Interesting
AndrewTR30 said:
The prop that Vans sells (Part Number = PROP MTV12B/193-53) has a TBO of 200 hrs or 72 mos, whichever comes first, per MT.
In speaking with one of the US distributors, they tell me that the reason for this is that since MT can't test every engine/hub/blade combination, the low TBO is done for liability reasons. This sort of makes sense, since the same hub with other blades has a 2000 hour tbo on there website. They also said that since we're experimental, that we the builder can determine when the prop needs to be overhauled. If that's the case why publish a TBO at all? How necessary is it that the prop be overhauled at 200 hrs?
Interesting!
I think its CYA or really cover their's. 200 HOURS! OMGosh. I was told, although I never saw the test or approval that MT did test there props and clear them for our typical Lyc's and even EI, but that I guess was not true or they just don't want to be responsible when it's on an experimental.
Every body knows I'm a Hartzell/Sensenich fan; If you
don't NEED a lighter weight prop or an electrically operated C/S prop, than Hartzell is a better value IMHO. I guess if you also have a radical high compression engine with EI than composite prop may be better?
Whirl Wind prop company did a similar thing with their TBO limits as MT did; they lowered their TBO when Hartzell came out with their revelation about the affect Electronic Ignition (EI) had on their props. Whirl Wind just unilaterally cut their TBO, indicating they did not test it or have service experience for the new design, which is the prudent thing to do. I guess that is why Hartzell says you should have a certified prop.
This is not to bash against MT or WW. No doubt the MT is capable of going more than 200 hours between TBO, but this gives MT a leagle safety chute if something happens, "hey its experimental, we told you to overhaul it every 200 hours". To be fair MT has good service history in general, and I found only one MT blade seperation AD for one of their other models.
Also to be fair, if you're running high compression pistons on your Lycoming, Hartzell has not tested that config. Since Hi-comp engine configurations are untested there's no guarantee, but if your engine is stock or stock with EI, than Hartzell has you covered you with test, analysis and history, as if it was certified for the RV.
In the spirit of full disclosure, there are Hartzell AD's on older model props where TBO's are shortened to 1000 hours -OR- there are intermediate inspections. The newer Hartzell props do not have TBO limits (2000 hours typical) or extra inspections. However older HC props, for example some older HC2YK/F7666's (which are popular on RV's) now have a 100 hour on plane inspection. It's not a bad inspection, but it's an extra pain. After 30 years of service history, a spacific area of concern had been addressed on the older design, so the newer versions of the C2YK/F7666 or the new "BA" prop have been corrected and don't have short TBO or extra inspections; they benifit from the service history of previous models and versions. Most important Hartzell has tested their props on the RV airframe. Prop performance and safety can be affected by the airframe. Metal props are more critical for metal fatigue. Hartzell's goal is infinite fatigue service life. MT's and whirlwinds with composite blades do not have the same fatigue characteristics, but their hubs are still metal. Which is probably their concern.
The other relevant thing I can say is a Hartzell overhaul usually can be done at a local prop shop and for much less money by a large factor. I think a MT overhaul is almost twice as much money and often needs to be sent out. Also the MT overhaul will take longer from what I hear, especially if it's shipped out, which is likely. Most prop shops in the USA can turn a Hartzell OH in a few working days.
