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Help me pick an engine for my Akromaster.

Old 05-20-2008, 07:29 PM
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Default Help me pick an engine for my Akromaster.

All,

My LHS has a SIG Akromaster kit for a good price, so I'm going to pick one up & build it.

Any suggestions for the best choice from the following engines I have on hand :-

Enya .09-III
OS 10 FSR-S
OS MAX-III .15
OS MAX .15
Enya .19-IV 4004
or even build super light and use a Norvel .061?

My gut feeling - the .10 FSR-S.

cheers,
Colin
Old 05-20-2008, 08:55 PM
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Default RE: Help me pick an engine for my Akromaster.

Hi Colin
Going by the ad for that plane from [link=http://www.modelflight.com.au/rc_model_power_planes/sig_akromaster_cl.htm]Model Flight[/link] it's designed for a 15-19 size engine so I'd go for your Enya 19.
Old 05-20-2008, 10:21 PM
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Default RE: Help me pick an engine for my Akromaster.

Actually the 10 would be ideal. I had one on mine and it was perfect with a Thunder Tiger 7x4.5 prop. I have been running a Supertiger x-11 on it lately just to run it a bit. Plenty of power! When you build the plane, the plans show cutting the leading and trailing edge shorter than they are supplied. Many people have built 2 extra ribs and left the wing full length and it flies great with a few more sq. in. of wing .
Old 05-21-2008, 04:20 PM
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Default RE: Help me pick an engine for my Akromaster.

I agree with Scott...

When the SIG Akromaster came out engines were much less powerful than those of 'the recommended sizes' today. Most reasonable priced OS engines require litlle break-in before they become dependable and reliable. An .061 is a bit too far toward the low end, unless the model is EXTREMELY light (<10 oz?) and you're willing to fly on 35' lines...

But almost all engines need at least a few familarization (for you!) runs. Best is to do what is recommended in the instructions in the box. If it doesn't work, you can file a legitimate gripe; if you you go crazy some other method, any problems are likely on your responsibility. (Shouldn't be problems, but if there are...)

BEst of luck and enjoy flying in the best of circles!
Old 05-21-2008, 05:58 PM
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Default RE: Help me pick an engine for my Akromaster.

My vote goes to the MAX-III .15...darn good engine.

George
Old 05-21-2008, 06:00 PM
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Default RE: Help me pick an engine for my Akromaster.

An OS.15 will do the job very well for you on 50' lines. I use a MA 8x5 prop and a home made uniflow tank. The Akro is a great little model to fly.
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Old 05-21-2008, 06:31 PM
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Default RE: Help me pick an engine for my Akromaster.

But almost all engines need at least a few familarization (for you!) runs. Best is to do what is recommended in the instructions in the box. If it doesn't work, you can file a legitimate gripe; if you you go crazy some other method, any problems are likely on your responsibility. (Shouldn't be problems, but if there are...)
Amen to that. I am currently struggling with finding the sweet spot on the MAX .15 (1970s baffle piston drop-in liner type) in my new JR Flite Streak.

Losing the OS 702 muffler helped (the engine did it for me, by throwing the muffler off in flight after vibrating out the strap retaining screw) - I have had better flights running open exhaust. My flying site is not noise sensitive, and in fact I haven't attracted a single uninvited spectator yet.

The problem I'm having with the MAX .15 is that it seems to go screaming lean far too easily, but I cannot get it to richen up enough to find a sweet spot for stunting. Taipan 8x4, 20% castor, 10% nitro. Peaked setting is around 14,200 RPM. I want to back it off to a launch RPM of about 12,000 but when I open the needle further it just doesn't seem to slow down, which makes me think I may have a fuel draw problem or over-sized venturi. The venturi may not be the normal MAX .15 one - its an R/C conversion and I think the venturi I put in it was originally from a MAX .20 or .25.

The funny thing about this is that when flying yesterday, while having OS .15 problems, my mate Steve and I managed to accidentally set a Black Widow .049 in a little profile stunter to do a 4-2 break. First time I've ever heard such a small engine do it. It was burbling rich in level flight and leaning in the verticals.

