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wing incidence question - 7/18/2003 7:06:13 AM   
Buz^


 

Posts: 491
Joined: 2/27/2002
From: vancouver , WA, USA
Status: offline 		thx for checking, A friend of mine has a knock-off scale bipe, but looks allot like a tiger-moth. My question is , where to set the wing incidence's ?
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Re: wing incidence question - 7/18/2003 9:25:33 AM   
Tall Paul



Posts: 4692
Joined: 6/23/2002
From: Palmdale, CA, USA
Status: offline 		[QUOTE]Originally posted by Buz^
thx for checking, A friend of mine has a knock-off scale bipe, but looks allot like a tiger-moth. My question is , where to set the wing incidence's ? [/QUOTE]
.
On the full-scale, both wing's incidences are +4.
Horizontal at 0.

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wing incidence question - 7/18/2003 9:08:27 PM   
Rodney



Posts: 4879
Joined: 12/8/2001
From: FL
Status: offline 		I built a 1/4 scale one and had best results with stab+0, lower wing +0, upper wing -1.5, 3degrees down thrust and 3 degrees right thrust, flew great./

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wing incidence question - 7/24/2003 6:30:23 AM   
Hal deBolt


 

Posts: 385
Joined: 4/12/2002
From: Sun City, FL, USA
Status: offline 		Hi Buzz,
Should say biplanes are bipes and all eat at the same table.
There is a well proven force arrangement, such as>
Thrust> zero
Top wing one degree positive
Lower wing zero degrees
Horizontal tail three degrees positive
Balance on a line from upper to lower wing centers of lift.
Good luck and have fun!

Hal deBolt [email]hdebolt1@juno.com[/email]

_____________________________

hal deBolt

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wing incidence question - 7/24/2003 6:32:39 AM   
Buz^


 

Posts: 491
Joined: 2/27/2002
From: vancouver , WA, USA
Status: offline 		Thx allot guy's for your responses, will put it to use on my proctor antic

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wing incidence question - 7/24/2003 8:26:40 AM   
scalebldr


 

Posts: 541
Joined: 11/8/2002
From: allenstown, NH, USA
Status: offline 		Hal,
"Balance on a line from upper to lower wing centers of lift"
maybe i am just tired but am having a hard time comprehending this.please elaborate.i thought you took the chord measured from leading edge of forward wing to trailing edge of trailling wing and then used a 25-30 percent amount depending on airfoil type.

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wing incidence question - 7/25/2003 12:15:05 AM   
bschriv


 

Posts: 6
Joined: 7/11/2003
From: santa rosa, CA, USA
Status: offline 		scalebldr,

The center of lift of an airfoil is a point where the pitch moment generated by the aerodynamic forces on the foil is independent of the pitch angle (angle of attack). (Aside: A cambered section in a fluid flow generates circulation, which produces a lifting force, a drag force and pitching moment force on that section). So you can also think of it as the point where the lift force and the drag force grab onto and this point does not move when the angle of attack is changed. This change needs to be within a reason, because when you get close to the stall angle this point will start to move due non-linearities of the flow physics.

You are correct that this point is located somewhere in the 25% to 30% cord range. This depends on the foil' pressure distrubution, which is dependent on the overall foil shape.

A flat plat when put into a flow stream with a small angle of attack will have a theoretical point of 25%. This can by shown with math alone. Airfoils are is a sense flat plates with camber and improved flow characteristics, so this point is also in the neighborhood of 25%. This point is also called the Aerodynamic center or ac.

For stability reasons you want to locate the longitudinal center of gravity of the airplane slightly forward of this point, the father forward the more stable the flight characteristics become, the farther aft less stable. Aft of the ac the planes becomes instable and very difficult to fly.

Hopes the helps.

Bschriv

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wing incidence question - 7/25/2003 3:06:18 AM   
Tall Paul



Posts: 4692
Joined: 6/23/2002
From: Palmdale, CA, USA
Status: offline 		For biplanes, where the lower wing can be seen in a planform view, the c.g. is located using the observed total chord.
The c.g. can also be located in this manner, but the wings should be constant chord...

