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Speed,Combat,Scale,Racing => Combat => Topic started by: phil c on September 10, 2017, 04:36:49 PM

Title: Fora 21
Post by: phil c on September 10, 2017, 04:36:49 PM
I know some of you have tried the Fora 21 for slow combat, and there have been problems.
My buddy Oleg got a couple the season before last.  They broke in pretty easily, maybe 6-10 runs, starting a bit rich and working the needle in a bit after each flight.
But they never settled down and ran well.  By comparison, the standard Fora 15 would break in in 4-5 flights.  By then it steadied down and started running very reliably and steady while gradually getting faster with each flight.

The 21 never settled down.  We tried different fuels, different size venturis, different props, new bladders, and different needle settings.  He gave up for awhile and switched to a couple LA 25's which broke in and ran fine(Japanese built silver ones).
This summer he brought the Foras out again and still had the same problems.  Out of frustration he swapped the long plugs he'd been using in the LA 25 for an OS A3(a short plug).  Next flight it ran perfectly with the usual slightly rich setting on launch.  It also ran fine on the APS 8/4, the 9/3N, and a few other props.  As a bonus it ran over 6 minutes on barely 3oz. of fuel.

This may not be a cure-all, but it's worth a try.
Title: Re: Fora 21
Post by: Bob Mears on September 11, 2017, 07:29:15 AM
Thats good info! I finally gave up on mine and threw it in the engine drawer. Maybe tie to dig it out and give a short p
lug a shot!
Title: Re: Fora 21
Post by: phil c on September 12, 2017, 03:35:59 PM
It might be something to do with compression.  The exposed threads with a short plug also probably foul up the combustion a little, keeping it from firing as hard.
Title: Re: Fora 21
Post by: tim lackey on September 13, 2017, 07:50:19 PM
Thanks for this info. I got one two years ago tried everything
I could think of props, fuel, venturis, plugs nothing worked.
I didn't try a short plug though definitely worth a shot!
Tim
Title: Re: Fora 21
Post by: Dick Tyndall on September 13, 2017, 10:00:31 PM
   By going to a short glow plug you are delaying the fuel ignition in the combustion chamber, or retarding the timing, like in an automobile engine. To clean up the combustion chamber you might want to machine a smaller dome in the combustion chamber and make it like a "double bubble" head. With the engines we race in our R/C boats we sometimes advance the combustion timing by pulling the glow plug coil wire out of the plug slightly. You just may find out some interesting information playing around with pulling the wire on the glow plugs, using different heat ranges, etc.
Title: Re: Fora 21
Post by: Ken Burdick on September 14, 2017, 09:14:26 AM
Both Dick and Phil are correct in my opinion.

This is the first I have seen of this thread and would like to know about the fora .21. Is it a sport engine in their line of high performance engines? In a N.W. proto speed event, I have pushed the LA .25 to many limits and when there, the head with a double bubble really begins to cause problems. A step back to a simple hemi seemed to cure this. I'd like to say I understand combustion and what the true effects are, but mostly it's trial and error.
Who sells the Fora .21? Techno?

Thanks

Ken
Title: Re: Fora 21
Post by: Bob Mears on September 14, 2017, 11:12:02 AM
I got mine from Yaro. It says its a 75mph engine. Andy got his to work a little better than mine, but still not good enough to depend on in an event.    I did built an exhaust restrictor plate on my 21 so I could slow it down a bit. It was adjustable so I could dial it  the right speed.  The problem is still just holding a setting. Mine and Andys both acted like many of the LA 25's. Run great for two minutes then go lean, or rich, or just quit. Acts like a temperature thing. They started great. Andy Finally ran an F2D prop on his....scary!  We finallyboth just put 8/4's on our F2d ships and called it good.
Title: Re: Fora 21
Post by: Ken Burdick on September 14, 2017, 02:45:32 PM
for s/l I have always used B grade F2D motors, here that is 80 mph so a 7 x 3 apc works great. Slow down to 75 is a problem but the prop you use would do it. No fuss no bother with the 2D engines. Always work and run well.
Title: Re: Fora 21
Post by: jim gilmore on September 14, 2017, 06:26:13 PM
What or who is Yaro ?
Title: Re: Fora 21
Post by: tim lackey on September 14, 2017, 07:14:08 PM
My experience is the same as Bob's. I actually launched for him a few times at brodaks two years back. Mine came with a large Yaro venturi and a small stock one both do the same run great mabe one or two minutes then quit. Very easy to restart no cool down time needed. Going to try per Phil a short plug.
Title: Re: Fora 21
Post by: Bob Mears on September 15, 2017, 07:42:21 AM
What or who is Yaro ?
http://aerohobby.ca/store/
Title: Re: Fora 21
Post by: Fredvon4 on September 15, 2017, 07:48:11 AM
Yaro is a guy in Canada that sells a lot of combat stuff mostly Eastern European sorced

http://aerohobby.ca/store/index.php?main_page=index&cPath=1
Title: Re: Fora 21
Post by: kenneth cook on September 15, 2017, 02:05:16 PM
               Phil, I remember Oleg flying the Fora when he just received it. I heard it in the background and it was sounding like a F2D engine. I was quite shocked to see it was similar to the LA's that day in terms of speed. I don't recall any issues with the engine runs on that day. Has he been using the Fora on a regular frequency?
Title: Re: Fora 21
Post by: tim lackey on September 20, 2017, 05:12:25 PM
Well I want to give a big thank you to Phil. After rummaging through my old,and never used model stuff I came across some 40 year old short fireball plugs.  It's like a different engine easy needle setting and it holds. Six flights one after another about five minutes on two ounces 8x6 tiapan prop. Running small stock venturi  om going to check the speed pretty sure it's to fast.
Tim
Title: Re: Fora 21
Post by: phil c on September 20, 2017, 08:32:16 PM
               Phil, I remember Oleg flying the Fora when he just received it. I heard it in the background and it was sounding like a F2D engine. I was quite shocked to see it was similar to the LA's that day in terms of speed. I don't recall any issues with the engine runs on that day. Has he been using the Fora on a regular frequency?
  One of the things Oleg did was run the 21 on some fiberglass 6-1/2 or 7in F2D style props.  That's probably what you heard.  It ran better but had big time trouble pulling through maneuvers.

Regarding the engine, just like the Fora F2D engines it meticulously built and fitted, but considerably cheaper.  It isn't timed for 30,000+ rpm, more for RC combat.  Side exhaust, similar weight to an LA 25.  Just saw the newer ones come with a Nelson plug head.  I think it comes with 2 venturis.  The smaller one is the right size for 75mph combat.