FoamCub Swappable

[ShaunMartin]

Swappable FoamCub!

This is a thread to accompany the main FoamCub article.

Did you build it?
Did you improve it?
Did you customize it?
Did you give it an awesome paint job?
Did you build it out of Dollar Tree foam board?
Did you build it totally stock with no mods whatsoever?
Did you scale it down to 60% to see what would happen (ultramicrobe!)?
Did you smash it to smithereens on maiden?

Start a build thread or post it here!

There's at least one person (me) who wants to see what you did, and probably others.

FoamCub threads I know about:

• FKreider's build

 

[ShaunMartin]

Wishlist Item: Leading edge cuff/droop

At the top of my wishlist for upgrades to this plane are leading edge droop tips or cuffs (Wikipedia).

Due to lack of washout, a straight wing (no change in airfoil), and lack of any STOL features (except flaps), the FoamCub's stall can be a little sharp, not gradual (tenpenny_05 noted this in his comment on the main article). I'd prefer a soft, mushing stall over the current tendency to suddenly drop like a rock.

This could be done with washout, but I think the leading edge droop looks cool.

This Robin has a good-looking wing configuration.

Here it is on a Quest Kodiak (which I just flew in this weekend!).

 

[tenpenny_05]

Here I am! Hope this thread takes off! Heres a picture of my Cub, I'm trying to think of a name, the front runners so far are "Disco Cub" and "Pinky Brewster"

(Landing gear isn't complete in this picture.

Build is almost 100% to plans with the exception of a fixed dubro tailwheel ($3) and 3.5" wheels instead of 5" (supply issues)
My power setup is out of my crashed dynam peaks airplane:
650KV detrum motor
50 amp detrum esc
3 cell lipo
13x6 prop (its what i had)

The build took me less than a week, I started last Wednesday and was wheels up yesterday (Wednesday). I mentioned on the comment thread that this plane flies beautifully, stalls aren't exactly predictable but it may be attributed to my heavy build and heavy (3200mah) battery I was flying with. I think I had too much flap programmed in, but thats an easy fix. My big complaint is the landing gear didnt last for more than two landings. It may be attributed to me not using the correct materials, but I'm not familiar with "music wire" and maybe grabbed the wrong stuff.

Here is a video of my maiden, I didn't use any flaps this first time around, but it doesn't really need it for normal flying. (If you keep an eye on the right side of the screen you can see smoke from the wild fires going on in San Diego) EJOY!

 

[Montiey]

This looks nice!
is that a simple soarer tail?

 

[ShaunMartin]

It does look very similar to a Simple Soarer tail, but I think it more closely resembles the tail of a Multiplex FunCub which the plane was designed after. Here is the main article for the FoamCub.

 

[ShaunMartin]

tenpenny_05 - I replied to your comment on the main article, but I'll repeat it here: awesome job! Thanks for posting.

 

[Liemavick]

Plans are printed and all taped up to DTFB. Cutting should commence tomorrow. Only change I may make is to double up the spars and extend them out of the wing with the angle on the extended parts. I will make adjustments at some point and just have the double spar reduce to a single spar at the wing joiners. FT Spitfire has a similar design so shouldnt be to hard to duplicate.

Thanks again Shaun for the plans.

Brian

 

[OrcaSea]

At the top of my wishlist for upgrades to this plane are leading edge droop tips or cuffs (Wikipedia).

Due to lack of washout, a straight wing (no change in airfoil), and lack of any STOL features (except flaps), the FoamCub's stall can be a little sharp, not gradual (tenpenny_05 noted this in his comment on the main article). I'd prefer a soft, mushing stall over the current tendency to suddenly drop like a rock.

This could be done with washout, but I think the leading edge droop looks cool.

This Robin has a good-looking wing configuration.

Here it is on a Quest Kodiak (which I just flew in this weekend!).

View attachment 23635

I wonder if eliminating the bottom score cut and leaving it more of a flat bottom airfoil rather than a semi-symmetrical would tame the stall a bit? Also, I noticed the aft spar is the same height as the front spar, making the camber of the wing flat on the top. Was there something in the design or experimentation that led you away from a more gradual taper towards the aft? I ask because I am wondering if the extended chord has anything to do with the accelerated stall?

Also, have you tried dialing in any flaperons? I know "droop ailerons" are pretty effective full-sized STOL features for reducing outboard stall (at least when the flaps are utilized).

Love the detailed design! Great job!

Curtis

 

[thegreatpumpkin]

Just finished my cub with custom paint job by my son. Awesome plans Shaun. This was literally exactly what I was looking for a couple of weeks ago when I felt the urge to do a scratch build. I built mine out of Dollar Tree foam board (black was all they had, but seems to work just fine). I addressed the no-spar issue you mentioned in the build videos by elongating the short, v-shaped connectors that go inside the wings to about 5 inches long on each side. But it may not have needed it. The DTFB is pretty light and I am running a lighter set up. I also didn't need the beefed up landing gear with decreased weight. I think it's 3mm piano wire from the hardware store that I have on there, something I had lying around from another build. I am running an Emax 2215/15 brushless from Headsuphobby.com and an APC 8x4 prop with 30amp HURC esc and 3s 2200mah battery. I get about 35 oz. of thrust from the motor/prop combo. The motor might be a bit small but its what I had lying around. I haven't had the maiden flight yet but took it out to the alley behind my house for the taxi test and turned around into a very light head wind. I wasn't trying or expecting it, but the cub just started floating! Almost crashed because of my surprise at the unexpected take off. It only took about 10ft maybe 15ft with flaps down and it was up. Very much looking forward to a true maiden when the wind dies down around here. Thanks again for sharing the great design!

