OK, so I was thinking about my 3rd foam scratch built and decided I wanted to do something different. I wanted something different from the numerous Yaks and Extras so I decided on MX Aircraft's new MXS (debuted this year in the Red Bull Air Series). At first It was only going to be a shocked profile foamy but I decided to up the bar and make a full fuse version with airfoil wings.

I started with the 3-view that I found at the MX Aircraft website under the specifications and drew up some plans from there. You can see here the original 3-view and my design 2-view.

In addition I have documented the start of the build with pictures of the paper templates and some of the cut parts. Also the first assembly which is the fuse crutch assembly (6mm Depron) is depicted.

I have a busy family life with 3 small children so I only get to build a little every day after they go to bed so I will be posting progress as I go on this thread.

Enjoy!

- Birger

Edit: I have posted preliminary plans, if you have a few scratch built foamies under your belt and would like to try this one you can find them in post #43.

Nice choice, looks like it should fly well will be watching this with interest
Hugh

Very nice drawing and build, Birger. I am very impressed by the crutch assembly, it almost looks like those laser-cut balsa structures!
What's your expected AUW and what power system are you going to use?

Currently I have not calculated the AUW, I'm kind of making it up as I go along. I am hoping that it will come in somewhere between 14oz and 18oz but time will tell. My first thought process is to have a Hacker A20-XXL which is specked for 3D up to 19oz (whether this is true or not I can't vouch for) and for sport up to 28oz. I'm mostly a sport flier though I'm starting to get into 3D. I do have a profile foamy (Tim Hart's Shocked 3DX) so if this one turns out to be a sport flier I will still have a 3D option. For now I am more interested in foam and foam construction techniques as well as the advantages of e-flight. I am coming back to the hobby after several years off to raise a family and this is all new to me. I was an old balsa and nitro flier before.

- Birger

Birger,
14~18oz. (400 to 500g) certainly seems doable but you'll have to be careful when choosing the power system - most likely the LiPo will account for approx. 100g. So I am guessing you'll end up nearer to 500g. The Hacker is a good choice.
I recently built a smaller monoplane with similar looks, the Owl-RT which you can see in my blog here at RCGroups, using 3mm Depron. With a 31.7" WS it ended up just shy of 10oz.
I noticed you are being very careful to carve out your crutch parts; when building the Owl-RT I found out that this is not really required, as Depron foam is extremely lightweight, so weight saving are minimal and the parts loose some strength. It does look good though.
There is a thread here in this forum with the title "Depron tips and tricks" or something like that, you may want to take a look at it.
Good luck with the building and keep us posted, I'll certainly be following this thread!

Not that much "building" happened yesterday but a fair amount of cutting. Got the wing skins and most of the fuselage components cut out. That only leaves control surfaces and doublers to cut, maybe Monday night I will get that done. After that I will continue with assembly. No work tonight since I will be getting ready to go flying tomorrow.

- Birger

Well, I'm done for the day but the football game is not over so I figured I would post the update tonight while I was watching instead of tomorrow.

Finished cutting out all the parts tonight so we are now down to assembly and setup .

For most foam to foam assemblies I like to use Ultimate RC Foam Glue. I like the work time, the flexibility and the bond strength. The down side is the dry time which should be at least 12 hours before stressing the joint. My build schedule is ideal for this since I can only get in a couple of hours a day anyway (no marathon single day builds). Unfortunately for you people reading this thread progress may be pretty slow and you will only get a little progress at a time .

OK, back to the build, when I was done with the cutting I started by attaching all the doublers to the fuselage sides. This includes the strengthening of the wing mount area as well as all the top and bottom joints.

One last note, I have radio gear on order for this plane, unfortunately it is currently not in stock so at some point in time the assembly may have to be put on hold until that gear arrives.

More to come soon.

- Birger

OK, so there hasn't been too much progress but there are valid reasons for this:

Both of my current planes went out of commission last 2 weeks ago and I was out of town last week so the little time I have had available I have spent working on my main plane and soon I will work on my secondary plane. In addition, I'm still waiting on radio gear for this plane so there is only going to be so much I can do before it arrives (late November I'm told ).

Nonetheless here are some pictures of the few things I have worked on.

- Birger

P.S. one more piece of bad news, my camera broke (not the camera itself, just the LCD but I still can't use it). I need to see what I will be doing about this but it may be a while before I can post new pictures (or at least centered pictures).

Off topic rant: I have had several Sony digital cameras in my life and they have all been great. They have some kind of shield on top of the LCD to protect it and never had a single LCD break on me. Unfortunately the rechargeable battery on my previous Sony camera finally kicked the bucket and the replacement was just too expensive so I figured I would buy a new camera. I found a great deal on a manufacturer rectified Kodak camera and as far as things go it had been working very well and I was pretty happy with it, it seemed a little lighter than my old Sony's but nothing to be concerned about. Then one day with the camera in my pocket I leaned over the edge of my workbench and heard a crack, there went the LCD. I was flabbergasted I hadn't really put any weight on it. I went to look for replacement LCD's on the internet figuring I had the know how to replace it myself if I could find the spare. Sure thing, I found spares, at 80% of what I originally paid for the camera (plus shipping and handling). My next thought was to find a used camera on eBay that I could scavenge the LCD out of, even a broken one would do. I literally found dozens of them on eBay, most of them broken or more expensive than my original purchase. Every single one of the broken ones had... you guessed it, a broken LCD. I wish I had looked into this earlier but for what it's worth this was my first and last Kodak camera, I now clearly know that it's more important for me to have survivability than tons of features. I guess I will probably end up looking for a new Sony camera.

