Mythbusters
 

Over in the gas engine forum they started a thread about engine myths. I thought it would be fun to do the same here about aerodynamic myths. I will kick it off with a couple.


1. A nose heavy airplane is more stable and easier to fly.

2. A heavy airplane flys better in the wind.


Add some or debate whats here.....................

RE: Mythbusters
 

Technically both are true... but the minute you add in phrases like "easier to fly" and "flies better" it becomes a matter of personal perspective. And it also depends what the task in hand is.

1.) Adding noseweight (or more correctly: moving the CG forward) increases the Static Stability Margin. The model will become more stable in pitch. That means it will 'hug' a certain airspeed. But it may well make it 'harder to fly', causing what is sometimes called ballooning, a nose up pitch response to increased airspeed. It's a matter of perspective. It also increases tail loads and trim drag, which could even mean the tail stalling in extreme cases. There is a sweet spot between not enough stability and excessive stability.

2.) A heavier aeroplane (technically: a higher wingloading) makes 'penetration' easier and reduces disturbances due to gusts. It's not just about wing loading though - the airfoil (particularly camber) is also a factor. Whether or not it 'flies better' depends on the task you want to achieve. It may make landing faster than is comfortable...

RE: Mythbusters
 

Jolly good thread, here's a couple more.....

3. There is no skyhook that you can hook a plane onto tokeep it in the air..

4. A plane flying straight and level, but do so with a "tail down" attitude is tail heavy...

5. Square, flat wing tips (such is found on most aerobatic planes ) are more aerodynamically efficent than ronded ones (such as on a Piper cub)..... or vice versa...

6. Flat tail feathers (i.e. sheet balsa) is not as good as a tailplane with a shaped (ribbed) profile....

7. Barn door ailerons are more efficient than strip ailerons....

8. Large elevators with little movement is better than small (thin) elevators with large movement...

That ought to throw a cat amongst the pigeons... http://www.rcuniverse.com/forum/js/f...wink_smile.gif

Cheers

Bundu</p>

RE: Mythbusters
 

:D EXCEPT FOR SKY HOOK ,I LIKE THEM,, MOST ARE TRUE.

RE: Mythbusters
 

9. Some planes are always too hot to land.

10. Flutter cannot be avoided, it will destroy your plane sooner or later.

11. Midair collisions happen easily.

RE: Mythbusters
 

Good job guys, keep them coming!


Yak, I think you nailed #1 but #2 is a little more difficult. Yes more mass needs more outside influence to be disturbed, that we can all agree but what I think we see is something different. Most of what the airplane see's is airspeed. So when it encounters wind it really is a matter of a change in airspeed. If the airplane is not trimmed optimal then it react to the change in airspeed whether it be an increase or decrease.

RE: Mythbusters
 

With enough thrust , airfoils are meaningless

RE: Mythbusters
 

Nothing like shooting 10-15mph gust crosswind landings with a nose heavy 40 size trainer.

RE: Mythbusters
 

With enough thrust, and enough gas, airfoils are meaningless

RE: Mythbusters
 

Cows have plenty of gas - but they can't fly

RE: Mythbusters
 

HEY! As I recall there was some bright wig that patented a scheme for using bags attached to the hind quarters of farm animals to collect the gasses while bypassing the solids. The aim being to harvest the noxious fumes to use as "natural" gas for fuel.

Of course this begs the question of what happens if some dullard farm hand attaches the cow size bags to sheep. Is the methane or any other gases lighter than air? Will be be inconvenienced by flocks of floating sheep during our relaxing drives in the country to reach our flying fields?

As for #2 about heavy planes..... There's no doubt that a heavier model will react to velocity changes due to turbulent conditions with less effect than a lighter model. But being heavy brings its own price in terms of good flyability. On the other hand a truly light model is only at its best in calm to light tubulence.

Note that I said "turbulence" instead of "wind". If the wind is smooth and steady overly light or overly heavy models will still work just fine. It's when thing in the sky turn to conditions such as found in washing machines that having a slightly heavier model can become a good thing.

RE: Mythbusters
 

3. There is no skyhook that you can hook a plane onto to keep it in the air..

If only.... :D

4. A plane flying straight and level, but do so with a ''tail down'' attitude is tail heavy...

Simply false. If a model looks like that then it's simply a poor wing to fuselage incidence angle setup in the design.

5. Square, flat wing tips (such is found on most aerobatic planes ) are more aerodynamically efficent than ronded ones (such as on a Piper cub)..... or vice versa...

Haven't heard that one before.

6. Flat tail feathers (i.e. sheet balsa) is not as good as a tailplane with a shaped (ribbed) profile....

True actually. But they work well enough that the designs with them work fine.

7. Barn door ailerons are more efficient than strip ailerons....

True again. Barn door ailerons put more area out where it does more good. And since they are generally a wider percentage of the chord compared to strip ailerons they affect the camber and angle of attack of the portion of the wing where they live. With strip ailerons the inner 1/3 to 1/2 is just a connector piece to join the center area mounted torque rods to the outer half to two thirds of the aileron that actually does anything worth mentioning.

