Projects

DB Moth 40 - John Emms

The Moth was built from the original 58 inch (1473mm) wingspan DB Moth 40 kit in 1988. I built the airframe, and my good friend Malc Ager finished the model, to have a long service life when used with the original Saito 40 Mk2 (which the model flew with on a number of occasions until 2002). In 2007 I prepared the model for electrification by removed the engine, fuel tank, throttle servo, and throttle linkage. I washed the complete airframe in hot water with a generous squirt of washing up liquid. Stubborn castor oil build up in the engine bay was removed using cellulose thinners.

Although the Mega 22/30/4 with Graupner clamp motor mount was to be fitted directly to the original engine mounting plate, the new motor at half the weight of the original engine created CG problems. A simple balancing moments calculation showed that by placing the RCM Pelikan 4S Shark Lithium Polymer battery in the fuel tank bay, and moving the receiver battery to directly under the motor, the model would balance perfectly. By taking out most of the former in front of the forward instrument panel, cooling air is allowed to pass through the motor and Jeti 40 OPTO speed controller, over the battery pack, and out through the forward cockpit. We had left the original engine cowl off because a large part of it would have had to be cut away anyway, and no cowl allowed easy access to the engine. I ordered a new cowl from DB Sport and Scale, only to find the original cowl in a workshop clear up as I was waiting for the new cowl to arrive! I assembled the cowl, which I then painted with enamel paint, and hinged it at one side using a double tape hinge (Graupner hinge tape). The cowl is fixed at the other side using square tabs of industrial grade hook and loop material. The cowl is quick and easy to open and close, and remains very secure in flight.

Other changes to the model? I originally designed and produced a near scale closed loop rudder control using an alloy arm that extends out of both sides of the fuselage, and is controller using a very short pushrod to the rudder servo. After experience with my earlier Flair Magnatilla, I fitted a Sopwith Pup type sprung undercarriage using an additional full width axle that is bound with fuse wire and soldered in the centre to the original fixed axle. The suspension is provided by rubber bands wrapped around the new axle, and the shortened fixed axle stubs. The suspension is very effective when flying from rough grass fields.

And more? After experience of the initial test flights, I would only fly this model as rudder/elevator on the calmest of days. Changing the model to full 4 function control transformed the model, and it is now a very practical every day flyer. Of course, along with almost all flat bottom wing models (and full size aircraft) the Moth does need to have at least 50% aileron differential (the up going aileron goes up further that the down going aileron). My Moth uses mechanical differential from the single standard size aileron servo, but it would be far easier to achieve now, and greater control throw would be possible using two Hitec HS82MG servos. The receiver battery is mounted in the lower fuselage below the motor using my normal industrial grade hook and loop method. One final thing: I always check the length of the grass on the runway, as excessively long grass can grab the axles on all early type aircraft with the associated risk of damage.

Performance? In it’s first electric form, the model with the Mega 22/30/4 (600 size 220g motor), using 11x5,5 APC Thin Electric propeller, Jeti 40 OPTO and RCM Pelikan Shark 4S 3700 LiPo gives at least equal performance to the original Saito 40 powered model, allowing all scale aerobatics (plus extended inverted flight). I had always felt that the model would benefit from a larger propeller, and instead of using the spare Mega 22/30/4 (that came out of a Pelikan Dingo) with a Jeti 40 OPTO lying on the bench, I had considered fitting a new Mega 22/45/3E with Jeti SPIN 44 or SPIN 66 (that would need no receiver battery). As everything already fitted neatly in place, I asked Mega if they would be so kind as to produce the prototype Mega 22/30/4E which I fitted with an APC Thin Electric 12x8 propeller, and with a slightly lower current draw of around 34A (440W) improved the static thrust to give faster acceleration. The increased static thrust shortened the take off run to no more than 5 model lengths on a normal grass runway, and allowed the first half of a loop to be extended for a better scale appearance. Following repairs, oil soaking, and the use of heavy covering, my model is now flying at 7lb (3,2kg), but a DB Moth 40 built for electric can easily be flying at around 5,5lb (2,5kg), extending the current 8 minute flights to 10 or 11 minutes. As a result of my testing with the prototype Mega 22/30/4E with 12x8 propeller and RCM Pelikan 4S 3700 LiPo power system, we are recommending it (along with the Mega 22/45/3E) as the best near direct drop in replacement for .40 four stroke engines in vintage models up to 8lb (3,6kg) for a good take off performance – all the more remarkable as the Mega 22/40/4E is the same size and fitting as a 600 can motor!

