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Propeller Torque and Hub Drilling

Old 04-11-2011, 07:43 AM
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ka9fax
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Default RE: Propeller Torque and Hub Drilling


ORIGINAL: Tired Old Man

Bolt torque is normally determined by the size and material type of the fastener, and the material it is threaded into. Can't do that with propellers because you have a hub composition/compression issue. A wood prop normally has a softer hub than a composite prop. Or at least should. One manufacturer found the previous out the hard way when they suggested a screw torque value in excess of 100 inch pounds for wood props with one of their engines. Crushed a lot of wood hubs...

Wood props can achieve maximum clamping force somewhere between 40 and 60 inch pounds, depending on the fastener, engine size, and hub density. Carbon props should achieve max clamping force in the area of 65 inch pounds. Their hubs permit greater screw torque without deforming the hub. Never exceed a fastener's maximum suggested torque value. From 60cc and down, 40-45 inch pounds works for both wood and composite props.

The link in the previous post cannot be accessed because it has been blocked by the administrator as ''forbidden weapons''. Seems the Second Amendment is not viewed kindly here. A standard inch pound torque wrench and 1/4''-3'' drive hex keys works for everything that uses a multi bolt hub and allen head cap screws.

Pe:

Based on known usual hub compositions, we're talking about the same manufacturer. I will not post the makers name because it was a custom blade product.
Hi T.O.M.
last season i followed the info u gave on this. I have a 50cc and went to 45lb on a Xaor 23X8. no more crushed hubs, thank you. It worked great. Now I have my 1st 100cc and will be using a 27X10 wood Xoar prop what do u suggest for prop bolt torque.
thanks,
Tony
Old 04-11-2011, 08:01 AM
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Tired Old Man
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Default RE: Propeller Torque and Hub Drilling

Actually, pretty much the same on a wood prop. Typically you have more fasteners on the 100 than you would on, say a DA 50 or DLE 30. So 45in. lbs. to 65 in. lbs. The increased number of fasteners increases the clamping force distribution.

For carbon props 65 inch pounds works out very well. I would not exceed that value with a wood prop. Hub crushing will always indicate when you are using too much torque.
Old 04-11-2011, 08:33 AM
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ka9fax
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Default RE: Propeller Torque and Hub Drilling

Thank You T.O.M.
Old 04-13-2011, 07:30 PM
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rt3232
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Default RE: Propeller Torque and Hub Drilling



Ok Guys

I just found this thread and spent the last hour reding it, and found it vary intersting and informitive, BUT back a long time ago win I worked for a major aircraft company one of the things that was considered was bolt hole tolerance they had to be a snug push thru fit, a slide thru or slip in was not good and would be rejected. so when I have drilled the center hole in a prop it is all ways fitted as above and then balaanced, 3-9-6 & 12 BTW I am using wood props.

So I am a sport flyer G-38 and 1/5 warbird's G-62's, in 15 years never had a problem with single bolt and full hub size washers, now I have been introduced to a multi 4 bolt hob and will maiden the engine this spring, I have drilled the center hole and the 4 clampng bolt holes to the above tolerance test, and balanced as above. Btw the clamp bolts have been replaced with Grade 8 Amarican made cap screws.

So my question is do I use 40 / 45 inch lbs or 65 and I don't mined safty wiring if that is sugested and needed, new engine is a YD-A-56 via Henry

And thanks for your ansures in advance

cheers Bob t
Old 04-14-2011, 08:48 PM
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TheLynk
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Default RE: Propeller Torque and Hub Drilling

Glad I found this thread!

Seems like every one here has a good deal of info to share...so some advice would be great...

I am running an older BME 100 cc with a Laminated Xoar 27-10. I ran it yesterday for about 5-7mins at my friends house, then today when I went to start it at the field i realized that the prop had slipped about 90 degrees! I reset the prop to a better angle to start the engine and ran it for about 10 mins. I went tight again and it still slipped after running it. I am not using a spinner.

I did not use a torque wrench but tightened the nut and the jam-nut tight, but was worried about crushing the prop. As this is a BME it only utilises a center nut and washer, not bolts like the DA /3W's.

It seems like the consensus is to torque bolts at 45-65 in/lbs. Does that hold true for the BME which only has the center nut?

Obviously, I don't want to fly the plane until I can stop the slipping,I am going to run to Harbor fright in the AM and get a torque wrench...

BME's site has a manual, but no Torque values.

Thanks in advance for the help..!


Old 04-15-2011, 07:55 AM
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Default RE: Propeller Torque and Hub Drilling

Single nut/bolt hubs slip. A plain fact of life. If you apply enough torque on a single fastener hub to prevent the prop from slipping you'll crush the prop hub on a wood prop. That's carries a 100% guarantee. The slippage experienced with a single fastener hub is not really an issue unless you're using a spinner and both prop and backplate don't slip equally. They never do.

I wouldn't go past 60 in. lbs. although you certainly can. The prop hub will tell you when you've gone too far. You can, however, drill the engine hub and install a couple of alignment pins that prevent slippage. Works every time. Pretty much what BME did with the 115-116. All the oute screws only serve as locators/anti slip. The center nut does all the real work.

Fro rt3232,

Prop bolt torque remains the same, 40-45 in. lbs. for wood, 60-65 in lbs. for carbon. For our model engines having a slip fit screw is not an issue.
Old 04-15-2011, 09:16 AM
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DadsToysBG
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Default RE: Propeller Torque and Hub Drilling

I've been using a torque wrench at 40in pounds for some time. I use Vess props. I check mine every week as part of my pre flight. I keep the wrench in the plastic case it came in. I have a 100 and 150cc 3-w. Dennis
Old 04-15-2011, 09:36 AM
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Default RE: Propeller Torque and Hub Drilling

You called out an important aspect of propeller maintenance. Periodic checks of bolt torque. As you've pointed out, they are not a tighten and forget item.
Old 04-15-2011, 05:07 PM
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rt3232
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Default RE: Propeller Torque and Hub Drilling



Ok TOM

I did the 40/45 snd safty wired them will most likly run at least 2 or 3 tanks of fuel but will pull the prop and inspect for cracks and possible failure be for maiden, I do plan on using blue lock-tite along wit the safty wire. may be a little over kill but it is what it is.

Thanks for your ansure
Ceers Bob t
Old 04-15-2011, 05:14 PM
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Default RE: Propeller Torque and Hub Drilling

Big mistake and waste of time. You will need to check the bolts on a new wood prop installation every few flights until they and the prop hub get "set" and stay at the proper torque value. After that you should check them at the beginning of each flying day just to be safe. Do not use Loctite, if they do wind up shearing you won't be able to get the broken pieces out and will have to replace the whole hub rather than just a hand full of bolts.

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