| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 1241.1 | Washout Is A Good Idea | CLOSUS::TAVARES | John--Stay Low, Keep Moving! | Mon Sep 10 1990 21:46 | 14 |
| As an expert crasher of airplanes, I wholeheartedly recommend
some washout. I have about 1/2 inch in the PT40, per the
instructions, and it allows the plane to handle without tip
stalling well below the point where the ailerons, and even the
rudder, are ineffective. In fact, this is my only criticism of
the plane; that it can be operated this slowly!
I'm doing a scale design now, from scratch, and will also put
washout into this plane's wing. The only possible objection to
this is if the washout spoils the wing's scale appearance -- for
my plane, I don't think it'll be visible, for a Helldiver it may
be a problem. On the other hand, I understand that warbirds in
general are notorious for tip stalling, so you pays your money
and takes your chances.
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| 1241.2 | I'd use 2 to 3 degrees of washout in a scale bird | UPWARD::CASEYA | THE DESERT RAT (I-RC-AV8) 551-5572 | Mon Sep 10 1990 22:08 | 20 |
| Ollie,
Opinions on wahsout vary and good arguments can be made for both sides
of the question. I happen to prefer washout, _especially_ for highly
wing-loaded scale models as it forces the wing center section to stall
_before_ the tips. This is highly desireable when landing and any
other time your low and slow...a snap-roll into the ground with a nice scale
ship really ruins yer' day!!
My MiG-3 has 2 1/2 degrees of washout in the tips and I'd recommend
using between 2-and-3 degrees in the Helldiver. Consider 3-degrees the
maximum as more than that produces too much drag and effectiveness is
lost. Besides, it begins to show beyond 3-degrees where it's very hard
to spot the 2 1/2 degrees in the MiG.
__
| | / |\
\|/ |______|__(o/--/ | \
| | 00 <| ~~~ ____ 04 ---- | --------------------
|_|_| (O>o |\)____/___|\_____|_/ Adios amigos, Al
| \__(O_\_ | |___/ o (The Desert Rat)
|
| 1241.3 | USE OF WASHOUT | FDCV27::P01YATES | | Tue Sep 11 1990 12:36 | 8 |
| Al, this is gooood information. Please let me beg some more from you.
Is the 2 1/2 degrees measure at the trailing edge of the wing tip???
Why not use a decimal measurement (e.g., 1.2 inches)??
Regards,
Ollie
|
| 1241.4 | ROBART HAS THE ANSWER.... | UPWARD::CASEYA | THE DESERT RAT (I-RC-AV8) 551-5572 | Tue Sep 11 1990 14:54 | 23 |
| Ollie,
The reason I use degrees as a unit of measurement for washout is
because the physical dimension will vary according to the wing size,
regardless of whether you state it in inches, milimeters, parsecs or
whatever. :B^) But, the 2-to-3 degrees stays constant irrespective of
size.
Yer' next question is gonna' be, "B---B---But how do I measure it?"
Simple; you go out and buy yer'self a Robart incidence meter ($20.00 or
less mail-order) which every properly equipped shop should have anyway.
You can even use the meter on the building board and there's no need to
zero or level anything...simply read the wing at the center-section and
note the reading. Now, block up the trailing edge near the tip 'til
the meter reads 2-to-3 degrees more than the center-section reading.
Make sure you get both wings identical or you'll wind up with a
built-in left or right bank.
__
| | / |\
\|/ |______|__(o/--/ | \
| | 00 <| ~~~ ____ 04 ---- | --------------------
|_|_| (O>o |\)____/___|\_____|_/ Adios amigos, Al
| \__(O_\_ | |___/ o (The Desert Rat)
|
| 1241.5 | easy to calculate .... | GENRAL::KNOERLE | | Tue Sep 11 1990 16:30 | 31 |
|
If you don't want to buy the device to measure the angle, you can
easily calculate what the hight of the trailing edge should be in
reference to the leading edge.
HEIGHT = tan a x WIDTH HEIGHT- difference in height to
leading edge [inch]
WIDTH - width of your wing at the
point of measurement [inch]
tan a - value 2.0 degree = 0.03492
2.5 degree = 0.04366
3.0 degree = 0.05240
you find this on technical calculators
type <2.5><tan>, the display will
show 0.04366.
Example : your wing is 10 inch wide at the tip (or close to the
tip) - you want to have 2.5 degrees
The height at the trailing edge of the wing tip ( or
close to) should be
0.04366 x 10 inch = 0.4366 inches above the wing center
section
be careful to measure the center of the leading edge and the center
of the trailing edge in the wing center section being the same
height above your working surface.
