Eraser Re-build - RC Groups
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Dec 27, 2009, 06:59 PM
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Eraser Re-build


Getting closer to finishing the Eraser project. I got the plane with lots of wing damage and no tail, but the fuse is in great shape. The spar appears perfect, but the rest of the wing had lots of rips, tears, gouges, dents and delams in it. Lots and lots of repairs later, here's the stats and some pics. I think this is the Eraser T/D-F3J version (standard construction) ( The wing is all fiberglass and foam and the fuse appears to be all fiberglass.

Here's some specs:
Estimated AUW: 71-72 oz.
Wing Span: 122 inches
Estimated Wing Loading: around 10 oz/sq ft.
New 5 cell Eneloop AA battery pack.
New wiring harness.
New HS-125MG servos for Ailerons
New HP-DS13-TMB (Hyperion digital servos) for Flaps
Used HS-81MG servos for V-tail.
I have a few receiver options and I'll decide a bit later which one to use (72Mhz versions).

I still have some more repair work on the wing and then have to mount the wing servos and repaint the wing in red and black. the AUW looks about right for this ship. Out of curiosity, anyone with a fresh (non damaged) Eraser care to share their AUW's? What's the lowest possible? When I can afford them, I'll get some digital servos for the tail and mount them behind the battery. I'll also use carbon rods. I know an ounce or two really doesn't matter in the long run, but for just a little more work, why not?

Thought about making my own ballast using some lead shot and brass tube. Not too sure if that will add enough weight to make a big difference. Can anyone tell me how much the ballast weighs?

Scott M.
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Dec 27, 2009, 08:29 PM
Lover of fast slope gliders!
glasairIII's Avatar
Looking good Scotty! I've got ballast molds, all sizes. Shoot me a dia and I'll let you know a weight.
Dec 27, 2009, 09:27 PM
Registered User
The ballast tube inner diameter is 0.45 inches or 11.4 mm and the length is 12 and 11/16 inches or 32.23 cm. This length will also leave a little room for a small end plug to keep the ballast from falling out.

Dec 27, 2009, 09:56 PM
Lover of fast slope gliders!
glasairIII's Avatar
Originally Posted by wsmorton
The ballast tube inner diameter is 0.45 inches or 11.4 mm and the length is 12 and 11/16 inches or 32.23 cm. This length will also leave a little room for a small end plug to keep the ballast from falling out.

I'll pour a 11mm slug and give you a weight. Won't happen till later this week.
Dec 27, 2009, 10:26 PM
Registered User
Thank you, but you don't have to. I should have though of this sooner and used some of that math stuff I learned in school.

From the dimensions of the ballast I need and the density of lead, the weight of the ballast will be right around 1.5 lbs or 24.5 ounces, giving an AUW of 95.5 oz. That would give the plane a new wing loading of about 13.3 oz/sq ft. That's a 34.5% increase in AUW. That should be heavy enough to tell a difference in flight characteristics. Although, I wish I could add another 1.5 lbs. Maybe I can make something that I can attach to the tow hook on the inside of the fuse in addition to the ballast tube.

Dec 28, 2009, 06:32 AM
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lesterpk's Avatar
I use this for ballast planning.
Dec 28, 2009, 06:02 PM
Registered User
The matweb site is great! After I checked my calcs, I saw that I fat fingered a number and messed up the calculations. Time for a new calculator with larger buttons! :>)

The new numbers are:
Ballast = 0.82 lbs or 13.1 ounces.
An 18.5% AUW increase and an 11.7 oz/sq ft wing loading. That seems like not much at all. I guess I'll have to make the ballast and try it out to see just how much a difference it will make.

Dec 30, 2009, 09:36 AM
Registered User
Scotty, nice work. Did you consider using any other material besides balsa to fill that gap? I don't have any alternate ideas... I was just wondering. Two other questions, did you sand the surface before you added a layer of fiberglass to kind of countersink it? Also, what kind of resin did you use and did you use cloth as well or just resin?

