|May 27, 2013, 11:37 PM|
Hobbico Cessna 182 Skylane Brushless Conversion
About eight years ago, in 2005 I put together a GWS DHC-2 Beaver that flew for 40~50 minutes between charges. Since then, neighbor had been at me a few times to put together a plane for him that could provide something more than the 5~7 teasing minutes of barely-able-to-climb that his Parkzone J-3 Cub offered up. It so happened, that in 2010, he bought a used Hobbico Cessna 182 from a relative of his. Using the older stock NiMh pack and a possibly worn out direct-drive brushed 380 motor with a slightly bend shaft unwillingly swinging a 7x3 2-blade propeller, it didn't have enough cowbell to lift off the ground. I can validate that, because I tried it firsthand. Fuggetaboudit! So, one day while visiting him, and I said I was ordering some parts from Hobbyking and would be happy to select the components and convert the plane over to brushless and Lithium polymer power. He took up the offer, and now I want to share how I did it for anyone out there who has wanted better climbing power or speed, but wasn't sure where to begin. This setup will not provide 30~40 minutes flights, as the wing loading does not permit that. With that said, it will provide longer flights and good performance. Read on by clicking on the Comments...
|May 27, 2013, 11:47 PM|
I started by unscrewing the top wing screw, and the screws on the bottom of the fuselage that held the wind struts. I really like the method of attachment they used here. Two plastic pins insert into the front of the wing, and the rear is held by a screw in it's own plastic holder. The struts are thick and strong, and the wing can take a beating. It already has, clearly. The nose wheel is bent, that will have to be rectified prior to a flight. DuBro makes a 1/2A set of steerable nose gear that can be fit to planes like this.
Carefully reaching inside the body of the plane, unplug the aileron servo, and set the wing aside.
Moving to the front of the plane, unscrew the spinner screw and then remove the prop nut, and propeller. One small sheet metal screw on each side of the nose holds the cowl in place, remove these and keep them in a safe place. The nose cowl will pop off relatively easy, exposing the motor and it's mount. Two elastics hold the motor in place, remove the motor. Three screws hold the plastic mount on the nose, remove these. Moving back to the top of the plane again, work to remove the radio and brushes ESC. A plastic battery tray can also be found at the bottom of the fuselage, only remove the long top cover with the round holes. It might be glued and may take some work to break free. Moving back to the front the of the fuselage, unscrew the nose landing gear and set it aside in a safe place. Now for the fun part- using a small flathead screw driver, pry along the edges of the plastic firewall until it comes free. It may take considerable time but it will loosen, as it is held with a rubber adhesive. Once free, remove the excess rubber adhesive both from the firewall and fuselage, paying particular attention to the crevasses where the firewall sits into. This will make it easier to reinstall, later.
The HXT 85/36mm Alloy Composite Firewall Mount has to be ground down a little on top, and cut shorter to accommodate the Cessna's plastic noise cowl. Using a bench grinder makes it easy. Wear ear plugs and eye protection.
The D2822/14 brushless motor is a direct fit to the new motor mount and is held in place with the four included screws. Small but mighty, this motor can provide 160W of power with a 7x4.5 prop on an 11.1V Li-Po pack. Feel free to use 2-blade props from 7x3 to 7x6.
Below, the thrust angle mimics the stock setup.
Gauging by my pictures, you can gauge how much cutting of the metal motor mount is needed and will also depend on your metal motor mount placement. When standing behind the Cessna, the motor points several degree to the right, and several degrees downward. This counters torque roll when you advance the throttle and the tendency for the plane to climb excessively when throttling up.
Simply bring it as close to stock as possible without wasting too much time on the particulars, as many people have very different feelings about how a model aircraft's thrust angle should be set. Laying the firewall flat, set up the motor and mount with the includes screws and nuts, and test-fit the nose. Mark the firewall for the motor mount placement and re test-fit to ensure that the prop shaft and spinner sit where you want them in relation to the nose cowl. You may have to enlarge the nose cowl hole to accept the new prop adapter. Easy.
When it all looks good, you can drill the firewall for the four screws. You may have to remove a small amount of plastic from the rear if anything is obstructing the placement of the nuts. Next, using a drill and by placing the lock nuts in a vise, drill out some of the lock nuts' nylon compound so that it still has some hold, but doesn't require great force to install or remove a screw. That is very important and only takes a minute. If the lock nuts are very tight, you may run the risk of breaking them loose from the firewall after its all installed. You want this motor mount to be removable from the firewall because you may wish to try other motors in the future.
