Last weekend had a spun prop at the field. Of course afterwards all sorts of questions popped like - How often should you torque the bolts? - How much should you torque the bolts? Should I get new ones from Ace Hardware??

I feel motivated to get accurate verbage out on this since a prop leaving the airplane at anytime is not good!!!!!
So I decided to do a little digging to see what I could find on this issue.

I found a prop torqueing guide on Troy builts website::
I called DA and Aircarft International and asked for their recommendations..I totally agree with flying it and retorquing but I'm not to sure putting locktite on the bolts is such a good idea?? Im not to sure I agree with putting washer underneath the bolts is good thing either?? I am not saying dont do it.. I just don't agree with it..

HOW TO TIGHTEN A PROPELLER

When installing your prop, special techniques must be employed. Just tightening up the prop bolts one time won't do it! You will lose your prop on the second or third flight otherwise! See the video page of a prop coming off in flight!

Proper procedure for tightening prop bolts:
1) Obtain thin steel washers and place them under the heads of the socket head screws. The heads of the socket head screws without the washers will gall the aluminum spinner hub and will prevent full tightening of the socket head screws.
2) Tighten the screws a little at a time. Tightening one screw as much as possible without the others being tight will cause uneven pressure on the prop hub. Tighten one screw some, then go to the screw 180 degrees from it and tighten that screw. Go around and around several times. Don't over tighten so that you crush the prop.
3) Fly the plane for 5 minutes. You can leave off the spinner cone (of course have the backplate in place).
4) Land the plane and retighten all the prop bolts. (Not too tight!)
5) Fly a standard length flight.
6) Retighten all the prop bolts
7) Fly one more time
8) Retighten all the prop bolts. If they don't move this time (they should not). Then you have two options: a) leave it alone or b) remove one screw at a time, put on some very light thread locking compound (not too strong!), and reinstall the screws one at a time. It is not necessary to use thread locking compound, but if you lost a prop before and now you are jaded, this is your extra insurance.
9) Check the bolts every once in awhile, though the prop should never loosen if you followed the above procedure.


OK I called DA and asked them about what do they recommend for torquing props.

1) Using a washer underneath the bolt is a neutral issue with DA.
2) DA recommends that you DO NOT use locktite on the bolts as the remaining locktitie will eventually cause galling in the hub and possibly ruin the hub.
3) DA does recommend to torque the bolts to 80 inch lbs.
4) Both DA and AI(3W) do recommend buying prop bolts from them. the reason behind this one is that the prop bolts are a special grade. If you purchase a to hard bolt(brittle it will snap off) If get a to soft a bolt it fail also.
5) The bolts are 5mm bolts with a 4mm Hex head. Yes a 5/32 hex driver will work but don't use it for long or you will chew up the bolt head - use a 4mm hex driver is the right way to go on this.
6) DA says to check the prop bolts for tightness after every flight(whether its carbon or wood). Personally I think every other flight to every 5 flights is good-IMHO...

Both DA and AI(3W) do recommend to use spacers(spinner backplates) to get the correct amount of thread grip. Some prop hubs are thicker than others depending on pitch and such. Key point here - Do Not bottom out the the bolt in the hub when torquing this will strip and gall the hub and possibly ruin the hub.


If you think you may need new prop bolts they are relatively cheep - IMHO...

DA-50 prop bolts(45mm long) - .75 each
DA-100 prop bolts(50mm long) - .85 each
DA-150 prop bolts(55mm long) - .75 each

Disclaimer - These are purely recommendations I have solicited from the manufacturers. This in no way holds them liable.

I hope this helps clear up any misconceptions about properly torquing props.

Get a good 4MM hex driver and check those prop bolts frequently.

Most of all be safe!!

Ronster

Good info Ron, Thanks

ron are you sure on the 80 inch pounds.i have allways heard 41 inch pounds.i would hate for people to streatch the bolts and have them shearoff but don't want them to leave the engine ether.just checkin

I have been using 37" pounds for wood and 40" pounds on carbon for 8 years now without a problem. When going above these numbers I have found that the wood props will just keep compressing and then eventually crack along the length of the hub. I think 80" pounds is way to much.

I dont use locktite on the bolts either. I have used both methods of washer or no washer under the heads. I personally like the washer better because it does not chew into the alum prop hub plate.

