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buzzltyr
09-06-2006, 04:29 PM
Brian Eberwein at Mountain Models/Laser Arts was kind enough to offer me a beta kit of his new J-3 Cub. I'm always excited to have a new project, and even better, a new scale project, to tackle. http://static.rcgroups.com/forums/images/smilies/biggrin.gif

This one is a little larger than the usual MM kit, with a 48" wingspan, and 332 sq in. Weight on Brian's alpha is 12.6 - 13.4 oz depending on the battery, with a wingloading in the 5.5 - 5.8 oz/sq ft range. The model is obviously light enough to be flown with a lot of different power systems, from small outrunners to geared inrunners. I haven't picked a power system yet, but have a couple of GWS Pico servos for the ailerons, and a couple of Hitec 55's for rudder and elevator.

Brian has been terrific about getting me started, and answering a ton of emails. Keep in mind that this is a beta, being built without plans or a manual. I'm sure that production kits will have some changes as Brian tweaks the design, so future builders should note that their kit may vary slightly from my build pics.

The first pic is the obligatory shot of the contents of the kit.

Mark

buzzltyr
09-06-2006, 04:32 PM
Because nothing screams "J-3 Cub" to me like the tail feathers, and because I knew they'd be easy to do, that's where I started. Everything, of course, is laser cut, out of quality wood. Part's fit was smooth and tight.

Mark

buzzltyr
09-06-2006, 04:37 PM
The fuselage was next. The center area formers are tabbed/slotted into one of the sides, glued (hopefully perpendicular to the fuselage side), and then the other side added. The cabin top is also inserted at this point, creating a sturdy "box" in the center of the fuselage. The other formers are then put in place. The very tail area is sanded, using laser-scribed lines, so that the fuselage sides mate nicely. Everything is tabs, slots, and laser cut joints, so building a nice straight fuselage should be an easy task.

More to come later!

Mark

Twmaster
09-07-2006, 01:30 AM
Darn it! Now I will have to buy yet another kit! (when available)

Nice, I'll be watching this thread.

buzzltyr
09-07-2006, 02:18 AM
Mike,
Buy one. You won't be disappointed. Even though it is a pre-production kit, it's a lot of fun to put together.

Mark

buzzltyr
09-07-2006, 10:01 PM
The fuselage build continues with the rest of the formers, sanding the rearward tail area, and mating the ends of the fuselage. Here's a pic of the rest of the formers installed.

Mark

buzzltyr
09-07-2006, 10:04 PM
Here's a pic of the basic fuselage completed, from the top. Looks pretty good to me! http://static.rcgroups.com/forums/images/smilies/smile.gif

Mark

buzzltyr
09-07-2006, 10:06 PM
Next the cabin sides are installed. Easy to do with everything tabbed, slotted and laser-cut joints. It's starting to look like a J-3!

Mark

buzzltyr
09-07-2006, 10:08 PM
To finish up the basic fuselage construction, the tailpieces are installed along with the fuselage longerons on both sides and the top. There are also side longerons that stick out from the side of the fuselage, to give the appearance of the original's structure. The second picture shows the detail of the tail area. If you enlarge the picture, I think you can see the side longerons.

I forgot to take a picture of it, but the nose area forward of the dashboard is sheeted with some 1/32" balsa.

Mark

buzzltyr
09-11-2006, 12:36 PM
The wing consists of a three piece main spar and a two piece rearward/trailing edge spar. Probably the most complicated part of the whole build (according to Brian) is the center section of the wing, which is built up first on the main spar. A very small amount of dihedral is built into the main spar. The wing is built as a one piece unit.

Mark

buzzltyr
09-11-2006, 12:37 PM
After the leading edge area of the wing is built, the center trailing edge section is built and added.

Mark

buzzltyr
09-11-2006, 12:39 PM
Now the rest of the ribs are added to the wingtip. The horizontal part of the leading edge is now installed. Other than the center section, I haven't glued anything else together yet.

Mark

buzzltyr
09-11-2006, 12:41 PM
The vertical part of the leading edge has been added, as has the trailing edge piece between the aileron bay and the center section, and the wing tip.
If you look at the picture, you can see that the third rib from the tip is a little thicker just aft of the main spar. That's two pieces of 1/64" ply that are glued on either side of the rib to provide the aileron servo mounting area.
The aileron servos are hidden inside the wing. These pieces should be glued onto the rib prior to installing that rib. Also, cap strips top and bottom complete the main spar, giving you a very sturdy wing. The wingtip consists of two pieces which slot into the outermost rib, the main spar and the rearward spar that also makes up the aileron bay trailing edge. Piece of cake!

At this point I glued up all the ribs, wing tip, trailing edge, etc.