LN Accord 2200 - John Emms

The Accord was assembled from a set of parts produced by Libor Nezbeda in the Czech Republic. This electric version is a 500g lighter version of Libor’s original design for a 40cc petrol engine. The Accord 2200 is 2,2m wingspan, and 2,2m long with a flying weight of 5,7kg (12,5lb). One of the original Accord 2200 was fitted with an AXi 5330/18 to win the German 3D championships, and Chris Martindale prepared one to the same specification. I wanted to test my theory that this low wing loading model would benefit from the use of a larger propeller fitted to the higher wind or softer AXi 5330/24 with 21x14 APC Thin Electric propeller, Jeti Advance 99 OPTO controller (the SPIN 77 OPTO is more than capable), and RCM Pelikan 10S Shark 3700 batteries, so mine was fitted with this system. After testing the two models at the same time, we came to the conclusion that the 5330/24 system was preferable for this model, giving both longer flight times on the same batteries (up to 11 minutes on the 3700s at up to 60A (around 1900W) to give a takeoff inside one model length in still air, and true vertical acceleration – the model appears to be capable of flying at the same speed at any angle, up or down. A big thank you goes to Chris Martindale for producing some fittings for this model, and following the demise of Chris’ own model, my Accord 2200 is now resident with Chris.

Reichard Okapi - John Emms

The Okapi was assembled from the Reichard kit produced in Brno, Czech Republic. Okapi is 1,5m (60 inch) wingspan, and was designed to use only electric power. The model is designed around 10 NiMh cells, and the Mega 22/30/3 with a Graupner CAM 10x6 propeller and Jeti Advance 40 speed controller at around 380W for a 4,5lb (2kg) flying weight. The model takes off from grass with ease, climbs out at 30 to 45 degrees, and performs relaxing turn around aerobatics with this power system. When my Okapi was damaged as the result of an accident, I fitted the fuselage internals in a new fuselage moulding and took the opportunity to try my Okapi with a more powerful system. I fitted a Mega 22/30/4, Graupner 11x6 CAM Propeller, RCM Pelikan 4S 3700 Shark LiPo, and a Jeti SPIN 44 to allow the use of BEC at the higher voltage (although when I moved the lighter battery forward to balance the model there was room for a receiver battery right on the Centre of Gravity). The new power system provides about 470W for the now 4lb (1,8kg) flying weight Okapi, which provides an incredibly wide speed range due to the very low wing loading, and true vertical performance. I have also used the Graupner 10x6 CAM Prop with this power system to draw less current and for flying off grass. The Okapi is one of my regular sports models.

Changes to the model? As I initially flew my Okapi off some very rough grass fields, I replaced the plastic snake inner for the nose wheel steering with a simple piece of 1,5mm welding rod. After I had glued the battery tray into the fuselage, I then cut away the battery retaining plate in the top of the fuselage moulding to allow more flexible access for the battery. I then used my normal industrial grade hook and loop with a Velcro tie to retain the battery. I side hinged my canopy using Graupner hinge tape, and the canopy is held closed by two pairs of neodym magnets. The canopy is very quick to open and close, stays in position during all flights, and cannot be lost!

Any Advice? I used heavy duty foam wheels, 2 of 73mm for the main legs, and 1 of 63mm for the nose leg. This combination allows excellent grass field performance, and also allows the Okapi to sit at the correct angle for operation from tarmac. I always start with the CG suggested by Mr Reichard, and I mark the battery position to achieve this. After initial test flights, both batteries were moved back about 10mm for subsequent flights.

Reichard Svist - Chris Martindale

The Svist is 2,7m wingspan, with a flying weight around 2kg. The model climbs at about 45 degrees using the power system specified by Mr Reichard: Mega 22/30/3, Jeti Advance 40 BEC speed controller, 12x6 Graupner CAM propeller blades, and 8 SubC NiMh cells. Chris, always wanting to push the boundaries, after using a geared conventional motor found that he got the same performance for less input power using the MVVS 5,6/690 Glider motor with Jeti Advance 70 OPTO controller, 14x9,5 Graupner CAM propeller blades, and Pelikan 4 Series Shark 3700 LiPo batteries for 700W of input power. The Svist with this power system climbs true vertical from launch, and has proved to be an excellent all weather thermal soarer. Chris frequently performs a reversal from height (with little or no elevator input) levelling out along the flight line, and then performing a 4 point roll at high speed. Of course, Svist is not intended to perform high G manoeuvres, and because of the very flat glide, spoilerons should be used for landing (both ailerons up at 20 to 40 degrees).

