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observer uav

(Updated  See bottom of article)  A project article on this Aerial or FPV aircraft from Hobbyking.  Formerly known as the Volantex Ranger it has been updated and re-marketed by HK as Quanum Observer.  The popularity of models with the abilty to carry video cameras has increased dramatically especially if you include multicopters.  However this fixed wing model looks more of a Drone, with it's new grey colouring and rather dramatic looks giving it that menacing appearance.  The airframe is made from blow moulded plastic, slippery surface like nylon, a texture similar to supermarket milk bottles.  The fuselage at just over a meter has a wide body up front and the wing is EPO at nearly 2 meters span with curved down wing tips.  The electric aircraft is of the pusher prop variety.

Now you may need that big wide wing because this model could be expected to carry quite a payload and has all the options to do so.  There are positions for camera mountings and gimbals under the fuselage forward of the landing gear, a camera position in the nose (ideal for FPV cam), possible use of the canopy area for camera mounts.  Halfway down the tail boom is a flat area designed to carry a video transmitter. At the end of the tail is an EPO stabiliser and fin.  There is nothing needed to glue, it all fits together simply and quickly with screws - or does it?  That is not the case in reality when I took delivery of this model!

The model came well packed as is usual from the Far East nowadays, shame though that they do not always apply the same mindset when creating a model!  Anyway, we get a fuselage with motor and 40 amp ESC fitted, two wing halves, fin, stabiliser, wing spar, landing gear and a big bag of hardware comprising wheels, screws, rods, clevises, canopy,etc.  The limited manual is not that helpful either, more of a photo album but hey this is simplicity apparently.

 Original Specification

  • Wingspan: 1980mm
  • Length: 1170mm
  • Flying Weight: 1500g w/o BatteryMotor: 
  • 3715 1000kv brushless Outrunner
  • ESC: 40A w/BEC
  • Prop: 10 x 6 Unbranded plastic
  • Servos: 9g x4

An Aerial Platform...

I am not planning to use this model as a FPV platform per say but the option is there if wanted or needed.  Primarily intended as an aerial photgraphy platform and to scan the surrounding fields for downed models especially when the crop has become quite tall.

Fuselage and Mods

The tail fin and stabiliser connect to each other and then are located on to the fuselage and secured by two screws from underneath.  This model could be fairly heavy with all equipment onboard and expect to fly for long periods. With that in mind I was not too happy about the foam hinges on the rudder and elevator.  I cut these two items off after marking the positions of the forthcoming hinges, cleaned up any rough edges and using a 3mm twist bit and Robart Hinge guide, hand drilled three holes for the rudder and four for the elevator. Using Vaseline on the hinge metal pin and UHU-POR to glue the hinges in place.  Now I had two virtually friction free control surfaces and well secured.

Looking at the landing gear location and only two bolts?  And screws into what inside?  I removed the screws securing the fuselage floor and with some effort managed to pull the whole assembly up and out of the fuselage.  The foam part at the back of the floor is glued with something like UHU-POR to the fuselage bottom.  Glued into this foam on the underside was a piece of 3mm ply with two spike nuts, the latter for the landing gear.  Not really man enough in my opinion allowing for less than perfect landings.  I removed the ply and sliced out another 3mm foam.  Using the original ply plate as a pattern I cut out another 3mm piece.  Glueing these together now gave me 6mm.  The new ply plate was then drilled out for new 4mm spike nuts, two in the original locations plus two more.  The new gear plate was then epoxied on the foam. It will again get sandwiched between the foam and the fusleage floor.  The whole assembly was then re-inserted into the fuselage and secured with UHU-POR in the foam area and it's original screws.

The original motor although looking quite reasonable and pre-fitted was not really up to the job with the supplied prop even on three cells pushing the 40 amp ESC (branded Volantex) near it's limit in my opinion, preferring to have more capacity in respect of current demand.  On a trial fit of 2 x 3300, 3 cell Lipo packs they did not give nearly enough weight up front to balance the plane.  Referring to power and current checks with various prop sizes and pitches, I could not get what I thought was an ideal power to weight ratio, always siding with more power on most of my planes.  After all, this UAV could possibly weigh up to 6lbs easily with onboard camera equipment.

