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IFR and x-c stability?

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deuskid

Joined: 18 Feb 2006
Posts: 26
Location: St Louis, MO

Posted: Wed Aug 23, 2006 5:12 am Post subject: IFR and x-c stability?

there was a thread that I read yesterday that I can't find today that was asking about 'stability' for x-c by an ex F-4 driver..  I know the RV folks say the 7 and the 9 are pretty good IFR platforms because of their wing area.  I know it isn't as simple as sq-ft but it is one significant variable and so I researched each's ft^2:



Lightning:  91

RV-6:  110

RV-7: 121

RV-9:  124



is there some quantifiable way to come up with a 'stability' quotent?  



I am ignorant [but trainable].  Ignorant because I'm not yet a pilot but I may have a long long-term commute in my future and if it comes to be I'm researching options.



thanks,



John

N1BZRich(at)AOL.COM
Guest

Posted: Thu Aug 24, 2006 4:43 am Post subject: IFR and x-c stability?

In a message dated 8/23/2006 9:13:16 A.M. Eastern Daylight Time,  empire.john(at)gmail.com writes:

  	  Quote: 	
		  is there    some quantifiable way to come up with a 'stability'  quotent? 	


 

 Wow, John, that's a big question.  We appoint you to lead  the effort to research that topic and report back to all of us.  You  will find lots of written information in various aeronautics and astronautics  text books, lots of articles, and obviously lots of hangar talk sessions.   But as a start, yes, wing area is one indicator of stability, but it is not as  simple as that.  Other things to consider are airfoil, aspect ratio,  dihedral, fuselage length, tail size, and on and on and on.  Actually, wing  area alone is probably a better indicator of stall speed, but that too is an  over simplification.  But hey, you are thinking (so many do not) and  that is a good thing.  Keep up the good work.

 Blue Skies,

 Buz

  [quote][b]

cliffw(at)model.com
Guest

Posted: Thu Aug 24, 2006 8:25 am Post subject: IFR and x-c stability?

N1BZRich(at)aol.com wrote:



 	  Quote: 	
		   In a message dated 8/23/2006 9:13:16 A.M. Eastern Daylight Time, 

 empire.john(at)gmail.com writes:



     is there some quantifiable way to come up with a 'stability' quotent? 



 Wow, John, that's a big question. We appoint you to lead the effort to 

 research that topic and report back to all of us. You will find lots 

 of written information in various aeronautics and astronautics text 

 books, lots of articles, and obviously lots of hangar talk sessions. 

 But as a start, yes, wing area is one indicator of stability, but it 

 is not as simple as that. Other things to consider are airfoil, aspect 

 ratio, dihedral, fuselage length, tail size, and on and on and on. 

 Actually, wing area alone is probably a better indicator of stall 

 speed, but that too is an over simplification. But hey, you are 

 thinking (so many do not) and that is a good thing. Keep up the good work.

 Blue Skies,

 Buz


	




I'd been led to believe that wing loading was a good indication of 

"stability". Here is an excerpt from answers.com:



 	  Quote: 	
		   In aerodynamics, wing loading is the loaded weight of the aircraft 

 divided by the area of the wing. It is broadly reflective of the 

 aircraft's lift-to-mass ratio, which affects its rate of climb, 

 load-carrying ability, and turn performance.



 Typical wing loadings range from 20 lb/ft² (100 kg/m²) for general 

 aviation aircraft, to 80 to 120 lb/ft² (390 to 585 kg/m²) for 

 high-speed designs like modern fighter aircraft...



 Wing loading also affects gust response, the degree to which the 

 aircraft is affected by turbulence and variations in air density. A 

 highly loaded wing has more inertia and a small wing has less area on 

 which a gust can act, both of which serve to smooth the ride. For 

 high-speed, low-level flight (such as a fast low-level bombing run in 

 an attack aircraft), a small, thin, highly loaded wing is preferable: 

 aircraft with low wing loading are often subject to a rough, punishing 

 ride in this flight regimeL.. The F-15E ("Strike Eagle") has been 

 criticized for its ride quality, as have most delta wing aircraft 

 (such as the Dassault Mirage III), which tend to have large wings and 

 low wing loading.




	


-- 

Cliff Walinsky (Lightning-builder wanna be)

Portland, Oregon

max.givan(at)ngc.com
Guest

Posted: Thu Aug 24, 2006 11:18 am Post subject: IFR and x-c stability?

Since I sort of started  this stability issue thread, and I do this stuff for my real job (design  military aircraft), I guess I need to expand a bit on this subject. Sorry but  this will necessarily be a bit long. Pete, please note that I am a BIG fan of  the Lightning, however with the responses I have seen on this topic, I am trying  to bring some closure to this. This issue is similiar to the experience  Lancair (360) and Glasair II had with some of earlier models and much  insight might be gained by reviewing their history and flight test results.  

