short wing chord, what am I in for?

[citabria]

I'm scratch building a park flyer style wing with a 5 1/8" chord. The length will be about 44", it will have a 3 degree dihedral. I have sufficient wing area for the size and purpose of the plane (it will be a sport/fun flyer in the 13 to 15 oz range). What I am wondering is if I am in for any surprises with such a small chord relative to the wingspan? I know chord length changes the reynolds number. Is there anything I need to look out for?

Scott

[DeaninMilwaukee]

I read here once that the limit of good slow speed handling was 5" chord. I've stuck to that 5" limit and always had easy ahndlnig planes.

The span/chord ratio is'nt a factor as far as the reynolds numbers are concerned, but it does affect glide performance, roll rate ect.

[BMatthews]

It's a long aspect ratio by power model standards but not that bad by glider standards.

The long span for that much wing area will make it slower to roll into turns and other maneuvers than if it was more stubby but other than that it's fine.

[Ollie]

Given a wing of a certain area, there is a trade off between increasing profile drag with decreasing chord and increasing incuced drag with decreasing aspect ratio. Where the best balance between these conflicting objectives falls depends on the particular airfoil and the particular airspeed of the model. For aerobatic models that have lots of power to overcome drag and weight, the drag consideration is swamped out by the high priority of maneuverability. For endurance models and sailplanes, the question of drag reduction has the highest priority.

So, the design decision is a question of priorities that stem from the purpose of the model.

[citabria]

Thanks everybody. Slow rolls I don't mind. This is not designed to be a pattern ship, so I think I am in the clear. Thanks again for passing on your knowledge.

Scott

[raptor22]

Long thin wings will give best effeciency at low speeds that are closer to stall (and therefore provided less drag for airplanes that need to fly slow to use the least engine power and keep the plane in the air longer), while shorter wings are more effecient at higher angles of attack (and therefore provide less drag for maneuvorable, high speed models).

--Alex

[Ollie]

The advantage of low aspect ratio wings is that they can be lighter for the same bending strength and they have much lower moment of inertia in roll for a higher roll rate. However, they almost always have drag that is greater than high aspect ratio wings, seldom less.

[raptor22]

the drag curve is diferent; max effeciency is at a higher speed

[Ollie]

Yes, and both the profile and parasitic drag go up as the square of the air speed. It takes more power to fly with low aspect ratio wings because they have to fly faster to fly at the air speed where their efficiency is maximum. An electric park flier will fly longer and climb better with high aspect ratio wings.

Stubby winged aircraft have superior maneuverability. Skinny winged aircraft have longer range and greater fuel (energy) economy.

[Sail 'n Soar]

A 44 inch span and 5.125 inch average cord corresponds to an aspect ratio of 8.6, which is higher than most sport planes, but not unreasonable, I am flying a high-wing cabin job now with a 7.9 AR and about 4 degrees dihedral, RET. It's very responsive to rudder and elevator inputs, yet has an excellent glide ratio and, hence, low cruise power requirement. Your geometry isn't that much different.

The critical issue with going to moderatelty high AR's, especially constant cord ones with relatively thin airfoils, is making them structurally sound without excess weight. Unless you have a specific design reason for chosing the 44" span, you might consider going to on the order of a 37 span by 6 1/8 inch cord wing. This would result in approximatly the same wing area and an aspect ratio of ~6, which will still give relatively low induced drag, a little lower profile drag due to the 20% higher Reynolds number, and a lighter required wing structure. It will also be more responsive due to the shorter span. Other than the slightly higher induced drag, all of these changes are good.

[citabria]

Wow I thought this thread was long gone. I'm glad I stumbled upon it again. Since the time that I asked for advice I have already built the wing! It's for a scale plane (Air Tractor) so the span and chord dimensions were essential. I tested the awkward wing this week and it flew quite well! Stalls were predictable and (most importantly) no tip stall tendencies. There was one odd thing I noticed:

The ailerons were sloppy for coordinated turns. The plane would hesitate before it rolled. But despite this, once it finally started rolling the roll rate was amazing. Aileron rolls looked more like a short semetrical wing. I'm using sone pretty huge ailerons, and the linkaged were not that tight. The next flight I'll have everything tweeked and I'll see if the trait persists.

This build and all the input has been a great experience. I'm learning lots. Thanks everyone.

Scott