Curious about simple aerobatics

[Jim Sower]

<... Remember - Jim's flying a Velocity at 125 - 150kt. The Cozy at 200+ will be a LOT quicker to turn...>

True. Although my references to maneuverability derive from flying my Long-EZ (O-235, 140-160 kts). Go a lot faster and everything happens faster.

 

<... I really wish I hadn't mentioned the mountain, or the clouds, for that matter...>

So do I. Since it was not particularly relevent or useful and generated more heat than light, let's pretend that part of the discussion never happened.

 

<...It's just that in one ear I'm hearing Berkut drivers blacking out at 9 G, yet in the other ear, pulling the hardest manouevre I can think of, from 200mph, only results in me stalling inverted at 20mph. I'm guessing there's some middle ground...>

There certainly is. Interestingly enough, that's exactly where the reality lies.None of these airplanes will maintain (that's a key word discussing hi-G) 6G or even 4G for any length of time. Truth be told, even fighters can't maintain a 6G level turn in basic engine, much less 9G. It's not so much what kind of G you can pull, but how long you can sustain it and what you have to do to sustain it longer. That varies both with airframe and engine (but let's talk just canard community here). An O-235 Long-EZ will not be as acrobatic as it's O-320 brother, and will pale alongside an O-540 Berkut. All will do overheads if you start fast enough but obviously the O-235 EZ (mine) has to start a lot faster (like 170 or 180 kts or so to complete a decent loop) than the 240hp Berkut.

 

As John Slade pointed out ....

<...acclimatization ... heavy G aerobatics ... concentration on recovery from unusual positions ... get used to being totally disoriented (under the hood) ... making the RIGHT moves to recover ... more prepared ... for the JFK jr syndrome ... problem with disorientation is that you're likely to make the WRONG moves and make the situation much worse very quickly ... training teaches you to read the gauges and totally ignore what you're butt and ears are telling you...>

That is exactly the point. That's where this whole discussion was/should have been going when we got sidetracked by all the silliness and minutae. Most of that is on me.Thank you John!!

 

<...I heard of a Long EZ climbing in a steep turn, that sort of information can save your life...>

Yes, but only to the extent that you know how long you can climb in how steep a turn before you run out of peanut butter. That varies so widely from one airplane to another that you have to work it out for your own ride. It's fun to see how long you can sustain these types of maneuver and work out how best to recover when the initial maneuver ends.

 

An excellent example of this line of thought might be the guy who was flying up a canyon, trying to climb out of it. The canyon got steeper and narrower faster than he could climb. He ended up killing himself trying to make a level 180 in too tight terrain. If he'd practiced wingovers and hammerheads and the like, he'd have known how much space, altitude and airspeed he needed to make his "emergency 180". But he hadn't. Pontificating that he should never have entered that scenic valley (which is what it was before things started deteriorating) begs the issue.

 

I think we're getting back on track here.

[mjgundry]

Originally posted by John Slade

I believe strongly that UP training is essential for any pilot, just as I believe that skid pan training is essential for any driver. I wish they has public skid pans in the US like they do in Europe. Skid training has saved my butt many times over.

 

Skid pan training? Isn't that what church parking lots are for.

 

Though I suppose they don't get quite as icy down in Florida as they do up here.

[John Slade]

Skid pan training? Isn't that what church parking lots are for.

Right, or mall parking lots. The concreate bumpers can be a problem, though

 

>Though I suppose they don't get quite as icy down in Florida as they do up here.

No, but I did my 15 years in New York (per the immigration requirements) before they'd let me move.

 

Seriously - in UK they have large circular, slighly depressed in the center, fine tar areas with oily water running from the outside down into a drain in the middle. They put bales of hay around and let you take you're own junker car in there. Helluva way to spend a Sunday afternoon. Should be a part of every driving instruction course. Starts to get really fun when they let three in at a time. The point is that if you've experienced "it", then you've got a better chance of dealing with "it" when it happens unexpectedly.

 

Back to flying, Jim's right. The "emergency 180" is a perfect (if beginning)example. You need to know what you and the bird can do.

[No4]

Thanks guy's it's all becoming clearer,

I certainly hope I never get into the situation described by John, of trying to control any airframe whilst getting tunnel vision / blacking out.

I've spent a fair bit of time "under the hood" in my IFR training, with some unusual attitudes, but I'd hate to try it anywhere near terrain. Shivers...

I'm planning to do my aerobatic rating in a Citabria before easter, I guess by then I'll have a better idea.

 

Looking at the CAFE report, it mentions 30' degrees per second roll rate. So either a) pulling a max rate would take 3 seconds to 90' bank, or b) pulling an Immelmann (sp?), which I'm lead to believe is the fastest way to reverse direction, should take 6 seconds for the 180' degree roll, or c) a wing over, again 3 seconds to 90'; it seems three seconds are required to be at 90 degrees to your original path of flight.

200 mph is 100 metres per second, so even from high cruise the Cozy should be able to turn 90' in 300 metres or less.