Mark

buzzltyr
09-11-2006, 12:46 PM
Here's a pic of the wing with the aileron servo installed, a second pic of the ailerons built up, and a pic of the wing with an aileron in place. The ailerons have a ">" leading edge, so they will be CA hinged. Because I used GWS Pico's for the aileron servos (with their short leads), it looks like I will be using 24" servo extensions through the wings.

Mark

buzzltyr
09-11-2006, 12:46 PM
I am not a particularly quick builder. While I did not keep close track of my build time, up to this point I would say I am at 8-9 hours, for all of the major subassemblies (fuselage, tail feathers, wing). The wing struts consist of just three laser cut pieces, so that should be a five minute job. Overall, a very fast and straightforward (even easy) build.

Mark

buzzltyr
09-13-2006, 12:44 PM
A llittle more progress to report. The first is the landing gear and the rudder with the tailwheel wire installed. Brian provided the full size pattern for the scale gear. It was bent up from 1/16" wire, and secured with lashings of Spiderwire and thin CA. I have used this technique on models weighing 2 1/2 to 3 lbs, and have yet to have the gear fail. The tailwheel wire is simply epoxied in place.

Mark

buzzltyr
09-13-2006, 12:45 PM
The wing struts were assembled in about two minutes. http://static.rcgroups.com/forums/images/smilies/smile.gif

The rudder and elevator servos were installed, based on the location provided by Brian and his experience with the prototype. I used a Dubro Parkflyer guidetube/wire set as I had it on hand.

Mark

buzzltyr
09-13-2006, 12:49 PM
With all of the major subassemblies done, I thought it would be time to see what the airframe weighs. The weight shown includes all the balsa plus the four servos (two Picos and two HS55's). 6.125 ounces. I think Brian's weight of 13-14 oz. is very reasonable, depending on the motor chosen and the rest of the scale bits. At 332 sq in, I think this model could easily be converted into rubber free flight. http://static.rcgroups.com/forums/images/smilies/biggrin.gif

Mark

buzzltyr
09-13-2006, 12:51 PM
Because no build thread is complete without the "in the bones" pictures, here are two of the assembled model. Time to start covering. It certainly looks like a Cub! Brian told me over the weekend that he hopes to be able to get me a prototype cowl this week.

Mark

PerlAddict
09-13-2006, 03:24 PM
Really cool build thread! Can't wait to see what it looks like once it's all finished up. =D

buzzltyr
09-13-2006, 04:45 PM
Can't wait to see what it looks like once it's all finished up. =D

Hi PerlAddict,
Me too! I'm anxious to get this one finished up and in the air. It really has a nice presence, due to the 48" wingspan.

Thanks for posting, btw. I was beginning to think that no one was looking at this thread.

Mark

PerlAddict
09-13-2006, 05:45 PM
Oh no, I'm definitely keeping up. I just am new to the hobby and have absolutely no idea where to even start to talk shop on kit building. :D But being new, it's nice to see a detailed journal of a build with lots of photos along the way to get a better idea of what goes into a project like this rather than just, "Here's what it looked like when I got the box, here's what it looks like all finished." I certainly appreciate all the time and effort so far in your updates. Keep up the good work! =)

- Dave

dmmalish
09-13-2006, 09:44 PM
i love the j3's always have do you have a link for this kit??

buzzltyr
09-13-2006, 10:40 PM
Dave, thanks again. This one is a pretty easy, straightforward build. It could be a first balsa build if you took your time. Because this is a pre-production kit, I don't have instructions, etc. I built the MM/LA P-51, and the instructions were detailed and excellent, so I have no doubt that the instructions for this kit will be of the same caliber.

dmmalish, the kit is not yet available. But it should be very soon. You will be able to find it at mountainmodels.com when it is in production.

Mark

dmmalish
09-13-2006, 10:45 PM
look like reasonable prices on there kits how does the p51 fly and what are you using for a power system on that? thanks
dave

Twmaster
09-14-2006, 01:31 AM
Mark, I too am following your thread. Please keep the updates rolling. I will be ordering this when offered by MM/LA.

She's looking like a Cub! :D

buzzltyr
09-14-2006, 02:12 AM
dave, here's a thread I started here on my P-51, with the power system, etc.:
http://www.wattflyer.com/forums/showthread.php?t=4403
In terms of flight characteristics, it is a parkflyer, but also definitely a warbird. It likes a little speed. You can also look at rclark's thread, to see his thoughts on the P-51.

Mike, thanks. I think this one will be a great addition to the MM/LA line of kits. A little larger than their other models, but very lightweight and still a parkflyer.

Mark

PerlAddict
09-14-2006, 02:56 AM
That is one cool lookin' plane!! I'm a huge fan of warbirds and trying my very hardest to patiently wait as I learn to fly before buying one. But man oh man ... so pretty! Dad is a massive fan of retracts, too.

