RCU Review: MCM Kestrel 19 semi-scale RTF glider


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    Contributed by: Laurent Caekebeke | Published: May 2015 | Views: 17609 | email icon Email this Article | PDFpdf icon
    RCUniverse.com MCM Kestrel


    • Overall design and scale look
    • High quality construction
    • Great thermal capability



    • Limited accessibility of rudder servo

    Open class gliders are the oldest and original competitive soaring class, having received its name only following the introduction of the other soaring classes. The open class has nearly no restriction, other than the maximum size of the plane, and is the favorite class for introducing new research prototypes. These planes are often the top performers, but they also sometimes carry a big sticker price.

    The Kestrel 19 was developed to enter the open-class competition. This glider is an evolution of the Kestrel 17, which itself was a licensed build of the Glasfugel H-401. The Kestrel ranked first twice in the British national championship (1972 and 1975), and performed strongly in the world champions, although it never won.

    This glider has some great features such as flaperons, which means that the flaps are operated as ailerons for better control. The plane is also equipped with a landing parachute, which increases the drag on landing to slow down the glider.

    MCM, an RC aircraft manufacturer based in France, reproduced the Kestrel 19 as a motorized semi-scale glider. The plane has a one-piece fiberglass fuselage and foam core wings and stabilizer. It is designed for a 600W power plant, to quickly get to thermal altitude. The Kestrel is first and foremost a thermal soaring machine, which means that it is designed to catch even the smallest lift.

    The plane can be procured in 3 different levels of completion:

    • The kit version: the wings, rudder and stabilizer will need to be covered and adjusted to the fuselage. Additionally, all radio equipment and motor will need to be installed.
    • The advanced version: the wings, stabilizer and rudder are pre-covered. Like in the kit version, the radio equipment and motor will need to be installed.
    • Ready-To-Fly (RTF) version: the plane will be delivered completed with only the receiver needing to be installed and the radio needing to be programmed. 
    Today, we are testing the RTF version.





    The fuselage comes ready to go out of the box, with the motor installed, and the cockpit adjusted.


    The receiver I chose for the review is the Futaba S7008SB. This receiver is now on all of my largest gliders for which the telemetry brings the great benefits of getting the battery voltage and altitude in real time.

    The decoration of the Kestrel 19 matches the scale plane: it is mainly plain white! The sticker showing the name on each side of the fuselage brings a nice visual touch.

    The fuselage is really wide, and routing the wire to the tail servos is an easy task. Note that the holes on each side of the rudder serve also as exhaust ports for the cool air running past the motor, battery and ESC.
    Manufacturer Information
    Price:
    Kit: 387.50 ?* ($423.30**)
    Pre-assembled kit: 707.50 ?* ($772.87**)
    RTF: 1183.30 ?* ($1292.64**)
    * prices do not include tax,
    **currency rate may vary
     Overview

    The Kestrel is a semi-scale model of the high performance German glider designed for the open-class world championship. With this model we wanted to offer a glider which was both easy to fly and highly capable of catching even the lightest thermals.

    To achieve this, we used the wing profile that made our CUMULUS 3.7mm a success, and combined it with a moderate-wing ratio. A lot of attention was given to keeping the wing loading on the light side. With 45g/dm2 and an all-up-weight of less than 3kg, this glider has great soaring qualities, and remains easy to land.

    The plane?s structural strength allows flying in any wind condition, and opening the flight envelope to some aerobatic figures.



    Specifications:


    Wingspan: Wingspan: 3.5m (137.8in)
    Weight: 3000g (6.5lbs)
    Battery: 3300mAh 4S 30C LiPo
     Airfoil:
     SB 1.8 118
     Wing loading:
     45g/dm2 (15 oz/sq.ft)








    MCM built a simple support for the battery, which makes the installation and removal of the battery extremely easy: no Velcro, no tape, no screws. It uses the compression of a foam block fixed on the battery to keep two pieces of wood interlocked. This secures the battery in place and also guarantees good consistency in the battery location. Optimizing the CG in a glider is the secret of the art; let's not jeopardize all these settings with a poorly positioned battery.

     




    All the servos are glued in place by the manufacturer. The aileron servos are located in a pocket under the wings, carefully adjusted to be flush with the wing surface. The tail servos are glued inside the rudder, and only the elevator servos show behind the access hatch. This is actually my only grief with the plane, as it makes replacing the rudder servo quite a challenge!

     





    The assembly with the RTF version only consists of the field installation and that is it! The wing has an aluminum tube to convey the wing load to the fuselage. A steel rod locks the wing rotation around the tube, and sets the proper wing incidence angle. The servo wires slide through an opening in the fuselage and are connected directly to the receiver.

     


    The crate built for the battery makes the installation at the field very quick. The battery simply slides in place, and it is ready to go. The stabilizer is mounted on two metal rods, and is simply held by friction. The maintaining force can be increased by slightly bending the extremities of the smaller rod. I used a pair of Z bend pliers on both ends, and applied very little force, just enough to have a minimum deformation on the rod itself.




