'rattling good fit' of the crankshaft.........
With a broke in engine, had no overheating problems with the 6x3 and the 7x3 props, even during break in.

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(6) Starting was pretty much the same hot or cold (ie it didn't deteriorate when the engine got hot
I opened my needle valve 2-1/2 turns to start, then peak 2-1/4 to 2 turns. Starting either hot or cold worked best to open back to 2-1/2 turns.

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(7) The engine stops easily with a brief touch of the finger to the intake-I did the whole test on about three 10cc tanks, stopping part way through each tank to change props
I ran 5 tankfuls on a 30 cc (1 oz.) tank. Half were on 6x3 prop, the other half 7x3 prop.

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results: Taipan 7x4 white nylon 9,200rpm
APC 7x3 rigid 11,300rpm
Bingo!

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Cox 7x3-1/3 black 10,400rpm
Master 7x3 rigid 12,100rpm
Master 6.5x3.5 10.800rpm
APC 6x3 rigid 15,200rpm
Feels about right ....

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Cox 6x4 grey 14,300rpm
Cox 6x3 grey 15,600rpm
Tornado 5-1/2x3 nylon 16,800rpm

These figures show that the engine is not the dog a lot of people think it is-but it is clearly not too good on bigger props-6x4-6x3 and perhaps the APC and Master 7x3 sizes seem to be about the best.
Concur, my observation, APC 7x3 (don't have Master 7x3) seems to provide the best thrust.

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The engine ran particular well around the 14,000-15,000 mark and was easy to set at that rev band. I think Peter Chinn was right-potentially the 07 would run up to close to 20,000rpm on a small prop-the Tornado needed more attention to balance and centreing-so most of these figures might be improved upon.
I'm not sure if it is worth running this engine at that RPM when it can turn a slightly larger prop (7x3) with better economy (longer run time).

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I think providing it is used in 049-06 sized C/L models it will be adequate-it is certainly no Norvel!
Yup, concur. It's a sport engine.

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The hot running concerns me though-I don't know how the engine would handle runs of 5-10 mins in C/L or R/C models-and if this hot running was typical-then I can see there might have been problems when installed in the moulded plastic RTF C/L models it was made for-potentially melting the cowl mouldings or distorting the engine mounts.
Well, I'm not sure what makes your's different than mine. Perhaps I put more fuel through mine, finishing the break in process?
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Old 11-27-2012, 08:17 PM
  #105
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Default RE: Cox 049 RPM ???

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ORIGINAL: MJD If anybody is all excited about one of these engines now, check it out: [link=http://www.ebay.ca/itm/EXCELLENT-VINTAGE-GILBERT-11-GAS-MODEL-AIRCRAFT-ENGINE-/271109595077?pt=US_Character_Radio_Control_Toys&hash=item3f1f641fc5&_uhb=1#ht_500wt_1414]Gilbert .11[/link]
Wants $21 US for shipping, a little steep for me.

Come to think of it, with lighter weight equivalent power from Cox Sure Starts, some of the colorful offerings from Cox International and a few others, I've already got a Gilbert .07 and .11, I bought them since I had a love for the older technology and was also just curious. With that and the modern Norvel .074, Thunder Tiger .07 available with the power of the .11 and the Coxes at the power of the .074, unless one is collecting, for the money, having one copy is enough for me. (Unless something is ridiculously priced cheap.)
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Old 11-28-2012, 04:46 AM
  #106
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Quote:
ORIGINAL: GallopingGhostler
... I'm thinking about putting the Glibert .074 in a 1/2-A CL profile plane. Now I understand why Scientific's 1/2-A's designed by Walt Musciano and a few others would specify ''.020 to .074'' in their 18'' (460 mm) wingspan CL designs. Prior to having this engine, I thought an .074 would have been an overkill.
When Walt designed those kits in ~1950 the engines he used were mostly OK Cub .049's. There was a Cub .074 but it doesn't put out much more than the .049. They were redesigned (cheapened) in the mid sixties with thinner wings and updated engine options to include the Babe Bee, Pee Wee, etc.

When you consider an old kit you must take the power available in engines during their design period. A NV or NORVEL .074 puts out as much power as a .15 of that period. Some engines in addition to .049-.051's of the early/mid fifties were K&B Infant (.020), Spitzy (.045), Royal Spitfire (.065), and Cub .074. In the mid/late fifties Cox brought out the PeeWee (.020).

