Krill Extra 330SC 31% - Electric Build Log - RC Groups
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Aug 28, 2017, 04:03 PM
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Krill Extra 330SC 31% - Electric Build Log


Hi there,
I had not found any build logs for the Krill EA330SC for electric power. Indeed, I emailed Krill and their response was that they don't have any experience with this plane as electric.
Here is my plan:
XPWR60CC Motor w/ 24 x10 prop.
Castle Creations 160HV ESC (recommended by Extremeflight)
Glacier 6s 30c 6000mah batteries, two in series for 12s operation.
Hitec servos and Jeti Radio.
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Aug 28, 2017, 04:14 PM
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Trim Cowl


The cowl is shipped with no cutouts for the motor or cooling inlets. Using a drill, pair of Lexan scissors and my Dremel tool I made the openings the best I could. I finished them up will a round and flat metal file. I've found with my 26%EX330SC these types of openings provide enough cooling for the EXPWR motor without added ducting. I will check the motor and ESC temps the first few flights to make sure its getting enough cooling.

I used my drill with a brad-point wood bit to make a series of holes. Then I used the scissors to make the rough opening. Then I used the Dremel with a 1/2" sanding drum to get closer. I'm not so steady so I needed to finish up with the files to get the edges as smooth as I could. It looks perfect, 10ft back

A few spots I nicked the finish, which left white scratches. I hit these with a black sharpie to hide them. I should have wrapped everything with masking tape to protect against the mishaps.
Aug 28, 2017, 07:51 PM
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Motor Attachment


The method to locate the bolt holes for the motor mount is as follows:
1. Put masking tape on the fire wall so you have something to draw on,
2. Hold the fuselage vertical with the firewall level,
3. Place the motor and stand-offs on the firewall,
4. Slide the cowl on,
5. Place the spinner on the motor shaft,
6. Center the motor so the spinner is in the perfect location,
7. Carefull remove the cowl without moving the motor,
8. Trace around the motor mounts,
9. Locate the centers of the tracing and drill the holes.
10. It is a long reach in the fuselage to bolt the motor up!

I thought this may not work so good. But it was easy to do. I made a wood cradle to support the fuselage with the wing rod hole. I put a piece of split pipe insulation on the rudder to protect it. The cradle was well worth the effort to build it. I've seen photos of the gas guys hanging the fuselage off a banister from the landing gear! My method was super stable and safe.

I must say this was the only time I needed a ladder to build a model airplane.
Aug 29, 2017, 10:41 PM
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Rudder Tab Repair


The top rudder hinge tab was broken on my airframe. I'm not sure if it was shipped broken or if I did it. I was thinking to make a new tab, but ended up putting it together with epoxy. I reinforced it with a bit of fiberglass.
Aug 29, 2017, 11:00 PM
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Landing Gear


The airplane's legs are not pre-drilled for the axles. The kit came with 1/4" dia. axles.

I set the holes for the axles at 1/2" centers. I drilled a small pilot hole, then drilled a 1/4" hole. I needed 5/16". When I tried my 5/16" bit, it grabbed and did a little damage to the leg. Hopefully it will not break here.

Much better choice is to use a step drill (Unibit) Worked like a charm.

I have Airman wheels for 3/16" axles and 3/16 titanium axles from MIP. But the axles are oversized and the bearings from the Airman's wouldn't fit. I managed to press them on but one axle got a little bent. So I will not use them.

I'm going to try Spot-On wheels. I think they are bored for 1/4"

http://www.aztechaeromodels.com/inde...product_id=683


It seems like airplanes between 25% and 35% are an odd size to find parts for.
Sep 01, 2017, 08:44 AM
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Wheels


The Krill kit came with 1/4" x 5/16" axles. The holes in the legs were drilled to 5/16 " and the shafts are 1/4". I had got Air Man 3-1/2" wheels, which came with bearing for 3/16" shafts. Initially I had planned to use the MIP titanium axles, but there bolt-end in 1/4" and I drilled the holes already. And the MIP axles are not true 3/16" and the bearings didn't fit.

I checked McMaster-Carr and found bearings for 1/4" shafts that fit the Air Man wheels. I order the bearings with flanges. When I slid the wheels on the axles I noticed that the bearings were sticking out past the cir-clip slot by 1/32". So I machined the wheel nub to make the assembly less long. My lathe is down for repairs so I used my drill press. (I need mill and my lathe would be fixed if I wasn't building model airplanes!)

The wheels fit on perfectly. There is no side-to-side slop and they roll easy.

