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Old Sep 07, 2003, 12:10 AM
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What to do? W/lb of poor man's F5B (long post)

I have been experimenting with some different setups this afternoon to get my B50 11S powered Ariane to climb a little faster still. I am using 14 cells and a 16 x 16 narrow RFM prop for 67 A of current draw and 294 W/lb power.

I also had a chance to play with the Hacker B50 7S carbon motor and tried 8 cells with the same prop. It was drawing 69A and though it shaved a fair bit of weight from the plane (in the form of 6 fewer cells), still resulted in a decrease of overall power due to the much lower pack voltage (down to 226W/lb)

Then I tried 10 cells and got 84A with a total power of 261 W/lb.

The question is, what type of power/unit weight are F5F (and 7 cell F5B) planes flying at? I started with a 14 cell system, and it seems that though heavy, the higher voltage allows a reasonably low current to result in still a fairly high power/pound.

The main reason why I thought of this is that perhaps making my Ariane lighter will make it a little more fun to fly in the glide phase, instead of just being a space shuttle that will only thermal in a terribly strong burst of lift. Also, I did get a little flutter in the wing last week in a super duper terminal dive and think that maybe lightening it will prevent me from getting to that dangerous speed again.

I will try the 7s and 10 cells to see if I like the glide of the plane better (even though the climb will be slightly weaker)

The other option is to add prop to my current setup and aim for something closer to 100A. Perhaps a 17 x 18 wide blade prop will get me there...resulting in 396W/lb, and I'll just have to keep in mind that a terminal dive will stress the airframe too much.

What should I do? Overall, the B50 7S didn't seem as hot as I would have expected.

Thanks,

Ryan
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Old Sep 07, 2003, 01:06 AM
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Ryan,

I am interested in how this will turn out. As it stands, I plan on powering my s11 with the b50 11s on 12 cells and an 18.5x12 rfm prop to get started.

according to motocalc this gets me 229 w/lb. Also according to motocalc, it appears this set up will not fly well on anything over 20 cells. I thought this motor would take 24 cells...

comments welcomed...
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Old Sep 07, 2003, 02:52 AM
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Re: What to do? W/lb of poor man's F5B (long post)

Quote:
Originally posted by 96S14
The question is, what type of power/unit weight are F5F (and 7 cell F5B) planes flying at?
A "typical" 7 cell F5B weighs 1200g and uses about 6v*120A or

720 watts in for 1.2kg

A "typical" 10 Cell F5B 9v*120A/1600g

1080 watts in for 1.6kg

So, the answer would be:

275watts/pound for 7 cell

300Watts/Pound for 10 cell

If my conversion is near enough..., the 7 cell might be nearer to 300W/Lbs .

FWIW , Stefan De Hauwere says his ZOEF 9 F5B flies much nicer with 7 cells than with 27... It still goes vertical well enough ( this one is 130A and 1120g I think)
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Old Sep 07, 2003, 09:30 AM
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Greeley, Colorado, USA
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Ryan,
You're right that keeping the model light will make it more practical for sport flying and thermalling. You didn't say what cells you're using.

I'd go with that 7S on 14 CP1700 cells for a light setup with good power. Prop it for at least 100 amps and you'll have some fun

I've got a 7S that I use with a 12 cell pack of CP1700's as a lightweight setup for test flying new F5B planes. This setup does not maximize the power system, but since I only use it for test flying I don't care.

Soho,
That 18.5x12 will have lots of pull, but not much speed. That prop is better suited to a large LMR or scale type plane than an F5B airframe. Better to use more cells with the 11S or switch to a hotter wind motor to match your 12 cell pack. Then you'll have more prop options.


Good luck,
Lenny
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Old Sep 07, 2003, 10:27 AM
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Calgary, Alberta, Canada
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Re: Re: What to do? W/lb of poor man's F5B (long post)

Quote:
Originally posted by WimH
A "typical" 7 cell F5B weighs 1200g and uses about 6v*120A or

720 watts in for 1.2kg

A "typical" 10 Cell F5B 9v*120A/1600g

1080 watts in for 1.6kg

So, the answer would be:

275watts/pound for 7 cell

300Watts/Pound for 10 cell

Well, if that's the case, then right now, I'm flying at a 7 or 10 cell F5B/F5F power level with my B50 11S on 14 cells...only bonus is I get that same power at a "measly" 67A of current draw (at the expense of more weight in the glide). If I want to climb faster, I think I will stick with the 14 cells, since that will be the only way to get noticeably more power out.

I'll still try the 10 cells and the 7S today hopefully to see how the plane handles in the glide.

Soho, I'll keep you posted with my findings. The 11S on 24 cells will be very hot...I think you'll be running a reasonably small prop.

Thanks for the replies,

Ryan.
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Old Sep 07, 2003, 10:31 AM
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Quote:
Originally posted by Lenny970
Ryan,
You're right that keeping the model light will make it more practical for sport flying and thermalling. You didn't say what cells you're using.
I am using GMVIS 2400's so my pack is farily hefty. It weighs about 825g (27.5 oz?) with 14 cells in the pack. I like the 2400's since they seem to put out so much better voltage under load. As it is, I get a full 2 minutes of motor run time and about 940 watts of output power.
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Old Sep 28, 2003, 01:22 PM
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Well,

I finally tried the B50 7S Carbon and 10 GMVIS 2400 cells yesterday on the RFM 16x16 narrow prop.

