quote:

ORIGINAL: RaceCity
Stalls have NOTHING to do with CG.

quote:

ORIGINAL: mesae

Seems to me Jimmbbo just re-stated what RaceCity said, while still taking exception to his post for some reason. I did not get the impression RaceCity was suggesting we ignore the CG position. What he said is correct in that as CG moves forward, it becomes "harder" for the elevator to cause the wing to reach the critical AOA, and the critical AOA does not change with CG position, weight, load factor or speed.

What nobody seems to have mentioned is that a tip stall, not just any stall, is an asymmetrical stall, caused by being in a slip or skid at the moment of stall. This can be accomplished by applying excessive or insufficient rudder at the moment of stall. Since it's difficult for an inexperienced model pilot (or any model pilot) to know when their models are exactly coordinated under all conditions, a tip stall can be considered evidence that when the stall occurred, the airplane was not flying in a coordinated fashion, assuming the airplane was built straight. In the above context, "coordinated" means ball centered. In aerobatics, "coordinated" means the airplane is doing what it is supposed to be doing, whether it is slipping, skidding or neither.

One way to test this is to perform power off stalls with the wings exactly level, applying rudder as necessary to prevent the airplane from changing heading up to the stall. Even a small rate of heading change or skid in this case can cause a tip stall with a snappy airplane so this must be done accurately. All but the very snappiest airplanes can be made to stall straight ahead without rolling in this manner. Without active and accurate rudder input, it is unlikely that the airplane will be exactly coordinated during any given stall, due to the many variables involved, not least of which are the turning and rolling tendencies generated by a propeller, and the vertical stab and/or rudder offsets applied at "neutral" to compensate for these in "cruising" or normal flight.

Stalls are generally easier to accomplish, and tend to progress farther before recovery, with an aft CG position. If one wing stalls before the other, the "ball" was off center at the moment of stall (for any number of possible reasons). Put another way, the resultant lift vector was not perpendicular to the wingspan, again assuming the airplane was built straight and true.

Also, I fly my models based on attitude and power setting (same way I fly full-scale), not 'apparent airspeed', by which I assume Jimmbbo means groundspeed (please correct me if I'm wrong here) since we have no immediate way of knowing airspeed without telemetry. Using only groundspeed to estimate airspeed is dangerous. I have seen model pilots get into trouble many times by using groundspeed instead of attitude. I have seen this most often in the case of a downwind deadstick landing. The pilot thinks the airplane is going too fast because of its high groundspeed, and continues to raise the nose, causing a stall. Another common trouble spot is at fields where it is usually windy (like in Hawaii, Texas and Oklahoma). On calm days, pilots sometimes (perhaps subconsciously) attempt to slow the airplane to near the same groundspeed they see on a windy day and accidentally stall or develop a high sink rate and land hard. This type of accident can be prevented by knowing and using appropriate attitudes and power settings for landing approaches. The same attitudes and power settings for a given model, with small adjustments, will work for all wind conditions and density altitudes, without regard to groundspeed.

quote:

ORIGINAL: dick Hanson

Frankly -I don't like that FAA "advisory--Especially the "it will often" phrase .
To be quite blunt - I find thru experience -on models - that forward CG is more desireable and prevents unwanted , loss of control stalls .
The more forward the cg - the greater the "balancing load " at the tail required
That load ,to me was ,is and will remain ; INDUCED DRAG
In order to hold wing at constant AOA whilst increasing this drag (moving CG forward ) , the speed has to increase. Obviously
So tho the wing will oerate at a higher AOA for a given airspeed -- the wing loading (true loading not induced load) remains the same------------- the actual stall will be more predictable and actually easier to manage due to the high elevator inputs required to get there. On the aft CG- it is far easier to accidently induce the excessive AOA There - I just wasted 5 minutes .
and edited the darn thing 5 times

quote:

ORIGINAL: Jimmbbo
...WADR, my response was narrowly aimed at the comment that "Stalls have NOTHING to do with CG" which is incorrect. My comments addressed that point, and I believe them correct within the context of that remark. Since there are a number of new pilots on this site, I think it important to address statements that I believe incorrect, so as to minimize confusion or misunderstanding among folks who are trying to learn the fine points of the hobby.

With regard to flying attitude or airspeed, I should have added that attitude works great if you have a good view of the model close up, but when the model is farther away, the speed of the model is the only guide available, considering current winds, that gives control of the margin above a stall..

Cheers!

Jim