Can we have too much stability?

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Norman

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One example technique to increase stick-free stability is the servo tab in all moving horizontal tails.
Anti-servo tab.
A servo tab tends to push the control surface away from its neutral position thus lightening the load on the pilot's hand. An anti-servo tab tends to push the control surface back toward its neutral position thus increasing pilot feedback, which is often too light in stabilators.
 

Eugene

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With all your threads, it is clear you have out grown your aircraft.
No, somehow I don't feel that way. I suspect if that ever happened this project will become boring to me and to move forward wouldn't make any sense anymore. Sure there is all kinds of guys left and the right from me having nice flyable airplanes. Don't know why, but I don't get jealous. For some reason they knocking on my door and coming to see what I have accomplished again and what else is new that I learned. I don't go to them and ask where did they fly for breakfast last weekend.

My original question about possibility of creating aircraft that is too stable was pure theoretical. I realize of course that in my situation when I will be increasing horizontal tail volume from 0.35 to 0.45 and tail arm from 2.2 MAC to 2.6 I am far away from that kind of "danger".

There is another real life question about stability:
Three years ago in the process of removing horizontal swept from my wings and making it straight I accomplished CG movement 2.3% as compensation for heavier 912 engine. I found one easy way to connect struts by fabricating new brackets, but I lost wing dihedral from 1.5° down to 0.8°. I was told by very smart people that high wing aircraft doesn't need any dihedral at all and because of that I wasn't concerned.

This time I moved my whole fuselage forward again to compensate for future new tail another 2 inches. Will be redoing my struts again and I need you guys to tell me what kind of dihedral angle I should go for this time.

I don't want my Skyboy to drop the wing if autopilot stop working. I want it to fly better than Bonanza!!!;)
 

User27

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Stick pressure can be reduced with large aero balance surfaces on the elevator or moving the pivot aft in the case of an all flying stabilator.
Indeed, but balance surfaces are destabilising stick free - everything is a compromise. The aircraft I'm referring to had (variables gearing) servo tabs on the elevators to reduce stick load and very large spades on the ailerons. The spades as designed were too large and gave almost no feel, moving the spade plate aft slightly made it much easier to be precise in roll still with low stick forces throughout the envelope.
 

Tiger Tim

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With all your threads, it is clear you have out grown your aircraft.
On a more philosophical front, why couldn’t or shouldn’t one remake their Ship of Theseus - Wikipedia as a speedboat, or a battleship, or whatever suits what they want?

In a more grounded and aviation context, while you have accomplished clean-sheet designs coming from the likes of Rutan and such, there are also good performers changed one piece at a time from their source airframes. I’m thinking of planes like Draco and Voodoo which I think are both widely revered for what they could do.
 

Aesquire

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Why get a different plane? He's got a plane, a hobby, and he's learning. What more can you ask? ( except a backup aircraft, for when yours is in the shop )
 

Eugene

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Why get a different plane? He's got a plane, a hobby, and he's learning. What more can you ask? ( except a backup aircraft, for when yours is in the shop )
Thank you! Three years ago I checked out in local rental airplane. Never used it, even once. So, option for flying is always there at $120 an hour.

Will anybody tell me what kind of wing dihedral I should settle for? Should I change it back to original 1.5° ,or go for more?
 

Heliano

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Norman, you are 100% right: anti-servo. I've just used a generic reference to servo tabs. Hinge forces in an all-moving tails are generally light if not inverse, depending on the cordwise position of the hinge, type of airfoil, tail angle of attack, airflow downwash, existing bob weights, etc.
Eugene, you mentioned "I was told by very smart people that high wing aircraft doesn't need any dihedral at all". IMHO yes, it is generally close to the truth. What causes the so-called "hi-wing dihedral effect" in a hi-wing aircraft is the distance the CG is below the wing. The farther it is, the more dihedral effect you have. Now if your engine is above the wing, may be you need some (little) geometrical dihedral.
 

Eugene

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Now if your engine is above the wing, may be you need some (little) geometrical dihedral.
Thank you, I really like this explanation. I remember landing my aircraft few times in the relatively gusty conditions. It felt like wind is trying to flip me over and my workload of keeping wings level was unbelievable. Maybe I will go back to 1.5° just to make sure I did everything right. Remember I wanted to be better than Bonanza!!!

Of course maybe my small tail has something to do with that as well
 

TarDevil

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I want it to fly better than Bonanza!!!;)
Goodness! All this Bonanza hate! 😁

I'll say I was grateful for the autopilot flying that thing IFR, and it wasn't all that challenging without it. IFR in my Sundowner was a lot more relaxing, though. But in gusty cross-wind landings I'd sure rather be in the Bonanza than a C172...with the following exception:
Flying alone the Bonanza felt fairly normal in pitch, but anything you put in the cabin was aft of CG and after burning off fuel, the elevators got quite light with passengers and baggage.
(BTW, I heard from a good friend that the Bonanza performed delicious rolls!)
"Too stable" was taking my ex-wife's seriously overweight cousin for a ride in a C172 on a relatively short runway. I learned quite a lesson about stability and elevator authority on that take-off.
 

