Hammerheads

[whifferdill]

I was going to follow up on this post I made, but figured I'd move it to the acro section. Since I'm coming from the acro competition world, I guess I'm a little more of a technique freak than most. Anyway, just a little perspective on what makes a "perfect" hammerhead in the precision acro world: Pivoting such that the CG of the airplane moves laterally no more than 1/2 a wingspan, Staying perfectly vertical in pitch and yaw before and after the pivot, Making a clean pivot with consistent yaw rate, while staying perfectly on plane. Unofficial factors that go into a good hammerhead is timing the pivot such that the up/down trajectory is symmetrical about the 180 degree pivot rotation...meaning that by the time the airplane has pivoted 90 degrees, it momentarily has zero up/down movement. Some examples below. These videos should be cued up.

This one is a nice hammerhead and would score well in competition, but compared to the perfection standard, the kick was very slightly early. The pivot radius could have been very slightly smaller by waiting a moment longer. Everything else about it was virtually perfect.

This is shamefully presented as one of mine. Hard to find good videos of hammerheads good or bad. This one scored well, but judged against the unofficial perfection standard, the kick was a tiny hair late. The airplane came virtually to a complete stop before pivoting, meaning the up/down trajectory was not perfectly centered about the pivot rotation. Though this is not a judging criterion in IAC competition. To maintain the max. pivot radius before deductions are made, you'll more likely achieve this by kicking very slightly late than slightly early. It takes an airplane with a higher power-to-weight ratio and a bigger rudder than mine to do a good pivot from zero vertical momentum.

This one is an example of a hammerhead that would not score well in competition. Yeah, I know this is airshow flying and nobody cares. But I still like to see precision and skill applied to airshow flying. This pivot was initiated very early and "flown over". There was a wide pivot radius, the pivot near the end did not have a consistent yaw rate, 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).

And below an example of one person's learning process in a low-performance airplane (Citabria 7ECA). I'm only picking on Diana because she was cool enough to post this video early in her aerobatic "career" when first learning this maneuver. I'm sure she does them very nicely now. You can see the progression, and some interesting hammer attempts in the first few while she's sorting out the timing of the pivot, remembering full throttle, and working on the proper rudder, aileron, and elevator inputs. To me, a perfect hammerhead is one of the prettiest maneuvers there is. Deceptively complex.

 

[Jeanie]

The video of Diana wasn't included. I watched yours but don't have on my glasses ... I'll look again after awhile... Looked a little like your downline was a scosh positive... Prolly just my eyes.

I have started doing hammers solo yet. I'm still concerned about kicking too late. Plan to practice with my aerobatics friend/mento this coming week. Not going to do the hammerfest this year. Have you seen the sportsman sequence? Yeesh.

 

[Geico266]

I seem to remember a 1,500' agl floor after the maneuver is complete unless you have a waiver.


Nice hammer head BTW.

 

[whifferdill]

The video of Diana wasn't included.

Are you on mobile? Looks like the embedded video may not show up on mobile, but it seems to work (at least on my mobile) if you click on the open space below the text in my post. Otherwise:

http://vimeo.com/3318944#at=0

Looked a little like your downline was a scosh positive... Prolly just my eyes.

Yep - was likely good after the pivot, and then looked maybe slightly positive after the 1/4 roll down due to a little inadvertent elevator movement during the right aileron input. So...next thread will be on doing proper vertical rolls.

I'm still concerned about kicking too late. Plan to practice with my aerobatics friend/mento this coming week. Not going to do the hammerfest this year. Have you seen the sportsman sequence? Yeesh.

Do you have a piece of yarn on your jury strut? That'll keep you from accidentally tailsliding if you're by yourself. The best way to learn to time the pivot is with knowledgeable help from the ground.

Yeah, the Sportsman sequence is a little different this year due to the lack of spin and no x-wind correctors. Intermediate doesn't have a spin this year either, but put in a half snap, which is a bump up in difficulty from the full snap.

