Can we have too much stability?

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flitzerpilot

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Pops, a mission statement for a Flitzer would have to consider the phrase 'dual personality' in its handling description.

The useful CP migration of the USA 35B foil of between 45% and 30% of MAC between cruising flight and an active pitching manoeuvre alters the feel totally: from rock steady, hands-off stability at Vc which makes for relaxed X-country navigation to extremely active in-pitch manoeuvrability, which includes steep turns. Recovery from max stick travel/positive or negative pitch displacement at trimmed cruise results in a return to level attitude hands-free with no excursion through level flight attitude, ie. fully-damped. Control feedback is 1:2:3 in terms of aileron:elevator:rudder which is almost ideal (on the prototype at any rate). Controls are light but not over-sensitive. Trim on the prototype is via rpm as fuel is burned.

So I would respectfully challenge the idea that an aeroplane can only be one thing or another in terms of control, stability or manoeuvrability. I have tried to maintain these qualities through the various Flitzer evolutions with good results so far.

Kind regards,

Lynn
 

Richard Roller

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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.
(BTW, I heard from a good friend that the Bonanza performed delicious rolls!) Yes they do!
 

Pops

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Pops, a mission statement for a Flitzer would have to consider the phrase 'dual personality' in its handling description.

The useful CP migration of the USA 35B foil of between 45% and 30% of MAC between cruising flight and an active pitching manoeuvre alters the feel totally: from rock steady, hands-off stability at Vc which makes for relaxed X-country navigation to extremely active in-pitch manoeuvrability, which includes steep turns. Recovery from max stick travel/positive or negative pitch displacement at trimmed cruise results in a return to level attitude hands-free with no excursion through level flight attitude, ie. fully-damped. Control feedback is 1:2:3 in terms of aileron:elevator:rudder which is almost ideal (on the prototype at any rate). Controls are light but not over-sensitive. Trim on the prototype is via rpm as fuel is burned.

So I would respectfully challenge the idea that an aeroplane can only be one thing or another in terms of control, stability or manoeuvrability. I have tried to maintain these qualities through the various Flitzer evolutions with good results so far.

Kind regards,

Lynn
From the first time I saw a picture of the Flitzer I liked it. Its one of the airplanes I would like to build and fly. Puts the fun in flying.
 

Eugene

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So I would respectfully challenge the idea that an aeroplane can only be one thing or another in terms of control, stability or manoeuvrability.
But real life situation is telling us that you have to choose. That you can't have everything in one package. Sounds like Cessna 172 is very successful compromise in between. But still a compromise. Going back to my driving picture, or you inside of the round tunnel, or are you on top of it, or are you on the table driving. Stable, but not exciting, unstable and excited.
 

flitzerpilot

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Thanks Pops,

I consider that praise indeed from someone with a huge amount of experience in aeronautical matters.

I should have stated too that the basic Flitzer Z-21, with its big. lower-wing located. high aspect-ratio ailerons, exhibits low break-out forces and a high roll-rate. The response is similar to that of Jungmann, while later four aileron types have an exceedingly high roll-rate, similar to a Pitts. Pitts pilots who've flown both compare the types handling-wise. Unless one were planning to enter competitive aerobatics, I don't think the four aileron examples are worth the extra time, cost and weight - but they are enormous fun. The Z-2 Schwalbe two-seater has four ailerons, but that was to ensure that the roll-damping effect of its broader, square-tipped wings, would not deliver a slower rate of roll than the single-seaters.

Looking at the Z-1 component weight list today, I note that an upper wing panel, finished, covered, doped and painted weighs 16 lbs. That is a clue to its good performance on an 1834cc VW. I attach a recent black and white image of the Flitzer Z-1R (Rotec R2800) being serviced in the field, surrounded by 'contemporary' 1920s types! :0) The other image is of the Vale Stormcock which is a Flitzer evolution, representing a light fighter biplane of the inter-war period, based loosely on the Lincock.
 

