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Blanik 4.2m with retractable EDF (electric ducted fan)

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  • Blanik 4.2m with retractable EDF (electric ducted fan)

    I thought I would pass on some information about my 4.2 meter Blanik from E-flite. I bought the Blanik after hearing the rave reviews and now having flown it myself, also attest that it is one fine glider. I bought it because it had fixed gear (I have an aversion to retracts) and could do some acro and sloping too. One day in the middle of a cold Minnesota winter I elected to design and build a retractable EDF fan system for it.

    I won't bore you with the details of build of the glider (which is very easy, btw) outside to say I used digital servos on the control surfaces. Rather I'll focus on the EDF parts and installation.

    I have about $500 total in parts for the EDF system, plus batteries. Commercial systems of similar size and power cost around $2000.

    It runs on 10S using two 5000 mah, 5S (25-35c) batteries in series pulling about 100 amps or 4kw. It will self launch off a smooth runway and will soar fine once the unit is retracted. Run-time WOT is about 5 minutes and everything stays cool.

    The EDF system comes out via two M6 screws making it easily converted to a pure glider. Total added mass for the EDF is about 3 lb. When in pure glider mode, I install just one battery and a bit of lead for 850g. In doing that, the installed lead nose weight is greatly reduced. There are two 2500 mah LiFe A123 batteries from NoBS for the on-board electronics mounted underneath the main battery tray in the nose area.

    The AUW is 23.5 pounds as a pure glider, and 26 pounds as a EDF assisted glider.

    The CG is set at 50mm in both pure glider and EDF configuration. Do not set up this plane at the factory 15-20mm number per the manual! I did just that before consulting a friend who had many hours on his and ended up removing a lot of nose lead.

    For the EDF lift I first I did a little CAD work to come up with a mechanism. Since there is a lot of room in the Blanik fuse, I elected for a linear solution using a scrap igus bearings and rail from work. A Hitech winch servo drives a rack and pinion to raise the EDF. The video here shows how it works:

    Here are the components I used:
    Efflux-built JetFan 90mm with the HET 700-68-1400
    It produces 4.7kg thrust @ 99A (on the bench).

    Hobby King YEP-120
    Mass: 5.8 oz (164g)
    Cost $124

    Lift Servo
    HS-785 HB sail winch servo, 3.5 turns with proportional control
    Cost: $49
    Mass: 3.4 oz

    Fan saddle
    Plywood, epoxied
    Estimated mass = 4 oz

    Bearing rail and bearings
    Igus Dryline rail, 7.5 inches long, mass = 5 oz after milling
    Bearings circa 1 oz each x2, 2 oz total
    Cost = free
    Mass: ca. 7oz total

    Rack and Pinion
    From Servo City
    Pinion 48P, 30 tooth, RSA48-HMG-30 .6250” PD ,.667” OD, $14.99
    Rack, 48P part number 48P-125-12

    Calculated stroke
    3.5 turns x pi x 0.625” PD = 6.872” total
    Total Cost, PMREDF: $515
    Total mass: 36 oz

    As far as modifications to the fuse, I cut some doors in the top, hinged the doors, installed a new main bulkhead (1/4" thick) to mount the fan rail assembly, installed a rear partial bulkhead to strengthen the door opening, beefed-up the landing gear, installed a nose gear, and fabricated a battery tray. I also re-routed the rudder pull-pull cables lower down in the fuse to clear the lift assy using Pekabe (ie, rc sailing) micro-blocks. A light plastic deflector keeps stuff from catching on the rudder cables. Shock cord closes the doors and cam blocks on the fan lift assembly open it.

    Motor wiring uses Castle 6.5 mm green connectors with a capacitor board cut in near the ESC.

    More to follow...


    Last edited by sekollera; 01-31-2016, 11:07 PM.

  • #2
    We'll thought out and engineered. Good write up also...You're hired, Outstanding stuff! excellent work and thanks for using our NoBS batteries

    Aviation Concepts
    Last edited by gunny11; 05-27-2015, 03:16 AM.
    Aviation Concepts rc


    • #3
      Here is a link to a video of the EDF lift inside the fuselage. You can also see how I beefed up the landing gear area.

      More to follow...


      • #4
        What "C" rating are the Power packs?

        Jeremy and Ben
        SCC AAA TT


        • #5
          25-35C, from hobby king.


          • #6
            Here are some more pictures of the final project. Outside of foolishly abiding my the factory CoG, the project worked out as planned. I've done a couple of ROG (rise off ground) takeoffs with it and while it works, if find the EDF is very useful as a sustainer and for powered acro flight (it surprises everyone).

            It also soars pretty well with extra 3.5 pounds in it.

            On to the next project....

            Last edited by sekollera; 01-31-2016, 11:29 PM.


            • #7
              Here are some videos I have on the Blanik 4.2 EDF showing the early cheap HK fan, later quality fan, retract system, and some flying.