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Old Nov 10, 2007, 05:32 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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Rodent Build Detail

I have a Rodent kit to build next, I believe it's an R2, but I'll check.

I'm wondering if there is any pertinent input from those of you that have built these beasts in the past?

Here are my intentions:

Stock wing, 4oz biased glass under 1/32" ply, and probably 4oz + 3/4oz bagged on the outside with a base coat of paint. Silicone hinges.

Wing servos, in the Hitec servo mounts. DS368's.

Ballast tube, 3/4"D x 13.5"L, same as my Trinity; I can use the same ballast. 9 slugs= about 36oz. Will extend 2" into the back of the starigh-cut nose cone, and I'll likely set it up to shotgun load from underneath. The nose cone will retain the last ballast slug/spacer.

I plan to close out the wing saddle with a layer of 1/32" ply and glass after the fuse build is done, with just a small hole for the servo wires. This should make the wing saddle area strong without a bunch of reinforcement glass there. There are already some reinforcements in the fuse layup.

Fixed stab with hinged elevator. Glassed/bagged parts. Hinge method unknown at this point.

I'm wondering if there is anything I haven't considered yet. I'm hoping to come in at 55-70oz RTF.


One of my biggest questions is about CG; I have heard a bunch of different places and am wondering what the furthest back is? That way, I can get the ballast tube in far enough back.

Thanks in advance for your input.

I have already read this thread; seems the CG ranges from 2-3/4" to 3-1/8" back-
http://www.rcgroups.com/forums/showt...ight=Rodent+CG

Target
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Old Nov 10, 2007, 05:42 PM
find me @samotage
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Melbourne Australia
Joined Jul 2005
8,362 Posts
Hey T,

Which wing have you got? Mine is a Don Ayers 6 percenter, and I rekon it has a more aft CG than praps some of the others, but then again, it's at precicely 1/3 of the chord...

I rekon you will be wanting more ballast. Remember Rodent has a minimum windpeed of 25 knots... Bigger is better. My slugs are 1 inch dia, about the biggest I could fit inside.

Elevator servo placement is a little of a headache... Mine is in front of the ballast tube, and had to do plenty of "releif" to get a nice kleen pushrod run. It's fine now, but took some delightful "French" to get it wot work well...

Your servo choice is fine, though analog is just as appropriate for this type of toy...

I don't think you need to cover up the saddle area. Just laminate layers of kevlar in the middle front and behind the wing. I have 3 layers of 6 oz. It's strong.

Use nylon bolts to secure the wing. I use 1/4 inch bolts, and they break before the wing does. A good insurance policy.

Go git'r'done! They are great fun, have an awesome presence in the air, and fly like a race truck.

Sam,
and his borax.
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Old Nov 10, 2007, 05:53 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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Hmmm.
MORE ballast?

Dang, I already rolled the tube, too.

I could use a piece of 3/4 pipe; it's 7/8"D... That would give me just a bit more room for the elevator servo install.

On the wing servos, I picked the DS 368's just because they are bullet proof, and fit the Hitec cans, and I have some here!

T
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Old Nov 10, 2007, 05:54 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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Can you post some pics of your Rodents' fuselage guts, Sam, or a link?
Thanks.

T
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Old Nov 10, 2007, 06:00 PM
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Southern California
Joined Sep 2003
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You'll want to hit the 70oz range if you're limiting your ballast to 9 slugs. OR-- ya could borrow my TUNGSTEN!!!

90% of your flight time will be around 70oz's at Fermin. MOST days will support that kind of wingloadings-- then ya can go lighter--or heavier to taste!

T
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Old Nov 10, 2007, 07:02 PM
slope'n the Colombian Andes
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Colombia, Antioquia, Girardota
Joined Mar 2001
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Target, regarding the CG: you'll have to calculate that for your particular planform, airfoil, and even moment arm and decalage. But it's not hard to TLAR it close and fine-tune it with flight tests.

Dieter Mahlein, ShredAir
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Old Nov 10, 2007, 07:22 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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I know, but there's nothing worse (well almost) than a ballast tube mounted too far forward. I suppose I could offset it a safe amount to the rear to begin with.

How about you, Dieter? Do you think 36oz of ballast is too little? I thought it would be fine:

60oz empty = 20oz wing loading
96oz full = 32oz wing loading.

T
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Old Nov 10, 2007, 07:27 PM
Vitruvian JART
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San Francisco
Joined Mar 2003
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Dude, if you can't make due with a 96oz Rodent...!

You guys know what I think, but I'll say it again. I prefer not to put more than a pound of ballast in a plane like this because it's better to have the weight built in as strength. Having said that, T-man knows what he's doing so I'm sure this heavy rat will be strong in all the right places.
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Old Nov 10, 2007, 07:41 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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I'm thinking more of a 25-30 MPH wind plane or for the guys with the stellar coastal hills (Reed), 15-25 MPH winds.

Having the ability to occasionally load up for 35-40 at Fermin would be good, but I really don't want to be able to 'only' fly in that amount of wind...

A well placed and well bonded ballast tube that runs from forward of the wing saddle to aft of it should make the plane stronger in that area, I'd think.

T
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Old Nov 10, 2007, 07:59 PM
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Joined Jan 2003
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70 oz is a good starting point. My Alias flies great right there.

I'd concentrate on reinforcing the "ramp" part of the fuse, where the wing climbs out as the wing bolts break. It's a hard place to repair once the plane is done, so I put a 1/4" ply scab inside the fuse and glassed it in.
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Old Nov 10, 2007, 09:23 PM
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Portland Intl, Oregon, United States
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Samo,

I suppose the answer to this is obvious but I just gotta ask

Great looking ballast tube but what holds your ballast slugs in the tube?

I built a Rodent a couple years ago but never got around to the ballast yet.

thanks

TIM
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Old Nov 10, 2007, 10:20 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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Thanks for the pics, Samo.
Tim, he probably utilizes a spring at one end, and the slug/spacer doesn't line up with the opening when it's loaded.

Tony-
good tip; I'll check that out. Sounds tough to do, though... The ply reinforcement is INSIDE the fuse?

T
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Old Nov 10, 2007, 10:28 PM
Feeling FrSky
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United States, CA, Santa Barbara
Joined Feb 2003
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Targ, maybe you've already seen it, but check out this page with a ton of great info from Craig Toutolmin:

http://www.thehelix.com/soaring/Rodent.html

Also, if you search for "open source rodent" you'll turn up that old thread, which Craig and others including Sled Driver chimed in on, there's a lot of great Rodent info in there too.

Steve
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Old Nov 10, 2007, 11:16 PM
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Joined Jan 2003
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Target- It's not bad. Cut the ply piece out and dry fit it by droppping it in place. Once youre satisfied, glue it in. Once its cured, a layer of glass will make sure it stays put. In a hard crash that wing will take out anything in its way.
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