Author Topic: Electrocuting the Atlantis (Read 19465 times)

Tim Wescott · « **on:** July 25, 2019, 10:46:16 PM »

Finally decided to pull the trigger on going electric. I'm starting with el-cheapo batteries and a Cobra motor (inexpensive, but some folks seem to like it). I have an old Shultze ESC that was given to me, and should work, and, of course, I'm friends with the wife of a guy who makes timers.

Comments from the peanut gallery on how to mount that motor are welcome. If it was all fresh dry wood I'd put a ring mount in the front, and front-mount the motor -- unless someone speaks up and tells me that Cobras don't like that. Part of me wants to machine a mount that'll catch the existing motor mounts and rear-mount the motor. That'll both give me something that's drop-in, and it'll be drop-out in the event that I decide I hate electrics after all.

Hopefully I've done my math/guessing right. For reference the plane is around 690 squares, and weighed 64 ounces empty with a 46LA. The starting setup is:

Cobra 2826-12 motor
Turnigy 3300mAh 5S battery (I got one 3300mAh and one 3000mAh, to figure out which is best)
Shultze ESC: fut-18.46K-F2B.gra (mit F2B Programm, es müssen kuhl sein!)
Some TUT or other.

I'll want to make room for a Recording TUT, even if I don't have the @#$% recording part working yet. I'll probably use Howard's AMA program, to go with the Shultze's F2B governing mode. Should have quite Hubin-esque flight characteristics, except for the Rushian slow take off.

I'm not sure what prop to use to start -- I'm thinking a 12-6, although the very first run may be a 12-6 cut down to 11-6, for ground clearance. Suggestions welcome...

The ESC has no BEC, so I'll have to tuck a voltage regulator in there somewhere. The TUT draws little enough current that I can probably get by with a 78L05 in some heat shrink.

Look at all the room in that equipment bay! Those things always look so sparse before you try to jam the last little bit-o-kit in there. Like the ESC. And the timer. And all the wires. Omigod, I'm doomed.

Howard Rush · « **Reply #1 on:** July 25, 2019, 10:56:58 PM »

Glad to hear you are going electrical. K2R spot remover (probably Cab-o-sil and a solvent) is good for sopping up oil.

People have had more success mounting the Cobra on the same side of the motor as the prop than on the opposite side from the prop ("front" and "back" definitions may vary).

I have some extra props. The APC is cheap and good, but you'll probably want one that goes the same way as your old engine.

Tim Wescott · « **Reply #2 on:** July 25, 2019, 11:24:54 PM »

Quote from: Howard Rush on July 25, 2019, 10:56:58 PM

I have some extra props. The APC is cheap and good, but you'll probably want one that goes the same way as your old engine.

I got "tractor" props. More props to experiment with would be good.

Should I stick with 12" and lengthen my landing gear, or is it even remotely sensible to hold the diameter to 11"?

Crist Rigotti · « **Reply #3 on:** July 26, 2019, 07:19:07 AM »

How much do you figure will be the final weight? Depending on the weight, I think you have too much battery. I'm flying on a 5S 2450mah battery with a weight of 52 ounces. I'm using @ 75% of the battery.

Tim Wescott · « **Reply #4 on:** July 26, 2019, 08:20:05 AM »

Quote from: Crist Rigotti on July 26, 2019, 07:19:07 AM

How much do you figure will be the final weight? Depending on the weight, I think you have too much battery. I'm flying on a 5S 2450mah battery with a weight of 52 ounces. I'm using @ 75% of the battery.

It's 64 ounces with the 46LA and all the slimer equipment. I'm assuming it'll be the same or slightly more with electrons.

If I just scale your figures by weight I get 3000mAh -- and that's what I would have bought across the board except that I chickened out and got a 3300mAh to try the first time, on the theory that an overweight plane in testing is better than a nice light pile of balsa trash after pooping out at the end of the pattern.

TDM · « **Reply #5 on:** July 26, 2019, 10:45:38 AM »

Welcome to the madness.
XOAR PJN-E or PJM-E 12x6 works great.
https://www.amazon.com/XOAR-Electric-Airplane-Propeller-Blade/dp/B07B9WQVMP/ref=sr_1_2_sspa?keywords=XOAR+12x6&qid=1564158946&s=toys-and-games&sr=1-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyQkpNOVBLMk1IUEM4JmVuY3J5cHRlZElkPUEwMDAxOTUyMUIxS01POTZETzFHQyZlbmNyeXB0ZWRBZElkPUEwNTY3NTc5OTY4SjhQSk02WDVKJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==
https://www.ebay.com/itm/XOAR-PJM-E-12x6-3-Pack-Black-RC-Electric-Airplane-Propeller-12-Inch-Wood-Prop/372525591771?epid=17026781507&hash=item56bc416cdb:g:dzgAAOSwvwRcCHWo
Perhaps Cobra 3520-14 is a better option for the prop chosen and I assume it looks like it is a 60 size ship.
I would cut out everything out that used to hold the motor or fuel tank out, the engine crutch the fuel tank floor etc. Make sure you have airflow around the battery ESC and motor. A undersized spinner works great and looks pretty cool. With the larger motor I do not expect the system to run hot at all but cooling always helps.