 

What Jets did you boys used to drive? Jim was it the A4 Skyhawk? John, I'm guessing anthing from the Hunter to the Tornado or Jaguar, or perhaps the Hawk? Please don't say the Lightning, as I might die with envy.

 

I agree about the skid pan training, I once had a very pleasurable afternoon in a matt green MK Bedford 4 tonner ( one, for the use of) performing donughts and hand brake turns on a concave skid pan which a nice man with an anger management problem had kindly sprayed with diesel and water.

[John Slade]

I think of Unusual Attitudes as a poor brother of Unusual positions. In UAs for IFR they're usually fairly tame and don't involve much if any disorientation. Shut you're hood down all the way, then get the guy to REALLY throw you around for a few MINUTES. Then have him pick a nasty position - like sliding backwards out of a hammerhead or descending inverted almost at VNE. Give yourself a 2 second glance at the instruments then take action. You can practise by getting a book filled with instrument situation senarios.

 

so even from high cruise the Cozy should be able to turn 90' in 300 metres or less.

I'm sure someone will get into the physics, but I'd bet that's not right. Just cause you can ROLL 90 in 3 secs doesn't mean you can TURN 90 in 3 secs.

 

Please don't say the Lightning, as I might die with envy.

Lightning.

No, just kidding. Lightning was a bit before my time. I did get my hands on an F4 once, though. I flew the Jet Provost (Strikemaster) two seat trainer. Was top in class in aerobatics. Bottom of class in instrument flying. They threw me out before I got to gNats.

 

Jim was one of those guys who can't land crosswind, so they have to turn the runway into the wind to help them land. A10s or warthogs, I think.

[Jim Sower]

<... Looking at the CAFE report, it mentions 30' degrees per second roll rate. So either a) pulling a max rate would take 3 seconds to 90' bank ...>

Sounds like you're confusing roll with turn. What you've done is put in full left stick, and in 3 sec you have 90' bank, but you're still heading north.

 

<... b) pulling an Immelmann (sp?), which I'm lead to believe is the fastest way to reverse direction, should take 6 seconds for the 180' degree roll ...>

I seriously doubt it's the fastest way to reverse direction. As you pull up, you keep slowing down, and you have to be able to fly after you roll out on top. You could do it in a Cozy, but you'd have to start pretty fast and you'd not have much to spare on top. NOT a maneuver for the box canyon scenario (you haven't nearly the entry airspeed you'd need to pull it off). As a matter of fact, for max rate turns, G rules. Consider: your level turn radius is a function of speed and how many G's you're pulling (increases with speed, decreases with G). The number of G's you can pull is a function of the square of speed. So if you double your speed at a given amount of G's you double your turn radius, but by doubling your speed you've increased the G's you can pull by a factor of 4, so if you pull all those G's, you reduce your turn radius very substantially. Theoretically, if you were structurally able to pull enough G's, you could fly up your own ass. What that all boils down to is that you're turn radius decreases with increased airspeed provided you pull all of the G's you are able to at a particular airspeed. At some point (maneuvering speed) you've reached the point at which you can pull all the G's you're allowed to and that's your minimum turn radius. Sounds counter intuitive, but it's so. Again, we're talking level turn, and you have to pull to buffet at whatever speed you're at. If a Cozy will juuuuust pull 4 G's at, say, 130 kts, and will juuuuust pull 6 G's at 160 kts, and you're at 130 and I'm at 160, I'll turn inside you every time.

 

<... c) a wing over, again 3 seconds to 90'; it seems three seconds are required to be at 90 degrees to your original path of flight. 200 mph is 100 metres per second, so even from high cruise the Cozy should be able to turn 90' in 300 metres or less...>

You're confusing pitch with roll with turn. What a wingover buys you is it allows you to turn around in a tight space. Not as tight as a hammerhead (you can reverse direction in a canyon with a width that juuuuust exceeds your wingspan) but it does (or can) approach that. It's not a level turn, it's not even done in one plane, so the rules in (b) don't apply, but it's comfortable and easy, safe and most important, has the lowest entry airspeed of any of the choices. Modify it a little and it starts looking a lot like a hammerhead but not nearly as abrupt.

[No4]

Sorry for not being specific, I was implying not simply the roll, which of course would obviously have you in the same direction, but also rear stick as well to the point where a) one is close to tunnel vision / blacking out or b)one's paint/filler is about to come off the wing, or alternatively the Immelman with a verticle pull up.

Anyway, I don't know how to calculated G loading, and that's the decider in slowing down/changing direction.

Rubbish of me to suggest the roll rate had something to do with it.

 

I understand completely what you say Jim, the wingover is the best way to turn around, short of an Immellmann or Stall turn, both of which I am unlikely to attempt in a Cozy.

Thanks

 

[Marc Zeitlin]

Originally posted by Jim Sower

As a matter of fact, for max rate turns, G rules. Consider: your level turn radius is a function of speed and how many G's you're pulling (increases with speed, decreases with G).

 

This much is true.

 

Originally posted by Jim Sower

The number of G's you can pull is a function of the square of speed. So if you double your speed at a given amount of G's you double your turn radius, but by doubling your speed you've increased the G's you can pull by a factor of 4, so if you pull all those G's, you reduce your turn radius very substantially.

