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Author Topic: Engines for Slow Open Power  (Read 5590 times)
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RobinB
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« on: August 21, 2009, 01:02:16 PM »

Engines for SLOP must be plain-bearing, 3.5cc / 0.21 cu.in. max, and run on gravity feed.
Glow gets 10 sec. run, diesel 12.
They must start easily.

So, what would you go for, and why?

Robin
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DaddyO
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« Reply #1 on: August 21, 2009, 01:18:50 PM »

Hi Robin, I don't fly SLOP so with that qualification I'm hesitant to make a recommendation... Undecided However I do read a lot of stuff and if I wanted a diesel I'd be looking for an AM 35 (Dave Hipperson and others have used this engine successfully)

For a glow I did have an OS MAX 15 (indeed I even built a model for it) It's a nice light engine with plenty of power.

PAW's are easily found and can be tuned by the factory for more power (or bought off the shelf pre-tuned) I like 'em but others tell me they are too heavy.

Diesels are convenient, what with lack of kit required, but you need to be sure about getting them started.

There are plenty of swapmeet motors around that will do the job and we are getting to that time of year... good luck with the search.

For a model don't forget the Dixilanders birthday bash this year Wink
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RobinB
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« Reply #2 on: August 21, 2009, 03:30:26 PM »

I should have made it clearer - I already have plenty of different engines. I picked up quite a few engines on an ebay buying spree a while back. (In fact, I may start a sideline selling some of them.

I'm interested in hearing what some of the experienced power flyers here would go for.

Robin
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danberry
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« Reply #3 on: August 21, 2009, 03:41:21 PM »

Cox Special MkII .15
400" plane with undercamber wing 'foil.
It wouldn't be slow.
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glidermaster
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« Reply #4 on: August 21, 2009, 04:11:10 PM »

Welcom to HPA, Robin (Robin and I were clubmates at Bristol and West some years back)

Cox Special MkII - pretty good for power to weight ratio, but not great for availability, spare heads or vibration. Don't forget the smaller TD engines, i.e. the .09 and the .049.

K&B 3.5 (per Phil Ball, I think) - lightened up, can be REALLY good.

My vote would certainly be for OS15FP or OS20FP (I think there are more modern versions of both) superbly made, decent power, etc etc.

If there's ever to be a Trans-Atlantic amalgamation of Slow type rules, a non-schneurle type might be needed, so;

OS Max III 15 is good (very 'tune-able'), and Per Dave Clarkson, the old Fox 15 can be good (light, good with nitro etc etc).

Diesels - PAW - available, reliable, well made etc etc, the weight thing is not a major concern in my view.

John

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danberry
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« Reply #5 on: August 21, 2009, 04:23:28 PM »

KB 3.5 isn't legal...ball-bearings.
Veco 19 would be a great choice, though.
The COX would really want a custom head for Nelson plug.
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« Reply #6 on: August 21, 2009, 05:02:51 PM »

KB 3.5 isn't legal...ball-bearings.

No - the KB Sportster .21 was the engine of choice at one time in England. I tracked down and shipped out quite a few for the Slow Power flyers then.
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RobinB
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« Reply #7 on: August 22, 2009, 04:15:03 AM »

Thanks for your input so far, guys - I know how power flyers like to talk about engines.

Cox 15 TD or Special: An engine man some of you might know, John Haytree, maintains that the problem with TD heads is nothing to do with nitro or rpm but that they burn out due to excess voltage. Perhaps someone could shed some light on this?

A 400 sq.in plane for a Cox ? Well, one of the plans I like to unfold and look at with a smile (admit it - you all do that!) is the Jays Bird 400. It would be competitive as a SLOP model, but also qualifies in the Classic category in the UK.

Classic Power models are allowed any type of fuel system, so if you've got a honking 15 or 19 that needs pressure you had, until recently, to put it in a 50+ - year - old design. Now there's also category F1C-UK, which allows plain bearing engines up to .15 with any fuel system in an F1C size model but with no minimum weight. Incidentally, F1C-UK has gone down like lead balloon so far but it's early days.

Veco 19 - the ones to get, I'm told, are the series 55. Bit rare, apparently.

Lots of people like the OS15FP - if I recall the numbers correctly, it's as good as the old 15 III in terms of power / weight ratio.

K&B Sportster 20 - I had a deal going with a clubmate that he would machine the excess metal off a couple of these for me. Unfortunately, he's a bit like me and gets sidetracked on to other projects a lot. Anyone know someone who does this sort of work?

No-one mentioned the OS MAX .19 - anyone had any experience with them? Better / worse than the 15?

Oh, and does anyone know anything about the Russian FORA plain-bearing .21?

I guess that's enough questions for one post.

Robin
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danberry
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« Reply #8 on: August 22, 2009, 10:52:16 AM »

The Cox Special MkII in JaysBird would be a good rig. Dumping some weight and getting in at 14-15 oz would really make it tough to beat.
The problem with the plugs is getting them.
OS 19 is a good engine.
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RobinB
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« Reply #9 on: August 22, 2009, 12:59:24 PM »

The Cox Special MkII in JaysBird would be a good rig. Dumping some weight and getting in at 14-15 oz would really make it tough to beat.

