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-   -   Looking for a decent engine (https://www.rcuniverse.com/forum/extreme-speed-prop-planes-104/2991906-looking-decent-engine.html)

2fast4-u11 05-19-2005 07:41 PM

Looking for a decent engine
Hi Guys

I am wondering if anyone knows of or have tested gms47 engines and if so how fast could if spin a 8 10 prop. I have orderd a dd clipped wing., and I would like a economical engine to power it. I know of jett rossi and such but I can purchase a gms 47 for 79.00 canadain.

On a side not to reach one hundred and fifty with this airframe I assume I would have to spin a 8 10 proop around 16000 or so once I get used to the speed and am comfortable with it I would not mind purchasing a proven speed set up. but until then if anyone has any combinations that they use to hit about 150 + mph please share with us


Flyboy Dave 05-19-2005 07:48 PM

RE: Looking for a decent engine
1 Attachment(s)
My turned a 9-7 (I think) at 16.2K right out of the box. ;)


Cyclic Hardover 05-19-2005 09:15 PM

RE: Looking for a decent engine
I went the "Kmart" route on a Shrike. 40 I have. I installed a 46pro with a 9/7 apc which turns 17000 rpms and goes about 120mph. Not too shabby for a cheapie. I am not fond of GMS mainly because I no nothing about them. It is my guess though that the engine with a 9ish apc prop on a Clipped DD will be an impressive handful.

Flyboy Dave 05-19-2005 09:18 PM

RE: Looking for a decent engine
Yo, Snoop....whaddaya want fer 65 bucks ??? :D

Atom Ant 05-20-2005 12:26 AM

RE: Looking for a decent engine
Tower Hobbies.46 is a simular engine and has a tuned pipe for the same price. It is a screamer.

Rcpilot 05-20-2005 01:09 AM

RE: Looking for a decent engine
I firmly believe that an engine is what you make it during break-in.

When I break in an engine--I prop it for MAXIMUM RPM. If the box says it'll turn 16,000--then I put a prop on it that will get it turning 16,000RPM or maybe a bit more during break-in.

For an ABC--that can be tricky. You MUST get it hot enough to break-in and get all the parts seated, but you still want it rich enough so that you don't cook it. Try and find a prop that will allow you to run it at a slightly rich 2-stroke--but still scream along at MAX RPM.

Typically--the break-in prop that you need to accomplish these high RPM will throw up a bunch of red flags in your head. Don't listen to them. Get a little prop and let it SCREAM.

Ringed engines are the same way. I keep them plenty rich for several tanks--but I prop them for absolute maximum RPM.

IMO-the whole key to making a screamer is to let it RUN. Let it run FAST.

If you take a .60 size engine and break it in with a 12-6 prop at 10,000RPM----then it'll always be a dog. Take that same engine and put a 10-6 or a 10-8 on it and let it rip along at 15,000 or 16,500RPM-------and you got yourself a screamer for many years to come.

Once you get it broke in--ABC or Ringed--then you can put your regular flying prop on it. Believe me--you'll be amazed at how much better it runs.

How did I learn this: Stupidity:D

I took a brand new OS 61FX and slapped an APC 12-6 on it and broke it in like you would any other ABC engine. I got it heated up, and ran it a bit rich for a few tanks--just like your supposed to do with an ABC. But- that engine just never would turn any real numbers. I can't remember now- but if memory serves me--it would never turn a 12-6 over 10,500RPM.

My mistake was slapping too much prop on it and not letting it build high RPM during the break in process.

I bought another 61FX a few years later. I broke that engine in with an APC 10-6 prop. It was screaming along at 17,000RPM+. I thought it would come apart, but I let it run wide open and just a bit rich. After 8 or 10 tanks of fuel--that engine was cranking a 12-8 prop close to 13,000RPM. (6000' elevation-so quit laughing)

I did the same thing with a ST3000. BIG ringed beast with heavy crosshatching on the cylinder walls. I started out with an 18-8 and I let that sucker run wide open and just silly rich for a couple 20oz. tanks. My buddy was standing behind me yelling at me--screaming at me-- to shut it down "TOO MANY RPMS--YOUR GONNA BLOW IT!!!!" I was grinnin' ear to ear- and he's looking at me like I'm an idiot.