 

I don't know what you're remembering here, but it isn't your physics or flight dynamics. The radius of a level turn is:

 

R=V^2/a

 

Where "V" is the velocity and "a" is the acceleration. Doubling your speed will quadruple your radius, and doubling your "G" loading (acceleration) will halve your radius. You had that backwards.

 

Originally posted by Jim Sower

At some point (maneuvering speed) you've reached the point at which you can pull all the G's you're allowed to and that's your minimum turn radius. Sounds counter intuitive, but it's so.

 

Sorry, but it is NOT so. Assuming you have enough power to maintain level flight, your minumum radius turn (level), as shown by the equation above, will occur at the MINIMUM speed with the maximum acceleration. I guarantee you that in a canard aircraft (or any aircraft, for that matter, that you're willing to fly at stall speed), flying at the maximum bank angle, stalled, with the stick all the way back, will get you the minimum turn radius. See Page 260 - 264 of "Performance of Light Aircraft" by John T. Lowry for graphs of the turn radii of a Cessna 172. It is obvious from looking at these graphs that flying right at stall at bank angles of 60 degrees or above AT THE MINIMUM POSSIBLE SPEED) will get you the minimum radii. He discusses the power needs as well.

 

Originally posted by Jim Sower

Again, we're talking level turn, and you have to pull to buffet at whatever speed you're at. If a Cozy will juuuuust pull 4 G's at, say, 130 kts, and will juuuuust pull 6 G's at 160 kts, and you're at 130 and I'm at 160, I'll turn inside you every time.

 

This makes no sense. AOA determines G loading. Instantaneously, you can pull whatever G loading the elevator authority will allow, and it will last for however long the power available will let it (or else you'll start down). If you can pull 6 G's at 160 Kt, you can do it at 130 Kt, and the slower speed will have a smaller radius. Instantaneous G loading is not dependent upon speed - I can do a 60 degree, 2 G turn at any speed above 85 mph (canard stall) in my plane. I can't MAINTAIN it for very long at anything over 100 mph or so, but I don't need to to do a 180.

 

At any rate, if it takes 2 seconds for me to roll to 60 degrees, and I maintain that at 100 mph, I've got about a 125 m radius turn. Having practiced these many times, I can tell you that it looks like I'm spinning on the inner winglet.

[No4]

Cheers Marc,

I was scratching my head at that one aswell.

I think you described it spot on.

[Jim Sower]

Marc,

I don't think we're quite on the same page (but almost - with mainly jargon and/or semantics getting in the way). Let's set up some parameters we can agree on:

1. SL, Std day - so we don't get into IAS/TAS issues.

2. Max Turn - pull to the onset of stall. Assume that max turn occurs at a particular AoA which is right where the Cl/Alpha curve breaks, where flow begins to detach and cal it "light" or "onset of" buffet (stall).

3. Sufficient Power to maintain a level turn at the G/AoA and airspeed we're discussing.

4. Any turn requires some G - 1 deg of bank offsets the lift curve and level flight will require 1.0001 G or something - you get my drift.

OK. That said:

A. Minimum airspeed, strictly speaking, occurs at the AoA we described above as our limit. Therefore there is only EXACTLY 1.0000G available, and it takes 1.00001 to turn at all so you can't turn and turn radius in infinite.

B. Increase airapeed just a tad from minimum, and you have, say, 10' bank available before you get to your "Critical AoA" and you can turn. IIRC the relationship between bank angle (BA) and G to maintain a level turn is something like G = 1/cos(BA). 60' bank will buy you a 2G level turn.

C. We are operating at the single AoA defined in (2) abve, so Cl is constant, Wing Area (S) is constant, q=kV^2 so Lift=KV^2. Double V and you quadruple Lift (so you're pulling 4G).

 

<... your minumum radius turn (level), as shown by the equation above, will occur at the MINIMUM speed with the maximum acceleration ...>

I'm not sure, but I think you're describing the Max Turn I described above but articulating it a little differently.

 

<...I guarantee you that in a canard aircraft (or any aircraft, for that matter, that you're willing to fly at stall speed)...>

YES!!! If you're not willing to fly at stall speed, you don't get to do a max turn because it only happens at stall speed.

 

flying at the maximum bank angle, stalled, with the stick all the way back, will get you the minimum turn radius...>

YES AGAIN!! I believe that's what I've been arguing all along (except I'm using the onset of buffet rather than "full stall" as the max practical AoA). The max bank angle is the arccos(?) of G. 1G supports zero bank angle, infinite turn radius. 90' bank requires infinite G to remain level (but buys ou infinitessimal turn radius), so somewhere between 89.9' and 90' bank, you "...flew up your own ass...":D

 

<...It is obvious from looking at these graphs that flying right at stall at bank angles of 60 degrees or above AT THE MINIMUM POSSIBLE SPEED) will get you the minimum radii. He discusses the power needs as well...>

EXACTLY!! Well, sort of. 60' bank, level, at 1.414 * wings level stall speed will buy you a 2G turn at buffet as I described above, and a 2G turn .....

