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Electric Airframes

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Dick Fowler:

Thanks Frank, kind of thought you were looking to reduce drag. You would be better off with a high aspect ratio wing planform. Gliders are a classic example of getting as much lift and as little drag as possible using high aspect ratio wings.

 

frank carlisle:
Thanks Dick,
I hadn't looked at it from that perspective. Kinda changes the picture I have in my head.
What about the overall length? Any reason not to make shorter moments? The lomg tail moment is to generate enough leverage to turn that heavy nose isn't it?
What if I start the design by figuring the battery to be the cg point? The motor to be the nose weight and the tail to get it level.
A guy could start with a wing and empeage then hang them on a stick with the motor up front, the wing centered on the battery, and then slide the tail back and forth to achieve a balance.
The first plane wouldn't need to have a front row finish. It would just be a bench mark. Right?

phil c:
Got any video of the 5 ft. radius turns Ron?

You can build too light.  It takes a certain amount of weight and speed to keep the lines properly tight.  A plane that is too light will lose line tension in tight turns, allowing the lines to flop the plane around.

Reducing the MOI of the plane by moving the batteries back towards the balance point can only help.  But like anything else, you have to balance the change with something else, maybe less control movement.  And with the batteries way back, you have to balance the plane, either by making the nose longer or adding nose weight.  The MOI is very dependent on the nose moment.  It is not hard to increase the MOI by using a lighter motor on a longer nose.  Take a look at Wild Bill's half A designs.  He had a very long nose and it took a 30%+ stab to control it.  If you want to minimize the MOI, mount the motor and battery as close together as possible, and then adjust the nose length for balance.

Dean Pappas:
Hi Frank and All,
You asked ...
"Am I correct in my assumption that a large part of the thick airfoil on clpa planes is to hold back the engine? "
I think that big flaps do that: brakes in the corner. But big flaps add less incremental lift versus drag than skinny flaps. As the electric governors get dialed in and prop diameterss go up, there will be no need for brakes in the corners. Furthermore, as CGs move farther aft, or as polar pitch inertia reduces with a CG that proiduces the same pitch stability, you will see the possibility of tighter corners and acceptable speed loss in those corners.
Yes, it may become easier to build an airplane that easily tolerates being flown too tightly ... but that is a piloting issue. Move the lines together at the handle!

In my opinion, there is no such thing as too light, just to twisty and flimsy. using weight to produce line tension will become an anachronism. Side force generation will permit solid 5.7 second laps. A prediction that you read here first!

later Friends,
    Dean Pappa

Dick Fowler:
"In my opinion, there is no such thing as too light, just to twisty and flimsy. using weight to produce line tension will become an anachronism. Side force generation will permit solid 5.7 second laps. A prediction that you read here first!"

Interesting... use a lifting fuselage (airfoil shape)? Ducted fan? Certainly could use some sort of lift overhead instead of depending on CF. Engine and rudder offset provide this however the Gurus feel that the drag isn't a fair trade. Probably not when you depend on speed to keep it out there.

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