Simon Chaddock

When you start out with electric limited flight time seems to be a constant problem. As you progress with more capable planes with a longer potential duration you find what you want to do in the course of the flight is more important than the maximum possible flight time. I suffered from exactly the "duration" problem when I started out in electric where 3 minutes was likely the best flight time for a simple plane. My interest in structures and aerodynamics prompted me to do something about it. Improvement in wing aerodynamic efficiency and weight reduction more than doubled the duration of the same basic plane to 8 minutes, mostly due to the reduced throttle required to simply stay up. The full power duration was little changed. I carried on with this theme with several versions of an improved lighter airframe, more efficient motor and prop with of course a bigger battery. Although keeping to the same span as the original plane a cruise duration of an hour was achieved then a theoretical 2 hours and finally this plane which has a potential "power on" cruise duration of nearly 4 hours. It has a 1200mm (47") span and it weighs 436g (15.4oz) with a 3800mAh 2s. Its maximum duration was never tested as after 2 hours on a flat site I gave up from boredom and a stiff neck. Maybe it ended up to be a rather pointless exercise however I do still fly it on calmer days safe in the knowledge that the one thing I do not have to worry about is how long it has been in the air.😉

toto Much of the weather problem when learning to fly is the need for the right weather on the right day. I remember the frustration learning to fly full size gliders. Although they of course were dual dual control so the actual flying bit once in the air was not such a problem but actually doing the take and landing was weather dependent and it is the take off (aero tow) and the landing that needs the most practise. The weather in the UK has always been a frustration to flying.

I have prepared a couple more EDFs to practise on but the weather says otherwise and likely so for a few more days yet. You never know it might eventually get calm enough to try the Douglas X3 again which was after all the reason for the EDF practise.

Robert The conventional wisdom is that high capacity AA NiMh cells have a high internal resistance so have to be charged and discharged very slowly to reach their claimed capacity. There is of course no guarantee how or even if the manufacturer ever achieved what "It says on the tin". If you are getting out what you put in at the sort of rates you are using then that likely the best you will get. If you know the actual discharge rate your TX requires and use that for both the charge and discharge you see a higher capacity. Remember the old NiCd AA cells were only 500mAh. They did have that capacity and with a lower internal resistance could deliver a good 10C (5A) at a push.

I find hard to believe an effective silencer is not possible particularly as a 4 stoke is much better able to handle exhaust back pressure than a 2 stroke. Is it just a case of providing the space for the necessary can volume?

I can only advise that you put equal thought into keeping down the weight of the Bearcat's pretty "tubby" fuselage. The lighter the overall weight the less power you need and the lower the stress on the wing. A quick strength test. When complete and including the battery try picking it up by just its wing tips. If this can be done without the structure making to many 'stress' noises it will put a bending load on the wing equivalent to pulling 4g or doing a 'proper' circular loop. If it feels like the wing is going to break before the plane is fully lifted then stop. The plane can still be flown but steer clear of any rapid or substantial elevator stick movements! I have physically tested all my planes this way except the Depron 2.1m span Antonov AN124. With a thrust to weight of just 0.4 : 1 it simply does not have the push for aerobatics but then neither does the full size.😉

250g is not bad at all for such a big span and chord wing.

Lipo Man That is very neat. However with a 6mm foam skin I do wonder how much work the spar will be doing apart from stopping the skin sagging between the ribs when it is under tension and buckling when under compression at the point of maximum stress. Alternatively you could argue that if the box spar is the primary source of strength than what is all that skin foam doing? Technically a box spar is used where torsional rigidity is required as well as bending strength however it is quite likely the "all over" 6 mm foam skin will actually provide all the torsional rigidity required thus making the box element of the spar redundant. I do appreciate there are construction benefits in having a box to work from but with such a thick skin I always worry how much stiffer or alternatively lighter any spar would be if it was flush with the outer surface of the foam skin. You can see where this sort of thinking lead me with foam wing construction. I too will be interested in how it pans out.

A bit more EDF practise today with the Depron North American XB70 Now very old for foam. Built in 2014 and last flown in August 2022. 70mm EDF exhausting through 6 scale nozzles which is not the most efficient set up but it works well enough. Just 3 minutes is all I got from its 2200mAh 3s but belly landed no problem. After 10 years it is now a bit "tatty". Needs some TLC.

I do chamfer the edges of each plank preferably on both sides so the plank to plank joint is normal to the surface. I use a sanding block with surprisingly coarse (60 grit) paper on it. New paper cuts the foam very easily with low pressure. I hold the plank in my figures and then locally sand the joint surface and when done work along the full length of the plank. It really only requires the block to "kiss" the foam. It does take a bit of practise to be able to judge how much chamfer is required as it changes depending on the radius of the surface the plank is covering. In general I have found it better to slightly under chafer. It does leave a small gap at the surface but that can be easily filled/painted. Acrylic paint is itself quite a good glue for small gaps! Over chamfering leaves a gap on the inside which you may not even see. Such a plank joint is rather susceptible to splitting from handling pressure. It is worth reebering that much of the strength of a planked structure comes from the plank and it joint with its supporting structure. It is twisting that puts load directly on the joint and than only in shear. Glue is good in shear and a plank joint is very long. The new hose glued on with the new printed "short" nose cone. It just needs the glue to fully harden before light sanding, filling and white acrylic paint. The battery box has been extended to allow the battery to more forward.