 

<...This makes no sense. AOA determines G loading...>

YES!!!

 

<... Instantaneously, you can pull whatever G loading the elevator authority will allow, and it will last for however long the power available will let it...>

NO!! You can pull whatever G loading the pitch authority AND AIRSPEED will allow. At or below "maneuvering speed" you will hit "high speed stall" (which we have defined above as where a "max turn" happens), at the G load corresponding to your airspeed, and THAT will determine your load factor and turn radius. Ever look at a Vn diagram? I wouldn't be surprised if they don't make them for Cessnas, but the heavy iron needs them and pilots need to know them well.

 

Incidentally, "maneuvering speed" is the lowest speed at which it is possible to load the airplane to it's G limit (6 for the Cozy). They call it maneuvering speed because that's the highest speed at which you CANNOT overstress the airplane. That's the speed at which you want to penetrate T-storms and conduct ACM.

 

<...If you can pull 6 G's at 160 Kt, you can do it at 130 Kt...>

NO! You can NOT!. Do the math. If "miniumum airspeed" is 60 kts (for the sake of argument), you can't make a level turn AT ALL at 60 kts. At 120 kts you have 4G available, at 180 kts you have 9G available.

 

<...if it takes 2 seconds for me to roll to 60 degrees and I maintain that at 100 mph, I've got about a 125 m radius turn. Having practiced these many times, I can tell you that it looks like I'm spinning on the inner winglet...>

But if you would pull to buffet, you'd get a 110 m radius. You're not in a max turn unless you're stalled. For our purposes, use "light buffet" like I alluded to repeatedly throughout (all of) my post(s). 60' bank only allows 2G level. Go to 120 mph, pull to light buffet (which will be 4 or 5 or however many G that airspeed will support) and you'll be turning even tighter. In the interest of caution, I'm assuming you have no reliable notion of what 5G feels like, so it would be a good idea to avail yourself of a G-meter before you get too deep into this. But, basically, get yourself 100 mph, a steep bank and pull into a light buffet. then go to 120 mph and pull to buffet (whatever it takes). Tell us what you discover.

 

The basic issues here seem to me to be:

A. G-load for a level turn is IIRC the cosecant of the bank angle (1/cos BA).

B. Turn radius for a level maximum turn plotted against airspeed then becomes a (slightly modified?) hyperbolic curve with th vertical asymtope(sp?) (turn radius) at "minimum" speed (infinite turn radius) and the horizontal asymtope at the x-axis (airspeed).

 

I think I didn't describe/articulate in sufficient detail what I meant by "max turn" and "buffet", and that you didn't try as hard as you might have to decipher my jargon ....

 

I think that, once again, we find ourselves in Violent Agreement... :D

[Marc Zeitlin]

I've deleted all the stuff we agree on - let's continue:

 

Originally posted by Jim Sower

NO!! You can pull whatever G loading the pitch authority AND AIRSPEED will allow. ........ Ever look at a Vn diagram? I wouldn't be surprised if they don't make them for Cessnas, but the heavy iron needs them and pilots need to know them well.

 

I am familiar with Vn diagrams, and they are available for GA aircraft. After a night of pondering, I agree that you are absolutely correct here - up to Va, you need airspeed to achieve a certain G loading - I missed that in my previous analysis.

 

Originally posted by Jim Sower

Incidentally, "maneuvering speed" is the lowest speed at which it is possible to load the airplane to it's G limit (6 for the Cozy).

 

I'm not sure where that 6G comes from. I did some calculations from the stall speed and wing area on my plane, and here's what I come up with:

 

Wing area (including canard): 110 ft^2

Max average Cl: ~1.4

Weight for calcs: 1800 lb.

 

These come from a stall speed of about 72 mph at that weight. Given that (at Sea Level), the Vn curve below Va for the COZY looks like:

 

0 degree bank - stall speed ~72 mph - 1 G

60 degree bank - stall speed ~96 mph - 2 G

70.5 degree bank - stall speed ~126 mph - 3 G

74.7 degree bank - stall speed ~142 mph - 3.8 G

80.4 degree bank - stall speed ~180 mph - 6 G

 

Since the Va of the COZY is about 140 mph (IIRC), I've got to assume that Nat picked the 3.8 G from the normal category of certification to get his Va. If Va was 180 mph, then 6 G would be the limit.

 

Anyway, given this info, increasing speed up to 140 mph will, as you said, give you the tightest turning radius - from ~125 m radius at 2 G to about 110 m at 140 mph and 3.8G.

 

Originally posted by Jim Sower

But if you would pull to buffet, you'd get a 110 m radius.

 

Bingo - pretty good guess :-) - or did you calculate that?

 

Now, at any speed OVER 140 mph, your radius will start getting larger again, since you're not allowed to pull more G's. So, for the conditions postulated (SL, any amount of power needed), Va will give the tightest radius turn.

 

Of course, the COZY can't maintain 140 mph banked at 74.7 degrees in level flight even at SL, so it'll never get this good :-).

