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C206 and Robertson STOL

All good info. I am currently in Texas transporting an aircraft. Will respond when I get home. Dave, let's talk on the phone.

Doug
 
Dave Calkins said:
Lots of ways to make this go. If I were Doug, I would be adding this to my RobbySTol 206 wing. I did it to a Cub with drooop ailerons, and it was a success. I have not even fiddled with it since the first flight,,,, it JUST WORKED! The scariness of a lightweight droop-aileron Cub with dubious control of roll and being left hanging with only rudder to save a prang is GONE if you have roll spoilers.
Click to expand...

What style of spoiler did you use on the Cub? Where did you place it on the wing? How far back from the leading edge?

It is interesting that the drooping aileron systems, which have been STCd by the FAA, were approved without some sort of spoiler control, especially with the large amount of roll control loss that is noticed with these systems. This being a system that is designed to lower stall speeds also reduces control effectiveness because of less air flowing past the controls. After all everyone should know that the up aileron has more effective force than the down aileron. You take away the up travel and you loose the "lift reduction" while increasing the down travel increases the angle of attack thus increasing the stall speed of that portion of the wing.

I'm sure that Doug will come up with a very workable solution. His slotted flaps are proof that he gets it.
 
Helio-style blade sticking up through a slot in the top of the wing. About 3 inches aft of the front spar. Several wing-rib-bays in from the wingtip. Cable actuated, spring return. Actuate in the last third of the control stick travel. Actuate coupled to ailerons ONLY WHEN DROOP is selected.

You made a statement above, not sure what you mean. "... increasing the down travel increases the angle of attack thus increasing the stall speed of that portion of the wing." Is that what you meant. "increasing" stall speed? Surely not.

Anyway, Doug and I have talked about stuff for a few years now. You are right, "he gets it".

MikeMCS, personally, I would rather stay away from electric gizmos unless there is zero chance of asymetrical deployment. Any number of pushrod, closed loop cable, or cable and spring return methods for actuation. I hate the idea of what a dead battery does to my use of the airplane. I have been there.
 
Dave Calkins said:
You made a statement above, not sure what you mean. "... increasing the down travel increases the angle of attack thus increasing the stall speed of that portion of the wing." Is that what you meant. "increasing" stall speed? Surely not.
Click to expand...

Yes that is what I meant. Though only in that portion of the wing that is ahead of the drooped aileron when that aileron is full down. Maybe the use of the term "stall speed" is not totally accurate. With full aileron deflection in one direction with the droops down, the up aileron has very little lift dump action and the opposite down aileron will make that portion of the wing have much higher angle of attack than a non drooped aileron. Thus my reasoning being that the stall speed of only that outboard portion of the wing will be higher thus reducing the desired rolling effect. So in effect the roll authority is degraded from the inefficiencies of both ailerons when drooped. Of course this will be most noticeable a minimum speeds.

I recall one time that I was checking out a new owner in a RSTOL 185 on 2790s. On very short, low final with a left crosswind just as we descended below the trees the left wing dropped and the ailerons would not pick up the wing. It was necessary to increase the power and speed nose down with full opposite rudder to salvage the landing. I feel that the left wing was partially stalled. That was close.
 
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skywagon8a said:
Maybe the use of the term "stall speed" is not totally accurate.

So in effect the roll authority is degraded from the inefficiencies of both ailerons when drooped. Of course this will be most noticeable a minimum speeds.

.
Click to expand...

I'll buy the above statement.

I would argue the statement "...increasing the stall speed..". in the context above.......That's all I meant. The rest is reasonable. I was just trying to see if you meant what I thought you said. In your descripton of the checkout scenario, is it possible that the left wing was in a rotor from the edge of the trees?? Just a question.

..anyway, this roll authority issue from a very slow flying a/c can be fixed by more "differential" aileron throw, and also a roll spoiler.....been there, done both of those ideas..works well. Will do it again.
 
Dave Calkins said:
I'll buy the above statement.

I would argue the statement "...increasing the stall speed..". in the context above.......That's all I meant. The rest is reasonable. I was just trying to see if you meant what I thought you said. In your descripton of the checkout scenario, is it possible that the left wing was in a rotor from the edge of the trees?? Just a question.

..anyway, this roll authority issue from a very slow flying a/c can be fixed by more "differential" aileron throw, and also a roll spoiler.....been there, done both of those ideas..works well. Will do it again.
Click to expand...

There could have been some roll effect from the trees. It has been many years now since that day. Another time taking off in very large high gusty wind driven waves using 30 or 40 degrees of flaps to get out of the water, I totally ran out of right aileron just after breaking water. The only way that I could raise the wing tip, which from my perspective was between the waves, was to momentarily quickly raise the flaps to get more rudder effectiveness. No crosswind this time. The droops and extra flaps were used to reduce the pounding. Of course this combination allowed the plane to fly at very minimal speeds.

