DA 100 throwing props/spinners

Gary Powers · 05-30-2007, 09:50 PM

I have a brand spanking new DA 100 on an Aeroworks X260. Each of the first two flights ended quickly with a thrown prop and spinner. When I checked the needle settings Monday, I found the low end at least a full turn richer than factory recommendations.

As a starting point, can I assume that I have found the problem with the engine, as in "back firing" and shearing the prop bolts (forgot to mention that)?

Gary

Jenko · 05-30-2007, 10:19 PM

I have an idea, ask the people who know best, Desert Aircraft.

3dubya · 05-30-2007, 10:31 PM

Get howie to help out jenko..

GremlinX · 05-30-2007, 10:59 PM

How tight are you or not tightening the bolts? The only time I have seen them shear is when they losen, or are not tight enough... carbon prop? Wood prop?

Freddy Warbird · 05-30-2007, 11:05 PM

I wouldn't think a backfire would cause prop bolts to shear off. IMO, Prop bolts don't know whether the engine is rotating one way, or the other.

I would look into how your fastening the prop to the engine. Not every propeller has the same hub thickness, some are thicker, and some are thiner. The fasteners may not be fully seating against the plate. They could be bottoming out -ever so slightly- against the rear engine hub giving a false indication of torque. Likewise, over tightening bolts with a wooden prop could crush the hub ruining the prop. Just my two bits!

JAS · 05-30-2007, 11:06 PM

Start with factory settings. Since you found the low end out, I'm assuming you have checked and reset both? Be careful not to over-tighten the needles as this will ruin the seats in the carb.
Make sure that your prop bolts are not bottoming out (not sure if the hub is drilled/threaded all the way through). Screw a prop bolt all the way in and measure the length that remains out. Then measure your set-up (prop/spinner back plate/washer) and make sure it isn't to thin. If bolt isn't actually tightening against the prop it's tightening against just the hub.
Call DA in the morning, I'm sure they have a more detailed list of things to check.

GremlinX · 05-30-2007, 11:15 PM

As for the backfire... I think it would not losen them. As for a backfire, that can shear off flywheel bolts on a car, but it's generally when there is a severe change in rpms... ie nitrous backfire. I think you would know it if it really did backfire. I think it is in the bolts/prop/hub. I do not think it is internal... give DA a call like they have mentioned.

dmcquinn · 05-30-2007, 11:15 PM

Almost certainly your prop bolts were too loose. Needle valve settings will not cause this. I use a torque wrench calibrated in inch-pounds (not foot-pounds). I use 37 inch-pounds for wood props. Re-tighten them after fllights 1, 4, 8, then every so often.

Kevin Y · 05-30-2007, 11:31 PM

	Quote: Originally Posted by JAS
	Make sure that your prop bolts are not bottoming out (not sure if the hub is drilled/threaded all the way through). Screw a prop bolt all the way in and measure the length that remains out. Then measure your set-up (prop/spinner back plate/washer) and make sure it isn't to thin. If bolt isn't actually tightening against the prop it's tightening against just the hub. Call DA in the morning, I'm sure they have a more detailed list of things to check.

You beat me to it Jason. Thats what I would look at!

Gary Powers · 05-31-2007, 12:05 AM

	Quote: Originally Posted by GremlinX
	How tight are you or not tightening the bolts? The only time I have seen them shear is when they losen, or are not tight enough... carbon prop? Wood prop?

Appreciate the responses. Wood prop, very tight! I should have mentioned that in addition to the two lost in the air, the first time I cranked it on the ground, it also spit the prop/spinner off and sheared all six bolts. I am assuming a backfire, since I really have never heard a bang or such. It happens as I throttle up.

Gary

Gary Powers · 05-31-2007, 12:06 AM

	Quote: Originally Posted by Jenko
	I have an idea, ask the people who know best, Desert Aircraft.

Well, I intended to put the question in the Desert Aircraft Support forum. In fact, I did. Hmmmmm.

Vic3D · 05-31-2007, 12:07 AM

	Quote: Originally Posted by Gary Powers
	Appreciate the responses. Wood prop, very tight! I should have mentioned that in addition to the two lost in the air, the first time I cranked it on the ground, it also spit the prop/spinner off and sheared all six bolts. I am assuming a backfire, since I really have never heard a bang or such. It happens as I throttle up. Gary

Hey Gary!

I'm starting to think that your ignition sensor might be off, which makes your timing bad. I would get that checked out with DA, also.

