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Bob Grimstead
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Posted Sunday, May 31, 2009 @ 07:43 AM  

Hi Folks,

I thought you might all like to know that, after a little experimentaiton, I have been able to fly a couple more 'impossible' manouvres in my RF4.

The Derry Turn came first -- rolling throught the inverted from a steep turn one way to the other.

Then came the rolling circle. It is feasible, although it does lose 300 to 400 feet in height because of the engine stopping all the time. I go to the left (both rolls and turns) because I can push the stick further to the left -- going to the right is back-handed for me.

Finally, I can now fly an inverted recovery from a stall turn (hammerhead).

Be very careful if you want to try this.
First, you need to be certain that your elevator down travel is exactly correct. Too little and you will exceed Vne and the negative G limit while inverted, too much and you will stall inverted, and possibly spin inverted if you are not exactly in balance.

The technique I use (and no, I do NOT reccomend that anybody else tries it) is to pull up into a stall turn (hammerhead) in the usual way. Kick at the appropriate speed. Keep on full ruder all the way around that 180-degree yaw. Then, when you are pointing straight downwards, immediately push the stick fully forwards to the stops. It takes forever for the nose to pitch upwards to the horizon. When you get there, you will be doing 120-140 mph and yo will have hit exactly -3g on the latter part of push-out.

BEWARE, if you pause, even for a moment, on the down-line before pushing, or if you use less than full forward elevator, you will exceed the -3g limit and you will get very close to Vne while doing it.
And once started in the manoeuvre THERE IS NO TURNING BACK.
There is no get-out from this manoeuvre.
You cannot roll wings-level or pull.
Either would result in exceeding Vne by a huge margin and losing your wings/ tail/ head etc!

It is fun when it works though.

I'll try to get video footage on YouTube some time.

Happy aerobatting.

Yours Bob

jb92563
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Posted Monday, June 1, 2009 @ 10:40 AM  

Since there was no "Get out" escape once committed I was wondering how you approached
learning this manuever (Hammer Head inverted)?

I imagine some inverted pushes on mild down lines to see if elevator throw was going to be sufficient?

I suppose the engine stops producing power part way through as well.

Ray

Bob Grimstead
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Posted Friday, June 19, 2009 @ 11:33 AM  

Hi Ray,

Yes, all of that, and of course it was only after five years and 300 hours of Fournier aerobatics.
Of course the motor stops the moment you start the push, right through to the end, so you lose 100 feet or so of height.
But you do end up around 120mph at the end, just right for the next manoeuvre.
But check your elevator down-throw first.
Various editions of the RF4 manual state different travels. You want the one with most down travel.
As I found out when we got the red English one and I was flying for a Display Evaluator (Mike Dentith of the Fournier Skyhawks).
My last pass is an inverted run.
I rolled inverted at 400 feet but could not hold up the nose, even with full forward elevator.
That was a very short inverted pass, finished off with a nasty, dishing-out barrelly roll to get the right way up again asap.
Lots of sweating and some knee-knocking later I found out about the two lots of elevator travels.

Yours, Bob

Sam M.
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Posted Monday, October 12, 2009 @ 11:11 PM  

Ive been toying with the idea of trying a English Bunt in the 4, has anyone else done one?
Bob Grimstead
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Posted Saturday, October 17, 2009 @ 09:27 AM  

Hi Sam,

Although I am originally English, I have no idea what an English bunt is. Can you describe it?

Yours, Bob

SteveBeaver
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Posted Saturday, October 17, 2009 @ 10:04 AM    YIM

A top down outside loop.

Trying this in a Fournier brings to mind the cartoon in Eric Muller's excellent treatise on aerobatics in which he shows someone trying to hammer in a nail with a Ming vase

Mira Slovak used to outside loop the Lunak, but from the bottom up, and that aircraft was somewhat suited to the maneuver in that unusually, (for a glider) it had very little washout.

I would not try it. I don't like accelerating figures (the speed and stress increases as the figure progresses) in a glider!