 

[Jeanie]

Diana's video worked with that link. Great music and the hammers seemed to get better.... Never fell into an inverted spin.
Aerobatics is hard in a citabria

I'll see if I can put some yarn where I can view it. I don't have a jury strut

 

[whifferdill]

I'll see if I can put some yarn where I can view it. I don't have a jury strut

Then you might want to put them back on before you fly the airplane again. Halfway up your main strut is smaller strut that's out of the propwash. Just tape a 6" piece of yarn to the front jury strut.

 

[Capt. Geoffrey Thorpe]

Diana's video worked with that link. Great music and the hammers seemed to get better.... Never fell into an inverted spin.
Aerobatics is hard in a citabria

1:07 ... If that had been me at the controls, even the camera person on the ground would have heard the bad words... I didn't know that a Citabria could be made to hoover inverted.

Nice camera work - it's hard to track an aircraft at that level of zoom.

 

[whifferdill]

I seem to remember a 1,500' agl floor after the maneuver is complete unless you have a waiver.

Which video are you talking about? If it's mine, it was shot at an aerobatic contest with waivered airspace in place. The "floor" of the Intermediate category I was flying at the time is 1200' AGL. Plus it was shot with a zoom lense. I was 1200' or more the whole time. That's an IAC rule, not a requirement of the waiver - waiver goes to the surface. Floor of the Advanced category is 656', and Unlimited is 328' AGL.

 

[Jay Honeck]

I can't get either version of the vimeo videos of Diana to work on my Nexus 7.

Thanks for the hammerhead primer, though. It's amazing how different a good one is from a sloppy one.

Of course, now that I know how hard they are, I will never be able to effortlessly do one again, dammit.

Just like golf. I was a natural, until I joined a club and learned how hard the game was. It was all downhill from there.

 

[Jeanie]

Then you might want to put them back on before you fly the airplane again. Halfway up your main strut is smaller strut that's out of the propwash. Just tape a 6" piece of yarn to the front jury strut.

Oh, duh, I was thinking of the siting devices at the end of the wing...

 

[Skylane81E]

As a former RC acro pilot I can vouch for the difficulty of the hammerhead, on the ground looking up at the plane it is rather easy, but from outside you have all the right visual cues, I can only imagine trying to do it without that good vantage point.

 

[whifferdill]

Aside from the inputs, another thing that's important is looking in the right places at the right time. I shot this video of the 2012 IAC Sportsman sequence, which has a hammer for Figure 1. 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 in the Pitts - it controls torque rolling, and it also tells me 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, that ends up being full right aileron.

Then I smoothly but quickly apply full left rudder simultaneous with about 6" of forward stick (the amount is aircraft-specific), then 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 stops crisply in a perfectly vertical attitude...again vertical in both pitch and yaw.

When I first started flying hammers, I continued to look over the nose as the pivot stopped. Then when I looked at 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 my left wingtip as it moves back 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 will let 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 removing the right aileron. Then shift your view back over the nose and hold that attitude for a perfect vertical downline. It was hard for me to pick up on small pitch and yaw errors by looking over the nose at the ground.

The other problem I had when first flying hammers in the Pitts was uncontrollable torquing during the pivot (even with full right aileron), and ending up off heading 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-performing airplanes, but the little Pitts with the 180 hp motor and metal prop creates a ton of torque. The secret, I discovered, was to apply the forward stick perfectly simultaneous with 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 that's not the solution. Lots of folks seem to 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.

 

[stearmann4]

Hammer heads are tough in a stock Stearman, almost no time to get established on the up line, probably worse than a 7ECA when the 3,000lbs starts uphill. Agreed, a work of art when someone nails it.

Mike-

 

[Diana]

And below an example of one person's learning process in a low-performance airplane (Citabria 7ECA). I'm only picking on Diana because she was cool enough to post this video early in her aerobatic "career" when first learning this maneuver. I'm sure she does them very nicely now. You can see the progression, and some interesting hammer attempts in the first few while she's sorting out the timing of the pivot, remembering full throttle, and working on the proper rudder, aileron, and elevator inputs. To me, a perfect hammerhead is one of the prettiest maneuvers there is. Deceptively complex.

