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Darren S

Well Known Member
Hi all,

I want to know if I'm making a bigger deal out of something or not.

History: I fly a -7, Superior IO-360, Hartzell prop, 630 TT engine, prop, airframe. I flew Primary last year, thinking about Sportsman this year.

The Sportsman sequence is a bit longer with a few more elements in it than Primary. On two of the figures, the 1/2 Reverse Cuban and the Humpty with 1/4 roll down I pull a good 4 G at the end to make what I hope is decent looking manoeuvre. If I don't, the plane picks up alot of speed on the downline.

I really love my plane and use it alot (400 hours in 21 months) so I want it to last. I have some long X-country trips planned this year ie. New York, OSH and Bahamas. Having said that I bought a new Garmin 510 with XM versus an inverted oil system. I love the cross country flying as much as the aerobatics, but chose to enhance the cross country capability more than the acro capability because......

My concerns is this: I feel like I am stressing the plane to the point that things are going to wear out prematurely and cause me grief in the future. I keep envisioning the stress on the crankshaft as I pull 4 G, especially with the weight of the C/S prop on the end. The stress on the engine mount too. These are not thoughts that should be running through my head as I'm upside down. As a result I don't pull as aggressively. I guess trying to "baby it". This will make for lousy scores too.

I don't have an AEIO engine and the load on that front bearing has got to be a lot. Maybe a bit more than it was designed for ?? I don't know and that's where I solicit the advice and knowledge of those more knowledgeable than myself.

Am I making a bigger deal out of this than necessary ? Anyone with similar thoughts/experiences or am I out to lunch? :)

I await the replies. I'm thinking that I may just stay in Primary or look for a share in a Pitts ?

Thanks,

Darren
 
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Hey Darren,

Here's my take on all this - The entire RV airframe was specifically designed for operational aerobatic loads of up to 6G. That means you can pull 6G on a regular basis without modifying the airframe due to stress. I would not worry about the airframe or engine mount being subjected to typical aerobatic stress. The only components that will wear significantly faster under regular aerobatic loads are your rubber Lord-type engine mount bushings. But you're still measing their life-span in years, rather than months.

Regarding aerobatic stress on your crank/flange, this is definitely stepped up when doing aerobatics. The new Lycoming AEIO engines have a solid crank flange as opposed to the flange with lightening holes. What kind of flange does your Superior have? Older AEIO engines that have the light crank flange have a recurring 25 hr AD to visually inspect the flange for cracks. But keep in mind that the AD was issued in the early 80's as a result of Pitts types flying lots of snaps, gyroscopics, and flat spins with metal props. Metal props are the worst for your crank/flange. CS vs. FP prop doesn't make too much difference, since all of the extra mass of the CS prop is right on the hub. Changing to a composite prop would drastically reduce stress on the crank/flange. Other than the heavy flange, the only other difference associated with the "AE" designation is that the oil sump is adapted for an inverted oil system.

However - a little perspective even on the crank/flange issue: You are doing mild linear aerobatics, as in no gyroscopics or snaps that rotate the prop disc very rapidly, and in multiple planes. The faster you rotate the prop disc, the more gyro stress is put on the crank/flange. Yes, you are rotating the prop disc every time you pull into or out of a loop. But the rate is fairly slow. The engine on my Pitts is an older Lycoming AEIO-360 with the light crank flange and the 25 hr AD. I still have the original crank from 1976, and the airplane has flown Intermediate-level competition aerobatics for the last 20 years. The crank flange is still fine, and the airplane has always run a 76" metal Sensenich prop. I am careful to limit my snap speed, and I don't do gyroscopics, but I would not worry about the light crank flange doing Sportsman-level aerobatics, even with a metal prop. Again, check the flange on your Superior - it may be heavier than the older Lycoming flanges with the lightening holes. That being said, I am replacing the Sensenich with a Catto so that I can get into Advanced feeling less guilty, which requires more snaps. Besides the flange, yes, you are putting a little more stress on your crank bearings, but again this is fairly mild aerobatics. But remember, you're not doing anything that hundreds of other RV pilots do on a regular basis with the same prop/engine setup. It's just that you're trying to do it with more precision...and in front of judges. :)