 

The book I mentioned previously, John T. Lowry's "Performance of Light Aircraft", has some excellent explanations and graphs of maneuvering performance of GA aircraft taking power and altitude into consideration, and has some good examples of how to get yourself into trouble in a climbing narrow canyon.....

 

Originally posted by Jim Sower

I think that, once again, we find ourselves in Violent Agreement... :D

 

Better that than violent disagreement :-).

[Jim Sower]

Marc,

I'm really glad we're back on track again :-))

 

<...I am familiar with Vn diagrams, and they are available for GA aircraft...>

I didn't mean to sound like I was talkin' down to you about Vn. I (mis)interpreted a couple of things you said to indicate you weren't too familiar. Mea Culpa.

 

<...I'm not sure where that 6G comes from...>

I thought that was what EZs/Cozys were stressed for, and used it as basis for Vn discussion.

 

<...Since the Va of the COZY is about 140 mph (IIRC), I've got to assume that Nat picked the 3.8 G from the normal category of certification to get his Va...>

Agreed. I would hazard a guess that FAA requires that spam cans withstand 4G to be certified as normal category, and he just went with that.

 

If Va was 180 mph, then 6 G would be the limit...>

Exactly. In that event, our Vn diagram would rise more or less parabolically from min speed to 180 mph/6G, from there horizontally to 220 mph or whatever is Vne, and drop vertically back to the x-axis. Am I safe in assuming that Nat's Va is pretty much what I'm referring to as "maneuvering speed"? - the highest speed at which you cannot overstress the airplane - and (not incidentally) min turn radius?

 

<...Bingo - pretty good guess :-) - or did you calculate that?...>

It was a sWAG (de)emphasis mine.

 

<...John T. Lowry's "Performance of Light Aircraft", has some excellent explanations and graphs of maneuvering performance of GA aircraft

taking power and altitude into consideration...>

I will look for it.

 

Hey - it just this minute occured to me that 140 mph might well be the speed at which you can make -3G (what with upside down airfoils and all). That would make it your best T-storm penetration speed since you don't know how the gusts/shear are comin' at you. That makes sense to me, and doesn't clash with the 6G Vn diagram. :-)

 

<...Better that than violent disagreement :-)...>

True enough. However, here in my dotage I have'nt the energy to support violence upon the good guys. I need to husband my resources so as to better deal with the assholes of the world.

 

In future interaction with you, my friend, I will endeavor to be less assertive and righteous. After all, right here recently, we've been in two or three pretty elaborate pissin' contests - only to discover, when the smoke cleared and the dust settled, that we'd all along been completely agreed on maybe 90% of the issues of any significance. Why do we do this to ourselves?

 

I'll try hard to tread more lightly - but don't think for a minute you can slip some bullshit by me!

[Marc Zeitlin]

Originally posted by Jim Sower

Agreed. I would hazard a guess that FAA requires that spam cans withstand 4G to be certified as normal category, and he just went with that.

 

Normal is 3.8 G, Utility is 4.4 G.

 

Originally posted by Jim Sower

Am I safe in assuming that Nat's Va is pretty much what I'm referring to as "maneuvering speed"?

 

Yes.

 

Originally posted by Jim Sower

In future interaction with you, my friend, I will endeavor to be less assertive and righteous......

And I to be more accurate in my statements.

 

Originally posted by Jim Sower

Why do we do this to ourselves?

The lack of face to face interaction makes it easy to misunderstand and get bent.

 

Originally posted by Jim Sower

but don't think for a minute you can slip some bullshit by me!

 

My raison d'etre is gone.......

[No4]

Ahh that's so touching, I'm all emotional, I think I'm going to cry....

 

Good Work Fellas! Thanks, I've learn't alot.

[cncdoc]

Or should I say, V speeds - what? a crock?

 

Before I start writing this stuff down in my Owner's Manual and order my custom airspeed indicator face, I was wondering, where does the data come from that you base your mathematical computations about Vne Va etc. Especially + and - G's.

 

If it is from Nat's specs, are those based on tested flying product or extrapolation derived from other known values of similar craft.

 

The reason I say this is because not all planes are built the same. (I think you all know where I am going with this)

I am not one for pushing the envelope of design specs in practice, but atmospheric conditions and the ooops factor which tightens the sphincter factor has been known to cause good pilots to push an airframe to it's "known" limits and beyond. Icing and overloading don't hold a candle to a bellyflop landing when it comes to strain.

So has this data been tested? Is it based on spam can engineering?

 

Curious minds want to know..

 

and, strangely enough, I do too.

[Jim Sower]

Doc,

Marc's figures as posted at 11:13 on 1/18 are, IMO. good as gold. To wit:

These come from a stall speed of about 72 mph at that weight. Given that (at Sea

Level), the Vn curve below Va for the COZY looks like:

 

0 degree bank - stall speed ~72 mph - 1 G

60 degree bank - stall speed ~96 mph - 2 G

70.5 degree bank - stall speed ~126 mph - 3 G

74.7 degree bank - stall speed ~142 mph - 3.8 G

80.4 degree bank - stall speed ~180 mph - 6 G

 

Since the Va of the COZY is about 140 mph (IIRC), I've got to assume that Nat

picked the 3.8 G from the normal category of certification to get his Va. If Va was

180 mph, then 6 G would be the limit.