Howard Rush · « **Reply #6 on:** July 26, 2019, 11:31:23 AM »

I use an 11” prop for a similar airplane at 73 oz. The CA 11” prop is inefficient, hence it takes more battery, but the performance improvement is worth it.

Crist Rigotti · « **Reply #7 on:** July 26, 2019, 12:03:10 PM »

Quote from: Tim Wescott on July 26, 2019, 08:20:05 AM

It's 64 ounces with the 46LA and all the slimer equipment. I'm assuming it'll be the same or slightly more with electrons.

If I just scale your figures by weight I get 3000mAh -- and that's what I would have bought across the board except that I chickened out and got a 3300mAh to try the first time, on the theory that an overweight plane in testing is better than a nice light pile of balsa trash after pooping out at the end of the pattern.

Yeah, 2700mah to 3000mah is all you need.

Tim Wescott · « **Reply #8 on:** July 26, 2019, 12:28:35 PM »

Quote from: Crist Rigotti on July 26, 2019, 12:03:10 PM

Yeah, 2700mah to 3000mah is all you need.

With the 3300mAh battery and the motor set into place (but no ESC, motor mount, etc.) it balances just about the same place that it does with the 46LA installed, dry.

So (A) the battery is going to get slid forward, and (B) I may just stick with the bigger battery for balance! (Because a tungsten motor mount would be silly, and I can't cut tungsten anyway).

Tim Wescott · « **Reply #9 on:** July 26, 2019, 12:29:35 PM »

Quote from: Howard Rush on July 26, 2019, 11:31:23 AM

The CA 11” prop is inefficient, hence it takes more battery, but the performance improvement is worth it.

CA?

Ken Culbertson · « **Reply #10 on:** July 26, 2019, 12:46:53 PM »

Quote from: Crist Rigotti on July 26, 2019, 07:19:07 AM

How much do you figure will be the final weight? Depending on the weight, I think you have too much battery. I'm flying on a 5S 2450mah battery with a weight of 52 ounces. I'm using @ 75% of the battery.

I agree with Crist - I fly a 2820/12 on a 4s 2800 with 35% remaining and I have flown my 2826 on a 4s 2200 with 18%. With the right prop a 3300 is almost enough for 2 flights but I wouldn't try it. The 5s is better but if size and weight are an issue a 4s will work just fine. If your ESC keeps the rpm's constant then they will fly nearly the same and your only issues will be heat and battery ware.

The COBRA's seem to fare better with a front mount. I am using both and I have yet to have an issue because of the way it was mounted. They do exert a tremendous amount of torque when changing speeds and they do it quickly. Make sure you have adequate space beside the rear of the motor if you front mount it.

What are you doing for cooling? The pictures don't show any. The esc and motor will heat up a bit and both need good ventilation. The COBRA's need a gap between the fuselage and spinner to vent if you rear mount them. 1/16 is plenty. Air will actually draw through the motor to cool it. Outside of the rotating housing you just need to be able to move the heated air out but you will not get much cooling from airflow on the outside the motor. Also put a hole somewhere in the top, sort of like that little hole we put over an IC. They will stay hot and need a place to vent after the flight. The ESC and battery need the wind so keep the airscoop from the IC and try and put the battery and esc in it's path. If you had a pipe in there and still have the tunnel then you have a great place to put them. On one of my conversions I mounted all of that stuff on the bottom of the IC Cowl and cut some humongous vent holes at the back. Just keep it cool. The bigger the "S" values of the battery, the cooler they run. One more point on heat. An IC can be cooled by restarting it making back to back flights safe. IMHO this is not true with electric. They need to cool down a bit before going up again for a full pattern.

The clips are a rear "through the mount" where the motor uses the rear mount and prop adapter. This one currently has a 2826 on it. The nose views are to illustrate how you can use the pipe tunnel to advantage. I have moved the ESC to mount over the wing so that I can fit a 6s battery. The one in there now is a 5s 3000 Turnegy. I mount them skinny side down to get as much airflow around the battery as possible and give me room for all of those wires and crud. I mount the timer on the side of the fuselage with all of the pins pointing up. Biggest mistakes I made at first were locating the timer where it was difficult to hook up the programmer and putting the safety plug too close to the esc so that the wires wouldn't bend. Finally, when you locate stuff do it with everything connected (except the battery of course). The connectors don't bend and it really sucks when you have finally found the perfect place for the timer only to find out after you mounted it that the ESC cable won't attach or you can't get to the starting switch connector.

Have fun and you are doing the right thing asking. I just blundered into it a couple of years ago and made a whole bunch of really dumb mistakes. Like most IC types, I was focused on the motor, With electric it all starts with the prop. I don't think I will ever fully understand what changes what in electric but there are a whole lot of people here that do, so ASK, they will only occasionally bite your head off or call you an idiot.