Sig Rascal 110 - John Emms

My involvement with the Sig Rascal 110 came after a conversation with David Morris at Kavan who said that the Rascal 110 is a very popular model for glider towing in mainland Europe. I was also aware that at least two had been electrified, and I was torn between using a 24 NiMh or 8 Series LiPo power system with the AXi 4130/20, or using a down rated version of my Accord 2200 power system . My wife, Sandra, was adamant that if I was to prepare a Rascal 110 then it would have to be impressive! From experience with my Accord 2200, I was wary of using the same near 2kW power system in the Rascal, and so I used the same AXi 5330/24 with the same RCM Pelikan 10S Shark 3700 LiPo batteries, but used a Jeti 77 OPTO controller that was an easier fit in the cowl, and an APC Thin Electric 20x13 to reduce the power to a more realistic 1600W for this 14lb (6,4kg) flying weight model. The motor was fitted using my now usual 4mm light ply box on the front of the firewall method (using 6mm birch ply for the front motor mounting plate). The battery slides into a purpose built light ply box (with cooling holes) from underneath the nose. The batteries can be connected to the speed controller by leaning over the nose of the model, and I am then well clear of the propeller. Despite this model falling outside the legal requirements for a large model, I feel it is wise to use a fail-safe, and treat it with the respect that a model of this size demands.

Performance: Take off occurs in about two model lengths on a calm day, and on freshly charged batteries, the climb out can be true vertical. The functional wing struts keep the wings absolutely rigid, and all normal aerobatics can be performed with complete confidence. The Rascal 110 does the most gentle and beautiful aerobatics, and I remain aware that it is not a precision aerobatic model – and does not pretend to be. Of course, simple circuit bashing provides a pleasure all of its own. The only change I made to the CG and control settings in the instructions is to couple 5 percent rudder with aileron just to keep the model flying more accurately when close to the stall or on approach to landing. With the slight coupled rudder, accurate spot landings are very easy to perform.

Experience with the kit: The instructions say to study the build sequence before starting, and then allow 10 hours for assembly. My model was complete from the firewall back with all controls adjusted in less than 10 hours from opening the box using all of the fittings in the kit (I only added 2 lock nuts for the control quick links from my spares box), and I am sure that if using an IC engine, the model could have been ready in the 10 hours quoted. The MVVS 26 IFS petrol engine fits in the cowl perfectly, and although the additional power is not required, the MVVS tuned pipe fits perfectly down the fuselage side. The sheeted flat top deck to the rear fuselage is the perfect basis for a towing hard point, and of course, when used to tow any of the Reichard ¼ scale gliders, both models may exceed the 400ft limit that applies to models over 7kg.

Steen Skybolt – Chris Martindale

The Modell Studio Steen Skybolt is a 1,7m wingspan nearly ¼ scale model with a flying weight of nearly 9kg (19,5lb). The power system was decided by what would fit sensibly in the cowl, what would balance without the need for excessive use of balance weights, and of course it had to be adequately powered. The MVVS 40 fits sensibly in the space allowed, and requires no additional balance weights. The MVVS 35 to 40 tuned pipe is also used with a modified header pipe or manifold. The propellers used are 20x10 Bambula and Xoar beech, though the MVVS 40 and pipe combination are quite happy with propellers up to 22x10. Chris uses a 2S LiPo battery for the ignition with the ICU ignition in battery check (LiPo) mode.

Performance? The engine is primed by turning the engine over at least 6 times with the ignition off, and the choke closed. The choke is then released, the ignition turned on, and the engine is running within 3 flicks. After a relatively short take off run, the model will climb out vertical, and can fly fast turn around aerobatic manoeuvres, and of course as an aerobatic biplane the Skybolt is very suited to manoeuvres that include snap rolls. Chris is also enjoying the low speed handling of this model which has become a regular Sunday flier.