DER question

[swoeric]

If somebody were to make a valve train change in a motor lifters and cam how much testing is involved? I know a lot but how many hours? when does the FAA seem satisfied? how much equipment needs to be trashed? can us just spin the required parts by secondary source?.....right now i dont care about the paper work as much as im trying to figure out the required physical testing required

[Ragwing nut]

Re: DER question

if you are installing a new cam and lifters, I would follow the new break in precedure covered in the overhaul manual. If you don't have one, you or your a&p do not need to be doing the job.

[barnstmr]

Re: DER question

Eric,
We have both PMA camshaft and lifters we have tested and approved here at RAM Aircraft on the big 6-cylinder continental engines. We have done probably 10 to 15 times the amount of testing that the FAA requires just in our own development testing. We have learned a lot about materials for lifter bodies and cam lobes, though I cannot say I am very knowledgeable about lobe profiles. RAM's famous RAM "economy" CAM lobe profiles were designed by Harvey Crane and Jack Riley, Jr back in the 1980's.

Anyway, to address your specific question, the FAA is going to require at least the standard 150-hour endurance test... straight out of the regs. 14 CFR 33.49. In addition you'll have to address durability testing to satisfy 14 CFR 33.19. The amount of testing for this can vary, depending on which parts are proposed and what the scope of the change is. Usually though, the FAA defaults to an additional 150-hours. There is an advisory circular covering durability AC 33.19-1. The main premise is that you need to test through enough cycles to verify the design of a part is sufficient to surpass infant mortality, normal life, and onward to the "infinite" life part of the life cycle bell curve. The FAA uses a rule of thumb of 10,000,000 cycles to show this. You have to do the math for a 4-stroke 4-cylinder engine to determine what RPM and # of hours will equal the 10M cycles for the part you're testing. If your changes are not too drastic, you might get away with less than 10M cycles total, but it can be as much as 300 hours of run time to satisfy FAA.

We have not been successful in getting the FAA to allow testing on anything other than a fully functioning engine. We have a test rig that we call the "electric engine". This is basically an engine assembled with a crankshaft, gears, oil pump, camshaft, and lifters, pushrods, valves, and springs. But it has no rods or pistons. For the big bore 6-cylinder it takes a 10 hp electric (3-phase) motor to drive this with a multiple belt arrangement. We welded up the crankshaft oil passages that squirt up the rods and modified the crankcase to squirt oil onto the camshaft lobes trying to simulate the actual cam splash internally. We have a heater in the oil pan, but we found with friction alone (no combustion and no cooling airflow) in the hangar above 50 F, the oil at high RPM will heat up to about 175 F. This is with an insulating blanket over the engine. On some of the hot Texas summer days, no heat was required to get to redline (around 225 F). You do need heat on cooler days.

This test rig has helped us learn a lot about camshaft and lifter design. If a lifter face spherical radius or the camshaft lobe taper design is not perfectly in the correct tolerance, lifters will not rotate. A non-rotating lifter, even if the metallurgy is perfect, will wear out within the first 25 - 100 hours. You can run a new cam and new lifters on our electric engine for 6 to 8 hours and then stop the test and inspect to determine if rotation is happening or not. We have run some lifters for over 1,500 hours with long runs at max RPM. This test rig has saved us a lot in fuel. But the FAA is still not willing to allow its use for certification.

[swoeric]

Re: DER question

Thank you so much Terry...that was a perfect answer to the question i was asking..Looks like i may be looking for a core to build a test bench like you mentioned...it was this type of testing that i regularly see in other industries engine development programs....so maybe a hundred hours on the test bench gets me 10m cycles...


Does the FAA require that the running engine test be performed in an airframe and in flight hours or are they ok with ground running?

[barnstmr]

Re: DER question

Eric,
Engine tests for FAA certification are most commonly run on a test stand or test cell under controlled conditions. Sometimes PMA manufacturers collaborate to share the cost of such tests because it is very expensive... not just fuel, but costly documentation, test plans, FAA conformities, instrument calibrations, etc. If you decide to build a test stand, let me know. I probably have contacts in the industry that might want to partner on the testing. (so they can test some of their own parts). What engine models are you planning to include in the part eligibility? Be aware that your test conditions should be for the "worst case" engine in terms of loads and operating conditions. i.e. if you want to certify a part that fits A50 continental through O-200, then you probably want to test with an O-200 or build a hybrid engine that makes the full 100 hp at the same RPM as an O-200.

[swoeric]

Re: DER question

I would love the 0200 and might start there for the excremental and proof of concept...I think the money to pay for it is in the I0 360.....Looking to do a roller lifter and cam to take advantage of some of the newer cam profiles available...reduce some heat etc....I have looked to the VW folks and seen a few methods to keep the lifters aligned but need to test it...possible a complete roller setup although i dont think there is much advantage in the rockers at this low or RPM..it would be nice to team up with an accessory or ignition group

[Ragwing nut]

Re: DER question

I would love the 0200 and might start there for the excremental and proof of concept...I think the money to pay for it is in the I0 360.....Looking to do a roller lifter and cam to take advantage of some of the newer cam profiles available...reduce some heat etc....I have looked to the VW folks and seen a few methods to keep the lifters aligned but need to test it...possible a complete roller setup although i dont think there is much advantage in the rockers at this low or RPM..it would be nice to team up with an accessory or ignition group

well, looks like I was not even close to what you were wanting to do. Cost to approve something like this would be prohibitive in todays market.

[Pearson]

Re: DER question

Why not just eliminate the bulk of the valve train and go with individual overhead cams driven by a flex drive between the cylinders?

[astjp2]

Re: DER question

Isnt that called a jabiru?

Why not just eliminate the bulk of the valve train and go with individual overhead cams driven by a flex drive between the cylinders?

[Pearson]

Re: DER question

I don't know anything about a Jabiru.

[swoeric]

Re: DER question

anyone know where you can find engine component prints...im looking to find the sizes of the valves and a few others