Wing Strakes as a viable alternative to a vertical Stablizer?

Temperate

New member
Hello, and thanks for letting me on the forum.

My question is basically the title. I'm building one of those infamous "pizza box" fliers (a square piece of foam with a motor, elevons, and a vertical stabilizer).

One of the issues that led to today's fatal crash was it kept on trying to pitch up and stall. My 2 solutions are: Moving the motor to be more in line with the middle instead of above like high-wing aircraft (they tend to pitch up violently with throttle, making it a mid-wing is probably easier than playing with thrust angles), and shifting CG more forwards (20%). Part of idea for the second solution is downgrading from 4 to 3 channels, by going elevons only and not using a rudder. Strakes that are along the length of the wing will concentrate less mass at the back, thereby shifting the CG forwards.

So are strakes with a large enough area a viable substitute for a vertical tail fin? Is there something I'm missing about the aerodynamics?
 

Piotrsko

Master member
Thrust angles are as simple as adding small washers under the motor mount screws between the motor and the firewall. Strakes on the trailing edge are indeed equal to a rudder, think XB49 and 50 flying wing But not winglets like on a 737max. General starting point for CG is either 25 to 30% from front at max chord. There have been many flat boxy structures that fly decent, @L Edge might be convinced to show some of his.
 

Temperate

New member
Thrust angles are as simple as adding small washers under the motor mount screws between the motor and the firewall. Strakes on the trailing edge are indeed equal to a rudder, think XB49 and 50 flying wing But not winglets like on a 737max. General starting point for CG is either 25 to 30% from front at max chord. There have been many flat boxy structures that fly decent, @L Edge might be convinced to show some of his.
Thanks! That clears it up.
 

Merv

Site Moderator
Staff member
...So are strakes with a large enough area a viable substitute for a vertical tail fin?...
It depends on where they are located. Only the part that is aft of the CG is replacing a vertical stabilizer. The part that is forward of the CG is working against you. If you want make wing strakes more effective, keep them aft of the CG and give them a slight toe in.

My opinion, moving the vertical stabilization forward (tail fin or wing strakes) to adjust the CG is a bad idea. Use something else to adjust the CG.
 
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Piotrsko

Master member
Well actually you place the strakes behind the center of pressure which isn't necessarily at the CG. FULL SCALE designers do move surfaces to make the cg occur at a specific place, as do model designers. Burt Rutan comes to mind with his canard and tandem designs.
 

Thomas B

Member
Well actually you place the strakes behind the center of pressure which isn't necessarily at the CG. FULL SCALE designers do move surfaces to make the cg occur at a specific place, as do model designers. Burt Rutan comes to mind with his canard and tandem designs.

Designers actually move surfaces to make the Center of Pressure occur at a specific place. This in turn drives the CG location. Full scale designers also move equipment around to help the CG, just as we modelers do.
 

L Edge

Master member
Thrust angles are as simple as adding small washers under the motor mount screws between the motor and the firewall. Strakes on the trailing edge are indeed equal to a rudder, think XB49 and 50 flying wing But not winglets like on a 737max. General starting point for CG is either 25 to 30% from front at max chord. There have been many flat boxy structures that fly decent, @L Edge might be convinced to show some of his.

Why I asked for a picture was to see what it looked like. You still need to solve the yaw problem with a flat plate?

One way is to have 2 motors where you use a FC and use differential thrust and elevons to make it work.

 

Robyle3

Active member
Two winglets at the tips should help tremendously with directional control (think of folding down the tips of a paper airplane’s wings), and maybe moving the CG forward with a touch of sweep (no more than 2-5deg) will add again to directional/attitude control

Flying wings generally come in that typical v-shape because it is a very efficient way to adjust both the CG and add natural directional control without adding/removing any weight