 

Anyway, given this info, increasing speed up to 140 mph will, as you said, give you

the tightest turning radius - from ~125 m radius at 2 G to about 110 m at 140 mph

and 3.8G.

 

You can verify them all while you're flying off your hours. It's not a big deal. Pick a series of airspeeds (80, 90, 100, 110, 120, 130, 140, 150, etc), set yourself up at each one, start a steep turn and pull to buffet. If you can't maintain your speed in a level turn (a certainty above 100 mph or so), let the nose fall into a spiral so you can maintain buffet, G and airspeed long enough to get a good G reading (don't know where you might borrow a G-meter - that's up to you). After you obtain all your data points, plot a graph and that's your Vn diagram.

 

Or take it on faith that over the past 4 or 5 pages of posts, Marc and I have flailed some usable truth out of one another. For my own part, I am going to convert Marc's airspeeds to knots, plot his numbers and be done with it (at least until my airplane is flying).

 

As a practical matter, 140 mph (I will be using 120 kts) is the number to remember in that it is the speed to use in severe turbulence. The lower numbers are of interest just to instill in your mind that below about 130 mph you don't have squat for maneuverability (re the "box canyon" scenario). When scud running or flying up "valleys" that you haven't been in, ...keep your Mach up ...!!

 

180 mph (156 (use 155)) kts is the highest speed at which you cannot pull the wings off the airplane. It is also the speed for the absolute shortest radius turn you can do without damaging the airplane. The 180 figure ("corner" of the Vn diagram) is of no particular interest or utility in the Cozy community - beyond trivia questions and sea stories. Many years ago, in another life, it was a really really important thing for me to know.

 

That was then, this is now .... Jim S.

[Marc Zeitlin]

Originally posted by cncdoc

If it is from Nat's specs, are those based on tested flying product or extrapolation derived from other known values of similar craft.

 

The Vne and Va number I quoted were from the COZY MKIV manual. I will not presume to state where Nat got those #'s from, but the Va (which is what we're interested in here), seems to match up with the 3.8 G limit for Normal Category aircraft, as verified by the performance numbers of my plane in particular, and the published performance data from Nat's plane.

 

Originally posted by Jim Sower

180 mph (156 (use 155)) kts is the highest speed at which you cannot pull the wings off the airplane. .... The 180 figure ("corner" of the Vn diagram)

 

The only issue I have is this 180 mph number, and it's relation to the 6 G figure. I have no clue where this 6 G limit came from - I don't ever remember seeing it in the owner's manual, or anywhere else, for that matter. If you've got some reference for that, I'd be very interested in seeing it.

 

Personally, as a LIMIT LOAD #, I'd use the Normal Category limit of 3.8 G, which is what Nat seems to be recommending by his claim of 140 mph as the Va.

[LargePrime]

I too would be interested in seeing something related to this 180/6G number.

 

As far as I know no one has said our airframes can only go "X" G's before fail. If this is incorrect please let us know

[Wayne Hicks]

I emailed Tom Staggs, the Long EZ pilot who performed on the airshow circuit for a number of years in his Long EZ. He graciously emailed some articles that he wrote.

 

I will post them consecutively here.

 

These articles should separate the wheat from the chaffe.

 

...Wayne Hicks

[Wayne Hicks]

Introduction from Tom Staggs:

 

Over the past few weeks (Hicks: This email was written several years ago), there have been a series of posts about Canard aircraft and aerobatics, inverted flight, deep stall, parachutes, and bailing out. As I have a fair amount of experience in 4 of the 5 topics (never left the plane), I thought I'd pass along some experiences and observations on the different topics.

 

To allow the follow-on conversations to address the individual topics, I'll separate my comments into separate posts. I'd appreciate it if anyone who has any ideas or opinions PLEASE post them. If we don't share our thoughts, we run the risk of repeating the mistakes of those who have already learned the lesson.

 

For those of you who didn't see the message by John Bullens the other day mentioning that I flew aerobatics in my EZ, let me explain. I am a professional airshow performer flying low-altitude aerobatics in my Long-EZ throughout North America. I hold an unrestricted low-altitude waiver from the FAA and Transport Canada, although I have higher personal limits for all my maneuvers. I have flown at 56 show sites in 17 American states and 5 Canadian Provinces.

 

I have managed to log over 1,000 hours in the EZ, including over 300 either practicing or performing aerobatics. My Long-EZ is basically a per-plans plane, with a few noteable exceptions: I have an 160-HP O-320-E2D, beefed up the engine mount extrusions for the torque imposed by aerobatics, installed a NACA inlet on the belly, and extended my aileron span (absolutely no effect on roll rate, by the way!!!!).

 

I look forward to hearing everyone's comments and suggestions.

 

Fly safely,

 

Tom Staggs

Long-EZ N13YV

Arlington, WA

[Wayne Hicks]

Aerobatics in an EZ

 

There is a big difference between "capable" and "suited" when it comes to aerobatics. Someone pointed out in an earlier posting that Tex Johnston managed to roll the prototype 707 in front of a crowd, but that didn't mean that all 707's should be rolled, or that it was a bright idea.

