Birdy's RC Blog: DIY: Multiplex Easyglider 4 with Flaps

A few months ago, I was looking for a small glider for my slope soaring adventures. It should be electrified to test sketchy wind conditions on the slope, rather small, compactly to transport, sturdy and enable easy landing – which makes flaps mandatory. After doing some research on the web, I decided to go for a Multiplex Easyglider 4 and then try to build flaps in the wing… I saw a few YouTube videos of folks already done this, but I noticed that they were cutting out the flaps apparently too small (they used the same depth for flaps as for ailerons) which was my mainly explanation for the viewable low braking performances. I wanted to do it better...

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Flying experience

Firstly: no surprises there – an Easyglider flies like an Easyglider and that's not bad. Secondly: What about the flaps? Well, after I have done some flights and setup modifications, I am ok with the flaps work. The braking impact has its limits because the flaps are not wide enough, hardly one third of the wingspan. You can not fairly increase that, because the ailerons are already cut out as shipped. But as they are the flaps are helpful for landing on the slope (which should be spot on and slow) what the suggested spoilers are surely not. What I figured out is bringing up the ailerons additionally (what's the so-called butterfly) is counterproductive for braking and speeds things up – which we want to avoid. Also, a flare out before landing is not to do with ailerons up in spoiler-style. So I finally ended up with only 2 mm ailerons up, just to hinder tip stall. But what you need drastically after that is elevator compensation for preventing a nose up attitude when you apply brake at normal speeds. By the way: never do it on high speeds, the brake might break! Make sure you have enough throw for the elevator and set up an appropriate mixing curve in your transmitter! Actually you will experience that kind of thing more or less with any glider when you apply butterfly, but in this case it's more distinct – somehow expectable – it’s not meant to be…

If you ask: There is no significant weakening of the torsional rigidity of the wing by cutting out the flaps because the spar has a square cross-section and fits all over very tight in the wingpanels, with the result that the spar will take these loads.

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What you have to do, if you want to do it like I did
Use a sharp knife to cut out the 65 mm to 58 mm wide tapered flaps. Cut or sand flaps sidewise approx. 2 mm to give play and a V-shape gap between flaps and wing to make upwards flap deflection possible (which will give you better roll rate if you mix flaps to ailerons). Fix flaps with tape to the wing (do some testing which sort of tape sticks best on the foam). Now decide which servo and linkage you want to use, then cut and mill out foam respectively. Make sure that you do the leverage right to enable up to 80 degrees downward flap deflection. Glue in servos and levers, mount clevis and pushrods. I bought a spare part kit to get the two extra servo covers, which was not too expensive.
Ok, now you have 4 servos in the wing, and you need 2 more cables and connectors to the receiver in the fuselage. I was thinking a lot about how to do that in the best and easiest way. Well, my solution is indeed simple: just add a connector in the same way as supposed for the ailerons and it's fine. In the wingpanels though, you have to mill off additional space for the extra cable to zigzag them around the small bars when mounting the wing (check out pictures below for a better understanding...). Finally, be accurate with the length of the servo cables – voilà! – they will disappear in the fuselage if the wing is flush-mounted. Tip: use top flexible-style servo wiring!

There are some more modifications I did on this Easyglider:

The spar is light and seems to be strong enough, but a recent product recall from Multiplex because of a potential risk of a spar failure (due to production flaw) led me to put a carbon tube inside it to make things sturdy. This adds 19 grams of weight, which is no trouble at all.
When you have a foam model and fly it outside, you will sadly know: you can’t really avoid getting dents and a dirty bottom. To make this side of the fuselage more resilient, I glued a plastic skid there.

Surprisingly, the all over weight of this modified Easyglider is at 1065 grams, which is lower than the 1100 grams as the manual states.

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Conclusion

The Easyglider flap modification makes sense. Especially for slope flyers, flaps are very useful. I wouldn't have chosen the Easyglider without that DIY-option in mind. Bonus: you get higher roll rates for aerobatics and if you like you can play around with flight modes through cambering the wing to get the maximum out of your small foam beast. 😏

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Equipment
Battery: Lipolice 3s – 2200 mAh
Motor: ROXXY C28-34-850kv (was in the kit)
ESC: ROXXY BL-Control 720 S-BEC (was in the kit)
Servos:
Elevator and rudder: Hitec HS 81
Flaps: Graupner C 2081 (from my treasure chest – not available any more - choose
similar in size, preferably with metal gearing)
Ailerons: Dymond D 60
Receiver: Jeti Duplex REX 7

Data
Wingspan: 1800 mm
Lenght: 1080 mm
Wing area: approx. 40 dm²
Weight: 1065 grams
Wing load: approx. 26,5 g/dm²
CG: 70 mm from leading edge

Easy solution: servo wiring from the fuselage to the wingpanels for aileron and flap servos. I used two standard servo connectors per side glued together on top of each other.

Servo wiring connected. To do it is somehow cumbersome, but you get used to it.

Nothing spectacular - standard electronics inside.


Here is what you want to see: flap size and linkage.

At each base of the wingpanels you have to mill off some foam and set the small bar (2) lower in order to make space for the two cables which are supposed to go zigzag when you mount the wing. An added small plastic plate (1) holds the wiring in place.