The plane glides very nicely now and the landing is 10000% easier (though it never was truly difficult...you just had to pay attention)

As for the climb, the plane seems to feel lighter (which it is) and climbs truly straight up with that cool visual vertical acceleration that the 24 cell planes have. Only thing lacking is the top speed as the pitch speed still seems a little down.

Sooo, seeing as I'm borrowing this drivetrain and will one day actually have to return it, I need to decide on a new motor. Do I get a 7S, or the 6S...with the intention of running 10 GMVIS 2400 cells and the 16 x 16 from now on.

As it sits, the plane is pulling around 80-82A static. In the air, I got 1:15 of total motor run and was able to pull 590 mAh out of the pack at the end of the flight on my Schulze. I don't know what that relates to in actual in-flight current draw, since the packs are likely not putting out a full 2400 mAh at that discharge level.

How much hotter is the 6S than the 7S? Will I be well into the 100A range by keeping the setup the same and switching only the motor? Motocalc predicts 21A more current draw...but Motocalc is next to useless as it overestimates my current setup by 29A. How much better will the climb be? I think Lenny970 will have the best knowledge of these two motors. Maybe you could chime in?

Anyways, I have not had the chance to test the 11S on any larger prop, and now that I've flown the plane with 10 cells, I can't see myself going back. It just flies so much better. Sorry for the lack of useful info there Soho...

Thanks for any input.

Anyone wanna buy a B50 11S geared with only about 15 flights on it?

Ryan.
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Old Sep 28, 2003, 08:05 PM
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Ryan,
I'm not familiar with those cells, but assume that they are equal to zapped Sanyo CP2400, Sanyo 2600 Nimh, or GP3300.

If you want to stay with the 16x16 narrow prop, go with a 6S motor. The 7S on 10 cells needs more prop to come alive.

I ran a 6S on 10x2600 with a 16x17 prop. Good power and speed and around 120 amps static.

Good luck,
Lenny
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Old Sep 28, 2003, 08:42 PM
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why not use the hacker F5F motor?

ryan,

the fact that you are using 10 cells screams the use of the hacker f5f motor, any reason you don't want to use it? The numbers seem a LOT better with the F5f. see the attatched file...

jay
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Old Sep 28, 2003, 08:47 PM
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sorry, I redid the comparisons...

this time I used hrsc 2600 cells and I compared all three motors F5F, 6s, 7s. Of note the 6s will be pulling 130 amps!!!!

jay
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Old Sep 28, 2003, 10:37 PM
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Amazing...

I am facing this exact same question right now. I want a motor for the Seledkin, and I'm trying to decide between the B50 6S and 7S. I want to run only 10 cells, probably GP3300s or 3000s. and I may make up a 12 cell pack. Lenny, how does the 7S do on 10 cells, and the 18x16 wide RFM?

~~fred
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Old Sep 28, 2003, 11:10 PM
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Jay,
I agree the B40-F5F motor would also be a good choice, especially if motor weight is an consideration. If you don't mind the extra weight though, I still favor the 6S. I think the heavier motor will be slightly more effecient.

The calc data is interesting for comparison, but don't hang your hat on it. In real life, the 6S on 10x2600 pulls 115 amps static with an RFM 16x16.


Fred,
I haven't tried that, but it sounds like a reasonable combination to try. I have seen a 7S turning a 17x18 on 10xGP3300. This performed very well until the controller shut down. The current was measured at 140 amps!

Lenny
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Old Sep 29, 2003, 08:56 AM
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Thanks to all for the tidbits of info. I think I'll end up with the 6S, since the 7S was very good, but not quite enough to make me grin like a crazy dude (at least with the prop I was using).

I guess the other option would be to use a larger prop and go with a 7S. Lenny, would you still go with the 6S on the 16 x 16 or get a 7S and a bigger prop? Or would I just end up with the same thing?

Also, I am using the Hacker Master 105-3P controller. Can it take this 115A abuse in a LMR application? Is there a surge spec for this controller anywhere?

The GMVIS cells are a Sanyo RC2400 that is zapped. They come from Germany I think, but I use them since I can get them at a very reasonable price here in Canada.

Thanks again for the input,

Ryan
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Old Sep 29, 2003, 01:03 PM
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Ryan,
The 7S is also a fine motor, with the right prop. I don't know which one would be better, but I think that any difference between the two would be very small (assuming an optimized prop selection in both cases). Both motors are being used succesfully in F5F setups. Personally, I favor the 6S.

My 120 amp setup uses the HM-105 controller with no problems.
Hacker lists the current limits as 150 amps for less than 15 seconds.

Good luck,
Lenny
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Old Sep 29, 2003, 03:02 PM
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I use a Hacker B50 7s in my seledkin and it goes really really well. If I want to realy go nuts I put the RFM wide 16x16 on and draw 105 amps but for fun flying and great vertical performance I find the 15 x 13 aeronaughts fantastic and only drawing 80 amps. So it really boils down to what you want from your plane, but if you can help it try and draw a lower amp setting unless you are competing serously, there is no doubt that you are putting everyting under stress over the 120 amps mark.

Regards


Shaun
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