  

 This can get very complex  and mathematical, however to address my concerns here we can keep it very  simple. Static stability refers to the airplanes natural tendency to return to  its initially trimmed pitch, yaw and roll angle after it is disturbed by gusts,  control movements, thermals etc. So long as control surfaces are not  repositioned/retrimmed, a statically stable airplane returns to where you  trimmed it after any small disturbance. This is nice in that it reduces pilot  workload. The pilot can look at maps, tune radios, beat on kids, take a nap -  (no maybe its not that stable) and the airplane sort of stays at  airspeed, altitude and heading it was trimmed at. Like most things,  however, at least for pitch stability, which is my concern here, too much  of a good thing is not so good! Very high levels of pitch stability cause higher  stick forces to maneuver aircraft and also cause higher trim drag for off  nominal conditions. Trim drag is also strong function of Cmo = pitching  moment at zero lift. When an airplanes CG is at its aerodynamic neutral point,  it has no tendency to return to initial trimmed state after a disturbance.  In fact if you look at trimmed horiz tail position vs angle of attack(think  airspeed),

  it is a constant  deflection. This means that stick (and tail) position no longer relates to a  specific angle of attack (or airspeed) but has become a pitch rate only  command which is not good. So - for a 'good' pilot friendly airplane, we  really do need a minimal, but not too much, static stability. There are also  dynamic considerations but we will stick to static pitch stability for now. The  way we classically measure the degree of stability is by static margin which is  simply how far foward of the aerodynamic neutral point the CG is located.  When we design military aircraft, we look at many other metrics, however for  conventional aircraft like the Lightning, we can pretty well predict pitch axis  flying qualities by looking at the static margin and the stick force  characteristics which relate to the sticks mechanical design as well as the tail  size and static margin. Lets stick to the static margin. We traditionally  measure it in % of mean wing chord or  %c_bar. Aircraft with good flying qualities will have CG located at least 3  to 4%c_bar foward of the aerodynamic neutral point. Note when the CG actually  goes aft of the neutral point really really bad things happen! Dont go  there!

 Now in aircraft design  phase, we would use sizing criteria such as tail area x tail distance aft  of CG and we would do wind tunnel testing to determine exactly where  the aerodynamic neutral point is located as function of airspeed. Yes,  it will move foward and aft with airspeed changes. Fortunately  for us, at the airspeeds our aircraft operate, the neutral point  is approx at a constant location. So, when I build MY Lightning, I  will want my CG to stay at least 4% foward of the neutral point. Simple  huh? Wait a minute, we dont have any wind tunnel data, so where ist that darn  neutral point located?  

 Well, I think we might  have a good data point for that. My  concerns began when I talked to Gregg Hobbs right after he flew first time fully  loaded. Now Gregg has the (not production) 'heavy fuselage' and thus his CG is  well aft of current production versions. Gregg was still pretty excited  (scared?) about the flight characteristics he experienced that day when I talked  with him. Enough so that he interupted his flight and sent plane back to  Shelbyville via truck. Well, thats one way to do a cross country I  guess.

  

 My conclusion is that his  CG was at or very close to the aircrafts aerodynamic nuetral point. I dont know  the actual cg value he was at but if he does, we can use that to determine where  we might want our CG range to fall. His airplane will have the same  aerodynamic neutral point as current production versions. I believe his is  different only in its weight and CG characteristics.

  

 There are a lot of other  issues to consider but from pilot reports I hear, I believe the Lightning has  very nice yaw and roll stability characteristics. I know the pitch stability has  been worked (lighter aft fuselage thus CG farther foward) but I would like  to know a little more about current characteristics. 

 Of course I will fly it  before I would start building one however I would also like to know about what  static margin the basic aircraft has?

  

 Several of your emails  also discussed wing area and much more importantly wing loading. While wing  loading is an important parameter, and lighter wing loadings will result in  larger aircraft responses to vertical gusts, the Lightning is actually better  than most of new crop of Light Sport aircraft and actually very similiar to many  old timer GA aircraft. I ran a few numbers for selected aircraft at published  max gross weight and at approximately 

 (empty weight + 175 Lb  pilot + 1/2 hr fuel).

  

                                                     Wing Loading - (Lb/SqFt)

 Aircraft         Wing Area      Max  GW        Empty + pilot + min  fuel

 Lightning          91 SqFt         15.7                     10.9

 C-172            174                14.7                      10.7

 C-182            175.5             17.7                      11.9

 RV6                110               14.5                     10.6

 RV9               124               14.1                        9.8

 RV10               148               18.2                      11.7

 G36(Bonanza)  181               20.2                     15.0

 Pulsar  XP         80                13.7                     10.0

 Tecnam Sierra  123.8             10.7                       7.5

 Zodiac 601XL    132                10.0                       6.8             

  

 Since in terms of  aircraft gust response, larger numbers for wing loading will be better, that is  less 'bouncy' in turbulence we can see that in this regard, the Lightning is exemplary. While it is a very light weight  aircraft, its relatively small wing area results in very good numbers for wing  loading.

 note that while its not  going to make Bonanza drivers smile (at least until they stop at gas  pumps), the C-172, RV and most of the LSA crowd will 

 be impressed. Based  on wing loading only, this aircraft has potential to be as good or better than  most GA aircraft.  

  

 In summary, based on  numbers I have evaluated and what I know from others flight experiences, I  believe the Lightning is one of if not the best of the Experimental and new LSA aircraft available with the possible  concern about STATIC MARGIN, however iIF? that is still an issue, it is fixable  via larger horiz tail mods and/or center of gravity changes (move  engine foward slightly?). I still want one!   

  

 Max  Givan



   From: owner-lightning-list-server(at)matronics.com  [mailto:owner-lightning-list-server(at)matronics.com] On Behalf Of  N1BZRich(at)aol.com

Sent: Thursday, August 24, 2006 5:44  AM

To: lightning-list(at)matronics.com

Subject: Re:  IFR and x-c stability?

