RA Cores: Mini Extra Foam Kit


I met Jim Reith several years ago at the Toledo Expo. Later that same year, I ran into him at Watts over Owatonna. While at Watts, I sat down with him and talked shop on his line of airplanes. Going by the name RA Cores, Jim’s company has been around for a long time. He manufactured the Gremlin RC combat airplane, and was in that market for quite a while. Though he has recently discontinued the Gremlin, Jim is still manufacturing his Yak, Extra, EPP Warbirds, and BluFo aircraft. The Yak and Extra families keep growing by getting smaller – originally a 32″ wingspan, Jim has redesigned the Yak and Extra to span just 22″! The subject of this review will, of course, be the new Mini Extra. The Mini Extra is pretty cool – its small enough to be flown indoors (if you’re lucky enough to have that option) and large enough to be flown outdoor and use readily available electronics. Interested? Well, you SHOULD be – Read on to find out more on this newest addition to the RA Cores lineup!


Product Name:   RA Cores Mini Extra

Available for Purchase at:   www.racores.com/Mini-Extra-22inch-EPP

Price:   $24.95 USD   (Unpainted)

Price as Reviewed:   $54.95   (Painted – Red/White/Blue)

Wingspan:   22 inches   (558.8 mm)

Length:   20 – 1/4″   (514.4 mm)

Weight:   2.70 oz   (76.54 g)

Weight w/ Battery:   3.25 oz   (92.14 g)

Required to Complete:

2100 kV Brushless Outrunner Motor, 6Amp ESC, 1- 5 gram servo,

2- 3.7 gram servos, 4-channel transmitter and receiver


Mini 6mm EPP Completer Kit: Available at www.racores.com

Battery:   2S 300 mAh LiPo Battery

Electronics Used

To complete the RA Cores Mini Extra, I used my Hitec Aurora 9X transmitter and a Hitec Minima 6L 6-channel micro receiver.


Can be purchased pre-painted or plain white

Uses inexpensive radio gear and electronics

Easy assembly

Small size is good for indoor and outdoor small space flying

Looks great


None as tested

First Look

The mini Extra arrived in a plain brown shipping box. Inside, I found the kit contents sealed in a single plastic bag. The 6mm EPP foam sheets were removed from the bag and laid out – I found the pre-painted version of the mini Extra to look really nice! I especially liked the color difference between the top and bottom sides of the wing and tail, which will definitely help with orientation while flying.

Laser cut light ply parts are included with the mini Extra – the cutting is perfectly done, and the parts nearly fall out of the ply sheet. The motor mount is already removed from its ply sheet, and is ready for installation in the plane’s nose.

There’s also several pieces of carbon fiber and music wire included in the kit – the round rods and flat carbon fiber strips are cut to the correct length. The music wire pushrod ends will need to be bent to shape before installation. Heat shrink tubing sections are also included to assemble the pushrods.


The manual is well laid out and includes great illustrations and written instructions. They are definitely clear enough that anyone with even a little building experience will be able to build the Mini Extra.

Completer Kit from RA Cores:

Jim has even gone to the trouble to put together a completer kit for the Mini Extra and Mini Yak. It includes a C1822 micro brushless outrunner 2100kV motor, 6Amp ESC, one 5 gram servo, and two 3.7 gram servos. This completer kit is available for $39.95 from Jim, and is definitely easier than trying to order everything separately from somewhere else!

Also Required

You’re also going to need a propeller and a prop saver. Jim has the 6×3″ propellers for $1.00 each and a bag of TEN prop saver O-rings for also $1.00. He also included a 6×4.5″ propeller to try, but it makes the Mini Extra fly too fast for my liking.

For this review, I will be using  Turnigy Nano-Tech 2S 300 mAh LiPo batteries – only one at a time is needed, but you’ll probably want to have a hand full of them to fly many times before charging!

Foam Tac ashesive will be used for most of the assembly, aside from a few steps. Jim has the Foam Tac available in three different sizes – a two ounce bottle for $10.00, a one ounce tube for $7.00, and a six-pack of 5 ml tubes for $7.00 as well! The one ounce tube it the best option, in my opinion.

A few other things you’ll want to have on hand are as follows: a flat surface (mine is a small piece of thick glass), a cutting knife, a straightedge, some medium CA and accelerator, and a small piece of sandpaper. For the Mini Extra, I will be using ZAP-A-GAP Medium CA and ZIP Kicker available at www.franktiano.com/zap-adhesive to assemble the pushrods.