Holm- und Rippenbruch, Bernd
|
| 1241.6 | Washout Made Easy | FDCV27::P01YATES | | Thu Sep 13 1990 14:34 | 17 |
| Mucho thanks for all the good information on how to build washout into
the wing.
It seems the more I get into the construction of the semi scale
Helldiver, the more questons come up.
Soooo, here's the next one on washout. The tapered wing has both flaps
and ailerons (which extend to the 2" solid balsa tip).
Question: Should I build any washout in the outside part of the ailron
or should I just build washout into the 2" wing tip??
Hope this question "grabs" you and prompts your response!!
Regards,
Ollie
|
| 1241.7 | Washout is progressive and built in | UPWARD::CASEYA | THE DESERT RAT (I-RC-AV8) 551-5572 | Thu Sep 13 1990 16:21 | 49 |
| Re: .-1, Ollie,
Washout is a progressive thing, that is, it starts at the
center-section or (in the case of a Hellcat, Hurricane, Dauntless,
Mig-3 type wing) from the dihedral break and progressively increases
out to the tip where it will measure the desired 2-to-3 degrees.
What you'll want to do is lay up the wing with just the basic parts,
i.e. lead and trail edges and maybe one upper and one lower spar. But,
glue the spar-to-rib joints lightly or not at all except for at the
root and tip ribs. Now, use the Robart Incidence Meter to determine
how high to block up the trailing edge at the tip to attain 2-or-3
degrees of washout measured at the tip. Just for drill, let's say you
need to raise the T.E. 3/4" to achieve the desired washout. Cut
identical blocks and precisely block up both tips at the T.E. the same
3/4". Double, triple, fourple-check both tips with the meter 'til
satisfied they are identical. The result should be that the T.E.
begins to lift from the bench top almost immediately and lifts
progressively higher all the way out to the tip. What you've done is
built in a deliberate warp/twist in both wing panels.
You may find it necessary to go to extremes to keep the L.E. nailed
down to the bench top. This is why you want to block in the washout
before too much structure is added; not only will it resist the twist
yer' trying to achieve but, when added _after_ blocking in the washout,
the subsequently added structure halps lock the twist in place
permanently. I recommend you recheck the washout frequently, like
after adding each additional part, to assure that the twist is holding.
Once the wing is completed and sheeted, it's almost impossible to
correct washout so be certain you get what you want as yer' stuck with
whatever you get at this point.
As you can imagine, building the ailerons and flaps into the blocked up
wing forces these surfaces to follow the washout so, once the wing is
complete, you just carefully cut them free and they should fit like a
glove.
BTW, it'd be almost impossible to build the washout into the 2" tip
alone and, if you coupld, it'd look pretty silly and be ineffective
anyway. The 3/4" I used as an example is not exaggerated...you'll most
likely block up the T.E. about that much to get 2-3 degrees of washout
so I think you can appreciate that this amount must be distributed over
the entire span, not just the last 2". Hope this helps.
__
| | / |\
\|/ |______|__(o/--/ | \
| | 00 <| ~~~ ____ 04 ---- | --------------------
|_|_| (O>o |\)____/___|\_____|_/ Adios amigos, Al
| \__(O_\_ | |___/ o (The Desert Rat)
|
| 1241.9 | For monokoted, open wings! | CURIE::ANKER | Anker Berg-Sonne | Mon Sep 17 1990 15:29 | 14 |
| A quick haskout comment.
Al's procedure is the only way to build washout into a
fully sheeted wing. For a mainly monokoted wing there is another
approach I would advocate: I believe it is extremely inportant
to build the wing straight without bumps, burps and warps. This
is easiest if you start by building it compeletely flat, without
the washout. To create the washout I cover the wing and then
heat the monokote with an iron while overtwisting it until it has
the proper washout after cooling. Using this approach you get
exactly what Al insists you need: a steadily increading washout
angle across the entire wing.
Anker
|
| 1241.10 | Washout maintained by Monokote is unstable over time | WRASSE::FRIEDRICHS | Kamikaze Eindecker pilot | Mon Sep 17 1990 15:52 | 11 |
| Al's method works just as well for an open structure, and is much more
accurate and will maintain the washout better than relying on the
covering....
As the plane gets heated and cooled in your car or at the flying
field, the covering (especially monokote) may lossen and you
will lose your washout.. What's more, you may only lose it in
one wing...
jeff
|