 

  In a message dated 8/23/2006 9:13:16 A.M. Eastern Daylight Time,  empire.john(at)gmail.com writes:

  	  Quote: 	
		  is there some quantifiable    way to come up with a 'stability' quotent? 	


 

 Wow, John, that's a big question.  We appoint you to lead  the effort to research that topic and report back to all of us.  You  will find lots of written information in various aeronautics and astronautics  text books, lots of articles, and obviously lots of hangar talk sessions.   But as a start, yes, wing area is one indicator of stability, but it is not as  simple as that.  Other things to consider are airfoil, aspect ratio,  dihedral, fuselage length, tail size, and on and on and on.  Actually, wing  area alone is probably a better indicator of stall speed, but that too is an  over simplification.  But hey, you are thinking (so many do not) and  that is a good thing.  Keep up the good work.

 Blue Skies,

 Buz

[quote]



ronics.com/Navigator?Lightning-List



[b]

Kayberg(at)AOL.COM
Guest

Posted: Thu Aug 24, 2006 1:01 pm Post subject: IFR and x-c stability?

Like Buzz mentioned, I have grown accustomed to hand flying  experimentals.  They are usually out of balance for a number of  reasons.

  

 I also love autopilots for serious IFR work. In my Piper Arrow, I would hit  the AP and fly with the heading bug as soon as the gear came up if it was an  important flight.  No question AP's cut fatigue and calm the  mind.   But I dont want an IFR Lightning.  We really need some  time on the airframe in VFR conditions.   I would just note that when  you encounter turbulance,  stability seems to not help all that much.   You just gotta fly it.   In smooth air, finger pressure will do.

  

 While Max's thought processes exceed mine, I do believe this thread  overlooks and important flaw in the ointment.

  

 It is not a production aircraft.

  

 We are finishing up our Lightning as the first one NOT built in  Shelbyville.  Since no manual is available( not that we would acually  read it anyway) we are using some pictures, phonecalls and our previous  building experience to rig the bird,  align the tailfeathers, and install  our own dash and doo-dads.   I would expect it to fly differently from  Shelbyville Specials.   It may fly better, it may likely fly  worse.

  

 But in an aircraft that weighs around 700lbs MT with a 90+ sq foot  wing, with massive flaps and amateur rigging, it wont take much to make it fly  in a non-standard way.   While it is not likely to fly rock-stable  immediatly, it may not be wildly divergent either.  Of course we will let  everyone know how it is going, but it will be in our terms.  For example,  Just rigging the flaps to hang slightly low will likely make it more stable but  slower.   Reflexing the flaps will make it faster but less stable I  would guess.

  

  A couple years back, I happened to find the owner of a 1964 Cessna  310 that had belonged to a Cessna executive and had been specially rigged for  him in Wichita.  It was at least 10- 20 mph faster than all the rest he had  ever flown.  It was bone-straight and set perfectly. Even Production models  each have some difference that can effect stability.

  

 I would expect the addition of a lard-butt in one seat or the other to make  a significant difference in flight charactoristics.   Sandbags dont  move. People do.   Adjusting your underware to deal with in-flight  chafing is enough to create unusual attitudes (on the part of the plane, not  just the passengers)

  

 Just some thoughts to take the edge off pure science.

  

 Doug Koenigsberg

  

 In a message dated 8/24/2006 3:20:35 PM Eastern Standard Time,  max.givan(at)ngc.com writes:

  	  Quote: 	
		     Since I sort of started    this stability issue thread, and I do this stuff for my real job (design    military aircraft), I guess I need to expand a bit on this subject. Sorry but    this will necessarily be a bit long. Pete, please note that I am a BIG fan of    the Lightning, however with the responses I have seen on this topic, I am    trying to bring some closure to this. This issue is similiar to the    experience Lancair (360) and Glasair II had with some of earlier    models and much insight might be gained by reviewing their history and flight    test results. 

    

   This can get very    complex and mathematical, however to address my concerns here we can keep it    very simple. Static stability refers to the airplanes natural tendency to    return to its initially trimmed pitch, yaw and roll angle after it is    disturbed by gusts, control movements, thermals etc. So long as control    surfaces are not repositioned/retrimmed, a statically stable    airplane returns to where you trimmed it after any small disturbance.    This is nice in that it reduces pilot workload. The pilot can look at maps,    tune radios, beat on kids, take a nap - (no maybe its not that stable) and the    airplane sort of stays at airspeed, altitude and heading it was    trimmed at. Like most things, however, at least for pitch stability, which is    my concern here, too much of a good thing is not so good! Very high    levels of pitch stability cause higher stick forces to maneuver aircraft    and also cause higher trim drag for off nominal conditions. Trim drag is    also strong function of Cmo = pitching moment at zero lift. When an    airplanes CG is at its aerodynamic neutral point, it has no tendency to return    to initial trimmed state after a disturbance. In fact if you look at    trimmed horiz tail position vs angle of attack(think airspeed),

    it is a constant    deflection. This means that stick (and tail) position no longer relates to a    specific angle of attack (or airspeed) but has become a pitch rate only    command which is not good. So - for a 'good' pilot friendly airplane, we    really do need a minimal, but not too much, static stability. There are also    dynamic considerations but we will stick to static pitch stability for now.    The way we classically measure the degree of stability is by static margin    which is simply how far foward of the aerodynamic neutral point the CG is    located. When we design military aircraft, we look at many other metrics,    however for conventional aircraft like the Lightning, we can pretty well    predict pitch axis flying qualities by looking at the static margin and the    stick force characteristics which relate to the sticks mechanical design as    well as the tail size and static margin. Lets stick to the static margin. We    traditionally measure it in % of mean    wing chord or %c_bar. Aircraft with good flying qualities will have CG    located at least 3 to 4%c_bar foward of the aerodynamic neutral point. Note    when the CG actually goes aft of the neutral point really really bad things    happen! Dont go there!