Like shown above, the actual placement will hardly align centered or level, but the prop spinner will and that is all that matters. This is normal and is due to the aforementioned thrust angle. I used super glue to fasten the washers to the rear of the firewall after a final test-fit, then super glued the lock nuts several minutes later. After leaving them to cure for 24 hours, I liberally applied 30 minute epoxy over the nuts and press fit the firewall against the fuselage mounting position. A little bit of foam will have to be removed for the nuts, and then the firewall can be epoxied or held with rubber adhesive in place. I set the plane on it's nose to keep pressure on the firewall while the epoxy took a firm hold on the foam, leaving it to sit overnight. After the epoxy has set up, remove the metal mount and the motor, and apply a very small amount of low strength thread locker to the motor screws to prevent them from coming loose at the most unfortunate of times- in flight!
The prop adapter's threaded shaft had to be cut down a few millimeters to permit the Cessna's stock prop nut and spinner to fully install. I also ground 3mm off the motor shaft length, and used a $15 dremel power tool to form a new set-screw flat spot on the motor shaft using an included micro cutting wheel. Make sure there is no debris inside the prop adapter, and you may have to use a power drill to bore the furthest portion of the shaft hole. Loctite # 641 will also help hold the prop adapter on the motor shaft. I ground the rear of the APC-style props on my bench grinder so that they would sit flat and accept the spinner completely and securely, and they sit perfectly flat. There are several ways to avoid this, such as using the stock propellers, but the 7x5 will provide more thrust at lower rpm, and will offer a higher top speed should we ever need it. Sometimes you go for a flight and the wind suddenly picks up out of nowhere. There is only one way to fight it- MOAR COWBELL
At this stage, I have good news. The most difficult part is over and now you simply install the ESC, radio receiver, and make a battery cage. I coil my wires to form a low pass inductor. This can greatly reduce noise from some lighting systems or long servo leads in telemasters, etc, and even though you may not notice any interference either way, its a worthwhile precaution that costs nothing but a moment of your time.
My neighbor uses a Hitec optic 6, and had a spare Supreme 8II receiver to use in his Hobbico Cessna. Quite heavy by today's 2.4GHz standard, but these 72MHz systems have never given either of us any problems, anywhere. The Nano-Tech 1000mAh 11.1V pack fits easily through the bottom hatch and only a small battery cage needs to be made. I used paperback foam board to make the cage, and soft open cell foam to provide a good grip on the pack, yet it allows it to slip into a pre-determined position that is decided during your initial balancing. The battery is installed at a 30 degree angle and slides back. Once the main wing is installed, the balance point is stated at 38-42mm behind the leading edge of the wing. There will be some setting up of the Mystery ESC, which is done with the propeller removed, but apart from this your balanced plane will be ready for its next flight. Enjoy, and I hope you had as much fun as I did.
-D2822/14 Brushless Outrunner 1450kv, PRODUCT ID: D2822-141450
-HXT Alloy Composite Firewall Mount (85/36mm), PRODUCT ID: SC-FWM-2530
-Mystery 30A BEC Brushless Speed Controller (Blue Series)
PRODUCT ID: MY30ABEC
-Turnigy nano-tech 1000mAh 3S 45~90C Lipo Pack, PRODUCT ID: N1000.3S.45
-APC 7x5, PRODUCT ID: 074000054
You may even wish to use a three blade propeller, but keep in mind the 1" stock cessna spinner only works with two blade props, and the motor is not rated for full throttle on three blades.
-Prop adapter to suit 3.175mm motor shaft, PRODUCT ID: JJ3.175
You may wish to use a different adapter, but in any case you will be best to use a set screw/ grub screw type similar to this. A knurled backplate would be even better and would make prop-nut tightening easier. In any case, do not use a collet type adapter, because the nose cowl will prevent proper tightening. Save your Hobbico's stock prop nut, you will need it to use your spinner.
-Epoxy or Rubberized Adhesive. Used to reattach the firewall to the fuselage. Do not use non-electrical grade silicone adhesives or caulk.
-Loctite #641 Retaining Compound
-Loctite Thread Locker, Low Strength.
|May 28, 2013, 01:13 AM|
I did something very similar with this exact same airframe. It worked almost too well; the original crashed into a tree because I used too small a field for the test.
The rebuild worked well, but, I wound up tip stalling it and yes, I stuffed it in. You're right about the wing loading.
So, the present incarnation works very well although I haven't flown it in some time. I just have to remember not to be too aggressive on the ailerons. I'm using a Tactic 2.4GHz sport radio for now, but I might go to a radio which will allow me to adjust the end points. I might swap in a Spektrum receiver from a less fussy model, fly that model with the Tactic and the Cessna with the DX6i.
And yes, that Dubro 1/2A nosewheel works great. It's a pleasure being able to actually taxi the thing.
I'm using a 1000mAh 3S lipo, but I had to remove the roof of the battery compartment to get it to fit. I use Velcro to stick it to the side of the compartment.
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