I was one day looking for information about Rutan's Grizzly, a three surface STOL bush plane which doesn't look at all like the Piper Cub. Today, I found a related patent, how Burt Rutan managed to implement fowler flaps without external supports which create drag on cruise.
You can read it here: http://www.freepatentsonline.com/4614320.html?query=PN%2F4614320+OR+4614320&stemming=on
4 comments:
Wikipedia tells that the plane was scrapped after testing.
"Grizzly: Rutan designed the model 72 Grizzly to investigate the possibility of a STOL canard aircraft. It was retired after testing."
Must be that when you fly slow using all the wing, you also need all the elevator there is to keep it so. But if you don't have any elevator, what do you do? Maybe it requires too much canard and finally stalls very badly?!?! Falling down backwards so that it flies finally as nature ment?? :)
First of all, Grizzly was not a canard aircraft. Secondly, it was donated to museum after testing because Rutan figured out that a bush plane needs to be high wing to wings clear the bushes. Your thinking is not correct on this. Most of Burt Rutan's aircraft have been donated to museum after testing, and that may be because of the experimental category limitations they belong to - they are not necessarily experimental amateur built (as they have been built by a commercial company for research and development of new products). They may not be all that useful after testing, FAA may have some restrictions of their use.
Grizzly was a three surface aircraft, it had canard, main wing and tail. The usual canard problem of main wing overcoming the canard when its lift is increases (if the canard's lift can not be increased accordingly) do not apply. Three surface is the most efficient design when it comes to Clmax.
By the way, canard aircraft does not fall down (=deep stall) when the canard stalls, only when the main wing stalls. No matter how badly the canard stalls, what you are describing can never happen. Canard aircraft is stall proof when designed correctly, meaning that the canard always stalls first and the main wing is let never to stall.
Three surface design is like conventional, but it has canard in the front which reduces trim drag and functions as pitch trim.
I personally think that there would have been plenty of use for planes like Grizzly, but back that time it seems that Burt Rutan was fixated to Alaska bush flying and that a STOL plane has to be fully bush-capable. There are couple of European designs which are not bush capable, but which are STOL, for example Dynaero MCR01-ULC, and these have plenty of use in Finland on grass fields etc.
Falls backwards uncontrolled... that is exactly what it must do when all wings stall. Why?
Since at that point the plane is controlled only by the flat plate drag and if I look the Grizzly I see that is has very much wing surface at the front of the plane.
Now, why we have delta wings? Why is delta wing so superior? Simply because if the whole wing stalls it has the tendency to put the nose down. If you have reverse delta wing (or more win in the front), it will always put your back down first and stall backwards.
Check this video for example:
http://www.youtube.com/watch?v=r-RZ2Cn5ESs
>Since at that point the plane is >controlled only by the flat plate >drag and if I look the Grizzly I >see that is has very much wing >surface at the front of the plane.
That never happens because in any aircraft, the tail never can be allowed to stall. And it never stalls. Stalling tail in any aircraft results in flat spin or deep stall, and see, the tails don't stall. Grizzly is tuned so that the tail never stalls, and the forward wing always stalls first. Pretty simple as that. The size of the surfaces don't matter when the their relative lift distribution and the CG is in balance.
And your reasoning about Grizzly is wrong. If it stalls, the nose comes down first. The heaviest weight is located in the nose, and even in free fall, the nose will come down, the drag from the front wing is not big enough to resist that.
Delta wing by the way is not superior. It is inferior in subsonic flight. Delta wing has lots of cross-flow which hampers laminar flow. Delta has very little, if any, use in subsonic flight. Subsonic delta wing aircraft is possible, but not efficient.
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