Aerobatic potential vs. wingloading

Aerobatic potential vs. wingloading

Post by Erik Joseph Guidr » Fri, 29 Nov 1996 04:00:00



I am curious about the effect of wingloading on aerobatic
potential.  For instance, consider two CGM Extras, one powered
with a .61 2-stroke and weighing about 7 pounds and one powered
with a 1.2 4-stroke and weighing about 10 pounds.  Assuming all
other things are equal (CG, surface throw, etc.), which plane
will have better aerobatic capabilities?  Of course, the 1.2
version will have superior vertical performance, but aside from
this, will one or the other be any better?  It's pretty clear
the lighter version will have a lower stall speed and probably
land easier.  Will it also respond faster to control inputs
because of less inertia and momemtum?  Will the heavier version
perform better snap maneuvers because of the higher stall
speed?  I would love to hear anyone's thoughts on this.
--
Erik Guidroz

 
 
 

Aerobatic potential vs. wingloading

Post by Dave Tatosi » Mon, 02 Dec 1996 04:00:00




Quote:
>I am curious about the effect of wingloading on aerobatic
>potential.  For instance, consider two CGM Extras, one powered
>with a .61 2-stroke and weighing about 7 pounds and one powered
>with a 1.2 4-stroke and weighing about 10 pounds.  Assuming all
>other things are equal (CG, surface throw, etc.), which plane
>will have better aerobatic capabilities?  Of course, the 1.2
>version will have superior vertical performance, but aside from
>this, will one or the other be any better?  It's pretty clear
>the lighter version will have a lower stall speed and probably
>land easier.  Will it also respond faster to control inputs
>because of less inertia and momemtum?  Will the heavier version
>perform better snap maneuvers because of the higher stall
>speed?  I would love to hear anyone's thoughts on this.

I'm curious: is this strictly a hypothetical weight-vs-manueverability
question, or are you actually trying to compare the same plane with different
engines with some basis in reality?

If the latter is the case: an OS120-Surpass II (normally aspirated) weighs
under 2 pounds with its silencer. In comparison, a non-pumped OS.61SF weighs
roughly 22 ounces with muffler - ie: only 10 ounces less than the 1.2SP-2.
That's a lot less than the three pound difference you're starting from - and
ought to give you a more realistic base to start the hypothesizing from...

fwiw: I'd opt for the 1.20 SP-2 over the .61 - if only because you'd have an
amazing amount of torque available to play with compared to the .61 (not to
mention the sound of those 1.20's is pretty kewl! ;^)

Cheers!

/dave

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Aerobatic potential vs. wingloading

Post by Jerel Zarestk » Mon, 02 Dec 1996 04:00:00


Quote:



> >I am curious about the effect of wingloading on aerobatic
> >potential.  For instance, consider two CGM Extras, one powered
> >with a .61 2-stroke and weighing about 7 pounds and one powered
> >with a 1.2 4-stroke and weighing about 10 pounds.  Assuming all
> >other things are equal (CG, surface throw, etc.), which plane
> >will have better aerobatic capabilities?  Of course, the 1.2
> >version will have superior vertical performance, but aside from
> >this, will one or the other be any better?  It's pretty clear
> >the lighter version will have a lower stall speed and probably
> >land easier.  Will it also respond faster to control inputs
> >because of less inertia and momemtum?  Will the heavier version
> >perform better snap maneuvers because of the higher stall
> >speed?  I would love to hear anyone's thoughts on this.

> I'm curious: is this strictly a hypothetical weight-vs-manueverability
> question, or are you actually trying to compare the same plane with different
> engines with some basis in reality?

> If the latter is the case: an OS120-Surpass II (normally aspirated) weighs
> under 2 pounds with its silencer. In comparison, a non-pumped OS.61SF weighs
> roughly 22 ounces with muffler - ie: only 10 ounces less than the 1.2SP-2.
> That's a lot less than the three pound difference you're starting from - and
> ought to give you a more realistic base to start the hypothesizing from...