I wondered why my Vimeo stats shot up.

I wouldn't have had the nerve to make this public if it wouldn't have been for supportive comments from Dave Pilkington. He posted part of this video on a site for his aerobatic students. There are some good examples in the video of what not to do and what can go wrong.

Aerobatics is hard in a citabria

It was for me, for several reasons, including inconsistent instruction.

1:07 ... If that had been me at the controls, even the camera person on the ground would have heard the bad words...

There might have been a few words like "Oh, pooooooo....!!!!!"

I didn't know that a Citabria could be made to hoover inverted.

I didn't either!

Nice camera work - it's hard to track an aircraft at that level of zoom.

My husband did pretty good. All my videos were made at/over our farm.

 

[Cessna150C]

This is very true for a Pitts S1. I've never done hammers in anything else, so maybe you can get away with adding the forward stick later. That is the technique I also started with, but learned by trial and error to add forward stick and rudder at the same time. BTW, this is even with a 14 lb. Catto prop.

The other problem I had when first flying hammers in the Pitts was uncontrollable torquing during the pivot (even with full right aileron), and ending up off heading 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-performing airplanes, but the little Pitts with the 180 hp motor and metal prop creates a ton of torque. The secret, I discovered, was to apply the forward stick perfectly simultaneous with 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 that's not the solution. Lots of folks seem to 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.

 

[somorris]

It looks pretty easy when you do it .

The hammerhead looks really cool. Maybe one of these days!

 

[Jeanie]

Diana, I re watched your video. Boy, you got a lot better towards the end. I admire your determination!

 

[Diana]

Diana, I re watched your video. Boy, you got a lot better towards the end. I admire your determination!

Thanks, Jeanie. There's hope for me yet.

 

[David]

Thanks for videos and the descriptions. As a aspiring aerobatic pilot, I enjoy reading your posts. I have a question about your hammerheads. In my plane, the engine spins the other way, hammerheads to the left are more difficult to control than hammerheads to the right. At least that's what the manual says. I haven't really noticed much of a difference but my hammerheads aren't very precise. My plane has an 81" metal prop.

Is there a difference in technique left versus right in your Pitts?

Thanks
Dave

Aside from the inputs, another thing that's important is looking in the right places at the right time. I shot this video of the 2012 IAC Sportsman sequence, which has a hammer for Figure 1. 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 in the Pitts - it controls torque rolling, and it also tells me 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, that ends up being full right aileron.

Then I smoothly but quickly apply full left rudder simultaneous with about 6" of forward stick (the amount is aircraft-specific), then 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 stops crisply in a perfectly vertical attitude...again vertical in both pitch and yaw.

When I first started flying hammers, I continued to look over the nose as the pivot stopped. Then when I looked at 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 my left wingtip as it moves back 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 will let 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 removing the right aileron. Then shift your view back over the nose and hold that attitude for a perfect vertical downline. It was hard for me to pick up on small pitch and yaw errors by looking over the nose at the ground.

The other problem I had when first flying hammers in the Pitts was uncontrollable torquing during the pivot (even with full right aileron), and ending up off heading 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-performing airplanes, but the little Pitts with the 180 hp motor and metal prop creates a ton of torque. The secret, I discovered, was to apply the forward stick perfectly simultaneous with 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 that's not the solution. Lots of folks seem to 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.

 

[djpacro]

Been years since I have done hammerheads (stall turns) in a Chippie or Tiger Moth so just a general comment that a big aeroplane with more inertia and low power so low power to weight ratio means that at low speeds the power effects are less significant.
I regularly teach hammerheads to left and right in a Decathlon with 150 hp and a fixed pitch prop - not a lot to say about the different directions.
I also teach them in a Pitts S-2A - I brief the different directions just as much as if they are entirely different manoeuvres.

