View Full Version : Wooden Propeller Torque
07-23-2006, 07:39 PM
I have a wooden propeller on my RV-4 and about a 4 or 5 inch prop extension. Propeller bolts are about 7 to 8 inches in length and are 3/8" bolts. Can anyone tell me what torque I should use for tightening them?
Seems I've seen something on this here before but a search didn't come up with anything.
07-23-2006, 08:17 PM
Documentation with my Pacesetter 200 says to torque to 25 ft.lbs.
An accurate answer requires that you know what kind of wood. Crush strength perpendicular to grain varies quite a lot. Among common propeller woods, mahogany is least, yellow birch is midline, sugar maple is high. Know what you have?
Dan is right. Proper torque on a wood prop should be specified by the manufacturer. Some of the "many laminates" props get up to the torque limit of the bolts. Check with the manufacturer to be sure.
07-23-2006, 09:21 PM
Thanks guys for the info. Unfortunatly I can't find the maker which is Aymer Demuth. I did find an email address but it was kicked back with a delivery failure notification. I've been using 30 ft lbs and it has been working just fine but wanted to know for sure if I was in the ball park.
Thanks again and any more help is always appreciated.
07-23-2006, 09:36 PM
I think the specs for 3/8 bolts run around 16-20 ft lbs. I'm not sure it varies much from mfg to mfg. You could try Sensenich wood for some good info. Also, I think Ed Sterba would give you some specs. Aymar Demuth has been around forever and I'm sure Van would have a phone number for them.
Here's the procedure I use FWIW:
1. Set your torque wrench to 90% of the torque spec. Say 18 ft-lbs. tighen each nut and make sure none of them move. If any move, then you're interval since last tightening was too long.
2. Loosen all the nuts. Do this right before or after draining the oil :-).
3. Let the prop sit for 30 minutes (or until the oil is fully drained).
4. Begin tightening the nuts to 10 ft-lbs using a cross pattern just like torqueing a cylinder head. Next go to 15 ft-lbs and repeat. Then go to your final torque spec. When complete, go around all the nuts one more time and make sure all are at the final spec. When you tighten one, you have a tendency to loosen the one opposite. The final check is to make sure this didn't happen.
5. Lastly, don't forget to check the tracking. Set the prop vertically and move a milk crate up to the bottom blade. Rotate the top blade to the bottom and make sure it is very (1/16") close to the milk crate.
Don't forget to put new oil in the engine and change the filter :-).
It's harder to type than it is to do. Good luck.
07-23-2006, 09:42 PM
I also have 3/8 bolts on an O-320. Obviously, 7/16 bolts or 1/2 (O-360) would have higher specs. I use 20 ft-lbs. I have a Sensenich as well as a Sterba. Both wood.
07-23-2006, 09:48 PM
My Aymar/Demuth prop calls for 18 ft*lbs. I have an O-320.
07-23-2006, 10:59 PM
FWIW, my Falcon prop calls for 200 INCH lbs, + or - 25, or 14-19 ft. lbs & it uses 3/8" bolts. Track limit is specified at 1/16" and they suggest checking track peridically while tightening bolts. They also suggest loosening the bolts, letting it rest an hour, then retightening using the same procedure.
Kyle may have supplied your answer, as he has an Aymar/Demuth. Probably yellow birch given the torque spec; the 200 in-lb figure mentioned by Mr. Scott is common for a birch prop on a SAE1 hub.
Could be maple, but you don't need to guess. Just look at the prop. Assuming clear varnish, yellow birch has a nice amber to yellow shade, maple is closer to white, and mahogany is dark brown/red. Here's the good news. If you're sure it isn't mahogany, 200 in lbs is fine for birch or maple. If you are sure it is maple, you can go higher and gain some frictional insurance.
The bolt torque figure for a wooden prop on an SAE1 hub has nothing to do with allowable tension on the bolts themselves. The bolts are way understressed. The issue is wood crushing.
07-24-2006, 08:40 PM
Thanks again for all the help guys.
I am going to use the 18# as recomended by the Aymer - Demuth owner. Don't know the type of wood as it is painted both sides. Also, I was wrong on the bolts & length & pitch. The bolts are 7/16" and 9 3/8" long (have a long extension for the original long cowl). The prop is 68" in length and 76" pitch.
I just got back from the airport and having the engine/prop balanced. Wasn't out much but now runs like an electric motor. I found it interesting that my tach is reading about 100 rpm less than they were reading with the balance machine.
Anyway, I really appreciate all of your help. :D