 

[Liemavick]

Looks sharp TGPumpkin, Nice work. Welcome to the forum I assembled Shauns Cub, finished most of the build last night. Electronics are next and Im looking forward to testing his design. Hopefully the wind takes a break for both of us, its been blowing here in S. Fla. for months.
Brian

 

[ShaunMartin]

thegreatpumpkin - Awesome! Thanks for the report - love the stealth/Picasso look. Please do report on how it flies. You're making me want to try a Dollar Tree build!

 

[thegreatpumpkin]

You got it. Looks like this weekend may calm down enough to fly. I'll make sure to report back.

 

[OrcaSea]

I built a hybrid, modified Clark-Y Armin wing (see how they are built here) https://www.youtube.com/watch?v=karr67ZYho4 for my DTFB Cub.

I used a main and aft aux spar (shorter, to match the slope of the airfoil) with extended dihedral spars. As you can see there are intercostal webs between the dihedral spars. I also made a larger dihedral jig with a base so it would support the wing through the gluing process. I matched up the L & R wings and, with the 'dihedral' wing supported (and the upper skins still open) I glued the dihedral spars, and then joining plates on the interior lower skin. This is where the most stress is going to be on the wing. Be aware that the spars are NOT where they are on Shaun's original design. The maximum camber on a Clark-Y is at 30% of the wing chord, so the spar, the wire access hole and the servo cutouts will all have to move appropriately.

In hindsight I would delete the full-length aft aux spar altogether, as well as the intercostal webs - it makes it difficult to apply glue to four joints - the leading edge 'joint', the main spar, aux spar AND trailing edge. Also (in a classic 'Duh' moment) I realized that I would have to cut notches in the intercostal webs in order to route the servo wires. So, I'm not certain how effective they are after notching, especially as the Armin wing is, essentially, a full monocoque design with all the stresses in the wing skins. A short aft aux spar might help support the joint and dihedral spars, so it might be advisable to put one in.


Here you can see the spars with the upper skin held down in position:


After gluing the lower skin, spars and joining plates in, I then 'shaped' the upper skin center with a dowel (as shown in the wing assembly video) and hot glued the upper skin to the spars and trailing edge of the 'flat' wing. Then after it cooled moved the dihedral jig to the other wing and repeated. I used white duct tape on the upper skin join after injecting hot glue.

Here is the completed wing:


It's light, strong, with a classic modified Clark-Y airfoil shape and should work fine for a DTFB Cub, especially as I am going to use a smaller motor with more of a 1:1 thrust/weight ratio. Be aware that after moving the wire access hole you will also need to modify the wing locating plate.

 

[cardinals1225]

ShaunMartin

Thank you for the work you did. That was an incredible build video. In the process of building it as my first foam plane ever, cant wait to see how she fly's.

Kevin

 

[OrcaSea]

Agreed, Kevin.

I've watched the build vids a number of times, and Shaun's Cub build (and supporting documentation, blogs, etc.) are the best I have seen in RC foam building, period.

This is the bar everyone should shoot for. Great job, Shaun!

 

[ShaunMartin]

You guys are very kind. I'm glad you're finding the build videos/stuff useful - man, it took FOREVER to put all of it together! Hopefully it won't take so long next time. But thanks for your kind comments.

OrcaSea - that curved airfoil is beautiful! I can tell you're a finesse builder - nice job.

Kevin - awesome! I'd love to see how your plane turns out.

 

[OrcaSea]

Shaun,

My pleasure! The SC is a class-act in all respects (the support & documentation, especially). I work in video production, and so I know what it takes, so even more respect on my part. Can you imagine trying to edit in all the close ups and various shots that they do on the FT build videos? Yeah, it's an unimaginable amount of work!

If you haven't seen Ed's videos on the Armin Wing, he is truly a huge innovator in foam board aircraft design & building. The wing is simple, effective & elegant. I use a vertical spar instead of his layered foam sandwiches (which actually bend the wrong way - with the stress!) but they are a great design.

Another thing I found myself doing lately (especially for those who like the scale or semi-scale look without the tab-and-slot construction being visible) is hiding the slots by treating the slots like 50% cuts and leaving the skin intact on the outside. I use a 6" metal scale to 'loosen' the material in the scored slots until the material separates from the exterior 'skin' paper. (This is easy to do on DTFB, not so sure about Elmers - I haven't tried that). Then I shorten the 'tabs' a bit so they don't make a bump or protrude on the exterior skin (it also so it makes room for hot glue in the slot). I even did this with the Cub landing gear doubler on one side (I considered both sides, but it's hard to fit the doubler otherwise when gluing the last fuse side in to place). That way if you are into the external finish and plan on painting or covering you don't have the slots & tabs to deal with - a nice smooth exterior skin

I'm really excited about seeing the Cub come together! GREAT job, Shaun!!

PS - have you considered what other planes the high-power swappable might 'swap' with? Have you tried it on the Spitfire or Mustang? Do you have any other projects stewing in their own juices yet? Eager to see what else the Martin Design Bureau comes up with next!

 

[Latubi]

Here's mine, flies great!

 

[Foam Addict]

How well would this fly on say a DT-750?

 

[Latubi]

How well would this fly on say a DT-750?

I tried a dt-750 and 12x6 prop. It's a bit lazy with 3s but 4s gets it up in the air nicely! I'm using 3000mah both but, I just don't know where to stick the battery