Attachments
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Click for fullsize

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wing incidence question - 7/25/2003 7:51:45 AM   
captjack


 

Posts: 89
Joined: 2/28/2003
From: bow, NH, USA
Status: offline 		tall paul
i believe the drawing you provided proves what i said above.you show a footprint chord of 9.25 inches due to the stagger and 30 % of the 9.25=2.78 inches which is a hair from your calculations.
you are corect when i was assuming constant chord wing with no sweep.i was tired last night.

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wing incidence question - 7/25/2003 8:02:05 AM   
Hal deBolt


 

Posts: 385
Joined: 4/12/2002
From: Sun City, FL, USA
Status: offline 		Hi ya'll,
Locating bipe balance point, fore and aft. Not center of gravity
which has a vertical; vector also.
On paper> draw 2 horizontal lines depicting the chord and
relationship of the wings, wings can stagger or what ever.
Determine the size relation of the wings. Drawing must be scale!?
Say lower wing is 2/3 the size of the upper.
Assume the high point of the airfoils is the center of lift.
If there is taper or sweep back the average chord location
will be used.
Connect the wing's center of lifts with a straight line.
Lower is 2/3 upper?
This line has a length?
On the line measure from bottom line towards top and mark
2/3 of the length. Draw a vertical line through this point.
This vertical line represents the fore and aft balance point for
the Bipe.
No concern about having the balance forward of the C/L
It is the lift neutral point which is of concern and traditionally
the neutral point is aft of wings C/L/
Need more? Ask!
Good luck!

Hal [email]hdebolt1@juno.com[/email]

_____________________________

hal deBolt

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wing incidence question - 7/27/2003 7:52:25 AM   
Flyin Woodbutcher


 

Posts: 836
Joined: 12/16/2002
From: Ashland, VA, USA
Status: offline 		Hey Hal what reason for the 3 degrees on the horizontal?

Kent

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wing incidence question - 7/31/2003 7:32:09 AM   
Hal deBolt


 

Posts: 385
Joined: 4/12/2002
From: Sun City, FL, USA
Status: offline 		Hi Kent,
There is a good reason for the horizontal tail setting.
But first you must be aware of the deeds the tail does.
With all aircraft the H. tail controls the attitude of the wing (s).
If we wish the craft to maintain the same flight path over a wide
range of air speed there must be a proper proportion of lift
between the wing (s) and the tail.
Lift increases as a square of the air speed.
Example> say air speed increases 10 mph and as a result wing
lift increaes 10 oz. Wing lift is a force, so is tail lift and it is ar the
end of a moment arm (lever). Say the moment arm is a factor of
5. Then to be in proportion with that speed increase the tail must
produce 2 more ounces of lift.
Happily the tail is nothing more than a "rear wing" so it sees a
lift increase as does the wing.
Lift is generated by 3 factors plus air speed. Area, airfoil and
angle of attack (incidence to the line of flight)
The proportion can be made with any of the three.
With that under our hat back to bipes.
The wing span of most biplanes is similiar to a monoplane of that
type. But, the bipe has considerable more wing area.
That should require a large increase in tail area if we were to
stay with mono requirements.
However, deigners have found that stability wise a bipe does
not NEED the larger tail. so a size simliar to a mono is used.
But the tail now must control two wings and their additional lift.
Remember the proportion> tail lift must be in proportion to wings
lift. With more wing lift, tail lift must be increased, recall there are
3 options to increase lift.
Wishing not to increase area the needed additional lift can be
had by increasing the incidence setting, especially if the tail has
a decent airfoil.
For efficency the tail should be airfoiled.
Hope that answered your question, took some "hot air" to do it?
The bipe force arrangement given before was (is) the result of
extensive bipe development in past years.
Good luck and be good!

Hal [email]hdebolt1@juno.com[/email]

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hal deBolt

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wing incidence question - 7/31/2003 7:50:40 AM   
Buz^


 

Posts: 491
Joined: 2/27/2002
From: vancouver , WA, USA
Status: offline 		Hal, thx for the info

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wing incidence question - 8/1/2003 2:00:50 AM   
Ben Lanterman



Posts: 1284
Joined: 10/27/2002
From: St. Charles, MO, USA
Status: offline 		In my younger years I wondered why Hal set his designs with the positive tail setting relative to the wing. When I became an aero eng for a living I finally realized that the tail was lifting ( see the discussion in the forum http://www.rcuniverse.com/forum/tm.asp?m=990135 ) and it became obvious.

