Roger Dyke

Hi Dad_flyer, Thanks for that. At the moment the plane uses a 3536 1050kv, but I do have two 3542's. One a 1000kv and the other an 800kv. It may be something to think about if my prop swap to the 10x6 doesn't work (or I might just leave it the way it is).

Sorry Shaun, you are right, It's too big. Thanks for trying though.

Hi Nigel, The wing area is indeed 500 square inches. The gross weight all up is 5.0 lb. Many thanks for your reply. The plane has already had extensive surgery to get to the stage where I am now and no further surgery is possible. It also has quite a slim fuselage. I have really come to the end of the road regarding the airframe so I was really just asking for any advice on the proposed prop change.

Shaun: Absolutely no room whatsoever for a bigger battery than I currently have. When I converted this plane, I researched the market on battery power verses size and the battery I am using was the very best I could come up with which is 105 x 35 x 30 mm. Any longer, higher, or wider will not fit. But thanks for the suggestion. Peter: Thank you for your comprehensive reply. I have taken on board your thoughts and your interesting suggestions. At the moment using the 9x6 prop, 5 minutes flying time leaves about 40-50% in the battery. I was sort of thinking that with the 10x6 prop I could probably still maybe achieve about 5 minutes leaving about 25-30%. By the way. In carrying out my battery discharge time calculations, I am taking the figure of 80% of battery capacity use. I do have a more powerful motor but I don't know how that really helps me as I am controlled by the battery power. Either high voltage, low current or low voltage, high current. The power remains the same

Hi Dennis, Thanks for the link. Unfortunately my battery length limit is 107mm and if I go to the 4S then the current capacity drops from my 3S 3000mA to 4S 2200mA so will be very little improvement as I will have to reduce the current taken considerably to keep to the approx 5 minute flying time. I think that I have visited nearly all of the battery suppliers and for the space available I think have the best compromise I can get. Thanks for your suggestion though.

Allan: Thanks for your useful info. Simon: The plane is a CAT 500 (the one in my avatar photo). At it's current weight and power it is sitting at about 70 watts/lb which I know is quite low. The plane does have to be "flown" though in the true sense of the word, not like a lot of the 'overpowered' foamies that seem to be around now. But I don't mind that. The plane holds a lot of sentiment for me as when I was building it back in the 90's, my flying pal suddenly passed away and he was always asking me if I had finished it yet. Following his passing I shelved it for years and put it 1/2 built in storage. A couple of years ago I decided to finish it off as a tribute to my friend. So it's more than a plane, it's a memory so it has to fly. Perhaps the bigger prop will be a good thing to try. Then if it doesn't feel any better, I can always revert back to the previous one.

Hi Dave, Thanks for your reply. Yes, I hadn't considered the unloading aspect.

Hi All, I have recently converted an IC plane to electric. As is usual with these conversions, the model is a little on the heavy side for the powertrain available. Due to the fuselage size my maximum battery that I can fit is a 3S 3000mA. This limits me to about 33A to achieve a 4-5 minute flight. The motor I have fitted (1050kv) has a max current loading rating of 34Amps. I have been using a a 9x6 APC thin prop very successfully with a max current of 28-30A @ 10900 RPM. I have been thinking of trying a 10x6 APC thin prop to try and squeeze out a little more performance. In a static test with the 10x6 and a freshly charged battery the current is 36A @ 10400 RPM for about the first half minute falling back to about 32-33A as the battery voltage drops. Motor temperature was monitored during tests and found to be okay (hot but not too hot to touch). Would the prop change be worth the risk to the motor, or should I leave things as they are? Roger

Thanks for that Frank. I'll give it a go.

Don't see any facility in eCalc to be able to do that. It just says "all data without guarantee - Accuracy +/- 10%".

Hi Simon, Don't get too despondent. I too get the same with eCalc when I compare it's results with my own static tests. Usually the current in eCalc is about 25-30% less that what I record. And that's with all the boxes filled in as accurately as possible. It's a great tool to play with though when looking at prop affects etc.

Cuban8 and Capt Kremen, All good stuff this. Thanks for your replies. Contents noted.

leccyflyer: In my flight box that I take to the field I have one of each for all the planes I have. They are in a plastic "pouch" and sit in a special compartment in my box. In the bottom drawer I have every tool you could think of (and more) for any unscheduled event at the field. At home I have about 20-30 more props that I have accumulated over the years and they are kept flat in a drawer in a dark garage. I have a length of round section cable threaded through them and are thread on by size. I will probably never ever have a use for most of them again as they are all IC and of the sizes and types that I don't tend to use nowadays. Richard: Thanks for the info.