Regarding staying in Primary, keep in mind that Sportsman does not require you to fly the airplane any harder than you would in Primary. No need to pull more than 4G in either. If I were you, I would keep flying my airplane as is, don't worry about it, and work toward Sportsman. Remember, it's about precision, not how hard you stress the airplane. And also, remember you only live once. :) And maybe save for a composite prop if it makes you feel better. :)
 
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We fly them pretty hard

Hey Darren,

Just from my personal perspective I don't think you should worry at all about the level of aerobatics you're anticipating doing. We fly our planes about as hard as anybody I know of in the RV world and have had very little if any maintenance on the airframes that we can tell. I have heard of some loose bolts that hold the horizontal stab to the fuse. If these do start to stretch or loosen, you can definitely feel the movement by pulling up and down on the stab. That's the only thing I can recall hearing about on the airframe.

I routinely pull 4.5 - 5 g's during a show. I'm careful to avoid rolling g's and everything is done pretty smoothly, but still, we fly'em hard. I've had no loose rivets, fuel leaks, engine or prop or mount problems. My cowling did show some sings of rubbing on the spinner but I had a bolt length issue there.

We are extremely watchful on mtc. We inspect each others planes, did FWF inspections on every airplane and fixed ANYTHING that somebody didn't like. I'd also suggest you put some kind of kill switch on the fuel and smoke pump that shut's everything flammable down in case of an accident. Just cheap insurance.

Things are going to move around a bit, but that is what they are designed to do.

I'd say go out and enjoy what your planes really likes to do..
 
Hey Guys,

That's just what I wanted to hear. Eric I knew I'd hear from you and thanks for the Sportsman "head cam" video you sent me the other day :) It was very helpful.

I see and watch what Team RV does and I didn't read anything in the recent Kitplanes on adverse stressing of the aircrafts. And you guys do this alot more than me.

I will call Superior and see what type of flange I do have, just for my own piece of mind.

My instructor said the same thing that gyroscopics are the big stresser to the flange but I'm not doing any of that so no worries there.

I'll watch the horizontal stab for "play", give the FWF area a good look over when the cowls are off and watch the Lord mounts for sagging.

Thanks again for the replies and peace of mind.

One thing I didn't understand is, "How is a metal prop worst for the flange than a C/S prop" ? I can see a wood/composite prop being lighter and less stressful on the flange, but a C/S prop is still metal with a big ole' hub. How is that any different from a metal Sensenich ?

Darren
 
Darren S said:
One thing I didn't understand is, "How is a metal prop worst for the flange than a C/S prop" ? I can see a wood/composite prop being lighter and less stressful on the flange, but a C/S prop is still metal with a big ole' hub. How is that any different from a metal Sensenich?
Click to expand...

Metal blades obviously have much more mass and less flex than composite or wood blades. This causes much more gyroscopic stress applied to the crank/flange compared to a prop with wood/composite blades. Even though the total weight of a CS prop w/ composite blades may be a little more than that of a FP metal prop, it's all about mass distribution. The composite blades weigh very little compared to metal. The mass of the CS hub is very close to the axis of propellor rotation, meaning the polar moment of inertia is very small. With metal blades extending out over 3 feet in each direction from the center, there is a much higher polar moment of inertia tranferring stress to the crank flange. Composite blades have the same polar moment, but much less inertia due to their light weight. Combine this with the fact that they flex more than a metal blade, this further reduces stress on the flange.
 
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Hey Eric, I'm following your drift but I don't have a C/S prop with composite blades. I didn't know they made such a thing. My prop is an older square tip blade from 2007. Not the blended airfoil.

I've dressed a few small nicks with a file so I'm pretty sure it's metal:). So isn't this the same as a Sensenich with regards to crank flange stress?

Darren
 
Just a little caveat..

Hi Darren, just a few comments. I am sure these planes are very strong, and I plan on flying mine in Sportsman as well. I was a pretty aggressive pilot when I was a serious competitor, but I also flew as smoothly as I could. I was happy with the results.

Beyond all the usual judging criteria there are many nebulous but important things that will help your score a lot. Sharper corners will help your figure grade (they shouldn't by the rules of course, but they do) , but I believe overall smoothness will actually help you more. If your routine looks like it is deliberate and each maneuver is done exactly when and where you want it (not rushing into each maneuver), all your rolls stop and start like the wing hit something hard - NO BOBBLE, and the same with your lines (there is one trick of popping your stick forward slightly as you hit an upline to unload the wings, this makes the line look very straight and hammers easier as well, same with pulling it off the line for a humpty or whatnot, if you pop the stick back quickly but very slightly and then ease into the pull around the top humpty, then pop the stick slightly forward when you hit the down line - this helps your presentation immensely, lines are well defined lines, and loops or portions of loops are well defined loops. It's hard to talk about, easy to show, hope you see what I am saying.

I flew an Advanced Unknown once when I was feeling a little poorly, I remember the G meter was pegged at 4 when I landed (I usually pulled 5 or 6 in a routine). A friend of mine said to me after the flight it looked like I was on Valium. I still scored well enough to win the flight. And it wasn't even at my home field!;)

Why do I emphasize this?

As I say, I am sure the RV's are very well engineered and plenty strong, and most likely you could fly them for a very long time, doing Sportsman acro to your heart's content, BUT, unlike a Pitts or Extra or any other serious acro mount, the wings are still made of metal, and metal fatigues, even if it is operated within structural limits. Metal parts in commercial aircraft are usually time or cycle limited if they operate under stress, even just the stress they were designed for. It may take a million pulls of 4G's to fail an RV spar, but maybe it would take less. My feeling is, a smooth pilot will get many more cycles out of the airframe than a hamfisted one. I do remember watching a few RV 4 or maybe -3 pilots back in the 90's that made me cringe some.

I also remember watching one of your videos, and you fly pretty smooth as I recall, so that's good.

So keep it smooth. Stay on top of the speed. What I liked about a Pitts or Extra was, you could stay on the downline until you got whatever speed you wanted for the next maneuver. Then just pull hard enough, and the airspeed stays right there, it doesn't increase around the corner. That may take more than 4 G's in the RV, I just don't know because I haven't flown one yet. I am going to do my best to pull no more than 4 G's, but we shall see.

Smooooooooth!:D

Oh yeah, and as to the crank, what Eric said is dead on. I was told by a fairly well known engine modifier the hardest thing on a crank are multiple flat spins at full power, next being gyroscopics, then snaps. That may have changed these days, after watching Rob Holland fly at S&F. I've seen a lot of people replace front bearings after they start flying Unlimited.
 
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About snaps...

Darren,

Agree with everything Eric says. (He's a pretty sharp guy!) I do snaps and avalanche maneuvers in my RV but the gyroscopic maneuvers are much more tame than a Pitts. The RV just won't rotate that fast because of the longer wings and fuselage and comparatively smaller control surfaces. So snaps are really (sorta) gentle. I do have a composite CS prop (200RV) so that helps reduce the stress on the crank flange. After nearly 1300 hours of very abusive flying I see no issues other than the stretched horizontal stab bolts that Widget mentioned, and I'm not sure if that was due to aerobatics or normal wear and tear. I do a VERY close inspection of everything forward of the firewall at every oil change and the airframe gets a good inspection every season.
 
Thanks to all for the feedback. I seem it be overly concerned for nothing.

Fly smoothly, limit things to 4 G (since I don't have composite blades), inspect FWF closely, watch for wear on the rubber mounts, check the horizontal stab more often and fly smoothly....oh yea said that already:)

Darren
 
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