The tail angle of attack ( and therefore it's contribution to airplane stability ) can be written as

tailalpha = wingalpha - downwash

A big hairy discussion is in the book Airplane Performance Stability and Control by Perkins and Hage. It is pretty interesting. They discuss the effects of this on the stability term dCm/dCl. There is also a discussion of power effects.

Anyway to get the tail angle of attack the same as the wing angle of attack (and removing the effect of downwash) Hal has set the tail to a positive angle which is approximately equal to the downwash angle at the tail. This makes the tail contribution to stability constant and nice. The downwash could be computed, measured or as Hal has done, it can be determined by observing the airplane response through a lot of hours of flying.

However it only works when the airplane is upright (which is most of the time usually). Put the airplane inverted and the horizontal tail isn't at the optimum angle anymore. But it is perhaps close enough.

You do end up with an airplane that is very nice for the times it is doing level and positive g maneuvers and OK at negative maneuvers.

In a no downwash world the wing and tail could be set at the same angle. A bipe such as the big TOC Ultimates with minimal weight are basically this case. Doing a TOC type of maneuvering sequence you will sacrifice some upright response and handling qualities in order to get a machine that will be exactly the same upright or inverted. An indeed since the handling qualities are excellent anyway you set all of the angles equal to 0 and go for it..


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Ben Lanterman

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wing incidence question - 8/3/2003 8:38:43 PM   
Flyin Woodbutcher


 

Posts: 836
Joined: 12/16/2002
From: Ashland, VA, USA
Status: offline 		Thanks Hal and Ben for the great info. Do you fellas have any thoughts on the mono planes that tend to balloon on landing?

Thanks Kent

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wing incidence question - 8/3/2003 11:30:55 PM   
Tall Paul



Posts: 4692
Joined: 6/23/2002
From: Palmdale, CA, USA
Status: offline 		Seeing Hal DeBolt here regularly sends me way-back-when to the time when I became active in r/c... started in '55 with a Berkeley Royal Rudder Bug, Fox .19, Citizenship single-channel radio kit...
Hal's Live Wire was -the- airplane at the time. Probably got most people of that time into r/c.
Note its aerodynamic setup, with the forward c.g. and lots of incidence on the wing, and lots of incidence on the horizontal; typical of a free-flight and a motor without a throttle, it was a one-speed speed airplane. The motor had more than enough power to keep the plane in a climb. Altitude was controlled by turning/diving.
MOF, loops and rolls were easily done by turning/diving, and neutralizing the rudder, for a loop, or neutralizing rudder then putting the other direction in to roll.
All exploiting the single-speed aerodynamic layout.
When the Bonner compound escapement made motor control possible... 2 speeds, full power and something less with an intake restrictor, then more control of the pitch axis was possible. The second speed could be set for level flight or a slight descent.
I recall Fremont Davis' son had a Live Wire Kitten (seriously modified) with rudder only proportional and motor, doing touch-and-goes, using the motor and the rocking feature of the Live Wire setup.... a rapid switching between left and right rudder in a descent would raise the nose... touchdown, add power, climb out..
When multiple channel radios became available, the force setup changed. The pilot now provided a major portion of the longitudinal stability, with elevator trim, and/or power. As most sport fliers don't use the motor channel for anything more than a on-off switch, the elevator trimming feature became important..
And the usual free-flight semi-automatic stability and constant climb went away.
More modern airplanes now use a horizontal set parallel to the FRL or engine thrust line. Little wing incidence, and that due to setting the "flat" part of the aft bottom parallel to the FRL...
Pattern planes use 0-0; no wing or tail incidence. Engine thrust offset to suit the low-powered portion of the flight.
Go-fast planes went to 0-0-0 early on.
In essence, any fixed aerodynamic setting will be "good"... that is, no trims needed, at a single flight speed. Go faster, the elevator trims down. Go slower, it trims up unless you want to climb/dive.
Those fliers that never fly slower are amazed to find this out, and when it makes itself known ask questions like "My plane climbs under power. How can I stop that?"... Um, if the airplane can't climb, it's a car. Go to a different forum

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