 

[whifferdill]

Thanks for videos and the descriptions. As a aspiring aerobatic pilot, I enjoy reading your posts. I have a question about your hammerheads. In my plane, the engine spins the other way, hammerheads to the left are more difficult to control than hammerheads to the right. At least that's what the manual says. I haven't really noticed much of a difference but my hammerheads aren't very precise. My plane has an 81" metal prop.

Sure, the propellor slipstream attempts to yaw your airplane to the right just like my Lycoming tries to yaw the plane to the left at low speed. Going against this slipstream yaw is just fighting what the airplane really wants to do. I only once tried a right rudder hammer in my S-1S when I first got it. It almost wouldn't pivot. Never bothered to try again. In general, it's totally pointless to go the opposite way. It'll never look as good as pivoting with the slipstream.

But there are rare instances in competition where it could possibly be advantageous to pivot in the opposite direction - that is if you can do it well enough. If there is a strong wind, it's best to pivot into the wind to reduce the appearance of "fly over". A knowledgeable judge will be able to tell the difference between true "fly over" resulting from bad technique vs. wind effect, but it's still a disadvantage from a presentation standpoint to pivot downwind. The competition video of mine in the original post here had a pretty strong wind blowing down the x-axis of the box. I deliberately did the 1/4 roll up to the right so that I could pivot into the wind. Makes for a very tight pivot radius (actually had a slight negative radius here). Pivot radius is part of the judging criteria. In most cases (especially if pivoting on the y-axis) you can adjust your position such that you can pivot into the wind. You may not always have this option when doing hammers on the x-axis, but in all the competitions I've been to and flown, I've never seen anyone pivot in the opposite direction.

Is there a difference in technique left versus right in your Pitts?

But if you wanted to pivot in the opposite direction, there are some differences. Gyroscopic precession acts in the opposite direction, so when with a normal hammer you'd apply some forward stick, the opposite hammer will need some aft stick during the pivot. And because you have significantly less rudder effectiveness when attempting to pivot opposite the slipstream yaw, it will help to "slide" your vertical line to increase your rudder effectiveness at the top.

The way you slide your upline is when pulling into the vertical line, make a subtle bank input one way or the other. This will cause the flight path of the airplane to move sideways a little, and will also cause the airplane to have a vertical yaw attitude error if uncorrected. So as you fly the radius into the vertical line, you apply some rudder before reaching the vertical upline to yaw the airplane back to a perfect vertical attitude. The airplane is now sliding sideways as it flies the upline. This requires you to continue to hold some rudder all the way up.

So in your Chipmunk, if you want to hammer left, try making a very slight left bank as you pull into the vertical upline. Before reaching vertical, apply some right rudder to bring that left wing up so that you're vertical in yaw by the time you reach the vertical pitch attitude. The airplane will now be skidding to the left, and you'll need to hold right rudder on the upline to keep the airplane vertical in yaw. When it comes time to pivot, you'll have additional left rudder authority and "power" due to the fact that you're holding some right rudder before the pivot. And remember the aft stick rather than forward stick during the pivot. But even with the difference in technique, don't expect it to be as pretty as a hammer in the "normal" direction.

 

[David]

Been years since I have done hammerheads (stall turns) in a Chippie or Tiger Moth so just a general comment that a big aeroplane with more inertia and low power so low power to weight ratio means that at low speeds the power effects are less significant.
I regularly teach hammerheads to left and right in a Decathlon with 150 hp and a fixed pitch prop - not a lot to say about the different directions.
I also teach them in a Pitts S-2A - I brief the different directions just as much as if they are entirely different manoeuvres.

"Stall Turns" so there is someone else on here that knows that term . I didn't think about the reduced power to weight ratio. The chipmunk is probably a bit worse than your Decathlon. I imagine solo, I'm probably around 1800 lbs with 145 HP.

