Today's Message Index:
----------------------
1. 05:43 AM - Re: IFR and x-c stability? (N1BZRich@AOL.COM)
2. 09:25 AM - Re: IFR and x-c stability? (Clifford Walinsky)
3. 12:18 PM - Re: IFR and x-c stability? (Givan, Max)
4. 02:01 PM - Re: IFR and x-c stability? (Kayberg@AOL.COM)
5. 02:13 PM - Re: IFR and x-c stability? (Brian Whittingham)
6. 02:19 PM - Re: IFR and x-c stability? (Brian Whittingham)
7. 02:24 PM - Re: IFR and x-c stability? (Pete)
8. 03:29 PM - Re: IFR and x-c stability? (nick otterback)
9. 04:09 PM - Re: IFR and x-c stability? (Brian Whittingham)
10. 08:38 PM - Re: IFR and x-c stability? (N1BZRich@aol.com)
Message 1
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| Subject: | Re: IFR and x-c stability? |
In a message dated 8/23/2006 9:13:16 A.M. Eastern Daylight Time,
empire.john@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
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| Subject: | Re: IFR and x-c stability? |
--> Lightning-List message posted by: Clifford Walinsky <cliffw@model.com>
N1BZRich@aol.com wrote:
> In a message dated 8/23/2006 9:13:16 A.M. Eastern Daylight Time,
> empire.john@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:
> 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/ft (100 kg/m) for general
> aviation aircraft, to 80 to 120 lb/ft (390 to 585 kg/m) 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
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| 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@matronics.com
[mailto:owner-lightning-list-server@matronics.com] On Behalf Of
N1BZRich@aol.com
Sent: Thursday, August 24, 2006 5:44 AM
Subject: Re: Lightning-List: IFR and x-c stability?
In a message dated 8/23/2006 9:13:16 A.M. Eastern Daylight Time,
empire.john@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
Message 4
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| Subject: | Re: 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@ngc.com writes:
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@matronics.com
[mailto:owner-lightning-list-server@matronics.com] On Behalf Of N1BZRich@aol.com
Sent: Thursday, August 24, 2006 5:44 AM
Subject: Re: Lightning-List: IFR and x-c stability?
In a message dated 8/23/2006 9:13:16 A.M. Eastern Daylight Time,
empire.john@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
ronics.com/Navigator?Lightning-List
Message 5
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| Subject: | IFR and x-c stability? |
--> Lightning-List message posted by: "Brian Whittingham" <dashvii@hotmail.com>
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.
Message 6
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| Subject: | Re: IFR and x-c stability? |
--> Lightning-List message posted by: "Brian Whittingham" <dashvii@hotmail.com>
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.
Message 7
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| 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@matronics.com
[mailto:owner-lightning-list-server@matronics.com] On Behalf Of Givan, Max
Sent: Thursday, August 24, 2006 2:18 PM
Subject: RE: Lightning-List: 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@matronics.com
[mailto:owner-lightning-list-server@matronics.com] On Behalf Of
N1BZRich@aol.com
Sent: Thursday, August 24, 2006 5:44 AM
Subject: Re: Lightning-List: IFR and x-c stability?
In a message dated 8/23/2006 9:13:16 A.M. Eastern Daylight Time,
empire.john@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
ronics.com/Navigator?Lightning-List
Message 8
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| Subject: | Re: 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@model.com> wrote:
--> Lightning-List message posted by: Clifford Walinsky
N1BZRich@aol.com wrote:
> In a message dated 8/23/2006 9:13:16 A.M. Eastern Daylight Time,
> empire.john@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:
> 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/ft (100 kg/m) for general
> aviation aircraft, to 80 to 120 lb/ft (390 to 585 kg/m) 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
---------------------------------
Message 9
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| Subject: | Re: IFR and x-c stability? |
--> Lightning-List message posted by: "Brian Whittingham" <dashvii@hotmail.com>
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.
Message 10
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| Subject: | Re: 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
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