Steve

Jorgen
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Posted Sunday, October 18, 2009 @ 04:00 PM  

Hi Guys,
we used to have a "gathering of aeronerds" each spring with some friends, rent aerobatic one single and one two seat glider and under the lead of an instructor friend explore "the curvature of space". I tried both the bottom up and the top down bunt with a Pilatus glider. Once you got used to the "Boeing, boeing" sound of the wings as they absorb various G-forces (which can be a bit discouraging) I found the bottom up preferrable since I found it much easier to control the entry speed from the bottom than trying to get the correct speed for the upward half after half a bunt from the top.

Bearing in mind that the Pilatus is a forgiving glider to aerobat since it is somewhat reluctant to pick up speed in the dive I´m not overly inclined to try it in the 4. Partly because I don´t know if there is enough elevator, partly because I think it might put unnecessary stresses on the engine. To me, it´s something you might try at a proper height wearing a parachute (and a rented aero you are more or less consciously beating the shit out of), but it´s not a confortable maneuvre that I´d incorporate in a routine and I think your Ming vase/hammer simile is a valid one, Steve.

But I must say that I admire your enthusiasm and curiosity, Sam. I´ve said it before and I´ll say it again- you make a great job of rejuvenating the forum!

May the 4´s be with you/ Jörgen

[Edit by Jorgen on Sunday, October 18, 2009 @ 04:05 PM]

Sam M.
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Posted Monday, October 19, 2009 @ 10:11 PM  

Im trying to put together a routine for Santa Paula's airshow 2010. Im thinking of coming up with a Glider routine(engine Off) and Bunt would be a good ending figure.
Bob Grimstead
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Posted Saturday, October 24, 2009 @ 11:09 AM  

Hi Sam,
Sorry, but I would never try to bunt the RF4 downwards, even from a speed below the stall.
I've tried pushing it upwards from near Vne with my inverted engine power mod, and can't get there.
It runs out of puff at about 45 short of the horizontal and falls back.

Look at your elevator throw.
Trailing-edge down is much less than trailing-edge up, so you do not have enough elevator authority to push it through that 180-degree bunt without exceeding Vne and tearing off the wings.

I find the 90-degree push out of a stall turn/hammerhead exciting enough. I need to whack the stick against its forward stop the moment I am pointing downhill (with almost nothing registering on the ASI) to safely complete the maneuver. That gets me to 110-120mph in level flight at the finish, with exactly -3g on the g-meter.
A single moment's pause will increase the finish speed and the negative G.
Remember -3g is the limit.

And check your elevator throws agains the manual (there are at least two versions) before you try it.
See my post on this topic somewhere on the site.

What you can try is the half-roll to inverted (at minimum possible rolling speed, and on a slight up-line) and pull-through. It will lose you a huge amount of height and you'll be going almost supersonic at the end, but you should not exceed +4g.
But do let the speed reduce as much as possible before pulling.

Yes the English bunt would be a good ending figure.
You would lose around 1,500 feet.
And your life.

Yours, Bob

[Edit by Bob Grimstead on Wednesday, January 13, 2010 @ 00:20 AM]

Bob Grimstead
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Posted Saturday, October 24, 2009 @ 11:38 AM  

Hi again Sam,

Maybe a better ending figure might be a slow roll heading directly towards the crowd on a slight down-line to keep your speed up?

I used to end with an inverted pass along the runway. Pulling into a loop from 120-130 mph and 500 feet, I would start that run at maybe 800-900 feet, fly upside-down the length of the runway, and roll back to erect at the other threshold, ending up at 500 feet, but quite slow (90ish). That roll has to start with a push to get the nose well above the horizon and plenty of top rudder, or you will dish out badly. As always, practice it up high the first hundred times.

Nowadays, I finish with a Derry turn (a half roll from a steep turn one way, through the inverted to a turn the other way). Turning towards the crowd from the A-axis, half-rolling through the inverted, and ending up turning back into my original direction, but closer to the crowd. This looks quite good, carries very little risk, and gets me into position for a low, waving pass along the crowd-line.

Your final maneuver should always be a low-risk one, because by then you will be tired and low, and low on energy (mental and aerodynamic).

