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02-04-2017, 07:05 AM
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Join Date: Oct 2010
Location: La Feria Texas
Posts: 3,822
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Stop Rumbling Sounds
A friend was having some problems with a rumbling sound, seemingly affected by airspeed and speed of the engine. He finally traced it down to the floor right and left of center line, just behind the baggage bulkhead! I found that I could touch either side on mine lightly and the other side would oil can - badly! We fixed this quick and simple by riveting on an angle to the center of each side, if you look closely at the attached photo, you can see the fix. This is a photo taken from under the seat area looking backwards.
[IMG]  [/IMG] |
02-04-2017, 07:26 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,514
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Just a note for annual inspection.
Hey Don, that should fix the rumbling but also be sure to add the ends as an inspection point. A stiff member has been added that will now accept longitudinal loads from that part of the airframe. It tends to result in cracks or loose rivets at the end point.
Suggest your friend adds this to the annual inspection to keep an eye on it. This way if it occurs it won't get out of hand and become a surprise one day.
Some 7's have an oil canning on the rear under side of the fuse as well. Solutions were discussed at length 3-4-5 years back in the VAF, and some effected one like your post. They had issues at the ends as mentioned.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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02-04-2017, 07:34 AM
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Join Date: Oct 2010
Location: La Feria Texas
Posts: 3,822
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Thanks, I will keep my eye on that area. I was not certain this was the best fix, but could not come up with a better idea so used it on mine as well (the photo is my plane)
The oil canning was so bad I worried about cracks from the flexing!
My first thought was to glue something to the inside.
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02-04-2017, 11:04 AM
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Join Date: Jan 2005
Location: San Antonio, TX
Posts: 1,024
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To keep it from causing cracks at the ends of the added angles, the angles should be attached to the two bulkheads at each end. A joggle to lap over the flange at an existing rivet or a 90 bend and riveted to the bulkhead if the flange is on the other side of your stiffener.
__________________
Steve Formhals
A&P, Tech Counselor & Flight Advisor
RV3B
RV8
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02-05-2017, 04:27 AM
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Join Date: Feb 2010
Location: Perth, Western Australia
Posts: 1,647
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Anti-yaw strakes, Don? Will be interested to see how they work out. 
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rgmwa
RV-12LR 912ULS
120346
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02-05-2017, 06:30 AM
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Join Date: Jan 2011
Location: Eatonton, GA
Posts: 215
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I added a stiffener to the belly skin in my RV-8 when I did my build.
I was careful to taper the stiffener to reduce stress at the ends. Should I be concerned enough about cracking around the rivets to crawl back there and tie the ends to the formers?
A related question: I am in phase 1 now and seem to get a roar resonating that comes in right at cruise speed. Any ideas which skin panels to start looking at? I do have bent down exhaust tips.
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Jeff Green
2016 RV-8 #82985
1968 E33C Aerobatic Bonanza
Pleased to donate Dec 2019
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02-05-2017, 06:57 AM
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Join Date: Mar 2005
Location: Dallas area
Posts: 10,761
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Quote:
Originally Posted by ILikePike
I added a stiffener to the belly skin in my RV-8 when I did my build.
I was careful to taper the stiffener to reduce stress at the ends. Should I be concerned enough about cracking around the rivets to crawl back there and tie the ends to the formers?
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YES, the skin WILL develop cracks at the ends if you do not attach to the bulkheads. I've seen it happen numerous times.
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Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>
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02-05-2017, 07:01 AM
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Join Date: Jan 2005
Location: Cincinnati, Ohio
Posts: 1,060
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The roaring at cruise might be the canopy skin against the fuselage if there is no felt or something between the two.
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Jon Thocker
Habitual Offender
RV4, RV4, RV6A, RV8, RV8, RV8,RV8, RV8, RV8, RV12
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02-05-2017, 08:05 AM
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Join Date: May 2010
Location: Spring Hill Fl
Posts: 734
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Alleviate the stress at the end of the angle.
Jeff
I agree with Mel however the stress relief you added to the end of the angle goes a long way to alleviate the stress at the end of the angle.
To improve your design remove the angle leg before the last rivet. ( soften the end )
I really don't think you will see any cracks in the way you have it in your life time
My View
Joe Dallas
Quote:
Originally Posted by ILikePike
I added a stiffener to the belly skin in my RV-8 when I did my build.
I was careful to taper the stiffener to reduce stress at the ends. Should I be concerned enough about cracking around the rivets to crawl back there and tie the ends to the formers?
A related question: I am in phase 1 now and seem to get a roar resonating that comes in right at cruise speed. Any ideas which skin panels to start looking at? I do have bent down exhaust tips.
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Last edited by joedallas : 02-05-2017 at 08:07 AM.
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02-05-2017, 08:10 AM
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Join Date: Oct 2010
Location: La Feria Texas
Posts: 3,822
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Maybe not clear, but my angle is attached to each bulkhead (former).
Last edited by DonFromTX : 02-05-2017 at 08:43 AM.
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