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siclick33

Member
Hello all,

I have just started to consider building a Vans kit and am researching some of the major purchases that would be involved.

One of the areas that I am confused about is the engine and, in particular, the use of standard Lycoming type engines on aerobatic aircraft. I have searched this forum and the internet but can't find any limitations or handling advice to suggest what sort of flying is, and isn't, acceptable. I would hate to spend that sort of money and wreck the engine within a few hours.

I assume that gentle positive g manoeuvres (like a loop) are ok. What about inverted flight? Does the standard engine have an inverted time limit or does any amount of negative g need an inverted oil system?

I have read that the inverted oil systems don't work too well at zero g (such as in uplines for stall turns). Is there a time limit for these conditions?

Does Lycoming publish this sort of information in an official document?
 
acro

Any Lyc will be ok for gentleman aerobatics. On a carbed engine any significant negative g will cause the engine to lose power. With fuel injection the oil will be the limiting factor. Any of the popular fuel injection systems will handle negative g. Except for the H engines, any four cylinder Lyc can be converted for inverted oil. All bolt on except for the possible requirement to weld a fitting to the sump. Raven is one popular oil system, I believe Aviat still supports the Christen system. With either there will be momentary losses of oil pressure. This will occur in maneuvers most people will not be doing in an RV. If the oil tank is on the right side, sustained 90 degree bank, left wing down, will cause loss of oil pressure. Right wing down oil pressure is maintained. On a maneuver referred to a humpty-vertical up line, in this case followed by a relatively small radius outside half loop, oil pressure will drop momentarily. None of these mamentary pressure losses will hurt the engine. Sustained obviously will. You can google Raven and Christen for more info.
 
Simple answer?

The difference between an AEIO-360 and an O-360 is mostly bolt on options such as an inverted fuel system (The “I” stands for Injection). The inverted oil system referred to in the above post turns the 360 into a “dry” or partially dry oil sump with an external oil reservoir and some check valves so that oil gets to the engine in most negative G maneuvers.

If you want to do those negative G maneuvers, you will also want to put a flop tube in one of the fuel tanks so your injection system will always have a ready supply of fuel.

If all you want to do positive G maneuvers such is loops, rolls, spins, etc. a simple carbureted engine will work just fine. You can add the flop tube during your build and add the injection and inverted oil systems later.

Just keep in mind, that if you add the inverted fuel system (flop tube and injection) without an inverted oil system and start playing with negative G’s, you could possibly damage your engine due to oil starvation.

PS. Welcome to the VAF forum.
 
And if like me you really don't want any interruption to oil flow (plus the ability to pressurise the oil system before start) you can also add an accumulator from Summit racing.

The weld on fitting is deirable because the standard pick up fitting (at least on a FF sump) is on the front of the sump. Thus in sustained uplines (hammerheads) the oil will go to the back of the sump and possibly starve the oil pump.

In my experience with the accumulator this has been a non issue. If i were building again however i would weld on a seperate pick up on the back half of the sump.

Frank
 
RV engine Constant Speed Prop option.

Also, consideration should be made concerning a hollow crank for constant speed prop options, prior to engine ordering.
 
Thanks very much for the info.

I wouldn't be after competition aerobatic performance, just the ability to do slow/4 point rolls and hammerheads (as well as loops/rolls etc).

It sounds like an inverted oil system and sensible placement of sump pickups should keep the oil pressure up for long enough.
 
Bill R
Your on the right track, but not quite acurate as far as the oil sump.
In the Christen system the original sump is still used as the sump when right side up, then when inverted the upper part of the engine case is used as the oil sump. There is an oil separator with a valve in it that makes the top of the case or the sump be the breather depending on if your inverted or not. And a valve to let oil go to the pump from either the top of the accessory case or the oil sump.
Hope this helps. If this link works it shows you the system operates.
http://www.rv7factory.com/files/inverted_oil.pdf Bill B
 
Welcome to VAF!!!!

Bill, welcome to VAF.

Thanks for posting the info on the Christian oil setup.

Good to have you aboard.
 
Think Positive...

Sick Lick,

Again, welcome to the site. Positive G Aerobatics have been performed for many years without inverted fuel/oil. Lycoming does have nomenclature on their various engine types based on the certified capabilities status on their website. Here is a great thread explaining the differences: http://www.airtalk.org/aerobatic-engine-io-360-aeio-360-comparison-vt16343.html The IAC website also has some great information about aerobatics in non-inverted system airplanes. http://www.iac.org/

My Hybrid RVX(my third RV type) has a 150HP Lycoming with a carb and FP Catto prop. My oil system has a M20 air/oil separator which helps with oil thrown overboard. Previous HR2 had a slimefighter which worked very well also. You don't have to add the weight, cost and complexity of a Inv/FO system to have fun.

My advice? Keep it light and simple...

Here is video of the possibilities:
http://www.youtube.com/watch?v=Um3MZwrqPhQ

Smokey
 
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