I strongly feel that any 'spectacular' manuvers should come early in a sequence, when you are nice and high and fairly distant from the crowd. That way, if you do make a cock of it, you have the height and space to recover safely and continue with a curtailed sequence (something I often have to do, because I frequently stop my propeller, either in the stall turn at the top of the quarter vertical upward roll, or in the subsequent stall turn with the push recovery. If this happens in the latter maneuver, that immediately becomes a pulled recovery, followed by another stall turn to get me going back in the right direction.

Try making a list of all the maneuvers you can fly well.
Write each maneuver on a Post-it, and then string them together in a sequence with a simple, central maneuver (loop, roll, four-point roll, barrel roll etc) between each pair of turn-around maneuvers (hammerhead, half-Cuban, reverse half-Cuban etc).

Remember, it is always better to stop after three minutes, leaving them wanting more, than to bore them with six minutes of repetitive flying.

Do you have wing-tip smokes?
It makes all the difference to a display.
Remember the RF4 is not an aerobatic display airplane, merely a quite capable long-winged, low-power, graceful machine, so go for graceful maneuvers, not spectacular ones -- that's just my opinion. You can't compete with the Pittses and Extras, so try to do something quite different.

Yours, Bob

Bob Grimstead
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Posted Friday, October 30, 2009 @ 11:08 AM  

Hi Sam,

If you want details of my smoke system, e-mail me at:

bobgrimstead@compuserve.com

Be patient, Matt & I are flat-out assembling his RF4, but I'll get back to you within a couple of weeks.
If you're interested, that is.

It uses marine distress smoke canisters, about $40 to $ 50 apiece, and you need four for each flight, so it's an expensive commodity, but vital for a good display in my opinion.

Yours, Bob

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Posted Friday, October 30, 2009 @ 05:39 PM  

Hi Guys,
I agree with Bob that you need to be careful with this type of manoeuvres, and I have no experience trying anything like it in the RF 4. I also do not think it´s a good idea to have such a difficult figure at the end of a glider-type display, which would mean to do it at low altitude.

When I tried in the Pilatus I started out inverted at a high altitude, pushing up to the vertical and a hammerhead to positive G. Falling out of the vertical is a somewhat familiar situation (at least for me) and as long as you got plenty height, to me it is a logical way of getting a feel for the manoeuvre. I never did care much for the "going down" half of the bunt though, horridly unconfortable. And don´t forget that the absolute majority of spectators (=non pilots) won´t notice that it´s an unusual maoeuvre anyway. Your 4 looks so dashing good that you will stunn people by just the grace with which you fly it!

Incidently, there are other fun to be had in a 4; today this baloon happened to be stuck right on my track. It took me three circles to make the passengers cover their ears, sorry about the crappy pic but I was laughing all the way....

May the 4´s be with you/ Jörgen

Bob Grimstead
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Posted Wednesday, November 4, 2009 @ 12:24 PM  

Hi again Sam,

I do apologise for being unnecessarily harsh with you in an earlier post. My problem is that I am split between two powerful emotions. On the one hand I am really delighted to see you flying increasingly advanced aerobatics in your RF4 and I am keen to help and encourage you in any way I can.
But, on the other hand, I have had more flying friends, heroes and acquaintances than I care to count killed while performing low-level aerobatic displays. No fewer than four well-known and well-respected men – those at the top of their game – have died this way in the past 12 months.
I am very keen to see you progress and increase your ability and repertoire, but I could never live with myself if, as a result of my advice or encouragement, you died or hurt yourself.

Aerobatics are the ultimate three-dimensional expression of flying artistry and skill, but the moment you come below 1,000 feet, you completely rob yourself of one of those three dimensions. You can go left and right, or back and forth, but if you go just one foot too low, you’re dead.
In other, more powerful airplanes, if you start getting too low you can climb, but the RF4 has so little power this is just not an option.

