EF Extra 300 EXP 91"

on Wednesday, 16 January 2013. Posted in Building and experience reports

Bigger is Better!

After beeing very happy with my Extreme Flight 48" Extra / Edge and 60" Extra / Edge i wanted to have something bigger. Fortunately the 91" Extra EXP was just release, so i made sure i get one from the first Europe badge!

Since we fly electric only, the 91" Extra will be powered by Amps instead of gas!

bigger is better

Dimensions EF 91 ExtraEF 91 Setup

Before we start the build, there are 2 things that are already mentioned in some forums:

After mounting the cowling, it is possible that it won´t sit properly on the firewall. In my case it was some mm as well. By carefully sanding the parts you see in the picture (please sand carefully and try the fit after you sand), i got rid of the problem.

Motordom Cowling Fix

Some wingtubes seem to be not 100% for a clean fit. I had a little room on both, the tube for the wing and the tube for the elevator halfes. Just wrap some thin tape around it and you are good to go.

Landing gear:

That´s an easy part of the build and is well documented in the manual as well, all parts that come with the kit at labeled - very nice!

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Just put the axle through the pre-drilled hole in the landing gear, secure the wheel with the wheel collars. The wheel pants are made for fitting between the landing gear and the locking nut. The axle is secured by the washer + locking nut. The holes for the 2 woodscrews you need for mounting the wheel pant are also already pre-drilled in the landing gear. So it´s just aligning the wheel pant, drilling the 2 holes in the wheel pant and screwing it on.

For the more "scale" look, you get a pair of fairing with the kit. Actually it´s 2 plastic fairing and a rubber tube. You need to slit the tube so you can place it around the edge of the fairing. Just secure it with thin CA.

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The manual says you can attach the fairings to the fuselage by using silicon glue. I went with Chris Jewett´s method and epoxied them to the landing gear (sand the CF before gluing). I used 5 Minute epoxy here.

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Let´s start with the Elevators:

First of all i cleared the servo arm holes and ironed all spots that needed a little heat.

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I use UHU Endfest 300 for everything that need´s 24h epoxy.

To prevent the epoxy from getting in the knuckle, put a drop of silicon oil on it before you start with any epoxy. Don´t have it at home? Just use some Oil from the kitchen... better than nothing...

Fill the pre-drilled holes with epoxy, put the knuckles in about 50% and wipe off any epoxy that is beeing pushed out. Push the knuckle in all the way ( in a 90° position) and again remove all excessive epoxy. Since you won´t be able to stop the epoxy 100% to get to the knuckle, clean all of them with a paper towel with some denatured alcohol. Also watch out for any fingertips or other epoxy spot you might have gotten on the covering and remove that as well. 

Damit das Epoxy nicht in das Gelenk gelangt (100% ist schwer zu verhindern...) kann man vorher einen Tropfen Silikonöl draufgeben, Sonnenblumenöl aus der Küche tut es jedoch auch.

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Let it dry for several hours before you glue the elevator on.

For the Elevator make sure you leave a proper hinge gap in case you ever feel like - Hey i wanna try 80° elevator power! 

We seal all our hinge gaps with OraCover transparent covering.


While the elevator is drying, let´s do something else in the meantime. For example, opening the cooling hole in the cowling:

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After you opened a hole with a dremel and a smooth hand, you can just work your way out to the desired hole shape. When you are done with the Dremel, come back and sand the edges clean and seal them with thin ca.

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Gluing the Horns:

Before you start gluing the horns to the control surface you should sand the horn, this helps the glue to stick to the horn.

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Remove the covering and make sure the control horn is just over the hinge line (picture is just to demonstrate, not final position), secure the 2 horns with the according screw while the epoxy dries.

IMG 0868RNIMG 0871RNIf you like you can paint the control horns to match the aircraft design, mine are all black now (a black pen is enough). All hinging and mounting of the control horns are the same for all control surfaces so i won´t talk about each of them. The rudder needs a ball link to accept the tail wheel. Again before you glue it in, sand it. You need to drill a hole in the bottom side of the rudder for the ball link.