Hi again,

I believe that I will have radio gear and a new camera as soon as next week so I will be able to post new build updates then. Also, with everything I need in hand I will hopefully will be flying within a couple of weeks.

For now I have been playing with the decoration scheme and this is what I have come up with. Still needs to be tweaked but it's a start .

- Birger

Birger,
Just my $0.02.
If you test your wing spar you'll probably notice it flexes somewhat, even though you used CF strips on top and bottom. This is because you have oriented your CF strips horizontally, parallel to the loads the spar will bear, and the vertical Depron (even 6mm thick) is a too soft material compared to plywood, balsa or spruce. Depending on the wing skins, final AUW and intended flight envelope, this may or may not be a problem.
In the case of my smaller, lighter Owl-RT I found that the Depron spar was not strong enough to prevent the wing from flexing beyond acceptable limits. I ended up with a sandwich of Depron and spruce.
If you test your wing spar and decide to reinforce it, I have found that 4mm balsa "walls" (vertical grain) provide a lot of strength for negligible added weight. 3mm plywood is even stronger but heavier. Square spruce (8x8mm in my case) is the simplest and cheapest solution but I noticed you have a tapered spar so in your case I don't think it fits the bill.
Paint scheme looks great, btw.

Hi ADB2,

Thanks for your comments, I designed the wing spar using principles I learned when doing composites manufacturing (carbon, honeycomb, carbon sandwiches). It works under the theory of an I-Beam, strong top and bottom, compression resistant middle. I know Depron does not have the best compression characteristics so I was curious to see how the spar would perform in static tests. I clamped one end to the granite bench in my kitchen and loaded the other end with some heavy weights I had around. I got about 6mm deflection on about 20Kg of weight. I believe that this should be fine for what I need but if I do sense that there is too much wing flex I will go ahead and sheath the Depron foam in the next one I build with some balsa to add to it's compression strength.

On a completely separate note. I looked hard at my graphics design and decided to add some more variety to the overall design so I made some small changes, results are attached.

- Birger

P.S. I got my camera so hopefully I will be posting some more build pictures this evening.

6mm flex with 20kg weight sounds more than strong enough!
I like the new paint scheme design on the tail, it looks really good!

Well I promised pictures so here are the first batch:

I completed the gluing of the fuselage sides to the crutch assembly a few days ago, this included the insertion of the vertical tail element. After that I moved on to the firewall; the crutch assembly had a Depron firewall at the front. This firewall has been sheathed with 1/16" lite ply on both sides (one piece on the front, two pieces on the back to clear the main crutch member). Once these were glued in place the firewall-fuselage skin junctions got balsa triangle doublers.

Next I moved on to the landing gear; I had some RC Foam, Mini Electric Plane CF landing gear lying around so it seemed to be a good match for this project. I quickly drew up a ply reinforcement design and integrated the mounting into the second bulkhead. In the pictures you can see also an external ply doubler to strengthen the Depron. All the ply pieces are 1/16", inside there are two on each side, the inside (not visible ones) have groves cut into them to accept the CF gear and give the assembly the necessary strength. Next time I will probably cut the external doublers from 1/32" plywood, the 1/16" seems a little overkill now that it is installed. One last note on the gear, it is still missing balsa triangle stock doublers, the inside ply pieces will get the exact same treatment as the firewall.

The final set of pictures in this batch show the gluing of the canopy and the top rear of the fuselage, it is currently on my bench drying.

More to come soon,

- Birger

Here are some more quick updates and pictures

closed the fuselage, both top and bottom; mounted the steerable tail wheel and I am currently working on all the hatches. There are three hatches total, the servo hatch is under the wing and is now complete. The receiver and ESC hatch are below the crutch assembly on the bottom side of the plane (in order to leave the space for the batter clear, this will let me use different batteries and easily change the CG without anything getting in the way. That of course means that the battery hatch will be on the top side of the airplane and will go from behind the firewall to in front of the canopy.

Next I will move onto the wings. I am about to glue the trailing edges but I'm still deciding if I will insert a few Depron ribs to help with the wing shape, maybe a few, will see. Since its Monday Night Football today I will probably get a long evening of building in so hopefully the wings will be drying by the end of tonight.

My plan is to have the plane done by the end of the week, let's hope everything works out OK.

- Birger

Second update today, previous one was actually for work done over the weekend.

So I played hooky from work today (actually had to babysit my youngest) so I had some time to do some work. I concentrated primarily on mounting the rudder and tying in the tail wheel. Once I was done with that I completed the wiring and cleaned it up. Finally I applied some more decals. All that remains to complete the fuselage are the two final hatches, wheels and wheel pants

I will be working on the wings tonight.

- Birger