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RV-9A stall testing with wing tufts

Yep, the -9 stalls with very little loss of aileron control. If you accelerate the stall you get get to extend past the ailerons and even get a bit of a tail stall. That one gets your attention, but still docile. Those of us/you that have stalled a C152 with wings out-of-rig will have a hard time finding a similar stall induced excitement out of the RV9

Thanks for the video. I'd love to seem more (approach, accelerated, departure, cross-control, tail)
 
my question

why does the wing stall inboard first? It's a straight wing with constant cross section.

I like it. excellent control at slow speed.
 
Can't speak for the -9, but if it is like every other wing I know about there is a washout in angle of attack as you proceed toward the tip. The inboard section has a higher angle of attack and stalls before the tips, allowing aileron control through the stall.

Don
 
cfiidon said:
Can't speak for the -9, but if it is like every other wing I know about there is a washout in angle of attack as you proceed toward the tip. The inboard section has a higher angle of attack and stalls before the tips, allowing aileron control through the stall.

Don
Click to expand...

I see in your signature you have an 8. By plan at least there's no washout in those wings.
 
I don't think any RV's have "washout" or "Twist", but I'd love to hear one of the smart guys here in VAF explain how the "Hersey Bar" wing produces the inboard aft stall that progresses outboard to the tip. I know it has to do with "spanwise" air flow that artificially lowers the stall speed at the tips, but for the life of me I can put it into intelligible words.
 
aerodynamicist (not me) says

"Because of the fuselage interference, the wing root is likely seeing a lower flow speed as flow wants to move away from the fuselage (transverse direction) towards the wing tip at the wing root. Therefore the axial flow velocity at the wing root is lower than the wing tip and that is why you are seeing separation at the root first. From the motion of the tufts, I see that when the inboard separates, the separation is from the LE all the way to the back (80-90% chord). Not sure what your speed was at those points, but I would imagine that this is a laminar flow separation starting at the wing LE. The solution to this could be as simple as putting a series of vortex generators (1-2 rows) to induce some turbulence and suppress the premature flow separation."
 
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With a subsonic aircraft, the air ahead of the aircraft starts to move a bit before the aircraft gets to it. The air pressure above the wing is lower than the atmospheric pressure - that is a big part of why the wing develops lift. As the wing approaches the air mass, the air ahead of wing starts to rise a bit, as it is "sucked" towards the low pressure area above the wing - this rising air ahead of the wing is called "up wash".

The up wash ahead of the wing causes the angle of attack to be a bit higher than it would be if the air stayed completely still until the wing hit it. With a constant chord wing, the upwash is greatest at the wing root, and lowest at the wing tip. This means the local angle of attack is highest at the wing root, and the stall should start there and progress outboard.

All the above is true for constant chord wings with zero washout. The story changes a bit if the wing is tapered.
 
You did a lot of work to set up that test and video and I want to thank you. I understand my 9A wing better now. Any plans for a VG test?
 
This makes sense to me.

Kevin Horton said:
With a subsonic aircraft, the air ahead of the aircraft starts to move a bit before the aircraft gets to it. The air pressure above the wing is lower than the atmospheric pressure - that is a big part of why the wing develops lift. As the wing approaches the air mass, the air ahead of wing starts to rise a bit, as it is "sucked" towards the low pressure area above the wing - this rising air ahead of the wing is called "up wash".

The up wash ahead of the wing causes the angle of attack to be a bit higher than it would be if the air stayed completely still until the wing hit it. With a constant chord wing, the upwash is greatest at the wing root, and lowest at the wing tip. This means the local angle of attack is highest at the wing root, and the stall should start there and progress outboard.

All the above is true for constant chord wings with zero washout. The story changes a bit if the wing is tapered.
Click to expand...

The above statement makes sense to me.

No plans for VG testing for me. Like my wife says to me about herself, don't mess with a good thing.
 
Confession: had VG's on two certified high wing planes. They performed as physics said they should. Pain in the butt though...
The RV9 has such pretty wings. Mine will have no more than paint on them. Not even a gopro.
But I really do like your efforts to make the invisible come alive for all of us..
Smart wife BTW.
 
Very interesting

Steve,
What a great teaching video. Not only for stall info, but it helped me explain to my wife why frost on the wings can cause so much trouble. I found it very interesting watching the strings flutter as you increased the angle. Thanks for posting it for us to look at.
 
science shows

I did this primarily because I thought it would be beneficial to add it to my "show" for kids to explain how a wing works. Plus, I thought I could learn something more about my aircraft. I will add it to my Bernoulli Ball and miniature wind tunnel demo for kid science shows. I am that goofy guy that arrives to kids science shows with fans, wind tunnels and wing diagrams your mother warned you about. The first science fair this year is this Friday at a local junior high school. My youngest daughter is helping me this year. I appreciate the input from guys on this forum.
 
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Kudos!

Steve:

Your thoughtful preparation for, and execution of, stall and recovery cycles is very evident; I'll work to be that smooth.

We're planning our 2nd Science, Technology, Engineering, and Math (STEM) event for middle school students; with this as a great example, I'll apply a little rudder input ;) to the curriculum.
 
RV-12 Flaperons

Wonderful video!

It gives a nice feeling to to know that there is still some aileron control in a stall for the RV-9. I couldn't help wondering about the RV-12 wing with flaperons. I wonder if that wing has similar stall behavior, and if there is any control from the continued air flow on the outboard end of the flaperon.
 
Great Video!

The small cameras show many what only one saw before. Knowledge is spread.

The stall as shown seems to be gradual from the trailing edge, for approximately the inboard 1/3 of the wing, then zips out to the tip.

Is that visual stall, what you actually feel yourself?

That is, can you feel and can you control, holding just short of the complete stall, that matches the visual stall?

I will try again, can you see the "drop" with the tuffs as you feel it?
 
you bet

whd721 said:
Great Video!

The small cameras show many what only one saw before. Knowledge is spread.

The stall as shown seems to be gradual from the trailing edge, for approximately the inboard 1/3 of the wing, then zips out to the tip.

Is that visual stall, what you actually feel yourself?

That is, can you feel and can you control, holding just short of the complete stall, that matches the visual stall?

I will try again, can you see the "drop" with the tuffs as you feel it?
Click to expand...

yes, you can feel it and see it at the same time.
 
Great job!

Thanks for a very good video! It was very useful seeing how good that wing is in real life.
Great idea with the full flap stall too. (The -7 video)
If you are to do more tests; any chance that you can do one with t/o flaps on the -7?

Once again: thanks for the effort! Job well done!
 
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