Dave i lsted 2 motors i like , i had the NTM 500 kv motor on hand and did a watt test, 14x7 prop, 6 cells around 1050 watts and around 44 amps, now i would like to find a 550 to 600 kv motor to see if that gets any better , i think most any other 500 kv motor would get around the same results.

Originally Posted by doxilia

Scott,

I think your FMS model is probably a very good indicator of what performance you can get from that setup in a modern F3A type model. Unlike classics or even sport planes, the emphasis on current pattern is to have very high torque imparting a considerably higher thrust/speed ratio than what was, and still is, required for classic pattern. In the latter the ratio is inverted reason for which we often talk about ballistic pattern. Classic pattern is more akin to a pylon model setup than it is to a scale model setup as today's F3A models require.

Getting to the point, I was trying to comment that a vintage design like a Kaos, if you wanted it to fly like it did when used for classic pattern with a glow engine, you need to replicate that setup by using a higher Kv and current draw power plant. If you set it up with the same parameters that you have on your FMS model, but reduce the prop size and increase the model weight considerably, you'll wind up with a flying crate.

With that in mind, if you keep the Kv down, you need to up the cell count and reduce prop size for the Kaos compared to the FMS model. Conversely, you can keep the cell count the same at 6s but then you need to increase the Kv keeping the prop size more or less the same as in the 8s setup and that will also yield classic like performance.

Another way to look at it is to do it inversely, you set the power/weight ratio desired for the model - say 150W/lb. If you then fix the model weight say at 8.5 lbs you'd require roughly 1300W. From experience, these 60 size classics fly better at a slightly higher max power of 1400W+. Then, since power is the product of voltage and current (W = V x A), you can see that voltage and current have an inverse relationship given a constant power; increase voltage, decrease current or vice versa. If you then equate cell count to voltage and prop size to current, you can see where my comments above come from. Increase cell count, decrease prop size or vice versa. The motors Kv can be thought of as a constant multiplier in the equation. Increase Kv, increase power without having to significantly increase either voltage or current. I like to think of the metric as a sort of additive in fuel like nitro. You want more glow performance, increase nitro; you want more electric performance, increase Kv...

David

Scott,

Take a look at the full specs of the Rimfire 60 and you'll be in the classic pattern space. Any two good motors with similar specs will, like you say, essentially perform in a similar way. The Rimfire 80 is the same identical motor but wound differently and so is able to produce more power on larger props at lower RPMs - not what you really want in a classic. Your two motors mentioned are more akin to the R80.

David

Very good reference for estimating what performance you may get from an electric setup.

http://rcwebclub.com/rcwebclub/PAR.aspx

I like the rimfire 60 but dont like the cost of the motor , its more then half the cost of the plane kit but the numbers look like what i want tho.

I would like to see the Kaos covered with Monocote,too. However, I guess $180 doesn't buy much anymore. Someone offered a Great Planes Super Kaos kit yesterday for $150.

Originally Posted by doxilia

Extensively, I agree. And yes, we do need the right tool for the job.



IMO though, this is not the answer. Inrunners work well on DF's because of their low inertial mass compared to a prop. They also rely on multiple low pitch blades rather than two higher pitch blades like a typical prop does. Inrunners, simply put, don't have the torque required to turn a prop efficiently and generate the power required by themselves. They are used with some success in modern F3A with planetary gear reductions (notably motors like the Hacker C50 if memory serves) because modern pattern is more akin to scale in its thrust requirements than it is to ballistic pattern which requires or desires higher speeds.

Outrunners were sort of invented to overcome the torque issue with inrunners in prop applications. So there is actually nothing wrong with using outrunners for classic pattern. The only problem is that generally speaking we kind of insist in setting them up as one might for a scale or F3A model. Why? Because it gives lower current consumption, longer flight times while still delivering the thrust to fly.

But..., if we want ballistic pattern, there is no way around the need to increase Kv with the current state of the art which unfortunately demands higher current consumption and corresponding battery capacity.

So in a nutshell, for me, the right tool for the job with classics, all else being equal, is higher energy density battery chemistry. I believe that will come before or simultaneously with other developments in electric power.

Incidentally, this entire discourse on e-power parameters for classics vs modern F3A is directly akin to the concept of describing a piped two stroke vs a muffled four stroke. Another analogy yet, for me, is to think of Kv as a tuned pipe. Low Kv, no pipe, high Kv, pipe. Four stroke, big prop, two stroke, small prop.

