current Formula 1 structural safety factors

[bill shoe]

Civilian airframes traditionally have a 50% safety factor, so the wing (as example) can take 150% of maximum intended load before breaking. Elevator cables often have safety factors of several hundred percent.

I have the impression current F1 cars are well below a 50% safety factor, but what are the typical safety factors for things like monocoque, suspension arms, wing struts and wings, etc.?

I'm guessing it's not a simple safety factor anymore, but maybe a probability of failure when used for X amount of time or distance (monocoque may need to last for season, suspension control arm may only need to last for one race weekend, etc.). Getting this type of probability right depends heavily on the accuracy of the expected loading which in turn is probably based heavily on previous data.

Anyway, whatever is done I don't know much about it. Anyone with a bit of knowledge please fill us in.

[Tommy Cookers]

isn't passing the various impact tests of the structure the only formal requirement in F1 ?
so individual parts design loads and FOS etc are a matter for the designer and his test practices

load test-related design is a poor predictor of impact behaviour
the teams typically want eg the suspension linkages to fail on some impacts so to preserve the monocoque structure undamaged

they always include a substantial amount of high fracture work fibre with the carbon fibre in the areas subject to impact test

[Callum]

Bill, I'd be interested if you could source your Factor of Safety (FoS) of 1.5. I would expect it to be down in the 1.15 range.

An FoS is all about a factor of ignorance to your loads and worst case scenarios (as well as material properties, etc etc). I'd expect with the data logging abilities of todays cars that the worst case loads should be quite well known.

[Tommy Cookers]

everyone knows that iirc maximum permitted loads equivalent to - public transport category 3g, utility category 4.4g, 'unlimited' category 6g
are all certified by test to an ultimate load 50% higher than the above
see C.A.P 643 section T https://publicapps.caa.co.uk/docs/33/CA ... 02013).pdf
and for context https://arc.aiaa.org/doi/abs/10.2514/8.9385

here's one of the 'factors of ignorance'
eg a single 10 kN force event developed non-slowly will produce more structural response than the convenient single 10 kN force event developed slowly
this fundamental point is evaded too much in teaching, and eg escaped NASA when writing their faulty design specs for booster rockets
compliance with these official specs helped to produce a space shuttle disaster by underestimating booster's gantry clearance

afterwards NASA claimed to rescue the world by discovering this ('dynamic overshoot') that they had forgotten and denied in the first place
an abuse worse even than UK officialdom's attempts to dress up the Comet disasters
God bless Government 'science' !!

[bill shoe]

these official specs helped to produce a space shuttle disaster by underestimating booster's gantry clearance

I'm a big fan of hating the expensive and unproductive Space Shuttle program, but I hadn't heard that one. I thought the Challenger booster failure was due to transient sealing problems between segments (and the O-rings, etc.), but I hadn't heard anything about inadequate gantry clearance. Please explain.

an abuse worse even than UK officialdom's attempts to dress up the Comet disasters

I recently saw a good documentary on these crashes and the subsequent government investigation. Is there a short simple way to explain what you mean by "dress up"?, or can you give a link to more info of that nature?

[Greg Locock]

Real aircraft engineer says 1.5 for a/c but its complicated. blakmax's post here http://www.eng-tips.com/viewthread.cfm?qid=332986

Most parts on a production car are fatigue limited, and that's a whole different ballgame for design. As Callum says, FoS are really factors of ignorance, for one product I worked on we used a FoS of 1 , because we'd measured the loads ad infinitum, and were confidaent in our material specs etc,and the consequences of failure were trivial. If you think about it the crash structure in a car is designed with an FoS of 1, as it is designed to break (admittedly in complex ways).