    The flight recorder monitored the voltage and amperage, and the current reached 40A while climbing on 4s.
    Photo shoot









    This flight report is unusual in that it covers over a year of flying with the Kestrel 19. The plane flew for the first time in the sweet Texas spring before going through the heat of the summer, and then the less thermal glider friendly winter. We experienced exceptional flights and also the very bad one. So, let?s get to it!

    Hand launching is the best way to get the glider airborne. The glider is not lacking power: in spite of its 3.0kg, it very quickly gains speed making the launch very easy. No need to use a trolley or any other form of takeoff helping device. As a general rule, it is always better to ask for a charitable friend to throw the plane so the pilot can have both hands on the remote control from the start. However, no need to postpone a flight if there is no one around: the Kestrel is very well behaved, making it easy for the pilot to launch the plane himself. The fuselage is easy to grab in one hand underneath the wing, and the power from the engine literally pulls the plane from the hand. A light horizontal throw is all it takes to safely get the Kestrel 19 in the air.

    It takes around 40 to 50 seconds to reach 300m, which is a very good climb rate. I measured the sink rate on several occasions, on dead lift days, and I consistently measured between .50 to .55m/s. Granted, this measurement alone doesn?t tell as much as the usual L/D glide ratio, but it is indicative of good thermal capability. To glide from 300m (984ft) to the ground, the Kestrel would take approximately 10 minutes. The glide ratio is another important measurement, as it shows the capability of the plane to reach another lifting zone without losing too much altitude, independently of the time it takes to do so. Lacking the sensor to measure horizontal displacement versus vertical descent, I cannot provide the actual number for the glide ratio. Considering the relatively high speed of the model at minimum sink rate velocity, I would estimate this ratio to be on the high side for a scale glider. The real Kestrel had a very high glide ratio for its time with over 40:1, and this strong feature has been accurately reflected in the scale reproduction version

    The full moving elevator is very responsive, and the recommended throws are sufficient for both very precise soaring and aerobatic flying. The elevator is at neutral when aligned to the tip of the rudder. I made the mistake once of not centering the elevator after switching to a new radio (I know, rookie mistake!). At neutral, the elevator was slightly up, and that was all it needed to raise the nose right on takeoff, causing a premature stall. I thought my heart stopped when I saw the beautiful glider straight for a metallic fence, rightfully located to protect spectators. The damage looked pretty intense at the field, with the wings crushed, and the fuselage cracked in a few spots.
    Luckily, it only took one evening and a few layers of epoxy and fiberglass to repair the entire fuselage. The fuselage is molded and entirely open internally, making the repair easier as the wall can be fixed from both the inside and the outside.  A new set of wings was bought from MCM, and the manufacturer was extremely responsive and timely in delivering the spare parts. In a matter of only a few weeks, the Kestrel was back in the air.

    The plane is capable of aerobatic flight, even if that is not its preferred domain. The forward and backward loops are both easy to perform, thanks to a very good energy restitution. As for most large gliders, the roll rate is on the low side, and the pilot will have to work the rudder and the elevator to keep the roll centered.

    The 45-degrees test confirmed the CG to be on the right position, with a fuselage that slowly goes back to the horizontal. Nothing was modified from the original setting recommended by MCM.

    Landing is made easy by the powerful break, which consists of both ailerons being raised. The increased drag, coupled with the reduced lift, makes for a steep approach angle. Once the glider is a few feet above the ground, it is best to bring the ailerons back to neutral in order to reduce the vertical momentum. It is highly recommended to land the glider on a patch of grass. A runway or any hard surface used for landing could damage the bottom of the fuselage over time. The pilot must remain attentive at keeping the wing horizontal to prevent one of the wing tips from getting caught on the grass, causing the plane to spin around the yaw axis. The rudder is really exposed as it is low on the fuselage, and it could get caught on grass, which would stress the rudder servo and possibly break the fuse gear. If that happens, the rudder servo will have to be pulled out from the tail, and since there is no dedicated access window for it, the elevator servo will have to be removed as well. Considering they are both glued in the place, the job would be demanding.

    On most days, a flight with the Kestrel lasts around 1 hour, and it is interrupted mainly to give some rest to the pilot?s neck. The plane is very good at identifying thermals. The large wing will drop the opposite side to the thermal if it were to meet one. The pilot just have to finish the 270 degrees turn that the plane initiated to enter the thermal full frontal.

    The plane is generally very easy to fly. The stall happens very late, and is very gentle. The glider drops its nose and recovers right away. It is definitely the perfect first large scale glider, and opens the door to the large soaring class of RC aircraft's to any pilot who can fly a three-axis plane.















    The MCM Kestrel 19












    The Kestrel is a very well designed and manufactured plane. The quality of the build is superb, in line with the quality of MCM's other planes.

    The price puts the plane on the high end of the market, and is reflective of its excellent quality and individually hand-crafted components.


    It is apparent that MCM built from their previous successful models and combined them when designing the Kestrel 19. The Kestrel 19 is a good performer semi-scale glider, with no compromise on robustness and ease of flying. This plane is a keeper for sure.


    Links




    Pictures and videos were shot at:
    http://www.bayoucityflyers.com/
    General information on the Kestrel 19:

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    The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in products like the one featured in the review.

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