Biplane Wing Incidence - Well kept F3A secret or nobody knows for sure.
 

Hi,
There seems to be an information gap on this subject.
So I'll ask openly here and see what comes up ;
- How should an F3A Bipe be set up wing incidence wise and relative to thrust line ?.
- What is the reasoning behind the 0.5-ve top wing relative to bottom wing concept - I just can't get there in my mind ?.
- Why not set both wings the same ?.
- Does anybody know the recommended incidences for the Oxai bipes ?.

Any input appreciated :).

Regards.
Brian

Brian, I was really hoping some guys would have given up some good info here. I just got a YS 115 for warbird racing but was thinking it would be a waste of a good engine to only use it for racing. I was thinking of a 60" span pattern bipe. Being that the GC Ultimate is one of the best flying bipes I have flown to date I was going to go with its incidence settings of engine at zero, wings at zero and stab at positive of 2 degrees. I'm still hopeful someone will come in and give us some first hand knowledge.

Hi,,
Yes, normally this is a very helpful community. I think we a being a little 'camera shy' on this one !!?

Brian

Brian,

In the spirit of trying to kick off this thread, I pulled this off of a Google search:

The decalage (note the spelling) for most biplanes is set up just like Steve says, for exactly that reason. Because most biplanes have positive stagger (i.e.: top wing slightly further forward than the bottom wing), stalling the top wing first will shift the center of lift aft, which tends to hold the nose down and delay any stalling of the bottom wing. Of course if you're building a Beech Staggerwing or a Sorrell Hyperbipe (negative stagger), you would want to set it up with more incidence on the bottom wing to create this same effect.

One notable exception to this arrangement was the famous Bucker Bu-133C "Jungmeister" ("Young-my-stir", German for "Young Master"). Its incidence was 0.0 on the top wing, +1.0 on the bottom wing, with positive stagger. This had two effects. Because of some complex interactions I won't go into right now, there was no change required in elevator trim between upright and inverted flight. In addition, in a positive-G stall, the bottom wing stalled first, shifting the lift forwards, causing the nose to go up even more, triggering a stall of the top wing as well. The reverse happened if down elevator was added for recovery. As a result, the Jungmiester stalled like a lightswitch, either "on" or "off". This gave it extremely crisp entries and exits to stall-based maneuvers such as spins and snap rolls (" flick rolls" for you Brits). Most airplanes will recover predictably from a snap roll 9 out of 10 times, but watch out for that 10th time! Because of this, it's very important to have lots of altitude when doing these types of maneuvers, just in case. The Jungmeister would recover predictably 10 out of 10 times, making it ideal for this sort of dangerous nonsense. You can see a Jungmeister (modified with a modern flat-opposed engine instead of the old radial) doing exactly this in the movie "The Great Waldo Pepper", in the sequence showing "the famous ace Ernst Kessler" doing a 10-turn "death spin" at an airshow, recovering with the wheels almost touching the ground. It's been said that the Jungmeister was the only aircraft that could safely (if there is such a thing for this kind of stunt) do this, since it was the only aircraft that could be counted on to recover at exactly the right moment, EVERY time.

This fantastic ability for precise stall-based maneuvers proved to be the Jungmeister's undoing in competition. The man who compiled the dictionary for aerobatic maneuvers, Jose L. Aresti, whose book established the difficulty factors and scoring for modern aerobatic competition, flew a Jungmeister. Consequently, he gave low difficulty factors to the snap maneuvers Jungmeisters are good at, and high difficulty factors to the "yo-yo" vertical maneuvers that spell trouble for the Jungmeister's draggy (but extraordinarily strong and light) wire-braced wings. As a result, the modern rules favor the cleaner (but not as good at snap maneuvers) monoplanes, with their low drag airframes and internally braced wings.

Maybe it will promote some discussion?

Malcolm

Hi Brian,

This is not first hand information, so i was reluctant to post it here at first, but anyway here it is. About a year ago, a friend told me he measured an Oxai Citrin biplane and all incidences (wings and stab) were set to 0. I was very surprised to hear that... i hope other biplane pilots will share their setup.

Hi Malcolm,
What did 'Steve' say.
Re the Jungmeister set up in the comments ; Wouldn't that all be just fine if our schedules were predominantly based on upright manoeuvres.

Brian

Hi Alex,
Thanks ! - I hope so too :).
I'm not surprised at that set up at all - except for the stab !

Brian

He said more incidence on top wing!

Re the negative snap situation I think you will find that the same thing applies. Think about the leading edges of both wings being closer together than the trailing edges, they will be so upright or inverted.

Malcolm

Forget that last post, I didn't think that through enough!

Malcolm

Malcolm,
Can you post a link to that discussion please.

Brian

Brian,

Not a thread but a question on this website:

http://www.djaerotech.com/dj_askjd/d...edecalage.html

Malcolm

I measured my Citrin, with the stab set to 0 for reference the wings both sit at 0.6 positive. The plane has as close to zero mix in it as I can get it.

I did did adjust the stab incidence to remove up elevator trim so this was measured with the trim at neutral. Not sure what it came out of the factory with. The motor is about 1 deg down with this reference as well.

Hope it helps.

Hi Chad,
Thanks.
So your motor is 1.6 deg from square to the wings ?

I should have said already that my Midrex is at 0.75 +ve on both wings and 1 deg -ve on the contra. The model is at 5030g and has a slightly smaller top wing than bottom wing.

