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Old Sep 25, 2002, 05:39 PM
BEC
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Auburn, Washington USA
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I remember my 40th birthday - I think......

Here's a combination that looks appealing for me at sea level - the 10X7 on the "C" ratio (5.33:1) gearbox. Almost the same current draw as the 9X6 (just under 10 A), virtually the same pitch speed (37 mph) but three + more ounces of static thrust. A direction to go if the 10X7 proves to be too much for the motor or batteries on the "B" box.
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Old Sep 25, 2002, 05:58 PM
A Clinger
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Butte, MT
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I thought about the 'C' box and the 10x7; but with my motor and batteries staying 'cool'; I figure I must not be pushing 'that' hard with the 'B' box and spinning the 10x7 at 'max' RPM WOT. Going to the 'C' box would just slow the prop down and use less amps (at least that is what I am thinking) and then have to move to maybe an 11x7 prop to pick up performance. I think it's the altitude thing. Am I thinking right on this???

I just posted a question over in the modeling science to see if there is a 'rule' of thumb for prop size vs. feet of altitude for same performance. See what comes out of that....
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Old Sep 25, 2002, 06:25 PM
BEC
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Welllllllll.......

Based on my own empirical experiments in taking planes from here to as high as 7000 feet (Santa Fe, NM), I would go to 20% more pitch at your altitude over what I would use here, or lower the gear ratio about 10%. This is basically what I wrote in my "flying at high altitudes" article that's in the Ezone archives.

Conversely, I should go down in pitch here or up in gear ratio to get the power input you are seeing. But seeing as I can't get a 10X5.6 prop or a 4.9:1 gearbox, I have to juggle the variables another way.

Going to the "C" box on the 10X7 would put me down on performance (based on MotoCalc, anyway) to what you are seeing, but would be an improvement over the 9X6 on the "B" for about the same input power. That is goodness.

But, based on my Kadet LT-25 experience, once I fly the SB at over 100W/lb. I'll not want to look back unless something threatens to go up in smoke (see my thread in Sport Planes about how 100W/lb. is addicting). In any event the miniAC 1215/16 is surely going to put up with those power levels better and longer than the Mabuchi RK-370 we all started with.....but I may want to look into providing a cooling air exhaust in the aft fuselage bottom sheeting.
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Old Sep 25, 2002, 08:06 PM
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BEC,
Here's what I did. Pretty simple and seems to work well. I just cut front and sides of opening, pushed it into the fuse, added triangle pieces for the "tunnel" sides, added air dam, covered, done.

Randy
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Old Sep 25, 2002, 09:36 PM
A Clinger
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Butte, MT
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Bec,

Thanks, I read your article. That's what I was looking for !! So to get same performance of 10x7 at sea level; I'd need a 10x8.4 at 5000 feet for about the same performance. But of course APC doesn't have a 10x8.4, so maybe going up to 11x7 would be the way to go as APC 11x8.5 may be just to big a prop to spin ..... Anyway it gives one a starting place.... Trade offs, trade offs . Thanks for the 'research' .
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Old Sep 25, 2002, 09:42 PM
A Clinger
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Butte, MT
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RcFlyer,

Like the Air Scoop. Neat idea. I think I'd do it on the sides above the wing though to keep the dust and dirt out (I fly on a dirt field and the prop does blow some dust , I've also belly landed a couple of times due to retracts malfunctioning ).
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Old Sep 25, 2002, 10:28 PM
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rclark,
Since it's an exit and not intake, you're probably not likely to blow dirt in with it on the bottom. Of course, side exits would be fine, too... but it's "hidden" on the bottom
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Old Sep 26, 2002, 12:36 AM
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United States, CA, Ventura
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Flew my SB3D today with the 107. I have the MiniAC1215/16 in a GWS B gearbox powered by 8600AE's through a CC Phoenix 25. WOW!!! What a rush. That plane was haulin' some serious bootay! With a vertical or near vertical climb out from the takeoff roll I was in heaven. I flew 2 batteries. After the first I felt the pack and it was about what I would call normal for this plane. I used this 107 on the original 370 motor prior to putting the BL in and I remember the batteries being about the same temp. Second flight the motor sounded a little weird, this is my first BL motor, what do they sound like when they start getting a little hot? It sounded like it was sputtering a little.

