Today's Message Index:
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1. 12:30 PM - 701 Buffet at slow speeds (Philip Smith)
2. 12:59 PM - Re: 701 Buffet at slow speeds (Tommy Walker)
3. 01:35 PM - Re: 701 Buffet at slow speeds (Gordon)
4. 02:01 PM - Re: 701 Buffet at slow speeds (Mark Sherman)
5. 07:50 PM - Re: 701 Buffet at slow speeds (ronlee)
Message 1
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| Subject: | 701 Buffet at slow speeds |
OK Listers,
I have about twelve hours on my 701 - Rotax 912 ULS with Warp Drive three
blade (68 inches) set at 13.5 degrees. So far it's the most fun I've had
with my clothes on - at least since flying T-38s in the mid sixties...sigh!!
So what's bothering me??
In climb at very low speeds such as 40 - 60 I have a very stable platform
with no buffet or oil canning - however when I pull the power back to a
lower RPM (2000 - 4000) IN THE PATTERN such as turning base at 65 and
slowing to fifty or so on final - and below - I begin to pick up a "rumbling
buffet" that seems to increase as the plane slows. I think the key here is
POWER OFF OR LOW POWER SETTINGS - The buffet can be felt as a light buffet
in the stick and just sounds like a whole lot of oil canning.
I have also slowed the plane at altitude in level flight and get the same
results - buffeting and oil canning sounds.
I'm perty much convinced that it is caused by a separation of the air flow
over the cockpit and the front part of the top of the fuselage.
When I built the plane I put false ribs in the wings and also added diagonal
"L" braces between all fuselage stations in the rear - top, bottom and
sides. This seemed to take a lot of the "flex" out of the skin. I also
added sound dampener material - stuff used on HVAC ducts - to the back of
the baggage compartment wall and under the baggage compartment floor. This
also seemed to deaden the panels.
Been noodling with strengthening the top and sides of the fuselage from just
behind the top window back to the rear of the baggage compartment - in each
bay - with two diagonal "L's". Additionally, putting a single diagonal "L"
on the side walls behind the door and then in the next bay in the baggage
compartment. Also would add the sound insulating material to the inside top
and side. I added the material in the cowl boot area and behind the fire
wall and like the looks and it seems to quiet things down.
So what's the problem??? As usual I am trying not to reinvent the wheel and
asking what the rest of you 701 - 750'ers have done to control the buffet /
clatter.
Contact me off net if you like or leave your response for all to see on the
site.
Still grinnin
Phil
Buhl, ID
710, Rotax 912 ULS
Message 2
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| Subject: | Re: 701 Buffet at slow speeds |
Hi,
One 701 driver said the sound you hear is the built in 701 Stall warning
horn... lol.... rattles like a wagon filled with loose tin....
On Sat, May 7, 2011 at 9:56 PM, Philip Smith <madriver42@gmail.com> wrote:
> OK Listers,
>
> I have about twelve hours on my 701 - Rotax 912 ULS with Warp Drive three
> blade (68 inches) set at 13.5 degrees. So far it's the most fun I've had
> with my clothes on - at least since flying T-38s in the mid sixties...sigh!!
>
> So what's bothering me??
>
> In climb at very low speeds such as 40 - 60 I have a very stable platform
> with no buffet or oil canning - however when I pull the power back to a
> lower RPM (2000 - 4000) IN THE PATTERN such as turning base at 65 and
> slowing to fifty or so on final - and below - I begin to pick up a "rumbling
> buffet" that seems to increase as the plane slows. I think the key here is
> POWER OFF OR LOW POWER SETTINGS - The buffet can be felt as a light buffet
> in the stick and just sounds like a whole lot of oil canning.
>
> I have also slowed the plane at altitude in level flight and get the same
> results - buffeting and oil canning sounds.
>
> I'm perty much convinced that it is caused by a separation of the air flow
> over the cockpit and the front part of the top of the fuselage.
>
> When I built the plane I put false ribs in the wings and also added
> diagonal "L" braces between all fuselage stations in the rear - top, bottom
> and sides. This seemed to take a lot of the "flex" out of the skin. I also
> added sound dampener material - stuff used on HVAC ducts - to the back of
> the baggage compartment wall and under the baggage compartment floor. This
> also seemed to deaden the panels.
>
> Been noodling with strengthening the top and sides of the fuselage from
> just behind the top window back to the rear of the baggage compartment - in
> each bay - with two diagonal "L's". Additionally, putting a single diagonal
> "L" on the side walls behind the door and then in the next bay in the
> baggage compartment. Also would add the sound insulating material to the
> inside top and side. I added the material in the cowl boot area and behind
> the fire wall and like the looks and it seems to quiet things down.
>
> So what's the problem??? As usual I am trying not to reinvent the wheel and
> asking what the rest of you 701 - 750'ers have done to control the buffet /
> clatter.
>
> Contact me off net if you like or leave your response for all to see on the
> site.
>
> Still grinnin
>
> Phil
> Buhl, ID
>
> 710, Rotax 912 ULS
>
>
> *
>
> *
>
>
Message 3
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| Subject: | Re: 701 Buffet at slow speeds |
Phil,
Mine does exactly the same thing ---no false ribs or x braces.
Gordon
----- Original Message -----
From: Philip Smith
To: zenith701801-list@matronics.com
Sent: Saturday, May 07, 2011 10:56 PM
Subject: Zenith701801-List: 701 Buffet at slow speeds
OK Listers,
I have about twelve hours on my 701 - Rotax 912 ULS with Warp Drive
three blade (68 inches) set at 13.5 degrees. So far it's the most fun
I've had with my clothes on - at least since flying T-38s in the mid
sixties...sigh!!
