Interference drag on high wing birds

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Eugene

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When I'm looking at my airplane with no landing gear and no struts it's pretty obvious to me that for interference drag reduction I really should flip fuselage upside down. This way based on what I'm reading in Hoerner will be best to have it wide on top and narrow at the bottom.

But on another hand someone said to me that God didn't design low wing birds!!! So, he didn't know what he was doing in aeronautical department? All birds naturally do have same problem as my airplane with fuselage/wing intersection drag?

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Vigilant1

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But on another hand someone said to me that God didn't design low wing birds!!! So, he didn't know what he was doing in aeronautical department?
Well, what we can learn from nature does have its limits. All birds use muscles to fly, and they can only do work in tension (pull), not compression. Their flight muscles are on their chests, and they connect to the wing’s "shoulder." This provides a relatively long working stroke for the muscles. There's no simple, compact way to power the wings on the downstroke (in tension) if they placed on the bird's ventral side as a ”low wing." Also, having the wings on the back provides a handy place for them to fold up out of the way when not in use.
I think the biological and packaging constraints predominated over any minor aeronautical advantages a low wing might have offered.
 
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wsimpso1

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Most high wing airplanes do not narrow the fuselage at the top. There are several reasons for this:
  • Most of us are wider at the shoulders than at the waist and hips;
  • Most of us like room around our heads so we can look down, see around the nose, etc;
  • And of course, give vertical walled straight sections through the wing.
Since the Skyboy fuselage is already built, you are stuck with it. I suspect that the designer was trying to help air flow into the prop, but it does result in messing with the air around the wings. Compromises...

I suspect that you can add significant fillets around the roots of the wing below as well as around the cowling above, and that will help clean up the wing airflow and reduce drag. Getting the air to fill in behind the cockpit to go through the prop will no doubt require some calcs of boundary layer thickness and then some tuning of VG and/or turning vanes on the surfaces behind the cockpit.

Billski
 

BJC

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Eugene:

Have you looked at the suitability of the wing structure for higher airspeeds? What are the design’s Vd, Vne, and Va? What are the limiting factors? What Vh are you hoping to achieve?


BJC
 

Eugene

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Eugene:

Have you looked at the suitability of the wing structure for higher airspeeds? What are the design’s Vd, Vne, and Va? What are the limiting factors? What Vh are you hoping to achieve?


BJC
This is not the race for speed. I said it many times and I will say it again. I am trying to create pleasant to fly machine.

to improve drug will have effect in every department. Maybe glide ratio could be improved from 7 :1 to 9 :1 or so.

airplane by design has maximum cruising speed of 103 MPH. Never exceed speed of 128 MPH. I am not planning to fly faster than 100 MPH.
 

mcrae0104

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It seems that an expanding-radius fillet would help here, although it would require an afterbody that goes right through the prop disc...

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Vigilant1

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It seems that an expanding-radius fillet would help here, although it would require an afterbody that goes right through the prop disc...

View attachment 112139
That picture really shows the magnitude of the issue.

Easy and maybe "better enough" for a start: VGs, and maybe big ones, on the wing bottom surface and the fuselage sides. Make them of something that won't destroy the prop in case of detachment, and be prepared to experiment a lot. They might need to start fairly well forward, too (where the flow is still relatively straight and smooth)
 

Eugene

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VGs do offer visual picture improvement. But I wanted to say that in all my experiments with a small vortex generators or big ones, I was getting feel that I am against something bigger, something I don't understand, some kind of aerodynamic wall. Because it was really no improvement of how airplane was flying. Speed wise or handling wise. And of course I didn't know what I was doing at the time (I steel don't) and I am willing to do it again when I start flying someday.

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REVAN

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When I'm looking at my airplane with no landing gear and no struts it's pretty obvious to me that for interference drag reduction I really should flip fuselage upside down. This way based on what I'm reading in Hoerner will be best to have it wide on top and narrow at the bottom.

But on another hand someone said to me that God didn't design low wing birds!!! So, he didn't know what he was doing in aeronautical department? All birds naturally do have same problem as my airplane with fuselage/wing intersection drag?
High wing designs can achieve lower drag than low wing designs. However, the actual results will depend on many details that go well beyond this basic categorization of wing placement. More important than the size and radius of the wing fillet is the lift and drag distributions at the wing and body interface. Then the fillet comes in second to that. Since most designers largely ignore the first order drag influences in favor of making a simple to construct Hershey bar wing with a fuselage hanging off of it, the second order influences generally don't warrant, or get, a lot of attention either.
 

Vigilant1

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That's one way to do it. There's probably a lot of low pressure at the aft end of that cowling. Good for engine cooling, but carries a drag penalty. Maybe that penalty is less than the current situation you have now though.
 
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TFF

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I will tell you my old boss has flown a Seaker as a potential buyer. His opinion was the worst plane he has ever flown. An opinion for sure, but he does have 30,000 hours in aircraft with less than 350 hp. No airline flying, just GA types.
 

Eugene

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I will tell you my old boss has flown a Seaker as a potential buyer. His opinion was the worst plane he has ever flown. An opinion for sure, but he does have 30,000 hours in aircraft with less than 350 hp. No airline flying, just GA types.

I was thinking about this statement for a few hours and here is my philosophical respond/question -

I talked to Peter Garrison about this. Turns out he has flown Seabird Seeker at one point as well. He was telling me that he didn't see anything wrong with this aircraft.