Yes Dave you and I are on the same page. There should be some type of spoiler combined with the droops. I don't have a lot of time in a 206. Those wide chord ailerons should work better at low speeds.
 
...have seen a guy come off the water on a very high-wind day, get airborne nose high, and roll over and into the water. No RSTOL, just high, gusty wind, and in the air nose high. We gotta be careful no matter what magic carpet we drive.
 
The C208 Caravan has roll spoilers that work seemlessly with the airlerons. Could that archetecture be adopted for the 206 or 185?
 
Lasater said:
The C208 Caravan has roll spoilers that work seemlessly with the airlerons. Could that archetecture be adopted for the 206 or 185?
Click to expand...

Great question.

The carvan ailerons don't droop, so getting an "up" spoiler command when an aileron on that side of the a/c is "down" is the difference from RSTOL to Caravan......

That's the trick...figuring it out is not rocket surgery! A belcrank here, some differential there, a pushrod over here.............

.....and being able to select flap withOUT drooping the ailerons could be useful......however, with the one I have done with roll spoilers and lots of aileron differential, I always use droop aileron for landing, so far....up to an 18MPH crosswind. I do not bother to turn the droop off.
 
Just as an added bit regarding aileron authority when on floats: Landing is pretty simple. If you have a gusty crosswind, stack on a little extra speed and simply run the airplane onto the water at higher speed.

The TAKEOFF is what's going to bite you if you're not careful, and I've spent a few nights sleeping in airplanes when I landed somewhere I should never have landed, waiting for the wind to die down or change direction.

MTV
 
mvivion said:
Just as an added bit regarding aileron authority when on floats: Landing is pretty simple. If you have a gusty crosswind, stack on a little extra speed and simply run the airplane onto the water at higher speed.


MTV
Click to expand...

this brings up another "problem" with the RSTOL. Because the Robby is so awesome. :) ...........Because the whole trailing edge is drooped the aircrafts pitch attitude is much lower (nose is lower than stock) when you "run it on with higher airspeed".....and you will be up on the toes of the floats if you run it on with more than "...a little extra...".

...just saying. I heard it said once.
 
I am back home, I can start thinking about important things again like this project.

I am not the first person to think of or do this. I talked to a guy in Seattle that did this 20 years ago. He was trying to get a STC and decided it was too much work. He said it made a great performer but the tail did shake. The tail shake is a sign of buffeting and indicates that the horizontal tail is too small for the added pitching moment. 20 years ago VG's were not widely used and I think that with proper use of VGs and or the use of a reverse horizontal leading edge cuff, I may be able to counter act this.

If I used a lighter power plant and or moved the power plant aft so that the empty weight CG is moved aft, the tail shake will be reduced. From the Lycominga nd Contenital literature I have read, the parallel valve O-540's like the C4B5 model are lighter than even the O-470s. I think Bart could easily get me 300 HP out of a high compression IO-540-C4B5 engine. Still debating on the engine selection,which is a ways off yet. I like the idea of the MT prop, but am concerned about its ability to withstand the harsh environment I intend to use it in. There is a problem with using large diameter props on the Lycoming engines, more investigation is needed.

Adding droopy ailerons will only add to the pitching moment problem. With the reduced roll authority, added pitching moment, and added weight, is it worth it? Dave, I get the spoiler idea and am interested, but I want to keep the airplane simple and light. If the project gets heavy it will not perform to my expectations. Added electrical motors to deploy droopy ailerons sounds more complicated and heavier than I may be able to swallow. I have already added a weight penalty with the206 wings, wing extensions, and sportsman cuff. I cannot let the weight get out of hand, it will already take a lot of work to offset the wing mods.

Today, I am thinking of not doing the droopy ailerons, but I could have a whole new outlook by morning. Thinking about all this stuff is half the fun.

Thanks everyone for all the input and encouragement.

Doug
 
Doug, 206 wings on a 180 will be very cool. You do it without the Robby and there will be alot of performance "left on the table".

You'll get smoked by a droop aileron 180.
 
'cause an empty 185 with a RSTOL is pretty impressive.

I've yet to be "impressed" by an empty 206 as much as by an empty RSTOL 185. I guess I've never driven an empty 206, probably never saw one empty either.

Personal Opinion. D
 
Don't know the weight penalty off the top of my head but I could look at my 337 if that would help.

My 206 with Robertson and sportsman is the only a/c I've flown that, (and I've flown a lot of different types), is the least effected by load. It makes very little difference if I'm alone in the aircraft or at full gross, it just seems to work. I flew this aircraft over 30 hours this week in variable load conditions and in some pretty wild crosswinds for takeoff and landing and it seems to always leave me with a smirk on my face. I've flown with many different "observers" in the last several years that have had considerable experience in other 200 series cessnas and they are typically the first to make comments on performance.

206 with Robertson, sportsman and seaplane rudder is a combination that for our use is pretty hard to beat.