Ken

Tim Wescott · « **Reply #11 on:** July 26, 2019, 12:57:05 PM »

Quote from: Ken Culbertson on July 26, 2019, 12:46:53 PM

I agree with Crist - I fly a 2820/12 on a 4s 2800 with 35% remaining and I have flown my 2826 on a 4s 2200 with 18%.

With a steady-speed timer a pattern consumes an average of 7 watts per ounce of airplane weight (somewhere I have a spreadsheet where I worked that out from all of the then-extant planes on the "list your setup" thread). So you cannot just say "this battery + this motor = works" -- the motor supplies what energy it needs to keep the plane going, and keeps some for itself to keep warm at night. That's why I took Crist's 52 ounce weight and used it to scale up his battery usage.

Quote from: Ken Culbertson on July 26, 2019, 12:46:53 PM

The COBRA's seem to fare better with a front mount.

Thanks for that. The consensus seems to be that the best mount varies by motor brand. I certainly like a front mount better, although it means ripping into the plane more.

Quote from: Ken Culbertson on July 26, 2019, 12:46:53 PM

What are you doing for cooling? The pictures don't show any.

The current project plans say "TBD". I'm aware of the need, and will be doing (and verifying) something. I'm hoping to keep the look of the airplane, so I'm going to try to get enough air flowing through all the right places without messing with the outside envelope.

Quote from: Ken Culbertson on July 26, 2019, 12:46:53 PM

Have fun and you are doing the right thing asking.

Thanks.

Ken Culbertson · « **Reply #12 on:** July 26, 2019, 01:18:39 PM »

Quote from: TDM on July 26, 2019, 10:45:38 AM

Perhaps Cobra 3520-14 is a better option for the prop chosen and I assume it looks like it is a 60 size ship.

Check out the pictures above. The 2826 barely fits that nose. If you want to put in a 3820 you are going to have to rear mount it. The 2820 will easily match the LA46 and the 2826 is a tad stronger. If you can rebuild the nose then I would say go for the 3520. I really don't like the battery that close to the sides but I also don't see any other way. Also while we are in the nose, if that exit ramp at the end of the cowl is all there is then he needs to cut a whole bunch of slots in the back of it. About 4sq" worth. Exit area has to be greater than input area on an electric.

Ken

Sorry, I hadn't seen your last post before posting this. Glad you are keeping cooling in mind. It is really very different than IC. Just a couple of shots of how slots do not distort the look of the plane, especially if they are on the bottom. Some of the guys I fly with have twice that many.

Mike Alimov · « **Reply #13 on:** July 26, 2019, 07:06:57 PM »

Quote from: Tim Wescott on July 26, 2019, 08:20:05 AM

It's 64 ounces with the 46LA and all the slimer equipment. I'm assuming it'll be the same or slightly more with the electrons.

Unfortunately, not slightly more, but significantly more. You are probably looking at total up weight of north of 70 oz. That’s with 5S battery and 6” prop (more efficient, less battery consumption). 6S and 5” pitch prop, add another 2-3 oz.
Maybe better to leave the poor Atlantis alone and throw together something purpose built?

Tim Wescott · « **Reply #14 on:** July 26, 2019, 08:08:28 PM »

Howard's 73 ounce Impact is quite similar in size to the Atlantis, so I suspect I'll be OK if it's not too far north of 70 ounces.

Ken Culbertson · « **Reply #15 on:** July 26, 2019, 09:31:13 PM »

Quote from: Tim Wescott on July 26, 2019, 08:08:28 PM

Howard's 73 ounce Impact is quite similar in size to the Atlantis, so I suspect I'll be OK if it's not too far north of 70 ounces.

I think you are looking at about a 6 oz gain overall with a 10oz battery. Don't know of any 6s that light but there are 5s available. Fuel for a 46LA is about 4 so overall take off weight difference about 2. I have one that is 70oz but it has a 3520 in it. You are going to be under powered but in a different way. It will pull it OK but you are probably going to get hotter than you should be. You need something to get your feet wet and find what works for you. They do fly different and it takes a bit to get used to the constant CG and not having to think about the engine. If the plane was trimmed IC then I would use a normal rotation prop.

Ken

John Rist · « **Reply #16 on:** July 27, 2019, 11:04:49 PM »

Probably unnecessary advice but make sure nothing is rubbing agents the motor. Wires or anything touching the motor will cause drag, high current draw and smoke coming out of the motor. Also I have had good luck with the KR timer. It has built in safety featured that protects agents equipment failure. I have used them from the start and they have save more than one motor from my stupid actions. Also you can not run an electric setup on the ground for the full 5 minutes. It will more often than not fry the motor. In flight the motor unloads and the current goes down. Most working setups are running the motor near it's max power. This true because one want's the smallest, lightest setup that has the power to fly the pattern. Another concept to keep in mind is maxim prop size rules are different for electric and fuel motors. For the fuel engines too small of a prop will allow the motor to over rev and destroy itself. With an electric motors it will try and turn the same rpm regardless of the prop. If fact you can run an electric motor no-load (no prop) and it is happy. Put on too big of a prop and it will try and turn the no-load RPMs. This requires more power (more current) then the motor can handle resulting is smoke. The good news is that spare parts for the Cobra are readily available at a reasonable cost and you don't need $10 glow plugs. Glow power has it's problems. Electric has it's problems. Whatever you use there is a learning curve. But once you get electric to work it pretty much works the same every time you turn it on. Electric's two big advantages are no greasy clean ups and consistency in performance and run time.