I replaced the motor with a Turnigy 3536 1450kv and the ESC was replaced with a 60 amp Turnigy Plush.  Up front 2 x Turnigy 3300 maH 4 cells.  Using a 9 x 6 APC-e pusher prop I got around 580 watts. I estimated that this figures out at 100 watts per pound, ample.

New Specification

  • Motor: Turnigy 3536 1450Kv
  • ESC: Turnigy 60 amp Plush/w BEC
  • 2 x Turnigy 3300 maH 30C 4 cell Lipos (weight 720gms)
  • Prop: APC-e 9x6 pusher
  • Flying weight approx 2.3kgs incl battery/motor *

* Depending on camera equipment


The two 4 cell LiPos have a total weight of 720 gms and including the Mobius HD cam in the nose, to get the plane to balance I had to add another 100 gms of lead marked as "dummy camera".  This would be removed if and when a camera and gimbal is fitted.

The video transmitter, an Immersion RC 5.8hz TX sits on a dedicated position halfway down the the tail, midway between the prop and the vertical fin. See image.  It gets it power directly from the main batteries up front, it is capable of handling voltages between 7 to 25 volts.  An integrated voltage dropper supplies a 5v output to power the Mobius camera up front, keeping it charged up and constantly powered up.  A modifed cable links the camera and TX together supplying power and video signals.  A standard antenna with a SMA plug is screwed to the TX and set in the upright position. This antenna may be replaced at a later date with a circular polarised antenna if video transmission range is not acceptable.  This plane will NOT be flown out of visible sight for practicality and legality.  The signal will be received by a FR 632 Diversity 5.8Ghz ground receiver, this unit having twin antennas and three options for video output, video A ,B and Diversity.


Wings and Mods

Making up the up the 2 metre wings would probably be the easiest job.  The aileron servos were pre-installed and wired in.  Moulded positions for flaps are made up for you and round the same way avoiding mixes or reverse direction servos.  I used a pair of HS65HBs (Karbonite gears) for the flaps, fitting neatly and precisely in the slots.  Aileron horns found in a bag along with their screws are easily fitted as the holes are pre-drilled for you.  I was intending to use flaps so went to fit flap horns only to find not one screw in any bag was long enough to go through the wing.  I went ahead and glued in the flap servos using UHU POR after setting them up with a servo tester so I could fit the arms.  I'll sort out the control horns later. To lay the flap servo leads into the precut slots required cutting carefully through the inch wide glass reinforced tape.  Now I could lay into the slots the flap leads.  Being a grey model which would camouflage easily into our British skies, usually grey anyway I decided to fit navigation lights now while the slots are open.

I have had a cheap n cheerful set of LED nav lights hanging around for years in a draw so time to make use them.  All the wires of the set are colour coded and to make life easy I would cut them in the middle and add extensions to reconnect the leds to their prospective leads.  Finding very thin wires in multi colours may be a problem.  I found the answer to this by cutting open phone cable, lots of thin copper wires in mulitple colours.  A soldering iron, shrink wrap over the joints and I am in business.  With the aid of a small soldering iron bit I created some heat cut slots for the navigation light wires.  The LEDs are glued in with UHU-POR into recesses made by a craft knife.  Then is all that is required is to use Blenderm tape to cover all the slots right back to the wing roots.  The wings can be separated for transport if needed so the LED controller which is about 25mm square is held on to the underside of one of the wings at the root using hook & loop. Any lighting required on the fuselage can be picked up from here.