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flitzerpilot

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Eugene,

Biplanes, especially short-winged biplanes, tend to be inherently stable and do not require much dihedral. But with light controls and low-breakout forces, they can also be highly manoeuvrable: therefore to answer your question, I am neither inside nor on top of the tunnel, but the picture varies as I manoeuvre in pitch. In roll, I am stable until I wish to roll and 100 degrees/sec. is normal for the two-aileron machine. But despite much flying over time on the prototype I still find it exciting, but docile and entirely predictable and I never tire of it. It is in fact an excellent learning tool for basic aerobatics and the inherent biplane drag means that you cannot accidentally overspeed if falling out of a figure.
 

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Heliano

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Pops is absolutely right: aircraft are designed with a mission in mind. Doing aerobatics with a cessna 150 is like playing soccer with a square ball; trying to teach a newcomer to aviation how to fly on an Extra 300 is pure torture for both the instructor and the trainee.
 

mcrae0104

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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?
No, it is much more than that. Do you have a copy of Airplane Performance, Stability, and Control?

Personally, I consider the C172 to have poor handling qualities. YMMV.
Can you elaborate? Do you mean that it is a poor fit for your mission/preferences, or did you have something else in mind?
 

Eugene

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Not sure if this is related question. I think it is. But for sometime I am with another Skyboy owners scratching our head why taking passenger does transform this aircraft so dramatically. I call it "flying cow", but some guys call it "field with lead".

Here is a pretty good explanation of how CG movement affect Aircraft performance.


Passenger seat just like pilot seat positioned about 6 inches in front of leading edge. So, tail balancing load with passenger is much greater and CG moves from 36% to 24% MAC. Horizontal stabilizer incidents from the factory is 5.7° negative. Horizontal tail volume is 0.34. Tail arm 2.2 about.

If I build new tail longer and bigger will this feeling of "field with lead" while flying with passenger go away? I certainly hope that it will.

IMG_1246.jpeg
 

mcrae0104

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Yes I do. It's sitting on the shelf for some time and looking at me, but for some reason I'm not getting any smarter because of that!
I have the same problem with a lot of the books on my shelf...:)

Not sure if this is related question. I think it is. But for sometime I am with another Skyboy owners scratching our head why taking passenger does transform this aircraft so dramatically. I call it "flying cow", but some guys call it "field with lead".

Here is a pretty good explanation of how CG movement affect Aircraft performance.


Passenger seat just like pilot seat positioned about 6 inches in front of leading edge. So, tail balancing load with passenger is much greater and CG moves from 36% to 24% MAC. Horizontal stabilizer incidents from the factory is 5.7° negative. Horizontal tail volume is 0.34. Tail arm 2.2 about.

If I build new tail longer and bigger will this feeling of "field with lead" while flying with passenger go away? I certainly hope that it will.

View attachment 110502
The longer tail will extend your aft CG and improve the elevator’s authority (allowing you to trim out the heavy nose more effectively) but it will not cancel the increased stability added by the weight of the passenger.
 

BBerson

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f I build new tail longer and bigger will this feeling of "field with lead" while flying with passenger go away? I certainly hope that it will.
If "field with lead" is more stability, then it will not go away with bigger and longer tail.
But " field of lead" could be sluggish from weight. Hard to say without more precise technical words.
 
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BJC

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Can you elaborate? Do you mean that it is a poor fit for your mission/preferences, or did you have something else in mind?
Heavy controls, especially pitch when slightly out of trim, and mushy feeling in all three controls. And no, I’m not comparing it to an aerobatic airplane; I just like light and crisp controls. I don’t fly IFR.


BJC
 

Eugene

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If "field with lead" is more stability, then it will not go away with bigger and longer tail.
But " field of lead" could be sluggish from weight. Hard to say without more precise technical words.
At one time I was flying Cessna 172 with 160 hp and three big guys. I figure I was at least 200 pounds over gross. Almost all of my hours at that point was with only one passenger or mostly solo. This was completely different Aircraft and made me nervous right from the beginning on the takeoff. Plane was not responding to all your input and made a very lazy movements. "Sluggish from weight" is probably a very good description.

