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RA Cores EXTRA - Carbon Fiber Mods


Old 07-28-2018, 09:16 AM
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Default RA Cores EXTRA - Carbon Fiber Mods

Hi all,

I bought one of RA Cores Foamy "Extra" 3D kits that had already been assembled, I bought it from Anderson Hobby (since I live near Anderson Hobby).
Anderson Hobby acquired these assembled kits at the Joe Nall Fly-in after the Fly-in had been canceled due to predicted flooding.
The predicted flooding never happened but it's better to be safe than sorry! :-)

I done the maiden flight only to be disappointed on it's first vertical climbout, the plane wanted to yaw to the left really hard even after trimming the rudder for straight flight and there was literally no wind.
It may be worth mentioning that it flew in a left crab angle even though the track across the ground was straight.
After inspecting the motor mount, I discovered that the motor mount had been installed with about 4 of LEFT thrust instead of RIGHT thrust. I'm guessing that whoever assembled it had it upside down when they installed the motor mount. It was an honest mistake and I'm sure they were in a hurry to assemble them so they would be ready for the fly-in.
I added some thin washers under the motor mount tabs to correct the thrust angle issue and it flew and tracked straight with no crab angle after that mod.

The next thing I noticed was how bad the airfame twisted due to so much torque from the 24 gram BlueWonder 1300kv motor on a 3S Lipo.
I noticed that the amount of twist highly depended on the amount of throttle used which makes sense. When I was doing high speed knifes edges, it seemed fine until I decided to change throttle settings during the knife edge (mostly transitioning from a fast forward knife edge to a high alpha slow knife edge), I had a hard time keeping it straight since the airframe had different degrees of twist in it (again, depending on how much throttle was being used at the time).

I had some .8mm x 6mm carbon fiber strips so I decided to add a strip to the underside of the fuselage to make it more rigid and to act as a skid for landings (in cases where it's too hard to grab it while in a hover).
I also added a CF strip to the leading edges of the horizontal stabilizer to make that a fairly rigid point to fasten carbon fiber rods to (to further minimize the airframe twisting issue).
Then I added a 2mm CF rod from the left front portion of the wing (at the point where there is a short embedded CF strip) to the underside of the fuselage at the center and at the point where it meets the newly installed CF strips, then to the right underside of the horizontal stabilizer, this was done from left to right so the torque results in a pushing action rather than a pulling action from the nose to the tail (Click on Link to Photo below).
It worked great in my opinion because it eliminated the twist.
The added weight didn't seem to hurt flight performance much at all.
I added 11 grams of CF and glue bringing it up to a total of 190 grams and it didn't seem to effect the CG either, well..... maybe a tad but it was so minor that I didn't need to move the battery at all.

As for trim, before correcting the motor thrust angle issue, the rudder trim was to the right by at about 2.
Before the CF mod, I had to add a fair amount of aileron trim as well but after the thrust and CF mods, no trim was needed at all, the control surfaces are all neutral now (flat with mating surfaces).

I really like this bird! It's great to have something I can grab and go to our nearby school football field to have some fun.
The school allows people to use it for RC stuff as long as it's small and electric and as long as they aren't using it for games at the time :-)
Cool thing is there are lots of kids around that have become interested in RC airplanes. Now some kids use the field for flying small quads and some compete with each other. The school sees this as constructive activities (as opposed to doing illegal things and getting into trouble).
Nope, I'm not the one teaching these kids how to fly but some of them watch me fly. I'm not very good at teaching but I do give them tips once awhile when they ask.

Hope this helps someone who may be wanting to tweak their foamy for more stable flight characteristics.

RC Universe won't allow me to post photos or live links until I've had enough posts.

Not sure if the photo or thumbnail will show or not, if not, try copying and pasting the address below into your web browser.
Thanks!! :-)

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Old 07-30-2018, 07:12 AM
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While at the football field mentioned above, I decided to use the goal posts at each end of the field as an obstacle course.
I would fly through the center of the north goal, then exit by doing a steep bank around the left pole, then go through the center of the south goal post and exit by going around the right goal post, then do the opposite on the next pass.
That was a lot of fun but depth perception is the really hard part as you can imagine, especially while standing in the middle of the field 50 yards from each end.
To add even more to the challenge, there were trees about 15 yards beyond the north goal post and power lines about 20 yards beyond the south goal post.
This time there was a fair amount of wind but it only added to the challenge
I wouldn't even attempt doing this with any of my balsa planes, I don't mind patching a foamy but I'm sure it would totally destroy a balsa plane.
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