Wing Loadings

[drgondog]

Max gross weight is takeoff weight.

Not exactly. Max Gross Weight is the Mfr Design limit load at STP for the maximum load out of any combination of people, equipment, cargo, ammunition, oil/gas and/or ordnance. Take Off weight is whatever the mission called for - including training, reconnaissance, ferry, engine slow time after change, etc.

Well, there's max overload, but once you fire up those engines and start rolling down the runway, your fuel and oil burn is going to reduce your weight. By the time you reach the target, where you can expect some opposition, the fuel and oil burn is going to reduce you to about %50 fuel.

So, taking a B-17 for clarity, If the B-17 at the bomb run with 5,000 pounds of bombs and 50% fuel, is comparable in performance comparisons at Bombs away with Zero bomb load and 50% fuel?

Not counting bullets, the variable weight for a US medium was about 10,000 lbs of fuel and bombs.

So??

Suggest that you look to this discussion for better grasp of definitions and terms.

Performance Comparisions, discussion of the science behind it

I see so many performance comparison threads in this forum. For some of you, this is a review at best as I know you are working aerospace or have retired from such. I just thought it might be beneficial to discuss some of the science of flight so that the community can make better...

ww2aircraft.net

That said, here is a well defined, well explained and well documented Flight Test summary for Range testing for P-51D-15-NA
.http://www.wwiiaircraftperformance.org/mustang/p51d-15342.html

To fully understand what you are reading WRT "Full Combat Load-Internal" versus a stated Gross Weight at Take Off (which in this case is neither Max Gross Weight, or full Combat Load - Internal) you have to know that a 100% Combat Load - Internal for the P-51D is a.) Full ammunition load out for 6x .50 cal, b.) 269 gallons of fuel (85 Fuse tank, 184 wing tanks), c.) full Oil (15 gallons) d.) 200 pound pilot/equipment.

For this flight test at the stated GW of 9760 I would guess that some residual fuel existed in the 85 gal fuse tank but definitely not filled.

 

[Greg Boeser]

BOLD? REALLY?!!!!!
In regard to variable weight, I'm saying that bombers wing loading would vary even more than for fighters.
It is a well recorded fact that a bomber the moment after "bombs away" handled very differently than the moment before.

 

[drgondog]

BOLD? REALLY?!!!!!
In regard to variable weight, I'm saying that bombers wing loading would vary even more than for fighters.
It is a well recorded fact that a bomber the moment after "bombs away" handled very differently than the moment before.

Well yes - I was hoping you would see the absurdity of relying on '50%' fuel as a talking point, or 'gold standard' for Performance comparisons or wing loading comparisons.

Did you even glance at the link I showed you (Performance/definitions thread Crump started), that I hoped would be beneficial to your understanding?

 

[Greg Boeser]

But you are thinking I need to be convinced of something. I, in fact, agree with your point that unless you are comparing apples to apples, you are not really comparing anything.
The wing loading on any aircraft at max overload is going to be greater than that same aircraft after burning off most of its fuel and ammunition.
And, yes, I understand that the term max overload is also a meaningless term unless the parameters (pressure altitude, temperature, etc.) are spelled out.

 

[drgondog]

But you are thinking I need to be convinced of something. I, in fact, agree with your point that unless you are comparing apples to apples, you are not really comparing anything.
The wing loading on any aircraft at max overload is going to be greater than that same aircraft after burning off most of its fuel and ammunition.
And, yes, I understand that the term max overload is also a meaningless term unless the parameters (pressure altitude, temperature, etc.) are spelled out.

I've seen charts which give the "normal" weight as full combat load at 50% fuel.
Nothing. I was giving a common boundary condition for bombers.

These were meaningless comments regarding W/L comparisons. They are meaningless in comparing 'apples to apples'.

W/L can be a metric when specific Load outs are presented, calculated and tabulated for that aircraft at that condition. The airframe industry later adopted the definition and metric of 'fractions vs Fully Loaded conditions' to provide more discriminants in preliminary design studies as a 'rule of thumb comparison for past projects or other manufacturers' aircraft with similarities of mission envelope.

