Max Weight of Non Lift Producing Components

[[email protected]]

In addition to max gross weight, some glider manuals specify a max weight for non lift producing components. But I haven't found much discussion of the significance of exceeding the max or information that would allow one to calculate the weight of non-lifting components (like a breakout showing the weights of the wings, etc.)

Would appreciate some discussion by those in the know.

Tom

[Tony[_5_]]

the only way to know is to weigh the wings separately. That is what we did the last time we did a W&B on the Cirrus. That was part of incorporating the Tech Note from Schemmp Hirth to increase the weight of non lifting parts.

Some airplanes, especially twin engine airplanes, have a maximum zero fuel weight which is a similar concept.

[[email protected]]

From the BGA:

5. Non-Lifting Parts. For sailplanes where the Leading Particulars specify a maximum weight
of non-lifting parts, it will additionally be necessary to weigh the wings to enable the weight of the
fuselage and tailplane to be calculated; this is the empty weight of non-lifting parts.


I can't say what the significance of exceeding the max would be, but from general life experience exceeding the max of anything is usually a bad idea.

RC

[Larry Suter]

Lot of gliders have a maximum weights with water ballast that's a couple hundred pounds greater than maximum weight w/o water ballast.

I think the maximum weight of non-lifting components is so you don't think you can put all that extra weight in the fuselage. My POH also has this, "Note: Water ballast in fuselage belongs to non-lifting parts."

Larry

[[email protected]]

On Wednesday, November 29, 2017 at 8:08:26 PM UTC-8, wrote:
> In addition to max gross weight, some glider manuals specify a max weight for non lift producing components. But I haven't found much discussion of the significance of exceeding the max or information that would allow one to calculate the weight of non-lifting components (like a breakout showing the weights of the wings, etc.)
>
> Would appreciate some discussion by those in the know.
>
> Tom

I think Larry's interpretation seems plausible. When I've seen a separate limit called out for non-lifting components, it generally seems to be in the context of water loading. The wings are, in a sense, self-supporting in flight, whereas the fuselage hangs off of the wings. So it makes sense to call out a separate limit for the non-lifting parts; particularly when water is involved.
Tom

[Tango Whisky]

Le jeudi 30 novembre 2017 05:39:23 UTC+1, a écritÂ*:
> From the BGA:
>
> 5. Non-Lifting Parts. For sailplanes where the Leading Particulars specify a maximum weight
> of non-lifting parts, it will additionally be necessary to weigh the wings to enable the weight of the
> fuselage and tailplane to be calculated; this is the empty weight of non-lifting parts.
>
>
> I can't say what the significance of exceeding the max would be, but from general life experience exceeding the max of anything is usually a bad idea.
>
> RC

Exeeding max weight of non-lifting parts makes you exceeding the structural limits of the plane (i.e. you start eating up the safety factor of 1.5), which is generally acknowledged as being a fairly stupid idea.

MTOW is not really connected to max weight of non-lifting parts.

[Dan Marotta]

While studying for my Flight Engineer license back in the 70s (do they
have Flight Engineers any more?), it was explained that the max weight
of non lifting components had to do with the strength (bending moments)
of the wing spar.Â* Help us out here, Steve L.

MTOW has, I believe, to do with landing gear, brakes, tires, etc. Think
MV**2 during an aborted takeoff.Â* Higher weight -> higher takeoff speed
-> WAY higher energy to dissipate, that V squared component.

On 11/30/2017 2:40 AM, Tango Whisky wrote:
> Le jeudi 30 novembre 2017 05:39:23 UTC+1, a écritÂ*:
>> From the BGA:
>>
>> 5. Non-Lifting Parts. For sailplanes where the Leading Particulars specify a maximum weight
>> of non-lifting parts, it will additionally be necessary to weigh the wings to enable the weight of the
>> fuselage and tailplane to be calculated; this is the empty weight of non-lifting parts.
>>
>>
>> I can't say what the significance of exceeding the max would be, but from general life experience exceeding the max of anything is usually a bad idea.
>>
>> RC
> Exeeding max weight of non-lifting parts makes you exceeding the structural limits of the plane (i.e. you start eating up the safety factor of 1.5), which is generally acknowledged as being a fairly stupid idea.
>
> MTOW is not really connected to max weight of non-lifting parts.

--
Dan, 5J

[Charlie M. (UH & 002 owner/pilot)]

I believe you are correct, you don't want to overload the spar with fuselage weight, thus, spread it out through the wings.
I know some ships had water in the wings but also additional in a tank in the fuselage to get the wing loading up due to low volume wings. You would load the wings, then finish off with the fuselage. Dumping ballast is fuselage first, then wings.

As to MTOW, some larger aircraft also have a MLW, max landing weight which I believe is mostly due to loads when the mains hit the runway.
So, some aircraft can take off at a higher weight than they can land! So, if they run into an issue, they may have to fly around to burn fuel off to get within landing weight, or even dump fuel (don't tell the EPA!).

[Steve Leonard[_2_]]

On Wednesday, November 29, 2017 at 10:13:28 PM UTC-6, Tony wrote:
> the only way to know is to weigh the wings separately. That is what we did the last time we did a W&B on the Cirrus. That was part of incorporating the Tech Note from Schemmp Hirth to increase the weight of non lifting parts.


Or, if you want to know how much the fuselage and tail weigh, you can weigh them rather than weigh the wings and subtract that from the empty weight. The former gives you the weight you really want to know. The latter assumes the previous empty weight is still accurate, and there there have been no changes made to anything in the fuselage or wings.