Once the base of my manoeuvres drops below 700 feet I stop doing whatever is on my sequence card, and revert to loops, very carefully flown barrel rolls (statistically the biggest killer) quarter-clovers and gentle wing-overs (another surprisingly common killer). If I fly them carefully and the temperature and pressure altitude are not too high (and it’s not too gusty), I can execute these manoeuvres without losing height. My written sequence allows for this, but sometimes I have to abandon the more complex manoeuvres early.
Indeed, one hot and gusty day in Perth, I finished with a simple 360-degree steep turn, because I had gotten down to my 500-foot base limit height. Talking to the organisers and spectators afterwards, they all said what a great display it was, so much nicer than the previous year’s. Why? Because I was lower. They didn’t even notice that for the entire second half all I flew was simple manoeuvres and a steep turn.
The bigger lesson is that the local state champion lives nearby, and he was watching from his front lawn. He also congratulated me. Not because I had flown particularly advanced manoeuvres, nor because my flying was very precise (it wasn’t) but because I had the sense to stop pushing it and to fly safely once I got down below 1,000 feet.

I have some more general thoughts on RF4 display aerobatics, but because that’s a slightly different subject, and possibly of wider interest, I will start a new topic.

Yours, Bob

Sam M.
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Posted Wednesday, November 4, 2009 @ 03:29 PM  

Bob, I have never found any of your posts harsh or offensive, I ALWAYS appreciate you're posts.

Keep em coming!

Sam

jb92563
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Posted Wednesday, November 4, 2009 @ 05:02 PM  

On the note for the smoke cannisters being a little pricey I thought this might make it more economical by making your own
from a supplier of the materials.

http://www.skylighter.com/smoke-bombs.asp

There are totally home made recipes as well if you do a google search, but require more experimentation with proportions to get things right.

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org

Bob Grimstead
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Posted Monday, November 30, 2009 @ 10:58 AM  

Hey Sam,

When is the Santa Paula air show? What date?

I ask, because it might be possible for you to fly a full outside 360-degree negative-G rotation, but not by starting at the top.

I've been experimenting with canopy-up humpty-bumps, partly because Rob Dorsey says they're so nice to perform.
I don't really find them enjoyable, although they are satisfying.

Starting with that, I've now progressed on to the push recovery, meaning I fly 270 degrees of negative G.

Bear in mind that
a) I have a kind of inverted system, which means my engine keeps running. Yours won't.
b) There is no get-out recovery manouvre once you have gone through the vertical downwards, so you are committed. Any attempt at pulling here will kill you as the wings come off.
c) You need to be sure that you have the full 20 degrees of elevator down-throw before even attempting this.
d) You need to have lots of inverted time first, so that you are comfortable with negative G and the required rudder inputs (opposite to the erect-flight ones, natch).
e) You need lots of height.
f) You need lots of bottle.
g) You need low engine compression or the hand-starter to get the engine going again.

I start with a vertical climb (this alone takes lots of practice).
At 40-45mph, I push full forward stick (feel it whack against the stops and HOLD it there).

The ASI reads zero as I go over the top. Any faster and I stop and fly away level, because a faster entry speed means exceeding -3g and a high exit speed.

I keep pushing, use aileron to hold the wings level and rudder to stay in balance -- otherwise at these low airspeeds and high negative G it would be only too easy to flick into an inverted spin.

Having flown a few, I realised that I ended up in level inverted flight at between 100 and 120 mph, so I reckoned I could maybe keep on pushing back up to the vertical again. That's the full 360-degree rotation in pitch.

I managed to do so about ten or twelve times, hoping to kick into a hammerhead off the top, but every single time I failed, fell into a tailslide and had the propeller stop. Matthew was watching and said it was a great spectator sport.

I was finally stopped by nightfall, but I realised after landing that since I ended pointing vertically upwards at about 50mph, it should be possible to go around again.

I'm fitting a new engine to my British Fournier, so I won't be repeating this exercise until that is run-in, next May, but I'll try some more when I get back to Australia after Christmas.

Meanwhile, Happy Holidays to you all.

Yours, Bob

[Edit by Bob Grimstead on Wednesday, January 13, 2010 @ 00:25 AM]

Sam M.
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Posted Tuesday, December 1, 2009 @ 01:42 AM  

Its in July of 2010
Bob Grimstead
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Posted Wednesday, December 2, 2009 @ 08:44 AM  

Okay, so you have plenty of time for practice and experimentation.

