Interference drag on high wing birds

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Eugene

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The Australian Boorabee aircraft have a similar layout, two abreast seating, strut-braced high wing. HBA member @rotax618 designed it, and he has commented on his ultimately successful addition of VGs to address some problems. Any others problems that were avoided or fixed? Any remaining handling characteristics that are just inherent in this configuration? Maybe there are other lessons applicable to the FlyBoy.
I compared horizontal tail from rotax618 to my Skyboy. His tail if I remember correctly about 20% bigger, but his engine is two times smaller and it's sitting below the wing.

Could that simply be that tail size is simply very important for airplanes with this configuration? After all the rocket doesn't need tail at all
 

Eugene

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I think you have found some things to improve and you should finish them out.
Yes, I found some answers to some of my questions. I think. And I will get it done in time and hope result will be big improvement. If not, at least I tried.

As much as I enjoy this process, somewhere deep inside experimental approach to solve all these problems making me a little bit crazy. I religiously believe that for every problem there is solution. I agree that everything is possible but not everything is practical. Sometimes to fix the problem simply not worth it. But recipe for this fix usually very easy to find.

At work I am solving problems every day. I don't talk "experimental" to my customers. If you didn't find a way to fix this problem, you simply don't know what you doing. I always tell my customers and if I don't find the problem and if I don't fix it, they don't have to pay me and I will walk away. Sometimes you're spending whole day looking for something that is right in front of your nose. Some thing you should've checked in the very beginning when you showed up. So, you charging them for only two hours of your time and you walking away.

Are we experimenting with our airplanes because we simply don't know enough? I know that I don't for sure. But to find a rock solid information or a recipe to fix problem is not very easy task from what see. Sometimes you find recommendations like horizontal tail volume. But very few people follow those recommendations. Some engineers will even tell you that all this recommendations are complete nonsense and airplanes like piper J3 and Champ doing very good with horizontal tail volume only 0.33.

But it's OK for experimental airplane if you build it in your garage not to fly well. How is it OK for production certified airplane? That I don't understand
 

WonderousMountain

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Clatsop, Or
So, here's my take on it. Birds carry what might be termed secondary Aero structure. Your wing is very far back on your body. This might be ok if it were shoulder, or lower, but this shows acute angle seperation turbulance & probably als needs the other radius' fairings.

IMG_20210622_171307.jpg

I've drawn the wing modification, dicing away root trailing edge, as some birds do. Also a frontal view
with new drooping strake fairing, towards where door & window panel intersect. A side view of the same is not my best work, and below is a top section. Carry the upper surface of the wing to open venturi form. Quicker flow takes up less broad space.

Stall should start outboard, on the wing past root droop.

Sincerely,
~CK LuPii
 
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Eugene

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Joined
May 26, 2017
Messages
1,560
Location
Merrill, Wisconsin, USA
So, here's my take on it. Birds carry what might be termed secondary Aero structure. Your wing is very far back on your body. This might be ok if it were shoulder, or lower, but this shows acute angle seperation turbulance & probably als needs the other radius' fairings.

View attachment 112237

I've drawn the wing modification, dicing away root trailing edge, as some birds do. Also a frontal view
with new drooping strake fairing, towards where door & window panel intersect. A side view of the same is not my best work, and below is a top section. Carry the upper surface of the wing to open venturi form. Quicker flow takes up less broad space.

Stall should start outboard, on the wing past root droop.

Sincerely,
~CK LuPii
I will need to work with this picture to generate my own sketch. Just to make sure I understood idea correctly. Thank you
 

Orange4sky

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Apr 14, 2020
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This is how I understand it. Please, someone correct me if I’m wrong.

Interference drag does not create nearly as much drag on a high wing AC compared to low wing because the air has a favourable pressure gradient under the wing where the intersection is. On low wing AC, you have the interference AND an adverse pressure gradient which is very conducive to flow separation.

I looked into this and found very few examples of large fillets on high wing aircraft. The exception seeming to be with pusher prop configuration

Having said that, most high wing aircraft have a roughly 90 degree angle at that intersection. I don’t know how much worse your situation is but my guess is it’s probably not as bad as you think.

Kitplanes: Wing Root Junctions

In general, junctions on the upper surface of the wing are more critical than lower-surface junctions. The local airflow is moving faster on the top of the wing than on the bottom. The flow over the upper surface of the wing is much more sensitive to interference that might cause premature separation or stall than the flow over the lower surface.
 
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