> fwiw: I'd opt for the 1.20 SP-2 over the .61 - if only because you'd have an
> amazing amount of torque available to play with compared to the .61 (not to
> mention the sound of those 1.20's is pretty kewl! ;^)

I agree!  I've got a CGM Extra with an OS1.20 Surpass(pumped) and it is
loads of fun.  It's a little on the heavy side at 10.2 lb due to too
much scale detail (I didn't build it) but even at that weight it is a
blast to fly!

Jerel

--
Jerel Zarestky                          
Neutron Scattering Group        

http://scatterbrain.ssd.ornl.gov/NSatHFIR/NSatHFIR.html

 
 
 

Aerobatic potential vs. wingloading

Post by lundi » Mon, 02 Dec 1996 04:00:00




Quote:
> I am curious about the effect of wingloading on aerobatic
> potential.  For instance, consider two CGM Extras, one powered
> with a .61 2-stroke and weighing about 7 pounds and one powered
> with a 1.2 4-stroke and weighing about 10 pounds.  Assuming all
> other things are equal (CG, surface throw, etc.), which plane
> will have better aerobatic capabilities?  Of course, the 1.2
> version will have superior vertical performance, but aside from
> this, will one or the other be any better?  It's pretty clear
> the lighter version will have a lower stall speed and probably
> land easier.  Will it also respond faster to control inputs
> because of less inertia and momemtum?  Will the heavier version
> perform better snap maneuvers because of the higher stall
> speed?  I would love to hear anyone's thoughts on this.
> --
> Erik Guidroz


Higher wing loading meas it'll be faster.  If you want a really fast
snap-roll go for the higher wing loading.  I have found planes with higher
wing loading to tumble and cartwheel better.  I am not sure what you mean by
better aerobatics.  I have to say that if you're trying to build a plane for
better aerobatics you may be disappointed.  Just go practice and make
whatever plane you have become an extension of your fingers.  I've seen
junkie slow planes flown in horizontal loops with rolls by excellent pilots.
 The answers to your intertia and momentum questions are not simple.  But in
general the higher wing loading if not just a weighted floater will be
quicker responding.  This is usually due to short moment arms (elevators
close to wing) and big control surfaces operating at higher speeds.   Wing
twist and taper are also big players in fast response.  Then there's the CG
location.  It's also important to have surplus power.  Aerodynamic stability
and control is not simple.  I don't know your flying skill but if you want
to try to get confused then try a higher wing loading.  I have thought about
t*** the wing and fusleage on a Quicke 500 and making an Extra type
ship.  It would be cheap.
Happy Trails
Steve Lundin
 
 
 

Aerobatic potential vs. wingloading

Post by Max Fe » Wed, 04 Dec 1996 04:00:00


Quote:

> Higher wing loading meas it'll be faster.  If you want a really fast
> snap-roll go for the higher wing loading.  I have found planes with higher
...
> quicker responding.  This is usually due to short moment arms (elevators
> close to wing) and big control surfaces operating at higher speeds.   Wing

I don't think this is correct reasoning. A heavier plane will GLIDE faster,
but under power it will actually fly slower because it has to fly at a
greater angle of attack and there will be more drag.

A useful exercise in these situations is to picture an extreme case.
Add 4 pounds to your 60 size plane and if it can still fly level, it
will be doing so more slowly, labouring along. Now picture removing
4 pounds of weight via lightening holes - your plane will go faster
because the engine will have less drag to overcome.

Regards,
Max
--
Max Feil

Ottawa, Canada.

 
 
 

Aerobatic potential vs. wingloading

Post by Steven Spold » Wed, 04 Dec 1996 04:00:00




Quote:
>I am curious about the effect of wingloading on aerobatic
>potential.  For instance, consider two CGM Extras, one powered
>with a .61 2-stroke and weighing about 7 pounds and one powered
>with a 1.2 4-stroke and weighing about 10 pounds.  Assuming all
>other things are equal (CG, surface throw, etc.), which plane
>will have better aerobatic capabilities?  Of course, the 1.2
>version will have superior vertical performance, but aside from
>this, will one or the other be any better?  It's pretty clear
>the lighter version will have a lower stall speed and probably
>land easier.  Will it also respond faster to control inputs
>because of less inertia and momemtum?  Will the heavier version
>perform better snap maneuvers because of the higher stall
>speed?  I would love to hear anyone's thoughts on this.