By the way Cobra has some good prop charts. Once you pick a prop size and required RPMs make sure it is in the safe range of the motor you have chosen. https://innov8tivedesigns.com/

Mike Alimov · « **Reply #17 on:** July 28, 2019, 10:26:00 AM »

Quote from: John Rist on July 27, 2019, 11:04:49 PM

.... This requires more power (more current) then the motor can handle resulting is smoke. The good news is that spare parts for the Cobra are readily available at a reasonable cost...

I’m sure Tim knows this, but for the benefit of others starting in electrics: if the motor emits smoke due to overload, spare parts will not help, unless you know how to rewind the stator.

Ken Culbertson · « **Reply #18 on:** July 28, 2019, 01:11:16 PM »

Quote from: Mike Alimov on July 28, 2019, 10:26:00 AM

I’m sure Tim knows this, but for the benefit of others starting in electrics: if the motor emits smoke due to overload, spare parts will not help, unless you know how to rewind the stator.

I think the spare part he was referring to was a new motor. With electric, when there is smoke, there is an internet order about to happen.

Ken

Tim Wescott · « **Reply #19 on:** July 29, 2019, 12:07:01 PM »

Quote from: Ken Culbertson on July 26, 2019, 09:31:13 PM

... Fuel for a 46LA is about 4 so overall take off weight difference about 2. ...

The 46LA is an amazing engine. Fuel for a 46LA that's nicely adjusted to fly a 45 ounce plane is about 3 3/4 ounces. It's more like 4 and a tad for a 54 ounce plane, and for the 64-ounce Atlantis, it's just shy of 6 ounces. More power = more fuel, and the 46LA has an incredible range of adjustability for more or less power.

Tim Wescott · « **Reply #20 on:** July 30, 2019, 09:24:34 PM »

I forgot to order one. And I'm kind of out of cash until the next paycheck. So I made one from stuff lying around. I expect it'll work, even if it's ugly.

Tim Wescott · « **Reply #21 on:** July 30, 2019, 09:28:53 PM »

Quote from: John Rist on July 27, 2019, 11:04:49 PM

Probably unnecessary advice but ...

By the way Cobra has some good prop charts. Once you pick a prop size and required RPMs make sure it is in the safe range of the motor you have chosen. https://innov8tivedesigns.com/

Maybe, maybe not. But it is appreciated. I design motorized control systems for a living, or at least I have in the past. So I have made many of those mistakes with the boss's money.

Paul Walker · « **Reply #22 on:** August 01, 2019, 10:39:22 AM »

I generated this post and it didn't show up even after waiting 15 minutes. So I added the second post. Once the second was up, this first one appeared. Go figure.

Tim,
Before you do anything irreversible to the plane, get ALL the pieces together and weigh them. Generally conversions that start from an IC build come out heavy. Make sure you will not exceed about 70 ounces with that plane.

I would opt for a mount to fit the existing beam mount holes for the IC motor. That way you could go back to IC if the electric doesn't work out.

It also looks like you are somewhat limited for battery space, and room For the ESC and timer. It should be interesting to see what you come up with.

Good luck

Paul Walker · « **Reply #23 on:** August 01, 2019, 11:04:32 AM »

Tim,

Before cutting ANYTHING I suggest that you weigh EVERYTHING you will put in that plane and that includes the battery. IC to electric conversions usually come out heavy. Make sure you are not building a 75 ounce pig before you start.

If you can keep it at 70 or less, it might fly fine. I say 70 as opposed to the 73 you mentioned because there is less flap area on the Atlantis than the Impact. It will need the area.

The battery you show there looks massive. I don't use those, and can't read the number of cells, but it looks heavy. If it is a 5S, it might be about the right size depending on the prop used. As HR mentioned, the "CA" prop is the cat's meow for that plane. You are essentially wasting your time working with anything else. Your motor will need to spin it around 11,000 rpm.

I also would make a mount for the electric to mount to the IC beams and holes in case the electric does not work out. That is a possibility.

Others have talked about cooling. If there is space around all the components, precious little is necessary.

Good luck!

Ken Culbertson · « **Reply #24 on:** August 01, 2019, 12:11:32 PM »

Quote from: Paul Walker on August 01, 2019, 10:39:22 AM

It also looks like you are somewhat limited for battery space, and room For the ESC and timer. It should be interesting to see what you come up with.