8. Large elevators with little movement is better than small (thin) elevators with large movement...

Not in my experience. I've found that they are equal.

RE: Mythbusters
 

The one I see a lot is "more power up front is always better." That one is usually given to new or developing pilots with the explanation that you can always throttle back, but you can't get more out of the engine than wide open. The truth is there are negatives to putting a bigger engine on than is needed, so appropriately powered is the way to go unless one is doing hard aerobatics.

RE: Mythbusters
 

Agreed, I see guys that don't have the skill to fly an airplane on the wing, rely on power. I have suggested more then once that everyone should spend some time with a sailplane and learn to thermal. I get blank looks back LOL

RE: Mythbusters
 

In aerobatics the plane can never be too light or have too much power
There are a number of different types of flying -each requiring it's own skills

RE: Mythbusters
 

Hahaha, http://www.rcuniverse.com/forum/js/f...wink_smile.gifgood one


I agree with Speedracer, Engine power is very important but an expert pilot (also full scale i.e fighter aces, competition pilots etc) is one that manage and control3 dimentional forces acting on a plane in flight - maintaining inertia in dog fights and manouvres - that is where the men and hooligans are separated. Anyone can open the throttle wide on an overpowered plane, few can manage the power and inertia - more so inertia... ooops..http://www.rcuniverse.com/forum/js/f.../msn/47_47.gif

Cheers


Bundu

RE: Mythbusters
 

I'm just thinking with newer flyers putting a bigger engine up front gets suggested a lot. But since throttle control is probably the last skill that everyone learns, having too much power can lead to stressful flying and a plane that just moves too fast for the pilot to keep up with. Add to that the increased weight, torque, and P-factor (yes it does exist) and a tame sport plane can become an ornery barn burner.

RE: Mythbusters
 

YES!!!!! Well put.

Kurt

RE: Mythbusters
 

That's because they don't have the right airfoil :D
(Why do I get this impression of cows floating around a field suspended from their backsides by hot air balloons, mooing as they try to reach the grass?)

The problem is more often that people have different flying disciplines in mind when they approach these discussions. On many types of model the airfoil is 'meaningless' but that is not the case with all types (gliders!). Excess power is often used as an alternative to efficiency. In models where power is limited for some reason, rubber free flight or gliders, then all of a sudden airfoil choice becomes important.

We are spoilt by very high power to weight propulsion systems these days. It's amazing how little thrust is actually needed to fly when you have the right planform, aspect ratio and airfoil.




The reaction to a change in airspeed is mostly a stability thing. Gust disturbances are a combination of a change in airspeed and a change in angle of attack. This means inertia has an effect but also that a model flying faster (high wingloading) will experience a smaller disturbance in terms of the relative changes.

Again it depends on what you are trying to achieve and compromises must be made. Wing loading isn't everything. Thermal sail planes often need to be ballasted. Yeah the sink rate is higher but a low sink rate is irrelevant if you can't get to the next thermal!

RE: Mythbusters
 

Yak, in response to wind stability. I'm still going to hold my ground that a well trimmed light model will always handle wind ( and gusts ) better then the same model, poorly set up andcarrying an extra pound. The well set up model will always react less to any wind disturbance and when correction is needed, it will be a smaller input.

Your reference to sailplanes is interesting. Yes at times we will add weight to increase the wing loading of a sailplane. The reasons are completely different however. With the sailplane we are increasing the potential energy so we can convert it to a higher kinetic energy ( speed ). Usually at a slope or an F3B distance or speed task. Adding ballast because the wind has come up and we need the additional penitration to get from one thermal to the next is usually not going to happen. If the wind is blowing that much, the thermals are too weak and traveling downwind too fast for us to work them anyways. My 90 oz Synergy 91 does get bounced around just as much as a 60 oz Explorer even though it is heavier and I fly it faster.

RE: Mythbusters
 

I wouldn't disagree with that at all. Stability is more about trim and CG position than actual wing loading. But speed and particularly size will make a difference to how badly the gusts affect the model.

RE: Mythbusters
 

True enough, but irrelevant. We're not weighing a badly set up heavy model against a well set up light one. We're talking about simply the effects of weight on comparably set up models. And in that scenario, a little extra weight does help a model penetrate the wind better, all else being equal.

RE: Mythbusters
 

I completely and most hardheartedly disagree........... It's because they don't have a big enough prop. :D

Ken

RE: Mythbusters
 

If you really want to open a can of worms, here's one that's still in contention. It's settled in my mind, but I like to see the rabbits get chased, so here goes:

<span style="color: rgb(255, 0, 0); ">Turning a model plane downwind is no different than turning upwind or crosswind, the plane does not know the difference.</span>


<br type="_moz" />

RE: Mythbusters
 

True. At least where there are no wind shear effects due to the model descending or climbing through a wind gradient.

The pilots perception from the ground may make it feel different but the plane doesn't care.