Designing a UAV: Airfoil Selection Criteria

[kevjcarvalho]

hi,
i am a mechanical engineer currently working on the design of a UAV. Our rough sketch kind of resembles Burt Rutan's Long-EZ or Velocity. I am attaching a couple of sketches of the aircraft which my team and i have constructed using XFLR 5. We will also be using XFLR 5 and Profili for initial analysis. What kind of criteria would you suggest for airfoil selection? For example high or low Cm, what range perhaps, what Cl/Cd range. Thanks

 

[Cyrus]

"The best place for a canard is on someone else's airplane"

 

[dtango]

hi,
What kind of criteria would you suggest for airfoil selection? For example high or low Cm, what range perhaps, what Cl/Cd range. Thanks

Hmmm, it kind of depends on what the mission of the UAV will be - e.g. high altitude, slow speed surveillance, fast-n-nimble, how heavy is it going to be, etc. etc.

 

[mugaliens]

"The best place for a canard is on someone else's airplane"

Yeah, right...

Hey, talk to http://www.aopa.org/aircraft/articles/2008/081230100mpg.html?WT.mc_id=090102epilot&WT.mc_sect=gan"! Klaus Savier has managed to eke out 100 mpg from Rutan's Vari-EZ.

Rutan's design was phenomenal at the time, and it remains exceptional in many ways, particularly when one throttles back and uses a powerplant which is designed for max efficiency at that throttled-back cruise.

Consider:

Cessna 172 (4-seater) cruises at 122 kts with a mean gph burn rate around 8 gph at 122 kts (it's unpublished, as Cessna loves to fudge their figures) of for a milage rate of around 15 nm/gal.

Vari-EZ and Long-EZ (2-seater) cruises at 160 kts with a mean gph 5.1 gph burn rate for a milage of 31.4 nm/gal

There is a reason XCOR Aerospace chose to modify the Long-EZ for their EZ-rocket proof of concept racer. It's one heck of an aircraft!

Back to Canards, they settled on a http://en.wikipedia.org/wiki/Velocity_SE" as their entry into the Rocket Racer class.

I'm not sure why, given the nearly double fuel efficiencies of the Vari-EZ and Long-EZ. If it's a matter of velocity (hence the "racer" aspect), why not just go with the Berkut? It's cruise speed is 200 kts, and it does it with greater efficiency than any of the aforementioned aircraft.

To this day, if I ever entered this market, I'd opt for a Berkut!

This design was SO promising the countering lawyers' multiple counter-lawsuits strangled the entire effort by 2003. Only 20 aircraft were completed.

I flew one - AWESOME! But I've also flown a Lancair and a Glassair, also both awesome, and with respect to the avionics, much more nicely done. :)

 

[alphy]

Hello,

I would suggest considering the following criteria for airfoil selection in your UAV design:

1. Aerodynamic performance: The primary objective of an airfoil is to produce lift and minimize drag. Therefore, it is important to select an airfoil with a high lift coefficient (Cl) and a low drag coefficient (Cd). This can be achieved by choosing an airfoil with a well-defined lift curve slope (Cl/alpha) and a low drag polar.

2. Stability and control: The airfoil's pitching moment (Cm) plays a crucial role in the stability and control of the aircraft. It is important to select an airfoil with a stable pitching moment curve to ensure the aircraft's stability in flight.

3. Reynolds number: The Reynolds number of the airfoil, which is a function of airspeed and airfoil chord length, affects its aerodynamic performance. It is important to select an airfoil with a suitable Reynolds number range for the intended flight conditions of the UAV.

4. Stall characteristics: The airfoil's stall behavior should also be considered, as it can greatly affect the aircraft's handling and performance. A gradual and predictable stall behavior is desired for a stable and controllable aircraft.

5. Structural considerations: The airfoil's structural characteristics, such as thickness and camber, should also be taken into account to ensure its compatibility with the overall design and structural requirements of the UAV.

Overall, it is important to choose an airfoil that balances all these criteria to achieve optimal performance and stability for your UAV design. I would also recommend conducting thorough aerodynamic analysis and testing using tools like XFLR 5 and Profili to evaluate and compare different airfoil options before finalizing your selection.

Best of luck with your UAV design project!