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  #1  
Old 09-10-2021, 01:33 PM
bobnoffs bobnoffs is offline
 
Join Date: Jul 2012
Location: n. wi
Posts: 852
Default prop testing

i have a honda in my 12 and would feel much better about first flight if i had tested how hard my prop is pulling. does anyone have a good procedure to anchor the plane while the prop is pulling wide open throttle?
i have played a lot of scenarios in my head , i am looking for something tried and proven. a wild guess would be 300-400 pounds.in another build a jab 3300 pulled 370 if i remember correctly.
thanks.
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Bob Noffs
n. wi.
dakota hawk/jab 3300 built and flying. sold 6/18.getting serious about the 12. in the hangar now as of 10/15/19
RV-12 kit as of 9/13
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  #2  
Old 09-10-2021, 05:05 PM
Bob Y Bob Y is offline
 
Join Date: Jul 2017
Location: Piedmont, SC
Posts: 287
Default

I tied my tail down to a tie-down eyelet (catís paw) on the ramp when I did my dynamic prop balance. Iíve seen one post where the builder tied off to the back of their vehicle.
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  #3  
Old 09-10-2021, 09:15 PM
Charlie12 Charlie12 is offline
 
Join Date: Oct 2014
Location: Port Orange FL
Posts: 52
Default tail tie down

An old rule of thumb (the practical kind you don't find in modern textbooks) in prop design is that a well-designed prop will produce about 4 pounds of static thrust per HP. That should get you in the right ballpark for figuring how to secure your plane.

For various maintenance tests I have tied my tail to the trailer hitch on my car (with a 215 HP Lycoming and constant speed prop---not an RV--12) and to tiedown rings at the airport, all without any problem. On the RV-12 I have installed an eye bolt into the tail tiedown fitting and leave it there. It is surely strong enough to do this job.
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344 hrs as of 8/27/2021
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  #4  
Old 09-11-2021, 04:39 AM
bobnoffs bobnoffs is offline
 
Join Date: Jul 2012
Location: n. wi
Posts: 852
Default

i guess that is my big question...........is the airplane robust enough to take 400 lbs pull on that eyelet in the aft tailcone without any damage ?
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Bob Noffs
n. wi.
dakota hawk/jab 3300 built and flying. sold 6/18.getting serious about the 12. in the hangar now as of 10/15/19
RV-12 kit as of 9/13
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  #5  
Old 09-11-2021, 11:48 AM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,219
Default

I secured my RV-12 using the tail tie-down ring while doing a full throttle engine run up. Even if you have a 200 HP engine, I don't think the airplane will be pulled apart.
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  #6  
Old 09-11-2021, 12:19 PM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
Posts: 1,534
Default

I always take the overly cautious approach on ground runs. Sturdy rope tied to the engine mount and looped around a steel fence post. If tail dragger, the rope is draped over the horizontal stabs to keep the tail down. Plus wheel chocks of course.

I bent a tie down bracket once on a non RV type homebuilt, so shy away from using them.

Good fence post, through experience I know it's good for over 450HP.
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  #7  
Old 09-12-2021, 06:12 AM
bobg56 bobg56 is offline
 
Join Date: Nov 2018
Location: Peachtree City, GA
Posts: 196
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The use of wheel chocks and brake pressure should be enough, I've made several ground runs at full power during prop balance with no problem.
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  #8  
Old 09-17-2021, 04:07 AM
bobnoffs bobnoffs is offline
 
Join Date: Jul 2012
Location: n. wi
Posts: 852
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i talked to builders support at van's. he couldn't definitely say yes to the tail tiedown as they never tried pulling in an aft direction. for sure the main gear is ok, i would put the ropes as close to the fuselege as possible.
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Bob Noffs
n. wi.
dakota hawk/jab 3300 built and flying. sold 6/18.getting serious about the 12. in the hangar now as of 10/15/19
RV-12 kit as of 9/13
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  #9  
Old 09-17-2021, 01:44 PM
magiccarpet's Avatar
magiccarpet magiccarpet is offline
 
Join Date: Feb 2013
Location: Switzerland, Europe
Posts: 207
Default

I used the rear tie down ring and the two side steps to anchor for the thrust measurement process. Worked out very well. 356 lb. force
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  #10  
Old 09-17-2021, 03:11 PM
bobnoffs bobnoffs is offline
 
Join Date: Jul 2012
Location: n. wi
Posts: 852
Default

356 is about right on for what to expect.
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Bob Noffs
n. wi.
dakota hawk/jab 3300 built and flying. sold 6/18.getting serious about the 12. in the hangar now as of 10/15/19
RV-12 kit as of 9/13
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