Today's Message Index:
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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
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| Subject: | Re: Propeller? Gearbox? "Wow-wow-wow" resonance |
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
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| Subject: | Re: Propeller? Gearbox? "Wow-wow-wow" resonance |
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
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| Subject: | Re: Propeller? Gearbox? "Wow-wow-wow" resonance |
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
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| Subject: | Re: Biax Material for Europa classic wing |
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
>
>
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