It is a moving magnetic field that can effect a wire as it can induce voltages in the wire, particularly the tiny voltages in an aerial. As long as noting moves (vibration?) even a strong magnet will have no effect.

+1 That is exactly what I do.

Nigel I fear you have hit the nail on the head. I am sure IC engines will continue to be produced for many years but as you point out without a high volume the range of engines will reduce and the cost will go up.. Whilst this may no be too much of a problem for the current users it could mean a bleak future. After all has not the same sort of thing happened with ARTF and particularly with moulded foam scale? Accurate highly detailed electric power and maybe a "multi" at a price likely not far removed form the cost of buying the materials and parts to build the same from scratch.

The broken nose cut back to the inlets. Although important to have a good surface to work from it is always a concern as you are cutting away a lot of damaged but original airframe. Having cut out the L&R formers the new nose is built in exactly the same way as the original fuselage a half shell over the plan. When the planking is complete the half shell can be lifted and the other half of the formers added. Then the planking starts all over again but ensuring each plank is as accurately preformed as possible to avoid stressing the half shell and ending up with a twist. Although rather tedious it does mean the new nose will weigh exactly the same as the original/

Jonathan Unplug the battery after each flight as soon as possible. Remember unlike IC an electric motor can spring into life under some fault conditions. Further more an injury from a prop with an electric motor driving it is likely to be more serious that from IC. Some degree of obstruction may stop an IC but not an electric motor. It just keeps going! The only safe electric motor went it has a prop on is one that is physically disconnected from its power supply.

Yesterday was just about calm enough to try the Bluff nose Stiletto again. A bit better this time. The gyro managed to keep thing under control for nearly a circuit but it is still a bit tail heavy. Flight time nearly 15 seconds! Eventually it did stall despite my best efforts and as it was going a bit faster the impact was a bit harder. A seriously crushed nose. The battery actually broke free forward and disconnected itself! However on the positive side the Depron structure did its usual "crimple zone" thing so the rest of the airframe is completely undamaged It just needs a new nose ahead of the intakes to be built and to move the battery a bit further forward then try again.

martin Remember if any cell in a LiPo is much below 3V at rest it is chemically damaged. Such damage is not reversible. There are some tricks you can do to persuade the charger to put some capacity back but likely no more than 50%. Then you are faced with the issue that not all the cells are damaged. In use the damaged cell(s) will discharge first but the others will continue to provide current. This will damage the "weak" cells still further so making things worse each time that LiPo is used. Perhaps even more important with such a LiPo the risk rises that something might go seriously wrong. It the charger doesn't like a LiPo for low voltage it is a safety feature built into the charger to stop you using that LiPo. You should consider yourself warned. The advice is always get a new LiPo.

My only concern with your proposed technique is the foam board box spar is not ideal structurally. The box spar would be better made as deep as possible within the wing section particularly at the root where the bending forces are a maximum. Cladding a wing in a more flexible foam makes sense but it does rather ignore the potential strength of the foam itself. Some of it alter all will be at the maximum possible wing depth on what looks to be quite a 'generous' wing section. This does raise the question as to whether the box spar needs to go right to the wing tip. The B&Q XPS foam sheets do have some strength and like most of this type of material more stiffness and strength in one direction than the other. It is possible to build a complete wing out of just 5mm B&Q foam. The LH wing of an EDF Sea Hawk. I try to work on the principle that sheet foam is a 'thick' material and thus needs far less support than conventional thin wing skins. I will follow your build with interest.

In between repairing the Stiletto and getting my hand in flying EDFs I have been slowly working on the Big Dragon 3. On the BD 2 I used a small servo to work each elevator. I did this as I originally intended to use then as rudders as well but never did. It made quite a neat installation as the 3.7g servos fitted flush with depth of the tail plane and being "Y" lead only one servo wire went down inside the boom. On the BG3 3 I chose a single bigger servo to work both elevators. Each elevator has its own link rod to allow for the odd angles over the full travel. Each link rod goes to a separate hole in the servo arm. The L&R elevator horns are of different lengths so both elevators have the same travel. The near complete Big Dragon 3. The wing is actually a "spare" I built for the BG 2 some time ago. Only the Rx and some servo wiring still to go. The BG 3's "party piece" is the two section "fishing rod" boom is collapsible for storage. Longer than BG 2 and with a slightly greater 57" span but with 43% bigger battery it will be about 150g heavier at close to 900g. Not really Intended to be a powered glider but more of a reliable "fun fly". If it performs anything like BG 2 it should have an impressive climb and cruise endurance.