So what's bothering me??
In climb at very low speeds such as 40 - 60 I have a very stable
platform with no buffet or oil canning - however when I pull the power
back to a lower RPM (2000 - 4000) IN THE PATTERN such as turning base at
65 and slowing to fifty or so on final - and below - I begin to pick up
a "rumbling buffet" that seems to increase as the plane slows. I think
the key here is POWER OFF OR LOW POWER SETTINGS - The buffet can be felt
as a light buffet in the stick and just sounds like a whole lot of oil
canning.
I have also slowed the plane at altitude in level flight and get the
same results - buffeting and oil canning sounds.
I'm perty much convinced that it is caused by a separation of the air
flow over the cockpit and the front part of the top of the fuselage.
When I built the plane I put false ribs in the wings and also added
diagonal "L" braces between all fuselage stations in the rear - top,
bottom and sides. This seemed to take a lot of the "flex" out of the
skin. I also added sound dampener material - stuff used on HVAC ducts -
to the back of the baggage compartment wall and under the baggage
compartment floor. This also seemed to deaden the panels.
Been noodling with strengthening the top and sides of the fuselage
from just behind the top window back to the rear of the baggage
compartment - in each bay - with two diagonal "L's". Additionally,
putting a single diagonal "L" on the side walls behind the door and
then in the next bay in the baggage compartment. Also would add the
sound insulating material to the inside top and side. I added the
material in the cowl boot area and behind the fire wall and like the
looks and it seems to quiet things down.
So what's the problem??? As usual I am trying not to reinvent the
wheel and asking what the rest of you 701 - 750'ers have done to control
the buffet / clatter.
Contact me off net if you like or leave your response for all to see
on the site.
Still grinnin
Phil
Buhl, ID
710, Rotax 912 ULS
Message 4
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| Subject: | Re: 701 Buffet at slow speeds |
Philip
I have no extra braces on my fuselage. The only time I have oil canning is w
hen the ball is off center, at any speed.
I have done my best to get this thing to stall but all it will do is mush in
at about 900fpm. Quiet all the time, unless the ball is off.
I put L braces on the back of the baggage compartment, it would oil can on r
ough fields when landing.
Instead of adding all that weight you might just get a better head set.
701/912ULS 150hrs
Sent from Mark's iPhone
On May 7, 2011, at 7:56 PM, Philip Smith <madriver42@gmail.com> wrote:
> OK Listers,
>
> I have about twelve hours on my 701 - Rotax 912 ULS with Warp Drive three b
lade (68 inches) set at 13.5 degrees. So far it's the most fun I've had wit
h my clothes on - at least since flying T-38s in the mid sixties...sigh!!
>
> So what's bothering me??
>
> In climb at very low speeds such as 40 - 60 I have a very stable platform w
ith no buffet or oil canning - however when I pull the power back to a lower
RPM (2000 - 4000) IN THE PATTERN such as turning base at 65 and slowing to f
ifty or so on final - and below - I begin to pick up a "rumbling buffet" tha
t seems to increase as the plane slows. I think the key here is POWER OFF OR
LOW POWER SETTINGS - The buffet can be felt as a light buffet in the stick a
nd just sounds like a whole lot of oil canning.
>
> I have also slowed the plane at altitude in level flight and get the same r
esults - buffeting and oil canning sounds.
>
> I'm perty much convinced that it is caused by a separation of the air flow
over the cockpit and the front part of the top of the fuselage.
>
> When I built the plane I put false ribs in the wings and also added diagon
al "L" braces between all fuselage stations in the rear - top, bottom and si
des. This seemed to take a lot of the "flex" out of the skin. I also added
sound dampener material - stuff used on HVAC ducts - to the back of the bag
gage compartment wall and under the baggage compartment floor. This also se
emed to deaden the panels.
>
> Been noodling with strengthening the top and sides of the fuselage from ju
st behind the top window back to the rear of the baggage compartment - in ea
ch bay - with two diagonal "L's". Additionally, putting a single diagonal "
L" on the side walls behind the door and then in the next bay in the baggag
e compartment. Also would add the sound insulating material to the inside t
op and side. I added the material in the cowl boot area and behind the fire
wall and like the looks and it seems to quiet things down.
>
> So what's the problem??? As usual I am trying not to reinvent the wheel an
d asking what the rest of you 701 - 750'ers have done to control the buffet /
clatter.
>
> Contact me off net if you like or leave your response for all to see on th
e site.
>
> Still grinnin
>
> Phil
> Buhl, ID
>
> 710, Rotax 912 ULS
>
>
>
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Message 5
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| Subject: | Re: 701 Buffet at slow speeds |
My 701 does the same thing. What makes it do that I have no idea, but I do make
use it to control my speed on landings. It's like a built in stall indicator
except no conventional stall occurs, just the big controllable mush.
Do I wish the wing profile continued over the cabin, you bet. I truly believe it
would be a better plane if it did, as I suspect the buffeting MAY start there.
For one thing I could peer into the wing at a sight glass and know exactly
how much gas I have. I could run a vent line between the gas tanks to equalize
the pressure of the tanks so they would feed evenly, Cessna does it that way.
Does the stall (buffeting) start over the cabin long before the rest of the wing,
I have no doubt.
All in all I love to fly the 701 very much but believe there is room for improvements
in several areas. To be fair you could say that about any airplane though.
--------
Ron Lee
Tucson, Arizona
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=339277#339277
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