Forum: General F-22A Raptor forum

http://www.nationaldefensemagazine.org/archive/2012/January/Pages/AirForce%E2%80%98Snubs%E2%80%99F-22EngineCracks.aspx

It takes seven of them to cover the problem areas on each engine.

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This is how we get weight growth in aircraft over time. More of a problem for the F-35 at this point though.

hcobb wrote:

This is how we get weight growth in aircraft over time. More of a problem for the F-35 at this point though.

Ever think, perhaps, the new rubber snuber is replacing a metal bushing, and may be lighter than a part it replaces? (or any off the other metal components of the engine replaced by non-metallic ones) It may be a new part but we don't know that. Maybe PW can just crank up the thrust another pound or two?

Anyhow.....

This sort of modification is exactly why ALL the engines are subject to the CIP funding. F100, F101, F108, F110, F117, F119, F135, etc...

I'm sure you're all great engineers when it comes to figuring life cycle fatigue of metal parts that interact between the engine and airframe over the matter of a decade.

As an 'engine guy' I'm glad someone identified this situation and was able to remedy the issue before anyone got hurt.

Great job USAF/PW! Salute

TEG

This was a simple fix to a problem that was more annoying than dangerous. Every time the engine comes in to JEIM the J seal is NDI'd (my job), and any cracks (and there were lots) would be stop drilled. For a while we were doing it at every engine removal, but we've been able to back off that. The snubbers did their job. We haven't seen any new cracks at our base since they were installed. I believe the F-119 engine has proven itself the most reliable part of the Raptor. Works great, and is maintainer friendly. We took 12 jets to Mt Home in 2010 for over a month, and only had one spare motor with us. It stayed on the trailer the whole deployment. Wish the rest of the jet had the same performance. Mission capable rate is low, very few quick fixes to code 3 writeups, LO is a pain in the butt. I don't see how we'd be able to generate and sustain any kind of sortie rate if the shooting started.

That_Engine_Guy wrote:

hcobb wrote:

This is how we get weight growth in aircraft over time. More of a problem for the F-35 at this point though.

I'm sure you're all great engineers when it comes to figuring life cycle fatigue of metal parts that interact between the engine and airframe over the matter of a decade.

As an 'engine guy' I'm glad someone identified this situation and was able to remedy the issue before anyone got hurt.

Great job USAF/PW! :salute:

TEG

I won't claim the "great" label, but I was the engineer who developed the original design load spectrum for all the F-16 engine mounts back in 1975. A load spectrum means how many occurrences of all the load components on each of the mounts, including all the maneuver loads and all the thrust loads, over the entire life of the airplane. GD durability engineers then analyzed and tested the engine mounts and fuselage backup structure to those loads. P&W was responsible for certifying the engine side of the mounts, and we never saw any documentation of their work.

One thing about engine mount design loads, they do not include low level, high frequency vibration effects. It sounds to me like the F-22 mounts are being affected by vibration, since the airplanes have not been flown enough to develop cracks from maneuvering or thrust loads.

Engine mounts for automobile engines use rubber or urethane inserts to damp vibration, so putting rubber in the F-22 is simply using a well-proven idea in a new way. Normally turbine engines do not generate enough vibration to require rubber mounts, but the F119 may be an exception.

So TEG and retchief70 are right, this is not a big deal.

jw, your posts carry more weight than ever in my view. You can snub as much as you want, sir. Thanks for your education and interesting input. Wish you and yours a happy New year.

Thanks, geogen. Haven't seen any input from you recently. Hope all is well, welcome back.

What I was getting at about engine/airframe is the fact testing the aircraft for vibration and testing the engine for vibration, or even testing the two together doesn't get immediate results. Use over the years, wear, corrosion, maintenance actions (proper or improper), etc all will have long-term effects on vibration decades after production.

I know the Eagles have a PTO shaft issue that the Vipers don't. Something in their start system/airframe/engine combination, makes the Eagle F100's PTO shaft wear differently than the same engines used in the Viper.

I'm sure LM (F-22) and PW (F119) tested and certified everything needed for the USAF's approval, but after decades of combined use, some things aren't found until.... opps there is a crack, let's get it fixed!

Chief70's mentioning a "J-Seal" inspection during JEIM, indicates to me it's not an F-22 airframe issue, but something on the engine. (Not an engine mount) I'd suspect it's a seal in/near the inlet, or exhaust. Esp if it requires 7 of the snubbers to isolate the vibration? Sounds like somewhere this 'J-seal' is vibrating between the engine and the airframe, causing undue low or high cycle fatigue.

Again I'll say it's great that this was identified by the USAF/PW maintainers at the F119 JEIM facilities, and working together the USAF/PW came up with a fix before anyone scattered an F119 in a Hush House, or made a crater somewhere!

Glad to know there are still people out there in maintenance who are paying attention and making a difference!

(Not to mention this sort of 'discovery & fix' can be tested for and applied if necessary to other current and future engines...)

Keep 'em flyin' Thumb

TEG

The J seal is simply the front inlet ring. On the 119 it's actually manufactured into the inlet case instead of bolted on as with a -220. J seal cracks were a real pain in the butt when I worked those engines. The snubber is a new part. There never was anything there prior.

Forum: General F-22A Raptor forum

Air Force ‘Snubs’ F-22 Engine Cracks