Real Scratchbuilding a Mimi DLG

[sherchoo]

Yup... got a chance to launched this beauty yesteday and it launched beautifully. Great job Joe! I'm sure the next one will even be better.

[joe yap]

After letting the resin to cure over the weekend, it is time to see the result. First picture shows the wing panels, still in the vacuum bag, but you can see that the breather and PVC sheets are still tightly he wrapped around the them.

2nd picture shows the wing panel still in the PVC carrier sheets, but with the breather removed.

The 3rd picture shows the upper surface of the wing panel, after the PVC sheet is removed. The finishing of the wing is as good as the PVC sheet!

[joe yap]

Next, the fibreglass are trimmed and sanded to shape. The wing root are sanded to achieve the required angle. For the 3rd set of wings, we are going to reduce the dihedral to 10 degrees each.

[joe yap]

Next, the wing mounting area on the wing root are marked and the foam removed.

The 2 cavities are later filled with microballoons and the entire wing roots on both panels are applied with aircraft grade epoxy paste.

[joe yap]

I used masking tape to hold the 2 wing panels together on the bottom. The wings are propped to the correct dihedral angle and left overnight to set.

[joe yap]

The wing joint is reinforced with glasscloth on both top and bottom surfaces. I laid the glasscloth at bias orientation as well. The wing bolt holes are drilled into the microballoons and countersunk. I use M4 countersink screws for the wing attachments.

[joe yap]

I built a second Mimi. This one uses 6mm OD carbon tube for tailboom and lighter balsa for the tail surfaces. The fuselage nose is extended by 10mm, in order to reduce the need for nose weights. I also went easy on the epoxy during wing bagging. The AUW tips at 169grams, quite a bit lighter than the previous model. The CG is places at about 72mm from LE, a little aft from the recommended position , but it still flies well and launches high.

[sherchoo]

The sandwich is then placed into a vacuum bag, which I made earlier, before turning on the vacuum pump. Once the vacuum pressure is established, the wing panels are supported and weigh down with the foam wing beds and plenty of scrap metal blocks. I kept the vacuum pressure for about 4 hours to allow the epoxy to set. After shutting down the vacuum, I left the wing panels weigh down overnight to allow the epoxy to reach its full strength. My first pair of wings have some warps due to mishandling before the epoxy resin has reached its full strength. The result of this pair of wing will be revealed over the next few days.

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Hi Joe,

During vaccuming, will there be any excess resin squeezed out? If yes, where does it go?

[joe yap]

Hi Joe,

During vaccuming, will there be any excess resin squeezed out? If yes, where does it go?

Hi Sherwin,

If you control the epoxy used, there will be very little excess resin to be squeezed out. The PVC sheet carriers have extended trailing edges and most excess resin will ended up there, forming trailing edge flashes on the wing cores, which will be trimmed off later.

Any excess resin squeezed out from the leading edges will be absorbed by the nylon peel ply, which can be peeled away easily after the resin has cured.

[sherchoo]

Hi Joe,

Understood!

Can I check where can I get some peel ply and breather cloth?

[joe yap]

I use scrap breather and peel ply from my school's workshop. Both can be bought from some industrial composite suppliers. Pang knows one of them. For the breather, you can also use kitchen paper towels as well, no need expensive stuff.

[Pang]

SW, Spotlight has nylon cloth which can be used as peel ply layer, they also have thinner thermal insulation like cloth which can be used as breather.

And for vacuum bagging bags, we found that those clear thicker type Plastic bags from skp works better than those 'industrial' grade ones.

Just now could have pass you some. Next time pass you if you need.