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Extra long prop bolts?!

BruceMe

Well Known Member
Does anyone know where to source long prop bolts? I need 7/16-20 in 10" length.

Thanks,

-Bruce
 
Mfg that doesn't have them...

Aircraft Spruce (6")
McMaster Carr (8")
Fastenal (8")
ARP (6") * but they can custom mfg bolts
 
10", wow, must be a nice extension. I would think Sabre Mfg would be the go-to place but others can chime in.

Sabre goes to 7" :\

Yeah... it's a long extension, RV3 with a pretty forward cowl. It needs about 3.5" of extension and the Catto prop is pretty thick.

Thanks!

-Bruce
 
Sabre goes to 7" :\

Yeah... it's a long extension, RV3 with a pretty forward cowl. It needs about 3.5" of extension and the Catto prop is pretty thick.

Thanks!

-Bruce

They also make extensions with lugs in them and separately bolt to the flange. Much shorter bolt requirement.
 
I talked to Saber about the possibility of adding a longer "prop spacer" onto my RV9 back around 2017. we were also adding 10lbs of wt onto the crush plate for adjustments to a bit of aft CG on minimum fuel onboard. Here's what I got from him: It is possible to add the longer spacer you are asking for ( in my case it was a 2.75" prop spacer). He said the better way of doing that is let me mfg you a "PROP EXTENSION'. the big difference is the wood or composite prop mounting especially with a crush plate will be so much better than using those excessively long bolts. There's a good reason you can't find prop bolts that long. It is experimental and you can do what you like, but if it was me behind the prop I would use a prop extension and bolt it up hard to the Crank then use a second set of the shorter bolts on the prop and crush plate. The Results is a much better bolt up arrangement for transferring 160 HP to the prop. I did take that advise and go with the prop extension and never needed to look back.
 
It sounds like DRR is talking about something like this..

Earlier in RV building history when airplanes were predominantly completed using wooden propellers and the early version cowl that used a 4 inch extension, spool style extensions were used like this where separate bolts were used to attach the extension to the engine and attach the propeller to the extension.
The propeller crush plate was slightly slotted to receive the heads of the propeller attach bolts and then the nuts were located aft of the propeller at the extension. Since the bolt torque on wood propellers needs to be regularly checked, particularly during seasonal changes of humidity, this allowed for checking the torque at the propeller bolt nuts without needing to remove the spinner.
 
It sounds like DRR is talking about something like this..

No, he is referring to a spool extension and not a more modern prop extension that is solid and has 6 holes offset from the other 6 holes, not a spool extension. The holes for the crank attach bolts are recessed into the extension. A spool ext looks more like a wheel / rim.

What DRR and I are talking about looks like this:

https://www.aircraftspruce.com/pages/ap/prop_extension/ducspacer-jabiru2.php

Larry
 
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No, he is referring to a spool extension and not a more modern prop extension that is solid and has 6 holes offset from the other 6 holes, not a spool extension. The holes for the crank attach bolts are recessed into the extension. A spool ext looks more like a wheel / rim.

What DRR and I are talking about looks like this:

https://www.aircraftspruce.com/pages/ap/prop_extension/ducspacer-jabiru2.php

Larry

Larry, the Saber PROP EXTENSION I have looks more like a "spool piece" the length you spec and with flanges on each ends, one flange is hard bolted up to the crank flange and the other end is a flange that fits your prop with pressed in lugs to receive your shorter prop bolts. Like shown on the RV4 pic above, but not quite that long. We used PROP EXTENSIONS like that on a lot of Long EZs and never heard of any issues. But every thing I see now has lugs pressed in the prop end flange so you dont have any nuts on back of that fwd flange

This arrangement in place of the 2 1/4 inch PROP SPACER used on a lot of RVs where the Prop crush plate bolts travel thru the spacer and bolts into the lugs that are pressed into your Crank flange. And In this application uses 2 1/4 inch Longer bolts than you would need if bolted directly to the crankshaft flange.

The 2/14 inch Spacers have been used extensively on RV and work quite well.
 
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Larry, the Saber PROP EXTENSION I have looks more like a "spool piece" the length you spec and with flanges on each ends, one flange is hard bolted up to the crank flange and the other end is a flange that fits your prop with pressed in lugs to receive your shorter prop bolts. Like shown on the RV4 pic above, but not quite that long. We used PROP EXTENSIONS like that on a lot of Long EZs and never heard of any issues. But every thing I see now has lugs pressed in the prop end flange so you dont have any nuts on back of that fwd flange

This arrangement in place of the 2 1/4 inch PROP SPACER used on a lot of RVs where the Prop crush plate bolts travel thru the spacer and bolts into the lugs that are pressed into your Crank flange. And In this application uses 2 1/4 inch Longer bolts than you would need if bolted directly to the crankshaft flange.

The 2/14 inch Spacers have been used extensively on RV and work quite well.

Yes, those prop spacers are fine and the 2.25" version has reasonably sized bolts, however, I would not want to use a 10" long bolt in that application. Not an ME, so no data to back that up. Just gives me a bad feeling to ask a bolt that long to hold on a prop. It would appear from one of the posts above that the guy from Sabre shares that feeling. The fact that no one seems to make one that long also points to it not being a good idea. Could be coincidence I suppose.

Larry
 
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