   Now in aircraft design    phase, we would use sizing criteria such as tail area x tail distance aft    of CG and we would do wind tunnel testing to determine exactly where    the aerodynamic neutral point is located as function of airspeed. Yes,    it will move foward and aft with airspeed changes. Fortunately    for us, at the airspeeds our aircraft operate, the neutral point    is approx at a constant location. So, when I build MY Lightning, I    will want my CG to stay at least 4% foward of the neutral point. Simple    huh? Wait a minute, we dont have any wind tunnel data, so where ist that darn    neutral point located?  

   Well, I think we might    have a good data point for that. My    concerns began when I talked to Gregg Hobbs right after he flew first time    fully loaded. Now Gregg has the (not production) 'heavy fuselage' and thus his    CG is well aft of current production versions. Gregg was still pretty excited    (scared?) about the flight characteristics he experienced that day when I    talked with him. Enough so that he interupted his flight and sent plane back    to Shelbyville via truck. Well, thats one way to do a cross country I    guess.

    

   My conclusion is that    his CG was at or very close to the aircrafts aerodynamic nuetral point. I dont    know the actual cg value he was at but if he does, we can use that to    determine where we might want our CG range to fall. His airplane will    have the same aerodynamic neutral point as current production versions. I    believe his is different only in its weight and CG    characteristics.

    

   There are a lot of    other issues to consider but from pilot reports I hear, I believe the    Lightning has very nice yaw and roll stability characteristics. I know the    pitch stability has been worked (lighter aft fuselage thus CG farther    foward) but I would like to know a little more about current    characteristics. 

   Of course I will fly it    before I would start building one however I would also like to know about what    static margin the basic aircraft has?

    

   Several of your emails    also discussed wing area and much more importantly wing loading. While wing    loading is an important parameter, and lighter wing loadings will result in    larger aircraft responses to vertical gusts, the Lightning is actually better    than most of new crop of Light Sport aircraft and actually very similiar to    many old timer GA aircraft. I ran a few numbers for selected aircraft at    published max gross weight and at approximately 

   (empty weight + 175 Lb    pilot + 1/2 hr fuel).

    

                                                         Wing Loading - (Lb/SqFt)

   Aircraft           Wing Area      Max    GW        Empty + pilot + min    fuel

   Lightning            91 SqFt           15.7                       10.9

   C-172            174                14.7                          10.7

   C-182            175.5             17.7                        11.9

   RV6                  110               14.5                     10.6

   RV9               124               14.1                          9.8

   RV10                 148               18.2                        11.7

   G36(Bonanza)    181               20.2                     15.0

   Pulsar    XP         80                  13.7                     10.0

   Tecnam Sierra    123.8               10.7                         7.5

   Zodiac    601XL      132                  10.0                         6.8               

    

   Since in terms of    aircraft gust response, larger numbers for wing loading will be better, that    is less 'bouncy' in turbulence we can see that in this regard, the    Lightning is exemplary. While it is a    very light weight aircraft, its relatively small wing area results in very    good numbers for wing loading.

   note that while its not    going to make Bonanza drivers smile (at least until they stop at gas    pumps), the C-172, RV and most of the LSA crowd will 

   be    impressed. Based on wing loading only, this aircraft has potential to be    as good or better than most GA aircraft.  

    

   In summary, based on    numbers I have evaluated and what I know from others flight experiences,    I believe the Lightning is one of if not the best of the Experimental    and new LSA aircraft available with the    possible concern about STATIC MARGIN, however iIF? that is still an issue, it    is fixable via larger horiz tail mods and/or center of gravity    changes (move engine foward slightly?). I still want    one!   

    

   Max    Givan



         From: owner-lightning-list-server(at)matronics.com    [mailto:owner-lightning-list-server(at)matronics.com] On Behalf Of    N1BZRich(at)aol.com

Sent: Thursday, August 24, 2006 5:44    AM

To: lightning-list(at)matronics.com

Subject: Re:    IFR and x-c stability?

   

      In a message dated 8/23/2006 9:13:16 A.M. Eastern Daylight Time,    empire.john(at)gmail.com writes:

    	  Quote: 	
		  is there some quantifiable      way to come up with a 'stability' quotent? 	


   

   Wow, John, that's a big question.  We appoint you to lead    the effort to research that topic and report back to all of us.  You    will find lots of written information in various aeronautics and astronautics    text books, lots of articles, and obviously lots of hangar talk    sessions.  But as a start, yes, wing area is one indicator of stability,    but it is not as simple as that.  Other things to consider are airfoil,    aspect ratio, dihedral, fuselage length, tail size, and on and on and    on.  Actually, wing area alone is probably a better indicator of stall    speed, but that too is an over simplification.  But hey, you are    thinking (so many do not) and that is a good thing.  Keep up    the good work.

