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I made some notes on another forum when a hammerhead discussion came up. Reposting here to give the acro section some activity, and also incase anyone cares, or is learning to fly precision hammers. This is what I struggled with when I first got into competition acro and was trying to do "perfect" hammers: timing the pivot, torquing (rolling) during the pivot, and ending the pivot with slight vertical yaw and/or pitch errors.
I had a metal prop on the Pitts when I first started, and struggled with uncontrollable torquing during the pivot (even with full right aileron), and ending up off heading in roll to the left by 10-20 degrees as the pivot stopped. I had been following the advice of many of the aerobatic books, which describe a sequential input of rudder, right aileron, followed by forward stick. This may work in some lower power-to-weight airplanes, but the little Pitts with 180 HP and a metal prop at full power creates a lot of torque. The solution, I discovered, was to apply the right amount of forward stick perfectly simultaneous with the rudder input rather than immediately following the rudder input. Otherwise, it would torque every time unless I kicked too early. Kicking early means pivoting with more airspeed over the wings, which increases aileron effectiveness, but produces a large pivot radius (bad). That's not the solution. Initially (or for a long time even) lots of folks struggle with torquing hammerheads in the Pitts with a metal prop. Some even resort to pulling some power off during the pivot in an attempt to control torque. This makes for a lethargic pivot. It can be done at full power, but it's all about the timing and right amount of control input. A composite prop reduces the torquing effect.
Aside from the inputs, another thing that helped me was modifying where I looked, and when. On the upline, it's all about being vertical in pitch and yaw, and preventing the airplane from torque rolling. The left wingtip tells you everything you need to know. The progressive right aileron input near the top does two things - it controls torque rolling just before the pivot, and it can also tell you when it's time to kick. When I've reached a certain amount of aileron deflection with no roll reaction, I know it's time to kick. It's a good indicator. In my S-1S with the metal prop, it was nearly full right aileron.
After initiating the pivot, I shift my view over the nose to check that the nose falls through the horizon square with it (no torquing). Then it's a matter of applying opposite rudder at the right time so that the pivot crisply stops perfectly vertical in both pitch and yaw axes without any "pendulum" effect after the pivot.
When I first started flying hammers, I continued to look over the nose as the pivot stopped. Then when I checked my left wingtip, I could never seem to consistently end up perfectly vertical in both pitch and yaw. This is individual preference, but what worked much better for me was to shift my view from the nose back to the left wingtip so I can watch it as it swings up to the horizon. As it gets close, I can see how much rotation is remaining, and also how square the airplane is in pitch. This lets me know when to apply opposite right rudder, and also if I have the right amount of forward stick applied during the pivot. Then as the pivot stops, I immediately neutralize the rudder and elevator, followed by neutralizing the ailerons. Then I shift my view back over the nose and hold that attitude for the vertical downline. It was hard for me to pick up on small pitch and yaw errors by looking over the nose at the ground. I was never very good at "picking a point on the ground" to stop the pivot on. But lots of folks use that technique successfully in competition. It's all a matter of learning what works well for you. I like learning about different techniques incase I have trouble with one. To me, a perfect hammer is one of the prettiest maneuvers to watch.
I shot this video of the 2012 IAC Sportsman sequence, which has a hammer for Figure 1 and shows where I'm looking when, FWIW. Had the metal Sensenich at the time.
http://www.youtube.com/watch?feature=player_detailpage&v=Eg16eaYPuNI&t=20
And just some other examples of how we competition freaks pick these manevuers apart. Videos should be cued up.
This (at 0:52) is a nice hammerhead and would score well in competition, but IMO, the kick could have been delayed another fraction of a second to reduce the pivot radius slightly. Virtually perfect otherwise. Turn sound OFF for this one!
This (1:48) is one I flew at a contest last year during the Intermediate Known. Flown with the metal Sensenich. This one scored well enough, but the kick was very slightly late, IMO. The airplane came virtually to a complete stop before pivoting, meaning the up/down trajectory was not perfectly centered about the pivot rotation (descending very slightly before reaching 90 degrees of pivot rotation). Though this is NOT part of the judging criteria for hammerheads in IAC competition, it's still something I feel is a mark of a perfect hammerhead. It takes an airplane with a higher power-to-weight ratio and a bigger rudder than mine to do a "perfect" pivot from zero vertical speed.
On this subject, IAC rules simply require that the CG of the aircraft not move outside a 1/2 wingspan radius during the pivot before deductions are made. As long as this is maintained, notes are not made regarding kicking "early" or kicking "late". You'll notice the wind here. I deliberately did the the 1/4 roll up to the right so that I could pivot into the wind, which reduces the pivot radius. A good judge should be able to separate true "fly-over" from wind drift, but pivoting downwind is still a disadvantage from a presentation perspective, and should be avoided if possible. On the hammer, deductions are also made 1 point per 5 degrees of deviation from the vertical lines before and after the pivot. Same goes for any rolling off-plane (torquing) during the pivot, and roll heading isses after the pivot.
This (0:41) is an example of a hammerhead that would have problems scoring well in competition. Yeah, I know this is airshow flying and nobody cares. By competition standards, this pivot was initiated very early and "flown over" with a wide pivot radius well outside 1/2 wingspan. The yaw rate of the pivot was inconsistent, and the pilot started stopping the pivot too early, which made for a "soft" stop, and ended up underpivoting and dragging his right wing on the vertical downline (not perfectly vertical in yaw).
