Would slotted flaps still be effective in a light wing loaded model?

Would allow for an even Shorter Takeoff and landing?

Yup.

banktoturn

Ah, a man of few words....

Or you can KISS and use a higher camber airfoil and more area in the first place. As long as a fast cruise speed isn't a requirement. Any why would it be? You going places other than back to the flying field? Get yourself a copy of Profili and look into some airfoils in the 12% thickness and 6% camber range. Use one of those. I recomend the Gottingen 500 or 501. Have the 501 on one model and it's a delight to fly slowly with a very soft stall when it does happen. Lot's of warning before the stall too.

I agree, I had a goldberg eaglet 50 that was very light... it was a delight to fly low and slow... then my cousin rebuilt it with monster slotted flaps to make it even slower... all it did was increase the weight and turn it into a pig with all that drag. It couldn't even be landed with full flaps power off, but the 45 degree approach was kind of cool. Later I built a heavy lift plane with the gottingen 501 and Junkers style flaperons trailing below and behind the wing... it was great without the flaps down, but with the flaps down it was a pain to fly with all the drag. To get the benefit of the flaps you have to fly behind the power curve with substantial power on. That means lots of prop effects, lots of adverse yaw ect... very difficult with an RC. If you want a high lift device that doesn't add weight and is much easier to handle go with leading edge slats. I mounted fixed leading edge slats to a balsa USA stick 40 and I could fly it at 30 degrees AOA... again behind the power curve and fairly tough to do, but much easier then using flaps. Flaps actually lower stall AOA so you end up having to be very careful flying close to stall.... slats on the other hand increase stall AOA and make slow flight much safer and predictable.

Ty

I think a lot of it has to do with how MUCH flap angle you use. Ty, did you ever try using only about 15 degrees just to extend the low speed without adding the gobs of drag? Or was the model so slow already with the 501 that you didn't notice anything until you were into the high drag side of things? With the almost "built in flaps" of the 501 I could see something like that happening.

Yep...

One of my flying buddies, Greg Weeks, built a Senior Telemaster, which is a floater of course. I talked him into putting slotted flaps on it, since he wanted to try them on a future, "fancier" model. This airplane will not hardly come down! It's a fantastic touch and go machine, good for a relaxing period of flying at the end of the day.

I like slotted flaps on heavier models for the obvious reasons, but on a light model... Wow.

Okay, so Slotted flaps still have effect....

I'll expand my question a bit...

Are there features used on high wing loaded models which you would not recommend using on a light loaded model?

I am asking just to cover all the bases.


TIA, lunaticuav

lunaticuav,

The effectiveness of high lift devices is generally not dependent on wing loading, so you can assume any of them would be as effective for your lighly loaded wing as they would be for a more highly loaded wing. The only question is whether you need them. If you want to implement slotted flaps, or any other high lift device, so you can fly even slower, or just for fun, go for it.

banktoturn

Funny, I don't hear that a lot.

I know, your answer caught me off guard and caused a bit of a chuckle. Usually you're just as bad as I am at wordy answers...

Bruce,

I did experiment with low deflection angles on the flaps with the gottingen 501, and at low deflection angles it was fiarly easy to fly. The model was impressive... it would takeoff in about 50 feet with an 8lb lead weight on board... power was a K&B .65 Sportster, altitude was 5,200 ft. I found that the flaps were useful with the payload... I would put them down to a medium deflection to help on takeoff... and all the way down to 40 degrees for landing... but whithout the payload the flaps were useless... it's hard to tell the difference between an 6 ft takeoff roll and a 5 ft takeoff roll. Where they were kind of fun was slow flight into the wind.. the model could come to a hover in the slightest winds... and as long as you didn't have to turn it was easy to control.

The eaglet I talked about could only be set to full flaps at 50 degrees. The reason I didn't like adding flaps to that airplane was because even with the flaps up that extra servo and structure weight detracted from the flying qualities.

In full size design Flaps are used to minimise the wing area needed, or in other words to maximise wing loading. The higher the wing loading the better the range, cruise speed, ect... In my experience with models and high lift devices I think that light models with good airfoils like the Gottingen or Selig 1223 are more fun to fly then ones with complicated high lift devices. For me the fun with high lift devices on models was more in the design and construction then in the flying... the only high lift model I put a lot of hours on had the leading edge slots.. that was fun because it was virtually stall proof, it was so easy to fly low and slow with no worry about stalling and or spinning.

This is pretty wordy, but I have done a lot of experiments on high lift devices... both on models and in the wind tunnels at school.

Ty

I dont want to carry a lot of weight, so your suggestion would be to just choose a good airfoil instead of putting flaps on the plane. The extra lift generated is not worth adding a complicated and heavy flap system?

Got it in a nutshell Hatty. Unless you just want to play with them. Experimenting CAN be it's own reward.

Ty, very interesting reading. You pretty much summed up what I found with my flap experiments on the couple of occasons I tried them.

Our models don't have to cruise at a high and efficient speed for most of the time in the air and then slow to a speed that prevents overrunning the available runway like full sized aircraft do. Flaps on the big ones are there for a reason that we just don't have to deal with USUALLY. The only model category that uses speed control flaps to a great advantage is modern sailplanes. But they have set up the competition tasking so tightly that they NEED them to fullfill the tasks with a decent degree of control. It's all about picking the right tool for the job. I'm not considering coupled flaps and elevators in this as those are a special case. We are talking about speed and lift enhancements for slow speed flight here.

Don't think the complexity and weight of flaps helps at all on a lightly loaded airplane... slotted flaps usually are intended to increase wing area of a highly loaded wing, decreasing approach speeds and runway required. So now you can land and roll out in 10 feet instead of 12??

Another "issue" would be that further lowering a lightly loaded wing's loading makes it more susceptible to gusts on landing....

Overall... bad idea, IMHO...

HTH

Jim