Good luck

I find that a bit of an understatement. I converted a stock Nobler and had the same problem.
Just an FYI - I run a 5s 3000 of the same brand as yours and only use 65% on a 70oz pig. I have flown it on the same size Thunder Power which is lighter and about 3/4" shorter. Also you don't need a huge "C" value. Anything 25c or over is going to work. Over 35c and you are adding weight for no reason.

You are going to have to cut some rather large holes in the top of the fuselage if you even think of putting the ESC above that battery with no side clearance. Fortunately for me the Nobler nose is pretty deep and I could mount the battery upright. Yours doesn't seem to have that luxury.

The motor is not going to get "hot" if it is not over worked and with a front mount, which you are pretty much stuck with, it will vent through the spinner gap ( make the gap a tad larger than IC. 1/16 - 3/32 is enough) The airflow you need is over the battery and ESC. The ESC will get hotter than the battery, again by how hard it has to work. Smaller motor, heavy plane = more heat. It looks like your setup is going to have plenty of air coming in under the motor and battery but I don't see any exits over the battery. The openings for air to go out need to equal or exceed where it comes in.

Personally I would be putting a couple of about 1x1/2" vents in the fuselage side just aft of the battery, hollow out the cowl as much as possible and open it up at the back so that you have sort of a tunnel. I would put at least 4 more vent holes of the same size near the end of the cowl itself then I would mount the ESC and timer on the inside of the cowl.

If you have a better way, I am all ears. I am always looking for ways to make cooling these toys better.

Let me add to something Paul said. When you are gathering up all the stuff and weighing it, do your self a favor and hook it all up just like it will be in the plane. This is not just to test it, which is a good idea, but it is to let yourself ask what we all did the first time we did this - where am I going to put all of these (*&*^@) wires. And the good news is that the connectors don't bend!

Keep at it, it is worth it once you figure it out.

Ken

PS: I just read Paul's last post before I saved this and he is absolutely correct. If you have space around components you don't heed much cooling but I want to add to that - AFTER YOU KNOW WHAT YOU ARE DOING. It is very easy to make an innocent mistake, like using a prop the motor doesn't like and get things really hot. Until you learn these things, and I am still very early into that curve, it doesn't hurt to have more cooling. Properly matched components don't generate much heat, mismatched ones can fry eggs.

Tim Wescott · « **Reply #25 on:** August 01, 2019, 01:18:00 PM »

Quote from: Paul Walker on August 01, 2019, 11:04:32 AM

Tim,

Before cutting ANYTHING I suggest that you weigh EVERYTHING you will put in that plane and that includes the battery. IC to electric conversions usually come out heavy. Make sure you are not building a 75 ounce pig before you start.

If you can keep it at 70 or less, it might fly fine. I say 70 as opposed to the 73 you mentioned because there is less flap area on the Atlantis than the Impact. It will need the area.

The battery you show there looks massive. I don't use those, and can't read the number of cells, but it looks heavy. If it is a 5S, it might be about the right size depending on the prop used. As HR mentioned, the "CA" prop is the cat's meow for that plane. You are essentially wasting your time working with anything else. Your motor will need to spin it around 11,000 rpm.

I also would make a mount for the electric to mount to the IC beams and holes in case the electric does not work out. That is a possibility.

Others have talked about cooling. If there is space around all the components, precious little is necessary.

Good luck!

Thank you, thank you. Yes, this should have been obvious to me. No, it didn't occur to me -- and I'd been worried about final weight, because as it stands, when things are put roughly where they'll go (not as pictured here) the CG is about the same as with the 46LA and no fuel in the tank -- so the thing may well trim out with some lead in the nose (and, ultimately, a heavier motor, but for now, lead).

Currently at 60 ounces, to my astonishment. This is plane, battery, ESC, timer (a big TUT), motor, prop adaptor, an APC 13x4, arming plug, and the little baggie of connector goodies that came with the motor, just to add weight.

Even given that the final weight is just about certainly going to be more than this, it'd have to really grow to get over 70 ounces.

My current plan is to make a front-mount disk similar to the ones that Bob Hunt sells, only out of phenolic ('cuz I have some). Installation should be pretty low impact (as it were), requiring little or no wood removal, and being easy to chip out in the event that I don't like electric.

The motor has a Kv of 760, the battery is a 3300mAh 5S, which works out to the same Joules as Howard's 2800mAh 6S pack. This leaves me a bit marginal on the overhead for the CA prop (I'd run my numbers assuming 10000 RPM max). The battery is a near-perfect fit between the motor rails (thank you -- I'm glad that you had the forethought in 1990 to arrange that). So I don't want to change batteries -- but if I feel the lack of oomph at the end of a flight, I can switch to a 2826-10, and pick up some Kv.

Quote from: Ken Culbertson on August 01, 2019, 12:11:32 PM

Just an FYI - I run a 5s 3000 of the same brand as yours and only use 65% on a 70oz pig.