Steve Leonard

[Tony[_5_]]

We weighed everything together and then the wings. Felt that was easier than trying to hold the fuselage with tail attached upright and on the scales.

[Kevin Neave[_2_]]

So what does the main pin(s) count as?

KN

At 16:07 30 November 2017, Tony wrote:
>We weighed everything together and then the wings. Felt that was easier
>than trying to hold the fuselage with tail attached upright and on the
>scales.
>

[BobW]

On 11/30/2017 9:53 AM, Kevin Neave wrote:
> So what does the main pin(s) count as?
>
> KN
>
> At 16:07 30 November 2017, Tony wrote:
>> We weighed everything together and then the wings. Felt that was easier
>> than trying to hold the fuselage with tail attached upright and on the
>> scales.

Try flying without it/them in place and get back to the group how it went! :)

More seriously, and structurally, it/they are part(s) of the wing.

Bob W.

---
This email has been checked for viruses by AVG.
http://www.avg.com

[Dan Marotta]

Part of the wings, yes, but certainly not lift generating.Â* But you
can't do without them...

On 11/30/2017 10:15 AM, BobW wrote:
> On 11/30/2017 9:53 AM, Kevin Neave wrote:
>> So what does the main pin(s) count as?
>>
>> KN
>>
>> At 16:07 30 November 2017, Tony wrote:
>>> We weighed everything together and then the wings. Felt that was
>>> easier than trying to hold the fuselage with tail attached upright
>>> and on the scales.
>
> Try flying without it/them in place and get back to the group how it
> went! :)
>
> More seriously, and structurally, it/they are part(s) of the wing.
>
> Bob W.
>
> ---
> This email has been checked for viruses by AVG.
> http://www.avg.com
>

--
Dan, 5J

[[email protected]]

BGA has a concession which allows for non-aerobatic flights to exceed the maximum weight of non-lifting parts by 3%, so my that margin it should be fine.

Does anyone know, how exceeding that non-lifting weight influences the flutter of the wing?

Stefan

[Dan Marotta]

Screw the EPA!Â* When I was doing engine out maintenance recovery
flights, it was standard practice to open all the tank dump valves
before take off leaving only the wing tip nozzle valves to start fuel
dumping.Â* That might save a second or two should the situation become
critical.

On 11/30/2017 8:56 AM, Charlie M. (UH & 002 owner/pilot) wrote:
> I believe you are correct, you don't want to overload the spar with fuselage weight, thus, spread it out through the wings.
> I know some ships had water in the wings but also additional in a tank in the fuselage to get the wing loading up due to low volume wings. You would load the wings, then finish off with the fuselage. Dumping ballast is fuselage first, then wings.
>
> As to MTOW, some larger aircraft also have a MLW, max landing weight which I believe is mostly due to loads when the mains hit the runway.
> So, some aircraft can take off at a higher weight than they can land! So, if they run into an issue, they may have to fly around to burn fuel off to get within landing weight, or even dump fuel (don't tell the EPA!).

--
Dan, 5J

[Tango Whisky]

No, it doesn't influence flutter. Flutter is controlled by the eigenfrequencies of the wing.

[K m]

On Thursday, November 30, 2017 at 8:44:24 AM UTC-7, Dan Marotta wrote:
> While studying for my Flight Engineer license back in the 70s (do they
> have Flight Engineers any more?), it was explained that the max weight
> of non lifting components had to do with the strength (bending moments)
> of the wing spar.Â* Help us out here, Steve L.
>
> MTOW has, I believe, to do with landing gear, brakes, tires, etc. Think
> MV**2 during an aborted takeoff.Â* Higher weight -> higher takeoff speed
> -> WAY higher energy to dissipate, that V squared component.
Dan,
No more flight engineers. You have to go back to 727s or early 747s to find a Flight engineer panel and all of those have been retired in this country years ago. MTOW is based on 5 different Performance charts (4 of which are based on engine out performance). MLW is based on Landing Gear and brake energy. Zero Fuel Weight is based on bending moment just like you said. I checked with the factory on my glider and yes, Non Lifting is just like Max Zero Fuel WT is on a jet. Everything beyond this must be wing ballast.

[George Haeh]

The weight of the wings should not change much from the factory weight
until
repairs or refinishing.

In the fuselage, instruments, batteries, O2 system, pilot, chute,
documents,, tie
down kit, lunch and drinks need to be included.

It all adds up.

[Jonathan St. Cloud]

Northwest Airlines hated it when they got ride of the flight engineer, less people to play drinking games with all night before flight.

On Thursday, November 30, 2017 at 11:55:47 AM UTC-8, K m wrote:
> On Thursday, November 30, 2017 at 8:44:24 AM UTC-7, Dan Marotta wrote:
> > While studying for my Flight Engineer license back in the 70s (do they
> > have Flight Engineers any more?), it was explained that the max weight
> > of non lifting components had to do with the strength (bending moments)
> > of the wing spar.Â* Help us out here, Steve L.
> >
> > MTOW has, I believe, to do with landing gear, brakes, tires, etc. Think
> > MV**2 during an aborted takeoff.Â* Higher weight -> higher takeoff speed
> > -> WAY higher energy to dissipate, that V squared component.
> Dan,
> No more flight engineers. You have to go back to 727s or early 747s to find a Flight engineer panel and all of those have been retired in this country years ago. MTOW is based on 5 different Performance charts (4 of which are based on engine out performance). MLW is based on Landing Gear and brake energy. Zero Fuel Weight is based on bending moment just like you said. I checked with the factory on my glider and yes, Non Lifting is just like Max Zero Fuel WT is on a jet. Everything beyond this must be wing ballast.