If you want to compare apples and apples, I would consider power to
weight as the equalizer in performance. If you have a 10 pound airplane
that stalls at 20 mph, doubling the weight to 20 pounds increases the
stall speed to 28 mph, and doubles the drag at the higher speed. this
airplane now requires 2*sqrt(2) = 2.8 times the horse power of the 10
pound airplane to fly at the same relative margin above stall. The
heavier aircraft will fly larger maneuvers however. This would sugguest
that if hp1/hp2 = (weight1/weight2)^1.5 then the aerobatic potential of
each aircraft would be similar. The light aircraft would fly tight slow
maneuvers, while the heavy aircraft would fly large fast maneuvers. I
would pick the wing loading to fly the size and speed maneuvers you want,
and select the power plant accordingly.

You can see why light weight is important. In this scenario, a 10 percent
weight loss is equivilent to a 14 percent horsepower gain. An overweight
aircraft can increase the power requirements dramatically.

Sincerely,  Steve Spoldi

 
 
 

Aerobatic potential vs. wingloading

Post by Steven Spold » Wed, 04 Dec 1996 04:00:00




Quote:
>I am curious about the effect of wingloading on aerobatic
>potential.  For instance, consider two CGM Extras, one powered
>with a .61 2-stroke and weighing about 7 pounds and one powered
>with a 1.2 4-stroke and weighing about 10 pounds.  Assuming all
>other things are equal (CG, surface throw, etc.), which plane
>will have better aerobatic capabilities?  Of course, the 1.2
>version will have superior vertical performance, but aside from
>this, will one or the other be any better?  It's pretty clear
>the lighter version will have a lower stall speed and probably
>land easier.  Will it also respond faster to control inputs
>because of less inertia and momemtum?  Will the heavier version
>perform better snap maneuvers because of the higher stall
>speed?  I would love to hear anyone's thoughts on this.

If you want to compare apples and apples, I would consider power to
weight as the equalizer in performance. If you have a 10 pound airplane
that stalls at 20 mph, doubling the weight to 20 pounds increases the
stall speed to 28 mph, and doubles the drag at the higher speed. this
airplane now requires 2*sqrt(2) = 2.8 times the horse power of the 10
pound airplane to fly at the same relative margin above stall. The
heavier aircraft will fly larger maneuvers however. This would sugguest
that if hp1/hp2 = (weight1/weight2)^1.5 then the aerobatic potential of
each aircraft would be similar. The light aircraft would fly tight slow
maneuvers, while the heavy aircraft would fly large fast maneuvers. I
would pick the wing loading to fly the size and speed maneuvers you want,
and select the power plant accordingly.

You can see why light weight is important. In this scenario, a 10 percent
weight loss is equivilent to a 14 percent horsepower gain. An overweight
aircraft can increase the power requirements dramatically.

Sincerely,  Steve Spoldi

 
 
 

Aerobatic potential vs. wingloading

Post by Roger W Guin » Thu, 05 Dec 1996 04:00:00


Quote:


> > Higher wing loading meas it'll be faster.  If you want a really fast
> > snap-roll go for the higher wing loading.  I have found planes with higher
> ...
> > quicker responding.  This is usually due to short moment arms (elevators
> > close to wing) and big control surfaces operating at higher speeds.   Wing

> I don't think this is correct reasoning. A heavier plane will GLIDE faster,
> but under power it will actually fly slower because it has to fly at a
> greater angle of attack and there will be more drag.

> A useful exercise in these situations is to picture an extreme case.
> Add 4 pounds to your 60 size plane and if it can still fly level, it
> will be doing so more slowly, labouring along. Now picture removing
> 4 pounds of weight via lightening holes - your plane will go faster
> because the engine will have less drag to overcome.

