Wing stress

[Zacherof]

Does anyone have a
compilation of comparisons regarding the amount of stress different aircraft wings can take? Also what speeds, degrees, and gforces have as an affect to limiting manuevers?

[drgondog]

Simple answer - No. How to get there? 1.) get the design Gross weight for which stress calculations were performed, 2.) nail down the Structural design load factors - in general all US applied Stress = Yield for Design max and 1.5 Yield for Ultimate/Failure... for US the numbers were generally 8g Limit/12g Ultimate. P-51H was an exception as it was 7.5 for 8000 pounds, 11.25 for Ultimate.

I think that USN operated to same Spec.  The key is that you can assume 8/12 G as the boundary but the harder assumption is "at which GW".

For example the XP-51 was stressed at 8/12 for 8,000 GW - which was full fuel and guns, but the same GW for the P-51B was closer to 9100 - so it WAS NOT stressed at 8g/12 as it was already 1100 pounds greater GW. It was a Limit Load of 8000/9100 X 8,000 pounds --- 7.03G limit load.

The conditions that the design engineer looked at was high G/ZHigh AoA flight in a turn, the Pull out for dives - and next (if the guys were really good and had good aero load guesstimates - was the asymetrical load manuever like slow or snap rolls or a rolling dive manuever to evade.

[Karnak]

I have the data for the Mossie somewhere.  I'll see if I can dig it out when I have time.

[Zacherof]

If you can find it that wod be really awesome. And thanks for pointing me in the right direction 

[Gaston]

  
  The amazing thing is, they appear to never have tested how much those wings actually bent in an actual horizontal turn with a low-wing nose-puller... To this day even...

  I've been looking for those wing in-flight turn stress tests for years now... And no, dive-pull-outs don't count, and that is what they do if they do it: I checked... This is because in a dive, the propeller is, in large part, unloaded by the extra dive speed...

  For those who know my thinking about this, I think 3 G of turning at full power could equal 6 G of wing stress on these WWII fighter types, and the pilot limit of 6-7 Gs could mean 9-10 Gs of actual wing stress: Well within the ultimate failure limit...

  Those who claim this is a violation of physical laws seem to confuse force and energy... I remember reading the claim (elsewhere) that this is is like claiming a perpetual motion machine... This shows you how clueless are those who claim this violates physical laws...

  Unlike energy, yes you can get more force out of something than you put in... If you don't think this is true, you don't understand the difference between force and energy...

  Gaston

  

  

[Zacherof]

That is rather interesting. When inposted this I thought for sure someone might have this info.

[Rodent57]

Zacherof Sir,

There are lots of folks that likely know the answer to your question.

Some of them reside 50-60 miles north of your reported location.

If they won't let you onto the base, look for a cantina in the vicinity of Rosamond that has many old pictures of early test pilots and test vehicles on the walls.

Pose your question there (when the flight-suit clad folks show up). .  . if they don't know, they will likely take your name and number and figure it out...a bunch of inquisitive squirrels that lot!

Good Hunting!

- Rodent57

[Zacherof]

That is perhaps the best advice I've been given on BBS

Theres actually quite a few bases. Edwards(might be able to go on), march AFB,
and miramar. Now if I can find a way to get there...

Wonder if those chumps at china lake would let me on...

[GScholz]

Spitfire was designed to specification no. F 7/30:

Structural Strength

(a) The strength of the main structure when carrying the load specified in paragraph 3, plus 100 lb shall not be less than as specified hereunder

Load factor throughout the structure with the centre of pressure in its most forward position 9.0.

Load factor for wing structure with the centre of pressure in its most backward position in horizontal flight 6.0

Load factor in terminal nose dive 1.75

Inverted Flight

(1) Load factor at incidence corresponding to the inverted stall and with C.P. at 1/3 of chord 4.5

(2) Load factor at incidence appropriate to steady horizontal inverted flight and at the maximum speed of horizontal normal flight 4.5

(b) The alighting gear must be able to withstand an impact at a vertical velocity of 10 feet per second and at this velocity the load on the alighting gear must not exceed three times the fully loaded weight of the aircraft.

(c) When subject to the impact forces on alighting, as specified above, the load factor for the alighting gear must not be less than M/3, and for the remainder of the structure not less than 1- 1 /2. The load factor for the structure and the attachment fittings of the alighting gear must always be greater than that for the alighting gear itself by the margin indicated above.

(d) The maximum weight per wheel of the aircraft in pounds must not exceed 12 times the product of the wheel and tyre diameters in inches with the aircraft carrying the full load specified above.

(c) The above factors are to be determined by the approved official methods as published by the DTD and the detail requirements given in A.P.970 are also to be satisfied. With a view to minimising the risk of flutter, attention should be given to the recommendations of A.P. 1177, particularly as regards the static balance of ailerons.

(0 The wing is to be sufficiently rigid to withstand satisfactorily any torsional or other loads which may be encountered during service operations.

(g) Ribs (both mainplane and tail unit) are required to develop, on test, factors 20% greater than those specified for the aircraft as a whole.

[GScholz]

Of course for all fighters Rule 27 of the fighter pilots creed apply: “The aircraft G-limits are only there in case there is another flight planned for that particular airplane. If subsequent flights do not appear likely, there are no G-limits.”

[Zacherof]

Of course for all fighters Rule 27 of the fighter pilots creed apply: “The aircraft G-limits are only there in case there is another flight planned for that particular airplane. If subsequent flights do not appear likely, there are no G-limits.”

 

[drgondog]

Spitfire was designed to specification no. F 7/30:

Interesting in that there is no delineation between Design Limit (usually within elastic/Yield stress) and Ultimate (Failure and in US 1.5xLimit)

The Load factor in Terminal dive should be the Q load Does 1.75 seems to reflect that? But, if so what is the Design Q? Is it then a reflection of max positive G load to be undertaken in a terminal dive?

Next question - was F 7/30 a spec for the MkI at Mk I design GW or updated to reflect the increase in GW for say Mk IX or XIV?

[MiloMorai]

Spitfire was designed to specification no. F 7/30:

It was F.10/35.

F.7/30 was for Blackburn F.3, Bristol Type 123, Bristol Type 133, Gloster Gladiator, Gloster SS.19, Hawker P.V.3, Supermarine Type 224, Westland F.7/30

[Karnak]

Supermarine Type 224 was also to be called Spitfire, hence there sometimes being confusion.

drgondog,

Yes, there were increases in strength for the Spitfire's wing, though I don't recall when they showed up.  Mk V or VIII perhaps.

Gaston,

It would do you a wonder of good to invest the time and money in some physics and aerospace engineering classes.

[GScholz]

My mistake.