I have flown only one canopy-up humpty-bump with the throttle closed (ie, like your motor, no power when inverted).

It took a very long time to get around and back up to the vertical, so it takes quite a lot of bottle, but it can be done if I screw up my courage, don't flinch and keep that stick against the forward stop.

I did not note the height loss, but it was probably considerable.

Minimum airspeed (erect, level, when horizontal, going over the top in the first quarter) zero.

Maximum airspeed (inverted, level, horizontal in the third quarter) 120mph.

Maximum negative G -3.0g.

It is feasible, but I would not attempt it below 2,000 feet (for fear of flicking inoto a negative spin), which makes it no good for a finishing manouvre.

Please do not attempt it unless you have done all the foregoing practice, and have some means of re-starting your engine, because the propeller will stop when you're going uphill in the fourth quarter. And you will probably tail-slide out of it.

If I get a chance to fly some more when I'm in Australia (in the New Year, now) I'll let you know.

Yours, Bob

[Edit by Bob Grimstead on Thursday, April 28, 2016 @ 04:16 PM]

Bob Grimstead
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Posted Saturday, January 9, 2010 @ 01:13 AM  

Okay, Now I'm in Australia and have flown a few more of these 'outside/negative' loops - all with my 'inverted carb' mod.

I could not get the camera to cooperate, but starting at 3,000 feet, the lowest I got during the rotation was 2,750 feet (indicated, remember the lag). I tried pushing over the first humpty at 40 and 45 knots, and although that second 180 degrees seems to take forever, it IS possible to complete a full 360-degree rotation to end up pointing vertically upwards again.

The problem is that, by then, you are going VERY slowly (about 40 indicated). I've tried kicking into a hammerhead/stall turn but by then there's no fuel left in the float bowl to push the tail around, so I just tail-slide out (I tried ten of them).

Yesterday I tried pushing on over for the full 540-degree rotation, ie, starting from the up-vertical, pushing 360 degrees back to the up vertical and then keeping on pushing over the top to the down vertical. You can do it, but the airspeed is so low going over the top the second time that my propeller stopped all four times I did it.
The height used by the bunt is 250 to 300 feet, but then I lose anonther 300 feet diving from zero airspeed to Vne to get the propeller spinning again.

More experimentation required.

If you want to see the simple push to level from a stall/turn hammerhead, go to:
http://www.youtube.com/watch?v=hVKZg842hZo

It happens at time 2:00.

More info when I have it.

Yours, Bob

Bob Grimstead
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Posted Wednesday, January 13, 2010 @ 01:04 AM  

Hi again Guys,

Now I have flown that 360-degree negative-G rotation again, but ending it with a 180-degree down-vertical roll.
I took my camera in the cockpit and filmed it to read a few instrument figures.

The result is on YouTube at:

http://www.youtube.com/watch?v=M53Bhowf_cg

Note:
Because of my rudimentary ‘inverted fuel system’, the engine keeps running until I reach the up-vertical the second time.
That push-though takes a looong time, even with the help of the motor. (Actually it is only 14 seconds, but it seems like a lifetime.
Once I get to the up-vertical again, the engine and propeller both stop.
As I flop ‘over the top’ the second time, the ASI registers a true zero (whereas it only drops to 20 knots on the first push-over). And it really is a ‘flop’ over.
The down-vertical roll starts at zero airspeed, but by the time it is finished I am at Vne, pulling +5 g and the engine is at red-line.
I HAVE ALSO LOST A FULL 1,000 FEET!

As always, this is just for your interest and education – basically so you that don’t go out and try it yourself. As you can see, there are several ways you can kill yourself flying this one, apparently simple figure. The most likely would be from G-LOC – G-induced loss of consciousness. After you have pushed –3g for fifteen seconds or so, it is just asking for physiological trouble to then pull +5g.
Needless to say (I hope) I shall not be doing this again.

So, DON’T TRY THIS AT HOME FOLKS.

And I’m sorry Sam, but I cannot see how any of this could possibly be incorporated into an airshow display. If you are high enough to complete the manoeuvre, even with a very small safety margin, you will be too high for the spectators to see that you are inverted. So you would be better off just to fly a simple pulling loop.

