Humpty and Sharks Tooth

Discussion in 'Aerobatics' started by Ed Haywood, Aug 30, 2021.

  1. Ed Haywood

    Ed Haywood Line Up and Wait

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    I am getting back into IAC competition after a 15 year break. These were not common Sportsman figures back then, but they are part of the 2021 Sportsman, so I am learning them on my own. I fly a Super Decathlon.

    When should I initiate the pull at the top? Is it better to carry it high and slow, like a hammer? Or should I go vertical just long enough to establish a line, then pull while I still have plenty of airspeed? Should I time the vertical length with a count, or is there a physical cue to pull? How much elevator?

    My first few attempts at a humpty went fine, but I just flew it like 2 halves of a square loop. Pull up to vertical, set, count one thousand, pull 180 radius to vertical down, set, count one thousand, pull out. Flew fine except for some yaw and roll over top that I now understand is from gyro precession and will be one of my practice points to refine.

    But I suspect my radius at the top is quite ugly, so that is my initial focus. When to pull, and how hard?
     
    Last edited: Aug 31, 2021
  2. whifferdill

    whifferdill Line Up and Wait

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    Ed, you can really only get this sorted out via ground coaching/critiquing, but regarding how to fly the radius on the top for both figures...fly it as tight and with as little airspeed as you can get away with. You definitely don't want to fly the humpty like a loop with flat spots on the way up and down. Same for the wedge (shark's tooth), don't fly it like a segmented half cuban. The tighter the radius on top, the harder it is to spot radius deviations and the better the figure presents. It also gives you time on the 45 line in the wedge to fly the roll without rushing or exiting with excessive airspeed. But you are NOT trying to draw a sharp point over the top of the wedge. It still must be flown as a constant radius.

    The common beginning mistake on both figures is flying over the top such that the radius expands as the nose is pulled below the horizon and airspeed builds. You generally fly the radius for both figures the same way over the top. Break the vertical upline by making a quick sharp small pop of the stick aft to definitively break the vertical line for the judges. You basically pop the stick and return it to near neutral and let the airplane float to the inverted position. The number one mistake here is pulling the stick sharply and yanking the nose all the way through the radius. What this does is establish an initial tiny radius that is impossible to maintain as airspeed builds after the nose is pulled below the horizon. The radius then inevitably enlarges, sometimes by a factor of 4. Major downgrades. So float slowly to the inverted position, then steadily accelerate your pull/pitch rate to close on the downline. On the humpty, you generally end up right on the buffet as you set the vertical downline. If you don't accelerate the pitch rate/pull, the radius will enlarge and you will "close low" on the downline.

    Same concept for the wedge, but since you're only pulling to the inverted 45, you don't have to pull all the way to the buffet, just accelerate your pitch rate from the inverted to the inverted 45 point and sharply set the stick on the 45 inverted attitude so the judges can clearly see where the radius ends and the line begins. If this sounds mechanical and jerky, it doesn't appear that way from the ground if you do it properly. It looks smooth and sharp and clearly defines the lines and radii to the judges. If you lazily move the stick to break the vertical line and set the downline, the radii and lines become murky to the judges and your scores will suffer.

    Decathlons can fly these sequences perfectly. Check the results in Sportsman and Intermediate from a contest this past weekend. And that was only a 160HP Decathlon in Intermediate. Good luck!

    https://iaccdb.iac.org/contests/763
     
    Last edited: Sep 1, 2021
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  3. Ed Haywood

    Ed Haywood Line Up and Wait

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    Awesome explanation, thanks. I definitely will get some ground coaching, but that probably won't happen for a month or so.

    Any advice on timing the pop to get the right airspeed? Can I work out a count from the initial pull based on trial and error, or is there a physical cue like the hammer? I read one tutorial saying to watch the airspeed, but seems like taking my eyes off the sight gauge would lessen the quality of the vertical.
     
  4. Isosceles

    Isosceles Pre-takeoff checklist

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    it is important to start and end the 1/2 loop at the top of the humpty at the same altitude. the radius is not a judging criterion but it is expected that it will be fairly tight. if you start the "pop" too late you will sink and fall out of that half-loop and never end it at the same altitude. unfortunately it is hard to tell if you are falling out of the loop without a ground coach. the hammerhead pivot airspeed will likely to be too slow. after you float at the top, you need to progressively add back stick to tighten the turn. in most aircraft usually you need to pull to the stall buffet just before vertical downline, though i don't remember what it is like in the decathlon.
     