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Mounting the Emcotec Wing Connectors:

For wing connections i like to use the Wing Connectors of Emcotec. The connectors fit and hold really well and correctly mounted this is a really nice solution. For the 91", since the elevator halfes are detachable as well, i use the wing connectors for the elevator as well. For mounting the connectors you need to make some custom wood parts.

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Mounting the rudder servo:

For the rudder servo i choose a Futaba BLS157 with 37KG of torque at 7,4v. I reinforced the mounting area with carbon. I use the recommended SWB 4" offset servo arm. The pull pull cables will be mounted with secraft Hardware... will talk about that later.

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Again you can use some colour here to give it a better look. The pull-pull cables will be attached by using secraft accessoires, but let´s talk about that later...

Since unfortunately i still have to wait for my ESC to arrive (hopefully in the next few days), let´s spend some time with the interior...

For the electric setup, a Safety-Switch from Emcotec (SPS 120A/240A) is going to be installed. This will allow to separate the motor from any power and to prevent sparks while attaching the 12S battery pack. For switching, you get a nice looking switch which is mounted on the side of the fuselage.

For marking, turn around the switch and mark the drilling holes at the desired position on the fuselage:

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Now just connect the previously marked spots to get the middle of the hole to be drilled. Drill the hole and file / sand if necessary to allow nice but strong fit of the switch. Screw the switch in with the wood screws that come with the kit, make sure to use the mounting ring (back side of the fuselage).

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Since it´s an electric setup and the LiPo´s will have a weight of approx. 1.5-1.6KG, you should consider to strengthen the are where you place the LiPo´s. I used some strong 2,5mm wood, and made sanded down the spots where the velcro will attach to secure the LiPo´s. To give it a better look, again, painted in black and glued with some Uhu Endfest 300 (24H epoxy).

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To get a little weight and pressure on the wood parts while the glue has to dry, just take same bottle´s (used empty glas bottles , approx 1.5KG) which helps to get a better bond.

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So le´ts go on,

after my mezon ESC finnaly arrived, le´ts go to the next steps. Since the motorbox isn´t long enough to mount the esc in a good way (provide proper airflow which means cooling) i had to create a little extension

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The extension is made of 2,5mm strong wood. Before epoxying, the motorbox needed to be sanded at the mounting spot for the throttle server. The whole mounting and glueing are must be sanded as well since the motorbox already is treated with epoxy.

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Drilling the motor holes:

Since i will use an electric setup, first i had to determine the correct spots for the holes (i think there is a drilling guide for the DA-60). Sure Determining the correct position can be calculated, but i wanted to visually see the result first

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Create a piece of wood that fits the hole in the motorbox

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Extend the marking from the motorbox to your piece of wood.

Drill a hole and e.g. put a carbon wing tube with the same diameter as your motor shaft in it..

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Mount the cowling and put the spinner backplate on the carbon tube to visually confirm a correct fit..

First look with the Hacker Q80-8M mounted looks good.

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The distance between spinner backplate and cowling looks good (allthough the picture isn´t that good because of the angle), i have almost 2mm between both parts. On the picture you can clearly see the default right thrust.

Lets go on with the interior

For power distribution, i use an Emcotec DPSI-Ampere, it is mounted directly above the wing tube.

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For every power port, there is a Jeti MUI 30 for telemtry data.

To achieve the desired CG (the Q80 is is quite iighter than a 60cc gasser), the receiver / servo LiPo´s need to be mounted in the motor box. I glued some wood mounts in place with 5 minute epoxy and screwed the Secraft LiPo bed on them.

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For mounting the Emcotec SPS Security swtich in the motor box (since the box isn´t that long), i put a little "house" in the box.

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You can see the cabling to the Jeti R18 here:

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This is how it looks with LiPo´s:

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A lot of people asked me on the forums about how to mount the motor. I mounted the Q80-8M with Secraft stand-offs (50mm + 25mm) between the stand-offs i mounted a second mounting cross for the Q80 which i got from Hacker directly.

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A quick note on the hardware that comes with the Q80, the counter nut can not be used since it´s closed at the upper end and you want bo able to screw it all the way down on the prop. So you need to cut the closed end off and open the counter nut.

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