Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Max rpm GS-45

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Old 08-06-2007, 08:59 PM
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samtech
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Default Max rpm GS-45

Hi guys,
Need some help here. I have a Supertigre GS-45 it's a little worked over with a jett pipe and carb "way good carb", spins 15500 on the stand with a APC 9x9. Crunched the numbers with a web calculator and its right around 1000 watts..... But of course I need to go faster.... minus the plane...haha it's some 130ish mph. So, I've been looking at different props. Calculated off my base line, 8.75 x 9.5 = the same 1000 watts and a 145 mph, just a slight rise in rpm 16000.... the limit according to the supertigre manuel. Ok?...?... So using that same cuuk'o'later... If I go with an 8x9.5,8x10 or 8x11 I'll really be singing 170-185 mph at around 1100 watts. BUT 16500 to 18700 rpm... Does anybody know how fast you can spin a GS-45 befor it goes into self destruct mode? Also, I think APC makes an 8x9.5 and an 8x10.... anybody know who makes an 8x11 or even an 8x12? In case you all are wonder... I'm stuffing the little beast in to an wildhare LR-1. Mawhahahahhhaa "evil laugh". [sm=devious.gif] Thanks.
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Old 08-06-2007, 11:45 PM
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Default RE: Max rpm GS-45

8x11 or 8x12 is HUGE for the 45 (I even think the 9x9 is too much for that engine). I assume you are just doing this for kicks with the 45? I am no engine guru but I bet it would take some major mods. to get a noticeable gain in performance---

Others will chime in with better info. I imagine-
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Old 08-07-2007, 12:59 AM
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Default RE: Max rpm GS-45

Well, yeah.... but it's still going in to my LR-1. The 9x9 is just about right for my GS-45, which is a bit hopped up. Jett pipe, nice increase...Jett carb, HOLY BAT$H!T. Best carb I've ever had. On the stand it screams 15500 with the 9x9. I tryed a 9x7 and then a 9x8 but the rpm was 17200 and 16200, past the 16000 supertigre states is the max. Hence the post. I'd like to pull more speed but I don't want to destroy my engine. The LR-1 is a pretty slick plane so I think I can trade in some static thrust for a bit more speed. Now then, I've been simulating different props based on the load. Watts at a given rpm range. I'm thinking the engine VE is going to take a steep dive much past 17000 and simply put it well outside of it's opperating range. A 8.5x9.5 or a 8x12 need about the same power "1000ish watts" at the same 16000ish rpm. But who makes a 8x12??? I haven't found anybody making such a prop.... So, more RPM is the answer...Right?
Well.... thats the question. How much rpm can it stand befor it destroys it's self? Hey, if it simply runs out of breath and can't hack 17500+ great! No destroyed engine....but what if it keeps pulling and seizes or worst yet goes bang. I'm fairly conservative and got a little worried with a 9x7.... and yet here I am begging for 18000+ Hey 8x10 = 170mph at 18000, thats 140+ on the plane! I'd much rather learn from your experances then toast a perfectly good engine experamenting. Even if it's a cheap motor.
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Old 08-07-2007, 11:52 AM
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Default RE: Max rpm GS-45

Oooo- you are trying to keep the rpm down and increase speed? Very unusual--- Bob27?
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Old 08-07-2007, 10:49 PM
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Default RE: Max rpm GS-45

Yes and no. If it can put up with higher rpm without getting destroyed, great. If not I'll trade in some thrust for speed. But I haven't found anybody that makes a 8x11 or 8x12. So that takes us back to the same questions. What rpm does it run out of breath "VE" and what rpm does it go into self destruct mode. If I can get away with 18000+ spining a 8x9.5 or 8x10 that would be ideal. Does anybody have experance spinning the GS-45 past 17500? Black nasty oil coming out? Excessively hot? Major changes in needle settings after the run? Ever run again? Con rod bushing damage?
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Old 08-07-2007, 11:25 PM
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Default RE: Max rpm GS-45

Actually a 8x12 (if you could find one or cut a larger prop down) is less load then a 9x8 according to ThrustHP. Not familiar with your engine but the timing may not be good for 18,000 rpm. I doubt the engine will self destruct though as long as it isn't too lean. If it did come apart you would have a good reason to buy a Jett.
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Old 08-07-2007, 11:54 PM
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Default RE: Max rpm GS-45

Oh those Jett's! Fire breathing monsters. Maybe one of these days..... when my wife isn't looking
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Old 08-08-2007, 01:10 AM
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Default RE: Max rpm GS-45

I really doubt that any RPM of 20K or less is going to hurt your engine. However in stock tune, the peak hp is at 16K. Raising the exhaust and crank timing modifications can move the peak hp to a higher rpm and increase overall power.