Regarding the Akromaster - had a closer look at my engines last night, and can easily configure the mount to take both the 10 FSR and either of the .15s - so I'll hedge my bets and do that.

cheers,
Colin

Old 05-21-2008, 06:57 PM
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Default RE: Help me pick an engine for my Akromaster.

Sounds like you must have something wrong there for sure, OS.15's are usually VERY user friendly. The .15 C/L venturi are still available new, your LHS should be able to order one. You might also have tank issues if you're not using uniflow, that would cause lean running for the last half of the flight. I use an OS A3 ( hot ) plug, 5% nitro and 20% all castor.
Put the muffler back on and try using pressure, if you think the venturi is too big. You could also put a sleeve in there to reduce the diameter slightly.
Old 05-21-2008, 07:26 PM
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Default RE: Help me pick an engine for my Akromaster.

Will a LA .15 or FP .15 venturi fit the older Max .15 I'm using?

I've got a new A3 plug on hand, I shall try that, although the plug in there now seems fine.

Its a Brodak wedge tank, 2oz.

This engine is very tractable on the bench, even with straight 80/20 fuel FAI fuel.

In the plane, when set right (ie. as good as I can get it), I can be get a reliable run but too close to peak (4 second laps). I cannot richen further. Engine run is consistent through overheads (I can tool around in tight circles directly overhead without the engine sagging). It burps a little bit on loops - just a glitch but quite noticeable, like the Fox .35 profile burp I've heard about on the forums.

I just want to dial in slightly richer run to get the lap times down a bit. Going to slightly longer lines (say 52 feet) will do the rest of the job of taming the model. Even with the 4 second laps its lovely to fly and maneuvers well, but I'd rather not feel like I'm flying a combat wing :-)

I'll try muffler pressure - I've sourced a light weight tongue muffler for the .15 to replace the OS 702 house brick.

cheers,
Colin

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Old 05-21-2008, 08:28 PM
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Default RE: Help me pick an engine for my Akromaster.

Colin, yes the FP/LA venturi will fit that OS Max you've got there. Kelletts Hobbies here in Liverpool find a few older OS parts for me, mainly venturi and NVA's, so your LHS in Bris. should be able to help. I've also found an Ebay Shop guy in Canada selling lots of parts for older OS engines......John
P.S. That's an OS.15 FP in my Akro.
Old 05-22-2008, 10:58 PM
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Default RE: Help me pick an engine for my Akromaster.

Raise the tank a bit.

The ideal way to set a tank is fill to 1/4 and try to dial in by moving the tank up and down and getting the engine to run exactly the same both upside down and upside up.

Good Luck.
Old 05-23-2008, 12:41 AM
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Default RE: Help me pick an engine for my Akromaster.

Raise the tank a bit.
Go on Col, tell 'em about the tank...
Old 05-23-2008, 08:24 AM
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Default RE: Help me pick an engine for my Akromaster.

I had a lot of fun flying .19 size engines during the '60's. My favorite models were the Flight Streak JR and the JR Satan.

The .19 is a joy to handle, most start easily and have no bad vices. A K&B Greenhead was probably the best overall when it came to handling, power and no problems.

My Fox .19 was excellent too but I had problems with the NVA getting loose and then it would snap if you tightened it too much. A K&B NVA finally solved the problem.

Those cheap redhead Testors/McCoy engines had excellent power but the shiny case version blew head gaskets quite often. Today I would make an aluminum gasket and throw the soft phillips head screws away in favor of socket heads. I have a lightning bolt case model which made it a better engine.

Yeah, I've never had an Akromaster but a .19 would make it fly well.

I have a kit for a Satan Jr and have been thinking about powering it with my Veco .19.
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Old 05-23-2008, 11:15 PM
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Default RE: Help me pick an engine for my Akromaster.

ORIGINAL: steve111

Raise the tank a bit.
Go on Col, tell 'em about the tank...
Was wondering when you would pop up on this thread. [sm=spinnyeyes.gif]

Already blogged that story on this site (see my profile). At least I've never had a whole engine come off in flight.

