alcarafa

Have a question for you guys ... is it possible flying this ballistic planes that one may produce a high speed stall effect?

Gene Margiotti

My Feedback: (4)

Simple answer - yes.

Gene

alcarafa

What causes the effect in a scale model ?

wind junkie

My Feedback: (1)

Sure. Just crank up your elevator travel and see what happens.

alcarafa

Thats exactly what I know ..but there is a person who insist a scale airplane may never have that effect, that is absolutly false laws of physics apply equally at any scale ..right ?

alcarafa

not the effect im talking about , a plane can produce a high spped stall due to speed without pulling up the elevator.. believe me !

EscapeFlyer

My Feedback: (1)

ditto...

And putting ANY wing past its critical angle of attack will stall the wing. This is true for every wing.

Thrust vectoring will keep an airplane in the air though...

Brian

wind junkie

My Feedback: (1)

I'd need to know what your friend means by "a scale airplane." I agree physics applies to everything and there is no magic dividing line between a scale and non scale plane.

Also I'd like to know exactly what you're looking for in a "high speed stall?" Do you expect a snap roll? Do you want the plane to just "mush" forward or in a gentle pullout?

Very much depends on these factors:

sharpness of leading edge
wing thickness
wing loading
"normal" stall speed
lateral balance

From my experience most modelers typically do not want to deal with a high speed stall, and therefore limit their elevator travels so at the highest speed possible the plane will not snap out of a loop (or turn). That's traditionally how instruction manuals would direct the modeler to set the max throw for a (non 3D capable) plane.

If you want 3D, of course all that goes out the window, and one must deal with the post stall (high alfa) flight regime of the wing.

Not sure how to make it sound simpler than that without addressing specifics of your original question which you haven't provided.

daggets

high speed stall means that the airstream is blocked due to the shockwave on the wing profile.....
this happens at speeds around mach 0.9, depending of the profile and the swept of the wing....
no way you can obtain such a speed on a flying model!!!!!!!!!!!!

apereira

Agree with daggets,

Even tough an airplane is flying in the subsonic or transonic speeds, the airflow over the wing might be supersonic, that's why the supercritical airfoils were developed, those are the ones with less curvature on top and complex curvature on the bottom, those, can be seen in any corporate jet capable of high subsonic speeds or airliners.

It is not possible at the moment to suffer from that effect on model airplanes, but lots of people think high speed stall is when you come really fast and at the pull of the elevator the model snaps as the tip stalls progress, but that is associated with the abrupt increase in the AOA, whether the real high speed stall is produced with no AOA change.

Regards

stuntflyr

I'm not sure what these posters are refering to;
Unless they're trying to explain Mach Tuck, where the C/L moves back so far that the airplane needs additional "up elevator" to maintain the same pitch attitude as it approaches supersonic flight.
I think there are problems with models that aren't balanced properly that have a tuck problem in R/C, usually the tail stalls on swept wing EDF's which are too nose heavy.
There are no transonic flow issues on model airplanes, no matter what one thinks, the model would have to go near 600 knots TAS to accomplish this, and that doesn't happen.
Chris...

Bootalini

I agree with Wind Junkie. To expand on what he said, by "normal stall speed", he means the stall speed of an aircraft/model at 1 G. One can induce a high speed stall by pushing/pulling hard enough on the stick at most any speed......the higher the speed, the higher the G force associated with the stall.

Ref setting control throws, I've always set mine based on achieving the required control authority I need at the lowest speeds I could expect to be manoeuvering at. That's why God invented dual rates, expo etc.

Bootalini

Chris, I'm with you on this and I have 5000+ military hours in the book, most of it on jets. I think the guys referring to what we would call mach crit over the top of the wing as mach approaches 0.9+ (or much lower depending on wing design).

stuntflyr

Yeah Jeff,
it just hit me, mach crit. I couldn't remember what the proper name was, too early or too old.
I doubt they are seeing that!
I wrote a little addition to my post, too nose heavy on swept wing edf's and they nose over when going really fast, usually in a turn. The tail stalls and most R/C guys don't know what happened. I heard a guy call it "hyper stall"! I crack up at these R/C terms.
Chris...

Rob2160

This post caught my eye...

Depends of what the original poster meant by "High Speed Stall"

Here is a nice explanation of stalling - http://en.wikipedia.org/wiki/Stall_(flight)

I understand a high speed stall to be an "accelerated stall" as per the above link..

Stall is a function of angle of attack.. Not airspeed..

The airspeed simply defines the lift or G being produced as the critical angle is reached..

Typically aerodymanic manuals state 16 degrees to be an average critical angle for an aerofoil, but this varies depending on a number of factors, camber, wing thickness, leading edge radius etc..

But in simple terms.. lets assume 16 degrees.

If you exceed 16 degrees angle of attack the wing will stall, a stall does not cause a total loss of lift, just a reduction in lift with any additional angle or attack past the critical angle..

If an aircraft stalls at 100 kts in 1 G level flight, then this is typically called its "Stall Speed"\

But it will stall just as easily at 200 kts and even 400 Kts, if you exceed 16 degrees angle of attack

the G being produced by a wing is a function of airspeed multiplied by the square root of the G..