[Bob Kuykendall]

On Thursday, November 30, 2017 at 9:00:07 AM UTC-8, Kevin Neave wrote:

> So what does the main pin(s) count as?

Very incisive question! That's a good demonstration of how the mass of non-lifting is a reasonable metric for the approximation of wing main spar maximum bending moment, but is still just an approximation.

At issue is that using a maximum mass of non-lifting parts to limit the wing spar bending moment is only valid when any mass added to the wings is distributed spanwise according to the wing lift distribution. So if for whatever reason you add a bunch of mass to the inboard ends of the wings (depleted uranium root ribs maybe?), you can be within the allowable non-lifting mass and within the load factor envelope, but still develop excessive wing spar bending moment.

Bottom line: Respect mass limits to the spirit and the letter of the published values. And if you want a glider with lots of non-lifting mass margin, build an HP-24. The one we finished last summer has an empty non-lifting mass of ~220 lbs (ready to fly with batteries, instruments, 24 ft^2 O2 bottle, etc) and a maximum of ~605 lbs, yielding a payload of ~385 lbs for pilot, parachute, FES, electric self-launch, BRS, etc.

--Bob K.

[Charlie M. (UH & 002 owner/pilot)]

Well.....all I can say is, the EPA is a major US government agency, thus, likely quite large.
So, either eat a huge amount of oysters or renew your prescription for your "little blue pill of choice" as it may be borderline on screwing the whole agency......
YMMV.......
;-)

Whatever.....the basics of what I posted is correct (minus stupid side comments on my part). I'm really concerned on the physics. I believe I am correct.

I'm not an engineer.
I know a few.
I can spell it.
I have not stayed at a certain hotel chain in a couple years.

:-)
LOL......

[Jim White[_3_]]

At 22:44 30 November 2017, Bob Kuykendall wrote:
>On Thursday, November 30, 2017 at 9:00:07 AM UTC-8, Kevin Neave wrote:
>
>> So what does the main pin(s) count as?
>
>Very incisive question! That's a good demonstration of how the mass of
>non-=
>lifting is a reasonable metric for the approximation of wing main spar
>maxi=
>mum bending moment, but is still just an approximation.
>
>At issue is that using a maximum mass of non-lifting parts to limit the
>win=
>g spar bending moment is only valid when any mass added to the wings is
>dis=
>tributed spanwise according to the wing lift distribution. So if for
>whatev=
>er reason you add a bunch of mass to the inboard ends of the wings
>(deplete=
>d uranium root ribs maybe?), you can be within the allowable non-lifting
>ma=
>ss and within the load factor envelope, but still develop excessive wing
>sp=
>ar bending moment.
>
>Bottom line: Respect mass limits to the spirit and the letter of the
>publis=
>hed values. And if you want a glider with lots of non-lifting mass
margin,
>=
>build an HP-24. The one we finished last summer has an empty non-lifting
>ma=
>ss of ~220 lbs (ready to fly with batteries, instruments, 24 ft^2 O2
>bottle=
>, etc) and a maximum of ~605 lbs, yielding a payload of ~385 lbs for
>pilot,=
> parachute, FES, electric self-launch, BRS, etc.
>
>--Bob K.
>
Ever wondered why commercial jets now all hang the engines from the wings?
Lighter spars and the added roll inertia in the wing component reduces the
effect of turbulence on the passengers.

[Kiwi User]

On Thu, 30 Nov 2017 10:07:57 -0800, phouchg278 wrote:

> Does anyone know, how exceeding that non-lifting weight influences the
> flutter of the wing?
>
Its more a structural thing than load related.

Increasing surface torsional stiffness delays the onset of flutter and
putting the CG of the flying surface in front of the torsion axis damps
it out.


--
Martin | martin at
Gregorie | gregorie
| dot org

[CindyB[_2_]]

On Friday, December 1, 2017 at 3:44:44 AM UTC-8, Kiwi User wrote:
> On Thu, 30 Nov 2017 10:07:57 -0800, phouchg278 wrote:
>
> > Does anyone know, how exceeding that non-lifting weight influences the
> > flutter of the wing?
> >
> Its more a structural thing than load related. >


For the non engineers that might read this..... a loading illustration
using two examples:

Use a (really long)tongue depressor and white glue to glue a hollowed out eggshell to the half span point. Let it dry. Take a wing tip and do anything you like to shake the egg off the stick. Not enough mass in the eggshell to part it from the stick. Safe scenario = under max non-lifting parts weight.

The worst case scenario is the same eggshell full of heavy stuff. Mercury would be great - but its impractical. Imagine it. Load that egg (fiberglass shell) to the max, and then introduce a bunch of G's via centrifical or gust(rotor flight)force. The eggshell will rip off the stick(spar). Or, the stuff inside the shell will rupture it and leave the scene - think an over-max-payload person attached to max 242 lb. (110 kg) seat belt attaching points.

There are recurring discussions about how much margin designers provide for protection from this and that (max non lifting, Vne, gust loads, seatpan loads). My response is always - do you know the life history of this pretty fiberglass? The controlrod end play? The hingepoint tightness? How many times someone flew it how close to/over Vne due to an antique instrument or partially plugged pitot line? I am not in favor of flying beyond manufacturer's limits for anything.....
thanks for the many contributors to good info on this thread.

