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Hammerheads (Stall Turns) printer friendly version
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Bob Grimstead
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Posted Wednesday, January 3, 2007 @ 03:39 AM  

This is e-mailed advice from other Fournier aerobatic pilots. I take no responsibility for your actions, but Iíll share some of it with youÖ

Climb to 5,000 feet over an unpopulated area. Trim to your maximum level speed (around 90 kt with a 1,200cc engine, maybe 100 kt with the 1,400). Flying the Fournier aerobatically is an energy management exercise. It is only a glider with noise in front.

HAMMERHEADS (STALL TURNS): This is the tricky one. I only got one so-so turn out of my first twenty attempts. The others all fell or tailslid. Horrid. Go to the right. Donít even bother trying to go to the left, unless you have a powerful engine, you wonít do it.

Nowadays they (nearly) always work. I have never spun out of one. Provided you keep the stick central when everything stops and goes quiet (even the motor) she just falls nose-down and you fly away perfectly normally. Just grip the stick hard so it doesn't slam the controls against the stops if you happen to go backwards for a millisecond.


This is a photo of one of my early stall turns (hammerheads) taken last year, before I was able to pivot around a wing-tip.

Again, start at 110 to 120 knots to give you a decent vertical line, wings level, ball centered. You have to get to the vertical quickly so it has to be a 'quick' pull Ė firm (4 to 4.5g). In doing a steady, gentle pull, by the time you are vertical you havenít enough speed to carry it through. I pull to 90 degrees (upper wing surface vertical), but you should start off at just 80 to 85 degrees. Going into wind, this looks vertical, anyway. Check forward with the stick as you hit your vertical, and then fly it (I find the stick needs to keep moving gently forwards).

Check both wings are equidistant above the horizon (which should pretty much bisect each tip), add left rudder as you slow (youíll need half deflection by the top). The vertical takes maybe three seconds max, so you havenít got long (not much power, see).

Hit full right rudder at around 45 knots with some (sometimes full) opposite aileron and a little forward stick to counter the propís gyroscopic force (yes, itís a small prop, but itís going around fast). Keep on that full rudder. As the nose drops through, check youíre not rolling. Add aileron to taste (I often need full left aileron). As your nose approaches the vertical down, hit full left rudder to stop any pendulum effect. Youíll need this earlier if the engine has stopped.

Check your down line and yaw by looking quickly at both wing-tips, and hold forward stick to keep the down vertical. Follow through on the down line (keep it vertical) and you will need increasing right rudder as the speed builds. When it gets to 70 or 80kts, pull firmly to the horizontal and check.

At the top, you have a knot or maybe two to play with. With a 1400cc or bigger engine, you have a greater margin.

If you hit the rudder at too high a speed, sheíll yaw through maybe 45 degrees, roll to the right a bit, then hover and fall (mostly backwards, but sometimes sideways). Hit the rudder at too low a speed and sheíll stop in mid-air and tailslide, then flip either backwards (canopy down) or forwards (canopy up Ė negative g Ė horrible). If she starts tailsliding, keep the throttle wide open to cushion your descent, and lock the controls hard with both hands and feet (jam your elbows and lock your legs) so they donít whack against their stops. That would be expensive.

I flew 'bridges' at first, but then tied a three-foot length of plastic tape to my right wing-tip (thin tape - it will get wrapped around your aileron, and you must be able to break it). Watching that told me when I was rotating within my wing-tip. Closing the throttle at the 45-degrees of yaw point helps (if your engine hasn't already stopped).

Good luck with your hammerheads. They can be done, but they sure sort out the men from the boys. You just need to persevere, and like all good things, they are well worth the effort.


Just to prove my hammerheads do now pivot around the wing-tip, I also enclose this photo of my scorched right wing-tip (the scorching comes from
the smoke as the tip goes backwards and sideways through the burning smoke.

GET PROPER DUAL INSTRUCTION

Let me know if you find a better way of flying a clean hammerhead.

Yours, Bob

[Edit by Bob Grimstead on Tuesday, February 26, 2008 @ 00:53 AM]



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Posted Monday, January 8, 2007 @ 10:40 PM  

Bob,

I have yet to try a H-H in the Fournier. Too darned cold out at the moment but I'm wondering if the technique Neil Williams (again) described would help. - It certainly does in the long winged Zlins and it works wonders in the YAK50 too. He suggests that (in the case of a Fournier turning propeller) you start the pull with the right wing about 5 degrees low. That way, when you reach the vertical, the line is inclined 5 degrees to the right, which you correct by applying enough left rudder to make it look vertical. (You are actually skidding a little to the right but no one will notice because the nose is pointing straight up) As the speed drops, you need more and more left rudder to keep the climb looking straight and by the time you get to the magic turning speed, (your 45 kts) you are carrying almost full left rudder. When you slide that right boot forwards to pivot, the rudder now moves not through 25 degrees (or whatever it is) but through nearly double that angle, giving you nearly double the rotational force.

Again I have never tried it in the RF4 so this is probably just BS, but I wondered if you had?