I had a metal prop on the Pitts when I first started, and struggled with uncontrollable torquing during the pivot (even with full right aileron), and ending up off heading in roll to the left by 10-20 degrees as the pivot stopped. I had been following the advice of many of the aerobatic books, which describe a sequential input of rudder, right aileron, followed by forward stick. This may work in some lower power-to-weight airplanes, but the little Pitts with 180 HP and a metal prop at full power creates a lot of torque. The solution, I discovered, was to apply the right amount of forward stick perfectly simultaneous with the rudder input rather than immediately following the rudder input. Otherwise, it would torque every time unless I kicked too early. Kicking early means pivoting with more airspeed over the wings, which increases aileron effectiveness, but produces a large pivot radius (bad). That's not the solution. Initially (or for a long time even) lots of folks struggle with torquing hammerheads in the Pitts with a metal prop. Some even resort to pulling some power off during the pivot in an attempt to control torque. This makes for a lethargic pivot. It can be done at full power, but it's all about the timing and right amount of control input. A composite prop reduces the torquing effect.
Aside from the inputs, another thing that helped me was modifying where I looked, and when. On the upline, it's all about being vertical in pitch and yaw, and preventing the airplane from torque rolling. The left wingtip tells you everything you need to know. The progressive right aileron input near the top does two things - it controls torque rolling just before the pivot, and it can also tell you when it's time to kick. When I've reached a certain amount of aileron deflection with no roll reaction, I know it's time to kick. It's a good indicator. In my S-1S with the metal prop, it was nearly full right aileron.
After initiating the pivot, I shift my view over the nose to check that the nose falls through the horizon square with it (no torquing). Then it's a matter of applying opposite rudder at the right time so that the pivot crisply stops perfectly vertical in both pitch and yaw axes without any "pendulum" effect after the pivot.
When I first started flying hammers, I continued to look over the nose as the pivot stopped. Then when I checked my left wingtip, I could never seem to consistently end up perfectly vertical in both pitch and yaw. This is individual preference, but what worked much better for me was to shift my view from the nose back to the left wingtip so I can watch it as it swings up to the horizon. As it gets close, I can see how much rotation is remaining, and also how square the airplane is in pitch. This lets me know when to apply opposite right rudder, and also if I have the right amount of forward stick applied during the pivot. Then as the pivot stops, I immediately neutralize the rudder and elevator, followed by neutralizing the ailerons. Then I shift my view back over the nose and hold that attitude for the vertical downline. It was hard for me to pick up on small pitch and yaw errors by looking over the nose at the ground. I was never very good at "picking a point on the ground" to stop the pivot on. But lots of folks use that technique successfully in competition. It's all a matter of learning what works well for you. I like learning about different techniques incase I have trouble with one. To me, a perfect hammer is one of the prettiest maneuvers to watch.
I shot this video of the 2012 IAC Sportsman sequence, which has a hammer for Figure 1 and shows where I'm looking when, FWIW. Had the metal Sensenich at the time.
http://www.youtube.com/watch?feature=player_detailpage&v=Eg16eaYPuNI&t=20
And just some other examples of how we competition freaks pick these manevuers apart. Videos should be cued up.
This (at 0:52) is a nice hammerhead and would score well in competition, but IMO, the kick could have been delayed another fraction of a second to reduce the pivot radius slightly. Virtually perfect otherwise. Turn sound OFF for this one!
This (1:48) is one I flew at a contest last year during the Intermediate Known. Flown with the metal Sensenich. This one scored well enough, but the kick was very slightly late, IMO. The airplane came virtually to a complete stop before pivoting, meaning the up/down trajectory was not perfectly centered about the pivot rotation (descending very slightly before reaching 90 degrees of pivot rotation). Though this is NOT part of the judging criteria for hammerheads in IAC competition, it's still something I feel is a mark of a perfect hammerhead. It takes an airplane with a higher power-to-weight ratio and a bigger rudder than mine to do a "perfect" pivot from zero vertical speed.
On this subject, IAC rules simply require that the CG of the aircraft not move outside a 1/2 wingspan radius during the pivot before deductions are made. As long as this is maintained, notes are not made regarding kicking "early" or kicking "late". You'll notice the wind here. I deliberately did the the 1/4 roll up to the right so that I could pivot into the wind, which reduces the pivot radius. A good judge should be able to separate true "fly-over" from wind drift, but pivoting downwind is still a disadvantage from a presentation perspective, and should be avoided if possible. On the hammer, deductions are also made 1 point per 5 degrees of deviation from the vertical lines before and after the pivot. Same goes for any rolling off-plane (torquing) during the pivot, and roll heading isses after the pivot.
This (0:41) is an example of a hammerhead that would have problems scoring well in competition. Yeah, I know this is airshow flying and nobody cares. By competition standards, this pivot was initiated very early and "flown over" with a wide pivot radius well outside 1/2 wingspan. The yaw rate of the pivot was inconsistent, and the pilot started stopping the pivot too early, which made for a "soft" stop, and ended up underpivoting and dragging his right wing on the vertical downline (not perfectly vertical in yaw).
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