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Thread: Magnum 1.08


  1. #1
    maineflyer's Avatar
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    Magnum 1.08

    I just bought one of these to put on a GP Extra 300 .60 size. I wanted to see what some prop choices would be. I am thinking about a 14x6 (recommended by manufacturer) and possibly a 13x8 but is anyone running something different. I am hoping for unlimited verical on this plane. I should come in around 8 lbs. The engine with pitts muffler is 28 oz. Let me know what you think of this setup.
    thanks,
    Jeff
    Jeff

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    Magnum 1.08 props

    Despite the manufacturer's recommendations, those aren't nearly enough prop for the engine. I have one on a 10+ pound Joss Stick. With a 14-6 prop it'll act like a mild .91. I think it will only turn up so much. Try a 16-6!

    The 16-6 sounded too large to me when I first heard about using one, but after trying a Zinger 15-6 and a Zinger 16-6, I found the 16-6 performed better in the air. The APC is also good and is my prop of choice. Set your engine where it leaves a light smoke trail for the first few minutes. I'm using Omega 10% fuel.
    Ed Moorman, AMA 553, Former R/C Report Fun Aerobatics Columnist. 76 and up to my old tricks!

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    Magnum 1.08

    Ditto.
    Aww $#!^.... I left the )@#& transmitter at home!

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    Magnum 1.08

    I hope you have better luck with your Magnum 1.08. I had one on a Joss Stick and no matter what I did to fix the problem, short of adding a pump, the engine would run lean after not more than 1 or two minutes. I finally put an OS 91FX on it and it had more power than when the Magnum was running at it's strongest.

    I use to run 16x8 props on an OS 1.08 that was mounted on a Sig 4* 120. That was the perfect prop for that particular engine.
    Mike in WV

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    maineflyer's Avatar
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    Magnum 1.08

    Thanks for the info on the engine. Anyone have any rpm levels for the 15 or 16x6? If I can get 9,000 or so that should be enough to pull a 8-9 lb plane verticle. Don't you think?
    Thanks again,
    Jeff
    Jeff

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    ASP 1.08 is clone of OS 1.08

    And I would prop it accordingly. Per rcfaq.com the OS 1.08 gets considerably less than 9,000 RPM on a 16-6. I don't see how the ASP would get much more. It pulls almost 10,000 RPM with a 14-8. I have an ASP 91 two stroke, the same engine with a smaller bore, and it swings a 14-6 APC at well over 10,000 RPM on FAI fuel. But the plane flys better with a 13-6 and the engine turns at 11,000 RPM. I would think the 14-6 is the right size with a light airplane. A heavier plane may need more prop. I would think you would want the smaller prop on that plane, not sure you would have the ground clearance for hard landings .
    Glow Head Brotherhood #15

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    Magnum 1.08

    Now I am confused (OK, so some think that is nothing new!). I keep reading that the Magnum and ASP engines are clones built in the same plant? If that is the case, then the two Red Head ASP's that I had didn't act anything like the Magnum 1.08's mentioned above as needing big props. Fact was, I found that the ABC ASP 1.08's acted like a high revving, high compression Rossi. With larger props, they tended to detonate and over heat. In other words, they did BEST with a 14 x 6 prop which allowed them to unload. Due to the big bore stock carb, fuel draw was always marginal, and I found that high RPM breathing helped this draw a little. I used my ASP Red Head 1.08's in the Goldberg Extra 300, which as I recall is just a tad larger than the GP Extra. Turning a 14 x 6 MA prop at around 12 K (LOW nitro, and low restriction pitts style muffler) unlimited vertical was NOT a problem.

    Now, if the Magnum 1.08 is NOT the same as the ASP, then forget what I just said!

    Lee
    Test pilots get to play with other folks toys!