Steve

Bob Grimstead
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Posted Tuesday, January 9, 2007 @ 07:50 AM  

Hi Steve,

Yes, that's exactly the way to do it, especially if you want to have some margin of speed for the kick.

Otherwise just pull straight up, and you'll need half rudder by the time you get to the top anyway, so you still swing it though a nice big angle. Better hope the engine keeps running, though - which it doesn't always do if you are precisely vertical - better to be five degrees short -- if you're going into wind it doesn't show anyway.

Yours, Bob

Bob Grimstead
Captain

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Registered: Dec 2006
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Posted Tuesday, February 26, 2008 @ 00:43 AM  

Hi again Fellow Fournier Folks,

As you can imagine, it's a bit difficult to get photos of my Fournier doing aerobatics, but I was recently sent this one by a friend.

It's of me flying a slightly better hammerhead, virtually pivoting around the wing-tip, although this time I'm a bit banked into the turn so it would still score low in a contest.

I actually managed to fly a few hammerheads to the left yesterday, although I haven't yet got an absolutely repeatable technique.

This only works with the 1400cc (or bigger) engine, and uses Steve's skidding climb technique with a kick at about ten knots or mph faster than to the right.

Roll on summer so we can all get into three-dimensional flying!

Yours, Bob

Bob Grimstead
Captain

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Location: Perth, Western Australia or West Sussex, England
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Posted Tuesday, February 26, 2008 @ 00:56 AM  

Other guys' comments on hammerheads (stall turns to the British):

I was having fifty-fifty success with stall turns by using a glider technique as follows. Going in with wings level, nose on the horizon. As you begin the pull hard to the vertical and before you lose sight of the ground, apply a little left rudder and offset it with right aileron. It's pretty tricky, as it's got to be quick and accurate so that you stay relatively in balance. As the nose passes through about 30 degs and you lose the horizon lock aileron and rudder in position. Hold the offset aileron through the rotation and the upline. Feed in left rudder in the upline to about half to three quarters and then give a BIG KICK with right rudder. (I had already figured out that she wouldn't go left - mouthfuls of dirt and all that). It worked sometimes. ha ha.

Another guy said: I tried stall turning the Fournier, but all I got was a face full of dirt from penduluming through the vertical. Did dozens, no luck. First I climbed sideways, then I stopped completely, then I fell to earth! I tried rudder at every speed Ė all that changed was the amount of sky.

Do persevere. Hammerheads are immensely satisfying when you do get them right.

Yours, Bob


Sam M.
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Posted Saturday, June 21, 2008 @ 08:05 PM  

Hey Bob,

our rf4 came with smoke wing mounts, im sure were not ganna put it on but just for grins, where did you buy the smoke pods? and how did you run the wiring?(if any)

Sam

Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
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Posts: 1669

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Posted Monday, June 23, 2008 @ 04:46 AM  

Hi Sam,

That's amazing. I thought only five RF4s ever had those smoke pods.

You can't buy them, I'm afraid. They were specially made for the Skyhawks and their predecessors, the Unipart Duo. John Taylor, who formed both teams is an old friend, and he gave me a set of the drawings so we could get some made up.

Actually they are not much good these days. They were made for special smoke canisters, eight inches long by two inches wide, but the guy who designed and made these was killed in a road accident, so you can't get these any more.

We have been using marine distress smokes, five inches long by three inches wide, but now Paines Wessex/McMurdo who make thes have changed the design, and they're now four inches long by six inches wide, which makes them very difficult to secure to the wing-tips. I'm pretty sure we're going to have to go for an alternative design of pod and smokes.

The wiring is easy. It runs from the insturument panel, out through the spoiler torque tubes to the end, which is the rib the outriggers attach to. From there they go externally along the recess of aileron cut-out to the balsa tips.

Let me know if you're thinking of fitting smokes, and I'll give you much more detail to prevent making mistakes and setting fire to your airplane.

Good luck.

Yours, Bob

Sam M.
First Sergeant

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Location: Santa Paula, CA
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Posted Monday, June 23, 2008 @ 01:54 PM  

Thanks for the info Bob!

i think it would be fun to have smoke, if my dad ever decides to go along with it(10% chance) ill let you know.

Sam

Bob Grimstead
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Posted Thursday, October 16, 2008 @ 11:22 PM  

Hammerheads to the left.

It is so good to be back in my little Blue friend. For some reason, despite them both having engines with exactly the same capacity and specification, the Australian one performs very noticeably better then the British red one.

So yesterday, as well as all the other stuff, I had fun flying a few stall turns to the left. They seem to go best with a little sidleslip on the way up (not adding the left rudder, and even maybe squeezin in a little right rudder). The wings end up nothing like level, but it gives you lots of rudder for the kick.

Kicking at around 50 mph (that's 5 mph more than I use to the right) she will sometimes whip around cleanly, but sometimes she won't. That's exactly how hammerheads to the right were originally for me, so I'll persevere, and try to get some video footage.

Yours, Bob

Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 1669

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Posted Monday, March 7, 2011 @ 04:54 AM  

Just to prove they can be done!

Yours, Bob


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