David

Okay. I think I've got you. Outrunners it is then. I guess I'd be willing to sacrifice some current consumption, flight time, and even performance in the name of authenticity.........at least until those better batteries come along.

Much nicer video up now.

Agree, much better
Here's the direct link:

Tower Hobbies Kaos 60 GP/EP ARF (2 min 37 sec)

Originally Posted by Trisquire

Okay. I think I've got you. Outrunners it is then. I guess I'd be willing to sacrifice some current consumption, flight time, and even performance in the name of authenticity.........at least until those better batteries come along.

Exactly, while things are where we are at now, we just need to insure to build as light as possible so that we can get 5Ah+ 6s packs in our classics without them becoming too heavy compared to their glow counterparts. It is actually possible to build some wood classics quite light so that we can even use 5s setups which save a cell in weight allowing it to be replaced by higher capacity packs.

On the other hand, for glass/foam models where it is harder to control weight or for those larger birds (Aurora, EU-1A, Brushfire, etc.) we can go to 8s or even 10s setups reducing the Kv and current consumption correspondingly and produce higher top power figures in the 2 KW ballpark while still turning "classic pattern props" at higher RPM's (12K+) rather than the more scale like 10K- typical RPM's.

David

Originally Posted by scottc39

I like the rimfire 60 but dont like the cost of the motor , its more then half the cost of the plane kit but the numbers look like what i want tho.

Cost of motors is related to quality not so much to specs. Find a quality/price point you like and just insure the specs are similar to a Rimfire 60.

IMO though, the RF60 is a middle of the range priced motor which if treated properly will actually deliver good reliable service without throwing magnets, bearings or bending the shaft and/or the fuse...

I've used cheap and expensive motors but tend to prefer higher quality motors in larger models. Then again, these things are entirely a subjective personal choice thing...

David

Originally Posted by doxilia

Exactly, while things are where we are at now, we just need to insure to build as light as possible so that we can get 5Ah+ 6s packs in our classics without them becoming too heavy compared to their glow counterparts. It is actually possible to build some wood classics quite light so that we can even use 5s setups which save a cell in weight allowing it to be replaced by higher capacity packs.

On the other hand, for glass/foam models where it is harder to control weight or for those larger birds (Aurora, EU-1A, Brushfire, etc.) we can go to 8s or even 10s setups reducing the Kv and current consumption correspondingly and produce higher top power figures in the 2 KW ballpark while still turning "classic pattern props" at higher RPM's (12K+) rather than the more scale like 10K- typical RPM's.

David

Looking at the SPA competitors guide aren't electric setups limited to a max of 1400 watts? Also it says that ALL SPA planes may not use a prop larger than 13.5X6??

Originally Posted by TonyF

Much nicer video up now.

Agreed.

Robert

Originally Posted by Capt. Roll

Looking at the SPA competitors guide aren't electric setups limited to a max of 1400 watts? Also it says that ALL SPA planes may not use a prop larger than 13.5X6??

I'm sure both of those facts are true and set forth in order to avoid electric models having an edge over 4-stroke 90 setups.

My comments however have little to do with the SPA specifically and are more generally aimed at how to setup electric powered classics - for SPA, CPA or just all around enjoyment.

David

PS large models like the Aurora or other 9 lbs+ classic are typically not flown or allowed in SPA.

This is the recommended motor for the 3,1 kg Schweighofer Curare ARF. On 6S and a 13x8 prop its power is comparable or better than with a piped OS 55 AX. I've flown both, and the only noticable difference is the electric has a bit more vertical performance.
http://www.der-schweighofer.at/artik...4025_12t-510kv

I would not hesitate using 6S on the Kaos if you want to go electric.

Here is were i get confused with electric set ups, i am afraid to run to small of a prop(this could just be not understanding the motors), in my past post i did a watt test with a 500 kv motor and i know that motor need a longer prop. I also did a watt test with a turnigy SK3 660 kv using a 6 cell pack and a 12x6 prop, got 61 amps and 1461 watts, i liked this but it went over the rated amps for the motor and my esc. this motor is only rated for a 5 cell tho.
I do have a tacon 46 670 kv rated for 6 cells and my thinking is i could use a 11x6 prop but for a plane 7/ 8.5 lbs it just seems like this set up would just froth the air more then any thing . so fill me in on high rpm setups.