I've destroyed a few con rods, usually at around 40k with a shaft run.
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Old 08-08-2007, 01:41 AM
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Default RE: Max rpm GS-45

Really? Well.... I might just have to try it. On the stand with temp gauge handy..... At this point I'm not going to move the ports up. A little blending here and there on the intake and transfers is one thing but changing the timing is a black art to me. Maybe when it's on it's last leg but it runs to good right now to take it apart. Gonna have to think about it....
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Old 08-09-2007, 10:49 AM
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Default RE: Max rpm GS-45

i was gonna say, mine i had on a magic swingin a zinger 11x4 had 15,500 without any problem what so ever. that was a good engine. i had it running for 3 years. it still starts and runs good but it started to lose power and wouldn't pull the magic like i wanted to any more so it is sitting on my work bench waiting for a good slow easing around plane. but i would say 18,000 wouldn't kill it in 1 run. ovcourse it wont last no 3 years like that but i would say a year. if you add a little extra castor oil to your fuel you might can squeeze 2 but i doubt it. my engine had a hard life. it hit the ground a few times and even hung a tree once or twice. it took a lickin and kept on kickin. them ST engines are like tanks. very good and reliable engines. i never been around one hopped up mostly because they are so heavy and most people want lighter engines when they go to soup them up.

but back to the 18,000. i have to say LET ER RIP TATER CHIP!!!!!!!
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Old 08-10-2007, 09:28 AM
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Default RE: Max rpm GS-45

Here's my BSE 35 in a LR-1 , tach's up 19600 static with APC 8x6 , not had a radar gun on it yet but she's pretty slick , it will get any bodies attension
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Old 08-10-2007, 09:31 AM
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Default RE: Max rpm GS-45

Sorry , that's the whiplash X with a JETT FIRE 50

Here's the LR-1
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Old 08-10-2007, 11:38 AM
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Default RE: Max rpm GS-45

ORIGINAL: samtech

anybody know who makes an 8x11 or even an 8x12?
ORIGINAL: Mike Connor

Actually a 8x12 (if you could find one or cut a larger prop down) is less load then a 9x8 according to ThrustHP.

Hi,

the GS-45 is a rugged cheap engine that can be modded with nice results, though I would not recommend running them above 20K unloaded due to insufficient long-run conrod strength.

8x11 or 8x12 speed prop sizes belong to another category of speed engines, namely to 10 to 15 cc converted ducted fan engines. So when talking anything below 10cc capacity, there’s a huge lack of torque for those oversquared prop sizes. For instance the most powerful superduper modified OPS 60 VAE engines over here turn 8x12 CF props about 22000 statically and up to 26000 unloaded. For that kind of rpms we need about solid 4 to 5 HP!

A highly modded GS-45 on the other hand will put out a maximum of maybe 2.5 HP (a short lifetime only untill the conrod blows).

Generally by calculating oversquared props using THRUST HP software, the results are complete bullsh.t. [sm=thumbs_down.gif]

For the Wildhare LR1 (called Speedcat over here in Europe), you can’t use props effectively having more than 9“ of pitch. For bigger pitches we need a much more clean airframe plus a rear exhaust engine setup with full cowl. So for best speed results a 8x8“ APC prop should be the optimum choice in combination with your GS-45 on the Wildhare LR1.

P.S. Simply cutting down an APC 12x12 to 8x12“ for instance will result in catastrophic prop aerodynamics.


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Old 08-10-2007, 11:53 AM
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Default RE: Max rpm GS-45


ORIGINAL: samtech

Well, yeah.... but it's still going in to my LR-1. The 9x9 is just about right for my GS-45, which is a bit hopped up. Jett pipe, nice increase...Jett carb, HOLY BAT$H!T. Best carb I've ever had. On the stand it screams 15500 with the 9x9. I tryed a 9x7 and then a 9x8 but the rpm was 17200 and 16200, past the 16000 supertigre states is the max. Hence the post. I'd like to pull more speed but I don't want to destroy my engine. The LR-1 is a pretty slick plane so I think I can trade in some static thrust for a bit more speed. Now then, I've been simulating different props based on the load. Watts at a given rpm range. I'm thinking the engine VE is going to take a steep dive much past 17000 and simply put it well outside of it's opperating range. A 8.5x9.5 or a 8x12 need about the same power "1000ish watts" at the same 16000ish rpm. But who makes a 8x12??? I haven't found anybody making such a prop.... So, more RPM is the answer...Right?
Well.... thats the question. How much rpm can it stand befor it destroys it's self? Hey, if it simply runs out of breath and can't hack 17500+ great! No destroyed engine....but what if it keeps pulling and seizes or worst yet goes bang. I'm fairly conservative and got a little worried with a 9x7.... and yet here I am begging for 18000+ Hey 8x10 = 170mph at 18000, thats 140+ on the plane! I'd much rather learn from your experances then toast a perfectly good engine experamenting. Even if it's a cheap motor.
Don't worry about the 16k it says in the manual ..... that is a real-world practice rpm number for a standard prop. Not a DNE number.