I want one! :D

buzzltyr
09-14-2006, 02:12 PM
I want one! :D

Then you should get one! :)

Mark

buzzltyr
09-14-2006, 02:18 PM
After I got the fuselage covered, I made a battery hatch, hinged with tape. I installed the tail feathers, and then glued together the two balsa blocks to make the vstab/hstab fairing, and installed those. A little covering, and it looks pretty darn good!

Mark

buzzltyr
09-14-2006, 02:19 PM
Here'a a pic of everything covered, and ready for all of the final install and set-up. I probably have another 7-8 hours into the build to get to this point.

Note the 36" ruler in the pic to provide some sense of the size of the model.

Mark

buzzltyr
09-18-2006, 11:43 AM
Brian provided me with three motor mount options. There is a stick mount, a short outrunner mount (for radial mounting) and a longer outrunner mount for front mounting outrunners.

I decided to use my 400XT and the short outrunner mount. The 400XT was sitting idle, so this seemed like a good model to use it in. Based on data gleaned from the threads on the motor, an 8x3.8 APC SF prop should give me just under 100 watts on a 3S battery, at just under 10 amps. The motor had a Phx25 already connected to it, so that's what I will use as the ESC.

Mark

buzzltyr
09-18-2006, 11:44 AM
I cut my axles too short, so I had to find some other wheels to use. I had some 2" MPI spoked wheels sitting idle, so I decided to use those. But, they just looked plain ugly, and not at all Cubbish.

So I cut some heavy bond paper to just over the plastic rims, painted them black, and glued them to the wheels. I used a penny as a template, cut two circles, painted them yellow, and glued them to the black paper disks. Not terribly cublike, but close. I also cut a couple of landing gear fairings out of 1/32 balsa, covered them and taped them to the landing gear.

buzzltyr
09-18-2006, 11:47 AM
Wednesday the mailman brought me another package from Brian: the cowl and engine details. Some fast scissoring, some painting and some glueing, and it's a Cub cowl. http://static.rcgroups.com/forums/images/smilies/biggrin.gif The plastic pieces are just beautiful. I wish my painting skills were equal to their detail.

That pretty much takes me up to final assembly. I have some graphics to install (thanks, Callie!), and then it's time to get her in the air. I'll post "completed" pics and my final AUW when I get to that point.

Mark

buzzltyr
09-18-2006, 11:49 AM
I finished putting the Cub together Thursday night, including the graphics.
Friday morning, early, I was on my way to NEAT. I got back Saturday night. Here are some pics of the completed MM/LA Cub sitting on the NEAT flightline.

Mark

buzzltyr
09-18-2006, 11:51 AM
I decided not to fly the Cub at NEAT. Just too much traffic for me to fly a maiden there.

So, I took her out yesterday morning, and the J-3 flew just fine. http://static.rcgroups.com/forums/images/smilies/biggrin.gif My final AUW, without battery, is 13 oz. With battery, it's 15.5 oz. This gives me a wingloading of right around 6.75 oz/sqft. The model flies very slowly, and is still very manueverable. Slows to a crawl to land (although I did tip her over on landing, but in thick grass). With my 400XT, most of the flight was at 1/3 power, maybe 1/2 power at take off. The 400XT is probably twice the power needed to fly this model.

I do have a wing warp issue I need to take care of, caused in part by one of the wing struts being a little too long. Brian has advised me that he has already adjusted the strut length, as he found a similar issue. As a result of the wing issue, I did need some left aileron trim to get her to fly straight and level. But after that, it was just a blast doing lazy 8's around the soccer field. I can envision flying this model 3-4 feet off the ground, doing just circuits and 8's for the entire flight. I'm no Cub expert, but I do think this model looks very scale just cruising around.

My setup for the maiden was:
Esky 400XT
Phx 25 (not necessary, but I had it on hand)
Hitec 05S receiver
PQ 3S 1100 battery (old, heavy 8-10C)
APC SF 8x4.3 prop

In terms of other set-up, I did put in aileron differential at a 60% level, and I put in 15% rudder-->aileron mix. After the flight, I decided to increase the R-->A mix to 20%, and I don't think 25% would be excessive, but I'll work up to that level, just to see the effect.

All in all, I'm very pleased with the way the model flew, and with its performance. Once I sort out the wing issue, it should be a hands-off flyer.
The wing issue, btw, is my fault, as Brian had told me I would need to adjust the strut length, I just didn't take out enough, which caused excessive washout in the right wingtip.

I also have to say that at the 48" wingspan, this model has a wonderful presence in the air.

I hope Brian will be able to get this model into production soon, so other builders can enjoy the J-3.

Mark

Twmaster
10-05-2006, 01:30 AM
Oh that is just gorgeous! I want one. NOW!! ;)

I was just on the MM/LA web site and didn't see the Cub yet....

