Help! pressure deployed wing slats questions

[badpilot27]

so i haven't really flown my rc trainer in a while and I want to upgrade the wing to make it fly better in some wind (wing is way too big rn so it gets thrown around in the in any wind) and i thought it would be cool if i added bf 109 style pressure deployed slats

some cad rn

on the 109 and other messerschmitts the slats deploy at high angles of attack where the low pressure above the wing pulls them out

im a little unsure if it would work at this scale as i worry that air pressure wont really have enough strength to lift the weight of the slat and that there may be too much friction

what do you guys think? would this concept work at this scale? what changes should i make to my design?

 

[Mr Man]

I don't have any answers, but this sounds like a cool idea!

 

[quorneng]

I fear you will discover that at RC plane sizes slots do not even act in the same way as full size let alone pull out automatically.
Remember the viscosity of air is still the same so compared to full size it acts more like treacle!
Indeed air's characteristics are part of the reason that models with "simple" wings can fly controllably at higher angles of attack than full size can.

The ease models are effected by turbulence is substantially due to their relatively low air speed & wing loading. More weight & power but with the same wing area it will fly faster and be more manageable in wind but take offs and landings becomes harder not to crash.

 

[Piotrsko]

Treacle = pancake syrup to Americans more or less (very high sugar content semi viscous solution) Molasses is the more approximate comparison, but treacle is not as roasted black as molasses at least when I was shopping in Morrison's bakery for breakfast

Back in the 1970's, I flew gliders with someone who was very intent on high AOA flow straighteners. he had a chain drive leading edge that seperated a pinkie fingers gap. Quarter span multi piece flaps. Never had a noticeable flight improvement, didn't clean up the stall, and weighed a bunch, required a 3 meter span. But Lordy, his glider flew slow with everything hung out. My 42" clark Y airfoil kicked his butt clear into next week .

OTOH, there was some success with STUKA style air fences but only at high angle of attack

 

[zbjanik]

It would be best to simply try this idea and put any doubts to rest. I believe some kind of connection is necessary between the slat ends on each wing half, so they extend parallel, but also to connect both wing halves. If only one side were to open, disaster would be certain. This connection could be made of carbon rod, supported in several places to prevent buckling. I would try...

 

[Merv]

...it gets thrown around in the in any wind...

It may work, but I'm not sure it's worth the effort.

I know adding any type of stability will greatly improve windy conditions. Adding weight also helps.

 

[Mr NCT]

I think it's worth a try.

It may work, but I'm not sure it's worth the effort.

LOL! We're making DTFB fly. If it's fun and interesting to you it's definitely worth the effort.

 

[Piotrsko]

It would be best to simply try this idea and put any doubts to rest. I believe some kind of connection is necessary between the slat ends on each wing half, so they extend parallel, but also to connect both wing halves. If only one side were to open, disaster would be certain. This connection could be made of carbon rod, supported in several places to prevent buckling. I would try...

Partial deployment of one side causes a very nice massive roll command

 

[badpilot27]

It would be best to simply try this idea and put any doubts to rest. I believe some kind of connection is necessary between the slat ends on each wing half, so they extend parallel, but also to connect both wing halves. If only one side were to open, disaster would be certain. This connection could be made of carbon rod, supported in several places to prevent buckling. I would try...

So I’m using bearings in the slat guide but I only have 10 bearings on hand at the moment. If each guide needs 3 bearings then I don’t have enough for 4 slat guides sadly so I guess I’ll have to try to get it work with one slat guide per slat. It will probably be fine if I get my tolerances right.

 

[L Edge]

As Merv mentioned more weight may help. Just make sure you put the added weight right under the CG.

Another factor that works well in gusty and higher wings is to move the CG forward (the range should be from 25% to 33%) so it is slightly nose down which helps you fly in the gusty and windy conditions. That is one of the tricks you can use when you do pattern maneuvers.

For trying your slat setup, if it works, you should see increase lift at low speeds and a STOL type of plane. Bad point, you can go into a snap stall quickly if your angle of attack is too great and speed is too slow. (Ask me how I know).

Only other method is to put a gyro on to fly in gusty winds.

