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RuneG 09-11-2020 04:14 AM

Bi plane wing

I have a wing on my own design biplan that has this messurments , each panel is 880mm long (total 176cm span) root is 330 mm and tip is 170mm , I think this maybe a bit to big , was thinking taking it down to 172-174 cm and also make root a bit smaler maybe 300mm and tip something 150mm . the sweep back is 20mm at the center off the wings trailing end and was thinking to make that 40mm
What is the typical mesurements on today bipe's ?? any one!
I have been out and messured but its wery diffrent on the planes!

ted32776 09-11-2020 05:15 AM

Hello Rune. May I suggest you contact..... speedracerntrixie ......here on RCU. Shaun has a very successful wing design on his bipe and may be able to provide your answers. He's very helpful and experienced. I'm building one of his designs now.

bandicootf16 09-11-2020 09:34 PM

Hi Rune
Why do you think your wing is too big. What flight characteristic arenít you happy with. I guess the function of the wing is to provide lift to oppose the weight of the model. Lift is a function of wing area and airspeed. So in deciding on a wing area I guess the models weight and desired airspeed must be considered. A lighter model and or higher airspeed will mean less wing area is required. It would seem most bips have a wing area of about 90 dm^2. Naruke has been designing bips for many years. The Advantage has a area of 92.8 dm^2. The root is 350cm and tip 150cm with a span of 1760. This is for IC so probably a take off weight of 5500g. I think you have a FH Neo Stage Bip which has a wing area of 92.3 dm^2 and span of 1800 cm. The Futaba Leader G (and A1) has a wing area of 90 dm^2 and span of 1720. The original Leader had a span of 1770 cm. Iím not sure what the original wing area was but the G redesign seems to have an increased root cord from the original. The Nurila Glacial has a span of 1740cm. The area is not quoted but the wing would appear to be similar to the Naruke Advantage. The Akiba Accel has a span of 1740cm and an area of 82.8 dm^2. The root cord is 310cm and tip 125cm. This is certainly the odd one out and it also has a so called dogtooth as per his Fantasista and now Interceptor.

It it would appear that snap performance was a major factor in the Leader G wing design with reduced wing span and very small tip cord. This has been compensated for by increasing the root cord to maintain the wing area. Another consideration in Biplane design is wing efficiency. Increasing the distance detween the top and bottom wing increases efficiency which potentially means a decrease in wing area. The Accel has a very deep fuselage so this might be the reason for the lower wing area at 82.8 dm^2 as opposed to 90. I would guess the design weight of the Accel would be 4750g. Again this allows a smaller wing say as compared to the Naruke Advantage with a flying weight of 5000g plus. Akiba is very fussy when it comes to weight. A model can be too light for itís designed wing and Iíve seen him add weight to a model because it was too light and didnít fly correctly.

The sweep on the Futaba Leader G would appear to be about 20mm, as per the Neo Stage and Advantage. The trailing edge of the Accel is actually sweep forward 10mm at the tip.

I guess you canít go too far wrong in following the Futaba Leader G wing design, a large root cord of say 350 and small tip of 130 to 150 with a span as you suggested. A double tapper might be worth considering or an curved leading edge.

speedracerntrixie 09-12-2020 07:50 AM

I agree that this thread could be more insightful if we knew what charictaristics you are trying to correct. By thinking you have too much wing area I can only assume that you feel the model is " floaty" in flight. Small air disturbances may seem to push it around a bit more then you like? If that is the case, I would be interested in knowing what the incidence is set at for both wings. My Divergent wing's specification is very close to your model's wings. The prototype Divergent weighs 5500g, the one I am currently flying weighs 4500g. No change in wing area between the two and the lighter one tracks in wind just as well as the heavier. My thoughts are that wing incidence plays a big part in how a bipe flies. On both of mine I have the upper wing set to zero. The light model has the lower wing set to +1 degree while the heavier one has +1.5 degree. I have the stab set to zero on both models and adjusted the lower wing incidence until level flight and straight up lines were achieved with the desired CG.

The offset incidence angles ( in theory ) fool the airplane into flying like it has a higher wing loading while in level flight. Change the flight AOA and then the additional area of the top wing kicks in. Invert the airplane and the incidence offset remains the same a certain amount. The now bottom wing has to be flown at a positive AOA while the now top wing is still close to zero. The difference now is that the stab and motor are at a slight positive angle and is verified by an increase in elevator sensitivity if the same throw is used for up and down. I currently run about 10% less down throw then up throw to compensate for this.

