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Terminoligy


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Hi, I am a born again modeller. In my younger days I enjoyed the ups and downs of modelling with rubber motors, balsa sticks and dope drenched tissue. Nowadays I play with electric motors and hot-wire cut foamies.  I would appreciate some enlightenment on the following terminoligies: Tip stall.  Ground loop.  What are they? what causes them? How can one avoid them?

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A tip stall is where the tip of the wing stalls before the rest of the wing, often resulting in a spiral/spin. More likely with highly tapered wings. Tendency is reduced by having washout on the wing - a twist where the angle of attack of the wing is less at the tip than the root.

 

A ground loop is where the plane makes a sharp turn on the ground, potentially up to 360 degrees.  Narrow undercarriages are more likely to result in this - e.g. Spitfire, Bf109, Fokker DR1.

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Hi Chris,  In theory, the best wing has infinite length, and goes on forever. Of course even the most ingenious modeller finds it difficult to achieve this, so wings have tips. The wing tips are seldom as wide as the rest of the wing, indeed they are sometimes very narrow. Have a look at the DH comet.        As our aircraft flies slower, the wing becomes less efficient, and eventually will stall, ie stop flying. But it's the narrow inefficient tip that stalls before the wide bit , so the tip drops, often quickly, and wow, it can catch the unwary out, often low down when you turn slowly to land.

 

Ground loops are much simpler, You have just landed, and for some reason, Perhaps a sticky wheel, a stone on the field, or a bit of wind, the model turns around on the ground, sometimes most violently, and spoils your perfect landing

 

ernie

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Interesting thread...  I'd like to ask about something that confuses me:      I often see posts in which the poster claims to have "scratch built" an airframe using plans or even a short kit.    I'm sure that, years ago, a scratch built aircraft was an own design, so, no plans or kit.      Did this change?  

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Words change. A bodger used to be a skilled woodworker. And the language adopted by the LGBT community can have me scratching my head.
I'm surprised having looked about Google, that there seems to be no reference to the term outside modeling and it’s off shoot hobbies. 

Anyone know better. 
Now I will scratch about for something to bodge into something useful, to get a job done. Is that it’s origin? Chickens feeding?

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I wonder if "our" earlier definition was itself a misuse?  The term is supposed to originate from the start line in racing where a competitor took advantage of a handicap to start in front of the scratched line where non-handicapped runners would start. "Starting from scratch"  is generally defined as starting from the beginning and with raw materials.

 

I think that the modern generations accept scratch building as building from plans, whether self drawn or obtained from other sources.  Although I started aeromodelling in the sixties so probably overlap with many of the purists, I refer to any models that I have built from my own plans as "own designs" which almost by definition, I've "scratch built".

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Back on post, PatMc supplied a nice answer. But in the ground loop, no workarounds we’re given.

Cause, wheels close together or ahead of the under carriage. For the brave, get the throttle open, to get the rudder working. Landing ends in a benign ground loop as it happens in the trundle to a halt stage. 
For forward undercarriages, toe in of the wheels helps, as the thing swings, the inside wheel runs straight, the outer wheel drags more, helping to counteract the swing.

And I’ve seen that bloke who used to campaign a dirt big interwar biplane airliner, memory returns DH Rapide, trying to take off, 2 goes into wind, failures with ground loops, and a take off with authority down wind. Don’t know why he did this. Better pilot than me by many miles

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