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    Sport_Pilot's Avatar
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    Magnum 1.08

    RLD,

    I think it's common to overprop these days, maybe the economy causes prior 4 stroke only people to try a 2 stroke, or maybe its just that some people just gotta have a big 16"!
    Glow Head Brotherhood #15

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    Magnum 1.08

    Now don't quote me but I have an SC 1.08 which I believe is either a clone or at least very similar to the Magnum, ASP, whatever.
    Running quite rich on straight 4:1 fuel and with an MA 15x6 prop it was turning 9000 revs and a 2000 idle. It's fitted with an Enya 60X carby (which is a straight drop in fit) because the original was broken. I've got the SC in an old 40 size trainer (OK, my rev head son did it ) with an all up weight of 6 pounds so vertical performance is adequate

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    Magnum 1.08

    After mostly breaking in my Mag 1.08 I tried several different props. Since I tossed the data this is what sticks in my mind:
    APC 15X8 = ~9300 RPM
    Zinger 15X6 = 10000+RPM
    Zinger 16X6 = ~9700 RPM
    MA 14X6 = ~14000 RPM

    I Custom fit a Slimline Pitts made for the O.S. 1.08. Fuel was 10% N. Increasing Nitro didn't seem to make much difference except to make the engine run hotter. A high performance plug, (slightly cooler element), helped to keep temps down with the 16X6. I'm running it on a 9lb. Cap that currently doesn't have landing gear so I can't verify RPMs.

    This engine/prop combo EASILY pulled my Cap around like a racer and had no probs shooting straight up and up and up...

    It does seem that this engine likes to spin around 10K or better-temp wise.

    Mineflyer, what kind of Pitts muff do you have? My engine alone weighs 24.8 oz and my Pitts weighs 5.2 oz.
    If I were you I'd try a 15X6 after break-in on your Extra.
    Aww $#!^.... I left the )@#& transmitter at home!

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    Volfy's Avatar
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    Magnum 1.08

    Yes, ASPs and Magnums share very similar genes, but direct comparisons are not very good without knowing the relative vintage. The latest ASPs are 3rd generation designs. Likewise, the Magnum line is seeing constant revisions. Bear in mind that if you bought these engines directly from overseas, they may not come with head gaskets that drop the compression to be more suitable for the 10%-15% sport fuel common here in the US. Either order head gaskets from the US Magnum distributor or stick with 5% or FAI to avoid pre-ignition or detonation.

    Right now I have a Magnum 1.08 that is waiting on a Sullivan Dynatron to get started. The large bore (10mm) carburetor just spat raw fuel in my face instead of sucking it into the combustion chamber when I tried to hand flip this beast, as my standard duty starter couldn't turn it over even on 24V. I will break in on the recommended 13x6 and report some RPM figures.

    BTW, my 1.08 does not have thru bolts for mounting the muffler. Magnum is currenly updating their big 2-strokers to be more like OS with thru bolts mounting. The new 1.20 and .91 are already out. I believe the updated 1.08 is on its way, which explains why Magnum has been putting them on clearance pricing.
    Si vis pacem, para bellum.

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    maineflyer's Avatar
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    Magnum 1.08

    I will have to look into the pitts muffler to get the brand, don't have it at my fingertips (at work). It came with the screws to install it. My Magnum came from the left coast last month and does have 2 gaskets to attach the muffler. I haven't taken the head off yet. I plan to strip the engine prior to break in to check it for any debris from manufactor. I plan to try several different prop 13x8 - 16x6 to see what it will like. I also plan to run a castor blend fuel probably 10% Nitro. Thanks for all your imput and I would love to hear more comments on RPMs, proping, experience on break-in and running. I am concerned about oeverheating in the enclosed cowl and will probably stick to lower nitro.
    Thanks,
    Jeff
    Jeff

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    Magnum 1.08

    Just wanted you guys to know that there were 108 views when I decided to post!
    Glow Head Brotherhood #15

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    Magnum 1.08

    Volfy and Maineflyer,
    In order to start this "beast" it has to be primed till it's soaking wet with fuel. Hand starting was tough so I gave up trying and used my Tower Hobbies starter on a Dewalt 12V XR pack. The battery was only good for a couple starts so I switched to two 6 cell 1500mAH car packs in series and a heavy duty starter. No probs now! Gel cells really can't provide sufficient current flow. Voltage helps but, available current flow and motor torque seem to be determining factors when starting big beasties.
    Be sure your test stand and/or airplane are sturdy and secured firmly! Once it gets going with a sizable prop it puts my gas weedeater to shame!

    Best of Luck,
    Jeff
    Aww $#!^.... I left the )@#& transmitter at home!

