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Dec 10, 2007, 05:38 PM
Dave Segal
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Discussion

Building the SR X250


In 1999 Larry Sribnick of SR Batteries designed a small pattern-like model that produced rave reviews in the magazines the following year. ( www.srbatteries.com/ ) I have finally gotten around to building it and it is a pleasure to work with a well thought out kit design and a complete, understandable instruction manual. Not like the SE-5 built buy a fellow club member which at the end of 3 pages concluded with the helpful statement: "The experienced modeler will know what to do." (G)

The kit has fine wood, beautiful laser cutting and the most complete set of brand-name hardware I have ever found in a kit. On the first day the fuselage was assembled- on the second day a revised motor mount was installed and the wing commenced and nearly all of the carpentry was finished on day 6. A simple clamping jig made of balsa blocks does the job to keep the carbon tube wing spars in alignment during the assembly. But you can't be creative here, it is really necessary to follow the steps in the manual. The only awkward matter was connecting the aileron torque wires to the tiny ply blocks inset into the ailerons. Lining up the torque wire, the aileron and the blocks required more fingers than I have available.
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Dec 10, 2007, 05:41 PM
Dave Segal
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As the model was designed for brushed motors, some with gear drives, I had to make a new former to mount a brushless outrunner. This was a 1/8" lite ply plate installed 5/8" ahead of the stock firewall.
Dec 10, 2007, 05:48 PM
Groundloop World Champion
old_dude's Avatar
I have one partially built...... haven't decided which brushless to power it with as yet.... perhaps a PJS900.

What are you planing to use for power ?? Had you considered using two aileron servos, one in each wing ??? Thats the direction I'm taking.

Old_dude

ps: Have you seen this
Dec 10, 2007, 06:51 PM
Registered Snoozer
Neil Morse's Avatar
Dsegal;

I had an X250 back in the old days, and flew the heck out of it both with the stock set up and later with a Hacker B-40 brushless (waaay overpowered, but lots of fun). The X250 is a great airplane, but overbuilt by today's standards. It looks like you're doing a great job, but I'm a little concerned about your modified firewall for mounting your brushless motor. Is that tied into the original lite-ply rails in any way? If it's just glued between the balsa "cheeks" of the fuse, I would be concerned that it may not be up to the task of holding on a high-powered brushless.

Neil

Edit: Wow, they never throw anything away around here. I couldn't believe that these pics of my old X250 are still in the archives:

https://www.rcgroups.com/forums/show...ht=x250+hacker
Dec 10, 2007, 08:02 PM
Dave Segal
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The firewall is braced by triangular balsa stock on the rear side. And this motor is not a screamer- my fellow fliers would consider this a very modest setup.
Dec 10, 2007, 08:03 PM
Groundloop World Champion
old_dude's Avatar
"I had an X250 back in the old days, and flew the heck out of it both with the stock set up and later with a Hacker B-40 brushless"..... a HACKER B40 NASA uses those to launch the Space Shuttle...right ????

I thought that a HACKER A20-20L might be too much but heck, maybe I should use the A30-10XL instead

Old_dude
Dec 10, 2007, 08:04 PM
Dave Segal
Thread OP
> Had you considered using two aileron servos, one in each wing ? <

I decided to keep things simple and go with the stock setup (for a change!)
Dec 10, 2007, 08:06 PM
Dave Segal
Thread OP
With the covering nearly finished I was dubious about the canopy as I detest dealing with plastic canopies on any model- I hate trimming them to fit, glueing them in place, and either having to search for a suitable pilot figure or paint the interior of the canopy instead. So after much agonizing I decided to make a simple wooden canopy of laminated balsa and just paint it and glue it on. Very quick and easy alternative.
Dec 10, 2007, 08:09 PM
Groundloop World Champion
old_dude's Avatar
Way to go on the canopy...looks cool

But, rubber bands !! Do I see rubber bands holding the wing on ???

Old_dude
Dec 10, 2007, 08:11 PM
Dave Segal
Thread OP

A Side Note(While installing the servo arm on the elevator I was amazed to see how I


While installing the servo arm on the elevator I was amazed to see how I started out with just a pin vise to drill a hole and ended up with a table full of tools to mount the arm and adjust the elevator. I didn't use that much stuff to build the entire framework. And the photo doesn't include the soldering iron to attach the threaded couplers, soldering accessories, file, bench vise or hammer!
Dec 10, 2007, 08:22 PM
Registered Snoozer
Neil Morse's Avatar
Quote:
Originally Posted by old_dude
But, rubber bands !! Do I see rubber bands holding the wing on ???
Hey, that's what I used for my B40 powered job, and I never had a problem. Just make sure you check the bands regularly and don't let them dry out and decay.

Dsegal:

Your covering job looks excellent. I think you will enjoy this plane.

Neil
Dec 10, 2007, 10:45 PM
Dave Segal
Thread OP
Receiver is a Hitec Micro 05S with an Azarr antenna and the servos are Hitec HS55. Amazingly, all was complete and ready to fly (even if the weather isn't ready) in just 19 days. Weight is 19.6 oz. including 1 oz. of lead in the nose for balance. This compares with 24 oz. for the prototype with a brushed motor and nicad pack. Power is an Eflite 370/1200 motor, Jeti 12 ECO esc, 8x3.8 slo prop running on a 3x1320 lipo pack. This setup pulls 8.7 amps and produces 96 watts. It will be on the shelf until next spring!
Dec 10, 2007, 11:00 PM
Registered Snoozer
Neil Morse's Avatar
Dave:

Wow, how can you wait that long?

I say, ditch the little motor and the 1 oz. of lead and go with a slightly bigger motor. I predict you will like the plane enough to want some more power. And why add lead? Something like an AXI 2212/26 could get you over 200 watts on the same battery with the same AUW. Just my $0.02. Beautiful job on the build.

Neil
Dec 11, 2007, 09:18 AM
Dave Segal
Thread OP
> I say, ditch the little motor and the 1 oz. of lead <

That is a possibility I have considered. But I was being cautious after giving up on two over-powered small models last year that climbed like rocket propelled grenades and gave me heart palpitations. The Axi will be next choice if this setup seems too tame, but it is only 0.4 oz. heavier.

> Wow, how can you wait that long? <

Uh, this isn't California. Our field will be cold for months and often soggy from rain or melting snow. I don't find these conditions fun so I settle for the fact that in the Middle Atlantic states we have 5 months of great "building weather" every year. (G)
Last edited by Dsegal; Dec 11, 2007 at 11:57 AM.
Dec 11, 2007, 12:51 PM
Groundloop World Champion
old_dude's Avatar
Yeah....... please don't be offended by my negative rubber band innuendo In our low humidity, high ozone, desert environment rubber bands just don't last that long .

Your building season is our flying season and our building season is your flying season except mother nature has dumped rain on us for the last five days

Please post more about your XR250 when its been flown.

Old_dude


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