   Blue Skies,

   Buz

 	  Quote: 	
		  



ronics.com/Navigator?Lightning-List





	
	


 

  

  [quote][b]

dashvii(at)hotmail.com
Guest

Posted: Thu Aug 24, 2006 1:13 pm Post subject: IFR and x-c stability?

As Max and Buz have pointed out, wing loading, or any other single element 

alone wont' tell you if the plane is stable or not.  For instance you could 

have great wing loading and a horizontal stabilzer that is too small for a 

given distance back.



Now, if it were Greg's plane that we want to talk about let me give some 

additional info.  First off, Greg's plane wasn't shipped back, it flew back 

to Shelbyville.  Nick did the first couple of flights, then Greg wanted to 

fly it rather than let one of us fly it and get the kinks worked out.  I 

understand you're coming from an engineering background Max, and you sound 

like you'd be a really interesting guy to sit down and talk with for a few 

hours, but let's consider a few different variables here when evaluating the 

Lightning based on Greg's plane.  (by the way have you talked to him in a 

while about how much better his plane flies now?)



He did start for Arizona and then turn back.  I think that he kind of scared 

himself.  Why did this happen?  Was it because of stability, control?  Well, 

first off let me say that Greg, while he's a great guy, admitted that he 

isn't the greatest pilot and he doesn't really enjoy flying just to fly, but 

uses it as a tool to get from one place to another.  (personally I think 

he's better than giving himself credit for, just needed a little more time 

to get used to the plane before embarking cross-country)  Now if that were 

my only case it wouldn't be worthwhile.  He asked me to fly the plane out to 

Arizona with him.  He didn't feel confident enough that he knew the airplane 

well enough to fly that distance.  He also wanted me to fly because I have a 

little more experience flying in the weather.  Mostly he wanted me because 

I'd been flying time off of these planes and engines and know what to look 

for and if anything little started to look out of place then I might 

recognize it earlier than he would.



When Greg left out the first time he had filled the baggage compartment 

full, and did it with heavy stuff.  So much so that he was most likely too 

far aft of C.G.  Now we all know that isn't a good thing in any airplane.  

That wasn't all that was the problem either though.  The first time that I 

flew the plane I knew something wasn't quiet right.  Nick, who had flown the 

prototype, gave me an hour transition or so in the airplane.  It was Greg's 

plane.  While I was controlling the airplane ok, the stick pressures were a 

little wierd.  I told Nick to "watch this" and turned loose of the stick and 

the airplane decended, even with full aft trim and at high speeds, low 

speeds, any speeds.  At first I figured that the trim had come loose and 

wasn't trimming.  That should mean that at some speed that it would stay 

straight and level though.  So it was unfavorable, but manageable.  It 

wasn't what I'd desire.  Nick said that the prototype didn't do that.  We 

messed with it a bit and found that you had to trim opposite of what you 

would think as you accelerated.  There was also a roll to the right I think 

which was because one flap wasn't quiet positioned even with the other side. 

  That was easy enough to fix.



When we would come in to land we noticed it wanted to nose down and hit the 

nosegear which could make you bounce back into the air and we had to land it 

like a tailwheel putting the stick all the way back after you got the mains 

on.  So we scratched our heads.  No it wasn't a prototype, but it wasn't a 

production model either.  It was something slightly different, but why this 

change?  Now remember this was an airplane with two different guys working 

on the main structure of the plane at the same time and there was no 

builder's manual yet.  I believe that what we found out was that one or both 

horizontal stabilizers were mounted slightly off the angle of incidence that 

they needed to be at.  The problems were corrected before we headed to 

Arizona and it was a safe and good flying airplane out there.  Still needed 

a little less flap on one side because of a right roll.  The plane was 

slower than it should've been, but that was due to the fact that many of the 

fairings weren't fully on there, I had some aileron and rudder out there to 

correct for the right roll rate, etc.  These were all little issues of 

cleanup that he fixed once he got the plane home.



Oh, if this is where you got the mistaken notion that the Jabiru engines 

have heat issues I can explain that too.  Greg, not an aerodynamicist, but a 

tinkerer and thinker decided that his engine was warm.  Well, they all are 

warmer during break-in and running on straight mineral oil.  After about 25 

hours and switching to non-mineral oil the temps come down to more around 

normal.  So during engine break in he decided that the baffle just in front 

of the foremost cylinder head was flat and that it needed to be smoother 

going into there.  (there are also a series of baffles between each 

cylinder.  You don't want a laminar airflow over the heads, but a set amount 

of disturbance to direct the air eveny across each cylinder and provide for 

close to the same temps on all heads)  So Greg put in a ramp in front of the 

front baffle.  Then when you put any kind of an angle of attack on the 

cylinder heads would start to rise.  What was happening was that as the 

angle of attack increased the airflow was pretty much skipping over the tops 

of the heads and emptying out the outlet on the bottom.  Sometimes what you 

think will make it work even better, won't.  Trust the manufacturer and 

their recommendations.  As soon as the ramp, that Greg had fashioned and 

installed was removed, the CHT's were normal.  Also a lesson in the fact if 

it isn't broke don't try to fix it.