[bill shoe]

Tommy Cookers' comment about the difference between slow load build-up vs dynamic load build-up reminded me of a good thread on a similar technical forum--

viewtopic.php?f=6&t=13763

The video itself is gone (was Strad's) but it showed a 2012 Lotus front pushrod flexing in a buckling type of action. This pushrod presumably showed good strength on paper and on a test rig, but with real loads it had alarming behavior even if it didn't outright break. Might be static vs dynamic loading issue, might not. First two posts are musts if you go there.

[Tommy Cookers]

[quote="bill shoe"]
[quote="Tommy Cookers"]these official specs helped to produce a space shuttle disaster by underestimating booster's gantry clearance[/quote]I'm a big fan of hating the expensive and unproductive Space Shuttle program, but I hadn't heard that one. I thought the Challenger booster failure was due to transient sealing problems between segments (and the O-rings, etc.), but I hadn't heard anything about inadequate gantry clearance. Please explain.
[quote]an abuse worse even than UK officialdom's attempts to dress up the Comet disasters[/quote]I recently saw a good documentary on these crashes and the subsequent government investigation. Is there a short simple way to explain what you mean by "dress up"?, or can you give a link to more info of that nature?[/quote]

with apologies for the messy quotes - my archaic PC is struggling with the new state of the site
and strictly iirc and otomh and provisional because it's sensitive and I don't want to do any checking today or get further OT ......

tiling failures that lost Columbia were started by impact with material detached by (ongoing ?) booster dimensional conflict ?
maybe if they had not changed the proven tile adhesive for a new, user-friendly adhesive there would have been any problem
btw sealing weaknesses with Challenger boosters would not have been catastrophic if there had not been a ban on weekend working at the launch pad
because the launch would have been made before the weather turned freakishly cold


the Comet investigation outcome was rather presented to the public as we Brits having helped the world by discovering metal fatigue
Arnold Hall reported on the full fuselage tests that reproduced flight cycles of fatigue and so found the 'smoking gun'
but much design and test material from existing sources was gathered but not included the main report

the fault was essentially de Havilland's, for pushing its luck in design and manufacture and running rings round the regulator
fault in production window frames being rivetted, not adhesive bonded, (Bishop on his deathbed said he regretted this crucial concession)
when the required structural tests were done only on bonded frames
these tests measured up to 71% of UTS at normal load before any plane was sold (the worst point was surely over 71%)
other tests were accidentally done in a sequence that strengthened some parts, passing tests that they would have otherwise failed
the alloys (with Zinc, higher strength usual alloys with Copper), were less designer and regulator-friendly because more vulnerable to fatigue
this was a general issue ie affecting also many American aircraft (military anyway) with related scandals over contractual and procurement improprieties
some eg Le May wanted these alloys as a great enabler of jet aircraft regardless of airframe life issues
de H were also found to have made errors in structural design calculations for the 110 ?/Vixen (after its famous crash)

@ bill - I may be able to quote some sources by PM, but sorry not right now

[riff_raff]

The 1.5 FoS is used for analysis of metallic aircraft structures. It is used with the ultimate material properties listed in the MMPDS standard. A lower 1.25 analysis FoS is often permitted when structural testing is performed to validate the analysis.

[Tommy Cookers]

(from article 'Dynamic Overshoot' by Tim Furniss appearing in Flight International 24-30 Jan 1996)

the shuttle was designed for dynamic load factors after main engine ignition of 1.1 axially and 1.4 transversely

expected (tilting) moment at point of interest 350 million in-lb, lifting off at T+3.832 sec when thrust had ramped to 90%
to reduce fouling issues liftoff was by 1980 delayed till 100% thrust at T+6.332 sec and a moment of 150 million in-lb
but (NASA discovered years later) the 1980 etc launch method tilting moment peaked at 580 million in-lb

(NASA has since 1990 used a dynamic load factor of 2.0)

Ali Abu Taha (ex Comsat - says no-one at Comsat etc allowed for dynamic overshoot) discovered NASA's omission
and ultimately went public in Jan 1990 as NASA seemed to be in denial

there being 'DO' in many areas the consequence has been widespread strengthening and a substantial reduction in payload

