U.S. Marine Corps AH-1Z Zulu

[Otterotor]

AH-1Z first flight anniversary

H-1 Upgrade Fatigue Life Summary

Approximately 90% of main rotor components have been assigned 10,000 Hr. fatigue lives. The predominate vibration source for main rotor fatigue life limits is (approximately) the number of blades per revolution or 4/rev.
100% Nr for H-1 Upgrades = 296 RPM.
The calculation for predominate cycle count for H-1 main rotor components:

4/rev x 296 rev/min x 60 min/hr x 10,000 hr/life = 710 million cycles / one life time

Or 7 x the accepted cycle count of 100 million cycles for infinite life.
This implies that the components assigned a 10,000 hr. life are being subjected to oscillatory and associated steady load combinations below the endurance limit of the component and therefore the component will not fail due to fatigue loading.

Additional H-1 Upgrade Percentages

1) Greater than 100% increase in fatigue lives for many rotor components (compared with AH-1W).

2) Rotor & Drive train components are 100% interchangeable between Gunship AH-1Z and Troop Transport UH-1Y.

3) 84% of all helicopter components are common between Yankee & Zulu.

4) Installation of Bearingless Main Rotor has reduced parts count from a standard articulated rotor by 75%.

5) Installation of Bearingless Main Rotor has reduced overall vibratory levels by 70% from AH-1W levels, contributing to extended electronic equipment life. (life expectancy not-yet-quantified). The composite material (thick laminate fiberglass) used for the bearingless main rotor prevents corrosion from degrading those components, assisting with the overall durability of the rotor in service.

6) The only lubricated component in the main / tail rotor hubs/blades/controls is the main rotor swashplate bearing. Basically one installs new upgrade main and tail rotors on a new airframe and flies with the only replacement items being elastomeric main rotor shear restraints (qty 4), elastomeric / liquid dampers (qty 8), lubricate (grease) (1) swashplate bearing and replace tail rotor elastomeric flapping bearings (set of 4).

7) Page 4-9 Flt. Man. VNE = 200 KIAS. Stable flight demonstrated 223 KCAS in slight dive with symmetrical pull-up.

8) Original sized gonads proven to be adequate, thus no requirement for AH-64 Apache’s modified main rotor “Mega Nuts” (joke).

Congratulations are in order to the men and women of the United States Marine Corps who fly and maintain the H-1 Upgrade aircraft

AH-1Z’s 07 December 2018, 18th anniversary of first flight: 6574 days with zero incidents.

The four events that I am aware of (public data) are as follows:

1. 20 Jan 2017, engine warning light, precautionary night landing, Ikei Okinawa, Japan, instrumentation.
2. 8 Jan 2018, 4:45 P.M. local, T/R warning light, precautionary landing, Okinawa, Japan, wiring issue.
3. 23 Jan 2018, 8:00 P.M. local, warning light, precautionary landing, Tonaki Is., Okinawa, Japan, instrumentation.
4. 1 June 2018, low oil pressure warning light, precautionary landing, Fallbrook Airpark, N.E. San Diego, instrumentation.

Merry Christmas and Happy New Year OOH – RAH!