TFF

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So you are going to build yourself a King Air. You have to decide what is better. I don’t have the budget for a Bonanza, but there isn’t a better designed airplane. Maybe equals. Definitely different styles and needs, but not better. I personally would like the original in polished aluminum with red stripes. If you gave me a G 36, I’m probably not giving it back. The aerobatic version would be nice to own too. You have to be way more specific to describe better. Better has nothing to do with who owns them.
 

Eugene

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So you are going to build yourself a King Air. You have to decide what is better. I don’t have the budget for a Bonanza, but there isn’t a better designed airplane. Maybe equals. Definitely different styles and needs, but not better. I personally would like the original in polished aluminum with red stripes. If you gave me a G 36, I’m probably not giving it back. The aerobatic version would be nice to own too. You have to be way more specific to describe better. Better has nothing to do with who owns them.
I was kidding of course when I mention comparison of my airplane to Bonanza. For many years I was dreaming about getting myself J model from 1957. I do understand that for many years this airplane was absolutely flying Mercedes comparison to everything else that was produced out there. In-flight felt like mini airliner.
I was absolutely in love!!! I can sit and watch Bonanza cycle gear up and down and it will be much better than sitting at the strip bar and looking at those girls!!! Just like any other airplane, I have many questions, 3.5 inch CG range is one of them.

Later I discovered that certified world is unbelievably expensive and somewhat boring. Experimental world is much more affordable and much more creative!!!

Trying to do everything right as much as I can and that is the only reason for all my questions. Didn't mean to offend anybody. Sorry
 

Jimstix

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The true test of stability is handling qualities as defined by the Cooper-Harper pilot opinion rating score. 1= excellent, 10 = uncontrollable, with the worst "acceptable" score of 7. Airplanes like the C-172 are often rated as "1" (excellent, highly desirable); Bonanzas sometimes get a rating of "2 or 3" (good to fair). Unless your stick-and-rudder skills are well above average an airplane with a C-H rating of "5" or higher will at least be unpleasant to fly and at worst, kill you.
 

Eugene

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The true test of stability is handling qualities as defined by the Cooper-Harper pilot opinion rating score. 1= excellent, 10 = uncontrollable, with the worst "acceptable" score of 7. Airplanes like the C-172 are often rated as "1" (excellent, highly desirable); Bonanzas sometimes get a rating of "2 or 3" (good to fair). Unless your stick-and-rudder skills are well above average an airplane with a C-H rating of "5" or higher will at least be unpleasant to fly and at worst, kill you.
So, can we make a statement that reason Cessna 172 is so stable because of two things 100% of its weight below the wing and 1.5° dihedral? This way if you move engine above the wing you couldn't compete with a Cessna in this department anymore.
 

BJC

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The true test of stability is handling qualities as defined by the Cooper-Harper pilot opinion rating score. 1= excellent, 10 = uncontrollable, with the worst "acceptable" score of 7. Airplanes like the C-172 are often rated as "1" (excellent, highly desirable); Bonanzas sometimes get a rating of "2 or 3" (good to fair). Unless your stick-and-rudder skills are well above average an airplane with a C-H rating of "5" or higher will at least be unpleasant to fly and at worst, kill you.
Those handling qualities ratings should be referenced to a type of flying. Good IFR qualities are very different from good aerobatic qualities. Personally, I consider the C172 to have poor handling qualities. YMMV.

BJC
Looks like best selling LSA also have 1.5° dihedral.
The best reason to have some dihedral in a high wing is to improve fuel flow from wing tanks. BJC
 

Pops

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Each airplane is designed for a mission. Some towards having aerobatic performance and handling and some towards the stable end. The aerobatic handling makes a poor airplane for an IFR airplane and the same way around. A very stable IFR platform airplane is going to have poor aerobatic handling.
I have flown about every Beech airplane below a KingAir and don't care for the very stable handling, but they make for a good IFR platform.
Same for the Mooney's. Bellanca Super Vikings are somewhat better in handling than the Mooneys.
I'm more like BJC, I like a more neutral handling airplane. For me, the best handling airplane that I have flown is the RV-4. Put it where you want it and it stays there until you put it somewhere else. Never flown a RV-3, but I have been told its even better.
Single engine Cessna's don't do anything excellent, but they do everything well. Just a good middle of the ground airplane. Same for a lot of the Pipers. Cessna made some duds, same for Piper and same for Ford and Chevy.
 

TFF

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The 172 can build skills in two ways. One is the standard crawl to walk training. Two is walk to run, but it is rarely used this way, mainly because it is stuck in the first, or owners of 172s want to stay in the first.

Walk to run is because it is so stable, you really have to horse it hard and precise to get all out of it. I was watching a movie where the stunt man about 4-5 ft in the air danced the main gear left, right, left, right all the way down the runway during the big chase scene. Silly but it was impressive. That is what the next step is supposed to be in such plane. No one ever learns the real next step.

Light controls are delightful, but they can be just as much a skill crutch as the other. A 150 Aerobat makes you force the plane through a maneuver. No it can’t do a bunch like an Extra, but when you have as much “power steering” as an Extra it ain’t that hard as long as your body can take it. An Extra supposed to be flown to the point that the pilot is working as hard as the Aerobat pilot. An Avalanche in an Aerobat is a Lomclovak in an Extra. Both pilots are sweating it to get it right
 
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