Vic

05-30-2007, 09:50 PM	#1 (permalink)
Gary Powers Super Contributer Join Date: Jan 2006 Location: El Paso, Texas Posts: 127 Awards Showcase Total Awards: 1	DA 100 throwing props/spinners I have a brand spanking new DA 100 on an Aeroworks X260. Each of the first two flights ended quickly with a thrown prop and spinner. When I checked the needle settings Monday, I found the low end at least a full turn richer than factory recommendations. As a starting point, can I assume that I have found the problem with the engine, as in "back firing" and shearing the prop bolts (forgot to mention that)? Gary

05-30-2007, 10:19 PM	#2 (permalink)
Jenko Love Me Troopy! Join Date: Jan 2006 Location: Aussie Age: 51 Posts: 648	Re: DA 100 throwing props/spinners I have an idea, ask the people who know best, Desert Aircraft. __________________ "Life is not a Rehearsal"

05-30-2007, 10:31 PM	#3 (permalink)
3dubya Its All A Learning Experience Join Date: Feb 2006 Location: Stralya - down there aye bloke Posts: 3,161 Awards Showcase Total Awards: 3	Re: DA 100 throwing props/spinners Get howie to help out jenko.. __________________ 3Dubya XTREME COMPOSITE AUSTRALIA www.xtremecomposite.com.au 3W AUSTRALIA www.modeldesign.com.au Click here for me current logic imac program all cleaned up for sharing mode one only sorry..

05-30-2007, 10:59 PM	#4 (permalink)
GremlinX Father of the Scale Furum Join Date: Jan 2006 Location: Chapel Hill, TN Age: 31 Posts: 4,467	Re: DA 100 throwing props/spinners How tight are you or not tightening the bolts? The only time I have seen them shear is when they losen, or are not tight enough... carbon prop? Wood prop? __________________ "I'll have the roast duck with the mango salsa" Kit builders check out.... http://bobflies.com/ 2.4 GHz is for your home telephone... 14MZ and 72 MHz for huckin' baby!!

05-30-2007, 11:05 PM	#5 (permalink)
Freddy Warbird She's a Bad Ass Sukhoi Pilot Join Date: May 2006 Location: California Posts: 947	Re: DA 100 throwing props/spinners I wouldn't think a backfire would cause prop bolts to shear off. IMO, Prop bolts don't know whether the engine is rotating one way, or the other. I would look into how your fastening the prop to the engine. Not every propeller has the same hub thickness, some are thicker, and some are thiner. The fasteners may not be fully seating against the plate. They could be bottoming out -ever so slightly- against the rear engine hub giving a false indication of torque. Likewise, over tightening bolts with a wooden prop could crush the hub ruining the prop. Just my two bits! __________________


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05-30-2007, 11:06 PM	#6 (permalink)
JAS It's all about MGS Join Date: Feb 2006 Location: Around the USA Posts: 484	Re: DA 100 throwing props/spinners Start with factory settings. Since you found the low end out, I'm assuming you have checked and reset both? Be careful not to over-tighten the needles as this will ruin the seats in the carb. Make sure that your prop bolts are not bottoming out (not sure if the hub is drilled/threaded all the way through). Screw a prop bolt all the way in and measure the length that remains out. Then measure your set-up (prop/spinner back plate/washer) and make sure it isn't to thin. If bolt isn't actually tightening against the prop it's tightening against just the hub. Call DA in the morning, I'm sure they have a more detailed list of things to check.

05-30-2007, 11:15 PM	#7 (permalink)
GremlinX Father of the Scale Furum Join Date: Jan 2006 Location: Chapel Hill, TN Age: 31 Posts: 4,467	Re: DA 100 throwing props/spinners As for the backfire... I think it would not losen them. As for a backfire, that can shear off flywheel bolts on a car, but it's generally when there is a severe change in rpms... ie nitrous backfire. I think you would know it if it really did backfire. I think it is in the bolts/prop/hub. I do not think it is internal... give DA a call like they have mentioned. __________________ "I'll have the roast duck with the mango salsa" Kit builders check out.... http://bobflies.com/ 2.4 GHz is for your home telephone... 14MZ and 72 MHz for huckin' baby!!

05-30-2007, 11:15 PM	#8 (permalink)
dmcquinn Bad-ass Super Contributer! Join Date: Apr 2007 Location: Chesterfield MO Posts: 260	Re: DA 100 throwing props/spinners Almost certainly your prop bolts were too loose. Needle valve settings will not cause this. I use a torque wrench calibrated in inch-pounds (not foot-pounds). I use 37 inch-pounds for wood props. Re-tighten them after fllights 1, 4, 8, then every so often.

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