   Just a few thoughts for you there on the stability issues Max.  The plane 

is stable about all axis and you're right it does really well for a light 

sport in turbulence, compared to other light sport aircraft.  As I have said 

it is most closely neutrally stable (although not fully nuetral) about the 

roll axis.  This was no doubt to make it a more responsive aircraft to roll 

inputs.  I've had several people ask me if it were twitchy in pitch.  No, it 

really isn't.  It is responsive, but it isn't likely to overcontrol.  Soon 

I'm going to fly Earl's plane a little, which will be the first Light Sport 

Lightning.  Nick tells me that it is dialed in where it needs to be on 

speeds (both max and stall) and that it's climb rate is phenominal solo.  

(it's only been flown solo)  He says that it is a very well balanced and 

nice flying machine, not just in stability, but in the "feel" of the 

airplane.  I can't overemphasize that last part enough.  The feel, or the 

feedback from this plane is just absolutely wonderful.  The control 

pressures are perfect and the linkage just put you in harmony with the 

plane.  You really need to find one and take a flight Max.  I think that 

you'll be impressed.

dashvii(at)hotmail.com
Guest

Posted: Thu Aug 24, 2006 1:19 pm Post subject: IFR and x-c stability?

Doug,

   You're absolutely right.  A guy at our airport went in to get an annual 

inspection on a Bonanza the other day.  The mechanic checked everything out 

and decided it was time to replace some rudder cables.  He did and the guy 

came and picked it up.  On a cross-country shortly after he asked the 

mechanic what he did, to which he replied, "what do you mean, is it not 

flying right?"  The guy told him that he had always had to hold in a little 

aileron and that now he doesn't and the plane was 10-15 knots faster than it 

ever had been.  The rudder had been out of rigging slightly all that time 

and the rudder was deflected to one side.  Even though you couldn't see it 

with your naked eye on the ground, that's what happened.  Each airframe 

takes a little time to get everything tweaked.



Maybe I'm crazy, but I think finding out the little things and then having 

them fixed and flying again to see how it reacts is part of the fun of it 

all.  Brian W.

pete(at)flylightning.net
Guest

Posted: Thu Aug 24, 2006 1:24 pm Post subject: IFR and x-c stability?

Max,  

   

We’ve got to get your facts right.  Maybe Greg didn’t mention the 93 lbs of tools, baggage etc that he had in the baggage compartment when with his early fuselage should have had no more than 20 lbs. By our calculations his CG was 2 inches behind the aft CG limit.   Also- Nick flew the aircraft back to Shelbyville – without excess weight I the baggage compartment – without a great amount of pilot workload.  It was not trucked anywhere. I flew along side in the Jabiru J250 (Nick was kind enough to slow down when he wasn’t doing wide S turns around me to keep from going away!).  I think you may have received less than the whole story and perhaps that is where your perception of Lightning stability comes from.    

   

When properly loaded to the aft CG limit in the POH our calculations show the cg to be more than 4% of c_bar forward of the neutral point.  However, with the early fuselage and 93 lbs in the baggage compartment CG &neutral point are about in the same location.  

   

You might re-read Brian Wittingham’s accounts of the handling and stability of Greg’s aircraft without the 93 lbs in the baggage compartment when they flew it home to Tucson.  Those posts are recent in the archives of this list.  There did not seem to be a stability issue.  

   

Pete  Krotje  

Arion Aircraft, LLC  

   

         

  

From: owner-lightning-list-server(at)matronics.com [mailto:owner-lightning-list-server(at)matronics.com] On Behalf Of Givan, Max

 Sent: Thursday, August 24, 2006 2:18 PM

 To: lightning-list(at)matronics.com

 Subject: RE: IFR and x-c stability?  

  

   

Since I sort of started this stability issue thread, and I do this stuff for my real job (design military aircraft), I guess I need to expand a bit on this subject. Sorry but this will necessarily be a bit long. Pete, please note that I am a BIG fan of the Lightning, however with the responses I have seen on this topic, I am trying to bring some closure to this. This issue is similiar to the experience Lancair (360) and Glasair II had with some of earlier models and much insight might be gained by reviewing their history and flight test results.   

   

This can get very complex and mathematical, however to address my concerns here we can keep it very simple. Static stability refers to the airplanes natural tendency to return to its initially trimmed pitch, yaw and roll angle after it is disturbed by gusts, control movements, thermals etc. So long as control surfaces are not repositioned/retrimmed, a statically stable airplane returns to where you trimmed it after any small disturbance. This is nice in that it reduces pilot workload. The pilot can look at maps, tune radios, beat on kids, take a nap - (no maybe its not that stable) and the airplane sort of stays at airspeed, altitude and heading it was trimmed at. Like most things, however, at least for pitch stability, which is my concern here, too much of a good thing is not so good! Very high levels of pitch stability cause higher stick forces to maneuver aircraft and also cause higher trim drag for off nominal conditions. Trim drag is also strong function of Cmo = pitching moment at zero lift. When an airplanes CG is at its aerodynamic neutral point, it has no tendency to return to initial trimmed state after a disturbance. In fact if you look at trimmed horiz tail position vs angle of attack(think airspeed),  

 it is a constant deflection. This means that stick (and tail) position no longer relates to a specific angle of attack (or airspeed) but has become a pitch rate only command which is not good. So - for a 'good' pilot friendly airplane, we really do need a minimal, but not too much, static stability. There are also dynamic considerations but we will stick to static pitch stability for now. The way we classically measure the degree of stability is by static margin which is simply how far foward of the aerodynamic neutral point the CG is located. When we design military aircraft, we look at many other metrics, however for conventional aircraft like the Lightning, we can pretty well predict pitch axis flying qualities by looking at the static margin and the stick force characteristics which relate to the sticks mechanical design as well as the tail size and static margin. Lets stick to the static margin. We traditionally measure it in % of mean wing chord or %c_bar. Aircraft with good flying qualities will have CG located at least 3 to 4%c_bar foward of the aerodynamic neutral point. Note when the CG actually goes aft of the neutral point really really bad things happen! Dont go there!  

