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Fitting a Scale RC Fan/Spinner Combo to a 3-Blade Prop

Fitting a Scale RC Fan/Spinner Combo to a 3-Blade Prop

Ziroli Giant Scale Plans offers a very cool accessory for FW-190A enthusiasts. It’s a scale fan/spinner combo that the full scale FW-190A featured. It comes as a “blank canvas” and work of art considering the machining required to manufacture. It is a blank canvas as the spinner can be cut to fit a 2- or 3-blade prop and fan/backplate drilled for the motor/engine as required. This article will feature cutting the spinner for a 3 bladed prop and also balancing the entire assembly. The model being fitted with the combo is the Top RC Models 93 inch FW-190A ARF, all composite construction. Motor used is a 100cc equivalent running 12S Lipo’s (two 6S in series). Very nice model for sure. Needs to be seen in person to fully appreciate. The photos and captions will cover the required process.

Unit as delivered from Ziroli. Front view.

Combo as delivered. Reverse view. Beautiful workmanship.

First thing to do is to establish the blade pattern you are going to cut. I first traced the outline of the spinner on cardstock.

Since this is a 3 bladed prop, I laid out 120 degree markings. Use a protractor as this needs to be accurate.

Mark the spinner at the three layout points.

Since there is a lip on the fan portion, you must account for that in the overall height of the relief cuts. Lower line is the top of the lip. Upper line is the top of the cut.

A circle template is used to mark the spinner for the cut. Use a felt-tip marker for a dark cut line.

Once marked, you are ready to make the cuts. I used a Dremel Tool with dentist drill.

Cut appears rough, but that’s OK. Main point is to remove most of the material but not go outside the lines. Minor “slip marks” from the cutter can be easily smoothed out with 320 grit paper. If you have a different or better method to make the rough cuts, go ahead and use that.

With one cut made and smoothed out with files/sandpaper, you can see the backplate lip and how the height of relief-cut must take that into account.

With the relief cuts made, the 3 blade can be test fit. Looks good so far. You want to make sure the cuts are large enough to allow that the prop does not touch the spinner at any point.

Top view to get the cool-factor of the spinner and fan.

View of the fan/backplate/prop drilled for the motor bolt pattern. Note the close fit to the cowl. Very neat.

After the fan backplate was drilled for the motor bolt pattern, it was run with the 3 bladed prop. Very smooth, but still needed to be balanced with the spinner attached. As  you might imagine, the fan really does move a lot of air!

Combo on the 100cc equivalent motor.

Face-on view.

Although not photographed, holes must be laid-out and drilled for the bolts to secure the spinner. I used 8-32 cap screws, but Ziroli’s instructions suggest 4-40’s. I used larger bolts to lower the possibility of stripping out the smaller, finer-thread bolts. Be very exact in placing the bolts on the lip. There is a small margin to get them in the correct place. Too far forward and you hit the backplate base. Too far aft and you miss the spinner. There is a “sweet spot” and you must hit it on the dot. The tapping operation is kinda tricky as the drilled holes are on a “slight angle.”  This slight angle is actually required to keep from drilling directly into the backplate base. In the end, I removed the washers under the bolts as they are not required. A drop of blue Loctite on each bolt may be used once you get to the point of actual flight. Also, unless you can cut all 6 bolts to the exact same length, buy some factory-cut bolts from the hardware store, say 3/8” or 1/2” long. This is important for balance.

Important to remember, an index mark must be made for later balancing. Be sure to make this AFTER the prop is installed as it may not be able to match up later if you randomly made the marks without the prop bolted up. Trust me, it CAN happen. And remember to make sure you “clock” all future prop holes the exact same way.

Once you get the holes drilled and tapped, you need to balance the assembly. This is EXTREMELY important! Be sure to have the spinner and fan matched to the index mark you made previously.

Another view of the assembly during the balancing process. Use a good quality precision balancer. Balancing is done as in the previous article I wrote on spinner balancing here on M.A.N.

Note the balance rod goes through the spinner. Drilling this hole in the VERY CENTER of the spinner end is a MUST to get the balance correct. From inside the spinner, you must find the center “dot” on the cone and center punch it GENTLY. Then drill it with a 1/16” bit. Once the hole is established, enlarge the hole to 1/8” for the balance rod to pass through.

This is a false photo for effect, but shows how the spinner will look when painted black and white spiral added. This pre-painted spinner is from Top RC Models for their FW-190 ARF.

This is the real fan/spinner after balancing and painted flat black. Still needs the white spiral.

Head on view. Touchdown, extra point scored, game complete, victory! By taking your time, you can do this. But use the old rule of thumb when working on expensive parts – Measure TWICE, cut ONCE! And perhaps the most important thing, wear your safety glasses! Aluminum shards are not as easily removed from the eye as steel ones. Good luck.

TEXT AND PHOTOS BY LANE CRABTREE

Check out this terrific video of the working motor running at full tilt!

Top RC FW-190A Full Power Motor Run from wallace on Vimeo.

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2 Comments

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  1. Nice work! I will probably be faced with this when I try to install a 3 bladed prop to my Phoenix P-40 Warhawk. Seems like no one sells 3 – bladed spinners unless you hire True Turn to make you one. Good Luck with your FW-190!

  2. Hey, I’m putting together my first arf plane and I was wondering why you need the gap between the prop and spinner. Why would it make a difference weather I leave a gap or if I don’t.

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