For example the range of Fractions include: 100% for Max Gross Design Load, 'X' % for weight of total fuel/lubricants to MGDW; 'Y' % for Crew Capacity total weight; 'Z' % for Internal Armament weight (with mission specific items); 'B' % for External Stores weight (which can be distributed to other Fractions when desired for comparisons), 'E' % for GFE/Contractor installed equipment; A % for Airframe Weight - Empty, etc. etc.

For example to "50% fuel metric at Bombs Away" for B-17? Well what did the mission specify for distribution (%) of Internal Armament Weight at Bombs Away
?
Well, a mission to Regensburg, with anticipated long contact with enemy fighters might dictate 12,000 rounds of 0.50 cal (@ .33/rnd = 4,000 pounds) and 4,000 pounds of bombs and maximum internal fuel. Another Mission to Frankfurt with better escort coverage (1943) might dictate maximum fuel, 6,000 rounds (2000 pounds) and 6,000 pounds of bombs.

Both aircraft take off at Max Gross Weight, combined ammo/bomb load same, fuel load same, but the ammunition and bomb fractions differ. One planning metric for 8th AF HQ for Regensburg mission is to account for zero enemy opposition - in which case after Bombs away, that B-17 has 12,000 rnds of 50 cal left (4000 pounds) to carry back to England - so Maybe the Fuel fraction must be higher at the target than the Frankfort mission to return to base wit reserve.

Back to W/L discussion.

The Brequet Range Formula requires Integrating the derivative of Weight change with time (fuel) to Bombs Away - but the Regensburg mission retains a higher Weight (more ammo load) and requires a different 'Initial condition before calculating Range for return leg. CL/CD is of paramount importance n the equation, as well as specific fuel consumption and propeller efficiency. W/L metric begins at warm up for same MGDW and changes over time (as CL/CD changes over time); as Turn Rate, Acceleration, Climb Potentials changes over time: as Range and Endurance changes over time.

Sooooo, in conclusion: W/L as a PERFORMANCE comparison requires a lot more definition if comparing to other aircraft - and comparisons based on 50% fuel are largely meaningless -even for the same airplane.

Going more sophisticated, change of W/L should also be introduced as it affects Induced Drag which is part of both CL and CD which is intrinsic to Aerodynamics and Performance.

 

[Greg Boeser]

Thank you.
But don't be pissed with me. I'm not the OP. I didn't ask what the wing loadings for various aircraft were.

I am well aware that the wing loading of any aircraft is constantly changing. I merely pointed out that some manuals use a standard formula to calculate gross weight based on empty weight + basic useful load (crew + guns), + variable weight (expendables like fuel, bombs, ammo) to generate a value called normal gross load. In these manuals, the fuel weight is based on %50 fuel capacity, ammo is a standard load out for that aircraft, etc. It should be noted that there are examples offered for "normal load", Max bombs, and Max range. Each of these has a separate listing called maximum alternate load which generally calculates the same configuration but with full tanks, plus auxiliary tanks.

But the OP wanted some info regarding the wing loading of different models of aircraft for comparison. If we are going to compare different aircraft we need a standard condition. I offered one.

 

[drgondog]

Thank you.
But don't be pissed with me. I'm not the OP. I didn't ask what the wing loadings for various aircraft were.

I am well aware that the wing loading of any aircraft is constantly changing. I merely pointed out that some manuals use a standard formula to calculate gross weight based on empty weight + basic useful load (crew + guns), + variable weight (expendables like fuel, bombs, ammo) to generate a value called normal gross load. In these manuals, the fuel weight is based on %50 fuel capacity, ammo is a standard load out for that aircraft, etc. It should be noted that there are examples offered for "normal load", Max bombs, and Max range. Each of these has a separate listing called maximum alternate load which generally calculates the same configuration but with full tanks, plus auxiliary tanks.

But the OP wanted some info regarding the wing loading of different models of aircraft for comparison. If we are going to compare different aircraft we need a standard condition. I offered one.

