A new FPV/AP Scratch Built Airplane: The Nova

This week I'd like to announce the Nova - a scratch built RC airplane with a specific focus on carrying FPV and AP gear. This episode (while a little boring) details the design specifications and functions of the various sections of the airplane. A few key qualities/improvements over the GeekStar:

-Large interior (2.25in x 4.5in x 14in = 141 cubic inches, over 6 times larger than my GeekStar)

-Larger Tail Section (increased control for larger payload)

-Longer Tail Section (increase control authority over payload)

-Larger Control Surfaces

-Ailerons

-Taller fuselage to supper a 8x4 prop

-Reduced angle of incidence (to 3 degrees) of both motor and wing

-Top mounted wing (allow for various wing types/sizes)

-Large area directly under CG point for heavy gear

-Canopy covered with clear plastic to allow a good view for FPV gear while not reducing aerodynamics

-Tons of other small improvements in the build process for a stronger, lighter, higher quality build.

Equipment Used:

Motor: http://www.hobbypartz.com/75m42-optima450-2220-950kv.html

ESC: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=13429

Batt: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6306

Servos: http://www.hobbypartz.com/topromisesg9.html

Prop: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=5437

Estimated Stats:

Weight: 26oz

Thrust: 21oz

Wing Area: 3.33 square feet

Wing Loading: 7.8 oz per sq ft

Will be building over the next 1 - 2 weeks...

I'll be posting these plans on MyGeekShow.com in a few weeks after it's maiden flight (I want to make sure I've got the CG point properly located, etc.).

What do you think? Anything I'm missing?

Angle of incidence is nothing more than a starting point for your trim airspeed. The lift curve slope for something like a clark Y will have positive lift at 0 angle of attack (AOA). At about 3-6 deg you will be generating enough lift based on the lift coefficient cL to lift the airplane. If you set the incidence at 0 deg you would always have to fly nose up to achieve that 3-6 deg. Pre-cocking the wing to that 3 deg puts the plane with enough AOA to fly with the expected flight weight. The tail incidence is based on the same concept. It is usually slightly negative beings you are trying to counteract the nose down moment created by the airfoil. If you get your tail incidence in perfect trim you can reduce the drag a little beings you won't have to use the elevator to trim. It will be in trim (for the nominal trim airspeed) with no elevator deflection.

If you want to get into the nuts and bolts of calculating what they should be I'm sure you can find some quick programs out there to calc it up but yeah that's the whole idea: Pre-set your wing incidence so you don't have to fly nose high and pre-set your tail incidence so your tail is creating just the right amount of moment so you don't have to use elevator.

Good luck!

-Beall

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Comments

Trent at MyGeekShow December 4, 2011 at 5:58am

Jason: Next week's episode will be a build video, not super detailed, but you'll get the general idea... Someday I may make a very detailed (like 5-6 videos) showing step by step, but I want to make sure I've got the design right first... The foam I use is EPS aka bluecor, I get it in 8 x 4 foot sheets from Lowes. EPO has more of a "plastic" and "finished" feel to it, EPS I believe is lighter and more rigid. I've not used EPO a whole lot... but one thing is for sure EPS is CHEAP! (That entire 8x4 sheet is $15). I'm using a rear mounted motor as I've had a lot of trouble in the past with nose motors and them breaking on landings, and yes, a 8 inch prop is about as big as I want to get on it before I go to a new set up... maybe a twin? I will show efficiency on the Nova like I did on the GeekStar...

Alex: I really like the "cartridge" approach... this may be something I'll explore in the future!

Ryan: Thank you for the AOA help... I'm trying to experiment/learn through experience, let me know if I'm headed in the right direction. Thank you for your guidance, I'll try to implement!

Thank you all for your support!
Developer

Ryan Beall December 3, 2011 at 12:05pm

With that in mind, I'd keep my horizontal stab adjustable for the first couple flights and change the incidence until it flew trimmed at your cruise airspeed with a flush elevator. Then lock that stab angle down with some glue and that way you know you are optimized!
Developer

Ryan Beall December 3, 2011 at 12:01pm

Angle of incidence is nothing more than a starting point for your trim airspeed. The lift curve slope for something like a clark Y will have positive lift at 0 angle of attack (AOA). At about 3-6 deg you will be generating enough lift based on the lift coefficient cL to lift the airplane. If you set the incidence at 0 deg you would always have to fly nose up to achieve that 3-6 deg. Pre-cocking the wing to that 3 deg puts the plane with enough AOA to fly with the expected flight weight. The tail incidence is based on the same concept. It is usually slightly negative beings you are trying to counteract the nose down moment created by the airfoil. If you get your tail incidence in perfect trim you can reduce the drag a little beings you won't have to use the elevator to trim. It will be in trim (for the nominal trim airspeed) with no elevator deflection.

If you want to get into the nuts and bolts of calculating what they should be I'm sure you can find some quick programs out there to calc it up but yeah that's the whole idea: Pre-set your wing incidence so you don't have to fly nose high and pre-set your tail incidence so your tail is creating just the right amount of moment so you don't have to use elevator.

Good luck!

-Beall
Alex Lee December 3, 2011 at 11:52am

Trent, instead of designing with a big open space, I was thinking of designing a cartridge like assembly of the autopilot, esc, battery, fpv camera, and receiver. This would essentially be everything on one platform tightly spaced. This way I would simply design my plane around the cartridge. The plane of course would have the motor and servos and the cartridge would simply slide in and hook up. This way you can experiment with all kinds of designs to carry your specific payload.
Jason December 3, 2011 at 9:38am
No design, more flying, boo!!! I'm kidding of course. I am interested in the build videos *with* the flying videos. I do have some questions:
- What is the type of foam you are using and where did you get it?
- How does that foam compare to the EPO that is so common these days in RC?
- Why did you choose a motor mount behind the wing rather than on the nose? You have so much more space to work with in your current design, but you may get to a point that you need a larger prop and you simply don't have that option in this type of design.
- When you are doing your flight testing, please give some information to overall efficiency. My understanding is that a larger prop can turn more slowly to generate the same thrust as a smaller prop and that drag losses are less as a result (drag decreases more than thrust increases, more efficiency).
Thanks for the show,

J

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