This is exactly how I feel in my airplane now with passenger. Feels very much overloaded and nose heavy with CG at only at 23-26%. You don't feel such drastic difference if you take passenger in Aeronca at same CG at 25%. That airplane is heavier and have less power. And why overloaded? With 200 pound passenger we are at about 1200 pounds total 440 ft.² wing NACA 4412 and 100 HP.

Something else is changing and I don't know what it is. Maybe such small and short tail needs to ride at such aggressive negative angle to generate sufficient balance in load, it is essentially acting like air scoop or airbrake? I don't know. But my hope is that it will go away. But just like everything else if you don't have an explanation, then you don't know how to fix it.

This difference made my instructor pretty nervous at first. But flying solo he felt that airplane is handling just fine.
 

BBerson

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The Aeronca Chief has a greater wing span and not effected so much adding a passenger. But add enough and it will get sluggish. The cg moves aft with a passenger, so not much trim drag.
Almost all airplanes get sluggish at gross or overweight
 

Eugene

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The Aeronca Chief has a greater wing span and not effected so much adding a passenger. But add enough and it will get sluggish. The cg moves aft with a passenger, so not much trim drag.
Almost all airplanes get sluggish at gross or overweight
So, that is perfectly normal when Aircraft feels OK at 1000 lb and being already overweight at 1200?
 

Tiger Tim

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The Aeronca Chief has a greater wing span and not effected so much adding a passenger.
The Chief also hangs both occupants right under the CG so there’s minimal if any trim change required for different passenger loads.

@Eugene compare that to your Skyboy where both occupants sit in front of the wing. Balance of an aircraft is like a teeter-totter where more weight forward requires an equal amount of push down on the tail (well, an equal moment at least). The wing now has to hold up not just the extra weight of the second occupant but also however much down force is needed from the tail to counteract that passenger. When the variable load is ahead of the CG you effectively pay for it twice in your performance.
 

Eugene

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The Chief also hangs both occupants right under the CG so there’s minimal if any trim change required for different passenger loads.

@Eugene compare that to your Skyboy where both occupants sit in front of the wing. Balance of an aircraft is like a teeter-totter where more weight forward requires an equal amount of push down on the tail (well, an equal moment at least). The wing now has to hold up not just the extra weight of the second occupant but also however much down force is needed from the tail to counteract that passenger. When the variable load is ahead of the CG you effectively pay for it twice in your performance.

I have been talking about this for almost 5 years and I still don't know what I'm talking about. So, let me disagree, and let's see what happens.

IMG_1251.jpeg
When all this three airplanes flying together and all have CG at 25%, we really don't care where they have their seats in front of the wing or behind the wing. It really doesn't matter where engine is installed in reference to the wing as well. As long as you have your CG at 25% MAC.

Champ has wider CG spread than my Skyboy and horizontal stabilizer incidence is 5° with Vh=0.33. CG on Chief almost staying in one spot at about 25% and as a result horizontal stabilizer incidence is only 3° with same tail volume 0.33. This 2° difference is more than enough to handle CG movement apparently and aircraft feels almost the same solo or with passenger. Let's not forget that my 912 engine can make 75% = 75 hp all day long. Champ at 75% is cruising on 47 HP at 85 MPH.

I was told by very smart people that you cannot consider your aircraft with forward CG at all if your CG is at 24- 23% or so. My airplane is certified just like Chief to 21% max forward CG. It is impossible for me to load this aircraft this way, but I really don't want to even try it.

Someone offered me an explanation that I think makes sense. Time will tell.

All Skyboy's in flight have relatively high angle of attack.

IMG_5600 2.jpeg
There is thinking that something is wrong with the way how this wing actually develops lift. With open engine in the middle you end up having two separate wings with four separate tips. Lift is destroyed to the point that this aircraft flying like it has only 100 square feet wing area versus 140 ft.² and what really kills performance is weight of the passenger and not so much forward CG, because CG at 25 or 23% is not really too much forward.

Someday we will find out if beautifully designed engine cowling will change this aircraft dramatically. Someday in 2025 maybe
 
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