Flaps on poly-dihedral wings (simple soarer)

[duckduckgoose]

Hi! i've just built myself a 120% simple soarer (with ailerons because i didn't install a rudder, long story) and was wondering if anybody had experience putting flaps on a poly-dihedral wing like the SS. it already performs well, but id like to squeeze every bit of performance out of it, and i have used Flaps before on dihedral wings with great success. just wanted a 2nd opinion on whether they also work on poly wings before i start cutting things up and potentially make it worse. cheers!

 

[The Hangar]

Flaps should work just fine on it. I believe @OlliePackman put flaps on his.

 

[duckduckgoose]

Flaps should work just fine on it. I believe @OlliePackman put flaps on his.

cool!

 

[Michael9865]

Normally if you add flaps they are added to the inward sections of the polyhedral wing. Looking forward to your results.

 

[duckduckgoose]

Ready to test tomorrow

 

[danskis]

Nice job....looks good. I was wondering what advantage you hope to gain in performance? You did add some weight to a glider which is always a trade-off. Will you be using this for slope soaring (if so I'm jealous - no slopes around here)

 

[duckduckgoose]

Nice job....looks good. I was wondering what advantage you hope to gain in performance? You did add some weight to a glider which is always a trade-off. Will you be using this for slope soaring (if so I'm jealous - no slopes around here)

True, I did add some weight, but I think at this level of build quality (average to low) it is negligible. I'm using it for just simple gliding (like you I have no slopes anywhere near me), I just send the plane up nearly vertical with the motor, then once it is too far up to make out it's orientation, I kill the throttle and glide. I have added flaps to previous powered gliders (a twin boom using a 150% tiny trainer wing that was extended and flaps added, pic below) and the benefits were quite substantial. It just immediately slows right down and glides and glides. By glider standards they are probably fairly low performing but compared to flaps off, it's a big difference (for me anyway). Best days are still afternoons. I sometimes lose track of it for a few seconds haha. In fact I completely lost track of the plane pictured below, until I saw it disappear into the treeline. Miraculously it was barely scratched due to it flying super slow with flaps engaged. I think my PB for a single glide was 9mins from throttle cut to landing

 

[Piotrsko]

Haven't seen where typical flaps do much except increase drag unless they are wide span flaps that increase the camber. Spoilers OTOH..........worth their weight and complexity because down is really hard sometimes.

 

[duckduckgoose]

Could it possibly be that the lift to drag ratio is better at a lower speed with this particular plane? Therefore the extra drag doesn't cause as much of an issue? I may be getting a certain result for a different reason that I think but it seems to help, or it could mean I'm not flying it right haha.

 

[duckduckgoose]

Just got a 9 minute glide with the flaps deployed. Seems there's a fine Ballance between flaps and up elevator trim. The motor came loose just as I was about to cut the throttle and start gliding causing the prop to break off (0:17 secs). Still flew like a champ. Love this plane, can't believe I didn't try it sooner. I forgot to mention I made a nose extension by modifying the tiny trainer power nose. This allows for more room for batteries and makes balancing the plane much easier. Plus the stock SS power nose was quite ugly. Onboard Video coming soon

 

[duckduckgoose]

 

[Piotrsko]

Rate of sink is the defining point of soaring. Going up means the rate of sink goes negative. Deployed flaps do slow the plane down, but will increase rate of sink and change trim. Try different landings clean and then with the flaps deployed and see what happens.

It is possible that the flaps cause you to remain in lift longer before falling out. Too many variables to say what exactly is occuring to your L/D ratio, or trim angles, CD.

Final arguement: set your approach very short, deploy flaps, see where you land. If they work like you post, you'll overshoot.

 

[danskis]

Please excuse the ramble - or not. Yeah its complicated. I'm still playing with this on my flaperons (full length of wing) on my DLG. Typically on the DLG you use the flaperons for three things, ailerons, flaps and to adjust the camber of the wing. Ailerons are ailerons, flaps are flaps, but the camber adjust is pretty interesting. Camber adjust, moves the control surfaces the same way flaps are moved (both in the same direction up or down) but in a much smaller amount - 2-5mm. Typically you can use the camber adjust in a thermal to slow the plane down and increase lift by increasing the undercamber of the wing - this helps you stay in the thermal longer. You can also use them to speed the plane up for launch to get a higher launch height or cruise to the next thermal. I'm not very good with flaps but I use them for landing to reduce lift and slow the plane down to, hopefully, land where I think its going to land. Not having a motor I use the throttle control for flaps which give me full proportional flaps. Anyhow, this is my current understanding of flaperons and as I get more experienced I'm sure it will change.