IE if 100Kts = 1G, then

200Kts would give 4 G at the stall,

400 Kts would give 16 G at the stall (usually the wing would fall off prior to this... )

The maximum manouver speed is calculated by applying the design load limit of the aircraft to the 1 G stall speed..

IE, an aerobatic aircraft may have a certification of 9G...

If it stalls at 100Kts at 1 G, then it will experience 9 G at 300Kts if you exceed the critical angle..

So at any speed below 300Kts, you mathematically cannot over stress the aircraft and hence can apply full control deflections.

Above 300Kts in this case, be careful, because too much control input can break the aircraft...

Any aircraft can experience a high speed stall, from the smallest ultra micro aircraft to the Space Shuttle and an A380 Airbus..

Mach Crit is something completely different.. but I won't go into it as the original post said "High Speed Stall"

Hope that helps.

klhoard

My Feedback: (10)

.
I think the majority of R/C fliers refer to a "high speed stall" as a "radio hit" . . . . . .
.
As for getting a Classic Pattern plane's wing to go Mach Critical - I'MTRYING!!!
.

bjr_93tz

I suppose the only two stall type you get with a model airplane wing will be the "normal" run out of airspeed stall where you're trying to maintain 1G and you exceed the wing airfoil's stall angle of attack because you're going for more lift co-efficient as your airspeed drops.

The second stall is what I've normally associated with the term high speed stall, and that's where you exceed the wing airfoil's stall angle of attack at an airspeed higher than necessary to maintain 1G, for example in a banked turn. I've been in a full size private plane doing this flying well above "normal" stall speed pulling tight banked turns until the stall warning indicator started blaring at me which was only about 1.5G. Yep it wasn't a performance ship for sure :-)

Any airflow disruptions to do with critical Mach and/or transonic effects probably won't come into play at the speeds most models fly at unless your wing or some other appendage is trying really hard to accelerate airflow at a fantastic rate at one particular spot......

fred985

any aircraft of any size will stall at any speed if it has enough "up" or down elevator. elavator on a real airplane is set so it will be full up at the point where the aircraft slows down to the point that the wing looses lift. if propely designed it will be in the 3 point landing attitude. it will have full up,,,stall and have all 3 wheels touch the runway at the same time.

Rob2160

Not wishing to offend but this is definately not the case for any aircraft I have ever flown.

Aircraft approach at a safe margin above the stall speed, (IE 1,3 x 1G stall speed in the landing configuration)and are flown smoothly onto the runway at a speed above this stall speed.

Watch any airliner, corporate jet, fighter aircraft on landing.. They do NOT stall at the point where the wheels touch down.

In fact, these aircraft have stall protection systems that will PUSH the nose down if they get close to stalling.. That is the LAST thing you want just a few feet above the runway.

[youtube]http://www.youtube.com/watch?v=5GrwODV68R8[/youtube]

However there is much mis information and a common misconception that you should stall just at the point of wheel contact.. from websites like this.. http://stoenworks.com/tutorials/how%...airplanes.html

In small light aircraft it is not uncommon to hear the stall warning during the flare, but this is not a stall, it is a WARNING that you are approaching a stall, usually 5 - 10 knots above it..

Here is a reasonably good article that explains how larger aircraft are flown onto the runway.. not stalled..

http://en.wikipedia.org/wiki/Landing

fred985

for Gods sake rob,,,get out of your f-15,x-15 or 747,,,,i think you loose sight of the fact that we are talking about regular aircraft,,,r-c aircraft. none of my "real" planes had stall warnings and stuff like that. they were 450 stearmans ,,,j-3,,,howard dga 15-p.....i flew the patern at 65 to 60 indicated in the stearman and it stalld at 55 indicated. i guess the stall warning wound have worn out from sounding of to much. the 450 was real easy to get into a snap roll at 120 when doing a real slow roll . itt all gets silly to be talking about .99 mach tail stalls etc when this is a rc talk-about....the nearest i came to stall warners was in my uncles 180 and that barked just a second before all 3 touched down in a good 3 point landing.

Rob2160

LOL.. fair cop.... I'll just pull my head in.. engage autopilot and eat my sushi..

[youtube]http://www.youtube.com/watch?v=FkwT9Jj4nF0[/youtube]

stuntflyr

LOL! Hilarious...
Chris...

bjr_93tz

Instead of jumping to conclusions about what we think the OP thinks a "High speed stall effect" is, I'll just wait until he pops back in to tell us what he thinks it is and why his friend doesn't believe it can happen with planes our size.

Right now I've got no idea what he thinks he's on about other than the phrase "high speed stall effect" ???? , which is beginning to sound like it's used to describe more than one type of aerodynamic condition.

hook57

My Feedback: (21)

Wow, I think he really meant "hall effect"! You know, that thingknown asa transverse flow on a moving charge!!!!!!!!!!

hook

rctech2k7

My Feedback: (1)

Thanks Rob and Fred for that info, I should know that before. I read a lot of info about stall landing but I failed one time on my small hornet when I decided to abort and go around. Thank God because of that I learned to land with engine power, high alpha and full flaps even after touchdown she's still flying, however with spoiler deployed the plane still takes time while controlling steering and brakes specially with plenty enough fuel left.