UHS Spinners

[jiott]

I am using the Whirlwind GA 3-blade 70" prop. I bought the prop and spinner as a package from Kitfox. No trimming necessary on the spinner. It all just goes together easy. As I said though, that carbon fibre spinner is spendy-$300+.

[TY2068]

That's a nice set up. When I get a 912 I'll be looking at the Whirlwind or Prince prop. $300 really isn't that awful for confidence that the spinner (and prop) are going stay front and center.

[jrevens]

Like Jim, I have a Whirlwind and one of their carbon fiber spinners. For the classic Kitfox look, with the round cowl, the little skull cap spinners look great, but keep in mind that you eliminate the best & possibly only practical location to install balance weights if you don't use a full-size spinner.

[TY2068]

Hi John , I'm not clear on how one would add weights with a regular spinner vs. skullcap ?

I read an archive post here where a guy had his $50 skullcap spinner come loose and destroy his expensive new wood prop. My ugly exposed IVO hub is looking better by the day. I don't like the looks of how some cheap skullcaps are attached.

[jrevens]

Hi Ty,
The "skullcaps" that I've seen on the IVO props are relatively small diameter, attached with a single screw through the center. The small diameter equals a shorter moment arm for the weights attached to the inside surface of the spinner. So it would take more weight to get the same effect than if using weights attached to the inside of the backing plate flange on a "standard" spinner design. That flange is the usual and very convenient location for mounting balance weights. Trying to install reliable weights to the inside of a skullcap would be a difficult trick. On a Lyc engine with a large starter ring gear, weights can frequently be easily added to that flywheel. It's usually not desireable or convenient to add or subtract weight directly to/from a propeller in the field.

[Av8r3400]

In that case we used longer prop bolts and added the washers there.

[jrevens]

Yeah, there are all kinds of ways to do it... it's just that being able to add weight to the spinner back plate is so much easier. Test weights are easily & quickly applied using the spinner screws. I should have thought of that, Larry. Applying weights to a skullcap is probably never done... I just got off on a tangent trying to advocate for a bigger spinner with a back plate as far as dynamic balancing is concerned. Self-adhesive weights can be easily adjusted to a tiny fraction of a gram, there are many more possible positions for weight installation and the weight is further from the center of the prop, allowing for a more accurate balance with less/fewer weight(s). However it's done, it'll probably be a big improvement over an unbalanced prop. Like I said, I've balanced hundreds of props - on Lycoming, Continental, Rotax, Jabiru, Subaru, VW, etc., and only once in about 20 years did I find one that was so perfectly balanced that I didn't even touch it after checking - a Quickie II with an O-200 Cont. The out of balance condition is usually substantial and the pilot doesn't even know it.

[Av8r_Sed]

John, follow on question to balancing: Does dynamically balancing a prop on a certified aircraft require an A&P sign off? I'm guessing it does.

[jrevens]

Yes it does, Paul. I've done a few factory built aircraft over the years, when the owner's mechanic was willing to sign it off. I've pretty much done nothing but experimental homebuilts with the builder helping & making his logbook entries.

My story is that I bought the machine at a time in my life when I had a little more money than sense I guess, but it's been great to have. Shortly after I finished my T-18 about 25 years ago a local prop shop offered a "special" price of $250 to our EAA chapter (#43) for a dynamic balance job. They used an old Chadwick Helmuth balancer with the hand-held strobe light, etc. The quality of the job was dependent on the experience & skill of the operator. Long story short, after about 45 minutes, the guy said that was it. The numbers weren't particularily good, but I noticed a good improvement and could see the potential if a really good job was done. The newer technology was becoming available & more affordable, with micro-processors & photoelectric sensors, simplifying & making the whole thing pretty easy. I bought one of the ACES units & have never regretted it. It's a nice compact unit, but the newer ones like Dorsal has are even more compact. I've balanced all kinds of things with mine, including blower wheels, car engine flywheels, etc.

[gizmos]

Thanks guys, just placed my order with kf, all new engine and prop.