Stall Recovery vs Tail/Fuselage design

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by stankap, Feb 6, 2012.

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  1. Feb 6, 2012 #1

    stankap

    stankap

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    Another question to stir up some thoughts.
    In most aircraft design texts it shows the typical 60deg/30deg unstable air profile for the leading and trailing edges of the horizontal stabilizer relative to the vertical stabilizer/rudder. The point of the diagram is in correctly locating the horiz stab to keep a portion of the rudder surface outside this area in the clean airflow.

    My questions is this.
    Most aircraft designs I see do not take this into consideration and some are spinable and recoverable. During my instructor training we did spins in the C-150 and recovered fine, but in looking at the C-150 tail design the rule above does not look like it applies to the cessna design.

    Also,
    I read in several texts that a flat bottom on the fuselage aft of the cockpit actually will make it more difficult to get out of spins, yet I see more designs than not with this sort of aft fuselage geometry. Is it OK or not?

    Thanks,
    Stan
     
  2. Feb 6, 2012 #2

    orion

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    Regarding the placement of the horizontal, you're right, many designs don't seem to take the rule of thumb into consideration. In some cases the functionality is in the details of the design while in others it may be blind luck. For instance, as you indicated there are quite a few planes that do not have the ideal geometry but they do recover. The good example is in many Cessnas who seemingly place the horizontal in a location where it seems the vertical would be fully blanketed - but most Cessnas do well in a spin. However, notice that the empennage configuration is similar on the Skycatcher, yet it spun into the ground on two occasions. Similar holds true for the Cirrus line of airplanes where the horizontal does indeed blanket the vertical, thus necessitating the chute.

    But I think it is a good idea to consider and heed the placement of the horizontal - Cherokees, although not the best in a spin, are recoverable. One of the best designs in this manner are the French line of airplanes by Socata. They extend the tail-cone aft of the vertical, placing the horizontal at a locating where it does not interfere at all.

    Regarding fuselage shape, it's not so much the flat bottom at issue but more so the sharp corners, as evidenced in airplanes like the Grummans. These corners can either generate unpredictable vortex flows or just dirty separated air that could hamper said recovery. This however does not seem to be a significant issue and as you indicate, there are many airplanes with just this type of tail-cone geometry.
     
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  3. Jun 17, 2012 #3

    Southron

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    At one time, I thought doing Spins in Cessna 150's was really "COOL." At the flight school I attended, they had a doggy old Cessna 150 with the gyros already screwed up because doing spins in a Cessna with pristine gyros would supposedly "damage" them, even IF they were caged.-but I digress....

    Anyway, back to the subject at hand. A Flight Instructor buddy of mine and I were up doing Spins in a Cessna 150 one day and just as we completed the first turn of a Spin, I made the MISTAKE OF TURNING MY HEAD AND LOOKING BACK AT THE TAIL. OOPS!!! That tail was shaking and shimming like it was a Belly Dancer after drinking too much Kickapoo Joy Juice! My point-seeing that tail assembly looking like it was about to depart from the airplane cured me of doing Spins for fun!!!!
     
  4. Jun 23, 2012 #4

    Aircar

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    I once saw a C 150 with the tail cone twisted about 20degrees --it had been 'spun' but evidently turned into a spiral dive and exceeded the strength of the whole tailcone which had wrinkled up like an aluminium drink can after being crushed --the thing was landed in one piece like that but must have been a handful . the C150 has quite viscious spin characteristics if spun with any flap on --DO NOT try it with eg 30s degrees as the spin will be almost inverted but it is more likely to get into a spin in the landing configuration ( I did many spins in all sorts of flap settings and initiations right up to 40degrees flap --the 23012 /23015 airfoil has a sharp leading edge stall and lots of hysterisis as well so some unspins are quite different )

    The Victa airtourer had a sharp lower corner on the fuselage and the designer was formerly chief aerodynamicist for the GAF (Government Aircraft Factory) and had wind tunnel and spin tunnel test facilities which did show the vortexes that Orion referred to --the Victa was only approved for two turns (but did also execute a nice 'falling leaf' that was somehow related to the aft fuselage lift --did it with the designer who was then a lecturer in aeronautics ) -- I had only seen one depiction in an old tech book of the falling leaf manouver.
     
