Simon Chaddock

Henry No the rotary is rigidly fixed to the motor so the electric motor, the dummy rotary and the prop act as one! They are actually all connected by the prop driver so it can be disassembled if required. As the object is to portray true scale the prop is pretty big so it requires a small low kV motor and a low cell count. Not a lot of power but it will be incorporated into a light weight WW1 airframe. In today's video the rotary is using a scale diameter 12x6 prop. It is running at full power on the fully charged 2s and spinning at a about 6000 rpm. https://www.youtube.com/shorts/kOjTkcVH5x8 Only 51 Watts but with the large prop it still produces quite a bit of thrust. When the rotary is in a close fitting cowl that has a smooth inner surface the loss in RPM due to "rotary windage" is not that great. In full size a rotary was compact but relatively heavy and had to be close behind the prop which meant that such planes had really short noses so the weight of a dummy rotary is not too much of a problem. How many RC Fokker Triplanes or Sopwith Pups have non scale "extended" noses or have to add considerable nose weight actually in the cowling? A modern brushless motor is just not heavy enough.

In 1918 Fokker had 2 prototype monoplanes built basically using the Triplane fuselage and Oberursel 110hp rotary. One with a mid fuselage wing V17 and one a low wing V25. At the same time two similar were built using Mercedes DIII engines. They were entered into the ministry fighter competitions. The Mercedes versions although with an excellent performance were ruled out due to poor visibility as well as the limited Mercedes engine supply being reserved for the Fokker DVII. The two Oberursel prototypes were also declared unfit due to poor downward visibility. To overcome this objection Fokker built a prototype with a parasol wing that would be closer to the pilot's eye lane as the Fokker EV. It was accepted for production and was later renamed the DVIII. With its plywood skinned low wing the V25 was remarkably advanced for the period and predated what was to become the classic fighter layout by some 18 years! I have previously built a small 24" span sub 250g Depron RC V25. And it had a simplified Oberursel that went round with the prop! Flew well enough but was very twitchy and did not like landing on any sort of grass! https://www.youtube.com/watch?v=3Uv03i4kraU My intention is to build a bigger 40" version using the bigger scale Oberursel. Hopefully it will be a more manageable flier.

Just for fun a scale model of a 9 cylinder rotary that is fixed to the out runner so it goes round with the prop. https://www.youtube.com/shorts/roqPMTxWeM4 The 2212 1000kv on a 2s is driving an 11x3 printed prop and even that is not scale as it should be a 12"! Not yet run at full power either.

The LE 2204 has a 3 mm shaft. The folding prop comes from Ebay via China so you have to wait. The 5x3 I used with a 3s no longer seems available. This 6x3 folder & spinner for a 3mm shaft is about the cheapest at the moment. I use it with a 2s. May sound a bit expensive and ideally the motor cowl has to match the spinner but provided you "no power" land the prop will not get broken.

Of course on the Fokker Triplane the aileron actually extended beyond the wing tip.

I fly from a reasonably flat area but it is only cut irregularly by a council tractor gang mower hence the field is never a bowling green. ☹️ As a result virtually all my planes are hand launch/belly land and have where possible design features incorporated such as rear high mounted pusher props, folding tractor props or are EDFs. It does also mean you have to get used to glide "no power" approaches and landings. 😉 When the grass is short(ish) and with the appropriate plane a ground "slide" take off is possible, even with a scale EDF, but it does require it to have a pretty high thrust to weight ratio. https://www.youtube.com/watch?v=gPX54hVu1Xg

Fraggs Yes, I understand the marking is intended to be a battery hatch for a power conversion. However I did not use it on either of my FX707 conversions as they were aimed specifically at retaining a good glide performance using a relatively small motor and battery so a good CG could be achieved with the battery simply placed in the cockpit. Like you I was also concerned at the impact on strength and rigidity of the fuselage from such a big cut out placed directly under the already substantial opening for the wing mounting. I suspect if a bigger heavier motor sufficient to drive say an 7x6 prop rather than a 6x3 then the resulting bigger battery would likely have to be placed and accessed via the indicated underside markings. I note that many of the FX707 conversions posted on You Tube end up at 400+g so are "sport" planes rather than the 320g of my light weight power glider. It rather depends on what you are after.

4 strokes are hard on prop grip. The classic solution is a serrated prop driver like this. In this case a DIY job but it needs a lathe to do it.

