New to airplanes - a how-to question

[Base Glider]

Hi,

I've been flying RC helicopters for a while and got a little curious about airplanes. I've got a couple of ideas for an airplane design. So how do you go about planning a plane? Is there a software that one can use? you know with all the physics and dynamics involved? I'm looking to build something along the lines of a Zagi that's electric and can carry about a pound worth of wireless video and telemetry.

[rtideas]

Download MotoCalc from www.motocalc.com. You'll have 30 days to try it.

You can use the wizard and plug in dimensions and weights and see what motor/battery combo it reccommends and then refine it from there.

Something like 80", 1200 sq/in area, 4-6 lbs. 12 - 18 cells.

Or try FlyingFoam's Mothership (http://www.flyingfoam.com/products.html)

rt

[Ollie]

Begin by getting a copy of the October 2003 Flight Journal magazine, currently on news stands. Read the article by aerodynamist Bernard Wainfan. He describes the technical details of flying wing design in plain english and the difference between flying wing design and convention configuration design.

Design starts with a specific set of objectives. One of which you have already specified, payload. The physics and mathematics will allow you to analyze a specific design but it won't synthesize all the considerations that go into the design. That is why design is partly art. Nature designs its animals and plants by trial and error through a process of survival of the fittest. Aircraft design is analogous except the incremental changes are not random. It is also a process of trial and error except it is guided by human insight which greatly speeds the process. The designer starts with a seed design, analyzes it to see how close it comes to meeting objectives. Then the designer modifies the design, using his insight, to try to improve it. This is followed by testing the performance, with a computer program or by building a prototype, to see how much improvement the change made. So far I have described one iteration. The process is iterated until the designer is satisfied, can't think of any more improvements, time runs out or, the designer is exhausted.

Desk Top Aeronautics provides some of the programs that you might need: See:
http://www.desktopaero.com/
Another useful address for flying wing airfoils and design information is:
http://www.mh-aerotools.de/airfoils/

The essence of design is to find a compromise between conflicting objectives that best meets the over all purpose. "An airplane is a set of compromises flying in formation."

Flying wing design is unique in that any change in the design affects virtually all the design objectives more strongly than for conventional configurations. The flying wing designer must be especially wary of the law of unintended consequences.

My insight is that payload and electric power are very seriously conflicting. To resolve this conflict with a reasonable landing and take off speed will require a much larger and much, much more expensive airframe compared to internal combustion power.

[Ollie]

Here is a list of possible inital specifications (objectives) to consider:
1. Payload
2. Minimum stall speed
3. Takeoff distance
4. Landing distance
5. Maximum rate of climb
6. Minimum power off sinking speed
7. Yaw stability and damping.
8. Pitch stability and damping
9. Maneuverability
10. Control power to recover from unintended attitudes
11. Cost in dollars and effort
12. Top speed in level flight
13. Power duration under various flight conditions.
14. Mass distribution and structural strength.
15. Equipment access for installation and maintenance.

Which of these and other initial objectives you might choose to specify and prioritize will guide your design efforts in the direction you want to go and with the risks you want to assume. It is the prioritazion of objectives that allows rational compromizes between conflicting objectives.

As an example of how one design decision affects many other things: The selection of airfoils affect wing taper ratio, wing twist, wing aspect ratio, lift, drag, spar depth, spar strength, spar depth, spar material, wing torsional loads, wing torsional stiffness (assuming stressed skin structure), wing torsional strength, pitch stability, space for equipment, space for payload, minimum stall speed and top speed.

If you don't want to consider all this complication then you have to accept the associated risks to success that each simplification entails.

[MikeSt]

Someone can correct me, but I think you'll find that a flying wing is actually more complex and harder to design than a "traditional" plane.

Just in case that you thought it would be simpler to design "only" a flying wing, to avoid the complexities of the length of tail / size of rudder / elevators etc.

Mike

[Viper Pilot]

Base,

Check out ModelCAD (http://www.hallogram.com/modelcad/?source=google)

VP

[heli frapper]

Flying wing dont like carring weight very well compared to convention shapes
Do a search on cargo carrying competions where they try to lift heavy loads example 5kg for plane that normally weights 2.5kg and you wont see any wing at least I havnt

Modern electronics telementry today are quite light so a large eneogh wing may work but the lightest types cost more so swings and round abouts


Stephen