  5. whifferdill

    whifferdill Line Up and Wait

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    This is something you do more by feel than by counting or watching airspeed. The "count" will vary depending on your entry speed and DA conditions, which can vary. Similar to how you can sense the diminishing airspeed on the vertical line to a hammerhead without counting or looking at the ASI, you can do similar for the vertical line into the Humpty. Ground critiquing certainly speeds up this process.

    Radius absolutely is a judging criterion, but size is not. Every single radius you fly in competition whether it's a full loop or just a pull from a vertical line to a level line is subject to radius grading. Below is the excerpt from the rule book on "looping lines" which occur during any transition from any line to line.

    Closing the Humpty at a lower altitude is not a specific judging criterion, but because it's impossible to "close low" if a constant radius is flown, many judges use this to help visually ID radius issues.


    upload_2021-9-1_16-16-45.png
     

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    Last edited: Sep 1, 2021
  6. Isosceles

    Isosceles Pre-takeoff checklist

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    this. you can fly a wide humpty and it's not going to be a downgrade, though a tight one looks better.
     
  7. Ed Haywood

    Ed Haywood Line Up and Wait

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    I can't "sense" vertical speed in the hammer. I use the slipstream. When it starts drumming on the left side of the fuselage, it's time to kick. Obviously that would be too late for a humpty though.

    I'll play around and see if a solution presents itself.
     
  8. Ed Haywood

    Ed Haywood Line Up and Wait

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    After a couple of sessions, I worked out a general sense of when to pull. Carrying extra airspeed at entry (160 mph) and doing a 2 count on vertical up gives me enough airspeed after the pop to maintain control and fly over the top with level wings instead of falling out.

    Still working on the rudder inputs on second half of radius. I understand what needs to be done, so it's just a matter of practice to refine my touch

    Thanks for all the good advice!
     
  9. Ed Haywood

    Ed Haywood Line Up and Wait

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    Following up on this, in case anyone else stumbles on it years down the road. Flew these maneuvers about 100 times in the last few weeks to refine for Sebring (which got cancelled).

    Seems the key to both is carrying enough speed over the top to fly the maneuver instead of falling through it. A Super D does not have a lot of vertical, so what worked for me was extra airspeed (160mph) on entry, an aggressive pull up, count two thousand, pop to start the 2nd pull, then partially relax stick and fly it over the top. Relaxing too much will cause a wing to dip.

    On the humpty, aggressively increase the 2nd pull as the nose dips below horizontal, so that you reach the vertical down line with the stick nearly full back. As you pull through -45 inverted, look to your wing and apply rudder as needed to keep the sight gauge on the horizon and counteract yaw. Be sure to neutralize rudder right as you stop the pull, or you will yaw all over the place.

    On the wedge, no need to increase the pull, just watch the sight gauge and push the stick forward to set 45 inverted.

    Fun times. So much happy to be working on this again. Just got the 2022 Sportsman candidate sequence this morning, and already itching to give it a shot! No new maneuvers to learn, so I can focus on positioning, presentation, energy, etc.
     
  10. whifferdill

    whifferdill Line Up and Wait

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    Glad it's working out Ed. Just wanted to mention though that in order to keep it round, you do need to progressively increase your pull from the apex of the wedge radius to the inverted 45 line. If you don't, the radius will expand and the flight path will deviate similar to the red dashed line in the image attached here. As a line judge, I can't count how many times I've deducted points here because the pilot did not increase the pull to keep the radius constant all the way to the 45. It's really the same principle as the Humpty, you just close on the 45 rather than vertical. But I will admit that lots of judges seem to "load shed" a bit here, and are mentally anticipating the appearance of your 45 attitude rather than keeping up with potential radius deviations prior to the 45 line. Most judges do end up paying full attention to the Humpty radius though, since they're anticipating the pilot possibly "closing low", which is a radius issue. But you should really put the same care into the Wedge radius in order to maximize your scores. Too bad about Sebring.
     

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  11. Ed Haywood

    Ed Haywood Line Up and Wait

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    Thanks, excellent insight. I'm looking forward to flying some contests next spring and getting some score sheets. That will help refine my technique on finer points like your tips.

    I did get 2 practice flights in the box so it wasn't a total wash. I only live 30 minutes away, so the CD let me go home while we waited out the weather. I did not have to make a huge travel effort like others.

    The SE regional director said the IAC is hoping to have 3 contests next spring in FL and GA. Should be plenty of upcoming opportunity to get judged. Very motivated; I might even set my sights on flying in Salina just to say I did.
     
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