4ch. FT Mini Speedster ala Kens CAD Models style

Updated 18-NOV-2014 -  Added ailerons and added video

Just could not pass up the FT Mini Speedster. Had to build one, but then I am not a fan of DTF. It is not a bad product, I just do not like how the edges finish up, along with the added weight of the paper.

The engine cylinder details really add a nice touch to this build.

I wanted to get away from the card stock cowl and turtle deck as well. These things do not last as they tend to be sensitive to moisture.

So here is my stab at it. All MPF (Model Plane Foam). The fuselage outside is one piece of MPF sheet. The wings have the airfoil baked in, and I went with a straight dihedral wing. Replaced the mini motor pod with a fixed motor mount.

The landing gear concept was retained as I have never tried this method and found it to work very well.

Regardless of the changes I have made, Josh is selling these kits for $15. That is an exceptional bargain. Kudos to him and his crew for keeping the cost down.

Here are the specifications;

Wingspan 20.25"
Length 17.75"
Motor 1811-2000kv 10g
Propeller 7 x 3.5 GWS
ESC 6A Turnigy Plush
Servos 3.6g Hobby King units (Rudder and Elevator) and 5g HXT500 (aileron)
Receiver Orange Rx 410
Battery 300 mAh 2s
AUW 100g for 3 channel and 115g for 4 channel.

The 10g motor is more than enough in this model.

Ken :)

I made both wing styles to see what I liked best, and did test fly both. They seemed very comparable to one another and indoors one had no decided advantage over the other. They both look good.

There are a couple of concepts that I love to employ with MPF;

1. Bending - 

The fuselage is made from a single piece of foam and to accomplish this you need to be able to bend and shape the material. DTF is much too stiff to accomplish this with the paper on, hence the "A" and "B" folds. Not castigating that method, but as you get experience you want to learn new and more advanced techniques that challenge and hone your building skills.

In order bend this design from a single piece of foam (BTW, DTF material is very moldable without the paper and also very light. Lighter than MPF) I had to add some reliefs on the inside to allow the front and rear ends to transition to flat from round. This was the most challenging part of this process and also the most difficult piece to assemble. I made one scrap one before getting this one. 

2. Baking - 

This process allows you to permanently set the foam to a preset shape. This involves a simple jig that is easy for anyone who can build a model to make. Mine is made from some plywood and aluminum sheet. Flashing material from the home stores is suitable for this.

Preheat your oven to 200 degrees F. Also preheat the mold for 10 minutes. Place your foam part in the mold, clamp shut and allow it to bake for 10 minutes. When done, remove from the mold and allow to cool. It cools very fast. Then repeat the process if you have or need more than one. NOTE! you may need to test the temperature on your oven. If the oven gets too hot, then the foam starts to melt and shrink. Too cold and it will not hold its shape. Our previous home oven had some thermostatic problems which led to inconsistant temperature holding and I did have a few failures years ago.

I use this process for baking wings primarily, but have also baked fuselages on occassion. For this build it was only used on the wing.

I was able to leave the wing as one piece with small gores machined out to allow for the dihedral folds. Then bake the airfoil while is was flat, then fold the tips till the gore closed then glue and tape over the joint until it was dry. the Gorilla Glue fills any remaining gap and is quite light.

PDF illustration of wing bake jig

3. Machining / Folding - 

This process involves the use of cnc equipment. 6 years ago Mark and Trish Carew developed a product called the Phlatprinter. It was an economical way to aqccuire a cnc machine. I happened upon this venture on RCGroups and that led to me designing and making my own machine. Consequently, I machine nearly every design right out of the gate. I try to do all my development inside the CAD environment first. That said, here we go!

So I get this designed and have to engineer bevel folds in place of the famous "A" and "B" folds this involves programming in linear cuts with successively deeper or shallower cuts. This gives a "V" bevel feature that allows for various angle folds. The results are very clean and straight bend lines that are glued on the inside leaving no visible joint. This works for prehinging control surfaces as well.

Here the process is utilized for the FT Mini Speedster wheelpants.

Modified the straight wing in the last couple of days to add ailerons to it. Usually ailerons on undercambered wings are not the most effective. However, they were more effective by themselves than the rudder was at inducing a roll response. It was also a fainly simple mod to make. Here is  a short video illustrating what was done.

This airplane garnered a lot of attention at our indoor flying venue today. It is a smooth exceptionally stable flyer for a model of this wingspan. I would feel comfortable for someone to even learn to fly on it. I believe the 10g motor contributes to that especially well, since it is not overpowered. Too much power gets in the way for beginners.

Will post a flight video as soon as I can get someone to hold the camera.