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Old Feb 08, 2012, 11:57 AM
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United States, FL, Sebring
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Originally Posted by The Don View Post
I am torn between the stock fans on 3S with the 4800KVs or go 4S with the 4000s.

Don
Don, I love both of those combos. I think in this build, I decided against the 4s just because of the lipo. I wouldn't be able to use this particular 4s flight battery in any other plane where I have lots of other 3s planes.
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Old Feb 08, 2012, 11:59 AM
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Maple Valley, WA
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Hey Joe, when I was taking the afterburnerz out of carcass #6, two wires from one of the main burnerz came off. How simple is it to resoder them on?
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Old Feb 08, 2012, 12:00 PM
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Hey Joe, when I was taking the afterburnerz out of carcass #6, two wires from one of the main burnerz came off. How simple is it to resoder them on?
Wires came off from where?

On second thought..... roll it up like the way they came, along with the wire that came off and send it to me. I'll repair it, check it and send it back, no charge.
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Old Feb 08, 2012, 12:18 PM
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You are the man Joe!
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Old Feb 08, 2012, 02:32 PM
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Sacramento CA
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This is definitely a 4s plane...@ 64mm fans, of course...the wing is too small for real 70's and the batts they would need.
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Old Feb 08, 2012, 04:23 PM
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United States, WA, Ravensdale
Joined Jan 2011
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Originally Posted by The Don View Post
I am torn between the stock fans on 3S with the 4800KVs or go 4S with the 4000s.

Don
My last bird was running dynamically balanced 4800's on 3S, and I found it to be underpowered. Sadly, trying to find the happy medium between altitude and airspeed, I wasn't able to get mine much more than about 20 feet in the air... it just lumbered along until it got far enough away that I struggled a bit with orientation -- plus, I hadn't quite set up the rates and elevon mixing (had barely enough elevator, and TOO much aileron) the way I will this time, and it was too low to recover from the resultant dive as I was trying to figure out which end was up.

The 4S packs aren't that much bigger... you can stuff them into the battery tray (I'm going to add the battery tray off my last bird into my new fuse (just aft of the stock battery tray), which will make putting 2x 4S packs in there pretty easy) and I'm hopeful that the extra punch the 4S packs have will compensate for the slightly higher weight penalty.

I'm tempted to take one of the fans (with 4800kV motors) that still installed in the old fuse and do a bench test to see what they'd do on a 4S pack. I figure I've got little to lose, as the front half of the model was disintegrated in the crash, and I've got two new fans with the new kit in case the motor tears itself apart (which I'm partially expecting). To make this bench test a bit more scientific (assuming the fans hold up with 4800's), I'll slide in a 4000kV motor to the other side of the old fuse and see what the difference is. Apples to apples, I'm planning on just putting the fuse on a scale and running the motors up to see how many resultant grams of thrust each one provides.

If the amperage of the 4800kV at WOT is significantly higher, but the thrust produced isn't, then I'll just stick with my plan to put 4000kV motors in with the stock fans.

Anyone willing to admit whether they've already tried this? Perhaps you can save me from destroying a perfectly good fan...
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Old Feb 08, 2012, 05:00 PM
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Willoughby, Ohio
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I would think 700+ watts in this airframe would fly it nicely. The LX version of the SR-71 I had flew great on that setup (but so did my LX F-117). Maybe the Maxjet versions are not as good as the LX ones.

The 4800 on 3S in the 64mm fan is about 350-380 watts and going to 4S will up that by a factor of at least 1.8 so you looking in the 700 watt range which will be mostly heat and with time will cook the motor. Some guys have done it but I don't suggest it.
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Old Feb 08, 2012, 05:39 PM
but it's a nice obsession
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Sandy, Utah
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more 71 pics

Here are a few more pics from flights 3 and 4 - finally got a sunny day!

Thanks to our cameraman Leon!
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Old Feb 08, 2012, 06:26 PM
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Nice shots! That first one you could never tell it wasn't the FS!
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Old Feb 09, 2012, 02:06 AM
I always find software bugs!
United States, AZ
Joined Nov 2010
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Just my two cents...

Don, I am going with two of your balanced 4000+'s, twin 4S batteries, and dual 60 amp HW ESCs.

The only problem is that I am primarily into R/C helicopters and have been building a flybarless 600, a totally modded mCP X (CNC, carbon fiber, and brushless), and am trying to keep my current 400/450 in the air! :-) The SR keeps getting put on the back burner.

Aros, I haven't forgotten about your stickers, I'll get it out in a few days (its on my to do list!). If anyone else wants one, let me know because it is easier to do them all at once. See back a few pages for the details.

Its good to see the thread is alive and well!

J
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Old Feb 09, 2012, 10:01 AM
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Originally Posted by jgmtens View Post
Here are a few more pics from flights 3 and 4 - finally got a sunny day!

Thanks to our cameraman Leon!
Looks awesome!
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Old Feb 09, 2012, 10:03 AM
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United States, FL, Sebring
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Quote:
Originally Posted by The Don View Post
I would think 700+ watts in this airframe would fly it nicely. The LX version of the SR-71 I had flew great on that setup (but so did my LX F-117). Maybe the Maxjet versions are not as good as the LX ones.

The 4800 on 3S in the 64mm fan is about 350-380 watts.
Don, I've been seeing a bit more than that on 40C+ lipos. I get a peak of around 450 and usually setlles in at 425-430 for a bit. Certainly the draw is lower with less potent packs.
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Old Feb 09, 2012, 12:16 PM
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Sacramento CA
Joined Oct 2009
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One thing you should consider for 3s or 4s is the amount of equipment you plan on flying...AUW stock specs around 35 ounces (we're 11 ounces or so over that and landing speeds are hot but managable...no mistakes-or else)...4s batts are big, so LG, whaletail, rudders, pitot tube, camera, etc., can't all be in the same plane...a plane that's fun to fly, anyway. There is a bit of give and take...smaller batts-less air time, etc. It is still a small model and max wing loading is quickly gained in any build.

Awesome performance for 3s I might add...88 mph, a best so far, with 86 being the most consistent. Dives are shallow to maintain true power output. After 30 attempts, 100 mph is not possible with our set-up. I'm thinking about removing the 'cone plugs' for one more attempt at 100 mph. Leaving all the doo-dads off might do it, too. Not on this model, but the next, stripped down and 4s, pitot tube, elevons only and big, big batts...

Next time you're flying the SR, @ full speed, cut the throttle as the plane goes overhead and listen to the drag...about the loudest of any plane in our fleet...which makes these tiny 3s motors even more impressive.

Joe
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Old Feb 09, 2012, 12:50 PM
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Interesting post redlite...So do you think 100mph is not obtainable with this airframe? I thought my 1300 watts/Delta V/4S setup was going to get her there but I think 90 was the closest I came.
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Old Feb 09, 2012, 01:00 PM
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If this were glassed and all smoothed out, it would be quite a bit faster. Foamies are not very aerodynamic at all, the surface has so much drag. some parts could be thinned for drag reduction too.
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