Gusts envelope, different values

[chappy72]

Hello

I have a small question about gust envelopes.
In one envelope I found the values of 15 feet per second and 30 fps.

In another envelope I found 25 fps and 50 fps.

Is there a difference of certification, i.e. jet-airplanes and prop?
Or is certain certification of each aircraft individual, that means, as aircraft builder can I decide if my new aircraft will be certified for max. 30 fps or 50 fps gusts?

Has anybody an idea?

Thanks a lot.

Daniel

[Mad (Flt) Scientist]

FAR Part 25 including Amendment 25-91
published in the Federal Register on July 29,1997 (effective August 28,1997).
Corrections published in the Federal Register on 8/27/97 included in this
document:

Sec. 25.341 Gust and turbulence loads.
(a) Discrete Gust Design Criteria. The airplane is assumed to be subjected to symmetrical vertical and lateral gusts in level flight. Limit gust loads must be determined in accordance with the provisions:
.....
(5) The following reference gust velocities apply:

(i) At the airplane design speed VC: Positive and negative gusts with reference gust velocities of 56.0 ft/sec EAS must be considered at sea level. The reference gust velocity may be reduced linearly from 56.0 ft/sec EAS at sea level to 44.0 ft/sec EAS at 15000 feet. The reference gust velocity may be further reduced linearly from 44.0 ft/sec EAS at 15000 feet to 26.0 ft/sec EAS at 50000 feet.

(ii) At the airplane design speed VD: The reference gust velocity must be 0.5 times the value obtained under Sec. 25.341(a)(5)(i).

I'd imagine 23.341 may have gust specs for part 23, and so on.

[Volume]

Gust criteria depends on aircraft category.

Part 25 : 56 ft/s (17.07 m/s) at VC, 28 ft/s at VD, 25 ft/s (7.6 m/s) with flaps extended at VF

Part 23 : 50 ft/s at VC, 25 ft/s at Vd, 25 tf/s with flaps at VF

Part 22 : (Motorgliders) 15 m/s at VB, 7.5 m/s at VD, no gusts with flaps.

[Genghis the Engineer]

For all reasonable purposes of-course, 50fps=15m/s, and 25 fps=7.5 m/s. That particular difference is just rounding off into metric values.

G