It always amazes me how effective and light a pull/pull can be particularly if you use monofilament line. I used them for the elevator on both my FX707 chuck glider conversions. I feared a servo in the tail would be difficult to counter with the intended motor & battery in the nose. The servo was "let into" foam close to the rear of the cockpit with just its arm exposed. In this position the supplied servo lead easily reached the radio. The monofilament has been painted black so the camera can see it! The top and bottom elevator horn is positioned so the line has a clear run. I made use of the stretch in the monofilament line (it has a 10lb breaking strain or about 16 times the weight of the plane!) to put in a modest pretension so as to not put too much side load on the servo bearing or the elevator hinge and to avoid bending the foam fuselage! Note the forward position of the servo arm to give more down than up elevator travel. The XF707 has flaps so it requires quite a bit of a "down elevator" mix when the flaps are fully lowered. I wanted to ensure still more down would be available if required.😉 Note the line pretension is still there after a year and the XF707 still flies nicely. In fact I flew it this morning. Having said that I would not recommend a monofilament pull/pull line for anything but a real light weight.

Yes indeed about the weather, or for my planes the wind, so I will be there.

What is the likely weight of the elevator servo? I am always concerned at the weight of the servo linkage becomes significant in a really light plane. As soon as I started using micro 3.7g servos in my lightweights it quickly became apparent that a long snake and the servo mounting soon doubled the bare servo weight. I quickly began to favour mounting servos adjacent to the control surface, either within the tail plane itself or the fin with the shortest linkage possible. As a by product the resulting improvement in the linkage mechanical efficiency tends to compensate for the low power of the micro servo. As the servo become smaller the benefit of positioning close to the control surface is ever more apparent. I have 3 twin boom planes where remote servo elevator linkage would be complex so in all these cases the servo is in the tail plane. The only tedious bit is running the servo wire through the tail boom. As an example a 2.5g elevator servo buried in the tail plane of my sub 250g DH Venom. Even a 2.5g servo is thicker than the tail plane so it is obvious but it allows the linkage to be direct and simple. The Venom has three such servos (aileron x 2 & elevator) and they all run happily from a 1A BEC in the ESC. The full "stall" amps of a 2.5g servo is only 0.5A! I work on the principle that if the aerodynamic loads stall all three servos at the same time its going to crash anyway. 😉

Jon H I suspect it is the old fuel that is the problem. The ether in it evaporates very quickly. The smaller the engine capacity and the more exaggerated the porting to get the power the more important the ether becomes as an "ignition promoter". It does not surprise me you had no trouble starting a Mills 1.3. With its modest port timing and long stroke it will run on almost any diesel mix!

Just a point but servo action is measured in a fraction of a second however a differential thrust response is significantly slower due to the inertia of the motor & props. The danger is too much differential may be applied before the expected yaw reaction is noticed from the ground. The same will apply when removing the differential thrust. As a well practised "bank and yank" pilot adverse yaw can normally be kept well under control with differential aileron movement in conjunction with an adequate fixed fin area except of course for the notorious Super Cub!

Far too tidy for me. It means you have to remember where everything is. Now with age and a chaotic work bench you only have to remember where the last thing you put down is, everything else has to be searched for. This process does have the advantage that you "rediscover" things you had forgotten about! 😉

John If I can, and the weather is reasonable, I will be there. And with a couple of planes that are new to the site!

Just a point about UHU POR. It remains a bit "rubbery" even after it has set. This means it does not sand well so no problem if the joint is completely hidden but any POR showing om a "surface" joint will not sand at the same rate as the foam so it will tend to show. As most of my Depron planes are scale with double curve fuselages the skin tends to be planked that gives long surface joints as well as requiring the outer surface to be sanded. It was this problem that set me finding a XPS safe glue that dried truly hard so with care it could be sanded down flush with the foam. My glue of choice finally came down to Technicqll Polyvinyl Adhesive. Does not have the strong "contact" characteristics like POR but it does stick and sets truly hard in 24 hours. The double curve fuselage of my Venom demonstrates how well its planked skin can be sanded and painted to a truly "smooth" surface. "Foam to Foam" is as good but it is a bit more expensive and the tubes are only 50ml rather than 70ml. 😉

An example of overstated capacity between two AAA NiMH. Can the blue one really have 3 times the capacity? Panasonic are a reputable brand. I know which I would believe. It is possible the "no name" ones are actually factory rejects that are simply bought up cheap & recovered. The capacity is just a "made up" figure to promote sales.

"mylar hinges super glued in and they are quite stiff" Should the hinge on a control surface ever be stiff? A stiff hinge simply makes everything from the servo to the control horn work harder and thus liable to flex more.

