Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by BBerson, Nov 20, 2016.
Imagine this upside down. It sounds like what you were thinking about
I don't think it was mentioned, but yes the low wing offers advantages for undercarriage arrangements.
The Dehavilland DH53 picked low wing because it allows short wingtip hoops that drag on rough fields. (Instead of wide heavy gear)
Does anyone know why or what these enormous wing root fairings are called on modern low wing jets such as this: https://www.hondajet.com/#2
I am thinking this big tub fairing is several inches below the wing to make the wing think it is actually in a more favorable mid-wing like attached flow?
These fairings keep getting larger. This Citation X has a root fairing from the cockpit to the tail:https://en.m.wikipedia.org/wiki/Ces...50-0175_Citation_X_(7039507775)_(cropped).jpg
Apparently, the large underwing fairing on the Citation X (and others) is called a "belly fairing" in the trade. According to this discussion:https://aviation.stackexchange.com/...ection-of-the-fuselage-below-the-wings-called.
I might experiment with this.
There are a bunch of compromises that end up in the design of these fairings. First they don't want the spar through the cabin for standing height. Second the pressure vessel is relatively round so you have to something to blend the very low wing into a relatively round fuselage and above the wing that means trying to get sides of the fuselage vertical. This is for drag reduction for fuel economy. The rest in front and behind is shaped for both critical cruise speed at altitude flows and for low speed separation. Tricky stuff. The wing is also drastically swept and odd airfoils are blended at the root plus there is almost always some sort of change in taper and incidence inboard to keep the root from having a turbulent transition. At high speeds these airplanes are being pushed up near the compressibility limit so the shaping is also dealing with warding off Mach issues. And all that in one piece of fiberglass normally. Fortunately these companies have been at this for a while and they get a bunch of both CFD and wind tunnel time. CFD is getting better and faster.
For GA the speeds are lower other than that still the same task. Staring at these jet fairings tells you a lot about how to approach the design task.
"Does anyone know why or what these enormous wing root fairings are called on modern low wing jets"
Why - If I remember correctly, I read that the least drag configuration between a wing and an adjoining surface is either a 90 degree angle or a zero degree angle. Basically, they are building that area up with a large "fairing" to get as much of the fuselage to be as close as possible to a 90 degree angle to the wing or flush with it. Less drag, less burn and more speed.
What - not sure if there is a specific name for them.
I definately see the need for the 90° intersection upper fairing.
Not sure what the belly fairing extending below the wing does.
The prescott pusher is one the the sexiest designs ever that meet your requirements. Love this plane.
Actually, if you look closely at the Citation X, the bottom of the belly fairing is flat, or nearly flat, across the entire bottom. Then, there is a smooth radius curve that squares off the fuselage and brings it to 90 deg to the lower wing skin. There is a small 90 deg joint between the fuselage and the lower wing almost the entire length of the lower wing skin.
As someone already mentioned, this is also done to provide a way to cover up the wing spar after it has been pushed way down below the fuselage. These builders are trying to provide as much "stand up" cabin space as possible. It keeps from having to step over the wing spar while walking in the cabin. These large belly fairings help to "cover up" the wing spar and direct the slip stream with the least drag.
That's what I meant. Instead of the seemingly ideal, smooth flat bottom, they put a radiused curve pan under the belly. Same on HondaJet.
So a Taylor Coot, then?
I mentioned the Coot in post 1 of this thread here https://www.homebuiltairplanes.com/forums/threads/low-wing-pusher-configuration.26412/ but had forgotten about it. Last week I examined the Coot again in detail. Looks like Molt has laid the groundwork for my ideas. I am designing a single seat Coot, more or less. The only concern is prop proximity to wing effects.
Separate names with a comma.