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Flight Control "Harmony"

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N804RV

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I was talking to a friend, who's raced at Reno, about building a fast homebuilt airplane. I mentioned the GP-4, and he told me about his experience flying one and trying to fly formation with one. He said the flight controls were not well harmonized. He explained that pitch and yaw were not too bad. But, that roll was just too twitchy. He said the airplane was exhausting to fly because of this, and it was not a good aircraft for formation flying.

How would one go about fixing this? Is there a good book on the topic?
 

pictsidhe

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I read an investigation into a light aircraft crash, maybe an LSA. The aircraft was know. To have very light stick forces. It was believed that th pilot of that aircraft had knocked the stick forward while rooting around for something in the cockpit, causing his ejection. First time his harness, then canopy. Seems like a good advert to have sane stick forces to me...
There is an old mil standard for suggested stuck forces. This was based on American work started in WWII. To achieve those stick forces is control surface design. Are you wanting to fix an existing aircraft, or design a new one?
 

Victor Bravo

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Is there a good book on the topic?
I'd suggest the RV assembly manual :)

In my limited experience (RV-3 only) Van's airplanes are known to be a pretty solid guarantee of world class control harmony.

So whatever he does should be looked at as something to strive for in whatever your fast airplane discussion becomes.
 

Tiger Tim

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I used to teach in a nifty little low-wing that had well harmonized controls. The way they find-tuned that harmonization was to add what they called a balance tab to the elevator. I forget if it was a servo tab or anti servo but the idea was to bring the stick forces for pitch and roll in line with each other.
 

plncraze

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One of Flying magazine's Aftermath columns was about the GP-4. Garrison spoke with Mr. Pereira who verified that some of the flying qualities required experience to deal with.
Darrol Stinton has a book on flying qualities. That might provide some guidance. Also look at the NACA tech reports on handling. Sometimes the trailing edge angle can be modified to change the feel.
 

delta

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Without knowing the specifics of that particular hookup, I'd guess it wouldn't be that difficult to modify the amount of throw the ailerons receive from the stick, much like moving the linkage on a RC servo inward. The designers upper and lower throw limits would have to be maintained though.
 

TFF

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Fixing it on a built plane requires rebuilding something. Decreasing the leverage of the stick or making an anti servo tab. Being a cross country airplane, it has to be flying hands off pretty well I would expect. The ones I have seen had a sharp trailing edge. The ailerons and flaps could be rebuilt to be thicker at the trailing edge. What it does to speed is up in the air.

The a Tailwind is twitchy but really does not have a bunch of excess control. Wittman wanted it like that for cross country flying. He wanted to fly with his finger because no autopilot.
 

BJC

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Van's airplanes are known to be a pretty solid guarantee of world class control harmony.
The RV-7 that I flew briefly is the fourth best handling airplane that I have flown. The S-1S is tops, and the S-2A is second, and the S-2B is third. I understand that the S-2C is up there with the -1S.
I forget if it was a servo tab or anti servo but the idea was to bring the stick forces for pitch and roll in line with each other.
Servo tab sizes and actuation ratios can be adjusted to change forces and feel. Spades can be added easier than servos in some cases, but are a PITA to adjust. Servos make a four aileron Stearman a delight in roll. Servo tabs can be a source of flutter in faster airplanes, especially after they have developed some free movement due to wear, so be cautious if you go that route.
Sometimes the trailing edge angle can be modified to change the feel.
Really nice handling airplanes have ailerons that will seek the streamlined (“centered”) position, yet have minimal breakout force. Some factors that influence handling qualities are gap seals, shape of trailing edge, bluntness of trailing edge, hinge position, progressive sealing of the area forward of the hinge, and the shape of the lower aileron surface.

Leverage and linkage ratios are important. RV’s have long sticks that require long movements. Some like that, Ibdo not. Linkages can be designed to provide more surface deflection in the first part of control stick motion, or less.

Note that lots of HBA with cusped airfoils have ailerons that get really heavy above 170 or 180 knots. Some people like that, and some of us hate it.

This is a large subject with lots of interacting factors. A good approach might be to study the fearures of the better handling airplanes in a category similar to the GP4. One example is the Glasair with the flat bottom ailerons.


BJC
 

fly2kads

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As for books, I second Darrol Sinton's "Flying Qualities and Flight Testing of the Airplane." In addition to some academic treatment, there are numerous stories from his flight test career thrown in, including practical application of high-tech tools like string, cardboard, and duct tape!
 

N804RV

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One of Flying magazine's Aftermath columns was about the GP-4. Garrison spoke with Mr. Pereira who verified that some of the flying qualities required experience to deal with.
Darrol Stinton has a book on flying qualities. That might provide some guidance. Also look at the NACA tech reports on handling. Sometimes the trailing edge angle can be modified to change the feel.
Is this the article? Walking on the Wall
 

plncraze

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Go to an engineering library with a reciprocal arrangement with your local library and check out a copy. Be very careful leaving it too close to your scanner. You could suffer electronic osmosis of information on to your hard drive.
 

N804RV

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Maybe it's his formation flying technique?
I suppose it could be. Since I witnessed him qualifying and competing at Reno, in the Sport class, I tend to think he has at least some level of formation flying proficiency. You have to demonstrate that before they'll even let you participate in the rookie school.
 

Daleandee

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I've heard lots about the harmony of the RV series of kits. Seems that Dick VanGrunsven fella is pretty sharp. ;)

The Sonex is a fun airplane to fly and the controls are light. The pitch is lighter than the roll and it has lots of rudder authority. On the Sport Acro model they shortened the flaps and lengthened the ailerons to increase the roll rate.
 

Vigilant1

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The Sonex is a fun airplane to fly and the controls are light. The pitch is lighter than the roll and it has lots of rudder authority. On the Sport Acro model they shortened the flaps and lengthened the ailerons to increase the roll rate.
I'd say the handling of my Sonex is what I like best about it. The plane is very responsive, but certainly not twitchy. Pitch: My plane exhibits only very slight positive static pitch stability. The nose stays close to where it is put even with significant airspeed changes. Not so busy as to make it uncomfortable to fly cross country, but even with good trim technique, no one should expect to eat a sandwich and work a Sodoku and have the plane remain on altitude.
 

TFF

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I be he is trying to fly a tight formation for pictures, and I bet he is getting in wake turbulence. In that situation it’s tough noogies. It’s just the wrong type of plane for that.
 

Pops

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I hate flying an airplane that fly's like you are driving a dump truck. Never flown a Pits S-1 , just a Smith Mini-plane. I like the RV-4, I hear that the RV-3 is better, but never flown one. My Falconar F-12 was close to the RV-4 but the ailerons was just a little heavier. After putting gap seals on all the control surfaces the ailerons become better but just not quite as good as the RV-4, but close. Gained 17 mph in cruise with all the gap seals.
The F-12 stalled a lot like the reported GB-4 before installing the stall strips on the leading edge of the wing. Either wing would drop almost vertical and would spin in either direction. Very easy in and very easy out. No stall warning except for the high AOA. The reason I flew the pattern at 95 to 100 mph until on final.
 
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