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-   -   prop testing (https://vansairforce.net/community/showthread.php?t=199083)

bobnoffs 09-10-2021 02:33 PM

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.

Bob Y 09-10-2021 06:05 PM

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.

Charlie12 09-10-2021 10:15 PM

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.

bobnoffs 09-11-2021 05:39 AM

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 ?

Mich48041 09-11-2021 12:48 PM

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.

Ralph Inkster 09-11-2021 01:19 PM

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.

bobg56 09-12-2021 07:12 AM

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.

bobnoffs 09-17-2021 05:07 AM

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.

magiccarpet 09-17-2021 02:44 PM

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

bobnoffs 09-17-2021 04:11 PM

356 is about right on for what to expect.


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