How is it possible anyway to design and set up production for bad flying airplane???

If I purposely would try to design bad washing machine and start production. It would be impossible to do and impossible to sell. I would have so many people on my team who would try to steer me in the correct direction. They did go to school for this. I didn't go to school for this. We all want this project to succeed and make big money. You need to ignore so many things and spend so much money for this terrible washing machine. And after all nobody will buy this one, because there is so many different ones available with a much better performance!

I was under the impression that this is why we have Aircraft certification in place. If Aircraft is unsafe they're not gonna give you OK.

Story about my airplane is somewhat unique. We know exactly what happened today.

This Seeker they designed for specific purpose from ground up. Unbelievable amount of money was spend in the process. They didn't like few things in the beginning and they change them. I would assume that if they didn't like anything else they would change them as well. From what I have learned in the last few years that if you follow basic rules you should end up with pretty good flying machine. I refuse to believe that there is aeronautical engineers out there who doesn't know those basic rules. Even if they don't know something, professional test pilots will tell them what they think.

Just like in every day life almost impossible to build bad house. You simply not going to be able to pass inspection.

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TFF

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The people who brought it to the US would like to get a government contract that specifies its specifications, and since it would be the only thing with the specs, guaranteed a win for millions.

We were interested in the aircraft for infrastructure inspection to aid our helicopters. We thought we found the golden ticket. It was directionally unstable, takeoff distance was way unacceptable, no way to demist the windscreen much less have heat. Speed range was terrible. General handling just plane bad. He test flew a Carbon Cub that flew circles around it. At low level altitude for what that plane is designed for, pilot has to spend too much time wrestling the plane to ever take advantage of looking out the window.
We ended not pursuing airplane contracts and stuck with helicopters. Our problem was was market saturation of airplanes doing that task. If the AirCam was certified, we would have put it to work because it flys fine. We have plenty of fun flying one. My pick would have been the American Champion Denali.
 

Eugene

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It was directionally unstable, takeoff distance was way unacceptable, no way to demist the windscreen much less have heat. Speed range was terrible. General handling just plane bad. At low level altitude for what that plane is designed for, pilot has to spend too much time wrestling the plane to ever take advantage of looking out the window.
Thank you, thank you, thank you!

This description fits perfectly into my Skyboy! I will copy and forward this description to all my negative "supporters". I will send it to those guys who keep telling me to stop doing what I'm doing and start flying and enjoying life. Constantly wrestling the plane is not an enjoyment.

I'm sure we have smart people here who can give us pretty good explanation of why that airplane is behaving this way.

What I don't understand, is if it's not good flying aircraft, why keep moving forward? Why not improve situation in the beginning?
 

Vigilant1

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We were interested in the aircraft for infrastructure inspection to aid our helicopters. We thought we found the golden ticket. It was directionally unstable, takeoff distance was way unacceptable, no way to demist the windscreen much less have heat. Speed range was terrible. General handling just plane bad.
Thank you, thank you, thank you!

This description fits perfectly into my Skyboy!
So, two pod-and-boom pushers that don't fly well. Is there something about the configuration that makes it challenging to design one that flies well? We suspect flexibility in tailboom and/or burble off the pod (and into the prop).
Are there some planes of this layout that are known to fly and handle well? Anything to be learned from them? I haven't heard similar complaints about the Janowski series of aircraft (but, they have a much thinner pod--perhaps that is a clue). Anything to be learned from the pusher Kolbs?
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.
 
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TFF

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I hate to call it negative supporter. I think I’m in the camp of be happy you got something. Each airplane has its own identity; they are what they are. As an owner, you need to match the identity of the plane. You are always on a date trying to be convinced to get married. That is the relationship.

The Seekers biggest flaw, it costs a half a million dollars. There are airplanes that are considered handfuls and are beloved. There is always a point of just too much mess. You are not getting the rich party girl unless you are the rich party boy.

I think you have found some things to improve and you should finish them out. Tackling every flaw that is a part of its identity is impossible. People in the front, engine in the back has an identity just as engine in the front, people in the back. You may minimize the differences, but you can’t get rid of the differences. No matter how much plastic surgery you have on your face, it’s still your face.
 

TFF

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The rear facing plane I know is the AirCam. I know how it flys, so when my boss and I discussed the Seeker, I did have that frame of reference that we both understood.

The AirCam has the engines outboard of the fuselage. There is a lot less blockage to the props. Not as good as props facing forward. An AirCam will takeoff on one engine in about 100 ft more than two. When you drop the flaps , you can hear and feel the props cavitate.

Tandem seating with the AirCam is less of a CG shift. You have to have someone in the nose at the front to get the CG flyable. Second and third are barely in front and barely in back of the CG. It has more of the characteristics of a standard side by side plane like a Cessna 150, where tandem like a RV8 will have CG weight characteristics of side by side in front of the CG.

The problems with the AirCam is landing gear is not bush plane tough. If you are not tippy toe landing, you will wipe the gear out in time. The one I know has twice. The fuselage is weak at aft cabane struts. If it was landed like a bush plane a bunch , bet there would be issues. The controls are powerful but sloppy. It’s no precision aerobatic machine; probably smart. The heater instructions state, Fly heading of 180 deg until desired temperature is reached. Full face helmet and winter coat it’s tolerable at 32F for thirty minutes. It’s not a looker. There are smaller issues on the one I know, but most are builder issues.
 
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