Ray
 
ksecub said:
Adding droopy ailerons will only add to the pitching moment problem. With the reduced roll authority, added pitching moment, and added weight, is it worth it? Dave, I get the spoiler idea and am interested, but I want to keep the airplane simple and light. If the project gets heavy it will not perform to my expectations. Added electrical motors to deploy droopy ailerons sounds more complicated and heavier than I may be able to swallow. I have already added a weight penalty with the206 wings, wing extensions, and sportsman cuff. I cannot let the weight get out of hand, it will already take a lot of work to offset the wing mods. Doug
Click to expand...

You are correct about the pitching moment. The droop STC on my plane is placarded "Use aileron droop for take off only". When used for take off and initial climb only, the pitching moment is a non issue. When used during landing there is a noticeable reduction in up elevator and trim effectiveness. There is only one electric motor in the system and it is really not that complicated. The stall and take off speeds are reduced by 5-7 knots with the ailerons drooped. I have had both the wing extensions and drooping ailerons for about 30 years on my 185. Each was installed at different times. They both are worth their weight in gold and I would feel lost without them. My heavy amphibious 185, when lightly loaded, will leave the water indicating about 38 knots. It could not even approach this without the droops. When operating "heavy", it makes the difference as to whether it will fly or not.

If I were you I would use the Cessna cuffed leading edge and forget about the sportsman cuff. The few planes which I have flown with the sportsman cuff have all had slower cruise speeds than those with the Cessna cuff. Yes, the pre 1973 Cessna leading edge does need a small cuff for better over all performance. The latter ones seem to have the best cuffed performance.

How about a 206 sized horizontal stabilizer and elevator built to use a 185 trim system? Would that counteract the extra length of the 206 flap generated pitching moment? Or would the attachment structure in the aft fuselage require too extensive modification?

What were the conditions that the guy in Seattle had that caused the tail shake? How much flap deflection? How much power was being used? Landing? Take off? What CG was he operating at?

Keep up the program. I am curious as to how it works out.
 
I should add that the drooping ailerons are very helpful after take off while climbing out of a hole. The flaps can be retracted to reduce flap drag while leaving the ailerons drooped. The plane just seems to levitate. The angle of climb is greatly improved over a no flap/droop climb, without being on the back side of the power curve. This seems to be better than using 10 degrees of flap and no droop. There is no down wash from the flaps over the tail. A Robertson STOL kit can not do this.
 
That regime....drooped ailerons, retracted flaps..has always seemed scary to me because you are flying an airplane that has the wing effectively "washed-IN". It would seem that if the a/c stalls during that climbbout, it will not stall straight ahead......because it a the wing tip that will stall before the wing root, and roll you over.

...never done it, though.

What do yo think, Skywagon?
 
Dave Calkins said:
...effectively "washed-IN". It would seem that if the a/c stalls during that climbbout, it will not stall straight ahead......because it a the wing tip that will stall before the wing root, and roll you over.
Click to expand...

Dave, in my above scenario, the speed would be well above stall, around 70 knots or so. I do not agree that during a stall the droops would cause one wing to stall before the other. I will agree that the ailerons will likely, or could, loose roll control effectiveness before the rest of the wing stalls. If one wing stalls before the other as described above, it would be because of the effects of the P factor and rudder combination not being coordinated. I do not recall having done stalls in a droop only configuration. If I did, it was many years ago. I'll have to explore this next time I am flying around. I wonder what it will do during spin recovery? Maybe I should try that too? Though ailerons are not generally used during spin recovery. Both ailerons up or down should not make much, if any, difference. One up and the other down has an effect.

Many years ago I installed a set of 2000s on a 18 at Birchwood and flew it off a trailer. The rear strut forks were screwed all the way in. I questioned the owner about this and he said that everyone does this to shorten the take off. He was not concerned with any of the disadvantages.
 
skywagon, I simplified my point. But let me simplify it again.....:)

This is nothing new to you or any of us.....Stability in a stall....If the outboard portion of a wing stalls before the inboard portion of the wi...ng.....aw, heck, nevermind...........perfect pilots will always have the ball centered....and perfect mechanics will always tune an aircraft to fly perfect and straight, so......

.....yeah, nevermind:)
 
Ksecub what happened to your 206 wings on a 180 fuselage project, this is something I have wondered about for years. Sounds like a cool project.
 
Dave Calkins said:
this brings up another "problem" with the RSTOL. Because the Robby is so awesome. :) ...........Because the whole trailing edge is drooped the aircrafts pitch attitude is much lower (nose is lower than stock) when you "run it on with higher airspeed".....and you will be up on the toes of the floats if you run it on with more than "...a little extra...".

...just saying. I heard it said once.
Click to expand...

Dave,
Depends on the floats to a great degree. My procedure for strong crosswinds in RSTOL was 20 degree flaps and run it on. Not at all squirrelly. Done properly, of course. If you don't know the limits of your floats, explore that first


MTV
 
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