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    Magnum 1.08

    Jazzy, thanks for the tip. Interesting idea about using Dewalt battery packs. I have 6 of the 18V Cobalt XR2 - my deWalt drill/drivers last forever on one charge. But I can't think of a good way of hooking up the wires. Anyhow, my field setup is two 6-cell NiMH 3000mAh car packs wired in series as you described. I also tried 2 gel cells in series - at 24V the current draw only needs to be half to produce the same power as at 12V. My old standard duty starter is just not up to the task. Since I was wanting a new starter that can handle up to a Poulan 46cc, I went ahead and ordered a Dynatron with a single handle kit. 680 in-oz at 24V ought to be plenty.
    Si vis pacem, para bellum.

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    Magnum 1.08

    Volfy, 46cc? E-Gads! Now I understand!

    To hook up those Dewalt packs-without disassembly-get some large female spade connectors. You'll have to shape them a little with some needle-nose pliers. Crimp some 16 or 18AWG wire onto the spade connectors. You could cut the 'gator clips off of the starter and put on bullet connectors. The wires coming off the spades just get the mate for the starter wires. That way you could easily swap from 'gators to spades.

    Just curious, was your standard starter rated for 12 and 24 volts? You are absolutely right about 24V only requiring half the current to produce the same Watts. But, it doesn't always work that way when dealing with motors and their ratings. (Sounds like you and I work in similar fields.)

    Anyhow, what is the 2.8 going in? I wanna see!!
    Aww $#!^.... I left the )@#& transmitter at home!

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    Starting the Magnum 1.08

    I can't believe you guys have to use an electric starter on the Magnum 1.08! Choke 3 or 4 times, flip until is is wet in the cylinder, then pop it backwards once. If it won't start in 2 flips, something is wrong.

    I have tried many props, 13-8, 14-8, 14-6, 15-6, 15-8 & 16-6 Zinger & APC. I never would have thought it, but the 16-6 works best with my heavy, 10+ lb. Joss Stick.

    I just took it out of the box, poured 10% Omega fuel in it and ran it. I do break in all my engines on the bench and set them there first. When I was bench running it, the 1.08 started 1-flip 5 straight times. I forget what plug I have in it. Probably an OS.

    Now I will admit to hand starting engines since 1950, and I was a CL rat race pit man for several years.
    Ed Moorman, AMA 553, Former R/C Report Fun Aerobatics Columnist. 76 and up to my old tricks!

  18. #18
    Volfy's Avatar
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    Magnum 1.08

    Jazzy, I'll definitely give your deWalt idea a try. About the 46cc, after reading about others here like flipflop having a ball with that engine, I just had to have one. See here:
    http://www.rcuniverse.com/showthread...ghlight=Poulan
    It has been put on the back burner though, as I'm currently wrestling with a Cub Cadet 25cc conversion - can't seem to find someone that makes a hub adaptor to replace the flywheel so I can put an electronic ignition on it. I'm real bad about constantly being 2-3 projects ahead of myself and buying wayyy more engines than I got planes. So to answer your question, no, I have no idea what plane the 46cc will go on. My guess is probably something like a 1/3 scale Spacwalker.

    BTW, the starter I used is a Tower Hobbies basic starter, which for sure is not rated for 24V use. I just tried it briefly to see if the little extra oomph would turn the 1.08 over. Nope!

    Ed, put it bluntly - I suck at hand starting. Always have been, probably always will be. I probably could hand start the Magnum 1.08 after I break it in, but brand new it is as tight as (place your choice of colorful metaphor here) at TDC. It squeals like a pig.

    I am trying to master the backflip technique, though. I have tried it on other 2strokes and it works better than trying to hwack the prop past compression, especially for the bigger ones..
    Si vis pacem, para bellum.

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    Re: Starting the Magnum 1.08

    Originally posted by Ed_Moorman

    Now I will admit to hand starting engines since 1950, and I was a CL rat race pit man for several years.
    Seems we have one or two things in common...I hand start my SC 1.08 (usually first flick), been hand starting since the latish 50's, was a rat race pit man (we won a state championship in our first ever competition ) and I was an engine fitter on the F111C for 8 years.


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