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11-23-2006, 07:45 PM
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Join Date: Jan 2005
Location: Peoria, AZ
Posts: 1,053
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Quote:
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Originally Posted by lucky
Larry,
From which perspectives are the comments about "quiter" aimed? From passengers inside your plane comparing it to other RV8s or from people on the ground comparing your planes sound as compared to another RV8's flying by or both?
Lucky
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I tried the Picolo tubes on my RV-4. It cut the noise done by only 1-2 decibels in the cruise rpms and seemed to slow the rv down a couple of mph.
__________________
Regards,
Thomas Velvick
Goodyear, AZ (KGYR)
2020 Donation sent.
N53KT RV-6a finished 2018, Flying
N7053L RV-4 Wife's RV
N56KT RV-4 Finishing
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11-24-2006, 07:12 AM
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Join Date: Jan 2005
Location: 8A7 (NC)
Posts: 320
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Quote:
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Originally Posted by lucky
Larry,
From which perspectives are the comments about "quiter" aimed? From passengers inside your plane comparing it to other RV8s or from people on the ground comparing your planes sound as compared to another RV8's flying by or both?
Lucky
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These are observations from outside the plane.
__________________
Larry Bowen
RV-8 Built, sold, missed.
RV-7 Built, sold, missed.
RV-8 Emp in progress ...
RV-8A Purchased, flying.
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11-26-2006, 09:09 AM
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Join Date: May 2006
Location: Houston
Posts: 2,012
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Mine has had floor vibration/resonance since day 1. It's less of an issue at 2400 rpm and above.
IMO, it's 100% due to the pulsations from the exhaust gases. One of these days, or on my next -8, I'll stiffen the sheet metal and thoroughly insulate the sub-floor (read stuff it full of fiberglass) from the firewall back as far as possible.
__________________
Bryan
Houston
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11-26-2006, 09:58 AM
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Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,145
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Is this a problem that is generally seen only on -8's? Or is it common to other models as well?
__________________
Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2020 dues paid 
N16GN flying 700 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, 430W
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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11-26-2006, 11:19 AM
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Join Date: Sep 2005
Location: Maple Grove, MN
Posts: 2,333
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Quote:
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Originally Posted by Low Pass
IMO, it's 100% due to the pulsations from the exhaust gases.
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You may be correct, but what do you base it on? The prop pulses are proportional to the exhaust pulses, so the only way to separate them is to extend the pipes way back and see what happens.
The pulses from the prop are impressive, just stand up with the canopy open at idle power! (Not recommended for tip-ups  )
__________________
Alex Peterson
RV6A N66AP 1700+ hours
KADC, Wadena, MN
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11-26-2006, 07:14 PM
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Join Date: Nov 2005
Location: Tellico Plains, TN
Posts: 561
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The current Vetterman's exhaust instructions advise you to allow the exhaust tips to extend down low, near the cowl. The reason is to reduce the vibration effect the exhaust has on the floor. I did that on this -8, and can't say that it's any different from the first one where I had the pipes up high. Both vibrate, and you can change the tone by moving your feet around.
Cheers,
Rusty (6.3 hours)
__________________
RV-8, SN-80587, built, flown, sold.
RV-3B, SN-10751, rotary engine, built, flown, sold
RV-8, SN-82470, built, flown, sold.
RV-3B, SN-11351, purchased, , flown, sold
A&P - 2018
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11-26-2006, 07:58 PM
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Join Date: May 2006
Location: Houston
Posts: 2,012
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Quote:
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Originally Posted by AlexPeterson
You may be correct, but what do you base it on? The prop pulses are proportional to the exhaust pulses, so the only way to separate them is to extend the pipes way back and see what happens.
The pulses from the prop are impressive, just stand up with the canopy open at idle power! (Not recommended for tip-ups  )
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Good point. I hadn't considered prop wash. But it seems that stiffening the skin and damping the resonance with some filler would solve the prob in either case. Extending the pipes is not a very serious option for me.
__________________
Bryan
Houston
Last edited by Low Pass : 11-26-2006 at 08:03 PM.
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11-27-2006, 09:18 AM
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Join Date: May 2005
Location: San Ramon, CA
Posts: 402
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Stiffening the floor
Hi folks,
I am at the beginning of building the fuselage. Which skin are you suggesting stiffening and how would you go about doing so? If this is the forward section of floor, i.e. right under your feet and just aft of the pedals, then stuffing it with fiberglass wouldn't be difficult--but I am thinking that the time to do so is early in the construction process.
At any rate, if I should make this mod, I would really appreciate some advice on where exactly to beef things up.
Regards,
Michael Wynn
RV 8 (Just starting the) Fuselage
San Ramon, CA
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11-27-2006, 11:08 AM
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Join Date: May 2006
Location: Houston
Posts: 2,012
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Quote:
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Originally Posted by mlwynn
Hi folks,
I am at the beginning of building the fuselage. Which skin are you suggesting stiffening and how would you go about doing so? If this is the forward section of floor, i.e. right under your feet and just aft of the pedals, then stuffing it with fiberglass wouldn't be difficult--but I am thinking that the time to do so is early in the construction process.
At any rate, if I should make this mod, I would really appreciate some advice on where exactly to beef things up.
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I'd stiffen the cowling outlet air ramp and the outer skin immediately aft (the one between the gear penetrations, I believe). As for how to do it, there are many possibilities. Everything from refab'ing out of thicker sheet to adding angle stiffeners to laminating the sheets from the inside with some FRP material. Just have to look at the possible internal interferences and how you want to alter the sheet.
As for how to insulate. Many options here too. Use some batting material, spray foam, or just loose fiber stuffed liberally into the void. I'd do the latter, myself.
Done during the forward lower fuse assembly would definitely be easier.
__________________
Bryan
Houston
Last edited by Low Pass : 11-27-2006 at 11:12 AM.
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11-28-2006, 11:30 PM
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Join Date: Jan 2005
Location: Houston, TX
Posts: 868
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My -8 has a 180 hp O-360 with a 4 into 1 exhaust system; the single collector pipe runs out past the cowling and extends back maybe 10 inches or so along the outlet ramp and hangs several inches below.
This afternoon was its 4th flight for a whopping total of 4 hrs... so far it's been smooth on the floor, no vibrations or rattling; that is until I tried a bit of slow flight. As the speed bled back to around 55-60 kts indicated with power on to maintain altitude, I started hearing/feeling some vibration and rattling coming from forward and below. Dropped the nose, built up some speed and it went away.
So, after reading this thread I'm beginning to think that while at a high angle of attack and power on, the ramp skin starts rattling and vibrating from the slipstream and prop pulses... does this seem like a reasonable explanation? Anyone else run into this? It was a bit unnerving to hear/feel all that after being relatively smooth and quiet at normal speeds.
John
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