 

[David]

Sure, the propellor slipstream attempts to yaw your airplane to the right just like my Lycoming tries to yaw the plane to the left at low speed. ...

Thanks for the write up. I appreciate it. I'm amazed at your description of adding rudder, aileron, etc. at different points in the maneuver. I'm still at the point where things are going by a bit too fast but I'm working on it and I think I'm improving. My old instructor finally got his medical back. I'm hoping to get some more dual instruction in the next few weeks.

One more question, in competition with a known sequence, is the direction of the hammer head is up to you? Is the direction of rolls and spins also up to the pilot? Just curious, I've got no plans on doing competition aerobatics.

 

[whifferdill]

One more question, in competition with a known sequence, is the direction of the hammer head is up to you? Is the direction of rolls and spins also up to the pilot? Just curious, I've got no plans on doing competition aerobatics.

David, in any flight (Known, Free, or Unknown), hammer, roll, and spin direction is always up to the pilot. Though there are figures where you must roll in a certain direction based upon the direction your chose to roll in an earlier part of the figure. For example, take the simple hammerhead with a 1/4 roll up and 1/4 roll down. If the figure is drawn showing the entry and exit lines in opposite directions, then if you choose to do the 1/4 roll up to the left, then you have no choice on the direction of the 1/4 roll down (left) in order to exit in the proper direction and avoid zeroing the figure. In the cases of opposing rolls on a line, as long as they are done in opposite directions, the initial roll direction is the choice of the pilot.

Wind conditions will often dictate the most suitable direction. When rolls are done on level or 45 degree lines, roll direction makes no difference. It's when rolls or snaps are done on vertical lines that the choice of direction becomes more critical. The "y-axis" (cross-box) is non-directional, meaning the pilot can fly away from the judges or towards the judges, as long as they end up flying the correct direction once back on the x-axis (from judges left-to-right or right-to-left). So if there's a x-wind blowing toward the judges, and you're flying from the judges' right to left, and the figure is a 1-1/4 spin, it would be advantageous from a positioning standpoint to spin to the right so that you're exiting on the y-axis flying away from the judges, which will compensate for the x-wind blowing you toward the judges. Snap rolls or aileron rolls on vertical downlines work the same way...choose the direction for best box positioning and presentation. But again, regarding hammerhead direction - in general, the direction is never a consideration, and is always done the same way.

Eric

 

[David]

Thanks Eric.

David, in any flight (Known, Free, or Unknown), hammer, roll, and spin direction is always up to the pilot. Though there are figures where you must roll in a certain direction based upon the direction your chose to roll in an earlier part of the figure. For example, take the simple hammerhead with a 1/4 roll up and 1/4 roll down. If the figure is drawn showing the entry and exit lines in opposite directions, then if you choose to do the 1/4 roll up to the left, then you have no choice on the direction of the 1/4 roll down (left) in order to exit in the proper direction and avoid zeroing the figure. In the cases of opposing rolls on a line, as long as they are done in opposite directions, the initial roll direction is the choice of the pilot.

Wind conditions will often dictate the most suitable direction. When rolls are done on level or 45 degree lines, roll direction makes no difference. It's when rolls or snaps are done on vertical lines that the choice of direction becomes more critical. The "y-axis" (cross-box) is non-directional, meaning the pilot can fly away from the judges or towards the judges, as long as they end up flying the correct direction once back on the x-axis (from judges left-to-right or right-to-left). So if there's a x-wind blowing toward the judges, and you're flying from the judges' right to left, and the figure is a 1-1/4 spin, it would be advantageous from a positioning standpoint to spin to the right so that you're exiting on the y-axis flying away from the judges, which will compensate for the x-wind blowing you toward the judges. Snap rolls or aileron rolls on vertical downlines work the same way...choose the direction for best box positioning and presentation. But again, regarding hammerhead direction - in general, the direction is never a consideration, and is always done the same way.

Eric

 

[whifferdill]

Good old video from Rich Stowell.