The CA prop that Howard Rush and Paul are suggesting is inefficient, I'm told to expect more battery usage. Howard uses a 6S 2800mAh pack (224kJ); I'm using a 5S 3300mAh pack (220kJ). So aside from the fact that a ThunderPower pack may actually have more energy storage than advertised, while a Turnigy probably has less, I suspect I'm OK.

Quote from: Ken Culbertson on August 01, 2019, 12:11:32 PM

You are going to have to cut some rather large holes in the top of the fuselage if you even think of putting the ESC above that battery with no side clearance. ...

There's a beautiful spot for the ESC and timer under the battery. I could use it as-is and the ESC cooling fins would go right where the engine's head was. There's even an equipment tray in there when I was using the Atlantis for software verification for Howard's TUT program.

Quote from: Ken Culbertson on August 01, 2019, 12:11:32 PM

The motor is not going to get "hot" if it is not over worked and with a front mount, which you are pretty much stuck with, it will vent through the spinner gap ( make the gap a tad larger than IC. 1/16 - 3/32 is enough) The airflow you need is over the battery and ESC. The ESC will get hotter than the battery, again by how hard it has to work. Smaller motor, heavy plane = more heat. It looks like your setup is going to have plenty of air coming in under the motor and battery but I don't see any exits over the battery. The openings for air to go out need to equal or exceed where it comes in.

Personally I would be putting a couple of about 1x1/2" vents in the fuselage side just aft of the battery, hollow out the cowl as much as possible and open it up at the back so that you have sort of a tunnel. I would put at least 4 more vent holes of the same size near the end of the cowl itself then I would mount the ESC and timer on the inside of the cowl.

At the moment I'm planning on vents on the sides of the battery compartment, just ahead of the wing LE. That ends up routing the air right along the battery. For the ESC air I'll open up the back of the cowl. I'll probably put a bit of a scoop where the opening is for the motor now -- I need to think about that.

Ken Culbertson · « **Reply #26 on:** August 01, 2019, 02:12:12 PM »

Quote from: Tim Wescott on August 01, 2019, 01:18:00 PM

At the moment I'm planning on vents on the sides of the battery compartment, just ahead of the wing LE. That ends up routing the air right along the battery. Fo
r the ESC air I'll open up the back of the cowl. I'll probably put a bit of a scoop where the opening is for the motor now -- I need to think about that.

If you open up the sides a bit then you won't need the scoop but it would add to the looks. It might reduce, of all things, the amount of air entering the nose which would reduce the amount of area you need for it to exit!

Looks like you are almost there. One cool thing about electric is that you can fly it before spending all those hours making it look pretty. I have given to doing very basic wings level c/g right trimming before I even add primer. Much easier to hide major surgery marks before you put on the finish and nice to know much finish you can put on.

ken

ken

Paul Walker · « **Reply #27 on:** August 01, 2019, 02:37:01 PM »

Something seems wrong Tim..it started at 64, you removed an eight ounce motor, two ounce muffler, one ounce tank. That's eleven ounces. The battery alone weighs more than that.

How can it now weigh 60?? No battery???

Paul Walker · « **Reply #28 on:** August 01, 2019, 03:32:14 PM »

With your 670 KV motor with a 5S pack, you could uneasily have a slowdown in overheads and on. Dang, that's a good prop.
The APC 13x4.5 is a great flying prop, but is very hard on bearings as it buzzes badly in hard corners.

Now what prop can you use?

Tim Wescott · « **Reply #29 on:** August 01, 2019, 03:47:51 PM »

Quote from: Paul Walker on August 01, 2019, 02:37:01 PM

Something seems wrong Tim..it started at 64, you removed an eight ounce motor, two ounce muffler, one ounce tank. That's eleven ounces. The battery alone weighs more than that.

How can it now weigh 60?? No battery???

My scale was topping out and not telling me. The electric stuff, not yet hooked up, is 5.2 ounces more than the slimer stuff it replaces. So, technically still under 70 ounces total, if I manage to add less than 0.8 ounces...

Quote from: Paul Walker on August 01, 2019, 03:32:14 PM

With your 670 KV motor with a 5S pack, you could uneasily have a slowdown in overheads and on. Dang, that's a good prop.
The APC 13x4.5 is a great flying prop, but is very hard on bearings as it buzzes badly in hard corners.

Now what prop can you use?

I tossed that one on the pile as my probably-heaviest-prop. I've got a bunch to try, starting with an 11x5.5 or something like that.

I may be getting some CA props.

If the motor poops out late in the flight then I'll get a 2826-10, which has a Kv=930.

I'm not expecting this to be ideal -- but I've been meaning to get into electric anyway, and while the 46LA is a really good motor, it seems to run just a bit different every time I fly it. I actually got Randy Smith to price out everything I needed for a pipe conversion, but that plus my next case of fuel from Powermaster was more than the anticipated price of an electric conversion using cheap parts -- so cheap-parts electric it is!