It is worth remembering that for a given plane configuration weight does not alter the glide ratio only increases the speed at which it achieves that ratio. In other words it will still achieve the same distance from a given height but gets there faster hence the use of water ballast in full size gliders when the lift is strong. The ballast also increase the stalling speed. For models with their higher Reynolds number means they can never achieve the same L/D as full size. It follows that reducing induced drag is really all that can be done to maximise the performance from the airframe. Of course to make use of "weak" lift the glider sink rate becomes important. For a given airframe its minimum sink rate speed is indeed proportional to its weight.

shepeiro Bending even the thinnest foam around a leading edge is a nightmare. Have you thought of using a solid foam leading edge sanded to shape. It is after all what you do when using balsa. If you are going to Mylar cover the wing then the "open" structure of any sanded foam will not show. All my foam wings, small and large, use a solid foam leading edge.

Stringy Remember there are a lot of variables concerning the power a plane needs to fly. The term " lightweight park flyer" does not really describe a particular plane. Are designing your own planes? As Robin C points out by far the best way is to simply use the motor of something similar but even then how you want the plane to fly can make a considerable difference in the power required. Once you have identified a suitable equivalent plane to what you propose identify the prop is uses and the motor. Then get good at looking up the actual specification for that motor (kV , max amps and recommended prop) and then find the nearest equivalent to one that you can get hold of. Remember not all manufacturers use the same number system to describe their motors however "out runner" type brushless motors of a similar weight and kV will have a similar performance. Finally remember that weight is a vital part of how a plane flies. Avoid selecting bigger batteries and more powerful motors in the hope the plane will automatically fly better and for longer. A heavier plane has to fly faster so needs more power to even fly at all. The downside of more weight is it will be more difficult or may be even impossible to control. If you could post a picture of your plane with its size and weight there is plenty of experience on a this site to advise what would work.

My own view is it all about cameras. If a UAV, plane or rotary wing, has a camera in it of any kind then that is the distinction and different rules apply. A rather Luddite approach but the technology should be reserved for making the plane fly better.

To give the full P38 prop rotation picture the XP38 prototype props rotated the conventional "inwards over the top". This means in the case of an engine failure the torque of the good engine tends to lift the dead engine. However this configuration possibly due to the twin boom created tail vibration and stability issues under certain conditions. It was eventually cured after much testing by changing to "outward over the top" rotation. However this meant that an engine failure particularly during take off could result in a loss of control and in early service the P38 was considered dangerous with many deaths. Although the P38 could fly perfectly well on one engine the minimum control flight speed, particularly at high take off weights, was higher than the recommended take off speed. After more testing the recommendation in the event of an engine failure on take off was to reduce the throttle and thus torque on the good engine, not an instinctive reaction, reduce the climb rate and concentrate on increasing airspeed to the required single engine minimum. All explained in "Famous Fighter of the Second World War" by William Green.

The configuration of a tail dragger, particularly if the main wheels are set well ahead of the CG to limit a nose over, is actually directionally unstable once the tail wheel has little or no load. With any slight deviation in direction the CG position well behind the resistance of the main wheels will try to make the deviation worse hence the need for instant big rudder corrections. If this correction is delayed the deviation will be beyond the power of the rudder hence the ground loop. Once there is sufficient airflow speed the normal aerodynamics of the fin provide the necessary directional stability. It can help to use some "up" elevator to keep load on the tail wheel until the air speed builds up for the rudder to be effective but it does need fine judgment to detect when the tail must be allowed to rise to achieve a safe flying attitude and avoid a premature take off and stall. The same "ground loop" situation can occur on landing hence the benefit of a smooth "3 point" landing to allow the tail wheel to take over directional control at the slowest possible air speed.

Managed a few flights this afternoon with my 1.4m span pylon "pusher" home build - Big Dragon 3. Wing and tail are Depron sheet covered. wing ribs are printed, fuselage printed PLA and a fishing pole tail boom. It weighs 853g with a big 4000mAh 3s onboard so it should have a substantial power endurance, maybe an hour! The reason for the flight was to test the rebuilt printed fuselage which had started to delaminate. It was just a bit too lightly built. Called Big Dragon 3 as it is the 3rd plane I have built of the same layout and Big Dragon as it follows the same style as my first "modern era" RC plane the RTF 1m span Art Tech Wing Dragon. Although it looks basic it is actually quite aerodynamic and with the ESC prop brake set "on" it glides really well yet with sufficient power to achieve both a "grass slide take off" coupled with a vertical climb capability. Not intended to tear about the sky but just for the enjoyment of simple flying.