RuneG 09-13-2020 10:41 PM

Hi guys
Thanks for input
try to explain , yes it feels a bit light in Wind ( weight is 4650) incidience is 0 on top wing and +0,7 on the lower one, it seems to help a bit when I got from 0,5 to 0,7 i diffrence .
I was also think about a dobdel taper , a eliptical leading edge is not possibel on a foam wing ( to much job to build a wooden wing) , I also was thinking a dobbel taper to get more off the lift in the senter off the wing as I think that maybe will help With the feeling that it is a bit "light" in the wind

RuneG 09-21-2020 02:22 AM

If I calculated correct I have today 89dm2 on both wings (the aera in the fuse is not removed) so I think maybe it isnt that bad so I think I just make the wing a bit wider in the root ,do a dobbel taper so I move more off the aera to center, the prototype is also pretty low in weight so maybe a bit higher wingload would helped, so maybe I can build the next one a bit heavier!!

DagTheElder 09-21-2020 03:32 AM

Some Areas of Bipe
Citrin Bipe 92dm2
Hybird Bipe 88,5dm2
Acuracy Bipe 82,6dm2
Final Touch 82,9dm2
Ascent Bipe 2 dm2
Immortal Bipe 82,6
These measurments are taken from manufacturer sites. However, these figures will not be of help if not stab volum and tail moment are included in the calculations.

67685 11-19-2020 12:04 AM

Hi guys,
What kind of thickness is used in wing section for bipes you mentioned in previous post ?
..working on a pair of wings myself, dialing in about 87-90dm2 area, section between 8-9%.

Thanks in Advance

RuneG 11-19-2020 02:22 AM

Nice to see you are going to build again, I used 9% on my first and going to do that again .
I used profili to find the airfoil I would be happy to send it to you if you have this software

67685 11-19-2020 03:40 AM

Hi Rune!
Thanks for your offer, i have already fabricated templates, modified naca's at 9%, 36 +15, so i should be fine then.
Time to build a cutting jig, do some experiment with my icharger cutting program, find some decent foam and a good balsa supplier. No time to build balsa wings this time, and besides, a simplified fuselage construction.
Do you still order from Germany ?

RuneG 11-19-2020 07:49 AM

yes got balsa from Germany , but needed some more and was a quick trip to Norwegian and the have some fine balsa but you have to hand pick , if they have to a complete biplane I dont know.
And I agree balsa wings on a biplane is to much job, its ok if you have a kit !
Foam I got from Coop Obs localy I have tried to get lighter foam order specially before buts its not possible , I had to ordrer big if I should get it was the answer.

papaone 11-20-2020 01:20 AM

Hello Rune

Awesome job !
I think design of wings is good.
Flight of Xareltoo is excellent with these dimensions of wings :
root is 340 mm and tip 160 mm, lenght is 1740 mm, sweep back is 20 mm.


alderblee 11-22-2020 08:48 AM

I'm surprised by some of the airfoil thicknesses stated here. I heard biplanes often have thinner airfoils. But are they really as thin as 9%? A rough measure of a BJ Craft Encourage showed ~13% at the root to ~11% at the tips. Am I reading this correctly, or are there other factors that make thinner more desirable?

What would the expected effect be of thicker airfoils on the biplane?

67685 11-22-2020 11:50 PM

I may open a can of worm's here, but my personal point of view is that in general, thinner airfoils flies better in wind.
In my F3A monos, i tried different sections, from 13% down to 10%, slightly compensated wing area, all other factors the same; the behavior was noticable better in wind with 10%, flying P- Programs.
I don't have the same experiences with bipes, but what i have seen, i recognize the same behaviour, specially in windy conditions, but there are many factors included. The only way to find out excactly what you like is to do the effort and try different options.

orthobird 01-14-2021 05:12 PM

xarelto is the name of a blood thinner

drac1 01-14-2021 05:45 PM

Originally Posted by orthobird (Post 12657161)
xarelto is the name of a blood thinner

Umm, yep 🤷‍♂️

serious power 01-20-2021 03:16 AM

Xareltoo is not :)

orthobird 01-20-2021 03:22 AM

Serious Power, you are right, but sure is close!!

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