There were lots of performance improvements in the fifties/sixties in engines of all sizes.

AC Gilbert never had much of a chance because shortly after the engines came out the company went belly up. Still, they were intended as beginner engines thus the uncommon sizes. I got mine from a sell-off at Polk's. A couple still had plastic screwed to the mounting holes where they had been ripped out of RTF's. A couple of the .07's had a starter spring arrangement and a pusher prop. These were from a kite type airframe with a pusher prop. Some came unassembled in plastic bags...two with unfinished crankshafts that, unless I do a final fit, will not go in the crankcases.

I got my Gilbert .11 from a yard sale. It is missing the thrust washer, prop washer, and prop nut. I borrowed some from a Fox .15X to run the Gilbert .11.

For a few bucks in a sell-off I did not expect much. I fit engines into planes that they can handle.

None of my Gilberts were hard starting but I have not extensively run any of them...just break-in.

George
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Old 11-28-2012, 05:01 AM
  #107
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Default RE: Cox 049 RPM ???

Thanks for the bit of history and sharing your engine collection, George. Yes, although the Gilbert was a later entry, I was thinking of Walt Musciano's design being based on the engine technology of the time. These included the lesser efficient available technologies. Then came dramatic improvements in performance with Glenn Cox's offerings, and of course the follow ons with modern porting and ABC/ABN technologies, which improved the break in process.

They kind of remind me of the Russian older 1950's tech cameras that were being sold by Porter's camera store into the 1990's, a little rough but functional.

Well, I did find out that the humble older technology Gilbert .074 can perform, now looking for a stubby nosed sufficient wing area profile 1/2-A CL it can grace, something from the 1950's.
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Old 11-28-2012, 05:05 AM
  #108
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Default RE: Cox 049 RPM ???


Quote:
ORIGINAL: GallopingGhostler
Wants $21 US for shipping, a little steep for me.
All is not lost...that shipping is to Canada. The engines are in Ohio. If you are really interested you might call and ask how much shipping is to you. Probably just a few bucks.

Good luck.

George
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Old 11-28-2012, 06:14 AM
  #109
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Default RE: Cox 049 RPM ???

Thanks George, but for the moment I'm content with what I've got. BTW, now looking at a couple 1940's, 1950's stubby nosed half-A profile CL plans to put the Gilbert .074 in. Keith Laumer's Gee Bee Z might be a good fit.
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Old 11-30-2012, 08:17 AM
  #110
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Default RE: Cox 049 RPM ???

Combat what are you getting for RPM's out of your SWR in the video? That thing sure sounds like its twisting them up..
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Old 11-30-2012, 12:12 PM
  #111
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Default RE: Cox 049 RPM ???

George, the bid on that Gilbert .11 closed at $31 + $8 shipping = $39. I guess someone really wanted it.
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Old 11-30-2012, 03:49 PM
  #112
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ORIGINAL: klord125

Combat what are you getting for RPM's out of your SWR in the video? That thing sure sounds like its twisting them up..
Klord..this is what "Thrust HP" suggests might have been happening on that run. I don't remember what the static RPM was. This is all subject to the assumption that the Wavoscope MPH reading is accurate.
Regardless, this gives a ballpark idea of what the TD is capable of on low nitro.
IIRC...Jeremy Chinn [Matchlessaero] clocked a full wave piped TD at 123 mph on one of his designs. So AFAIK...he holds the absolute TD .049 RC speed record on a plane he called "Caliente". I believe he used a 4 pitch prop to do that..so his run would have required 32,500 RPM...!
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Old 11-30-2012, 04:31 PM
  #113
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Default RE: Cox 049 RPM ???

If my ears don't deceive me, I make the rpm at launch at about 21.5k, maybe pushing 22k as it cleans up. Sound about right?
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Old 11-30-2012, 04:42 PM
  #114
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Default RE: Cox 049 RPM ???

MJD...your ears are surely better than mine. I've got 74 db of permanent ringing in these ears that hearing aides have a hard time competing with.....[:@]
A "GOOD" TD should be able to run at 24,000 rpm with a 5x3 prop on 40% nitro...that will always be my standard reference. I'm not sure what a good TD should be able to hit on 10% nitro [static] with a 4.2x4...since all my TDs are worn out / patched together from the good old days of 1/2A Combat. None of mine have any "POP" like they used to. Thank God for the electric starters.
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