> Regards,
> Max
> --
> Max Feil

> Ottawa, Canada.a heavy aircraft MUST (as in HAS TO) fly faster! The reason is that the

only way to counteract weight (gravity force) is to generate more LIFT.
Lift comes from 1) Airspeed and 2) angle of attack (AOA) Increased lift
also means increased drag. Without the increased airspeed, we have the
big hole syndrome (assuming you get airborn in the first place). At some
point, you reach the point of "no matter how fast or how high an AOA, it
won't lift"-mainly because drag forces tear the wings off!
--
Roger W Guinn, PE
Structural Analysis, Vibration, Loads, Stress

"Take-off's are optional. Landings are Mandatory"

 
 
 

Aerobatic potential vs. wingloading

Post by Bob Burril » Fri, 06 Dec 1996 04:00:00


Quote:

> a heavy aircraft MUST (as in HAS TO) fly faster! The reason is that the
> only way to counteract weight (gravity force) is to generate more LIFT.
> Lift comes from 1) Airspeed and 2) angle of attack (AOA) Increased lift
> also means increased drag. Without the increased airspeed, we have the
> big hole syndrome (assuming you get airborn in the first place). At some
> point, you reach the point of "no matter how fast or how high an AOA, it
> won't lift"-mainly because drag forces tear the wings off!
> --

A heavy aircraft only needs to have a faster speed to maintain flight.
That has nothing to do with how fast the plane can fly.  In this case
Max is correct.  With lighter wing loading an aircraft can keep the same
lift at higher speeds by reducing the angle of attack.  Since most drag
is a function of angle of attack the drag will be less than a heavier
aircraft at the same speed.

BTW, the thickness of the wing will also play a very important part in
the amount of drag but should not affect wing loading.

Thanks,
rb

 
 
 

Aerobatic potential vs. wingloading

Post by dgamb.. » Sat, 07 Dec 1996 04:00:00


Quote:



>  >I am curious about the effect of wingloading on aerobatic
>  >potential.  For instance, consider two CGM Extras, one powered
>  >with a .61 2-stroke and weighing about 7 pounds and one powered
>  >with a 1.2 4-stroke and weighing about 10 pounds.  Assuming all
>  >other things are equal (CG, surface throw, etc.), which plane
>  >will have better aerobatic capabilities?  Of course, the 1.2
>  >version will have superior vertical performance, but aside from
>  >this, will one or the other be any better?  It's pretty clear
>  >the lighter version will have a lower stall speed and probably
>  >land easier.  Will it also respond faster to control inputs
>  >because of less inertia and momemtum?  Will the heavier version
>  >perform better snap maneuvers because of the higher stall
>  >speed?  I would love to hear anyone's thoughts on this.

        Well...... maybe I can offer sump'tin here.........

        I do a fair amount of test flying of new planes, and I'm often asked
to "Debug" some aircraft....   - I have had the opportunity to fly several
Ultimates, which , as many of you now know, need some "tweaking" to
become good aerobatic machines...

        Three stand out in my memory....

        A -   STRONG   OS 61, 7-3/4 lbs,
                Run out of steam at 250 ft vertical, glided well,
 tight manouvers, tumbled well, was the MOST  PURE FUN to fly. Light and
agile.

        B -  ST 90 ring, 8-1/4 lbs,
                Vertical till I said stop, handled about the same as  (A)
nor quite as agile, glided well, wind penetration a little better (had wheel pants
-A- did not)-------    

        (this is my own aircraft)

        C - YS 1.2  10 - 1/4 lbs,
                Vertical was BALLISTIC !   but........  it had the glide of a
cinder block, - dead stick was a panic with the weight penalty and the drag of
2 wings, struts etc. - snaps were too good, like - at the bottom of square loops
etc.  :)    Did everything required (like knife edge loops)  but could bite,  - the
owner had trouble with the landing gear bending  - prolly due to the wt and  
stalling a little to soon on landings that were  much faster than (A)  above.
Wind penetration was very good,( wasn't bounced around by the wind)

        Another observation...   The life span of the Goldberg Ultimate
appears to be inversely proportional to the increase in weight of the aircraft....

