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fuselage/wing root shape


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I'm wondering about the right shape to give to the fuselage/wing junction to minimize drag.

a general concept says that the fuselage portion that crosses the wing should be straight but this would not be very easy to do in our planes unless we want to have a very large tail.

some very good planes have absolutely no radius between wing and fuselage, other planes have large radius that are really nice to see but what about their effectiveness?

gliders usually have radiused wing/fuselage transitions and this should mean something, but our plans say nothing about this area.

Rutan's CAFE champion catbird had no radius at all.

the only radius plans talk about as an optional feature is the transition between canard TE and fuselage but no special instruction are given.

in this point the radius should go backward and upward but how much?

I have seen upwards radiused TE transition too but I think this is a mistake.

can you give me some good info??

Roads? Where we're going we don't need roads. (Dr. Emmett Brown)

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What you are looking for is a how-to on fillet.

You can start with these.

JD at Infinity Aerospace sent me this information on the subject when I was just gettin started on my project:


¥ HE SAID: The Fillet Radius should be at least 1" until reaching the thickest portion of the airfoil (unless the airfoil shape drastically dictates otherwise) at which time the Fillet Radius Calculations I found come into play. The problem with these equations that I found is that they are just general guidelines, but most definitely are better than not having any guidance to make Fillets at the aircraft junctures at all. The only way to properly determine your aircraft Fillet needs is with an aerodynamic program., tufting and a lot of trial and error.

¥ I FOUND: 2 equations from 2 different aerodynamic books (see enclosed and/or attached). From one book – "Typically a wing fillet has a radius of about 10% of the root-chord length . . .”; & From another book – . . . “divide the airfoil chord length into 3 sections (I assume they are equal in length). At point one (1) multiply the chord length from the leading edge times a range of 0.05 to 0.10 to find the Fillet Radius at that point. Point two (2) has no equation. Point three (3) multiply the chord length from the leading edge times a range of 0.10 to 0.20 to find the Fillet Radius at that point. Both these ranges to multiply the chord lengths at their appropriate points to find the Fillet Radius at that point fall within the 10% guidelines from the other book.

¥ HE ALSO SAID: to make your Fillet Radius's (you determine from the equations mentioned above) blend together so as to be parallel to the center line of the aircraft and horizontal to the chord.

¥ I CAN NOT FIND: Anything that gives guidance to how to complete the blend from the trailing edge aft to create and form the perfect "bite". Nor the “bite” at the leading edge of the wing and canard. Tufting and video taping the flight testing to watch the air flow at cruise is the only way I know of at this time to determine the best leading and trailing edge “bite”.

Plus these attachments:





T Mann - Loooong-EZ/20B Infinity R/G Chpts 18

Velocity/RG N951TM

Mann's Airplane Factory

We add rocket's to everything!

4, 5, 6, 7, 8. 9, 10, 14, 19, 20 Done

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wow, thank you!


I blended the wing root into the fuselage with a radius of 3,75", it's nice to see, but following the 10% rule the radius should be more or less twice, that means that it should involve the canopy in the upper part of the wing.

I wonder if this radiused junction is a good thing for flow separation or creates especially on the leading edge a lateral airflow running spanwise messing up the adiacent airflow: this is why I'm undecided on blending the wing root/fuselage intersection.

the strake is not an airfoil so there would be no lift loss but I'm afraid that the airflow separation could be worse.

Roads? Where we're going we don't need roads. (Dr. Emmett Brown)

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