Biplane design questions

[Chris Wells]

A few questions, for those in the know:

Both of the radio-controlled biplanes I've owned were designed with the lower wing at a higher AOA, so that it stalled first. They also had the upper wing farther forward than the lower.

If the lower wing stalls, the CG will be a little on the aft side of the upper wing. Wouldn't it be better for the upper wing to be behind, so that the CG is a little more forward? I've seen some biplanes like this, such as the Beech Staggerwing, but most seem to have the upper wing in front.

While my R/C had the ailerons on the lower wing (my other one had no ailerons), it seems most of the biplanes have them mounted on the upper wing. It would seem to me that the lower wing would be safer, because you'd have a harder time tip stalling that way - the upper wing would be able to keep flying after you tip-stalled the lower one. Why is it the other way around on most biplanes?

Also, it would seem only necessary to put washout in the upper wing, keeping the lower wing flat. Is this the case with most biplanes, or do they put washout in both the wings?

[Kyle Boatright]

"Chris Wells" > wrote in message
...
>
> A few questions, for those in the know:
>
> Both of the radio-controlled biplanes I've owned were designed with
> the lower wing at a higher AOA, so that it stalled first. They also had
> the upper wing farther forward than the lower.
>
> If the lower wing stalls, the CG will be a little on the aft side of
> the upper wing. Wouldn't it be better for the upper wing to be behind,
> so that the CG is a little more forward? I've seen some biplanes like
> this, such as the Beech Staggerwing, but most seem to have the upper
> wing in front.
>
> While my R/C had the ailerons on the lower wing (my other one had no
> ailerons), it seems most of the biplanes have them mounted on the upper
> wing. It would seem to me that the lower wing would be safer, because
> you'd have a harder time tip stalling that way - the upper wing would
> be able to keep flying after you tip-stalled the lower one. Why is it
> the other way around on most biplanes?
>
> Also, it would seem only necessary to put washout in the upper wing,
> keeping the lower wing flat. Is this the case with most biplanes, or do
> they put washout in both the wings?
>
>
> --
> Chris Wells

Interesting points, but I think you've got the washout thing backwards. If
the lower wing is designed first, don't you want wash-out in it to keep the
tip from stalling first and causing a wing to drop?

KB

[Kyle Boatright]

"Kyle Boatright" > wrote in message
. ..
>
> "Chris Wells" > wrote in
> message ...
>>
<<snip>>
>> Also, it would seem only necessary to put washout in the upper wing,
>> keeping the lower wing flat. Is this the case with most biplanes, or do
>> they put washout in both the wings?
>>
>>
>> --
>> Chris Wells
>
> Interesting points, but I think you've got the washout thing backwards. If
> the lower wing is designed first, don't you want wash-out in it to keep
> the tip from stalling first and causing a wing to drop?
>
> KB

I intended to type: "If the lower wing is designed *to stall* first..."

[Stealth Pilot]

On Fri, 30 Dec 2005 13:38:06 +0000, Chris Wells
> wrote:

>
>A few questions, for those in the know:
>
>Both of the radio-controlled biplanes I've owned were designed with
>the lower wing at a higher AOA, so that it stalled first. They also had
>the upper wing farther forward than the lower.
>
well they got it backwards then. the concept is a pair of lifting
wings on opposite sides of the CG.
the idea is to get the wing in front of the cg to stall first so that
the aft wing which is still flying automatically causes the nose to
drop and recover from the stall.

>If the lower wing stalls, the CG will be a little on the aft side of
>the upper wing. Wouldn't it be better for the upper wing to be behind,
>so that the CG is a little more forward? I've seen some biplanes like
>this, such as the Beech Staggerwing, but most seem to have the upper
>wing in front.

dont be guided by full size aircraft. full size has handling
characteristics related to the capabilities of a trained pilot.
models are generally built with some form of stability to make them
easier to fly.
>
>While my R/C had the ailerons on the lower wing (my other one had no
>ailerons), it seems most of the biplanes have them mounted on the upper
>wing.
model aircraft are setup with simple linkages that lend themselves to
being poked through the fuselage into the bottom wing.

most biplanes actually have ailerons on upper and lower wings that are
interconnected by a strut.