Brent Williams · « **Reply #30 on:** August 01, 2019, 04:30:13 PM »

What is a CA prop?

Just guessing by going off of the props that have been mentioned favorably in the past, Igor's 3 blade hollow carbon, Cox-Resinger 3 blade carbon, ect, ?

Tim Wescott · « **Reply #31 on:** August 01, 2019, 05:19:29 PM »

Quote from: Brent Williams on August 01, 2019, 04:30:13 PM

What is a CA prop?

Just guessing by going off of the props that have been mentioned favorably in the past, Igor's 3 blade hollow carbon, Cox-Resinger 3 blade carbon, ect, ?

It's Howard's name for a Cox-Resinger (Chris-Alan, also CAnada).

Ken Culbertson · « **Reply #32 on:** August 01, 2019, 05:57:06 PM »

Quote from: Tim Wescott on August 01, 2019, 03:47:51 PM

If the motor poops out late in the flight then I'll get a 2826-10, which has a Kv=930.

If you're prop and battery are at peace with each other it should not want to poop till about a minute after the pattern is done and you are changing batteries for the next flight. But when it poops overhead......whew

I am using a MA flat back 11-6 three blade on both my 2820-12 and 2826-10. 32% left on a 4s 2800 but the plane is only 52oz. Does just fine on an APC 12-6 two blade but the Whoosh, whuum, waaaa in the corners drives me nuts. Uses a bit more battery too. I tried a CA three blade and it was clearly better than the MA but not enough better to make me want to pay the price (cheap rules) especially when on our bumpy circles an 11-6 is usually a 10 3/4-6 after a couple of flights.

ken

Tim Wescott · « **Reply #33 on:** August 01, 2019, 06:30:28 PM »

Quote from: Ken Culbertson on August 01, 2019, 05:57:06 PM

If you are prop and battery are at peace with each other it should not want to poop till about a minute after the pattern is done and you are changing batteries for the next flight. But when it poops overhead......whew

I think Paul is referring to the voltage sagging to the point where the motor speed comes out of regulation, not the battery voltage sagging to the point of the ESC cutting out (although that certainly would be exciting!).

Ken Culbertson · « **Reply #34 on:** August 01, 2019, 07:18:42 PM »

Quote from: Tim Wescott on August 01, 2019, 06:30:28 PM

I think Paul is referring to the voltage sagging to the point where the motor speed comes out of regulation, not the battery voltage sagging to the point of the ESC cutting out (although that certainly would be exciting!).

He was, and so am I. First time it happens to you, and it will as batteries get old, it really catches you off guard. Rarely fatal.

Ken

Tim Wescott · « **Reply #35 on:** August 02, 2019, 04:59:50 PM »

Fitting the el-cheapo used Hanger 9 spinner to the collet adapter. I managed to achieve a sliding fit on the collet (I was hoping for somewhere between a sliding fit and a tight fit, I achieved tight, I'm happy).

Note the mix of ancient tools, tools improvised from hardware-store fittings, and el-cheapo import tools. The indicator is a Starrett #64, everything else is, well, found art. My shop is an adventure.

Tim Wescott · « **Reply #36 on:** December 30, 2019, 07:25:30 PM »

Hoo, boy, it's been a while. I've been busy both working a day job and taking care of my one remaining customer from Wescott Design Services, and fixing our cool-looking custom-made but poorly designed gate (it's better designed now, and the dog won't get out), and looking for a new day job (www.preact-tech -- I've done gone to work for a startup, oh my).

So I actually managed a couple of hours on the Atlantis today. It's the first time I've even touched the plane other than moving it out of the way of the gate project for months.

I shortened the shaft on the motor so that I can get it as far forward as possible in the fuse. I've made a phenolic front mounting plate (which will hopefully work!) that I need to trim down to fit into the fuse. That should be a pretty secure mount.

A test balance of the plane with the flight prop, spinner, etc., shows that I should have the CG at least sorta-kinda more forward than it is with the nitro setup. My sekrit plan if that doesn't work and if I don't want to add weight to the motor is to just let the motor stick out of the front of the plane by as much as it has to, with the battery that much farther forward. It's not like I'll lose out on appearance points...

Note the Bandaid on a couple of the pictures -- note to self, don't try to saw off your thumbnail with a coping saw...

Howard Rush · « **Reply #37 on:** December 30, 2019, 10:52:02 PM »

Do you need a spinner for the 3-blade prop? I can print you one like Fred's that goes on that backplate.

Tim Wescott · « **Reply #38 on:** December 31, 2019, 12:20:45 PM »

Quote from: Howard Rush on December 30, 2019, 10:52:02 PM

Do you need a spinner for the 3-blade prop? I can print you one like Fred's that goes on that backplate.

Oooh, yes, please.

Tim Wescott · « **Reply #39 on:** December 31, 2019, 07:49:00 PM »

A bit of progress, two days in a row. Wow. Motor mount taking shape; I'm fitting it into the available space, so it's a bit more work. I need to think about cooling holes soon.