Now in aircraft design phase, we would use sizing criteria such as tail area x tail distance aft of CG and we would do wind tunnel testing to determine exactly where the aerodynamic neutral point is located as function of airspeed. Yes, it will move foward and aft with airspeed changes. Fortunately for us, at the airspeeds our aircraft operate, the neutral point is approx at a constant location. So, when I build MY Lightning, I will want my CG to stay at least 4% foward of the neutral point. Simple huh? Wait a minute, we dont have any wind tunnel data, so where ist that darn neutral point located?    

Well, I think we might have a good data point for that. My concerns began when I talked to Gregg Hobbs right after he flew first time fully loaded. Now Gregg has the (not production) 'heavy fuselage' and thus his CG is well aft of current production versions. Gregg was still pretty excited (scared?) about the flight characteristics he experienced that day when I talked with him. Enough so that he interupted his flight and sent plane back to Shelbyville via truck. Well, thats one way to do a cross country I guess.  

   

My conclusion is that his CG was at or very close to the aircrafts aerodynamic nuetral point. I dont know the actual cg value he was at but if he does, we can use that to determine where we might want our CG range to fall. His airplane will have the same aerodynamic neutral point as current production versions. I believe his is different only in its weight and CG characteristics.  

   

There are a lot of other issues to consider but from pilot reports I hear, I believe the Lightning has very nice yaw and roll stability characteristics. I know the pitch stability has been worked (lighter aft fuselage thus CG farther foward) but I would like to know a little more about current characteristics.   

Of course I will fly it before I would start building one however I would also like to know about what static margin the basic aircraft has?  

   

Several of your emails also discussed wing area and much more importantly wing loading. While wing loading is an important parameter, and lighter wing loadings will result in larger aircraft responses to vertical gusts, the Lightning is actually better than most of new crop of Light Sport aircraft and actually very similiar to many old timer GA aircraft. I ran a few numbers for selected aircraft at published max gross weight and at approximately   

(empty weight + 175 Lb pilot + 1/2 hr fuel).  

   

                                                   Wing Loading - (Lb/SqFt)  

Aircraft        Wing Area      Max GW        Empty + pilot + min fuel  

Lightning         91 SqFt        15.7                    10.9  

C-172            174                14.7                    10.7  

C-182            175.5             17.7                     11.9  

RV6               110               14.5                     10.6  

RV9               124               14.1                       9.8  

RV10              148               18.2                     11.7  

G36(Bonanza) 181               20.2                     15.0  

Pulsar XP         80               13.7                     10.0  

Tecnam Sierra 123.8            10.7                      7.5  

Zodiac 601XL   132               10.0                      6.8              

   

Since in terms of aircraft gust response, larger numbers for wing loading will be better, that is less 'bouncy' in turbulence we can see that in this regard, the Lightning is exemplary. While it is a very light weight aircraft, its relatively small wing area results in very good numbers for wing loading.  

note that while its not going to make Bonanza drivers smile (at least until they stop at gas pumps), the C-172, RV and most of the LSA crowd will   

be impressed. Based on wing loading only, this aircraft has potential to be as good or better than most GA aircraft.    

   

In summary, based on numbers I have evaluated and what I know from others flight experiences, I believe the Lightning is one of if not the best of the Experimental and new LSA aircraft available with the possible concern about STATIC MARGIN, however iIF? that is still an issue, it is fixable via larger horiz tail mods and/or center of gravity changes (move engine foward slightly?). I still want one!     

   

Max Givan  

       

  

From: owner-lightning-list-server(at)matronics.com [mailto:owner-lightning-list-server(at)matronics.com] On Behalf Of N1BZRich(at)aol.com

 Sent: Thursday, August 24, 2006 5:44 AM

 To: lightning-list(at)matronics.com

 Subject: Re: IFR and x-c stability?      

In a message dated 8/23/2006 9:13:16 A.M. Eastern Daylight Time, empire.john(at)gmail.com writes:  

   	  Quote: 	
		    

is there some quantifiable way to come up with a 'stability' quotent?   	
  

    

Wow, John, that's a big question.  We appoint you to lead the effort to research that topic and report back to all of us.  You will find lots of written information in various aeronautics and astronautics text books, lots of articles, and obviously lots of hangar talk sessions.  But as a start, yes, wing area is one indicator of stability, but it is not as simple as that.  Other things to consider are airfoil, aspect ratio, dihedral, fuselage length, tail size, and on and on and on.  Actually, wing area alone is probably a better indicator of stall speed, but that too is an over simplification.  But hey, you are thinking (so many do not) and that is a good thing.  Keep up the good work.  

