F3A--Electric.

[Troy Newman]

I don't know for sure about the gear reduction drive....There may be some
noise from the gear reduction drive yes.....I would bet the majority is
still from the prop....I listened to the Carerra E setup that Quique has
flown...To me the noise was from the prop....Now I know the setup that Jason
is running is different from that in the Carerra E...but my belief is the
noise we are getting is from the prop.....I just found it very telling
running different props on the same model...same setup....and same
RPM....those with tip speeds up near the 400mph mark were the noisy
ones....if you busted the 400mph mark it busted the 94db(A) mark as well.

When the tip speeds were down in the 370-380 range the readings on the sound
meter were significantly lower like in the 90db(A) range...Now remember that
it is a log scale....so the level of the sound is exponentially higher at
93-94 than 90.....

Personally I think that the gear reduction unit is significant in the noise
the department but I doubt its the noise (93db) the meter is seeing....Now I
do understand what Earl has said regarding the frequency...and I would agree
with it....

I just see it interesting that I found the main noise contributor on two
different models as the prop noise.Compared that with other models guys were
running where the numbers said yep he's too noisy and yep he was on the
meter just by looking at the rpms and the prop used.......

Running the number on Jason's hearsay RPM of around 6000, and its a 22" prop
that tells me the tip speed on the prop is the same as my setup with he
17-12 or the 16.5-12W on my 140DZ.....That being the case, its the same tip
speed, is it coincidence that he is reading the same noise levels as what I
am getting on my DZ setup?

Now there is no question in the air I bet he is much quieter....but we are
not measuring anything that has number associated with it in the air.....its
all 3 meters away and 30cm off the surface....meter is on the right side of
the model (which is the opposite side of the YS exhaust header by the way)
and the mic is pointed right at the model 90deg to the flightpath....So
basically the meter is pointed right behind the prop....

I will concede that once you reduce prop noise there is another noise right
behind it that takes over as the bully in the system and that is most likely
the exhaust and or Vibration in the airframe.....And this is where as Earl
stated the Woody was 2db lower consistently.....I think what has happened is
if we tame the prop noise to say 370-380mph depending on the prop of
course....the other sounds like vibration resonating in the hollow composite
fuse and exhaust noise become the key noise makers to reduce next.


I am curious to play with the electric setup....and see why the noise is
where it is....But I think its really prop noise...the similar setup on the
Carerra E,  I have heard in person sounds like a whoosh or a turbine
sound.......its all prop noise to my un-calibrated ear. There is a whinny
sound from the gear box but I don't know that this is really the culprit....

it will be interesting to tell.....the real test would be different gear
boxes...I think the number I have heard is 6.7 to 1 or something...What
happens when you change gear ratios and keep the same tip speeds..this would
require different props for sure....but if the gear box is turning at
different speeds and the noise meter bumped up or down significantly then I
could assume it was the gear box...but if the noise stayed the same I would
think it was still Prop noise....because the prop is still doing its
390-400mph thing....

Just some thoughts....I really no nothing about the electric setup and where
the noise is coming from....I just thinks its a little ironic that the prop
tip speeds are the same as my DZ and the noise meter is hitting the same
values....

Troy

----- Original Message ----- 
From: "Bjorn Lehnardt" <blehnardt at att.net>
To: <discussion at nsrca.org>
Sent: Saturday, August 09, 2003 10:03 PM
Subject: Re: Re:F3A--Electric.


> Jason is getting a fair bit of his 93db from the belt reduction drive, no?
>
> ----- Original Message ----- 
> From: "Troy Newman" <troy_newman at msn.com>
> To: <discussion at nsrca.org>
> Sent: Friday, August 08, 2003 8:08 PM
> Subject: Re:F3A--Electric.
>
>
> Nope weighed with batteries in it....
>
> FAI sporting code is available via the NSRCA website and other
locations...
> It has the rules regarding the event of F3A...Continues to Surprise me how
> few read the FAI sporting code rules for F3A...they are shorter than the
AMA
> rule book
>
> In some cases the Battery pack is the flight pack also....therefore you
> don't weigh a model without its flight pack....This is a challenge in
> Electric F3A models because the batteries are the weight....There are not
> many full blown 2M models that will make weight on a full tank of fuel....
>
> Yet the Electric model takes off at under 5kg and flies the entire flight
at
> under 5kg...and lands at under 5kg....Adds a little to the consistency
mark
> eh?
>
>
> Also some have claimed its silent flight....Tony said the sound meter was
> tipping 93db(A)...That means prop noise is our greatest noise issue....Who
> cares about in flight noise...the Sound meter is 3M away from the
model....
>
> Just some FYI.....YS 140DZ turning a 17-12 at 7800rpm is 92-93db(A)...OS
> 140RX same 17-12 at 7800rpm is the same 92-93db(A) this is roughly 394mph
> tip speed....
>
> Jason is using a 22" prop at around 6000rpm its hit 93db(A) and if you
> calculate the tip speed its 392mph.
>
> So guess what prop noise is the kicker....its not silent flight when you
are
> tested at 3meters.
>
> This being said I think this is some cool stuff and has some real
> possibilities...servo pots that last 200-300-400 flights....Airframe
> vibration is less(still some due to the prop)...can't really build models
> much light with the electrics....as they still need to stand up tot he
> flight loads....I mean how much lighter are you going to build the
> wing?....Firewalls still need to hold the motors and the thrust
loads....Yes
> you can trade pipes, Hyde mounts, and fuel tanks...but you gain the
battery
> system....
>
>
> its all very new stuff....Its neat to see someone sticking his neck out. I
> wish I had the Brass ones to do it!
>
> TN
>
>
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