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Bob Grimstead
Captain
Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2046
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 Posted Friday, January 5, 2007 @ 00:00 AM
Fournier inverted flight is one of the most serene and ethereal aerobatic experiences I’ve ever had. I like to stop the engine and prop in erect flight, roll inverted and go for a nice long glide. It’s a great way to force the blood back into your brain cells. I once glid, glode or glided over ten miles back from an aerobatic sortie at 6,000 feet over the sea to my home airfield, silently rolled erect as I joined crosswind, pulled out the spoilers, and flew a normal dead-stick approach and landing. Nobody saw or heard me, but I loved it!
Inverted gliding gives a better view and cleans out the cockpit, so vacuum it out thoroughly first. And does it chuck out oil. See Heavy Breathing in the engine section. Thermalling is also a bit more challenging. Stop the motor and propeller before trying it, to minimize oil loss. Set the trim fully forward if you’re going to make a long inverted glide. That takes some of the pressure off your forearm and wrist.
I got these figures test flying my own RF4. Inverted gliding through 1,000 feet from 4,000 feet to 3,000 feet, prop windmilling, and throttle closed, tapping the altimeter (which, like any glider’s or jet’s sticks if you don’t).
@ 60 knots = 2:00 = 500 fpm
@ 70 knots = 1:30 = 667 fpm
@ 80 knots = 1:06 = 909 fpm
@ 90 knots = 1:00 = 1,000 fpm
I usually glide at 70 to give me a nice big stall margin, and accept the (slightly) reduced performance. As you can see from the top photo, the correct attitude is with the nose somewhat above the horizon. Since this is also pretty much where the horizon cuts the canopy at top speed in erect flight, and a useful reference for rolls as well as inverted flight, I've stuck a piece of PVC tape inside the canopy in the correct position. The nose is just a teensy bit too low in the bottom photo.
Minimum speed (with the stick fully forward, power off) is around fifty knots. I do not have long arms, so I originally found it hard to get full forward stick for the inverted glides (see my cranked stick in Modifications). I’m told you don't have enough forward elevator in a Fournier to stall it upside-down, and it seems that's probably right, although the feel does go very odd laterally at minus one G with full forward stick below fifty knots - a bit wing-wobbly, as if it is maybe just about to stall or flick.
Always ROLL out from the inverted. Pull-throughs come MUCH later (split-S) and are NOT an emergency recovery maneuver.
The emergency recovery from any inverted flight is
a) push the nose well above the horizon and
b) roll out.
If you don’t have enough speed to roll cleanly after pushing the nose above the horizon, allow the nose to drop a little, gain speed (to, say, 80 knots/90 mph) and then push the nose back well above the horizon before rolling out.
MAKE YOUR FIRST ATTEMPT AT A GREAT HEIGHT (5,000 feet is good, 6,000 feet is better).
BUT FIRST, GET PROPER INSTRUCTION.
Have fun, but DON'T PULL ANY G AT ALL after a period of inverted flight. Even a steep turn. If you don't know about G-loc, find out about it now. It has killed many (very many) highly competent pilots.
Happy Fournicating, Bob
[Edit by Bob Grimstead on Sunday, January 14, 2007 @ 11:40 PM]
[Edit by Bob Grimstead on Tuesday, February 26, 2008 @ 01:04 AM]
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Bob Grimstead
Captain
Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2046
|
Posted Monday, November 24, 2008 @ 00:49 AM
I found another inverted photo.
Yours, Bob
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Sam M.
First Sergeant
Gender: Male
Location: Santa Paula, CA
Registered: Jul 2008
Status: Offline
Posts: 228
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Posted Wednesday, November 26, 2008 @ 02:38 AM
Hey bob,
I was wondering if you had or could get some measurements as to were you put your PVC tape.
thanks,
-the lazy pilot
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Bob Grimstead
Captain
Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2046
|
Posted Saturday, November 29, 2008 @ 04:26 AM
Hi Sam,
No, you’re not lazy. There is no point you making flight after flight to get those marks in the correct place when somebody (me) has already done most of that work for you. But beware: the positions of those marks depends upon your own personal eye position within the cockpit, and that depends on where you sit, how high, how far forward and how reclined. My marks will be a starting place for you, so that you get them in the correct position for your eyes.
I started by making them with wax pencil (Chinagraph or Staedtler Omnichrom etc) and then replaced these with PVC tape when I was sure they were in the correct place (for me).
The one directly ahead of me gives me the required attitude for flight at maximum level speed at 1,500 feet. If I place that on the horizon, and leave the throttle wide open, the airplane should fly level once its speed has stabilized.
The top of my cowling is on the horizon at stall speed, so depending on my current speed, I should be able to plonk the horizon in about the right place somewhere between those two markers and fly away level from any given manoeuvre – important in competition.
It also so happens that if I place my ‘max level flight speed’ line on the horizon when inverted, the airplane glides at about the right speed, so it’s useful for that, too.
Above my head, in my sight line when I look up at 45 degrees is another line. If I put that one on the horizon, it gives me the 45-degree down line when I’m in erect flight, and the 45-degree up line when I’m in inverted flight. They are both most useful in a half Cuban or a half reverse Cuban. By making it a long line, it also helps me to keep my wings level.
The cross on the right of my canopy gives me the 45-degree climb and descent lines. Because a true 45-degree line is a bit risky (you can exceed Vne while rolling on a 45-degree down line, and completely run out of speed when rolling on a 45-degree up line) they are not quite at 45 degrees to the horizon, but closer to 35 degrees. Also, because the RF4 has a very different attitude inverted to its erect attitude (it is much more nose-high when inverted) they are not at 90 degrees to each other either. In other words, they are not symmetrical.
I’ll try to photograph then, so that you know what I mean.
Finally, when I look at that cross, it is superimposed on the root of my wing-tip sights, right at the forward edge of my wing-tip. By checking that before each flight, I know I am seated correctly, and so the other lines will work properly.
Tomorrow, I’ll try to remember to measure where the marks are, and that will give you a starting point.
Happy aerobatting.
Yours, Bob
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Sam M.
First Sergeant
Gender: Male
Location: Santa Paula, CA
Registered: Jul 2008
Status: Offline
Posts: 228
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Posted Saturday, November 29, 2008 @ 02:05 PM
thanks Bob!
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Bob Grimstead
Captain
Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2046
|
Posted Thursday, December 18, 2008 @ 08:05 PM
Hi Sam,
I didn't go down to the airfield for two-and-a-half weeks, which is dreadful when you consider it is summer!
Now I have measured those lines (remember, they're for my head and eye position).
The two horizontal ones are on the center-line, 12.5 inches and 25.5 inches up from the front of the canopy.
The center of the diagonal cross is 13.5 inches up from the right canopy lower edge, and 16 inches horizontally forward of the sloping rear edge. The diagonals are not quite at 30 degrees to the horizon, but you will have to experiment, not only for position, but to get the angles right for you when you are flying Cuban eights and reverse Cubans.
I hope that's useful.
Yours, Bob
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Sam M.
First Sergeant
Gender: Male
Location: Santa Paula, CA
Registered: Jul 2008
Status: Offline
Posts: 228
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Posted Sunday, December 21, 2008 @ 04:16 PM
thanks bob, Ill let you know how they work out!
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