Good point, and that's the thing that's stopped me building one yet - where to shave the weight? Could possibly go thinner on the LE sheeting... mm ... maybe.

The target figure for loading in the SLOP class is 25 sq.in./oz. (I find it easier to deal with numbers this size, hence the inversion of oz./sq.in. If you're a purist, sue me.) The effects of scale make this easier to achieve and/or exceed as model size increases. Annoyingly, the weight of the engine required doesn't increase proportionally, and there's a jump from 4.5 oz to 6 oz. (PAW CT3 diesel) or more. That's why those K&B Sportster 20s need all that metal machined off.

Still, if it was easy they'd all be doing it !

Robin
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danberry
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« Reply #10 on: August 22, 2009, 01:22:00 PM »

JaysBird diet---simplify the fuselage. No verticals,straight lines. Thin the pylon. Thin the ribs a bit. Drop the X ribs from the stab and just use diagonals. Same for wingtips. Shrink the TE to 1/2" wide. Lightweight engine and mount. UltracotLite covering.

Sporster 20 wouldn't high up on my list. The OS19 is probably light and maybe as much pop.
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glidermaster
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« Reply #11 on: August 24, 2009, 03:56:29 PM »

Some of the foregoing begs the question (to me at least) - what's available in terms of new engines?
Nearly all of the engines discussed so far are off eBay - nothing wrong with that, but is there anything suitable in current production (other than PAW)?

Bob Mattes (he has a web-site) can, I believe, convert a burnt out (original) Cox Special/TD head to take a Nelson plug, and there's a guy selling on eBay (Valentine?) who supplies a new head for the same engines that takes the OS Turbo plug. This is like the Nelson plug in that it seals on a chamfered face, rather than to a seating washer, so there's no wasted volume around the threads. I don't know if it's as good as the Nelson plug, and they are not interchangeable, but it is an option.

Beware of very light power models that move quickly - many Brits will remember some of Julian Hopper's spectacular mid air disintegrations of his 40 powered Superjacker. How many of Stafford Screen's models have you ever seen do that?

I would be a little wary of some of what Dan suggests - certainly as regards taking out structure - Jaysbird was designed to the old, light, FAI rules. Better to be VERY careful with wood selection and covering choice - in my opinion, that is.

Secure the engine mount properley, too, so you aren't throwing away power shaking the whole airframe.

John
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applehoney
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« Reply #12 on: August 24, 2009, 05:12:43 PM »

many Brits will remember some of Julian Hopper's spectacular mid air disintegrations of his 40 powered Superjacker.

Ah, yes .. impressive .....
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RobinB
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« Reply #13 on: August 24, 2009, 06:20:46 PM »

Some of the foregoing begs the question (to me at least) - what's available in terms of new engines?

Nearly all of the engines discussed so far are off eBay - nothing wrong with that, but is there anything suitable in current production (other than PAW)?"

The last suitable engine that was generally available was the Norvel Big Mig .15, wasn't it?

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Beware of very light power models that move quickly

Especially when they're coming down!

Quote
I would be a little wary of some of what Dan suggests - certainly as regards taking out structure - Jaysbird was designed to the old, light, FAI rules. Better to be VERY careful with wood selection and covering choice - in my opinion, that is.

Take your point, John. Those 'old-rule' FAI models were the precursor of today's SLOP, but we're often using a bit more power than some of them had.

Incidentally, this wouldn't be the right thread for it, but I'd be keen to know what coverings are working best on power models. Polyspan is great stuff, but with 3 coats of dope and fuel-proofer it starts to weigh a bit. I'm going to try Airspan on tips and stab of the next model.

Robin
« Last Edit: August 24, 2009, 07:14:48 PM by Forum Staff » Logged

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danberry
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« Reply #14 on: August 24, 2009, 06:29:53 PM »

Robin needs a plain-bearing engine. I don't know of a current production engines that would be suitable regarding a power-to-weight ratio.
My JaysBird FAI w/Olympic15 was 15.5 oz when new. I didn't reduce any structure, including the fuselage cross-members. That was with Monokote covering. I really think there's a lot room to play. It HAD to weigh 17 and change oz for FAI. Not so in SLOP. A hotrodded Veco19 would make it a beast. The Veco should be available on the cheap. It ain't legal for NosGas over here, so there's not much demand. The OS MaxIII 19 is good, but there's a market for it.

The turbo plugs work, but they cost about 8 clams. The Nelson goes about 4.50. Easy choice for me.

Ultracote and Ultracote have seved me well. I only use it on structures that don't need torsional rigidity from the covering as it adds none.
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glidermaster
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« Reply #15 on: August 24, 2009, 07:33:04 PM »

Checkout the Aerosmith (Bob Beecroft) - lots of Veco stuff. I would think Dan's right, that engine in the right frame could be a bit of a beast.

Covering - well I'm still stuck in the lightweight/heavyweight modelspan and Esaki era. I looked at Dave Parson's Jaysbird in May (which is also Cox Olympic powered, I think) - Iron on covering - it looked and felt pretty good to me.