  5. Jun 24, 2012 #5

    Tony

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    Rich Stowell wrote a book on this. Stall spin Awareness. Every pilot should read this. He goes over all this. You will be shocked if you read this. He says if you want to stall or spin a bird for fun it better have a chute on it if you go more then one turn before recovery. He had to Bail out of one bird and apply the chute I believe over 100 times. It might have been more.

    Tony
     
  6. Jun 24, 2012 #6

    Autodidact

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    Tony, this seems like a great book but there are many aircraft that are routinely spun and recover well at airshows every year, so I think that the complete story is more complex than the sensationalist statement above.
     
  7. Jun 24, 2012 #7

    Southron

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    In my "Younger and Dumber" Days (40+ years ago) one day, I and a friend of mine took up a Cessna 150, climbed up to 12,000' or 14,000' and put it into a Spin, to see how many "Turns" we could go through. What we quickly found was that the "Spin Wound Up," i.e., the first two or three turns were fairly gentle then subsequent turns became more and more violent and the Spin started to "Flatten Out."

    How many turns did we do? Probably around 6 or 8 (or maybe even more because both of us lost count). What was surprising to me was that I had figured all along that once in the Spin, the Spin would remain the same-it didn't it got worse!

    Even in my "Younger and Dumber Days" I would never even consider putting a Cessna 150 into an intentional Spin with the Flaps Down-NOT A GOOD IDEA! My theory is that the deployed flaps would "blanket out" much of the airflow passing by the tail section, causing definite "control issues" as far as the rudder and elevator are concerned.
     
  8. Jun 24, 2012 #8

    Tony

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    Rick wrote the book for the FAA on this subject. One would have to read the book to understand. What we know today about stalls and spins we know becuase of this man. Also airplanes have been changed because of this man.
    He talks about airshow pilots who died doing just what you say. We have a lot safer flying at these airshows becuase of his work.

    Like Patty Wagstaff said....Every pilot should read this book.


    Tony
     
  9. Jun 24, 2012 #9

    Autodidact

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    I agree, you cannot learn too much about spins. I am especially interested in the accounts of the aircraft that were modified and the testing of them. I am going to buy and read this book.
     
  10. Jun 24, 2012 #10

    Detego

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    Melmoth 1

    "Early tuft testing at Mojave. The flap attachment and the downwash along the aft fuelage, as well as the separated flow below the stabilator and under the fuselage, were interesting. The confused flow below the stabilator affected the anti-servo tab and produced an unpleasant shaking of the stick when the flaps were down. I began thinking about a T tail .. after the first flight."

    [​IMG]

    low-tail.jpg
     

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  11. Jun 25, 2012 #11

    clanon

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    Well the flap is cutting the fuselage belly for starters (not good for flow)
    Melmoth1 pictures
     
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  12. Jun 25, 2012 #12

    Tony

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    Rick Stowell said in his book if you plan on doing what is called a deep spin or let it progress past the first spin that you better have a chute on that bird. He also says some bird will never recover past the first spin. He talks alot about all the different Tail setups and how and why they do what they do.
    Myself I believe this should be required reading for all pilots. What I really liked about it was he went into great detail on how over the years planes have changed. If you read this book you will look twice before you buy certain birds made in certain years. After these years they are great birds, and not bad before, but there are things you must avoid in certain birds build in certain years. You can take the same model plane but built at different times. Cessna went to a slant tail for a reason and it had nothing to do with the way it looked to the man looking to buy a new bird. It was all about how it flew.
    Just imagine for one moment. You get up for work knowing you are going to spin and stall airplanes all day long, and on some days you are bailing out of a good flying airplane. All for you and me and every other person who ever wants to fly. Rick talks about bailing from a spinning bird more then once.
    Amazing stuff indeed. My hat goes off to this man and everyone who helped. We all owe him big time, more then most will every understand.