The way to think of using Depron i.e. thin sheet XPS foam, is to consider it as a stressed skin with an internal supporting structure. This internal structure could include carbon rod(s) for extra stiffness. It is likely the resulting structure will be thicker that a simple balsa 'frame' but it can be a streamlined aerofoil to compensate. It is quite possible that a good streamline shape can be twice as thick as a balsa frame structure and still create less drag. It is also likely to be aerodynamically more effective. Fully covering a Depron structure in some way will increase the stiffness but it can add significant weight. How much weight you can save will very much depend on how stiff you want the Depron structure to be. If you use Depron as a single slab structure it is likely to be too flexible even with leading and trailing edge reinforcement. Depron substitution in a load bearing structure is likely to require some experimentation to achieve a weight saving with sufficient strength. As an example the tail plane on my Bombardier Q400. It sits on top of the fin. All 3mm Depron except for the tapered balsa spar flanges are set flush with the Depron skin to give the maximum possible spar stiffness for minimum weight. Not exactly a 'simple' structure but strong enough for its purpose as a twin prop airliner and that includes doing a loop!😮

Still waiting for suitable weather but a picture of the X-3 with its long nose. This nose is not flight worthy. It is only for show as apart from any safety considerations the retaining magnets are not strong enough to withstand the likely aerodynamic forces from any pitch or yaw. If and when the X-3 does prove to fly well enough with the bluff nose I could in the privacy on my field tape the long one on just prove it will fly but landing with it undamaged is likely to be a different story.

It rather depends on what you want or expect winglets to do. A GG suggests they can be useful to create side area at which they can work well but If you are trying to improved the aerodynamic efficiency of a wing by controlling the tip vortices then they most unlikely to make any practical difference at model sizes and speeds. After all such winglets benefits are only measurable, and then only by a few %, on airliners on long duration accurately controlled flights.

Surely bearing heat expansion depends on where the heat is coming from. Uniformly heated and within the capabilities of its lubrication all the bearing will expand simultaneously. I would have expected in the average model IC engine the crankcase gets hotter than the crankshaft suggesting if anything the outer race will expand more than the inner thus increasing the ball running clearance. Just an observation. Now whether the highly penetrative methanol/oil environment of a two stoke may deteriorate a sealed bearing's lubrication over time is another question.

This afternoon was quite reasonable, not much wind and no rain so a bit more EDF practise so I got out my first foam build Hawker the Sea Hawk.I had not flown it for 2 years. Although the photo is nearly 3 years old it still looks exactly the same today. The inlet ducting is far from perfect. Any yaw any you can hear the fan note change and the direction of the inlet airflow is disturbed. With its generous area straight wings it does fly passably well although it needs nearly full power to climb. Like most 50s jets it has a low drag airframe so glides really well for and EDF. Managed 5 minutes 28 seconds which is rewarding. That leaves 2 more of my Hawker jets to fly. The P1081, the second swept wing Sea Hawk that crashed and the prototype Hunter. They are both painted all over pale sky blue that Hawker used on all their jet prototypes. It may be scale but they are just horrible to see at any distance!

The very limited flying over the winter means I need to get in some practise with EDFs as I hope to get the rather "extreme" Douglas X-3 flying. The better my flying skills are the less likely it will might not get any more damaged that it already has been. I decided to fly some of my EDFs that have spent most of last year "hanging on the wall", quite literally. First was the 50mm EDF DH "Swiss" Venom although on this occasion it was flown without the tip tanks. 44" span, it is a Depron job and light at 520g but with a 1300mAh 4s and a clean airframe it is no slouch. Those twin booms are delicate so a belly landing needs concentration and accuracy. Next calm day it was the exact opposite. The Depron Douglas Skray . 36" span and a similar weight to the Venom but with over twice the wing area. A gentle slow flyer but like all delta the drag rises rapidly in any sort of manoeuvre. Flown bank and yank nose drop in a turn is pronounced. Pull too many g and it almost stops flying! Next was the Hawker Hunter F6. 50 mm EDF 33" span and made entirely from 5mm XPS sheet (no balsa or carbon!). At 385g a bit heavier than the Venom although not quite as fast but flies very nicely. Decorated as a Black Arrow of 111 squadron who managed to loop 22 of them together in formation. Today late on (17:20) the weather improved considerably so it was the turn of the P1052 better known as the prototype swept wing Sea Hawk, Still a "portly" Sea Hawk fuselage with a modest power 55mm EDF. Like the Hunter made entirely from 5mm XPS sheet This was my second Hawker, the first was a Sea Hawk. I made a better job of the complex bifurcated inlet and exhaust duct so it had more thrust from just a 1500mAh 3s. Two were built. One still exists at IWM Cosford. The other was modified with a bit more thrust but broke up trying to go supersonic in a dive. The test pilot did not survive. Hopefully at the next calm day I will be able to try the Douglas X-3, again and be a bit better prepared to not break it.