Cindy B

[Bob Kuykendall]

On Friday, December 1, 2017 at 10:00:14 AM UTC-8, CindyB wrote:

> There are recurring discussions about how much margin
> designers provide for protection from this and that...

One of the more high-profile examples is this RV-10 airplane for which the amateur builder arbitrarily increased the gross weight by a hundred pounds. Designer Dick Vangrunsven rightfully took issue with this practice:

https://www.facebook.com/notes/vans-aircraft-inc/what-price-a-masterpiece-by-dick-vangrunsven/237594966250883

> ...I am not in favor of flying beyond manufacturer's limits for anything...

That's the best plan!

--Bob K.

[Bruce Hoult]

On Friday, December 1, 2017 at 12:15:07 PM UTC+3, Jim White wrote:
> At 22:44 30 November 2017, Bob Kuykendall wrote:
> >On Thursday, November 30, 2017 at 9:00:07 AM UTC-8, Kevin Neave wrote:
> >
> >> So what does the main pin(s) count as?
> >
> >Very incisive question! That's a good demonstration of how the mass of
> >non-=
> >lifting is a reasonable metric for the approximation of wing main spar
> >maxi=
> >mum bending moment, but is still just an approximation.
> >
> >At issue is that using a maximum mass of non-lifting parts to limit the
> >win=
> >g spar bending moment is only valid when any mass added to the wings is
> >dis=
> >tributed spanwise according to the wing lift distribution. So if for
> >whatev=
> >er reason you add a bunch of mass to the inboard ends of the wings
> >(deplete=
> >d uranium root ribs maybe?), you can be within the allowable non-lifting
> >ma=
> >ss and within the load factor envelope, but still develop excessive wing
> >sp=
> >ar bending moment.
> >
> >Bottom line: Respect mass limits to the spirit and the letter of the
> >publis=
> >hed values. And if you want a glider with lots of non-lifting mass
> margin,
> >=
> >build an HP-24. The one we finished last summer has an empty non-lifting
> >ma=
> >ss of ~220 lbs (ready to fly with batteries, instruments, 24 ft^2 O2
> >bottle=
> >, etc) and a maximum of ~605 lbs, yielding a payload of ~385 lbs for
> >pilot,=
> > parachute, FES, electric self-launch, BRS, etc.
> >
> >--Bob K.
> >
> Ever wondered why commercial jets now all hang the engines from the wings?
> Lighter spars and the added roll inertia in the wing component reduces the
> effect of turbulence on the passengers.

Having them in front of the wing also acts as a mass balancer, counteracting flutter and turbulence. This is very obvious on the A380, which rides incredibly smoothly. (it also has a funky 3 outboard aileron setup, and they are CONSTANTLY moving rapidly, in different directions from each other, obviously under computer control)

[Jim[_33_]]

I admit I am baffled by "max weight of non-lifting parts". I understand the issue of spar bending moment limits, and I think I understand that weighing a glider without its wings will give the current non-lifting (i.e., non-wing) weight, but I have a feeling there are subtle things here that I do not understand.

For example, the ASK-21 POH lists the following weights:

Empty weight: approx 780 lbs
Max all-up weight: 1320 lbs
Max weight on non
lift producing members: 902 lbs

I've rigged an ASK-21 and its wings are HEAVY! I haven't weighed them so I don't know just how heavy they are though. Certainly felt like more than 100 lbs each. Ask me how I know. I'll guess (I know, don't guess) each wing weighs 150 lbs. Likely more. If I subtract 300 lbs from 780 and then subtract that result from 1320 I'm still short of 902 - which I suppose is a good thing.

Oh well. This all just makes my head hurt. Maybe what I should be doing is adding the weight of pilots, water, parachutes, etc. to 780 to ensure that the total is not beyond 1320. I suppose I already do this when I use Foreflight to calculate W&B.

TIme for a nap.

[Dan Daly[_2_]]

On Thursday, December 7, 2017 at 7:27:02 PM UTC-5, Jim wrote:
> I admit I am baffled by "max weight of non-lifting parts". I understand the issue of spar bending moment limits, and I think I understand that weighing a glider without its wings will give the current non-lifting (i.e., non-wing) weight, but I have a feeling there are subtle things here that I do not understand.
>
> For example, the ASK-21 POH lists the following weights:
>
> Empty weight: approx 780 lbs
> Max all-up weight: 1320 lbs
> Max weight on non
> lift producing members: 902 lbs
>
> I've rigged an ASK-21 and its wings are HEAVY! I haven't weighed them so I don't know just how heavy they are though. Certainly felt like more than 100 lbs each. Ask me how I know. I'll guess (I know, don't guess) each wing weighs 150 lbs. Likely more. If I subtract 300 lbs from 780 and then subtract that result from 1320 I'm still short of 902 - which I suppose is a good thing.
>
> Oh well. This all just makes my head hurt. Maybe what I should be doing is adding the weight of pilots, water, parachutes, etc. to 780 to ensure that the total is not beyond 1320. I suppose I already do this when I use Foreflight to calculate W&B.
>
> TIme for a nap.

1320-904=416 lbs. I'd guess closer to 180 per wing when you consider an ASG-29 wing weighs 140. Also, the horizontal stab and elevator are lifting. I don't know if you count the 22 lbs per wing root baggage compartment or not... I think that's lifting too. So, 360 lbs of wing, 44 lbs of baggage (worst case) which leaves about 12 lbs for tail bits.

