I am designing a utility / sport jet and am going to use a thick symmetrical airfoil. I would like to keep things simple, and am considering full span flaperons, ie, dropping the ailerons maybe 20 to 30 degrees for landings.

Question: will this be OK or am I better to go with dedicated Ailerons and Flaps?

Please no "armchair theory experts" I would like to hear the opinions of those with some actual design and/or flight experience...

Thanks,
Andrew Coholic

Hey Andrew, why would you want to increase the effective angle of attack at the wingtips? The advantage of flaperons is the ease of installation, but the safer method is definitely the independent installation by forcing the inboard portion of the ring to stall first. The aircraft will be far less likely to tip stall with independent design and you will probably wind up being able to slow it down further on landing...

Then again, you could compromise in the middle and have the ailerons droop slightly as the flaps are deployed, although not to the same extent. I have a custom made prop plane with a setup like this. I can dive it from 100ft up, 100ft out and still land it...

Kelly

Andrew,

If the goal of your flaperons is to increase drag you might consider using them to reduce lift instead. Kick them up like we are doing on our Bobcats. Using them as "spoilerons" helps to reduce the lift, increase drag, and has the added bonus of increasing stability all at the same time. (Wash in instead of washout)

DavidR wrote:
and has the added bonus of increasing stability all at the same time. (Wash in instead of washout)

HUH???? Wash in increases stability??

Please explain...

Kelly,
I know about the possibility of tip stalling while using full span flaps, but since the wing is a constant chord with thick airfoil, it would/should stall near the root first, right?

David, I was hoping to add some lift not only drag - I am familiar with that spoileron mix on some of my 3D prop planes to bring them down in a hurry, but I want to shorten the take off and landing roll mainly for a short field.

Basically I want to save having two more servos in the wing, but if it IS better for the separate flaps and ailerons I can certainly do it.

If thats the route I choose, would 1/3 of the span as aileron and 2/3 as flaps be wise or shoudl there be more aileron than flap? My surfaces are going to be 4" wide and the chord of the wing (including movable surfaces) is 15 inches.

Thanks,
AJC

I thought drooping the ailerons relative to the root would equate to wash-in and raising is wash-out, or am I mistaken?

If the flaps are large and the ailerons still droop down albeit less than the flaps, the effect still could be called washout because the angle of attack is still seen as less at the tip compared to the root. It just depends on how much of a parachute you want it to be. David's lift spoiling approach would make it less likely to hop back in the air once it has touched down and the chance of a tip stall is very low. The mega-lift approach may have a problem there with not settling down and the increased drag may cause a flame-out landing to stall out and fall short of the strip.

Either way, I think the majority is already pointing towards an answer of independent control surfaces... If you build them separate, you can play with the geometry and find what's best.

Kelly

Hi Andrew,

Her'es my 2 cents...

Separate Aileron/Flap
Pros:
- Better aerodynamics. Ailerons more effective at the tip, inboard flaps promote stability.
- Flaps more effective (drop them further - or build slotted flaps)
- Reduced adverse yaw. (just because you use a symmetrical airfoil don't think you'll get away without it)
- Looks better (IMO )

Cons:
- More complex. Requires more servos, more planning, better execution.


Flaperons
Pros:
- Foolproof to install. You almost can't go wrong and it's really easy to produce a good quality installation.
- Sturdy.
- Simple

Cons
- More drag / Aerodynamics not as good.
- Less effective as flaps.


You say you're designing a utility/sport jet and you'd like to keep things simple. I would go the flaperon route if I was you. You want to be able to produce the most slop free installation (flutter isn't fun) so you shouldn't even consider a 2 servo wing that has separate ailerons/flaps. You can't beat flaperons for simplicity and low cost. I wouldn't worry about stability because a rectangular planform would stall first at the root even with flaperons.

Since you're using a thick airfoil I wouldn't expect a great increase in performance (read: reduction in stall speed) while using flaperons because: a) plain flaps are not really effective, b) you can't lower them all the way (say 30 deg max).

The 2/3 Flap, 1/3 Aileron proportion is good. Look at some GA airplanes, you'll see that these are the proportions they use. You'll be surprised at how little ailerons you actually need.

4" on a 15" chord sounds very large to me. Be sure to counter balance your surfaces and make sure you use good quality linkages. At the speeds jets fly large surfaces can be a liability IMO.

In a small UAV we're building in my university we're using flaperons as well. We could'nt find any reason to install separate ail/flaps as we have a very long runway to use

It all boils down to simplicity vs. performance. You can expect a marked difference between the two setups in both categories. What you really need to do is decide what's more important for you.

Good luck and keep us posted.

Originally posted by erazz:

"It all boils down to simplicity vs. performance. You can expect a marked difference between the two setups in both categories."

Andrew,

ER is right on the money. I have owned and flown BVM D/F jets from the early Sport Sharks through Aggressor III and Ultra Vipers. By the time I got the first Ultra Viper, I knew of the benefits of separate flaps and ailerons because my flying buddy Vernon had the flaperon setup on his first Viper. He never liked the way it handled in the landing pattern with the flaperons. It just wasn't as stable and predicatble as the Aggressors with separate flaps. When I built my first Ultra Viper, I installed separate flaps and ailerons on it. It made a huge difference in the handling of the aircraft. The Ultra Viper becomes a rock solid flyer at any airspeed all the way to touch down when using separate surfaces. The flap/aileron length is 20 inches on the Ultra Viper. It is split 50/50. That arrangement has worked very well for me on two Ultra Vipers. I set it up this way because BVM split the F/A 50/50 on the Agg. III. I just went and measured the Bandit. It measures F/A total length 24.5 inches with the aileron 11 inches. BV knows how to design great flying jets, so this should be a pretty good setup.

Hope this helps.

Dennis Lott

What I meant was washout will give more stability not wash in.

A couple more minor points to consider:

1) Separate flaps & ailerons allows you the option of crow-flaps.

2) Flaperons 'up' for landings does give extra drag, but it also raises the stall speed, so you have to land a little hotter.

For some of your other questions about how much flap vs how much aileron etc - if you don't get the answers you need here, try asking in the aerodynamics forum, or drop an email to Bob Parks (I can send you his email addy if needed). Bob's a certified genius as well as a heck of a nice helpful guy

Gordon

OK guys I can see the answer is probably to use separate surfaces... which is what I thought would be better

I think for the plane I am working on the flaperons would have been OK but best be safe and go for the extra two servos and separate flaps.

I very much appreciate all your replies - thanks again!

AJC