Make a long story short--after a couple gallons on the bench--I had that sucker turning a Pro Zinger 20-6 at 7300--7500RPM

Break 'em in SCREAMING like crazy and they will turn big RPM for ya later.

Just a theory--and I could be off my rocker--but it works for me.

I'd break that GMS .47 in with an 8-6 or an 8-8 prop and if it won't turn MAX RPM while it's still rich--then get a smaller prop.

daven 05-20-2005 07:26 AM

RE: Looking for a decent engine
You are not off your rocker, that is common practice to quite a few in the racing crowd.

I have a break in prop that I use for My Nelsons that turns just shy of 27,000.

You just have to be carefull that you don't lean them out to far too soon at those rpms. I like to start em, get em up about 1500 under peak and then slowly pinch the line about every 10-15 seconds so that it will slowly pick up in rpm warming things up. I do this for the first 3 tanks then fly.

Flyboy Dave 05-20-2005 08:30 AM

RE: Looking for a decent engine
1 Attachment(s)
Rcpilet....you're a Man after our hearts out here in the speed crowd. :D

I ran-in this plane in the same day as well....a little OS .40 FX in a Q-500,
A 9-6 MAS toothpick prop....over 16,000 as well. Both engines rated at
16K.....I wanna see 16K on the tach.

The other day I said a 12-6 APC would "dog down" any .60 engine, I took
some heat for it....:eek:....wanna "dog down" a .46 ? Put a 10-6 APC on it. :)

These days....when Guys are trying to make airplanes into helicopters, the
props they recommend are odd IMO. I got into it with a Guy about the OS
1.08 FSR here awhile back....he thought it was cool to run it at 9500, tops.
I like to run 'em at 12,500-13,000 if possible....they rate at 16K. :D

Today, these Guys run the biggest prop that will possibly fit on the plane. [X(]

....don't ask me....[sm=stupid.gif]


DHG 05-20-2005 10:51 AM

RE: Looking for a decent engine
Flyboy Dave,

When you say "MAS toothpick prop" I assume you mean a Master Airscrew.

Do NOT spin a Master Airscrew over 16,000 rpm.

Do NOT cut it down.

I learned both of these lessons the hard way. It almost cost me my life. The material they use is crap. Get an APC with the thick "D-1" hub, or better yet, buy a good wood propeller and cut it down until you get the rpms you need.

Oh, and never run an engine unless you are wearing safety glasses or sunglasses made of at least .060" polycarbonate. A propeller fragment travels at the same speed as a bullet. Polycarbonate will absorb the impact without shattering.

Just a word to the wise.


HighPlains 05-20-2005 04:54 PM

RE: Looking for a decent engine
Rated at 16K?????????

Every "SPORT" engine gives you a HP rating at some RPM. Depending on how flat the torque curve is, it gives you a range of props for maximum performance. But you DON"T want to prop the engine (the flying prop) to turn that on the ground, because when you are in the air and the engine unloads, then you will be operating above the rpm with the maximum power output. For a sport engine with a normal muffler, you should start with a prop that loads the engine to a value 1 to 3 K under the peak HP RPM, depending somewhat on the timing of the engine and how clean your airframe is. Also, set the engine a bit more on the rich side, so it will have the fuel it needs when it unloads.

Racing engines don't normally give HP rating, but we are working with something in the neighborhood of 7 HP/CI

To get more out of a sport motor, you can change the timing and add a tuned exhaust or magic muffler. But you will be giving a reliable idle and ease of operation.

