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SR71 blackbird

Old 02-24-2007, 07:40 AM
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Default SR71 blackbird

Forgot to ask. Is there a way to convert my 46 size nitro SR71 blackbird to electric? If so what so I need to get? thanks
Old 02-26-2007, 06:18 PM
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Default RE: SR71 blackbird

I would need to know a few more things. Please give me an idea of size, weight and wing area. Also how fast did the model fly with the 46?
Old 02-26-2007, 06:45 PM
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Default RE: SR71 blackbird

The bird flew as fast as my grandmother drives. I has an OS 46 with APC 10x8 prop. I'll say it looked like it was going about 30 to 40 MPH max. I was told to change the prop size down to 10x6 to make it fly better and go faster (which I going to try later on today). But I really would like to have it converted to a electric. It's because the way the engine is sits on the plane it gets fuel all over the vertical stab, wings, and is just a total mess after flying. So electric is my best bet to keep it clean and hopfully fly better and faster. Here are the specs I got from the instruction manual. Total lenght - 47 in. Wing span - 38 in. Wing area - 651 sq. in. Thanks
Old 02-26-2007, 06:47 PM
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Default RE: SR71 blackbird

OK. A couple more questions. Is the motor in the front or back ( I think from the description its in the front) ? What is the total flying weight of the model?
Old 02-28-2007, 05:45 AM
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Default RE: SR71 blackbird

The engine is located towards the back of the plane.
Old 02-28-2007, 02:26 PM
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Default RE: SR71 blackbird

OK, we almost have enough. what is the current flying weight? How fast do you want it to fly?
Old 02-28-2007, 06:35 PM
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Default RE: SR71 blackbird

The current flying weight is 5.5 pounds (without fuel). As for how fast I want this bird to fly. Well, I would really would like to see it do at least 70 plus mph. Is it possible to make this Blackbird fly at least 70 mph with an electric motor and prop restriction of 10" or smaller?
Old 03-02-2007, 11:54 AM
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Default RE: SR71 blackbird

Here's a try. This is based on a 6 cell 3700-4500 mah 25C or greater Li-Poly battery. The flying weight I am figuring is 90 ounces, which is just over 5.5 lbs.
I am going for a direct drive inrunner with geardrive for brute force and the ability to turn a prop fast.

Example:
Medusa MR-036-050-1600
Geardrive 3.3-1
Amps: 56
Prop speed: 119 mph
Thrust 110 ounces
Prop 10 x 10 APC E

Prop is moving at just under 12K RPM and motor is rotating at 42K. The max for the motor is 60K so we are good.

Let me know if this is in the ballpark for you.
Old 03-03-2007, 05:25 PM
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Default RE: SR71 blackbird

Thank you very much for all the information. I'll look into it and see if I can get my bird set up this way. I just hope it doesn't cost an arm and a leg to go electric. Thanks again.
Old 03-04-2007, 03:18 PM
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Default RE: SR71 blackbird

It wouldn't be much more than going glow, except for the battery. That kinda represents the total ful\el purchse if it was glow. The battery will cost approx 200-240.00
Old 03-07-2007, 06:05 AM
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Default RE: SR71 blackbird

I checked out the prices on going electric and like you said it's not too bad. I wanted to go with your recomendation and get a 4130-7 but there is hardly any room for 8S pack. So I might have to settle with the 3520-7 (might unless I find room for the packs). Now the question in mind is where can I get 10" pusher props that will work with the 3520-7 and, or a 4130-7 and what do you recomend for the pitch? I'm really looking forward to the conversion. Thanks
Old 03-07-2007, 02:45 PM
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Default RE: SR71 blackbird

You don't need a pusher prop with electrics you only need a regular prop. All brushless motors are able to run in either directions. Simply put the prop on the motor with the curved airfoil side facing forward (pusher or puller the prop still has to face the direction of flight) and set the motor to turn in the proper direction. When facing the front of the model that would be counter clockwise. To change the rotation of the motor swap any two of the three leads between the motor and the ESC. You may also be able to reverse the direction of rotation in the speed control software. That would dpend on the ESC being used.

