Author Topic: I really don't understand why people think this is so complicated (Read 1320 times)

Tim Wescott · « **on:** May 15, 2011, 03:05:12 PM »

One of my back-burner projects is to make a calculator for sizing the electrics to a plane (or a plane to the electrics). I really don't understand why folks get so tied up in this -- I've only got 24 different variables that relate to one another in ten different interconnected ways. It's really quite simple. Here's a map: the lines on the left show how the variables are interconnected.

See? No problem. Now to start writing some Java code.

   .- aircraft mass
   |- mass to power ratio
.- .- '- average power (design center)
| |- average to peak power ratio
| '- peak power (minimum motor spec)
|- flight time
'- .- total energy used
   |- battery energy efficiency
.- |- cell series count
|- |- nominal cell voltage
| .- '- capacity consumed
| |- charge safety factor
| '- .- total battery capacity
| |- parallel cell count
| '- cell capacity
|- motor speed constant (Kv)
|- battery voltage factor
'- .- motor speed
   |- prop pitch
   .- '- pitch speed
   |- pitch speed factor
   '- .- airspeed
   |- circle radius
   '- lap time

Dennis Toth · « **Reply #1 on:** May 15, 2011, 09:23:37 PM »

Tim,
I agree sometimes we can make something sound complicated when there are some much simpler ways. One simple rule is take the expected weight in oz divide by 10 pick the motor that is the next weight up i.e. all up model is 48 oz/10 = 4.8 oz pick motor around 5 ish oz with a kV of 800 to 900 (for a 4s1p battery pack).

Now the biggest problem is picking a motor with the quality needed for stunt, that's the tough part. There is very little information on motor quality about the only information I've heard is to check the resistance and if the kV is the same the one with the lower resistance is better. We don't know anything about torque from one brand to another, quality of bearings, max temperature limits etc. So what to do? One way is to look up what others have used in the List your Setup and used the Brands that our top fliers are using or you can just try some of the low cost motors and see what happens. I like to stick with some of the more well know stunt brands listed. When in doubt go with you get what you pay for.

Best, DennisT

Tim Wescott · « **Reply #2 on:** May 15, 2011, 09:36:39 PM »

Quote from: Dennis Toth on May 15, 2011, 09:23:37 PM

Tim,
I agree sometimes we can make something sound complicated when there are some much simpler ways. One simple rule is take the expected weight in oz divide by 10 pick the motor that is the next weight up i.e. all up model is 48 oz/10 = 4.8 oz pick motor around 5 ish oz with a kV of 800 to 900 (for a 4s1p battery pack).

Rules of thumb are really good for keeping you pointed in the right direction when you're within one step away from the beaten path. They're also good for leading you far afield when want to take two or three steps off the beaten path. They're a great source of funding for consultants -- I know, I often make good money putting folks' projects back on track after they relied a bit too heavily on rules of thumb.

I'm aiming at a little app that'll let you select motor/battery/ESC combos for anything that's reasonable to fly, not just another 40 sized stunter.

Howard Rush · « **Reply #3 on:** May 15, 2011, 10:16:20 PM »

I'd put in prop and motor efficiencies.

Mark Scarborough · « **Reply #4 on:** May 16, 2011, 11:39:42 AM »

air temp, relative altitude, airframe drag, induced drag, line diameter, yaw angle, hmm what else,,

Or you could just to to the thread that lists setups, and extrapolate what you need,, but then that is again a "rule of thumb" and it would remove your entertainment in the process,,

Tim Wescott · « **Reply #5 on:** May 16, 2011, 11:44:32 AM »

Quote from: Mark Scarborough on May 16, 2011, 11:39:42 AM

air temp, relative altitude, airframe drag, induced drag, line diameter, yaw angle, hmm what else,,

Or you could just to to the thread that lists setups, and extrapolate what you need,, but then that is again a "rule of thumb" and it would remove your entertainment in the process,,

I think there's too many variables to capture them all -- I'm just looking at getting a starting point.

The relationships above (and the constants that go with them) are pulled from the list of setups -- my biggest problem with it is that for knock-around sport flying I tend to like smaller planes, and that's not well covered in the list.

Keith Renecle · « **Reply #6 on:** May 16, 2011, 11:48:20 PM »

Quote from: Tim Wescott on May 16, 2011, 11:44:32 AM

I think there's too many variables to capture them all -- I'm just looking at getting a starting point.

The relationships above (and the constants that go with them) are pulled from the list of setups -- my biggest problem with it is that for knock-around sport flying I tend to like smaller planes, and that's not well covered in the list.