To each his own though???
Garrett

that's the same as i have been doin and with good flatwashers on the bolts i have had no problems with them coming loose

Yes 80 inch lbs I spoke to DA twice to verify this number.

Now it may be different for 3W-

I did talk to AI - they didnt give a specific torque.
I didnt feel comfortable putting out what AI recommended. Because of legal concerns.

On the other hand please feel free to call DA to confirm the 80 inchlbs torque value - I asked permission to publish the value on this forum.

Ronster

Garrett,

I could not get a get the folks from AI to coincide with the 37 inch lbs. I was trying to avoid any conflicts with the 3W numbers.

Although, I would recommend that anyone who has any questions about how to torque their 3W prop bolts to contact AI.

Now for my own personal opinion on the matter - I think that Garrett's numbers are safe to use.

This whole legal thing is making me nervous - My intent was to try and help some folks with as accurate info as possible.

Ronster

If you torque those "special" bolts you obtained from DA and 3W to 80 inch pounds I can guarantee you'll be cutting them off the hub when the allen wrench strips out the head. You're still stuck with pulling the prop off over the bolt shafts after that, and removing the remaining shaft from the hub. I would not want them additionally secured with Locktite should that condition occur. Been there......

Those "special" bolts are 75 cent pieces of garbage the will cause you more grief that you ever want. Get the hardened bolts and torque them to 40 inch pounds. 3W does provide a torque spec to their commercial (non hobby) customers: 40 in.lbs.

An alternate method to using a torque wrench is to use a "TEE" handled allen wrench. Follow the proceedures of opposing bolt tightening, doing each a little at a time, until the bolt seats firmly using only a one handed grip on the T handled allen wrench. Using a thin washer also protects the hub if and when you have to cut a bolt out, so use one.

As far as differences in DA and 3W engines are concerned, if you were to see the engineering drawings for both you would find the differences are too minor to matter when it comes to prop bolt torques.

This post may have seemed a little harsh, but I'd rather see you guys flying and not fixing. Others and myself have had had to cut out a lot of bolts, stripped and otherwise, out of prop hubs, and it was compounded every time by those soft "special" bolts.

What do you guys think about using some sort of glue or paint on the bolt heads once their torqued, (like they do on electronic components). Then you could pop the spinner and tell if anything has loosened up by the intact or broken paint line?

BP

Hey Silver Surfer,

Were you out at Columbia County near St Helen's last weekend before last???

I was hoping to see you last Sunday -

Darren and the guys said you were hucking it !!!

Ronster

I'm not sure if painting the bolts would be of benefit? I dont know for sure - hey it might show something. I have worked on full scale airplanes and painting bolts on hi vibration non moving parts is pretty common. I mean there may be the situation where the bolt doesn't rotate but the wood compresses underload - I could see that happening. Actually less with carbon...

I am thinking of trying the 40 inlbs myself and rechecking evey flight just for my own mental well being.

Just for the record. DA does recommend in their manuals to recheck the prop torque after every flight.


Ronster

Patrick,

What grade bolts do you use on the commercial (non Hobby)engines.
Are they 8 to 8.5 grade???
Are they AN hardware??
Thanks for piping in - Darren has told me that you have been around many many
of the UAV planes for quite some time now. Pretty cool when ya think about it!

Ronster

Ron, GREAT info dude!! Thanks for the post!

I also confirmed the 80 inch pounds with DA before I started using my 150. I have taken the bolts on and off a few times with no problems. In fact the first 3 times I flew it I was able to put a 1/8 turn on the bolts to get them back to 80. This is on a mej 32x10.

Huckin' it, is that whatcha call it? Had a lot of fun!! Yes, I was at the St. Helens field. Beautiful place but that tree is definately not ideally located. Thanks to all the members for letting me fly there, and to "Shakes" and Gary for inviting me out. Hope to do it again one of these days.

Grade 8 or close is good. They don't have to be AN specific. Just check the things after the first few flights on a new prop. You'll prolly have to set them again. Best is to also check them again before the next flight session, and do this everytime you go out. The "wobble" test works for between flights. Grab a blade and wiggle it to check for movement.

Wood props compress over time. Thrust action with the prop assures that eventually you'll have to replace a wood prop simply because the center has compressed too much. That takes quite awhile though.