I remember someone from Boeing aircraft wrote to Aviation&Space weekly saying it was basic stuff, they had always allowed 50% for so-called 'DO'

[bill shoe]

Here is link to the article about Dynamic Overshoot, good stuff --

https://www.flightglobal.com/news/artic ... oot-21000/

EDIT: Wow, I thought this would be interesting but it will probably be the best Engineering article I've read for many years. The "public" cause of the Challenger accident was an o-ring material that became brittle in low temps (OK, that probably had something to do with it) but behind the scenes NASA was furiously strengthening all Space Shuttle launch components until around 1990 or 1992. Massively. To overcome dynamic overshoot. And trying to deny that any change was taking place. This previously "lost" overshoot was stressing the heck out of the solid rocket boosters. When I think of a Formula 1 suspension component going through dynamic overshoot I think in terms of milliseconds, but the space shuttle is large and heavy enough to have a dynamic overshoot cycle that takes 2 or 5 seconds.

[Tommy Cookers]

my source re the Comet failures
https://books.google.co.uk/books?id=e8I ... ft&f=false
this P131 also P124 P148-9 P150-2 P155 P158-60 P163 P165

and this on fatigue of the KC 135 and others
the KC 135 ('tanker 707', used 7000 series alloy lower wing skins not 707-style fuselage failsafes and thicker skins of proven 2000 series)
https://books.google.co.uk/books?id=nZg ... 35&f=false

there seems to have been no regulatory requirement in either country for design re fatigue
the Comet's strength requirements in some tests were met only by accidents of reinforcement from test equipment or hardening from earlier tests
but neither regulation nor dH's diligence prevented in design the incorporation of measurable and avoidable overstressing near apertures
neither regulation nor dH's diligence prevented modifications to the original design eg windows and thinning of skins being taken largely on trust in design

the mandated FoS (anyway in designs less marginal than the Comet's) .....
apparently was adequate to secure by accident a tolerable fatigue life when using 2000 series Al/Cu type alloys as hitherto universal
but inadequate when using the thinner sections that the stronger but innovative 7000 series Al/Zn type alloy appeared to allow

the fatigue life of the Valiant aircraft was for decades said to have collapsed due to increased stresses from changing to low-level operation
only now do we know otherwise (the fault appeared in non low-level use) - that it was the fault of the design in 7000 series
the USA had similar problems with the KC 135 and particularly with the C 5
and eg in-service catastrophic structural failures of B 47 wing attachment when operations changed to low-level
http://www.307bwassoc.org/milkbottle.htm

[riff_raff]

tiling failures that lost Columbia were started by impact with material detached by (ongoing ?) booster dimensional conflict ? maybe if they had not changed the proven tile adhesive for a new, user-friendly adhesive there would have been any problem.

The cause of the Columbia failure was a large piece of urethane sprayed-on foam insulation breaking free from the external tank during launch and impacting the carbon-carbon thermal protection structure on the shuttle's wing leading edge. Nothing to do with the solid boosters or the RTV adhesive used to attach the orbiter's thermal protection tiles. However, the investigation determined the chunk of urethane foam insulation that broke free from the external tank during launch was likely due to changing to a more environmentally friendly foam type.

[bill shoe]

Link shows perfect side-view of a space shuttle at fire-up and launch. Enlarge the video to fit your screen and hover your mouse pointer at the top of the tan external fuel tank. Clear as day: when the shuttle engines fire-up, the tip of the tank flexes a few feet (!!!) sideways and then partially springs back by the time the bottom of the assembly (solid boosters) is released from the launch pad. And none of this was ever considered in the design. Or during the first 8 years of operation.

https://www.youtube.com/watch?v=s39mNwFuQDQ

[Cold Fussion]

What's the cause of it springing back? Is it because of the so called dynamic overshoot and the resulting reduction in moment once for shuttle thrust reaches steady state?