Yours, Bob

Mira Slovak
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Posted Thursday, January 14, 2010 @ 11:56 PM  

AMEN.

Mira Slovak.

Sam M.
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Posted Tuesday, January 19, 2010 @ 04:43 AM  

Thanks a bunch Bob! I always enjoy reading your posts. I am definitely scratching that figure, I think I spoke much to soon on the matter. I want to end up, up-side down at the end of the routine heading down wind around 800 feet. With a Ton of practice much, much higher of course. everything is still up in the air as far what figures to use for now.

Sam

[Edit by Sam M. on Tuesday, January 19, 2010 @ 05:02 AM]

Bob Grimstead
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Posted Monday, February 22, 2010 @ 10:08 AM  

Okay Guys,

I was finally able to get my good aerobatic buddy, David Brown, to video me flying this manoeuvre while I trailed smoke.
It's not full-on marine smoke, just a couple of one-minute hand-helds, but it does reinforce my opinion that, regrettably (because I enjoy the challenge of flying it) the manoeuvre is not worth including in a display.

I must have flown it about 25 times -- and thanks for the original idea Sam -- but only once was I able to complete it without the propeller stopping. That was the time I hit a massive, limits-busting negative 4.0g. After that one, I had to run a full airframe over-stress check, so I'm not about to do that again.

As you can see, I am starting at 1,500 feet, and it is barely even possible to recognise that I am inverted, let alone that I have full forward stick throughout. This time, like most of the others, I was able to get the prop rotating and the engine running again by about 1,000 feet (just as the clip stops), but on one occasion that day I was down to 500 feet abeam the threshold and expecting to have to land dead-stick before it started spinning. Of course, this lack of safe repeatability just is not acceptable in display flying.

Have a look, and see what you think. http://www.youtube.com/watch?v=Lj6-voTHyj4

Yours, Bob

jb92563
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Posted Monday, February 22, 2010 @ 11:57 PM  

It sure did take a long time to pull out inverted.

I was wondering if you have ever tried pulling spoilers on the down line or any time during your display for speed control?

I don't suppose the spoilers are terminal velocity brakes that keeps top speed in check on the vertical?

I somehow imagine that pulling spoilers inverted might delay the pullout even further?

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org

Bob Grimstead
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Posted Tuesday, February 23, 2010 @ 05:42 AM  

Hi Ray,

No, I've never used the spoilers during aerobatics. You will be aware from the handbook that they have a fairly low limiting speed, plus lower G limits than clean flight. But mostly with aerobatics in this little low-powered airplane everything is about conserving energy, and pulling the spoilers is the best way of throwing away energy.

Incidentally, that's a push-out, not a pull-out of course.

Yours, Bob

Bob Grimstead
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Posted Monday, March 21, 2011 @ 10:49 AM  

http://www.youtube.com/watch?v=wAU6oqk8fI4

[Edit by Bob Grimstead on Monday, March 21, 2011 @ 10:50 AM]

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Jorgen
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Posted Monday, March 21, 2011 @ 11:38 AM  

Very nice flying Bob,
so what did you do- alter the control throw? And how do you manage to keep the engine going for so long under negative G's? I bet that's what makes a lot of the difference.

May the 4's be with you/ Jörgen

Bob Grimstead
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Posted Monday, March 21, 2011 @ 08:26 PM  

No Jorgen, I certainly didn't alter the control throw, although I did ensure it was correct.

I had already completed the manoeuvre last year (see http://www.youtube.com/watch?v=Lj6-voTHyj4 ), but this was just a better clip.

I have flown it many times without the engine, it just takes longer.

Anybody can make the Zenith 28RXZ carb work for a while upside-down.
There are some clues in this thread:
http://sbeaver.com/cgi-bin/fournier/cutecast.pl?session=DdfbmL7ZiWPs7CtO0w80BsM7Gf&forum=19&thread=546

I will post more detail when I can find the photos.

Yours, Bob

[Edit by Bob Grimstead on Monday, March 21, 2011 @ 08:58 PM]

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