Hi Tim, what do you mean by "smaller planes"....... .15, .25,.40 engine equivalents??

I find that the nicest size for most purposes like "not-too-big........not-too-small" is the .40 size plane. It fits the back seat of a smallish car and is still nice to fly. A 4-cell 2200 lipo pack, +/-850 kv motor and APC 11 x 5,5 prop, 40 amp esc, governor timer and off you go! The power package will cost about the same as a sport glow engine.

The other nice thing about this size of model, is that the line length (up to 65 ft.) is long enough to fly a neat pattern. (I need space to miss the deck!) Shorter than 60 foot lines makes things a lot more difficult. You could fly a slightly smaller system like the .25 to .35 size motors on 60 ft. lines and use a 3-cell lipo, but the price difference is not that significant. I am developing a .15 size system here in South Africa but this is aimed at getting kids back to C/L. I always come back to a .40 size model for general flying and it comes close to flying my bigger competition models.

Keith R

Tim Wescott · « **Reply #7 on:** May 17, 2011, 09:37:54 AM »

The biggest airplane that'll fit in the trunk of my 2000 Ford ZX2 has a 47 inch wingspan. It's comfortably powered by an FP 20.

My goal is not to write code to cover the size plane that I like to fly and expect the rest of the world to bend to my preferences. My goal is to write code that'll work for anything from 1/2A sized up to the biggest thing that you can reasonably hand from 70 foot lines.

Dennis Adamisin · « **Reply #8 on:** May 17, 2011, 02:41:37 PM »

Folks coming over from IC think in terms of 15, 25, 40 etc. I think we need to STOP THE MADNESS.

I would like to propose power systems that are based on prop size. If someone is using an IC system with an 11" prop then they could find the common ground with an electric system sized to an 11" prop. It also dovetails nicely with Tim's desire to size systems from very small to very large.

BTW this is the approach I took with the power systems in the Brodak line-up but my methods were not nearly aas eloquent as Tim proposes. This will be a good project!

eric david conley · « **Reply #9 on:** May 17, 2011, 03:37:59 PM »

Over the past several years there has been more and more people trying motors instead of internal combustion engines in the cl carrier events. Now we are trying to combine e and ic into each event so we wont have so many different events. On our first attempt they chose "weight" as the only measurement. The .15 ic carrier event is called 15 carrier and now if you want to compete in that event your e-entry measurement is a plane that doesn't exceed 2.5 pounds. In .36 Profile Carrier and .40 CL-1 events the maximum weight is 3.5 pounds. The .41 to .65 CL-2 carrier planes are limited to greater than 3.5 pounds but not more than 4.5 pounds. All e-planes weights include battery ready to fly. There are some skeptics about this rule as far as being fair to the ic rules but I must say that it opens up a lot of different approaches to how you build your e-plane and I think it is quite refreshing and "so simple" when compared to the paragraphs spent on each class with the ic engines. Eric

Tim Wescott · « **Reply #10 on:** May 17, 2011, 03:49:07 PM »

Quote from: Dennis Adamisin on May 17, 2011, 02:41:37 PM

Folks coming over from IC think in terms of 15, 25, 40 etc. I think we need to STOP THE MADNESS.

I would like to propose power systems that are based on prop size. If someone is using an IC system with an 11" prop then they could find the common ground with an electric system sized to an 11" prop. It also dovetails nicely with Tim's desire to size systems from very small to very large.

BTW this is the approach I took with the power systems in the Brodak line-up but my methods were not nearly aas eloquent as Tim proposes. This will be a good project!

Does it map that neatly for CLPA? For most RC planes, the equivalent electric motor spins a bit slower and takes a larger prop than nitro. But CLPA doesn't value a screamin' fast motor (quite the opposite), so maybe it does.

I think that doing it by weight may be the way to go.

Author Topic: I really don't understand why people think this is so complicated (Read 1320 times)

Tim Wescott

I really don't understand why people think this is so complicated

Dennis Toth

Re: I really don't understand why people think this is so complicated

Tim Wescott

Re: I really don't understand why people think this is so complicated

Howard Rush

Re: I really don't understand why people think this is so complicated

Mark Scarborough

Re: I really don't understand why people think this is so complicated

Tim Wescott

Re: I really don't understand why people think this is so complicated

Keith Renecle

Re: I really don't understand why people think this is so complicated

Tim Wescott

Re: I really don't understand why people think this is so complicated

Dennis Adamisin

Re: I really don't understand why people think this is so complicated

eric david conley

Re: I really don't understand why people think this is so complicated

Tim Wescott

Re: I really don't understand why people think this is so complicated