Dan Bregar · « **Reply #40 on:** January 01, 2020, 04:04:28 PM »

Tim-- for what it's worth I have been flying the higher kv version of the motor you have and spinning the APC 13X4.5 cut to 12in. at about 9600 RPM with very good results for a few years now. About 2300mah used on 5 min 35 sec flight with 63 ft lines.

Airplane is a Pathfinder profile 525 sq in wing for reference.

Tim Wescott · « **Reply #41 on:** January 01, 2020, 07:33:32 PM »

Thanks Dan. The Atlantis is a much bigger airplane, so I may find out that the motor isn't enough -- in which case I'll get more nose weight in a "useful" way, so that's OK.

Dan Bregar · « **Reply #42 on:** January 03, 2020, 02:14:56 PM »

Tim--You are well on your way to figuring it out and you are allowing for "contingencies" so I'm sure you'll be in good shape.!

Best regards
Dan

Paul Walker · « **Reply #43 on:** January 05, 2020, 09:11:13 PM »

Tim, where do you anticipate placing the CG?

Tim Wescott · « **Reply #44 on:** January 06, 2020, 11:08:33 AM »

Quote from: Paul Walker on January 05, 2020, 09:11:13 PM

Tim, where do you anticipate placing the CG?

I think "place" makes me sound much more astute than I am. The first time around, I was going to keep the prop in the same place with respect to the nose (i.e., no 1 inch gaps between spinner and nose ring) and allow the CG to fall where it does -- then I was going to fly the thing and see what I thought.

With the plane fully assembled as a slimer and the tank empty, the CG sits somewhere around the back of the LE sheeting or maybe 1/8" forward. I remember you making a comment that with the muffler I was using and all you felt the CG was forward of where you had it. At the moment my test balances, without ESC, timer, or wiring, are putting the CG about 1/4" ahead of that point. The ESC and timer will move it forward even more (I'm planning on shoving the ESC as far forward as I can; I'll probably put an air scoop on the cowl and put the ESC well forward in that). I think the CG is going to land about 1/4 to 1/2" ahead of where it was with the 46LA.

So I think I'm going to hit the "put the CG forward of where it goes in a slimer" rule of thumb, but initially perhaps not as much as I'd like.

Speaking of which -- do you recall if the empennage is solid on that airplane, or built up? And would it be too weird to sand off the finish off of it, drill it full of lightening holes, and cover it with some lightweight plastic covering? (Oh, the humanity, I know -- but the horizontal surfaces are all just white anyway, and the dope is peeling).

Paul Walker · « **Reply #45 on:** January 07, 2020, 10:44:25 AM »

The HT is built up. I would not suggest cutting holes in it.

1/2 inch farther forward is a good place to start.

Look forward to seeing it fly.

Mike Alimov · « **Reply #46 on:** January 07, 2020, 05:48:25 PM »

Tim, I’m afraid the thin metal spinner backplate won’t suffice as part of a collet prop mount... and the worst part is that you will likely discover that once the plane is in flight. Throwing a prop on reverse wingover might result in an unfortunate demise of the Atlantis. I would recommend installing a commercial unit.

Tim Wescott · « **Reply #47 on:** January 07, 2020, 06:29:04 PM »

Quote from: Mike Alimov on January 07, 2020, 05:48:25 PM

Tim, I’m afraid the thin metal spinner backplate won’t suffice as part of a collet prop mount... and the worst part is that you will likely discover that once the plane is in flight. Throwing a prop on reverse wingover might result in an unfortunate demise of the Atlantis. I would recommend installing a commercial unit.

Uh, what? It's not part of the collet -- it gets sandwiched between the prop and the collet mount. Or is that what you're warning me about?

Mike Alimov · « **Reply #48 on:** January 11, 2020, 12:03:31 PM »

Tim,
sorry for the delayed reply; life got in the way...
I think I need to clarify some terminology, then clarify what I meant. The way prop shafts are typically mounted on the smooth end of the motor axle(shaft) is by using a collet mount system, consisting of the split collet itself (the part that slips over the motor shaft and has threads for prop nut) and the collet chuck (the knurled part that also serves as the prop driver washer, which has the reciprocal cone machined on the inside surface to compress the collet).
It was my understanding, based on the couple of pictures you posted, that it was your intention to replace the stock collet chuck/prop driver with a spinner backplate, with its center hole machined to match the collet cone. If that is NOT the case, never mind. But if that IS the case, my warning still applies - I do not believe that the thin spinner backplate will adequately replace the standard collet chuck/prop driver.

Tim Wescott · « **Reply #49 on:** January 11, 2020, 10:05:32 PM »

Nope. The machined hole in the spinner matches the step on the prop drive half of the collet, so the full collet is still being used. The only real sin I'm committing is to index the prop on the threaded shaft rather than the step on the prop drive.

You're now tempting me to machine an integrated backplate/collet. I intend to resist, but it'll be hard.