Mike
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Old Sep 26, 2002, 03:55 AM
(aka Cliff Lawson)
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United Kingdom, Essex
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Mike,

There's nothing quite like that rush of flying a brushless setup the first time is there? Yesterday on my fifth brushless flight I used a pack that had just come off the charger and with my 16/15/6 I was able to hover - only for a few seconds before it "fell out of it" but that's basically cos I've never had a plane that could hover before and I haven't a clue what kind of control inputs I should be making to keep it in a hover - but this is definitely going to be a "good game" for the future!

With the brushless ability to climb so well I also dug out an old Casio barometer/altimeter watch I had from a few years back and removed the strap and put it into my brushless Switchback and then flew it as high as I dared (I'm always a bit concerned about transmitter range!). After landing the Max. Altitude showed 680' AGL which is definitely the highest I've ever flown an r/c plane so far. The fact that it's still well within range of the Tx/Rx means that I may try to see how much higher I can get it but at that height (and in the fading light) it was already so small that I had no way of knowing which way up it was.

Cliff
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Old Sep 26, 2002, 11:20 AM
A Clinger
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Butte, MT
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Mike,

So you like it LOL? Fun isn't it!! Is your motor getting warm? Mine seems to stay cool (running 10x7 at 5000 feet though at 30-40F). I have not noticed any 'noise' difference in the motor. Mine is running smooth as ever. Prop loosening up maybe?

I did have the motor 'stall' (didn't start) on me once when throttling up the other morning. That's the only 'hicup' I've had with the motor.
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Old Sep 26, 2002, 01:06 PM
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Thanks again for all the tips, Guys!

I've decided to go with the following...

Motor: Model Motors Mini AC1215/16
ESC: Castle Creations Phoenix-25
Gearbox: GWS EPS-300C-B
Pinion: stock from gearbox
Prop: GWS 9 x 7 (stock for A-B comparison)
Batteries: 8 x 720NiMH

...for starters.

Anybody using an aftermarket pinion (i.e. Robinson 64pitch ??T)? I'm not too hip on using CA or Green Loctite for this. Also, I'm seeing quite a few prop options here with the NiCds, but what others might I try with the NiMHs & this combo? The same ones (10x7, 9x6, etc.)? Oh...I'm flying very near sea level, BTW.

Thanks again!!!

P.S. Great job on the vent, rcflyer11! My cooling solution is not nearly as elegant. I just opened up that triangular area within the landing gear mount.
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Old Sep 26, 2002, 01:34 PM
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02ViperTwin,
Thanks for the compliment. Your landing gear opening will probably help some, but I think it's a good idea to get air moving past the batteries. Ideally, the EXIT area should be about 3 times the inlet area. By placing the air exit behind the wing as shown, I am (hopefully) allowing air to move around and past the battery

Randy
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Old Sep 26, 2002, 02:11 PM
an earth bound misfit, I
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St. Pete, Florida
Joined Sep 2001
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Hi Randy, that's the best looking air outlet I've seen so far.

I tried to do sorta the same thing only with the sides curved like a naca duct on my first SB. I never did get the tunnel sides installed, just kind of propped it open. Totalled the plane before finishing the duct.

Yours actually looks better

Is the air dam functional or necessary? Or is it to strengthen the cut area?

Wayne
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Old Sep 26, 2002, 02:20 PM
BEC
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Auburn, Washington USA
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So far I've gotten away without green Loctite or CA.

The MM miniAC's shaft is 2.3mm or 0.0906 inch in diameter. For a moderate press fit, drill a few thousandths smaller. A number 43 drill is 0.089 inch.

I used one and just drilled the pinion, pulled from the 370 motor, while holding it in my hand (the gear is that soft).

Pressing it on was actually tougher because it's hard to get to the back end of the motor shaft to support it while doing the pressing.

But once on, no problems so far. I will try the 10X7 APC-SF soon, which would be the maximum load I'd put on this combo (miniAC 1215/16 in GWS 4.43 gearbox on 8 1100s) anyway.

On cooling air outlets - just a decent sized opening should be fine - and I concur it ought to be in the aft fuselage so the air can go over the motor, the ESC and the battery first. Even a little air movement really helps the ESC. I've suggested that Doug incorporate something like this in the event he should decide to upgrade the SB kit.
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Old Sep 26, 2002, 02:30 PM
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Basketcase,
The air dam is supposedly functional. I have a friend who used to do wind tunnel tests on race cars, and he suggested the air dam. I think it is helps strengthen the fuse after the cut, too. I was going to do the NACA shape also, but the friend told me that only works on intakes. By leaving the sides straight, it was real easy to add the tunnel sides

Randy
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