---------------------------------------------------------- Europa-List Digest Archive --- Total Messages Posted Sat 06/20/20: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:03 AM - Re: Propeller? Gearbox? "Wow-wow-wow" resonance (JonathanMilbank) 2. 06:13 AM - Re: Propeller? Gearbox? "Wow-wow-wow" resonance (clivesutton) 3. 10:58 AM - Re: Propeller? Gearbox? "Wow-wow-wow" resonance (budyerly@msn.com) 4. 08:38 PM - Re: Biax Material for Europa classic wing (Kingsley Hurst) ________________________________ Message 1 _____________________________________ Time: 05:03:16 AM PST US Subject: Europa-List: Re: Propeller? Gearbox? "Wow-wow-wow" resonance From: "JonathanMilbank" Hi Everyone, Thanks for all your replies with suggestions, several of which I'm now following up. After a thorough in depth investigation with engine cowls off, I've got a couple more things to try like unclamping the exhaust header tubes and moving the silencer slightly before tightening again. This is intended to move it a little further away from the air duct against which it might be vibrating in flight, when the engine leans over due to torque. Clive, my mobile 'phone is a Tesco 20 special, which only does calls and texts. The frequency of the 'wow-wow' doesn't seem to change when I vary rpm in the cruise, but then I'm only varying it by about 6%. I also can't say that I notice any change with airspeed. I switch the controller to manual during the cruise to reduce rpm from 5000 to 4700, so the CS function probably isn't a factor. Thanks for the pointer regarding one propeller blade tip tracking differently from the others. Although the wonderful Airmaster propeller which I've had for nigh on 20 years is virtually 'bomb proof', I'll definitely investigate. Best wishes, Jonathan. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=496966#496966 ________________________________ Message 2 _____________________________________ Time: 06:13:52 AM PST US Subject: Europa-List: Re: Propeller? Gearbox? "Wow-wow-wow" resonance From: "clivesutton" Jonathan, a further investigation suggestion that you can do from the comfort of your home: 1) Download this free sound tool onto your PC: https://www.nch.com.au/tonegen/index.html 2) Create two sine tones and adjust one to be 1hz higher than the first (i used 440Hz + 441Hz). Play it and you might get the effect you are hearing in the aircraft. The Wow-Wow you hear is effectively the difference between the two frequencies so a 'Wow' repeats every 1 second in this case. Play with different frequencies to get the effect you experience . . . [Caveat - audio speakers and headphones are not that good at reproducing low frequencies - so the quality of what you hear may be affected by that factor] 3) For an engine running at 4700 RPM and a gearbox reduction of 2.43, the gearbox shaft is turning at 32.23 rotations per second at that RPM. That shaft has three prop blades bolted to it - so the frequency of pulsation from any one blade is 32.23 Hz and the frequency of pulsation from all three blades passing in front of you at 4700 RPM is 96.69 Hz. 4) based on this logic, if any one of those pulsations is higher or lower than the other 2 (as a result of e.g. tracking or different pitch setting of one blade) i suspect that might be your Wow-Wow source. I'm not sure this rules out your gearbox - but it's something to check Read this topic online here: http://forums.matronics.com/viewtopic.php?p=496969#496969 ________________________________ Message 3 _____________________________________ Time: 10:58:12 AM PST US Subject: Europa-List: Re: Propeller? Gearbox? "Wow-wow-wow" resonance From: "budyerly@msn.com" Jonathan, By putting the Airmaster in MANUAL mode the prop is fixed, so hunting of the prop is unlikely if the warble persists at any RPM. As for blade tracking, if the blades are still firm and not twisting, that rules out a tracking issue normally. I left some super thin painters tape on all three blades one time after a touch-up. I know, a good preflight and proper workmanship would have prevented this... I couldn't figure it and quickly took the brand new plane down to the dealer. After hauling the plane down to have the gearbox checked, Lockwood could find nothing. When picking up the plane, I found the thin painters tape, pulled it off and behold, a good sounding engine again and I had a much lighter pocket book. Another "brain fart" I'm not proud of, an owner came in with a blade that was beginning to show signs of leading edge wear. The thin metal leading edge guard was slightly dented and pitted on his Warp Drive. I didn't notice it was becoming de-laminated (slight bubble). I should have caught it on a close inspection but didn't. This was not a warble sound from the outside, it was a sharp hum or buzz, but inside it seemed to have a warble. Rebuilt the blades (fairly cheap) and all was good. If your leading edges are unevenly worn or pitted, and or the trailing edge of your leading edge tape even slightly loose, refinish the blades. Folks are right, the book says for most gearboxes, an overhaul at 600 hours is required for continuing maintenance. Gearboxes are normally sent off for the overhaul (which takes 30 minutes at Lockwood). I pull the prop, the gearbox and drive down and have lunch with the boys, then come back. Nice visit and about $3-400 if no main gear parts are needed. The time is one hour and the new seals and bearings are quite cost effective. Exhaust resonance is tough to find. Exhaust leak soot and spring failures generally point the way that something is amiss. One must be very careful trying to troubleshoot this during ground runups. A problem with the sprag clutch can cause noise, but that is clearly heard around an idling engine, so I doubt that is an issue. Vibration noise from the airframe is tough to track. Loose gear components, speed kits, and anything that vibrates in flight will pick up a power plant frequency and resonate along with the other vibrations. A slight difference in frequency will cause a distinct increase and decrease (like that propeller sync example) giving you fits troubleshooting those type things. Keep us all posted. Bud Yerly Read this topic online here: http://forums.matronics.com/viewtopic.php?p=496978#496978 ________________________________ Message 4 _____________________________________ Time: 08:38:30 PM PST US Subject: Re: Europa-List: Biax Material for Europa classic wing From: Kingsley Hurst TobiK, The Biaxial cloth is SP Systems XE481 You may be able to get some from Europa. Cheers Kingsley in Oz On 19.06.20 9:14 pm, TobiK wrote: > > Hey Guys, > > I am actually building an Europa classic (blue foam) Wing. I am running out of material (biax cloth) and I would now like to buy some new. The problem is, I don't know what material the "biax" is. Does anyone of you can help me with a specification or typ of cloth? > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=496922#496922 > > ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message europa-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Europa-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/europa-list Browse Digests http://www.matronics.com/digest/europa-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.