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RoofTop Scale testing

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berridos

Well-Known Member
Joined
Oct 10, 2009
Messages
1,164
Location
madrid
While this thread could be understood as an RC model thread it still is the cornerstone of proper research before starting a real sized prototype and testing on the rooftop at the end is massivly cheaper and faster than producing a ton of rc models with tiny modifications.
As i am planning to start the construction of a delta i need to research the effect of several devices regarding lift (specially vortex lift), drag and stall speed as well as precise identification of the neutral point (not an easy task in tailless planes). Only stability is still a matter that can only be tested with rc-models.
I had a sleepless night designing the rooftop structure and can conclude that it is really a one weekend task, maybe two)). This morning i checked the bottom of my car and there is plenty of attachment points to the chassis.
I consider it vital to fly in clean air and therefor the structure would reach from the roof to the front wheels of the car (the front structure would be attached to the bottom chassis of the car).
Ingredients are linear guideways, levered arm-structure to change the aoa, pitot tube the works precisly at lower speeds, gopros to record the measurements all at the same time and 3 scales with remote reading (preferbly cilinders that measure pressure in both directions-never saw that type of scales, but i am sure the chinese have them)
The absolute measurements are not vital as i will compare to a benchmark design (so only relative improvements are critical).
In my case i want to build a 2m span prototype as a reflection of the 4,5m original design. The protoype will have three atttachment points, One at the center of lift and to others to check lift (in front and behind at an equal distance).

The point of this thread would be the discussion of scale effects that have to be taken into consideration.
In case of rcmodels, wingloading could be one of the parameters to match in order to replicate the behaviour of the 1:1 plane. Wing Loading, WCL & Conversion Calculator
But what is relevant on the rooftop?
-If i set the prototype at a certain AOA and drag it horizontally on the rooftop, can i paint a realistic liftcurve by iterating this exercise?
-Do you think that the stall could be identified on the rooftop by a sudden loss of lift at the lever arm on the scales? If for example on the rooftop that sudden loss of lift happens at 50kmh , do i need to scale this speed up to match the stall of the realsized plane?
-Another goal of the test would be to test the location of a belly flap that matches exactly the center of lift and therfor doesnt change the pitch attitude when deployed. That test would happen in free air. However could this location be wrong as in the real world the flap will be blown by the propwash of the tractor engine?
I have a dozen more test in mind.

I wonder if you could contribute other effects that could distort the direct reading of such tests and maybe shed some light on how to handle those effects.
 
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