Martin and Trevor, All useful stuff. Many thanks for your experiences.

Hi Andy, leccyflyer, Simon, RCPF, and Richard, I thank you all for your very valued and informative replies. I think that I now have enough info to make a decision as to what props to use. RCPF: I did notice that the hole in the IC props seemed to be bigger than the electric props. Fortunately I have a number of the special little spacers in my kit. Good tip though. Thanks again, Roger

Hi Frank, Thanks for the info.

Hi Bruce, It was the difference in weight that I was thinking about. But I wondered if it made that much difference if it's well balanced.

Hi All, Newbie to electric flight question. Is it okay to use the 'standard' (IC) APC props on electric models. If so, what is the advantage of the electric props over the 'standard'?

Hi Dick, Ah..yes, of course it is. You are right and thank you for opening my eyes. I was taking the simplistic approach and not thinking (normal for me). I was just taking the applied voltage and applying a straight DC ohms law type formula but of course when we involve coils and frequency we are into a whole different ball game. I remember from the dim and distant past my involvement with back EMF's regarding loudspeaker driving and transformer manufacture etc. Anyway, to yourself and Pat, Thank you so much for your expertise and valued contributions. I really am now out of this thread. Thanks again Roger

Hi All, I am out of this thread now as all I really wanted to post was my findings reference the bad wattmeter. Many thanks for all your valued posts. Roger

Pat: Apologies. In the initial post I mentioned both models having the same set up. What I meant was exactly the same test conditions that they were subject to, not the same components that they were built from. Bad phrasing on my behalf I'm afraid. I like your analysis reference the motor dissipation, although I'm not too sure about by increasing the voltage (3 cells to 4) with the current remaining the same (with a smaller prop) that the heat generated in the motor wouldn't rise (V squared over R). As mentioned, I am a novice to model motors so of course I will bow to your superior knowledge.

Pat: I wasn't driving the other aircraft anywhere near as hard as this one and also because the other aircraft's motor was in the open with no cowl at all. The setup was totally different. Different make and size of motor too. I got lucky. As I understand (from an electrical background) nearly all the battery power (watts) is dissipated in the motor (windings) apart from a small amount in the ESC and the BEC for the RX and servos. The motor is the main load on the system. Or am I missing something.

Hi Pat, I agree that when dismantling the motor I too was expecting to see discolouration of all the windings, not just one section. I think it was the bad under-reading wattmeter that really tipped the scales, as the motor was actually taking far more current (and a lot more watts dissipating) than I had planned for and therefore rapidly got a lot hotter quicker than I was expecting. Maybe it was a combination of both,

Hi All, Interesting ending to this thread. I recently obtained a new motor for this aircraft of the same make and model. In running some tests on it, I immediately noticed that the current figures bore no relationship to the figures of the previous one that went up in smoke. With the very same set up the current and power figures were much higher. Almost double in fact. Thinking this was strange, I double checked that my setup was the exactly the same, and it was. Well almost. This time I had used a newer wattmeter that I had purchased about 4 weeks ago. On the motor that burned out I used my other one (purchased last January). So I decided to connect the two wattmeters together in series and repeat the test. This time, the newer wattmeter was showing the same (higher) figures, but the older one was only showing about half. I then decided to raise the throttle from zero and to watch both the displays. Both wattmeters tracked almost identically up to about 20 amps. Then as they went through 20 amps, the newer one carried on in sympathy with the throttle stick but the older one hesitated then fell back to 19 then started to climb again but slower than the newer one. By the time the newer one was showing 39 amps, the older one was only showing 24 amps. Just to make sure I also used a tongue tester (clamp meter) on the setup and the readings agreed exactly with the newer one. So there we are. One defunct wattmeter. I opened it up to look for bad joints etc., but everything appeared fine. So one for the bin. I know that my habits and judgements are not the best in the world but my poor old motor must have been dissipating twice the power (watts) that I thought it was. No wonder it went up in smoke. Just thought you'd like to know the outcome. Roger Edited By Roger Dyke on 17/05/2020 14:09:26

Andy: That sounds like some useful gadget to built there. I have always used a loop of string around the tail of my aircraft with luggage scales attached to test my torque. With the electric, I also include my wattmeter. I used to use this method when experimenting with different sized props too. Like many things, once we have compiled endless amounts of data from all sorts of experimental scenarios we usually end up with just a few choices that 'fits all' that we are happy with. Martin: Thanks for the interesting story of your career. I always find long careers fascinating. I've found that as I've got older and have lots of older friends, that between us all we have a massive amount of different experiences from life and work gathered from our past and it is rare when asking around about a particular problem, that we cannot find someone who knows the answer to it or can advise.