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Airfoil database ld max 4 degrees4/23/2024 ![]() so my intention is to at least understand what the airfoil database data actually stands for, which brings me to my original question: Is L/D max or maybe Cl at L/Dmax, the measure of effeiciency and minimum cruise, that i'm looking for?Īt least then i may be able to choose the best airfoil for my needs, one that does what i'm aiming for better than the others EVEN if it doesn't quite achieve the high cl and performance figures quoted in the database. However, we have to start somewhere don't we. For example, just a bit of oversanding on the bottom of a clarkY would give it undercamber and a different performance! I do also fully realise that a home made/sanded and solartex covered section will be an ever so slightly not perfect reproduction of the intended proper airfoil section - and that, consequently the resulting section may not perform as per the database statistics. I'm afraid pimmnz, that just 'suck it and see' is not really an option on a ten foot wing - i can t afford to just run off a quick 3 or 4 full wings just to try out and compare sections! So - i just wanna be a bit more objective thats all. my big bird has a centre section chord of 18" so i'm guessing Re of 400-500K which is a bit more than your average parkflyer! Thats why i'm trying to take the airfoil section a bit more seriously (never have before - just used to do a very nice freehand version), i'm thinking at this size there may be some tangible benefit in using a real section. penetration in wind is not an issue and of course neither is any kind of aerobatting, BUT, an issue would be stability, so some undercamber is ok, but excessivley thickened bananas are not.įor interest, best candidates so far - if i read all this correctly are:: naca 4414, naca 4614, naca 6514 (they are all a bit thick, but i guess thats where the camber and subsequent high CL come from). 2) to allow the plane to cruise fairly slowly with low engine thrust (so it will sound good with a big idling fourstroke). Remember, i'm not after actual lift or drag numbers in lbs here - just a way of comparing the various suitable airfoils to tease out the best one for my big old timer - and by 'best one' i mean one that allows two conditions to be fulfilled 1) to get a very low minimum stall speed for landing - even at high drag penalty, since that will allow landing in a smaller patchj. ![]() That should compare airfoils which are producing their best lift for their minimum drag AND showing how much that lift is (as a coefficient). Ok, i get the min drag concept, but of course its no good achieving the minimal drag condition if the lift is then insufficient to maintain altitude - so perhaps then the airfoil stats to compare shpuld be "lift at L/D max" so do i now factor in the L/D max ratio). (what i can say is that to get the slowest speed without wild pitch inducing banana sections, i am considering mild undercamber with Cl max ranges around 1.5 and for structural integrity i want sections around 12-14% for example naca 4414 or Gott 550 - but there are so many others too. I'm surfing those airfoil comparison sites and looking at the stats and need a little clarification please. So thinking about it, i THINK the parameter i may be needing to compare is the L/D ratio or more particulary the L/D max figure. What i have realised is that whilst the Cl max allows me to find out how slow i can get the plane to fly before it stalls - but it doesn't address the issue of drag and i understand that thrust counters drag - so i could end up with a plane capable of a low minimum speed but only at relatively high engine output - so i need the high Cl but without excessive drag or at least less drag. I'm getting a handle to some extent on all this airfoil speak - and i can even do the 'minimum airspeed calc' using loading and Clmax (thats got me playing with stats for hours Lol) - however, where i'm a little unsure is how to determine the minimum engine power (in thrust terms) required to keep any particular airfoil at a given loading airborne, In other words if i find airfoil X keeps my plane airborne at exactly 1/3 throttle (or y pounds of thrust) how exactly would a change to a different airfoil allow me to reduce the throttle a bit without the plane descending (what statistical parameter should i be comparing to choose the ideal airfoil).? Hi guys, once more i hope to bathe in the light of your wisdom
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