To Vortex Generate, or Not?

[Space Bat]

days

The best thing to do is do an add hock wind tunnel if you are really interested in this stuff - you can buy a tunnel (kids activity tent/tunnel plaything) a fan and a high speed camera....lots of wool and some tape...

You can pretty much get close to a professional set up and you would be surprised how air and boundary layers work on a wing...it is nothing what people expect - such as flow reverse and flow collapse and boundary lifting....

We did a fair amount on my last job where we tested the vectored thrust system and worked out whether our vectored system had issues with flutter....

Some people know .... but I tested the engine and propulsion system on this bad boy...at Cranfield University UK....

http://www.youtube.com/watch?v=R1G-L7qvTKI

 

[teookie]

Thats a seriously cool blimp.

 

[Space Bat]

Thats a seriously cool blimp.

It will harbour death - this thing will watch over afghanistan with a wide field of view....Mr Taliban won't have his own way once this is in operation

 

[hone]

I don't know about all the technical mumbo jumbo but i put some VGs on my 60'' Extra Exp and it made a difference in the way the plane transitions from pre to post stall. It makes the transition much smoother and less noticeable. Also once in the stall you have slightly more authority on your control surfaces

 

[Dave102269]

Same here hone1er. My 60"Edge with VGs flies much smoother through transition to post-stall flight. Less "floppy" with more control deeper into the stall. Seems crisper at high speed also, but that may be psychological. I've outfitted a 48"MXS recently and will report how it feels once I get it to the field.

dd

 

[RCAddict16]

days

The best thing to do is do an add hock wind tunnel if you are really interested in this stuff - you can buy a tunnel (kids activity tent/tunnel plaything) a fan and a high speed camera....lots of wool and some tape...

You can pretty much get close to a professional set up and you would be surprised how air and boundary layers work on a wing...it is nothing what people expect - such as flow reverse and flow collapse and boundary lifting....

We did a fair amount on my last job where we tested the vectored thrust system and worked out whether our vectored system had issues with flutter....

Some people know .... but I tested the engine and propulsion system on this bad boy...at Cranfield University UK....

http://www.youtube.com/watch?v=R1G-L7qvTKI

That is seriously badass. Invisible to radar, the helium is at low pressure so even if its riddled by bullets so the gas would take days to seep out, and missiles just bounce off. Wicked!

 

[Steve_B]

That is seriously badass. Invisible to radar, the helium is at low pressure so even if its riddled by bullets so the gas would take days to seep out, and missiles just bounce off. Wicked!

I'd imagine that the idea would be to operate at an altitude where it was unlikely to get 'riddled with bullets' or hit by missiles. It's service ceiling is 22,000ft (over 4 miles up) so it would be pretty safe up there and I'm guessing it would also be a hard/impossible target for missiles to lock onto.

high winds may be an issue though...

Anyway getting a bit off topic here.

 

[Steve_B]

I don't know about all the technical mumbo jumbo but i put some VGs on my 60'' Extra Exp and it made a difference in the way the plane transitions from pre to post stall. It makes the transition much smoother and less noticeable. Also once in the stall you have slightly more authority on your control surfaces

Yeah, transition into stall is one area where i could see VG's making a difference. It's hard to see what they would do once the wing was fully stalled though, but there could be some effect going on that I've not thought about. It's always incredibly difficult to do meaningful testing when relying purely on 'feel'. It's almost impossible to remove subjectivity from the equation, especially so when the different tests are done on different days which invariably means slightly different flying conditions.

 

[Space Bat]

Yes the operating ceiling is high enough to prevent small arms fire....and due to no heat signature (SAMS key of high heat such as turbo props or turbines) - it would not lock.....and as RCaddict said...you could punch a massive hole in it and it would take ages for helium to seep out - enough time to still be operational bring it home patch it up and send it back out....

Some of the tech I can't discuss for obvious reasons due to all the paperwork I signed.....but this thing is scary clever.....I wouldn't want to be Johnny taliban when this thing has seen you

Back to topic....

The VG's were designed to reduce airspeed to allow for lower point of stall on wing surfaces...this allowed two things short take offs and short landing capability...allowing for planes to have better slow flight characteristics....with heavier weight....

On a rc plane the wing at high alpha is actually technically at a stalled position and airspeed under normal conditions would mean that the plane does not generate lift at the wings....one thing to remember is that with rc planes is that although not true to scale has incredibly low wing loadings to reality and large wing area's which normally in a real plane would be filled with fuel and because it's not - gives you a higher glide path capability at abnormal wing attitudes...so you can stall the wing and have enough cushion effects where the plane doesn't fall like a stone....however due to lack of airspeed over control surfaces you do not have any control authority.....as you would like... because 3d planes have typically 2-3 times the increased thrust to weight ratio employed due to larger than scale props and powerful motors - you are tricking the wing into not stalling because you have increased airflow around the wing and control surfaces - where the wing acts as if it had much higher than stall speed surface response with the boundary layer as if it was flying flat and not in alpha....by adding VG's you can increase the alpha state and or lower the thrust and forced air from the prop across the wing surface where you can still have effective control surface response....at much slower speed or high AOA.....

 

[Steve_B]

Space,

I'd debate the point that "a stalled position and airspeed under normal conditions would mean that the plane does not generate lift at the wings" As I mentioned in previous post with actual wind tunnel test data to back it up. Wings still do make plenty of lift post stall, in fact they can make more lift post stall than they ever did before stalling. The problem is they make this post stall lift at the expense of huge drag, which most 'non-3D' planes don't have the thrust to overcome, plus as you said most planes would be hard to control post stall.