Thorp Air Command - T18.net

Hey all,

My search-fu is really failing me here. Most of the time, I never have to ask any questions because they are already answered somewhere. I am sure this is no different, but I'm coming up empty, so point me in the right direction if you would.

In the midst of the annual on 33TB (nightmare) I have pulled the prop off to replace an alternator belt. This gave me the opportunity to finally figure out what the prop actually is. Or isn't???

The prop has no markings other than the name "Janesky" written in blue ink pen on the back, and "68-82" carved into it. This is a wood prop. Roger Janesky was a previous owner of this bird, and I am thinking it may be a totally custom prop. No idea.

That is somewhat besides the point though. When I bought this thorp, I was told that it had a climb prop on it, and that was why it was a good bit slower in cruise that it really should be. Well, needless to say, the 68-82 doesn't really strike me as a climb prop. In fact, if I ignore slip (yes, I know this is not realistic) that would give us a theoretical 200mph at 2500rpm. That doesn't sound very climb-prop like to me.

SO here is my question: for those of you who are running the o360 and do not have a CS prop, what size prop are you running? I found a good number of people talking about the props for o320s and o290s, and I found some guys running CS o360s, but what about the fixed wood o360 options? What is a good balance?

Likewise, I realize every bird is different, but what would you all expect to see as far as cruise performance on an o360 with a 68-82? I am curious if maybe I am just expecting more than I should be....

Thanks all!
-Ian Ahner
N33TB

Janesky's name is on the back probably because the prop maker wrote his name on it. Since different prop makers use different numbers, it can be hard to compare props based on their numbers. I have an 0360 with a wood prop from performance propellers. I don't recall what the pitch is, but he had experience building props for T18s and suggested a pitch for me. 95% of the time, I have my throttle set at 2300RM, and I see 150 KTAS. I have put the throttle all the way in a time or two in cruise flight, and when I would hit 182 KIAS, I would pull the throttle back out. Hope that helps in some way.

Yes, I agree about Janesky's name. I simply find it odd that the prop manufacturer chose not to brand label it anywhere. I also don't know if it was a standard offering or something that was made specifically for Janesky.

The cruise numbers are nice, and I also typically cruise around 150KTAS, but probably at a slightly higher rpm, and there's no way I could coerce 182KIAS out of it, even at sea level. I think flat out at 2000msl I'm getting somewhere around 160-170mph indicated. This seems a touch show to me. I would have expected with the o360 I should be able to get closer to 180-190mph....

Just curiosity now, do you have a manifold pressure indicator in the cockpit? If so, about what manifold are you running at 2300 when getting 150 true? Also, what typical range of cruising altitude?

Thanks for the help! It's certainly nice to actually get some numbers.

Hi Ian.... the subject of propellers is full of opinions and personal needs. If you're happy with your current performance, don't worry about it and move on. Diameters are obviously verifiable, but pitch numbers are not so comparable.

I always thought it would be fun to have a "prop swap" at one of the gatherings, but I"m not sure anyone else would be into it. We could easily burn a full day trading propellors.

Yes, wooden props are generally custom carved to suit your engine/airframe. They are not standard. I have a Felix which was specifically made for Bill Cox in 1996, the Builder Of Record. My engine is a derated O360. (168 HP)

As I understand it, props sometimes go back for a "tune up". You hear this occasionally about Catto props, and others as well. There appears to be some black magic and fairy dust involved. So they can be tweaked, but is it worth it?

My only complaint about a wooden prop on an O360 is the lack of inertia. This results in rough idle and abrupt starts and stops. Even for me with low-comp pistons. Guys who have metal FP props are happy with them, I think. Of course, CS props are the Cadillac.

Worry about your prop next year. Recover from the nightmare first.

DW

The idea of a "Prop Swap" fly in is interesting...
I have a manifold pressure gauge in "Feisty" and it has a wood prop. It's very informing. All climb and high speed flight at low altitude are "Over Square" which we are told never to do with a constant speed prop.
When I throttle back, the RPM and Manifold Pressure "Square" at about 2300 RPM & 23" Hg.

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE

BTW, Ian, your wooden prop should come off once a year regardless. You never know what you'll find.

In my own nightmare, the extension and spinner backplate interface was fretted all to heck and the bushings were fully buried in the prop hub. It was the first of many expensive discoveries.

D

AND - along the lines what Dick said. Re torque every 25 hours. PLUS - when the weather changes (cools down or cold) Torque again. I had an interesting experience years ago on a morning after the first cold snap of the year. The short of it was 2 bolt heads sheared, and the prop had to go back for repair.
It's always good to learn from other's goofs!

Terry

From memory, I feel like my MAP at 2300 is about 19 inches. I am usually anywhere from about 5,000 to 10,000 feet.

Terry, that's a good reminder about weather changes. I have become lax in conducting a re torque with a good change in weather.