Dec 30, 2009, 04:25 PM
Registered User
This plane is my first entry into composite wing repair. I researched a lot on RC Groups and talked to a few fellow fliers that also repair composite ships. From this, I decided to just use 1/32 balsa (as light as I could find) to act as the "filler" between the fiberglass. I start out by removing just the damaged area and then adding the cross braces. The cross braces are just 1/16 X 1/4 balsa stock. For larger areas where there is at least 1/2 inch or so of damage, I added a full layer of 1/32 balsa to the lower surface (like I did with the cross braces). This layer helps keep the wing skin in alignment and also adds a little extra strength. I then filled in the gap with two layers of 1/32 balsa sheet (trimmed to the exact shape of the damage and with the grain of the wood parallel to the spar). I used thin CA for the lower support and/or cross braces and used Z-Poxy finishing epoxy with some micro balloons to glue in the balsa filler. I then sanded (dry) the balsa flush with the wing skin. I then added a layer of 0.6 ounce fiberglass cloth on top of the sanded balsa (I also overlapped the fiberglass past the balsa by 1/2 to 1 inch). I used some wax paper, a 1/32 sheet of balsa and some weights to keep the repair as close to the shape of the wing as possible. When all of that was dry, I added the "Icing" to the areas that weren't even with the wing skin. I keept added the "Icing" and wet sanding until the area was as perfect as possible. I hope this helps explain it better.

I forgot to mention, that I used the Z-Poxy Finishing epoxy for adding the fiberglass (without microballoons) and dabbed a paper towel on the fiberglass to get out as much of the epoxy as possible. After this, I could just see the weave of the glass.

Here's some more pics of this kind of repair on an Onyx that recently had a mid air.

Last edited by wsmorton; Dec 30, 2009 at 04:30 PM. Reason: Forgot to mention..
Dec 30, 2009, 04:37 PM
Registered User
Also, the two layers of 1/32 balsa is thicker than what is really needed, but one layer of 1/32 balsa was too little. The extra thickness was sanded down to make it flush with the wing skin.

Dec 30, 2009, 04:41 PM
Registered User
Here's how to wet sand while indoors!

Dec 31, 2009, 03:21 PM
Registered User
Decided to do some painting today. Using Krylon Gloss Banner Red on top. I haven't done this before, so I am not really sure how it will turn out. I am putting about three coats of red on top and then going to let it dry completely (24 hrs) to see how well the paint covers the wing. I can still see the repaired areas after I spray it on, but I won't know for sure until after the paint has fully dried. I will probably do a final wet sand with 400 grit and then apply two more coats and then wet sand with 600 grit. ... We'll see...

Also finished the wiring harness.

Jan 01, 2010, 06:17 PM
Registered User

Eraser Rebuild - Aileron Servo Frames

While the paint was drying on a few of the parts, I decided to make some servo frames from the ailerons. I wanted the servo to be more flush with the lower skin and in better alignment with the control horn, so that meant I needed some kind of spacer to raise the servo to the correct height. If I bought the frames from a company, they would still sit too low. So DIY to the rescue.

Using 1/8 light ply, I cut 1/4 inch wide strips and used the HS-125 as a guide to build the frame. I laminated three pieces of ply to build up the frame. I then added a pocket to hold the rear servo tab. This way, I can slide the servo out of the pocket for maintenance. Since three layers of ply was too much for the rear of the frame, I sanded the bottom of the frame until the servo could slide under the skin of the wing, but not too much. I ended up sanding away 1/8 of the ply toward the rear. I will epoxy the frame to the wing skin. I aligned everything up and traced the frame on the wing skin with a pencil so that I didn't need the servo to be attached to the frame when I glued it in.

Hopefully, the pics will explain it much better.

Jan 02, 2010, 07:53 PM
Skye Malcolm, LSF Secretary
skye8070's Avatar
I've got an eraser v-tail version but with the curved up wing tips. I just went through all the pieces with the triple beam balance scale and see that the repair on the right wing tip made it 10 g heavier than the left one. All up weight with dual 4 cell 1500 NiMH battery packs up front and Voltz servos all around is 73.4 oz (unballasted) so I'd say you're doing pretty good! You'll like how it flies, just be sure to play with the camber if you need it to slow down in thermals. I used mine for the 0.6 km LSF III baby cross country flight and clocking it with the pickup's spedometer it scoots along about at 35 mph when the wing is all cleaned up and you're not pushing down on the elevator. It's deceptive because usually you're up so high but that speed sure comes in handy when seaching for lift.

By the way, my plane is in this picture (that's not me in the picture though):

I have the wings on the left with the fuse on the right.
Last edited by skye8070; Jan 02, 2010 at 08:04 PM. Reason: added link to picture

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