    

Blue Skies,  

    

Buz  

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vettin74(at)yahoo.com
Guest

Posted: Thu Aug 24, 2006 2:29 pm Post subject: IFR and x-c stability?

in an earlier e mail something was brought up about wing loading it was just meant that the lightning  had a higer wing loading than the esqual giving a better "ride" not stability at all....however the stability of the lightning is far better than the esqual and more that of a RV-6 or similar aircraft...if you really must have numbers i could give you them...but numbers aren't nearly as good as a few old fashion pilot reports and there are plenty of people on this list that have flown the lightning hundreds of miles on cross countrys and will tell you that it flies beautifully when properly loaded and configured.... 

   

  nick



Clifford Walinsky <cliffw(at)model.com> wrote:

  [quote]--> Lightning-List message posted by: Clifford Walinsky 



N1BZRich(at)aol.com wrote:



 	  Quote: 	
		   In a  message dated 8/23/2006 9:13:16 A.M. Eastern Daylight Time, 

 empire.john(at)gmail.com writes:



 is there some quantifiable way to come up with a 'stability' quotent? 



 Wow, John, that's a big question. We appoint you to lead the effort to 

 research that topic and report back to all of us. You will find lots 

 of written information in various aeronautics and astronautics text 

 books, lots of articles, and obviously lots of hangar talk sessions. 

 But as a start, yes, wing area is one indicator of stability, but it 

 is not as simple as that. Other things to consider are airfoil, aspect 

 ratio, dihedral, fuselage length, tail size, and on and on and on. 

 Actually, wing area alone is probably a better indicator of stall 

 speed, but that too is an over simplification. But hey, you are 

 thinking (so many do not) and that is a good thing. Keep up the good work.

 Blue  Skies,

 Buz


	




I'd been led to believe that wing loading was a good indication of 

"stability". Here is an excerpt from answers.com:



[quote] In aerodynamics, wing loading is the loaded weight of the aircraft 

 divided by the area of the wing. It is broadly reflective of the 

 aircraft's lift-to-mass ratio, which affects its rate of climb, 

 load-carrying ability, and turn performance.



 Typical wing loadings range from 20 lb/ft² (100 kg/m²) for general 

 aviation aircraft, to 80 to 120 lb/ft² (390 to 585 kg/m²) for 

 high-speed designs like modern fighter aircraft...



 Wing loading also affects gust response, the degree to which the 

 aircraft is affected by turbulence and variations in air density. A 

 highly loaded wing has more inertia and a small wing has less area on 

 which a gust can act, both of which serve to smooth the ride. For 

 high-speed, low-level [quote][b]

dashvii(at)hotmail.com
Guest

Posted: Thu Aug 24, 2006 3:09 pm Post subject: IFR and x-c stability?

Poor Greg, I think that he scared himself enough that he went overboard.  He 

did learn his lesson about flying a plane much aft of CG.  He took almost 

all of his stuff and shipped it home and only had a change of clothes and a 

fuel tools just in case we needed them when traveling.  He put all the tools 

in the side pouches which ripped the interior loose because of the weight 

pulling down on them.



It really was a smooth ride out.  I had a minimum acceptable level that I 

wanted it to meet but it far surpassed that.  I was really quiet surprised 

at how well it did handle.  I know I have used this comparison before, but 

given that I've only flown 25 different types of aircraft thusfar I compare 

it to a Mooney.  A Mooney is a lot bigger and will handle the bumps a little 

better, granted, but it has that sporty and responsive feel, but makes a 

pretty good cross-country cruiser!  When we started flying over the bigger 

mountains on the back side I braced myself for a good jolt.  There was a 

bump, but no worse than any other plane.  Very surprised and pleased with 

that.  (I have on occasion been in bad enough turbulence that you have the 

ever-changing CG because of the junk in the cabin floating around your head) 

  Brian W.

N1BZRich(at)aol.com
Guest

Posted: Thu Aug 24, 2006 7:38 pm Post subject: IFR and x-c stability?

Hey Max,

     Good run down.  I felt like I was back in Aero  101 at the Air Force Academy.  However, I wish you had mentioned your talk  with Greg Hobbs in your earlier message and we could have cleared this up for  you sooner.  The Lightning is a delightful aircraft.  I love my Esqual  LS (Lightning Stuff) but the Lightning is an all around a better airplane,  and I will be building one at some point in the future.  

     As a side note, yesterday I gave demo rides  to two individuals thinking of building a Lightning  together.  One is an experienced pilot, the other is a student  with 6 hours in a Cessna 150.  I put both in the left seat and  both flew 31BZ just fine.  In fact, the low time guy's comment was "I  could learn to fly in this airplane".  And he could, with no  problems.  He loved the way it handled and the fantastic visibility.   

     So for anyone reading this that still thinks the  Lightning is not a good cross country machine or not a good sport airplane, get  in touch with me an take a ride in 31BZ - and remember, the real Lightning is so  much better than my hybrid Esqual w/ Lightning Stuff.

 Blue Skies,

 Buz

  [quote][b]

Colin K.

Joined: 04 Sep 2006
Posts: 157
Location: Oklahoma

Posted: Thu Sep 07, 2006 5:31 pm Post subject: IFR and x-c stability?

I think we can safely add another plus to the reasons to build a Lightning,

and that is the knowledgeable engagement of numerous builders and aviators,

sharing their practical and theoretic experience with all who subscribe to

this list.



Thank you, Buzz, Max, Doug, Nick, Pete, Brian, Tex, Korky et al. Long may it

continue!



The only thing I am concerned about, is that by the time I bite the bullet,

the waiting list may be longer than I would like.

Colin K.

OK

_________________
Colin K.
OK

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