        FWIW,   (A) was the most fun to fly (unless you hafta rocket vertical
ALL the time),   (B)  is fun and I'm happy with it,  (C)   was a rocket  and provided
a special kind of fun but required an expirenced pilot to keep alive and a VERY
 reliable eng. (I hear he later added a glow driver)

        Cheers ! ...... Dave

 
 
 

Aerobatic potential vs. wingloading

Post by Roger W Guin » Mon, 09 Dec 1996 04:00:00


Quote:


> > a heavy aircraft MUST (as in HAS TO) fly faster! The reason is that the
> > only way to counteract weight (gravity force) is to generate more LIFT.
> > Lift comes from 1) Airspeed and 2) angle of attack (AOA) Increased lift
> > also means increased drag. Without the increased airspeed, we have the
> > big hole syndrome (assuming you get airborn in the first place). At some
> > point, you reach the point of "no matter how fast or how high an AOA, it
> > won't lift"-mainly because drag forces tear the wings off!
> > --

> A heavy aircraft only needs to have a faster speed to maintain flight.
> That has nothing to do with how fast the plane can fly.  In this case
> Max is correct.  With lighter wing loading an aircraft can keep the same
> lift at higher speeds by reducing the angle of attack.  Since most drag
> is a function of angle of attack the drag will be less than a heavier
> aircraft at the same speed.

> BTW, the thickness of the wing will also play a very important part in
> the amount of drag but should not affect wing loading.

> Thanks,
> rbAll you say is true. I was quoting for a GIVEN airfoil and aircraft. All

other things equal, the heavier aircraft must fly faster to stay aloft.
--
Roger W Guinn, PE
Structural Analysis, Vibration, Loads, Stress

"Take-off's are optional. Landings are Mandatory"

 
 
 

Aerobatic potential vs. wingloading

Post by Max Fe » Wed, 11 Dec 1996 04:00:00



Quote:
> a heavy aircraft MUST (as in HAS TO) fly faster! The reason is that the
> only way to counteract weight (gravity force) is to generate more LIFT.
> Lift comes from 1) Airspeed and 2) angle of attack (AOA) Increased lift
> also means increased drag. Without the increased airspeed, we have the
> big hole syndrome (assuming you get airborn in the first place). At some
> point, you reach the point of "no matter how fast or how high an AOA, it
> won't lift"-mainly because drag forces tear the wings off!

I was on vacation, so I did not get your message until now. As the followups
to your posting on rec.models.rc.air show, I think there was a
misunderstanding. You must have been assuming constant angle of attack, in
which case more power is needed to increase airspeed and therefore lift.

In either case the energy has to come from somewhere.  If an airplane is
already at full throttle, then it cannot fly faster when weight is added. It
therefore must increase its angle of attack and slow down. As more weight is
added the speed will decrease and the AOA will increase until the point is
reached where level flight can no longer be maintained.  At this point the
plane will descend and may even stall - but I don't think the wings will rip
off.

So if you take two identical aircraft and make one heavier, it will fly
slower (except in dives). Why else would the pylon racers and AT-6 racers
strive to build light?

In a glider the speed increases when weight increases because level flight with
respect to the surrounding air is never possible anyways. The extra energy
comes from increased descent rate. It's interesting to note that the "best
glide" ratio (max L/D) stays the same, i.e. adding weight to a sailplane
makes it descend faster but it glides just as far. In fact there can be
a miniscule improvement in best glide ratio due to reynolds number effects.
I know of a full size sailplane whose published max L/D is 40 at minumum
loading and 40.5 at max gross weight.

Cheers,
Max
--

UniCAD (CANADA) Ltd.    |------------------------------------------------------
CAD Software Development| I'm an "optimist wannabe".
Ottawa, Ontario, Canada.|
--
Max Feil

Ottawa, Canada.