 

The Long-EZ and Veri-EZE are both capable of simple aerobatics, but neither is well-suited to aerobatics. Why? Their roll rates are slow (approximately 50-degrees for a Long-EZ using coordinated controls compared to 180+ degrees per second in most aerobatic planes), they lack the ability to hold the nose up during knife-edge flight, they lack the ability to use prop blast over the tail to provide control authority at low speeds, and the planes' stability in true out-of-control flight is not predictable.

 

The bottom line: if you want to fly aerobatics, you should have built an RV or Pitts. Our planes are great for cross-country, but they just aren't good aerobatic planes.

 

Another thing to consider is how the planes' efficiency is a detriment to its ability to fly aerobatics. Given the clean lines, an EZ will easily out-accelerate most any other prop plane in their horsepower class, assuming the planes aren't climbing. When maneuvering with RV-4's with constant-speed props and 20 more horsepower, I can easily pull well out in front, all because of our wonderful aerodynamic efficiency. When flying aerobatics, should you accidentally allow the nose to get too low or stay down for too long, you can find yourself shooting through red line faster than you could ever imagine.

 

The elasticity of our fiberglass wings makes them poorly suited to safely flying aerobatics. When flying at maneuvering speed, if you rapidly apply full stick, your ailerons function more like large trim tabs, twisting the wing opposite the deflection of the control surface. I have been able to document this through videotape by recording the fore & aft motion of the winglet during aileron inputs. This twisting of the wing result in decreased roll authority during the first 30-degrees of a roll, a fact that is evident when reviewing my boresight videotape shot with "schnoz cam", a video camera mounted in the nose of my EZ.

 

It's worth noting that when Rick Fessenden was flying the Berkut in airshows, the stiffer Berkut wings with its Kevlar and Carbon fiber construction allowed him to achieve a faster and more responsive roll rate and a stronger ultimate load.

 

In swept wing airplanes, applying full rudder into the direction of roll increases the roll rate. The advancing wing's centroid of lift swings farther outboard from the center of mass, providing it with an increased moment arm, while the retarded wing has its centroid move inboard. This lift asymmetry results in a rolling moment around the center of mass. What it means to you is that your roll rate increases by using excessive rudder when compared to conventional "balanced" flight.

 

Just because a maneuver can be flown in an EZ, is it safe to fly it in an EZ? If you haven't been trained to fly aerobatics in a conventional aircraft designed for acro, then I'd recommend you not fly them in your EZ. Even with the training, beware of our planes' weaknesses. Remember, the nose of canard planes "fall through" most maneuvers, and once pointed down, speed will build up faster than you could ever imagine. I would recommend that you limit yourself to steep turns or wingovers. If you have to try something inverted, do so knowing that the plane might not forgive you your mistakes.

 

So what maneuvers can be flown in an EZ? Loops and rolls, as well as variations on the theme such as barrel rolls, wingovers, half-cubans.

 

Which can't be flown: spins, snaps, hammerheads, and tail slides. The first two can't be accomplished because of the inability to stall the main wing while simultaneously yawing the plane, the third because we lack air flow over the rudders as we approach zero airspeed, and the last because of the terrible post-stall gyrations encountered as the plane weathervanes after swapping ends (see the article in the CSA Newsletter last year).

 

As for the wide-body family of canard planes (Cozy, Velocity, AeroCanard, etc.), I would not recommend any types of aerobatics in these aircraft. Their widened fuselages result in more lifting area forward of the center of mass, decreasing the dynamic and static stability of the canard design. In cruising flight, they're very safe, but they should not be used for aerobatics. While flight testing one of these designs, I found out that rapid application of aft stick could actually result in an uncommanded increase in angle of attack, despite being countered by full forward stick. This was likely the result of the increased lifting area incorporated in these designs. Such a phenomena could easily result in overstressing the wings to the point of failure.

 

For those of you who have read this far, yes, I have scared the daylights out of myself flying aerobatics in the EZ. When I perform in a show, it's a routine that I have flown literally hundreds of times, always developing maneuvers above 5,000' AGL before moving them slowly downward. There are some maneuvers that although I can do, I have chosen not to include in my routine because they lack enough margin for error or ability to be reproduced consistently.

 

If you're still insistent on flying aerobatics in your EZ, please get together with a local pilot who has already mastered the maneuvers. Make sure that they really know what they're talking about; don't fly with someone who accomplish the maneuver by luck instead of skill. Above all, don't try to perform a maneuver based on advice or technique you read about on the internet....

 

Fly Safely,

 

Tom Staggs

Long-EZ N13YV

[Wayne Hicks]

(Hicks: WARNING: DO NOT TRY THIS AT HOME!!!!!)

 

 

Inverted flight in a canard

 

Over the past few weeks, there was a string of messages about whether or not our canard aircraft are capable of sustained inverted flight. I found the messages that assured us such a maneuver would be "impossible" to be rather humorous: as an airshow performer, one of the maneuvers in my routine is to fly my Long-EZ down the showline inverted.