Brian

Some people strongly believe that a biplane's upper and lower wings should be set at different angles of incidence. The relative angle being termed "Decalage". Often model airplanes are given up to 3 degrees decalage by the designer. By comparison most full scale bipes have no more than 1 degree decalage. There is a theory that positive stagger requires the lower wing to have more positive incidence than the upper whereas, with rearward stagger, the top wing should be more positive.Presumably, then, no stagger means no decalage.

Just to explore the Jungmeister setup a little more in the light of modern radios:

Assume both wings set at same incidence and this is adjusted relative to the thrust line for no pull to the canopy in vertical up flight.

Now we mix up elevator to down ailerons on the bottom wing. At the stall the bottom wing stalls first and the positive stagger induces a nose up moment from the top wing.

We also mix down elevator to up ailerons on the bottom wing and at the stall the bottom wing again stall first and the positive stagger induces a nose down moment from the top wing.

Of course we would put this mix on only in our snap flight condition so it was only affecting things then.

Might be worth a try.

Malcolm

Brian,
Was going to reply to your thread when you posted it but decided to put my Mangonel on my recently constructed rigging stand. Haven't checked the rigging for about 45 flights. In summary my results are
Model wing area- 700 sq ins each, model weight with 4950 mAhrs Dualsky pack 4790 gms. Set up datum is the hatch combing. Down thrust 0.9 deg, right thrust 3.4 deg. CoG at 29% MAC of top wing- no stagger used.Wings -section NACA 64-008A honeycombed foam/balsa/Monocote. The all moving stab trims at +1.2 deg. Top wing +0.25deg, bottom wing +0.42deg measured at the tips. Wings were originally set at 0.25deg so looks like there is a twist in the bottom wing but it is symmetrical. Only two mixes used
Throttle to down elevator 3% at low throttle to straighten the down lines and 4% rudder to elevator to correct proverse roll in knife edge. We didn't quite get the dihedral correct. Top wing has 0.7 deg anhedral ( flat across the bottom) and lower wing has zero dihedral. Motor Plettenberg 30-10 Advance with Spin 99 ESC. Falcon 21.5*13 prop. We are very happy with the way it is flying. Design by David McFarlane who flew in the Aussie team in the World Champs in Ireland. Uses a modified monoplane molded fuse( Arbalest ) also designed by Davidhttp://www.rcuniverse.com/forum/atta...mentid=1976046http://www.rcuniverse.com/forum/atta...mentid=1976047http://www.rcuniverse.com/forum/atta...mentid=1976048. Have attached some pics of it in the rigging stand with my home built incidence meter. Good luck with yours- wings look very inpressive. Bill

Oops- Correction rudder to aileron mix for proverse roll. No rudder to elevator mix needed
Bill

Hi Bill,
Love the rigging stand :) - and thanks.
Are your struts adjustable for incidence ?
What in the motor at relative to the rest ?

Brian

Hallo Brian,
Struts are adjustable - I use 4-40 rigging couplers. !/2 turn is the minimum which is a little coarse but seems to be working. Motor is -0.9deg to datum. Found that filming pulled a twist in my wings but with the film iron and strut adjustments they are at least symmetrical. The twist was a bit of a surprise. Last time I measured the wings were at +0.3 deg.
Cheers,
Bill

Bill,
The twist thing is definitely an issue with these skinny F3A bipe wings - on the building board then again under flight loads, especially in turbulent and or quartering cross winds.
That is why I'm going with the carbon veil method that I'm trying. Getting strong and light won't come easy with these bipes.
Strong and heavy/heavy-ish is relativity easy to do.

Brian

Brian,
I agree. Will be interested to hear of your experience with carbon veil. Any concerns about RF signal shielding? I have no experience with it.
Bill

Hi Bill,
Your question serves as a reminder to me - I had wondered then it left my mind.
Yes I must bear it in mind and locate the Rx antennae to give best los. There will be a lot of potential for shielding with it being a bipe - thanks.

Brian

Brian
The entire Shark Bipe Is built with Carbon, Veil/ Matt, Balsa Composite, Fuse And Wings.
Never had a problem with it over 500 flights. Don`t worry about it.

I have a 50cc Goldwing Ultimate. Everything is on "zero" except engine which is your standard 1.5 right and 1.5 down.
I fly IMAC and a little 3D and do not use any mix 90% of my routine. I am an old school flyer and we have an old saying:

"No need mix.....Learn to use your sticks".

Mixing is fine if that is how you want to fly but it can get in the way. Especially with a bipe. I do have mix
programmed into my machine but I have it all linked to one switch so I can immediately turn off or on all mix
with the throw of one switch.

With everything on "zero" and right-down on engine, flying characteristics are adjusted with CG changes
via adding or removing nose weights. All trims should be on "zero" if your plane is set up right. Throttle management
( speed ) is essential when entering and exiting a maneuver and maintaining a straight flight path. Flying
characteristics will change with flying speed if incidences are in play.

"I am not a Pro...............no one has ever paid me to fly my models!"

Hi Bryan,
That's good to hear - thanks.
I think the veil would not be nearly as effective at shielding as solid carbon like the glider guys use - they have to deal with it as it is a real issue in those rigs.
My fuz is glass/glass sandwich in the radio bay area but that area is right between the wings which will have veil inside and outside each sheet - so there is potential , hypothetically anyway, for shielding.
We'll see !.
Have looked at these ; http://shop.rc-electronic.com/ROBBE-...F0959400&p=865

Brian