I fly off a paved runway - so the wheels don't need to be big. But they sure look small compared to the overall size of the aircraft.
Sep 01, 2017, 08:59 AM
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Battery Location


I know the Krill will come out tail heavy if the batteries are under the canopy. The canopy is about a 1-1/2ft back from the firewall. I thought about making a mount to have the batteries slide all the way to the front of the inside of the fuselage. But this would make connecting the wires difficult.
I noticed a picture on the Krill website of an electric 330SC 31% with the batteries under the cowl. This appears to be an ideal location.
1. The batteries will be in the airstream for cooling
2. The wires will be short
3. The CG will be good without a bunch of added lead
4. The cowl will need to be split.

I plan to attached aluminum brackets to the motor mounts that the batteries will hang from. The Xtreme mounts have a bunch of spacers so this part is easy. I made four brackets. Two will go between the motor mounts and the firewall. I'm fabricating the brackets from L-1"x1"x1/16" Aluminum. I'll bridge them with a piece of G-10 to make the battery holder. I plan to have a stop at the bottom of the holder and to hold the batteries on I'll use a strap.

I plan to lighten the brackets up with a few holes. I think the entire mounting system will add 150g to the airplane. My packs are just under 800g each. So the battery/motor combo is about the same a 70cc twin.

The tricky part is going to be splitting the cowl . I like to make it so that only two screws have to come out to get to the batteries. If anyone has any ideas, I love to here them. Split cowls are cool.
Sep 02, 2017, 07:18 AM
Jus 1 more plane is all I need
NashVegas's Avatar
Quote:
Originally Posted by jimbo12
...... If anyone has any ideas, I love to here them. Split cowls are cool.
Hey Jimbo.... I converted a 30cc biplane to electric and it really needed some weight up front. I'm flying it on 8s. A friend of mine fabricated a wooden sled that the batteries stay mounted to. I'm now able to slide them under the cowl from the canopy area with the cowl on. Once the front of the sled gets under the front lip I secure the back of the sled with a nylon screw. I will have to get some updated pictures for you but here are a couple of shots while we were building them. I never remove the batteries from the sleds, even charge them that way. May prevent you from having to split the cowl and still get the weight all the way forward.
Richard
Latest blog entry: Extreme Flight 91" Laser
Sep 02, 2017, 09:29 AM
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NashVegas - Nice setup, thanks for the tip!
Sep 02, 2017, 09:51 AM
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Split Cowl from Krill Web Gallery


Here is a photo from Krill of an electric set up w/ split cowl. I'm basically copying the layout.
I don't like the way they put screws in the front. I'm thinking to make a frame for both sections of the cowl and use pins in the front.
Sep 02, 2017, 11:04 AM
Jus 1 more plane is all I need
NashVegas's Avatar
So the plan is to take the top of the cowl off in between each flight?
Latest blog entry: Extreme Flight 91" Laser
Sep 02, 2017, 07:00 PM
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Yes that is my plan. I want to have only two screws to remove. It is no more inconvenient than removing a canopy that is held on with two screws.


Quote:
Originally Posted by NashVegas
So the plan is to take the top of the cowl off in between each flight?
Sep 02, 2017, 07:15 PM
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Battery Brackets Completed


I finished fabricating the aluminum brackets and made the G10 battery plate. I drilled holes and trimmed the aluminum as much as I could to reduce weight and they came out looking like aircraft parts.
The G10 serves two functions:
1. It is a nice place to stick the velcro.
2. It has a bottom ledge which will make loading the batteries easier.

Cut the slots for the straps was tedious. The straps can wrap around the batteries real tight.

All the aluminum machining reduce the weight of the brackets from 70g to 50g, about 28% reduction. The entire assemble with the Xtreme motor mounts came in at approximately 250g.
Sep 02, 2017, 08:03 PM
Jus 1 more plane is all I need
NashVegas's Avatar
Quote:
Originally Posted by jimbo12
........It is no more inconvenient than removing a canopy that is held on with two screws.
Good point. Maybe you could somehow hinge the sides on the front, and have two canopy type thumb screws in the back. That would be really cool and functional.
Latest blog entry: Extreme Flight 91" Laser
Sep 02, 2017, 10:00 PM
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Preliminary CG Check


I just performed a preliminary check of the CG. The servos are not installed, the ESC and Jeti Main Switch are not installed. So weight is missing from both ends of the aircraft. However at this point the CG is pretty close to ideal. I think the forward battery position is going to be good.

I have a weight spreadsheet going. It's telling me the airplane will come in at 10,300g. About 10% over what Krill list for a gas-power version. This is about what I expected. 31% seems to be the limit for fiberglass aircraft. At 35% the weight is more favorable. At 31%, wood aircraft will be a kilo lighter.

I'm doing this project because it is different and more challenging.


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