Wing loading. more complex than weight/area?

[MotoMike]

Hi

Once again the intricacies of flight seem to be escaping me.

I have taken up model flying as I think I mentioned in my "Lift- more complex than Bernoulli?" thread. So far I have been flying models with wingspans in the 60 to 70 inch range. When choosing airplanes, I noticed that in planes of this size wing loadings of 18 to 23oz per square foot were more manageable than those with higher wing loadings. That I could land them slower giving me more time to react.

I recently read an article about a large model with 110 inch wingspan and wing loading of 60oz per square foot. My initial thought was that the airplane would be unflyable for all but the most experienced pilots, if at all. Of course it is for a more advanced pilot, but clearly many of them are out there being flown every day. The author made mention that on a smaller plane this wing loading would be a problem, but with the size of his plane it was nothing to be concerned about.

Of course this has led me to discuss it with other pilots who are ill prepared to describe why it is different. One told me that it had to do with Wing Cube Loading, but could not really explain what it was and how I could estimate if a plane will "fly light" or "fly heavy"

Any discussion on this topic would be appreciated.

Kind regards,
Mike

 

[rcgldr]

The wing loading gives you somewhat of an idea of the required speed for landing and take off and normal flight. Note that lift and drag for a given angle of attack increase relative to speed², so doubling the wing loading correlates to an increase of speed of sqrt(2) ~= 1.4142. There's also a scale factor for velocity (link to article about this below).

For example, the landing speed of a full scale Cessna 182 is about 70 to 75 mph = 112 kph to 120 kph, with a wing loading of 285 oz / ft². So a scale Cessna 182 with 20 oz / ft² wing loading would land at about 70 (20/285)² ~= 18.5 mph. For very small models, Reynold number will have some effect (mentioned in the article linked to below).

The "cubic" factor is probably a reference to scale. Volume is related to length x width x height, so a 1/4 scale model should weigh (1/4)³ as much as the full size model if density were to remain the same. There's also the issue of getting a model to fly at "scale speed". Link to an article:

scale_speed.htm

 

[CWatters]

Rather an old book but perhaps worth a read.

http://www.amazon.com/dp/1854861905/?tag=pfamazon01-20

 

[MotoMike]

Thanks for the quick responses. It appears I might be biting off more than I can chew.

regards,
Mike

 

[MotoMike]

CWaters
thanks for the recommendation. found one and have it ordered.

Mike