    Tony
    P.S I have read the book twice now. Its amazing stuff and I love it.
     
  13. Jun 25, 2012 #13

    Wagy59

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  14. Jun 25, 2012 #14

    Jay Kempf

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  15. Jun 25, 2012 #15

    Autodidact

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    The thing I read was that the FAA discontinued the requirement for spin training because, at the time (1949 or so), more people were dying in spin training than they thought they could save. Now the emphasis is on designing aircraft to be "spin-resistant", but one of the things in Stowell's book is the idea that designing an aircraft to be hard to get into a spin also makes it hard to get out; I don't know if that's a hard rule or if it is a general trend that can be abrogated with good design. I do think I will read the book, though, because I would like to design planes that can be spun and recovered nicely. That is just the type of plane I want to fly, and not one with prominent and easy to configure unrecoverable spin modes.
     
  16. Jun 25, 2012 #16

    autoreply

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    My experience with taking pilots up for some spins is that many SEP-licensed ones are just downright afraid of spinning and many of them were instructors.

    No wonder that spin training with them is dangerous if instructors just panic; big surprise that spin training ends up in crashes. But one could wonder whether spinning is that dangerous, or most powered pilots are simply not trained and thus incapable of it, which would "safe" (hard to spin) aircraft by definition more dangerous because they're more likely to spin in. If you can't recover from a spin, you shouldn't be flying an aircraft for you will one day be unable to stop your spin into mother earth...
     
    Last edited: Jun 25, 2012
  17. Jun 25, 2012 #17

    GrantR

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    A friend told me the Stearman Biplane would spin very perdictiably. He said the spins were very slow in rotation and stablized that way.

    I guess the older draggy planes had better spin characteristics than the newer slicker designs?
     
  18. Jun 25, 2012 #18

    bmcj

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    I've had the same experience. Took a friend up who was a young flight instructor who learned "by the book". He had never done spins and was terrified at the prospect of spinning... so much so that he was afraid to do full stalls and always chose to recover at the first sign of a stall (usually the stall horn). I took him up and ran him through the full gamut of full buffeting stalls (straight, turning, climbing, accelerated, power on, power off) and then let through breaking stalls with undeveloped and fully developed spins. I felt it was a crime to have a licensed instructor was afraid of stalls and spins and whose only experience with them was recovery short of an imminent stall.

    The 7AC Champ was a great airplane for that. When we crossed the high mountains and needed to get down on the other side, we would spin the Champ from 13,000 ft all the way down to a couple thousand feet. The fully developed spin was very gentle and slow.
     
    Last edited: Jun 25, 2012
  19. Jun 25, 2012 #19

    Southron

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    Back in the mid-1960's I was a student at Burnside-Ott Aviation Academy at the Opa Locka, Florida airport. Getting a Cessna 150 up to 14,000' or 16,000' was NO PROBLEM with two people aboard in the airspace above South Florida.
     
  20. Jun 25, 2012 #20

    Dana

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    The C-150/152 has a 2412, not a 230xx series airfoil.

    Depends on the plane (some wind up, some don't) and the loading.

    Back in my younger and foolish days, I took a 150 way up and did 16 turns. As I recall, it took 2 or 3 turns to recover, but recover it did. I did 20 turns in my T-Craft (which does have a 23012 airfoil) once, seemed the quickest way to get down through a hole from where I was, around 9000' where I was playing around on top of the clouds.

    I remember one flight school 150, doubtless bent by a student, that was very reluctant to spin in one direction, but would spin real fast in the other.

    -Dana

    If the government doesn't trust us with our guns, why should we trust them with theirs?
     

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