Jetmax SR-71 Brushless setup?
03-26-2010, 12:21 PM
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Jetmax SR-71 Brushless setup?
Just got the Jetmax(kit only) SR-71.... I know there hasn't been much success so to speak of with these from what I have heard but I want to give it a shot, but want to know what is going to get this going, I mean really going! Kind of new to electric and edf so need a little advice here. Thanks
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03-26-2010, 12:55 PM
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RE: Jetmax SR-71 Brushless setup?
Please define: "there hasn't been much success so to speak of "
I have not seen any problems with these planes.
Also define "Really going"
Are you talking about higher speeds or thrust?
If you are new to EDF's and Electrics, I'd advise you to look at a single fan EDF to start with.
I have not seen any problems with these planes.
Also define "Really going"
Are you talking about higher speeds or thrust?
If you are new to EDF's and Electrics, I'd advise you to look at a single fan EDF to start with.
03-26-2010, 01:23 PM
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RE: Jetmax SR-71 Brushless setup?
I have the Panther F9F 2, Great planes L39, and Exceed F-18 and have sucessfully flown them all..... with out failure. I have been in the hobby since my father put me on the sticks some 28 yrs ago so Im not completly illiterate I just dont have much to go from other than saying that it requires 2-40 amp esc's and 65mm brushless motors?? I need something a little better to go off of than that. Now if it was nitro.... I wouldnt be here asking. lol Thats all Im saying. just asking for a little help, hence the new to edf-electric thing, but not totaly new to the hobby....I have read a few articles as well as a few forums that some guys are dumping quit a bit of money into these just to get them moving faster than the stock 40 mph that they came out with and from what they are saying, 500.00 bucks is how much they had to put into them to perform to there standards or to just to get it to fly and not stall out. Most of them were complaining that was way to much to be put into a foamy....well I still think it can be done for way less my self and want to try. I already have 85.00 in the plane + 80.00 in both esc's and 40.00 on a battery. So if I can do it for 300-350.00 then its a win for me.
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03-26-2010, 03:47 PM
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RE: Jetmax SR-71 Brushless setup?
Ok, so let's assume that you are going for speed...
$500.00 is a LOT to put into a rather small foamy, but some of these guys go with really expensive stuff such as the German made Shnubler (sp?) EDF's made from CF, etc.
To optimize the power system, throw out ESC ratings, etc. and start over...
The advertised weight is 2lbs or so. Expect that a better performing plane will require heavier packs, EDF and motors, so let's raise this to 3.2lbs AU flight weight or more.
For any speed we want better than a 1:1 thrust ratio... and since EDF's are somewhat inefficient, we go for about 200watts or so per lb.
250watts x 3.2lbs = 800 watts
This would put the SR-71 in exactly the same weight and power range as my Ultrafly Spear btw, and that thing is - FAAAST! - ( well over 100mph) with the HET 2W-25 motor, 14.8v packs and HET plastic EDF...
You would be using two 64mm EDF motors and fan assemblies so you'll be looking for something in the 400 watt range.
Assuming you'll be using 11.1v LiPo's...
400 / 11.1 = 36A
So your pack will need to be able to sustain 36x2 A of current drain or 72A total, given a 20C pack, that equates to a 3600mAh pack or better.
Since the stock plane uses a 2500mAh pack, there is a high likelyhood you can get a 3000mAh pack in there.
Your maximum draw will be about 36A so you'll want to use TWO 40A ESC's.
Another way to go is to increase the voltage instead...
400 x 14.8 = 27 A, so you could use a 14.8v 4S 2800mAh or better pack instead.
A pair of 40A ESC will also suffice.
However at higher voltages, on board BEC's will fail VERY quickly, so you'll also need a separate BEC in this situation.
RC Lander makes an excellent 68mm aluminum EDF unit, but this may be too large for this plane... too bad...
So now you have a rough estimate of what you will need in terms of overall power.
The next thing is to find a matching EDF and motor.
Your biggest problem is finding a FAN unit ( if need be ) that will fit.
The KIT version of the plane already comes with plastic 64mm EDF's which may be suitable, but you'll want a better motor to bring up the speed...
Something like this: [link=http://www.hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=11166&Product_Name=HK_EDF64_Brushless_Power_System_3500k v_&_45A_ESC]Click me![/link]
Has a pretty high KV rating ( meaning lots of efflux speed ) and power handling that exceeds your need.
Assuming the advertizing is over optimistic and you get only 30oz of thrust, you'll still be way over the 1:1 ratio needed to get serious speed out of the plane!
You'll need to use 14.8v packs with those however.
You SHOULD be able to attain 80-100mph+ or more with this setup, provided the battery pack will keep up with the load.
$500.00 is a LOT to put into a rather small foamy, but some of these guys go with really expensive stuff such as the German made Shnubler (sp?) EDF's made from CF, etc.
To optimize the power system, throw out ESC ratings, etc. and start over...
The advertised weight is 2lbs or so. Expect that a better performing plane will require heavier packs, EDF and motors, so let's raise this to 3.2lbs AU flight weight or more.
For any speed we want better than a 1:1 thrust ratio... and since EDF's are somewhat inefficient, we go for about 200watts or so per lb.
250watts x 3.2lbs = 800 watts
This would put the SR-71 in exactly the same weight and power range as my Ultrafly Spear btw, and that thing is - FAAAST! - ( well over 100mph) with the HET 2W-25 motor, 14.8v packs and HET plastic EDF...
You would be using two 64mm EDF motors and fan assemblies so you'll be looking for something in the 400 watt range.
Assuming you'll be using 11.1v LiPo's...
400 / 11.1 = 36A
So your pack will need to be able to sustain 36x2 A of current drain or 72A total, given a 20C pack, that equates to a 3600mAh pack or better.
Since the stock plane uses a 2500mAh pack, there is a high likelyhood you can get a 3000mAh pack in there.
Your maximum draw will be about 36A so you'll want to use TWO 40A ESC's.
Another way to go is to increase the voltage instead...
400 x 14.8 = 27 A, so you could use a 14.8v 4S 2800mAh or better pack instead.
A pair of 40A ESC will also suffice.
However at higher voltages, on board BEC's will fail VERY quickly, so you'll also need a separate BEC in this situation.
RC Lander makes an excellent 68mm aluminum EDF unit, but this may be too large for this plane... too bad...
So now you have a rough estimate of what you will need in terms of overall power.
The next thing is to find a matching EDF and motor.
Your biggest problem is finding a FAN unit ( if need be ) that will fit.
The KIT version of the plane already comes with plastic 64mm EDF's which may be suitable, but you'll want a better motor to bring up the speed...
Something like this: [link=http://www.hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=11166&Product_Name=HK_EDF64_Brushless_Power_System_3500k v_&_45A_ESC]Click me![/link]
Has a pretty high KV rating ( meaning lots of efflux speed ) and power handling that exceeds your need.
Assuming the advertizing is over optimistic and you get only 30oz of thrust, you'll still be way over the 1:1 ratio needed to get serious speed out of the plane!
You'll need to use 14.8v packs with those however.
You SHOULD be able to attain 80-100mph+ or more with this setup, provided the battery pack will keep up with the load.
03-26-2010, 05:16 PM
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RE: Jetmax SR-71 Brushless setup?
Excellent!! Thanks so much, thats the information I was looking for! I appreciate it greatly and will use all of it to its full potential. I will post back of my outcome and the SR's performance. Thanks again!
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