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Old Sep 09, 2014, 07:45 PM
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Build Log
BBCC5 JETEX F4 Phantom - Dpetsel

Well....
2 weeks ago my beautiful 90 MM F4 lost an aileron servo horn through the styrofoam and did a beautiful roll onto it's back and into the ground. I have decided to reincarnate the Phantom as a 70 mm EDF balsa framework based on the FF model by Jetex.
I am currently working on my scratchbuilt proto of the Sukhoi SU26m, so it may be a couple of weeks before I can start the build. I have started CAD drawing of the model to estimate AUW, battery compartment and fiberglass ducts for the 70 EDF. I did some tests on a couple of EDF's I have and have found one that puts out about 1 lb 7 oz. of thrust on a 3 cell. My electronics weigh about 9 oz. If I can get the airframe to come in under 1.5 lbs it will probably be a flyer.

Here is a shortcut to the contest.
http://www.rcgroups.com/forums/showthread.php?t=2218067


For any of you that have never seen Jetex/Rapier FF jets fly there are a few neat videos on youtube.

Here are the plans.



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Old Sep 09, 2014, 07:51 PM
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Single fan or dual?

Andy
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Old Sep 09, 2014, 07:58 PM
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Right now it's a single Himax HA 2825-3600. Roughly a 28 inch wingspan. I have a couple of Het 2w20's with Wemo's that would really make it cook. I'm not sure if I want to go that big though. I would have to really do some creative designing.
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Old Sep 10, 2014, 03:15 PM
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I am subscribed.
But I'm worried it's going to weigh a lot more than a pound and a half.
The EDF in my 38 inch Vampire weighed a pound just by itself.
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Old Sep 10, 2014, 04:22 PM
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By the way, did you post in the BBCC5 thread also, and link it back here?
Please do that if you haven't. I need the link there so that I can make the list of all the entries at the end of this month.

I didn't mention it before because I was on my cell phone typing, but, nice build.
I hope it turns out great. I was just worried because the ESC, the 70 mm fan and motor, and the 3 (preferrably 4) cell lipo combined would wipe out your weight budget of a pound and a half. Not trying to pop your bubble, honest. I just don't want you to fall into the same thing I did with my Vampire. I ended up at about 2 pounds on mine, with a 38" wingspan. The 64 mm fan might be underpowered for the weight it needs to haul. Either I should have gone up with my wingspan or I should have increased the size of my EDF.

Welcome to the contest!
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Old Sep 10, 2014, 07:42 PM
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I do a lot of upgrades for guys that want screamers from their stock airframe. The stock motors from the major hobby shops on the web are usually very underpowered.

The 3 edf's I have to work from my spare parts drawer are:

Sapac MB1 - I had it in a L39 that weighed in at about 4.5 lbs and flew great.

I have an Het 2w20 with 70 mm Wemotec minifan 4 blade that puts out 3.3 lbs of thrust on a 4 cell.

Last one in the drawer is a Himax A 2825-3600. About 2 lbs of thrust on 3 cell.


Those motors give me a wide latitude in airframe weight. The thrust tubes will be toilet paper rolls impregnated with the West System Epoxy. I am drawing everything in CAD and will lighten up all of the fuse formers. I plan on .3 inch carbon arrow shaft as my wing main spar support. I don't think I'll add a rudder servo to save weight. The main thing now, during the design process is to keep all of the electronics positioned to keep my CG in position without adding any ballast.

I did post a shortcut to this thread from the BBCC5 thread.

This should be fun
Dave
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Old Sep 10, 2014, 07:58 PM
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Just weighed all my electronics.

Himax 70 mm edf unit
Turnigy 2200 mah 3 cell
Spectrum 600
Castle ESC
3x 9gram servos

All of this weighed in at 15.6 oz

With the Himax putting out 1 lb 7 oz thrust I can make the airframe (minus electronics) about 22 ounces.
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Old Sep 10, 2014, 08:42 PM
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Okay.
I'm anxious to see the results.
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