 

Having said this, it's time for my "don't try this at home disclaimer". I'm sharing my thoughts and observations here because I feel that the better we understand our aircraft, the safer we can be.

 

As many contributors to this news group pointed out, an airfoil couldn't care less about "up" and "down"; airfoils only care about the relative wind. In the case of the Long-EZ I fly, I have the GU25 airfoil on the canard (the original design), and the modified Eppler 1230 on the main wing. They're both flat bottomed, which implies very poor negative angle of attack characteristics.

 

With a flat-bottom airfoil the maximum coefficient of lift is typically substantially less than what it is for positive angles of attack. In other words, the maximum G's generated in inverted flight would be less than what they are for conventional, right-side-up flight.

 

In the POH for the Long-EZ, the performance envelope shows G limitations of +5, -2. I don't know whether the negative-G capability was ever proven in flight test, but I would suppose, knowing Burt's thoroughness, it most likely was. I know that my experience in a stock O-235 Long-EZ showed that these parameters were achievable, both at positive and negative G.

 

The inverted characteristics of my Long are quite reasonable, although they require a fair amount of forward stick force with a very steep force gradient. Coordinated turns are possible and actually easier to attain inverted than upright (I believe this might stem from the fact that my knees are braced during inverted flight, allowing for greater precision applying rudder inputs).

 

When I make an inverted pass, I always start it with at least 5 degrees nose above the horizon, and I never let the nose fall below the horizon. Just before I roll back upright, I push to about 20 degrees nose up before commencing my roll.

 

Now for the bad news: although the EZ should exhibit tame stall characteristics inverted (mine does), it is also significantly easier to enter a deep stall. I have twice encountered this phenomena, but have been able to recover from it by rocking the wings with the rudders, my guess is that they are not blanked when inverted like they are in an upright deep stall. In both cases, my CG was within the 103" limitation although towards the aft portion of the range (102.1" with an O-235, 103.0 with an O-320) and I was at very low airspeed "floating" over the top of the loop in mist or light rain. In the O-235 case, my engine was not producing power, but with the O-320, I was at full throttle.

 

Both times, I was applying more forward stick to hold my nose up, then applied even more forward stick. The nose seemed to hang above the horizon as I suddenly felt my shoulders dig into my straps. The stick then seemed to go lifeless in my hand; I could cycle the pitch with no apparent effect, nor did the ailerons seem to be capable of rolling the plane. In the first incident, I noticed my airspeed was still on the peg after approximately 2-3 seconds of "falling". In the second incident, I saw about 40 kts of airspeed and about -3,000 fpm on the VSI after a similar period of time.

 

In both cases, application of full rudder resulted in a simultaneous yaw and wing rock. After one or two more applications (too scared to remember exactly how many times I cycled the rudders), the plane sliced nose-low while rolling upright. As the nose feel through, airspeed picked up and I was able to fly away.

 

Lesson learned: Avoid large control inputs at negative G in an EZ, realize that moisture can impact the aerodynamic characteristics of the airfoils, and be ready to use the rudders to recover.

 

By the way, eliminate the inverted pass portion of my airshow routine when there's any kind of visible moisture.

 

 

Fly Safely,

 

Tom Staggs

Long-EZ N13YV

[Wayne Hicks]

From Tom Staggs:

 

The worst characteristic of the Cozy when doing aerobatics is that a sudden onset of positive G's can cause the plane to pitch up uncontrollably, easily overstressing the plane. This is the result of a Cozy having more projected area (when viewed from above) forward of the center of mass than the Long-EZ.

 

Another thing is the Hammerhead. Without propwash across the rudders, you can't kick the nose around at zero airspeed. The result is a tail slide, and I have never been half as scared as I was during my two unintentional tailslides when the nose oscillated +/- 135 degrees and then didn't dampen out until right as I approached redline airspeed going straight down.

 

 

Oddly enough, I just found the rough drafts of the messages I posted nearly 6 years ago. Here is the file containing them - please feel free to pass them along. (Hicks: These are the previous posts provided above.)

 

You might want to include a little post script:

 

I retired from flying airshows at the end of the 1999 airshow season after 8 years on the circuit. During that time, I had two close calls with the ground, both cases where my nose got buried and I didn't have the pitch authority to change my flight path. Since that time, I have become a visiting instructor at the USAF Test Pilot School at Edwards AFB. I have instructed 5 of the last 7 classes of seniors in the flying characteristics of the canard configuration, including limited aerobatics. All of the pilots love the way the plane handles but agrees that it is not a good aerobatic platform.

 

 

Fly safely,

 

Tom Staggs

Long-EZ N13YV

EAA Flight Advisor

[John Slade]

>These articles should separate the wheat from the chaffe.

Aint THAT the truth!

 

Facinating and very valuable info, Wayne. Many thanks.

 

One point that jumps out at me is that the 4 seat canard behaves vastly different to the 2 seat variety.

 

I guess it's steep turns for me.....

[No4]

Good work Mr Hicks!

Thanks for that, very interesting indeed.

Anybody else get deja vu?