Moral of the story ... don't trust my soldering skills.

The original topic of this thread is now a moot point, because I missed out on the Akromaster kit by a couple of hours. When I went to get it at lunch time today, I was told the last one had been sold that morning, and they won't be getting more SIG kits in until September/October. Should have rung ahead & reserved it.

Dan - what a beautiful collection of vintage .19s. Drool!!!! That K&B green head is stunning.

I have a number of .19s & .20s in my collection as well :-

2 x PAW 19 diesels - a 19DS and a 19DS-3
2 x Enya .19-IV model 4004
1 x Enya .19-V model 4005
1 x OS MAX .20
1 x OS MAX 20FP (really a .21 and more suitable for something like a Ringmaster).

No K&Bs, McCoys or Vecos 'though - don't tend to see as many of those down under.
Old 05-24-2008, 06:29 AM
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Default RE: Help me pick an engine for my Akromaster.

Thanks Colin,

If you watch ebay by .19 engine size there are a lot of them that go at very reasonable prices. Most CL stunt flyers want .35 or larger engines and there is a lot more interest in .15 engines than the old .19.

It's a very overlooked engine size and they offer puppy-dog handling with plenty of power to keep the lines tight.

One of these days I need to add an OS .19 and Supertigre G.15/19 to the flock.

Don't have one at the moment but a BB Veco .19 will fly most .35 models with ease.
Old 05-26-2008, 01:22 AM
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Default RE: Help me pick an engine for my Akromaster.


ORIGINAL: colingw

All,

My LHS has a SIG Akromaster kit for a good price, so I'm going to pick one up & build it.

Any suggestions for the best choice from the following engines I have on hand :-

Enya .09-III
OS 10 FSR-S
OS MAX-III .15
OS MAX .15
Enya .19-IV 4004
or even build super light and use a Norvel .061?

My gut feeling - the .10 FSR-S.

cheers,
Colin
Hi Colin,
You are on the right track with your gut feeling, The OS .10 FSR is a great choice.
The thing to remember with the Akromaster is that it only has 250 sq's of wing area,
so that you should try to keep the overall weight as low as possible. That means
that most .15's and .19's are out of the question because the engines are too heavy
and will require tail wgt to bring the CG to a proper position. Light .15's like the older Fox .15s
are what this model was designed for. I have two Akro's one has a Silver Swallow .15 diesel
in it and weighs 17 ozs....it flys, but it is a pig, even though it will fly a pattern on 60' lines,
it will not turn quickly. My second Akro is powered by an MP-Jet .061 diesel and it weighs 12
ozs ready to fly. It flys extremely well and turns very tight corners, somewhat like a Combat
ship. I venture to say that that Akro will out turn any Akro I've yet seen. I fly it on 45'x .008"
lines. Even though the box description sez .15-.19 engines recommended...give that statement
some thought...they wanted to sell kits... Some of the modern .15's and .20's will fly a full size
Flite Streak very well an 60' lines. I see that somebody bought the Akromaster kit that started
this thread...no matter, another kit will find it's way to you, Akromasters seem to pop up quite
often.

Tony G
Old 05-26-2008, 10:07 AM
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Default RE: Help me pick an engine for my Akromaster.

Another approach, especially if building from a kit, is to increase wingspan. The leading and trailing edges have extra length that is usually trimmed off. To increase wingspan, you need to make additional ribs, new bellcrank mount, and new fixed flaps. The results is a larger wing and lighter wing loading.

Here is a pic of one I did that way. Everything except the wing is box-stock.

The standard one (bottom) has a Fox .15 slant plug, and the extended one (top) has a OS FP-S .10 for power.

When choosing an engine, remember that the size range recommended was for pre-schnuerle engines, usually with no muffler.

George
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Old 05-26-2008, 05:52 PM
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Default RE: Help me pick an engine for my Akromaster.

Thanks all for the advice,

I've located another kit, at a store in Victoria. It'll be about $10 more after shipping, but I consider that the price to pay for being too slow off the mark (early birds & worms).

The extended wing looks like the way to go to me.

cheers,
Colin

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