2fast4-u11 05-20-2005 09:23 PM

RE: Looking for a decent engine
thanx for the info guys and I think I will try the gms and break it in with a 8 8 prop and hopefully after break in it will spin the 8 9 or 8 10 in the neighbourhood of 16000 17000

was also considering a 0s 32 because of the 22 000 rpm rating hp is a little low at 1.2 but if it would spin a 8 8 prop at 22 000 then that would be nice


Rudeboy 05-20-2005 09:32 PM

RE: Looking for a decent engine
No way the OS .32 is going to spin an 8x8 up THAT high...

My West .50 doesn't even get there on that prop, and that's quite a bit more engine than an OS 32...

You would be looking at 16,000 - 17,000 probably. On the stock muffler you'd probably have to run it WITHOUT a prop to get it to turn 22K :D... seriously...

As for the GMS, stick to a 9x6 or 9x7... these engines are not meant to turn mega rpm on small props.

2fast4-u11 05-20-2005 10:01 PM

RE: Looking for a decent engine
well thanx for the input , as I have never tested any of these engines it is all speculation at this point and as I do more research I will have a better idea of what to shoot for

pdxpaul 05-21-2005 10:12 AM

RE: Looking for a decent engine
Flyboy Dave,

I think all here have been trying to convert you to APC since the opening of this forum. If I sent you some free APC's, will you convert?


Flyboy Dave 05-21-2005 10:41 AM

RE: Looking for a decent engine
1 Attachment(s)
Not likely....I've been on these boards for ovr three years now. The only thrown
blades have been on APC's. I"ve never read about a MAS throwing one. The
MAS props are stronger....you can dig them into the ground takeing off or landing
no problem....you have to crash the plane dead on one to break it.

I tried the APC props on my prop-jets and speed planes....they stink. They
restrict the rpm, and speed . Why people think they are so good....

....I have no clue. [sm=stupid.gif]

cobratraxxas69 05-21-2005 11:05 AM

RE: Looking for a decent engine
I'm with you Dave on the Master Airscrews!! :):)It seems like APC has a cult-like following, with people looking at MAS with disdain (typical comment= MAS is only good for paint mixing) and never conceding that it might possibly be the better prop. I think the "high-tech" shape, the pointy tip, and the pretty grey color are mesmerizing to them (I like bright and shiny objects)! :D

I have noticed with my Shrike and Diamond Dust that the planes run at least as fast and probably faster with MAS versus APC (same pitch, same diameter). Plus an APC tip is SO easy to break, the slighest touch with dirt or pavement and POOF tip is gone. With our Shrikes, Whips and Dusts landing in the grass, it just doesn't make sense to go with APC.


Flyboy Dave 05-21-2005 11:19 AM

RE: Looking for a decent engine
I like the myth....MAS props flex....

....no kidding Dick Tracy....all props flex.

Look at the real reno racers, like the Mustangs. What do the props look like"
Four bladed MAS....thank you. If the silly looking APC type props were better, you
would see them on all the racers....you don't.

When APC's first came out, I tried them....I figured there must be something
to this new "modern" design.....wrong, another gimmick. They do....I guess run
quieter than the others. :eek: Why ? They have no thrust at the tips !!!

Yes, they do have a cult following....the misinformed. :)


Rudeboy 05-21-2005 02:46 PM

RE: Looking for a decent engine
I have only tried one MAS in my life... a 16x8... it was noisy, it was flexing like hell when I gave full throttle (blade tips moving forward close to an inch I guesstimate... I didn't dare to look at it properly from that angle... scary), and it generally sucked in the air. The only thing it had going for it was static thrust: it gave more static thrust than any of the props I tried on that engine.

I settled on a 16x8 Mejzlik afterwards... I can now hear my engine running... and the plane actually flies quite satisfactory. When I first took it up (with the MAS), I thought: what a dog of a plane. I'm glad the landing gear ripped out during an emergency landing... it broke the MAS too... switched to the Mejzlik after that... what a difference...

Now I am not saying they are BAD props... I just say that in my particular case, the MAS sucked. And I tend to extrapolate experiences...

HighPlains 05-21-2005 03:21 PM

RE: Looking for a decent engine
"(typical comment= MAS is only good for paint mixing) "

I wouldn't even use one for that.