Following the instructions, I glued the carbon fiber strips into the tail of the fuselage and the elevator before removing the parts from the EPP sheets. These strips will help stiffen these sections and keep them from flexing under load while flying.

Before gluing the strips in place, I roughed up the surfaces of the strips with the sandpaper and wiped them clean with denatured alcohol and a rag. I also made sure the pre-cut slots in the fuselage and elevator were open by sliding a razor knife through the slots.

The aileron and elevator hinge lines are created by cutting a bevel into the bottom of each wing half, aileron, the horizontal stabilizer, and the elevator. I attempted to create a perfect 45° bevel on each surface, and it turned out pretty close! The secret is to place the straightedge back a bit from the hinge line and cut the bevel on the bottom side of the surfaces. This will leave the topside of each surface to create the hinge! If you’re really unsure of how to perform this step, use some of the scrap pieces of foam for practice.

With the topside of the horizontal stabilizer and the elevator together, a thin bead of Foam Tac was applied to the ‘pointed’ part where the two bevels meet. The Foam Tac will become the hinge that keeps the stab and elevator connected. The two parts were then flattened and pulled apart for a second, before touching them back together at the hinge line.

The ailerons were attached to the wing halves in the same manner.

Again using Foam Tac, I glued the two wing halves together and installed the long carbon fiber strip. The strip fits into a slot in the wings, just like the elevator and fuselage.

The nose and mid section of the fuselage were glued to the wings and horizontal stabilizer to create the horizontal flat section of the fuse. Foam Tac does a great job sticking the EPP foam together!

A short carbon fiber strip was glued into the front of the wing/rear of the nose section. I used a fine tipped permanent marker to mark their location, and then cut the slot with a razor knife. The carbon fiber strip was glued into the slot with Foam Tac.

The same was done for the fuse to the stab joint, but only the stabilizer is cut – the carbon fiber strips are glued to the sides of the fuselage.

I glued the lower vertical part of the fuselage in place using Foam Tac. There’s a lot of gluing surface, so the joint ends up really strong! At this point, the tail stiffeners were also glued in place – these wedge shaped pieces of EPP foam were glued at a 45° angle between the vertical and horizontal fuselage surfaces.

The ply aileron control horn was glued to the servo arm that came with the 5 gram servo, then the assembly was installed on the servo. The servo was then installed in the forward slot in the top side of the fuselage. a ‘dab’ of Foam Tac under each mounting lug kept the servo secured nicely! Please make note that the front of the Mini Extra is to the right in the photo, and the output shaft of the servo is AWAY from the front of the fuse.

Again using Foam Tac, I glued the rudder to the vertical stabilizer. Foam Tac really does make a great hinge material on this EPP foam! The top half of the vertical fuselage was glued to the airframe to complete the Mini Extra fuselage.

After test fitting the C1822 brushless outrunner motor to the mount, I marked the ‘up’ on the mount to make gluing it in place easier. I used the ZAP-A-GAP Medium CA and Zip Kicker to glue the ply motor mount to the nose of the Mini Extra, but Foam Tac was used to glue the quarter-round motor mount gussets in place behind the motor mount. There are a total of eight gussets, making just enough for two per section of the motor mount.

The control horns were removed from the light ply sheet, and glued into the elevator and ailerons. If you’ll notice, there’s a slight difference between the elevator horn and the aileron and rudder horns. The flat edge of the elevator horn butts up to the carbon fiber strip previously installed in the elevator.

I bent the pushrod adjustment “V” into half of the eight music wire pushrod ends, and attached them to the four carbon fiber pushrods with ONLY the heat shrink at this point. Two of the other four pushrod ends were connected to the aileron control horns, then attached to the carbon fiber pushrods with ONLY heat shrink again. I temporarily connected my Hitec Minima 6L receiver to the aileron servo and powered up the Aurora 9x and receiver. with the ailerons and servo centered,  a drop of medium ZAP-A-GAP medium CA was applied to the pushrod ends at the heat shrink, and set with a quick shot of Zip Kicker.

The rudder control horn was installed, followed by the elevator and rudder servos. The elevator and rudder pushrods were assembled and installed in nearly the same manner as the aileron servos, with one additional step – a pair of light ply standoffs were slid onto each of the pushrods prior to installing the pushrod end at the elevator and rudder control horns. These standoffs were pushed into the EPP foam fuselage and glued in place to provide some rigidity for the otherwise unsupported pushrods.