[Scott Williams]

On Thursday, December 7, 2017 at 6:27:02 PM UTC-6, Jim wrote:
> I admit I am baffled by "max weight of non-lifting parts". I understand the issue of spar bending moment limits, and I think I understand that weighing a glider without its wings will give the current non-lifting (i.e., non-wing) weight, but I have a feeling there are subtle things here that I do not understand.
>
> For example, the ASK-21 POH lists the following weights:
>
> Empty weight: approx 780 lbs
> Max all-up weight: 1320 lbs
> Max weight on non
> lift producing members: 902 lbs
>
> I've rigged an ASK-21 and its wings are HEAVY! I haven't weighed them so I don't know just how heavy they are though. Certainly felt like more than 100 lbs each. Ask me how I know. I'll guess (I know, don't guess) each wing weighs 150 lbs. Likely more. If I subtract 300 lbs from 780 and then subtract that result from 1320 I'm still short of 902 - which I suppose is a good thing.
>
> Oh well. This all just makes my head hurt. Maybe what I should be doing is adding the weight of pilots, water, parachutes, etc. to 780 to ensure that the total is not beyond 1320. I suppose I already do this when I use Foreflight to calculate W&B.
>
> TIme for a nap.

Max weight of non-lifting parts;
Maybe it's listed that way to prevent the rationalization "the useful load is less than I want, I will use some of the water ballast allowable weight to justify excess pilot weight, and still be under max gross"

Nobody would do that would they? ;-)

[Bob Kuykendall]

On Thursday, December 7, 2017 at 5:59:55 PM UTC-8, Dan Daly wrote:
>...Also, the horizontal stab and elevator are lifting.

I don't think that's the generally accepted interpretation. It is definitely not the interpretation I apply when I publish W&B data.

Yes, they produce lift, but in most (but not all) flight regimes it's downward, not up.

--Bob K.

[Tango Whisky]

Elevator always counts as non-lifting.

[Kiwi User]

On Thu, 07 Dec 2017 21:40:48 -0800, Tango Whisky wrote:

> Elevator always counts as non-lifting.

Obviously: In every man-carrying aircraft I know of (computer-stabilised
beasts like the F-22 excepted) the CG is in front of the wing's centre of
lift, so the tailplane *must* generate a downforce during stable, trimmed
flight.


--
Martin | martin at
Gregorie | gregorie
| dot org

[Tango Whisky]

Le vendredi 8 décembre 2017 14:08:56 UTC+1, Kiwi User a écritÂ*:
> On Thu, 07 Dec 2017 21:40:48 -0800, Tango Whisky wrote:
>
> > Elevator always counts as non-lifting.
>
> Obviously: In every man-carrying aircraft I know of (computer-stabilised
> beasts like the F-22 excepted) the CG is in front of the wing's centre of
> lift, so the tailplane *must* generate a downforce during stable, trimmed
> flight.

No. (and by the ways, it's the neutral point which is important, not the center of lift of the wing).
What is important for stable flight is that the gradient of lift produced by the elevator over angle of attack is positive so that a pitching moment of the lift will be counter-balanced.
No if there is a gradient of lift over angle of attack for the elevator, the absolute value of the lift produced by the elevator will be zero for a defined angle of attack, negative below this angle, and positive above. the angle of attack for zero lift is a design parameter and is adjusted by chosing the fixed angle of the elevator in relation to the wing chord. Typically this angle is about -4°.

In any modern sailplane, you want to produce exactly zero lift at the elevator at max L/D speed, simply because this is were the elevator drag is minimum. As a consequence, the elevator will produce positive lift below max L/D speed, and negative lift above this speed.

[[email protected]]

Hey Tango Whiskey, sounds like you got your sierra together..............would you please address the "ideal" CG position in terms of percentage of allowable range?
Thanks,
JJ

[Tango Whisky]

Le vendredi 8 décembre 2017 16:03:18 UTC+1, a écritÂ*:
> Hey Tango Whiskey, sounds like you got your sierra together..............would you please address the "ideal" CG position in terms of percentage of allowable range?
> Thanks,
> JJ

Ideal for what? In terms of performance, this would exactly depend on how the elevator is rigged, which differs from type to type.

On my Ventus cM, I fly with max allowable aft CG. But not beacause I want it - I just don't have any choice if I don't want to exceed MTOW ;-)

[Charlie M. (UH & 002 owner/pilot)]

I doubt there is a "magic spot" across all glider types.
I would say, in general, pick the speed you will spend the most time at in a certain contest, then fly your normal stuff and see if the flying speed (no trim) matches. This means chute, snacks, water bottles, clothing for the ambient conditions, etc.
Adjust CG to allow "0" elevator (meaning chord of tail and elevator are even, thus no lift in either direction) so you can normally fly no trim.
This is least drag.
In engineering, as in life, there are compromises, fix one thing, likely to FUBAR another.

For most of us mere mortals, the biggest difference is the nut behind the stick.........

[Dan Marotta]

Let's not forget canard types where the elevator is in front of the CG
and always produces positive lift.Â* Rutan does it quite often with his
designs, but his glider was a bust.

On 12/8/2017 6:08 AM, Kiwi User wrote:
> On Thu, 07 Dec 2017 21:40:48 -0800, Tango Whisky wrote:
>
>> Elevator always counts as non-lifting.
> Obviously: In every man-carrying aircraft I know of (computer-stabilised
> beasts like the F-22 excepted) the CG is in front of the wing's centre of
> lift, so the tailplane *must* generate a downforce during stable, trimmed
> flight.
>
>

--
Dan, 5J

[Bob Kuykendall]

On Friday, December 8, 2017 at 7:03:18 AM UTC-8, wrote:
> Hey Tango Whiskey, sounds like you got your sierra together..............would you please address the "ideal" CG position in terms of percentage of allowable range?
> Thanks,
> JJ

JJ, Steve Smith has a good sermon on this, ask him next time you see him. He understands and explains it a lot better than I could.

I think it is cool that the tailplane lifts up at the low speed range, and down at the high speed range. Odd, but cool. So when you have the stick pulled back the tailplane is actually lifting up, and when the stick is pressed forward the tailplane is pushing down. As TW observes, it's all about the lift gradients. And pitching moment.

--Bob K.

[James Thomson[_2_]]

At 01:59 08 December 2017, Dan Daly wrote:
>On Thursday, December 7, 2017 at 7:27:02 PM UTC-5, Jim wrote:
>> I admit I am baffled by "max weight of non-lifting parts". I
understand
>=
>the issue of spar bending moment limits, and I think I understand that
>weig=
>hing a glider without its wings will give the current non-lifting (i.e.,
>no=
>n-wing) weight, but I have a feeling there are subtle things here that I
>do=
> not understand.

>> I've rigged an ASK-21 and its wings are HEAVY! I haven't weighed
them
>so=
> I don't know just how heavy they are though. Certainly felt like more
>tha=
>n 100 lbs each. Ask me how I know. I'll guess (I know, don't guess)
each
>=
>wing weighs 150 lbs. Likely more. If I subtract 300 lbs from 780 and
>then=
> subtract that result from 1320 I'm still short of 902 - which I suppose
>is=
> a good thing.
>>=20

Glider cockpit load limits are set by the lowest value determined by:
Max AUW
Seat strength limits
Max wt of non-lifting parts
Forward CG limit

For a ASK21 for which I have the actual weighing results:
Max AUW 1320 lbs
Empty weight, fully equipped, 884 lbs
Therefore disposable load is 436 lbs
Seat strength limit is 242 lbs, so with a max weight pilot the other pilot

cannot exceed 194 lbs

Each wing weighs 219 lbs, max weight of non-lifting parts is 904 lbs.
Fuselage, tailplane, etc wt is 884 - 438 = 446 lbs. Hence max load
considering only non-lifting parts limit is 904 - 446 = 458 lbs. The AUW

limit takes precedence.

On this aircraft forward CG limit did not determine max cockpit load.
Min cockpit load is set by aft CG limit.

[[email protected]]

Steve Smith told me that all sailplanes would climb and cruise better when the CG was at least 80% of the allowable range. I found out the Genesis-2 wouldn't climb in a weak thermal unless the CG was 90%. Fifteen years ago, I rigged up an in-flight CG Shiffter, mainly to investigate the handling of a flying wing with an extreme aft CG. It consisted of a 10# weight inside a 5 foot plastic pipe with fore and aft cables.............blue handle and red handle! Found the handling got a bit more pitchie at 90%, but I was able to climb with most ships. BTW, I found pitch control by shifting CG, didn't work, but aft CG was essential to get the G-2 to go up in a 1 to 2 knot thermal.
Random thoughts from JJ

[2G]

On Friday, December 8, 2017 at 1:45:06 PM UTC-8, James Thomson wrote:
> At 01:59 08 December 2017, Dan Daly wrote:
> >On Thursday, December 7, 2017 at 7:27:02 PM UTC-5, Jim wrote:
> >> I admit I am baffled by "max weight of non-lifting parts". I
> understand
> >=
> >the issue of spar bending moment limits, and I think I understand that
> >weig=
> >hing a glider without its wings will give the current non-lifting (i.e.,
> >no=
> >n-wing) weight, but I have a feeling there are subtle things here that I
> >do=
> > not understand.
>
> >> I've rigged an ASK-21 and its wings are HEAVY! I haven't weighed
> them
> >so=
> > I don't know just how heavy they are though. Certainly felt like more
> >tha=
> >n 100 lbs each. Ask me how I know. I'll guess (I know, don't guess)
> each
> >=
> >wing weighs 150 lbs. Likely more. If I subtract 300 lbs from 780 and
> >then=
> > subtract that result from 1320 I'm still short of 902 - which I suppose
> >is=
> > a good thing.
> >>=20
>
> Glider cockpit load limits are set by the lowest value determined by:
> Max AUW
> Seat strength limits
> Max wt of non-lifting parts
> Forward CG limit
>
> For a ASK21 for which I have the actual weighing results:
> Max AUW 1320 lbs
> Empty weight, fully equipped, 884 lbs
> Therefore disposable load is 436 lbs
> Seat strength limit is 242 lbs, so with a max weight pilot the other pilot
>
> cannot exceed 194 lbs
>
> Each wing weighs 219 lbs, max weight of non-lifting parts is 904 lbs.
> Fuselage, tailplane, etc wt is 884 - 438 = 446 lbs. Hence max load
> considering only non-lifting parts limit is 904 - 446 = 458 lbs. The AUW
>
> limit takes precedence.
>
> On this aircraft forward CG limit did not determine max cockpit load.
> Min cockpit load is set by aft CG limit.

This whole issue has to do with the design limits of the airfoil design. The non-lifting parts impart a bending moment at the wing root. This is, of course, anticipated by the designer, but has a design limit imposed upon it. Hence, the limit on the non-lifting components.

Tom

[Derry Belcher]

On Monday, 11 December 2017 at 15:45:27 UTC+13, 2G wrote:
> On Friday, December 8, 2017 at 1:45:06 PM UTC-8, James Thomson wrote:
> > At 01:59 08 December 2017, Dan Daly wrote:
> > >On Thursday, December 7, 2017 at 7:27:02 PM UTC-5, Jim wrote:
> > >> I admit I am baffled by "max weight of non-lifting parts". I
> > understand
> > >=
> > >the issue of spar bending moment limits, and I think I understand that
> > >weig=
> > >hing a glider without its wings will give the current non-lifting (i.e..,
> > >no=
> > >n-wing) weight, but I have a feeling there are subtle things here that I
> > >do=
> > > not understand.
> >
> > >> I've rigged an ASK-21 and its wings are HEAVY! I haven't weighed
> > them
> > >so=
> > > I don't know just how heavy they are though. Certainly felt like more
> > >tha=
> > >n 100 lbs each. Ask me how I know. I'll guess (I know, don't guess)
> > each
> > >=
> > >wing weighs 150 lbs. Likely more. If I subtract 300 lbs from 780 and
> > >then=
> > > subtract that result from 1320 I'm still short of 902 - which I suppose
> > >is=
> > > a good thing.
> > >>=20
> >
> > Glider cockpit load limits are set by the lowest value determined by:
> > Max AUW
> > Seat strength limits
> > Max wt of non-lifting parts
> > Forward CG limit
> >
> > For a ASK21 for which I have the actual weighing results:
> > Max AUW 1320 lbs
> > Empty weight, fully equipped, 884 lbs
> > Therefore disposable load is 436 lbs
> > Seat strength limit is 242 lbs, so with a max weight pilot the other pilot
> >
> > cannot exceed 194 lbs
> >
> > Each wing weighs 219 lbs, max weight of non-lifting parts is 904 lbs.
> > Fuselage, tailplane, etc wt is 884 - 438 = 446 lbs. Hence max load
> > considering only non-lifting parts limit is 904 - 446 = 458 lbs. The AUW
> >
> > limit takes precedence.
> >
> > On this aircraft forward CG limit did not determine max cockpit load.
> > Min cockpit load is set by aft CG limit.
> This whole issue has to do with the design limits of the airfoil design. The non-lifting parts impart a bending moment at the wing root. This is, of course, anticipated by the designer, but has a design limit imposed upon it. Hence, the limit on the non-lifting components.
>
> Tom


Food for thought: I cannot find a definitive answer to the question of why certain manufacturers state both a maximum all up weight (MAUW) and maximum non-lifting load. It seems more prevalent with German designs to state these two limitations and even the design book I have (Design of the Aeroplane by Darrol Stinton) has no reference to this.
The only explanation I can come up with is that the designer has to have a maximum load figure for designing the fittings that take the shear loads from the wings to the fuselage in flight and in heavy landing loads. On fibreglass gliders these are usually four metal pins that are either part of the wings or the fuselage that automatically fit into the applicable mating receptacles on the other component. The big rigging pin you put into place usually only holds the wings together to stop them coming apart and does not take the flight shear loads of wing to fuselage. In the case of older gliders such as the Schleicher Ka6, two big main pins are inserted that join the two wings and carry the wing bending loads from the upper and lower spar caps and there are still fixed shear pins that take the wing to fuselage loads in flight as well as forward drag-spar pins for each wing.
My rationale for the two limits is that from a design point of view, the fittings are capable of taking the maximum non-lifting load figure multiplied by the G load design requirements multiplied by the normal design safety factor of 1.5 (which could be what the BGA 3% is eating into for their overweight allowance for aging gliders unless limiting the max G loading - prohibiting aerobatics is one way but only goes part way to satisfying the Vn load factors associated with gust loads to airspeed) but during certification the gliders were only tested up to a MAUW figure determined to be sufficient at the time, hence when we reweigh a glider, we are limited to the certificated AUW first and foremost, but must not exceed the non-lifting figure which includes the payload (pilot etc). The dilemma we have is that the wings on a glider represent a major part of the structure and seem to get heavier with age for whatever reason, that is sometimes hard to understand, yet the wings alone do not essentially impart any detrimental bending loads to the spars or fittings in flight but technically speaking we are bound to adhere to the MAUW even when the maximum non-lifting figure says we could carry a heavier pilot from a structural standpoint.
DB

[Eric Greenwell[_4_]]

Derry Belcher wrote on 3/9/2021 3:14 PM:
> On Monday, 11 December 2017 at 15:45:27 UTC+13, 2G wrote:
>> On Friday, December 8, 2017 at 1:45:06 PM UTC-8, James Thomson wrote:
>>> At 01:59 08 December 2017, Dan Daly wrote:
>>>> On Thursday, December 7, 2017 at 7:27:02 PM UTC-5, Jim wrote:
>>>>> I admit I am baffled by "max weight of non-lifting parts". I
>>> understand
>>>> =
>>>> the issue of spar bending moment limits, and I think I understand that
>>>> weig=
>>>> hing a glider without its wings will give the current non-lifting (i.e..,
>>>> no=
>>>> n-wing) weight, but I have a feeling there are subtle things here that I
>>>> do=
>>>> not understand.
>>>
>>>>> I've rigged an ASK-21 and its wings are HEAVY! I haven't weighed
>>> them
>>>> so=
>>>> I don't know just how heavy they are though. Certainly felt like more
>>>> tha=
>>>> n 100 lbs each. Ask me how I know. I'll guess (I know, don't guess)
>>> each
>>>> =
>>>> wing weighs 150 lbs. Likely more. If I subtract 300 lbs from 780 and
>>>> then=
>>>> subtract that result from 1320 I'm still short of 902 - which I suppose
>>>> is=
>>>> a good thing.
>>>>> =20
>>>
>>> Glider cockpit load limits are set by the lowest value determined by:
>>> Max AUW
>>> Seat strength limits
>>> Max wt of non-lifting parts
>>> Forward CG limit
>>>
>>> For a ASK21 for which I have the actual weighing results:
>>> Max AUW 1320 lbs
>>> Empty weight, fully equipped, 884 lbs
>>> Therefore disposable load is 436 lbs
>>> Seat strength limit is 242 lbs, so with a max weight pilot the other pilot
>>>
>>> cannot exceed 194 lbs
>>>
>>> Each wing weighs 219 lbs, max weight of non-lifting parts is 904 lbs.
>>> Fuselage, tailplane, etc wt is 884 - 438 = 446 lbs. Hence max load
>>> considering only non-lifting parts limit is 904 - 446 = 458 lbs. The AUW
>>>
>>> limit takes precedence.
>>>
>>> On this aircraft forward CG limit did not determine max cockpit load.
>>> Min cockpit load is set by aft CG limit.
>> This whole issue has to do with the design limits of the airfoil design. The non-lifting parts impart a bending moment at the wing root. This is, of course, anticipated by the designer, but has a design limit imposed upon it. Hence, the limit on the non-lifting components.
>>
>> Tom
>
>
> Food for thought: I cannot find a definitive answer to the question of why certain manufacturers state both a maximum all up weight (MAUW) and maximum non-lifting load. It seems more prevalent with German designs to state these two limitations and even the design book I have (Design of the Aeroplane by Darrol Stinton) has no reference to this.
> The only explanation I can come up with is that the designer has to have a maximum load figure for designing the fittings that take the shear loads from the wings to the fuselage in flight and in heavy landing loads. On fibreglass gliders these are usually four metal pins that are either part of the wings or the fuselage that automatically fit into the applicable mating receptacles on the other component. The big rigging pin you put into place usually only holds the wings together to stop them coming apart and does not take the flight shear loads of wing to fuselage. In the case of older gliders such as the Schleicher Ka6, two big main pins are inserted that join the two wings and carry the wing bending loads from the upper and lower spar caps and there are still fixed shear pins that take the wing to fuselage loads in flight as well as forward drag-spar pins for each wing.
> My rationale for the two limits is that from a design point of view, the fittings are capable of taking the maximum non-lifting load figure multiplied by the G load design requirements multiplied by the normal design safety factor of 1.5 (which could be what the BGA 3% is eating into for their overweight allowance for aging gliders unless limiting the max G loading - prohibiting aerobatics is one way but only goes part way to satisfying the Vn load factors associated with gust loads to airspeed) but during certification the gliders were only tested up to a MAUW figure determined to be sufficient at the time, hence when we reweigh a glider, we are limited to the certificated AUW first and foremost, but must not exceed the non-lifting figure which includes the payload (pilot etc). The dilemma we have is that the wings on a glider represent a major part of the structure and seem to get heavier with age for whatever reason, that is sometimes hard to understand, yet the wings alone do not essentially impart any detrimental bending loads to the spars or fittings in flight but technically speaking we are bound to adhere to the MAUW even when the maximum non-lifting figure says we could carry a heavier pilot from a structural standpoint.
> DB
>
The MAUW affects landing gear design (strength, tire size, brakes, etc), and the various
aerodynamic numbers like stall and landing speed. It's not just a flight loads issue.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

[Bob Kuykendall]

On Tuesday, March 9, 2021 at 3:14:10 PM UTC-8, Derry Belcher wrote:


> Food for thought: I cannot find a definitive answer to the question of why certain manufacturers state both a maximum all up weight (MAUW) and maximum non-lifting load. It seems more prevalent with German designs to state these two limitations and even the design book I have (Design of the Aeroplane by Darrol Stinton) has no reference to this...

From a sailplane designer's perspective:

I cannot speak for my European colleagues, but I specify a maximum mass of non-lifting components (which most certainly _does_ include the horizontal tail) because it drives the most critical structural metric in my glider--the wing bending moment. That in turn drives the tensile and compressive stresses in the wing main spar upper and lower caps, and also the shear developed in the main spar shear web.

A simplified way of looking at it is to understand that the wing basically carries itself. So if you make the wing uniformly heavier, it does not increase the bending moment incurred under high-g maneuvering. Let's say for whatever reason you add 100 kg of paint and filler to the wings. Because the mass distribution follows the area distribution, and the area distribution is about elliptical, the stresses in the wing spar are not increased. Except of course for the landing case where the wings are supported by the fuselage and landing gear. But those are areas where adding extra margin has a much more modest cost than adding extra bending strength and stiffness to the wing spar.

For this reason, I am fairly open to increasing the maximum gross weight of my gliders by adding batteries and water ballast inside the wings, but there are definite limits to increasing the mass of the non-lifting parts, and there I hold the line.

--Bob K.