They do seem to be the prop of choice for the duffer that can't yet land.

cobratraxxas69 05-21-2005 03:46 PM

RE: Looking for a decent engine
What appreciable thrust is being generated at the tiny APC tip, where speed is the greatest. (all that speed is being wasted, unlike the MAS which still has bite and a substantial airfoil at the tip).

FB Dave made a good point when he pointed out that full scale racing planes do not have props even close to resembling the APC tips.

Rudeboy 05-22-2005 05:58 AM

RE: Looking for a decent engine

ORIGINAL: cobratraxxas69

FB Dave made a good point when he pointed out that full scale racing planes do not have props even close to resembling the APC tips.
Actually that is not such a good point at all... people have been looking at full scale for decades and tried to scale it down to our size... it does not work that way... not properly at least.

It is a fact though, that APC props seem to generate less thrust compared to wide bladed props... that makes sense.

Mike Connor 05-22-2005 12:00 PM

RE: Looking for a decent engine
I tested the APC and MAS 10x6 on a q-500 with a 46 FX and UltraThrust. The MAS had a higher static rpm but by flying and looking I could not tell a speed difference between the two props. Either the higher rpm or tip design of the MAS caused it to reach critical mach and make a lot of noise when unloading. From a performance stand point this would not be good but I could not tell one was faster then the other. A radar gun may have shown otherwise.

Flyboy Dave 05-23-2005 01:26 AM

RE: Looking for a decent engine
I just looked through all the pictures I took two years ago at the TOC, looking
for APC props....I found one (1).....some Guy had one a Funtana. :eek:

Big Whoop, huh ? But on the other hand....how many people are you going to
find....stupid enough to hand flip an big APC....answer none (0)....nada. :)


Razor-RCU 05-24-2005 12:06 AM

RE: Looking for a decent engine
Well- I suppose some topics never change! (I been away awhile)

I too am an APC believer, but Fly-Boy Dave is a Jedi master compared to me anyway and he likes MA props.! I have seen the performance of his MA's and it is impressive- and I am sure if you asked him about my Patriot/Jett-50 (APC 9x9) performance he would agree that it was satisfactory ;)

To each his/her own--- My Whiplash flew quite well with a MA prop. recommended by Dave, and they are hard to break (I know, I have tried)


Phil Cole 05-24-2005 12:36 AM

RE: Looking for a decent engine
Not in the speed range dealt with here, but I spent a couple of afternoons with my World Models T-34, OS46 AX, an Eagle Tree Seagull telemetry downlink and a bucket of props.

The fastest was an MA 10x7 at around 95 M.P.H. in straight, level (or, at least, the best I could do at straight and level :)), next was a Bolly 9.5 x 7 sport prop (1 - 2 M.P.H. slower than the MA). The quickest APC (10 x 7 sport) came in at around 90 or 91. APC pylon props (8 x 7.5, 8.5 x 7 etc., etc.) were useless - none of them got much above the mid-80s.

The engine was tuned as lean as I dared, and I made several runs with the top two (swapping back and forth, retuning each time) just to make sure the result was repeatable.

I could see the MA flopping all over the place when I ran the engine up. The Bolly (more flexible than MA, but not as stiff as APC) bent forward a bit, but didn't go in and out of track like the MA.

If I could get round pylons in a nice consistent manner, another test would be to look at how well the plane accelerated out of the turns. The airspeed dropped to something between 60 and 70 in the turns, and it typically took a couple of seconds to get back up to speed. When actually racing, the Bolly seems faster, maybe because there is something about it that allows the engine to pull through the turns and accelerate better.

Upwind or downwind didn't seem to make any difference in the max. speed (there were a few onlookers that were quite surprised at that!), so I am pretty sure I was getting up to the real maximum - the upwind leg took several seconds longer to fly, so the plane would have more time to accelerate if it wasn't reaching max. airspeed on the straights.

Changes in relative air density from day to day could also easily change the order of the top two, but I don't think the APC 10 x 7 would catch up.

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