I'm not 'pissed'. We are talking past each other. It doesn't matter what 'some manuals say'. On Face Value the term 50% fuel being coupled with Normal Gross Load is silly for combat operational airplanes - as a Standard. Begs the question as I illustrated above, "Standard for What"?

The reason the US Army and Navy contracted Flight Operation Chart for all accepted aircraft models was to remove ambiguity for planning for various load outs - so they post all 'defined' gross weights - ranging from Basic to Combat to Max Rec'd and War Max - at least for P-38 and P-47 manuals I just glanced at. The P-51B and D Flight Operations Chart is more detailed - and instead of posting Basic, Combat and Max Recommended - they simply break out combinations of fuel fractions for Fuselage Tank, Wing Tanks and Different Combat Tanks.

Use the Mustang as an example. 85 gallon auxiliary fuse tank, 2x92 gal Main wing tanks (180 used instead of 184). The operating chart variable presented is for Fuse tank fractions only (85gal =100%, 60, 25, 0). Every other table value assumes 100% in the Mains (180). Ditto P-47 and P-38.

Practically speaking, Zero combat operations in a P-51A/B/D were carried out with less than 180 gallons in wing (full). For you that would mean 180/269 = 67%. Of course it is possible to partially fill primaries - but Army/Navy believed 'keep it simple - fill them up'.

Same principle applied to bombers. Main Tanks and auxiliary tanks. The Op may call for short range - max bomb load. Fill the mains, load up the ordnance, but only a happy coincidence yielded 50% fuel from Max fuel internal capacity.

So, back to Wing Loading. To develop a W/L table that makes sense for Performance comparisons, the same array of comparable operating fractions should be understood for each aircraft - and tabulated for changes to the fractions. Dean performed a pretty good fact gathering process to lay out different conditions ranging from Empty to Basis to Combat to Max Rec'd Gross Weight at Take Off. The Navy used different nomenclature but 'Fighter' meant full main, empty auxiliary (usually 70-75% max internal), all other descriptions had full internal fuel.

Summary - 50% Internal fuel means nothing unless the Main and Auxiliary capacities are equal.

 

[thunderbird]

wing loading is horribly easy to calculate. Its simply gross weight divided by wing area.

Wing area more or less can be usually calculated as the wingspan x the median wing chord. But note that this is a reference area, and not a geometric characteristic; it often ignores unique features such as blended bodies. etc. ON simple tapered high aspect ratio wings, it usually includes the through the fuselage projection.

Turn performance improves with wing loading, but wing structural strength is also important. The lancaster's wings fold up at around 3 gees, or basically 1.4 times its stall speed, compared roughly to the seven gees or so an enemy fighter can pull.

 

[pbehn]

wing loading is horribly easy to calculate. Its simply gross weight divided by wing area.

Wing area more or less can be usually calculated as the wingspan x the median wing chord. But note that this is a reference area, and not a geometric characteristic; it often ignores unique features such as blended bodies. etc. ON simple tapered high aspect ratio wings, it usually includes the through the fuselage projection.

Turn performance improves with wing loading, but wing structural strength is also important. The lancaster's wings fold up at around 3 gees, or basically 1.4 times its stall speed, compared roughly to the seven gees or so an enemy fighter can pull.

How does turn performance improve with wing loading?

 

[JDCAVE]

….The lancaster's wings fold up at around 3 gees, or basically 1.4 times its stall speed, compared roughly to the seven gees or so an enemy fighter can pull.

Would you please provide your source for this? Intuitively this seems low to me.

Edit: see for example stall speeds of Lancaste here, data from Boscombe Down

http://www.wwiiaircraftperformance.org/Lancaster/Lancaster_I_LL905_Performance_handling_trials.pdf

Thanks,

Jim

 

[Greyman]

The Lancaster was good for 4.5g at 63,000 lb or 4.65g at 60,000 lb.

The design max speed was 400 mph ASI but in practice this was about 360 mph ASI mainly due to '... the use of elevator trimmer to help the recovery from dives is necessary beyond 360 mph ASI and since the trimmer may freeze solid under certain conditions or get shot away during enemy action.'