FYI:     A letter sent to Sven in respnse to some of his questions and comments. 
 

Subject: Your letter Friday 16th
Date: Sun, 15 Feb 1998 17:37:44 -0800
From: Jerry Sjostrand <firesgn@sierratel.com>
To: Eriksson <research@researchelectronics.se>

Hello again Sven,

(This is in reference to the aft shear web long layups)
    It sounds like you should manage very well on the long laminate. You
have already received my comments about doing it in pieces, inboard 3 Ft.
and then the outboard length. However, it can be done in one piece with the
right help.  It is true that you do not have to cut to size the width of the
layup. When I did mine, I marked the nylon full length with fold lines
(including a center line) and with the finish as well as the "oversize"
lines. The center line really helped when carrying the pre wet layup to the
position on the wing. One thing important is to keep the layup not too wide
or too narrow. There should be about 1/4" to 3/8" over on each side for
trimming.

     It is interesting that you were reading the Cafe article when I called.
I'm glad you had it already and could make some comments. When I was at the
Cafe Foundation facility we discussed what might be done to alleviate the
"blanking" problem". An enlargement of the vertical surface (picture) seemed
to be the first possibility. I even made a cardboard pattern of a frontal extension
that seemed to meet with their approval for a starting point. It would
increase the vertical surface by about 20% if you add upward starting just
below the "cross" of the surfaces and continue up rounding off to meet the
top of the rudder. I'll include a drawing. This can be done easily as you
build if you choose to do so.  It seemed to be the opinion of the "group"
that included test pilot and engineers, to increase the vertical area would
help but not eliminate the problem of "blanking". It seems that to increase
the area of the horizontal would only exacerbate the problem as it would
increase the blanking of the vertical surface. What do you think about this
theory?

    Regarding my personal feelings about the "blanking" problem":

    I don't intend to fly the Express anywhere near the extreme yaw and attack
angle required to create the adverse stall. Jim Warner found his aircraft did
exactly this and even offered to take anyone up to experience the "event".
Meaning, finding yourself upside down in a flat spin which he was able to
come out of in less than 2 turns. Not for me!!!. Even the Cafe people agreed
that, if this airplane is flown with a pre-cautionary attitude and knowing
that the craft will do an unusual attitude stall, it still can be flown
safely.  Since reducing the rudder travel to 20%, the problem changed from
"terrible" to "manageable".

    You mentioned Dick Lind's Express with larger horizontal stabilizer
surfaces and asked about any reports.  When we talked "airplanes" we never
discussed the "blanking" problem as it really has not been an issue with us.
The lack of horizontal stabilizer control surface to allow holding the nose
up on touch down was the issue. That can be and has been rectified by the
larger tail ,i.e.; the Ariga and Dick's addition. Dick and several of the
last builders to fly have IO540 engines which add weight to the nose. Since
our wing attachment point is fixed, the CG can not be changed there. It can
only be changed with the placement of weight for and aft with batteries,
light weight starters, etc.

    By the way, one builder did order his lower fuselage with the carry
through left unbonded so he could move it to his specifications. It happens
that he is making his retractable and needed the wing to move forward to
offset gear weight an CG problems.. My first thought was, "where is he going
to put his body as the carry through moves the seat forward"?

    Note::  To buy the body filler I referred to, you will need to shop at
a supply house that sells to the body and fender repair shops. We pay from
$10.00 to $20.00 per gallon. I must have used 4-6 gallons that included
bonding fixtures to the floor, body filling on the Express, and fixturing of
parts. As I mentioned, I stopped using the hot melt glue early on and
starting "fixturing" with small amounts of the body fill which sets up
quickly.  Using body filler instead of hot glue for fixturing allows you to
remove a part, clean up the surface with a bit of sanding, and re-fixture
all in a short amount of time. Automotive "Body filler" is a polyesther resin
product and compatible with our "vinyl esther resin".  It is structurally sound
--hot glue is not.

    Another thought about having to "straighten" the trailing edges. You may
find it interesting to build up the shallow areas on the outside with glass
cloth and resin and then remove the extra from the inside area. I did this
in several places where it did not effect the structural integrity of the
part. When you do the trailing edge of the horizontal stabilizer, you will
want to keep the shear web layups short of the opening. It seems that if you
fill the area from skin to skin, shrinkage will pull the surfaces together
and create a space problem. Since the elevator hinges are not attached to
the skin, you do not need the thickness such as you do on the wings where
you will attach hinges.

Enough for now.        Keep in touch.

Jerry
 
 

                The following is a drawing I made of a possible addition to the vertical
           stabilizer to increase yaw stability.    What do you think? Replys requested.

                                    
          Back to home page: