Best prop for aerobatics

[ronschreck]

Originally Posted by Maxrate

Thanks Ron. What are your thoughts on the 1/2 Raven being sufficient through the intermediate sequence?

You may have trouble with rolling circles at the Intermediate level. The most you will see is a 90-degree turn with a full roll but the roll will be rather slow with two knife-edge components and a long negative G push. I suspect you will be wanting a full inverted oil system when you get to that level.

[ronschreck]

Originally Posted by David Z

When does the aerobatic operation style prop become necessary or required?

With a non-aerobatic prop (no counterweights) you may have a few instances of runaway RPM when oil pressure at the prop governor drops. You will hear it immediately and it is easy to retard the throttle before the RPM gets too high. Pitts pilots have been regularly running their engines with fixed pitch props and see 3300 RPM all day with no issues so don't think that you have to overhaul your engine if you exceed 2700 RPM for a moment. I have never seen a RV in competition with an aerobatic prop and we all seem to do quite well without. If you would feel more comfortable with an aerobatic prop and have the money to spend on one that's great!

[emsvitil]

Would electronic ignitions with a rev-limiter solve the prop over-rev problem?

[spatsch]

Originally Posted by agent4573

The entry level IAC maneuvers don't require negative g, the most you'll have is near zero g if you mess something up.

I do disagree on that. You will never fly a straight roll if you don't see at least -1 to -1.5 g. Yes you can roll at +1g (lots of videos with water, cookies and other things..) but those roles are not straight at all and won't do for an IAC maneuver.

So even THE basic primary figure -- roll -- will get you into negative g.

On the other hand you really don't need anything special for that short negative g load. You have a couple of seconds before your oil pressure drops and much longer before you starve fuel even without flop tube and inverted oil. I tried down to Lycoming oil pressure minimus. I don't have a constant speed prop so I can't tell you if it has any impact on that but with a fixed pitch prop and a fuel injected engine you are good to go including Sportsman.

Oliver

[ronschreck]

Originally Posted by emsvitil

Would electronic ignitions with a rev-limiter solve the prop over-rev problem?

You would have to ask the manufacturer. Not sure they could catch it faster than the pilot.

[Maxrate]

Thanks again for the input Ron. I haven’t permanently stabbed the wings on so now is the time to install a single flop tube and look at the full Raven system. Ive watched your IAC sequence video and the RV can be a pretty impressive performer up to intermediate in the right hands and with the right equipment.

[David Z]

Originally Posted by emsvitil

Would electronic ignitions with a rev-limiter solve the prop over-rev problem?

I've always pictured the ignition rev-limiter as a last chance before bad stuff happens type device. Going from high power to zero power instantly can't be good on the engine. Then because the method was cutting spark, there's a ton of raw fuel in the exhaust system when the ignition turns back on. The recipe is ripe for a nice kaboom in the exhaust system. I suppose exhaust damage is better than throwing a prop blade or overhauling the engine, prop or both. However that's the least bad of several bad options. My thought is to set the EI rev-limiter at some overspeed tolerance for the engine or propeller. 2800 or 2900rpm, depending on what maintenance action is required after the overspeed for both the engine and prop. Basically analyzing the risk at various overspeed RPMs and deciding where having exhaust damage is preferable to what's happening with the engine and/or propeller.

[emsvitil]

There's 3 types of rev limiters.

1. Soft limiters reduce the ignition advance. The farther you're past red-line, the more ignition advance that's taken out. Taking out ignition advance drastically reduces power, and the engine is less likely to keep increasing rpm.

2. Hard limiters cut off the ignition. Then turn it back on when rpm drops a certain amount.

3. It's sort of 1 and 2. Ignition is randomly cut to a cylinder. The higher you're past red-line, the more cylinder cuts there are until ignition is off.

[Aero_Octaveus]

So after looking into this a bit. I've absolutely broke my brain trying to figure it all out. Help please
I really like the 180hp c/s fuel injected engine. Love the look of the James Cowl, and I wanna do some light aerobatics.

So if I go with Vans IO-360-M1B for 180hp/CS prop. Looking at James Cowl I'm forced to go with the long cowl. Which means I need an extended hub prop.

Question is: Is the Hartzell G2YR/N7605W-2X approved for light aerobatics? Does WW or MT offer any extended hub props that will work? (This info is crazy hard to figure out going off their websites)

Darn James long cowl dilemma

[David Z]

I was watching this thread hoping someone smarter than I would chime in. Well that didn't happen, so here I am.

It really depends on how you define "light aerobatics". Any maneuvers that approach 0g or go negative will introduce air pockets in the prop control engine oil. This will cause problems for the governor to control propeller RPM. Non-aerobatic props use oil pressure to coarsen the blades, so that pocket of air will make the RPM increase uncontrolled. It's likely an insignificant increase before oil is restored and RPM brought back in line. However, it could potentially cause an overspeed that means prop and/or engine teardown.

Prop extensions put more load on the crankshaft. It's a short lever exaggerating any maneuvering and gyroscopic loads.

Positive, low G maneuvers, it sounds okay. Inverted flight, high G or gyroscopic maneuvers might cause problems. No inverted snap rolls with your setup

Now we wait for someone smarter to prove me wrong