:(

buzzltyr
10-05-2006, 02:23 AM
Mike, the last I heard from Brian, he was finishing up some tweaks of the design, the manual, etc. I fully expect it will be available within a week or two. Be patient, it'll be worth it.:)

Mark

Twmaster
10-05-2006, 02:25 AM
Patience? Wazzat?

;)

--
Mike N

buzzltyr
12-01-2006, 11:29 AM
Brian at mountainmodels.com has put the 48" J-3 Cub up for sale on his website. There have been a number of changes to the kit since my beta build, making it even easier to build. It now has a more scale vstab/rudder as well. Brian sent me the manual to review, and it is very detailed and complete.

The details on the kit and recommended equipment can be found here:
http://www.mountainmodels.com/product_info.php?products_id=472

I'm attaching the "glamour shot" of the model.

Mark

Flyingace451
01-09-2007, 11:32 PM
I want one...ugh I even have a 400XT wanting a plane. Too bad I don't have a job...this one will have to wait.

Turbojoe
01-23-2012, 12:15 AM
This is such a sweet plane I gotta help get the word out. This is a cut and paste of my MM J-3 Cub maiden post on RC Groups:

This is gonna be long winded. Sorry.....http://static.rcgroups.com/forums/images/smilies/redface.gif

I've gone way too long without flying and just had to make it happen. I haven't flown anything in about a year and was getting antsy. I charged the TX, 2 2S 1000mah and 2 2S 1300mah packs and loaded up the Cub. I went to the local water retention bowl that has a huge flat bottom with close cropped grass. Just perfect for flying. Naturally that area was being used by the cricket players today. Cricket? C'mon, who plays cricket other than Brits. http://static.rcgroups.com/forums/images/smilies/rolleyes.gifhttp://static.rcgroups.com/forums/images/smilies/mad.gif That meant I had to fly in the lot above that is crushed gravel and rutted dirt. Less than ideal but what the heck. I wanted to fly!

I don't get nervous during maidens even after this long without flying. Then again I fly mostly Mountain Models. I KNOW the plane is going to be right from the start and I was NOT disappointed!

I went with the 1000mah pack for the maiden even though the CG was at the rear of the spar with this light pack. I prefer a rearward CG on everything anyway and wasn't too concerned about it. There was zero wind so I just pointed her down the least rough section of ground and very slowly advanced to about half throttle. She lifted her tail and broke ground just as scale as you please. Gave me goosebumps it was so sweet. No trim changes needed at all during climb out. On the 1000mah pack I flew 13 minutes before changing packs. On the 1300mah pack I flew 16 minutes. Between those two packs I realized I haven't lost my touch and go mojo. I shot no less than fifty 1 wheel, 2 wheel and 3 wheel touch and goes. Every one a thing of beauty and was exactly what I was trying for each time. A testament to the flying quality of this bird and not my flying skills.

I realized after changing to the heavier 1300 pack that she flies better just slightly nose heavy. Less tail drop in turns. She likes a lot of aileron throw and a pretty good bit of rudder/aileron mix for those really pretty coordinated turns. Aileron rolls are ugly because of all the rudder mix I have but I'm OK with it because this isn't an aerobatic bird. This is the best laid back, no stress, cruise around, touch and go bird I have. I knew it would be nice but I wasn't expecting it to fly THIS good! I may go ahead and get the clipped wing for her but I don't know, I'm just so happy with her as is. Wish I had flown her when I finished the build months ago. Stupid me. http://static.rcgroups.com/forums/images/smilies/frown.gif

Joe

Dereck
01-23-2012, 04:53 PM
Hi Joe

Cricket in AZ!!!

Did it start to rain halfway through the game? That's usually what happens in English cricket matches. Some say it's not really a sport, it's more an ancient religion's rain dance ;)

And, of course, as seen on tea towels and cook's aprons across the land (England, that is ;) ):

http://intermain.org.uk/john/what_is_cricket.php

Good to hear the little Cub's still flying. I haven't been able to get out much - maybe six flying sessions last year, so I can sympathise with you. Having built three other RC Cubs - GP's E-Cub and Sig's 1/5th J3 and 1/6th clipwing - the idea of a smaller, handier Cub appeals, and MM have always done great kits.

Years back, went to a full size fly-in in VA and saw a J3, well the military L4 version, do 'aerobatics'. It's one roll was a sort of amiably sloppy barrel roll, so I wouldn't get fussed over yours and its rolling abilities. My Sig clipwing wasn't exactly what you'd call a 'pattern ship' either, though I don't want to look like I'm trying to put you off a clipwing ;)

Rewgards

Dereck

Turbojoe
01-23-2012, 06:27 PM
Dereck,

Yeah, it surprised the heck out of me the first time I saw the cricket players a few years ago. For a country that hasn't embraced soccer the way the rest of the world has it's amazing how many good flying areas the soccer players take over on the weekends. Luckily this Cub can fly just about anywhere.

Joe