 

[Piotrsko]

Not bad for an understanding but the camber part is sketchy unless they are say 1/4 to 1/2 chord wide. Plot the airfoil and see what they do. If the mean camber line moves much it changed the airfoil. I have been found wrong before.p

Have you tried -2.5 flap for speed between thermals? Lance Niebauer from Lancair fame found that reflexed flaps incurred no lift penalty but gave a speed increase of 10 mph when his flap bracket broke.

 

[duckduckgoose]

Rate of sink is the defining point of soaring. Going up means the rate of sink goes negative. Deployed flaps do slow the plane down, but will increase rate of sink and change trim. Try different landings clean and then with the flaps deployed and see what happens.

It is possible that the flaps cause you to remain in lift longer before falling out. Too many variables to say what exactly is occuring to your L/D ratio, or trim angles, CD.

Final arguement: set your approach very short, deploy flaps, see where you land. If they work like you post, you'll overshoot.

Good point, I will do some tests playing with up trim without flaps. Either way I really just like how slow it can go without dropping.

 

[duckduckgoose]

So, in theory, i should be able to achieve an even longer glide time without flaps deployed the whole duration(assuming i get the trim right)?

 

[danskis]

@Piotrsko - well I'm pretty new to DLG but the flaps are at least 1/4 chord. Tribal knowledge (and we have a 2 time FAI world champ in the club) says flaps go up for speed (1-2mm) or stay even with the wing depending on wing design (some DLGs have built in reflex, I think). Thermal is 2-5mm down for thermal. If you're suggesting in the above that Lances "reflex" is up then we're all in agreement and if Lance's reflex is down well then it goes against local tribal knowledge (which doesn't mean its not true). The plane definitely speeds up with the flaps even or a little up. If I've learned one thing from RC its "Don't believe everything you think!"

 

[clolsonus]

So, in theory, i should be able to achieve an even longer glide time without flaps deployed the whole duration(assuming i get the trim right)?

You really have to perform careful glide tests to figure this out reliably. (px4 or ardupilot can collect the data you need and make it easier to fly stable profiles.) Climb to 400' and glide back down at different airspeeds (or pitch angles would be 2nd best.) Then you can plot out the results and see which airspeed yields your lowest sink rate ... or longest distance glide (probably not exactly the same speed.) You can repeat with different flap settings (or reflex) to see how that affects your results.

If you look at a pilot handbook for something like a C172, they will have done all these things already and will tell you in an engine out situation, how much flaps to put in and what speed to fly to stay aloft the longest (Vy) or cover the best distance over the ground (Vx).

Once you figure out what speed you are shooting for, you can dial in the approximate amount of elevator trim you need to hold that speed hands off as you float around.

 

[Piotrsko]

Or if you're like me and stubbornly back in the dark ages with no computer aided anything, do a flight and try to enter a high stabilized pattern for landing ( hands off everything except for turns) Play with flaps and trim there because you will have better 3 D references like light poles, trees, whatnot and you can actually see the results. The idea is practice your landings and see which settings make it go farther, since farther is the measure of efficiency. Finally, unless the stalls are non events, don't fiddle with any settings lower than maybe 10-20ft. This will make your landings even better.

Flying faster is not necessarily draggier and most people generally fly too slow. I still take my gliders to stall with up trim then add a couple three or more of down trim clicks until it sinks noticeably then back one up click.

 

[danskis]

Here's a very long engineering article based on current DLG design about the effects of camber introduced into a wing with flaperons. Most of this article is beyond me but my take away is that you've got to experiment with flaperons to determine what works best for your airfoil and its probably going to be between a 0 - 10mm drop for desired effect/optimum results

The Aerodynamics of a DLG Unravelled | by Theo Volkers | The NEW R/C Soaring Digest | Feb, 2021 | Medium