I think that a 6 cell pack is more than enough power for your airplane.
Old 03-07-2007, 08:23 PM
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Default RE: SR71 blackbird

Wow, all I need to do is turn the prop around and change the wire config on the motor, COOL. If it's okay, I would like to run by you what I'm thinking of getting for the electric conversion and the sites I'm thinking of getting it from. Hope this is not to much to ask.

1 each - Towerpro brushless motor 4130-7 (http://bigerc.com/shopping_cart.php?sort=3a)

1 each - 65A - 90A Brushless Motor Electronic Speed Control ESC (http://stores.ebay.com/rickyshowroom)

2 each - 10x5 electric prop. (http://www.graysonhobby.com/catalog/...roducts_id=137)

I know I need a motor mount but I guess there all the same.

2 each - GWS 3 cell lithium polymer 2200 Mah battery pack (http://www.allerc.com/product_info.p...oducts_id=1731

Thank you.....
Old 03-10-2007, 12:09 PM
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Default RE: SR71 blackbird

Wow! All chinese stuff. I cannot comment on the worth of this equipment because I have not used any of it. Personally I cring when people use Chinese Li-poly's because I do not see them being up to par compared to Korean made batteries. I would suggest that you consider going with better battery, and one that will most likely be backed up with a good guarantee. I would want to use at least a 20C battery such as Thunderpower, Hyperion, Duralite, PolyRC, Polyquest, Tanic. I would not think that a 2200 mah battery would be the correct size for this application. I would look at 3000-3700 mah batteries.

The ESC sounds like it will have enough power handling, but how is the warranty and will you have good after purchase support?
I can't tell too much about the motor except it does have the proper kv for a 5-6 cell battery. I would need the specs to give you performace on this motor. According to the website it recommends a 15 x 10 motor so I don't think a 10 x 5 prop would work at all.

So if you are willing to chance your model on this equipment (perhaps you have read or heard about others that have had good luck with this stuff?) and change the prop, and batteries, it might work OK. If you need to have a prop size of no more than 10" we will have to look at other motors.
Old 03-12-2007, 01:11 AM
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Default RE: SR71 blackbird

I really wanted to go with the Medusa Mr-036-505-1600. I've searched the internet and came up with just one site which http://www.rchover.com/inc/sdetail/76135. It has the Medusa Mr-036-505-1600-5. Is this the only site that sell this type of motor? By the way is it possible to run two 3 cell 2200 mah in parallel to produce 4400 mah?
Old 03-12-2007, 06:38 PM
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Default RE: SR71 blackbird

That is a good motor. I will have to do the numbers to see how it will work in your situation. I really hate to make a shameless plug[sm=75_75.gif], but we sell them too. Here is the webpage http://www.nesail.com/detail.php?productID=5174
Old 03-12-2007, 10:32 PM
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Default RE: SR71 blackbird

Thanks I'll look the site up. By the way is it possible to run two 4S 2100mAh 15C 11.1V together to make it an 8S 4200mah 30C. Will this work? I'm just thinking that if one cell goes bad on an 8S I need to get a whole new pack. But if one cell goes out on one of the two 4S I'll only need to change out one pack. Thought I'll ask. By the way is 11.1 volt enought.?
Old 03-13-2007, 09:54 PM
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Default RE: SR71 blackbird

You can take two 4s 2100 mah packs and make an 8S 2100 mah pack or you can make a 4S 2100 mah pack. The first is wiring together in series and the second is wiring together in parallel. In order to get an 8S 4100 mah pack from 4s 2100 packs you would need 4 packs. 2 each 4s 2100 wired in series, and those double packs wired in parallel.
Old 03-13-2007, 10:22 PM
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Default RE: SR71 blackbird

With all the information I got from you. I think I will be able to make the right choices on which type of motor, esc, and lipo battery I need for my SR17. If I have any other questions, I hope you don't mind me droping in for your professional advise. When it comes to electric conversions "YOU THE MAN!" THANKS!
Old 03-14-2007, 12:39 AM
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Default RE: SR71 blackbird

Anytime. Let us know how it works out for you.

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