The wings are joined by a carbon rod wing brace and locked together with a grey, quite sturdy curved plastic cover plate.  This plate has an integral level bubble and with the four 4 mm bolts pulls  locks into preformed slots in the top of the wing and is then secured to the fuselage.  The level bubble is to aid the setting up of gyro and heading systems, showing when the plane is level with regards to pitch and yaw and also with the centre of gravity.  The trailing edge at the roots has a recess which wraps neatly around the motor mount.

First Flight Test

On Saturday the 5th September with a brisk crosswind at the flying field, Jon Tappin, test pilot took the Observer up.  Some  members wee watching a monitor to get live video transmission from the the plane nose camera.  Anyway, on with the flight.  Rates were at low with 35% expo.  Full throttle would have about 600 watts of push.  It appeared to take a fair distance on roll out before climbing up but once flying and had gained height and levelled off it could be easily backed off to half throttle. Trimming the elevator for level flight it had soon ran out of notches.  Jon went through various manouvres some I add are not what the Observer is designed for but it did them anyway, big loops and rollings.

Back on the ground we used the TX's ATR settings to get some more movement from the elevator and rudder, the latter is really too small especially so when steering on the ground too.  It was also found that on opening the throttle from half upwards the plane would climb by itself.  I also took out the "dummy camera" lead weight of 110 grams on top of the batteries thus taking nose weight off somewhat.  This would hopefully give the plane more elevator.

A second flight was set up now that Jon had the feel for it and it's abnomalies so more partial aerobatics a were perfomed not to prove whether it can or not but that the airframe is sturdy enough.  It was very noticeable in the bumpy air that the 2 meter wings flexed quite a bit, a bit "Dreamliner" if you like but bear in mind this plane is about 5 - 6 lbs on foam wings albeit the wings are carbon tubed by two thirds leaving just the wing tips with independent bracing.  Seeing those wings flex that much is bit disconcerting but the carbon rod will keep it in check.

Back on the ground with ample battery capacity after two 6 minute flights I discovered why the plane climbed at high throttle.  The motor is secured to a round plastic mounting plate which sits into the split motor housing.  The mounting plate has a circular key way which sits into a slot in the motor housing.  This plate was sat correctly into the housing therefore changing the thrust angle in two directions.  My oversight after swapping the motor earlier.  That may help the elevator issue along too!

The Immersion 5.8G transmitter used was a 25mw UK legal unit, the signal being received by a FR632 Diversity RX and members said they saw no loss of transmission whilst the plane was being flown at our normal visible distances and heights we would use on any given day. The Mobius camera is sat on a firm foam bed, secured with a small velcro strap, looking though the nose and gave no shaky images to the ground station. It powers on when the plane is powered up.  Therefore searching for downed models when the crop is growing in the large fields surrounding us could be accomplished.

There is a bit more tweaking to do to get a full view on this camera ship but initial results show good possibilities.  I am thinking of moving the Video TX up front to the cockpit area therefore taking off a little bit of weight, unit and cabling, from the tail.


I feel it is early days yet but I think a bit more can be done with it.  Rudder and elevator definitely need more movement to allow more authority in varying weather conditions.  Power from the modified set up earlier described is plenty.  Longer screws to be found for the flap horns so these can be set up.  Mounting of a HDcam under the fuselage will make changes to the CG so the batteries may have be moved from there present forward position.


Check for Updates:

  • 08/06/2017: Now fitted with 2 x 3000 MAH 3 cell  25C Lipos but heavier brand (GensAce)
  • 03/03/2018: Receiver replaced with Frsky S8R.  Mobius mounted under mfront fuselage. Mobius 2 mounted in nose for VTX
  • 09/12/2018: Power LEDS now fitted to wing tips and fuselage (Position lights and Strobes)
  • 26/06/2019: Matek 405SE flight controller fitted.  RunCam Action 2 replaces Mobius lower camera.
  • 03/06/2019: RunCam Swift 2 now replaces Mobius in nose. VTX upgraded to Matek HV. Antenna RHCP replaces Omni standard aerial.
  • 03/07/2020: INAV fitted with Runcam 2 under nose and Eagle Swift Pro in nose.



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