 

[badpilot27]

Finally got the tolerances right. Rolls smoothly with a slight bit of wobble

 

[Mr NCT]

It's going to be really interesting to see how that works out! Keep us posted.

 

[telnar1236]

Looks like a neat project - I'll definitely be following this one.

Slats definitely work at model scales if done right (e.g. UMX Timber), but mostly we don't fly in a way we get much benefit out of them since we tend not to fly all that near stall most of the time. As Piotrsko said, asymmetric deployment is also a potentially serious issue and could make your plane uncontrollable (this was an issue in the full-scale aircraft that used this arrangement too).

As others have said, slats aren't too great for improving how a plane handles wind - adding weight helps reduce the amount of wing rock as does reducing lateral stability (reducing dihedral or similar changes).

 

[badpilot27]

Looks like a neat project - I'll definitely be following this one.

Slats definitely work at model scales if done right (e.g. UMX Timber), but mostly we don't fly in a way we get much benefit out of them since we tend not to fly all that near stall most of the time. As Piotrsko said, asymmetric deployment is also a potentially serious issue and could make your plane uncontrollable (this was an issue in the full-scale aircraft that used this arrangement too).

As others have said, slats aren't too great for improving how a plane handles wind - adding weight helps reduce the amount of wing rock as does reducing lateral stability (reducing dihedral or similar changes).

if the slats move properly i dont really think it would be much of an issue. if one slat deploys more than the other when wings are level, yes it would roll into the direction of the lesser deployed slat. however this increases the aoa on the slat's wing, helping it pull our further, and decrease the aoa on the other wing's slat, pulling it in a bit. this is all in theory though and would likely work a bit less consistently so we'll find out in testing.

the new shorter wing with all of its gimmicks will defiantly increase the wing loading a tad so maybe its enough to help with dealing with wind and i can always add ballast. thanks for the suggestions!

also im not putting slats to help with wind but looking back it defiantly seems like it with how i worded the first post

 

[Piotrsko]

Starters: modelers are so far out into the weeds as far as aerodynamic flow is concerned that it almost either doesn't count, or it is such a critical factor that it over rides everything else. Kinda like a bumblebee: they are so aero lousy that technically they can't fly but nobody speeks bee so as to explain it why they shouldn't fly.
Run a rc plane in a test tunnel at model speeds and the smoke trails go everywhere. Been there did that until they wouldn't let me anymore

 

[L Edge]

First al all, that is a slick mechanism for deploying the flaps. Very interested as you vary the open gap dimension and what it will do as you vary the AOA. I suggest you stay high when you deploy, so you can recover(if needed) from the stalls. Please take videos.
Did you watch the STOL competition videos and what they try? One entry did have the LE drop( by pressure differential) and retract as he leveled off.

 

[Piotrsko]

Did you watch the STOL competition videos and what they try? One entry did have the LE drop( by pressure differential) and retract as he leveled off.

Might be wrong (actually hope I am) but I suspect they work by adding wing square inches when deployed more than any flow modifications.

 

[zbjanik]

I thought that if I were to investigate the problem described by badpilot27, I would start with slats that were opened mechanically at my discretion. If they proved effective, I would then move on to automatic slats. Otherwise, we have several immediate problems: will they open, will they open simultaneously, will they be effective, and was it worth it? We can reverse this sequence and immediately know if it's worth it, and then proceed further.

 

[Piotrsko]

You can link them together such that they can only deploy symmetrically. A 90 degree bellcrank and fishing line might work.
If I understand correctly, you test fly it with them extended then retract for the test? Partial failure retract is probably not a crash

 

[badpilot27]

First al all, that is a slick mechanism for deploying the flaps. Very interested as you vary the open gap dimension and what it will do as you vary the AOA. I suggest you stay high when you deploy, so you can recover(if needed) from the stalls. Please take videos.
Did you watch the STOL competition videos and what they try? One entry did have the LE drop( by pressure differential) and retract as he leveled off.

hopefully the weather is good this weekend (and other weekends aswell) and i have some time to fly

i also really want to get building the stol pancake but i have more time to play around with slats at the moment