I installed the motor permanently, changed out the prop saver screws for a pair of screws that were a bit longer – Jim also has these for sale, but you’ll have to contact him directly to get them… The propeller had to be drilled out with a 13/64″ drill bit to fit on the motor’s prop adapter, and one of the “Ten for a Buck” prop savers attached the propeller to the motor.

In the photos above, you can see that the ESC and receiver have been installed on adhesive-backed Velcro. I poked three holes in the wing, and ran the receiver antenna through to keep it in place. Also, you can see the tail stiffeners in great detail in these photos. The motor and ESC wires are permanently soldered together and covered with heat shrink – no bullet connectors needed! A long narrow piece of Velcro was stuck on the lower right side of the fuselage for the flight battery. I left it long so I could move the battery around for balancing. Speaking of balancing, the CG is right on the carbon fiber strip that was previously glued into the wing – That makes for an easy location mark! I was able to move the 2S 300 mAh LiPo battery around to get the CG perfect! All up weight for the Mini Extra came in at 3.25 ounces with the flight battery installed, which seems to be a pretty good target weight for this plane. Jim said his weighed 85 grams (three ounces) without the battery. Mine tipped the scale at 76.5 grams (2.70 ounces) without the battery, so I’m feeling pretty good about the weight!

Photo Shoot

Flight Report

Well, after weeks of extra snow in April, and a month of rain in May, June finally gave way to a few days of decent flying weather! My good friend and video pilot, Jim Buzzeo and I got to the field ASAP and FINALLY flew some review planes… Though the sky was a bit hazy due to some wildfires in Canada, the wind was light enough to fly, the sun was shining, and it was a warm evening – After months of snow and rain, a nice day was warmly welcomed!

We readied the Mini Extra for flight by turning on my Hitec Aurora 9X, attaching the 2S 300 mAh battery to the Velcro, and connecting the battery to the ESC. A few seconds later, the Minima 6L receiver was linked to the transmitter, and it was time to fly! Though there are now landing gear available for the Mini Extra, we didn’t have them for testing. The Mini Extra is very easy to hand launch, though, and required just releasing the plane at more than half throttle!

The little plane flew away briskly, but the 6×3″ propeller keeps the top speed low. a few clicks of right aileron and up elevator had the Mini Extra flying straight and level. Now, because this type of plane is nearly indestructible, my normal ‘two mistakes high’ rule didn’t really apply – besides, at this size, two mistakes is still only about 20 feet in the air!

Testing started with a little high and low speed flight – as I mentioned earlier, the 6×3″ prop keeps ‘high speed’ to a minimum. It will accelerate quickly but she’s definitely not a pylon racer….  Low speed is also a bit of a non-issue. Sure, you can slow the Mini Extra down enough to stall it, but the plane doesn’t seem to really notice it isn’t flying – you just have to give it a little throttle, and the plane starts flying again. Even if you stall it close to the ground, it just falls to the ground. It’s not a big deal – just pick the plane up and fly it again!

We were on to testing aerobatics. Yep, the Mini Extra can do almost anything you mind can dream! Seriously, there’s enough throw on high rates to practice any 3D maneuver you can think up, and on low rates it’ll do sport aerobatics all day long – That’s why I said you’ll want a bunch of batteries for this plane – you’ll never want to quit flying!

We actually ran out of battery power before we were ready to land. Thankfully, the Mini Extra was close by, and close to the ground. The plane just sort of dropped a few feet to the grass near the end of the runway. Because of the EPP foam, the plane wasn’t damaged in any way, so the battery was replaced and the Mini Extra was flying again! Flying time on the 2S 300 mAh LiPo was around 8-10 minutes with throttle management, and was a lot of fun. This time, we decided to land with some power remaining. The extra was brought in close, and the throttle was pulled back. The Mini Extra dropped into the grass nicely, and was done flying – yes, it was that easy to land!

Check out the RA Cores Mini Extra in action!


I have had three of Jim’s RA Cores planes – the 32″ Yak 55, the TwoFo (Twin Blufo), and now the Mini Extra. I liked the TwoFo, and I really like my larger Yak 55, but I’m really loving this new Mini Extra! Its small size will give me an indoor airplane this winter, but it’s still got enough power to be flown outside. The Foam Tac glue and ZAP CA make  it really easy to assemble this plane, and the required electronics are readily available – you can even get most of it from Jim! This plane is economical to assemble and fly, and is a total blast in the air. Go out and get yourself one of the new Mini Extras from RA Cores – you’ll be glad you did!

Contact Information

RA Cores:   www.racores.com

Hitec:   www.hitecrcd.com

ZAP Adhesives:   www.franktiano.com/zap-adhesive




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