If you are using the Jett muffler, prop the engine so it turns right around 16,500 - 17,000 rpm on the ground at peak, so you can launch it comfortably at 16,000 just a tad rich. It will likely unload in to the low to mid 17K range in the air, and that is where the muffler sweet spot is (you are propping to the needs of the tuned muffler, not to what it says in the engine manual).

Select the prop that hits that range, and you will be quite happy. Stay away from the seriously over-square props.

The standard 9x7 and 9x8 should work well. APC 8.75x8W and 8.8x8.5 are also worth trying. If the rpm is just a bit short,, you can clip those down (.25" of each tip) and then balance the prop.

You can try what ever prop you wish..... just keep it running at peak rpm between 16,000 and 17,000 ------ 16,500 is an excellent target.
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Old 08-10-2007, 01:17 PM
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Default RE: Max rpm GS-45


ORIGINAL: I-Love-Jets
ORIGINAL: Mike Connor
Actually a 8x12 (if you could find one or cut a larger prop down) is less load then a 9x8 according to ThrustHP.
Hi,
Generally by calculating oversquared props using THRUST HP software, the results are complete bullsh.t. [sm=thumbs_down.gif]
[X(][X(][X(]
At what point does ThrustHP become unreliable or do you consider it always unreliable???
At what point does a over squared prop become a seriously over squared prop? I was thinking about cutting down a 9x9 and 9x10 to 8.5x9 and 8.5x10. Is this too over squared for a USA (non German speed cup types) faster then normal airframe?
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Old 08-11-2007, 10:12 AM
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Default RE: Max rpm GS-45

Model Airplane News uses the formula Lprop = D2(P) and it gives very different results from ThrustHP. Would this be a more accurate way to figure propeller load?
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Old 08-11-2007, 11:10 AM
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Default RE: Max rpm GS-45

Doesn't prop shape come into play as well?

Thanks, Terry
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Old 08-11-2007, 11:17 AM
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Default RE: Max rpm GS-45

.......weight of the prop as well, especially when looking at the wear and tear on internal parts. The APC grey props are about as heavy as you can get.
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Old 08-11-2007, 12:05 PM
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Default RE: Max rpm GS-45

I would think there is a formula that would give a decent ballpark figure as long as you compare similar props. APC sport props compared to APC sport props and not Master Airscrew or APC pylon props
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Old 08-11-2007, 11:16 PM
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Default RE: Max rpm GS-45

Hey allright! Ok, I went and bought a couple to try. An 8x8 and an 8.75x9.5, plus I have a 9x7, 9x8 and 9x9. I'll test them tomarrow on the stand. Bob, I'm taking your advice. I'll shoot for 16500-17000. Oh yeah. What sort of effects to you foresee with a 1/2 inch x 2 degree spacer inbetween the engine and the pipe? Mod for fitting an LR-1.
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Old 08-12-2007, 12:37 AM
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Default RE: Max rpm GS-45

Sam, you'll be able to tell us what happens after tomorrows' testing. I'm guessing not much will change with the spacer. Outside of breaking in engines, time spent with different props on the bench is only time well spent if you are looking for the best prop to fly that work table. Otherwise, the best thing to do is get out the timing equipment to see which prop is boss. I'll bet the 8x8 is the best for your plane for flat out speed.
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Old 08-12-2007, 09:59 PM
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Default RE: Max rpm GS-45

Check out this thread, really helped me get my GS running good. http://www.rcuniverse.com/forum/m_36...tm.htm#3605308
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Old 08-12-2007, 11:25 PM
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Default RE: Max rpm GS-45

Well gents,
It's not happening tonight.... Set up, got it running and watched an allen bolt drop out of the muffler mount.... No big deal...right.... Bolt broke off in the pipe. Drilled it out. thought I got it all.... and promptly broke off a tap in it. Rats.... Then I broke out the the side of the pipe trying to get the tap out.... I'll try to weld it up and machine it back down speck..... or I'm out another 65 bucks for a new pipe. Go ahead, roast away.
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Old 08-13-2007, 10:33 AM
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Default RE: Max rpm GS-45

Spacer will make the effective tuning rpm about 400-500 rpm lower. But its a trade for some torque, so its not really a loss.

Dub may be able to repair the muffler if required. Been done before.
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Old 08-13-2007, 11:08 AM
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Default RE: Max rpm GS-45

I had a similar problem and sent it back to Dub. He put a new front end on it and had in back to me in a week. Good as new. That is what I would do if I were you.

Blessings, Terry
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