>It would seem to me that the lower wing would be safer, because
>you'd have a harder time tip stalling that way - the upper wing would
>be able to keep flying after you tip-stalled the lower one. Why is it
>the other way around on most biplanes?
>
tip stall has nothing to do with dihedral.
tip stall is controlled by washout or some leading edge jiggery
pokery.
The full size aircraft considerations are considerably different to
those of RC models.

>Also, it would seem only necessary to put washout in the upper wing,
>keeping the lower wing flat. Is this the case with most biplanes, or do
>they put washout in both the wings?

go and read some aeronautical theory books. with your emerging level
of interest you'll find them fascinating.

Stealth Pilot

[Chris Wells]

"Kyle Boatright" wrote in message
. ..

"Chris Wells" wrote in
message ...

snip
Also, it would seem only necessary to put washout in the upper wing,
keeping the lower wing flat. Is this the case with most biplanes, or do
they put washout in both the wings?


--
Chris Wells

Interesting points, but I think you've got the washout thing backwards. If
the lower wing is designed first, don't you want wash-out in it to keep
the tip from stalling first and causing a wing to drop?

KB

I intended to type: "If the lower wing is designed *to stall* first..."



I figured if the top wing was still flying, there'd be enough lift to prevent a tip stall...maybe both wings need washout.

[.Blueskies.]

"Chris Wells" > wrote in message
...
>
> A few questions, for those in the know:
>
> Both of the radio-controlled biplanes I've owned were designed with
> the lower wing at a higher AOA, so that it stalled first. They also had
> the upper wing farther forward than the lower.
>


The lower wing that is more rearward is affected by the downwash from the upper forward wing, so the 'relative wind' on
the lower wing comes at it from an angle higher than the relative wind on the aircraft.


> If the lower wing stalls, the CG will be a little on the aft side of
> the upper wing. Wouldn't it be better for the upper wing to be behind,
> so that the CG is a little more forward? I've seen some biplanes like
> this, such as the Beech Staggerwing, but most seem to have the upper
> wing in front.
>

The upper forward wing is the one that is normally designed to stall first, unless it is an aerobatic type design where
both wings are designed to stall at the same time (better snap (or flick) rolls, etc).


> While my R/C had the ailerons on the lower wing (my other one had no
> ailerons), it seems most of the biplanes have them mounted on the upper
> wing. It would seem to me that the lower wing would be safer, because
> you'd have a harder time tip stalling that way - the upper wing would
> be able to keep flying after you tip-stalled the lower one. Why is it
> the other way around on most biplanes?
>

This is a control authority issue. Most bipes I see have the ailerons on the lower wing, and then the more responsive
ones have them on both wings.

> Also, it would seem only necessary to put washout in the upper wing,
> keeping the lower wing flat. Is this the case with most biplanes, or do
> they put washout in both the wings?
>
>
> --
> Chris Wells

[Chris Wells]

The upper forward wing is the one that is normally designed to stall first, unless it is an aerobatic type design where
both wings are designed to stall at the same time (better snap (or flick) rolls, etc).
_________

Why would you want the upper wing to stall first?

[.Blueskies.]

"Chris Wells" > wrote in message
...
>
> The upper forward wing is the one that is normally designed to stall
> first, unless it is an aerobatic type design where
> both wings are designed to stall at the same time (better snap (or
> flick) rolls, etc).
> _________
>
> Why would you want the upper wing to stall first?
>
>
> --
> Chris Wells

Not so important that it be the upper wing, but the forward wing. Same reason that stealthpilot posts "the idea is to
get the wing in front of the cg to stall first so that the aft wing which is still flying automatically causes the nose
to drop and recover from the stall."

[Richard Lamb]

Has nothng to do with tip stalling, guys.

Look at it from a balance standpoint.

When the forward wing stalls first, there is a nose down moment created.
If the aft wing stalls first, there is a pitch UP moment created!

Which condition will help recover from the stall?


Richard (the Saber Tooth Cave) Lamb