Another guy I corresponded with a while back, was Tim Lollar (now sadly deceased) and he had built a Dreamweaver - the late 50's version - and put an OS19 in it (after putting an Oliver replica in it originally). He spoke very highly of that combination. You've got to love those old Surbiton designs.............

John
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DaddyO
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« Reply #16 on: August 25, 2009, 04:06:52 AM »

Gorden Cornell was producing a SLOP specific diesel a while back - I don't have any details of it, but he used it in his own models (I remember it was reviewed in FMD&C; I'll try and find it)
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« Reply #17 on: August 25, 2009, 04:49:21 AM »

Gordon's diesel range was named Dynamic. He also produced an 061 for F1J, which didn't rev like a glow, but would turn a much larger prop - rather like the geared F1C motors of today. If I recall, he was also updating the ED Fury 1.5cc, which he designed while at ED all those years ago.

Peter - mine of useless information Cheesy
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glidermaster
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« Reply #18 on: August 25, 2009, 06:42:37 PM »

A question or point of Robin's went unanswered, pertaining to the TD/Special 15 and their glow heads;

Thanks for your input so far, guys - I know how power flyers like to talk about engines |-)

Cox 15 TD or Special: An engine man some of you might know, John Haytree, maintains that the problem with TD heads is nothing to do with nitro or rpm but that they burn out due to excess voltage. Perhaps someone could shed some light on this?


The enemy of heads and indeed plugs in general is running lean and/or undercompressed. The Cox really needs nitro, at least 30%, and running on too little for a given compression set up can give a similar sound quality to running rich - i.e. 'crackly'. You turn the needle in to compensate, and it sags - it goes lean. It is indeed possible to feed too much voltage to a plug (I've done it), but my experience is that people generally slighty under power them, which can make starting very hard, perticularly when flooded, and the element can't burn off the excess fuel. I observe that this is less of a problem these days with the widespread use of starters.

Dave Clarkson at one point made the claim that plugs should be run in and checked just like an engine - rogues do crop up occasionally - seals blow, elements are too thin etc etc. Rossi insert type heads were very variable at one point. You had to measure and mark them for depth, and check that the seals were good. I had some that required turning down to make them fit the bore of the cylinder - which was a bit of a pain without a lathe.

John
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RobinB
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« Reply #19 on: August 26, 2009, 05:24:09 PM »

Thanks for that info, John.

D'you run your OS15 on a similar level of nitro?
And is that a normal model-shop type engine mount on the Semislo?

Robin
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glidermaster
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« Reply #20 on: August 27, 2009, 10:35:11 AM »

I run the OS on about 20% nitro - it's a 'stock' engine, so beyond a few percent, adding nitro seems to make little difference.

My Dad used to use 50% nitro in his Eta 29s, and Mike Gaster used 70% nitro in his self built FAI motors - until straight fuel was mandatory in FAI, of course.
Yes, that is a std. '15' size commercial engine mount - it seems OK. It was a last minute decision when I built the model, so it's not on the plan I drew for it. I prefer to mount engines on metal.

John
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RobinB
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« Reply #21 on: August 27, 2009, 11:44:54 AM »

I'm pleased to see the OS15FP is well thought of, as I've been sitting on a couple for years. One is brand new, still in its' box.

Your mention of metal mounts had me rummaging and I found an OS mount I had at the time. It's threaded and spaced for the 15FP. Its' number is OS 909. I thought it had been discontinued, but Tower Hobbies now carry it as the OS15 LA mount. Pic attached (hopefully). It's got the same number, so I'm guessing it's the same item. If you know anyone with an LA, check that the mounting holes are the same.

Annoyingly, but unsurprisingly, it doesn't fit the MAX 15 III. It weighs 21 grammes.

I'm just finishing off a 'proper-job' starter box with a posh power panel, which has adjustable power to the plug. Big sewing machine foot switch on a long cable so George can trip over it |-). When it's ready I'll be able to give some of these engines a run.

Another OS geek item - if you need any backplate or head bolts (2.6 mm) you can get them much cheaper from modelfixingsUK than from OS. They also have 5-40 UNC socket head bolts for Cox .049 prop retainer.

Ratz Edit: replaced pic with correct one.
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glidermaster
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« Reply #22 on: August 27, 2009, 02:51:07 PM »

That mount looks good - it's got a lug for a leg, too.

I still hand start all my plain bearing engines - and yes, all digits on both hands are still intact!

JB

p.s. if it weren't for folding props, I would hand start all my engines.
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RobinB
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« Reply #23 on: August 29, 2009, 10:47:38 AM »

This is the FORA 21 I mentioned in an earlier post. Never run. Choice of venturis and optional diesel head

Robin
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« Reply #24 on: August 31, 2009, 12:35:35 PM »

Looks good, Robin, and I'd think it'd probably give you the most power available for the class (as a glow engine). If you're going to build something for it, give it plenty of area. My Dad's Slow model for OS20FP has a full 500+ sq.in. wing area, weighs 24 oz. and it isn't slow.

John
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