R.A.F. A/c Fatigue Index.

[Noah Zark.]

Can anyone enlighten me, please? I have seen an R.A.F. (or Ex-) Bulldog for sale, and in the description is the phrase "Fatigue Index xxx)" .
Does the Fatigue Index replace Engine/Airframe hours, does it work in conjunction with them, or is it not related in any way?
Thanks in advance. N.Z.

[Vee One...Rotate]

This might get some good replies in the flight test forum...?

V1R

[Genghis the Engineer]

I'm working from memory here, not having had anything to do with a Bloodnot for about 9 years, but yes, the FI is a more refined equivalent of airframe hours, which takes into account useage (i.e. more g = more index accumulated).

It doesn't replace A&E hours, so much as supplement them for fatigue critical components such as the mainspar.

That however is about the limit of my memory, if I needed a clearer answer (which you probably do) I'd go and speak to dHSL - de Havilland Support Ltd at Duxford, who hold the Type Certificate for the aircraft and should be able to give you chapter and verse.

G

[Mad (Flt) Scientist]

It's supposed to be a normalised flight hours count, where the FI accumulated during missions of type X is weighted according to the average fatigue spectrum for that mission. So 1 hour of S&L A-to-B will accumulate less FI than 1 hour of ACM, say.

IIRC, FI 100 was supposed to be "design life" but various fatigue extension programmes, and some early fatigue :( scuppered that as anything but a guideline.

[Genghis the Engineer]

ACM in a Bulldog?

G

[airborne_artist]

ACM in a Bulldog?

We tried, Genghis ....

[Megaton]

FI is indeed a normalised measured of aircraft life usually scaled to 100 FI units. Consumption depends on a number of factors include role fit (ie tanks, weapons, pods etc), fuel and sortie profile codes (SPCs). Normally, the FI per sortie is calculated using the Mid-Sortie Mass hence the rather tedious RAF F700 logbooks which require all sorts of figures and codes. I'm not familiar with Bulldog fatigue but some aircraft will have different fatigue lives for different components ie wing, fuselage and tailplane all have their own fatigue life which needs to be managed. I suspect, without any real knowledge to back this up, that even if a Bulldog was relatively high on FI, ie close to 100 FI units, that civil use is much less demanding than that dished out by the UAS' so you could probably get decent number of flying hours from an airframe even if short on FI. High FI airframes need to be carefully managed but as long as fatigue consumption is low they can soldier on.

[Noah Zark.]

Thanks for the replies and the info, guys.
Regards. N.Z.