Mylar seals for elevator

It seems to me that Mylar may only be necessary on the top of the
stab/elevator, since the top surface is the high pressure side. Has anyone
tried this?


"JJ Sinclair" wrote in message
...


I believe the main purpose of adding Mylar is to reduce drag, but if
you want added control authority, one can think about the combination
of Mylar and zig-zag. I use it on most rudders, but be careful adding
zig-zag to the elevator. I did on my LS-7 and the stall was the mose
abrupt I have ever seen..................took off the zig-zag!
Cheers,
JJ

On May 20, 2:25 am, "Bob Salvo" wrote:
It seems to me that Mylar may only be necessary on the top of the
stab/elevator, since the top surface is the high pressure side. Has anyone
tried this?


The top side is the low pressure side Bob!

nimbusgb wrote:
On May 20, 2:25 am, "Bob Salvo" wrote:

It seems to me that Mylar may only be necessary on the top of the
stab/elevator, since the top surface is the high pressure side. Has anyone
tried this?



The top side is the low pressure side Bob!

I don't think so, as the tail of just about every airplane or glider has
a download. That's how they achieve stability. So it's backward at the
tail, the top surface is indeed the high-pressure side.

On May 20, 6:39*am, Ed Winchester wrote:
nimbusgb wrote:
On May 20, 2:25 am, "Bob Salvo" wrote:

It seems to me that Mylar may only be necessary on the top of the
stab/elevator, since the top surface is the high pressure side. *Has anyone
tried this?

The top side is the low pressure side Bob!

I don't think so, as the tail of just about every airplane or glider has
a download. *That's how they achieve stability. *So it's backward at the
tail, the top surface is indeed the high-pressure side.

Just to add to this "pressure" discussion, my elevator has a shape
similar to the trailing edge of my wing. The top-side is convex, and
the bottom-side is concave. Wouldn't that be a clue as to where the
high and low pressure areas are? I would think the convex side is the
low-pressure side, which is on top.


Dave


P.S. Any other thoughts on using mylars and safety tape on the
elevator gap?

As long as the elevators produces a force downwards, the low pressure side
is on top. This is typically the case for speeds higher than best L/D.
For speeds closer to stall speed, the elevator produces lift, and the low
pressure side is on the bottom.
For an optimum design, the elevator produces no force at all (except
drag...) at the speed of best L/D. But then, not all designs are optimum...

Bert

wrote in message
...
On May 20, 6:39 am, Ed Winchester wrote:
nimbusgb wrote:
On May 20, 2:25 am, "Bob Salvo" wrote:

It seems to me that Mylar may only be necessary on the top of the
stab/elevator, since the top surface is the high pressure side. Has
anyone
tried this?

The top side is the low pressure side Bob!

I don't think so, as the tail of just about every airplane or glider has
a download. That's how they achieve stability. So it's backward at the
tail, the top surface is indeed the high-pressure side.

Just to add to this "pressure" discussion, my elevator has a shape
similar to the trailing edge of my wing. The top-side is convex, and
the bottom-side is concave. Wouldn't that be a clue as to where the
high and low pressure areas are? I would think the convex side is the
low-pressure side, which is on top.


Dave


P.S. Any other thoughts on using mylars and safety tape on the
elevator gap?

On Sun, 18 May 2008 13:45:39 -0700 (PDT), JJ Sinclair
wrote:

We have had a bail-out caused by lifting mylar
on the stab.
JJ

Hi John,

what happened?

Bye
Andreas

wrote:
On May 20, 6:39 am, Ed Winchester wrote:
nimbusgb wrote:
On May 20, 2:25 am, "Bob Salvo" wrote:
It seems to me that Mylar may only be necessary on the top of the
stab/elevator, since the top surface is the high pressure side. Has anyone
tried this?
The top side is the low pressure side Bob!
I don't think so, as the tail of just about every airplane or glider has
a download. That's how they achieve stability. So it's backward at the
tail, the top surface is indeed the high-pressure side.

Just to add to this "pressure" discussion, my elevator has a shape
similar to the trailing edge of my wing. The top-side is convex, and
the bottom-side is concave. Wouldn't that be a clue as to where the
high and low pressure areas are? I would think the convex side is the
low-pressure side, which is on top.

It's an airworthiness requirement that the glider will tend to pull out
of a dive. So, typically, the concave side is on the bottom to provide
increasing back pressure on the stick as speed increases (sort of like a
trim tab). In his 1989 article on increasing performance, Peter Masak
talked about reducing drag by filling in this bottom concavity. No
mention of the expected drag savings, but lots of words about flutter
concerns.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On May 20, 8:17 am, Eric Greenwell wrote:

trim tab). In his 1989 article on increasing performance, Peter Masak
talked about reducing drag by filling in this bottom concavity. No
mention of the expected drag savings, but lots of words about flutter
concerns.

Not to mention changing the pressure distribution on the aft section
of the wing/tail - thus changing its Coefficient of Moment (i.e. its
desire to rotate/torque around the center of lift). That effect is
less critical on the tail than on the main wing (doing so on the wing
might require an increase in tail volume to control the added moment);
but the bottom line is that you're essentially making a custom airfoil
when you fill that cusp. It isn't necessarily a bad thing, but if you
don't know what you're doing you could just as easily make it perform
worse...

--Noel

On May 20, 8:44 am, "noel.wade" wrote:
On May 20, 8:17 am, Eric Greenwell wrote:

trim tab). In his 1989 article on increasing performance, Peter Masak
talked about reducing drag by filling in this bottom concavity. No
mention of the expected drag savings, but lots of words about flutter
concerns.

Not to mention changing the pressure distribution on the aft section
of the wing/tail - thus changing its Coefficient of Moment (i.e. its
desire to rotate/torque around the center of lift). That effect is
less critical on the tail than on the main wing (doing so on the wing
might require an increase in tail volume to control the added moment);
but the bottom line is that you're essentially making a custom airfoil
when you fill that cusp. It isn't necessarily a bad thing, but if you
don't know what you're doing you could just as easily make it perform
worse...

--Noel

Dick Johnson changed the amount of cusp on his Nimbus 3 to reduce the
pitch up at higher speeds. Jim Phoenix has a nice note on it.
http://www.jimphoenix.com/jimphoenix...Nelevator.html

Craig

On May 20, 7:41*am, Andreas Maurer wrote:
On Sun, 18 May 2008 13:45:39 -0700 (PDT), JJ Sinclair

wrote:
We have had a bail-out caused by lifting mylar
on the stab.
JJ

Hi John,

what happened?

Bye
Andreas

If memory serves me (big assumption at 74) this intrepid aviator waxed
his ship and then changed the safety tape....................it lifted
but didn't come off and caused such a flow change over the elevator
that he (intrepid aviator) didn't feel he had adequate control to try
and land the bird (Ventus B). Soooooooo, he tidied up the cockpit and
stepped smartley over the side!
JJ