Hey guys I'm new to the forum.
I'm looking at a Pitts S-2E, and the engine is a Lyc IO-360-A1A with 260SMOH. The crankshaft flange has lightening holes in it, I am a little concerned it doesn't have the solid flange AEIO crank. The engine has a whirlwind 2 blade with a McCaully hub. Are those blades light enough for a "Lightened Flange" engine? This is my first aerobatic airplane, and I don't really plan on becoming an airshow pilot but I want an engine that will hold up. As far as doing snaps go, I would like to be able to do snaps but I don't have a whole lot of desire for Lomshavoks and other hard acro. I've read the problem is mostly associated with the heavier metal propellers rather than a lighter Whirlwind.
I have used the search button and read through some of the posts and read about the guys with the charger who had to get a new crankshaft because of this.
I own an S-2A that has the original crankshaft with the lightening holes. I compete at the Intermediate level and do snaps. Have never seen any of the crankshaft flange issues in 600 hours of pulling the prop every 25 hrs for the visual inspection per the AD.
Once upon a long time ago I called Lycoming about needing the solid flange. I came away with the belief that until I started flying Unlimited I did not need a solid flange unless I was really really tired of inspecting the crankshaft flange.
Your prop has lighter blades and puts less stress on the crank so I would not worry.
That said, is the prop counter weighted (200 series)?
While I can't put a Whirl Wind prop on my certificated airplane, I can report that Whirl Wind is a sponsor of my IAC chapter's aerobatic contest and all of the customers that I know are very happy with the props and the support. They might have an opinion if you ask.
Best of luck,
I have a hard time connecting this advice to the realities of competition acro in the Intermediate thru Unlimited categories. I wonder how much the Lycoming rep actually knew about competition acro. As you know, the only figures unique to Unlimited are tailslides, vertical (up) snaps, and negative snaps. Tailslides don't impose a high degree of stress on the flange, since the flipover is done at (or near) idle power. Snap rolls are the main crank flange stressors, since there are no gyroscopic airshow-type figures in competition, except in the Unlimited 4-minute Free, which is a separate thing altogether...and optional. The airplane's crank flange doesn't know the difference between positive, negative, up, down, or level snaps. The frequency of snaps is greater in Unlimited, but crank flange problems are a function of how hard the airplane is flown, and how often. IMO, a very frequent-flying Intermediate pilot could potentially impose just as much stress on their crank flange as a less frequent Unlimited flyer.
Originally Posted by WLIU
However, my Pitts has the original (light) crankflange from 1976, and has been exposed to many years of competition acro (including snaps) without any problems...yet. But I do limit my snap speed, and don't do a whole lot of them. I did switch to a composite prop for crank flange reasons. Potential problems are real, and it makes me feel better to get rid of most of the stress on the flange. OTOH, I heard of an IAC Advanced and airshow pilot who recently developed (light) crank flange problems on an S-1 Pitts with an MT (composite) prop. That airplane was flown very hard though.
IAC Tech Tips Vol. 3, (pgs. 17, 19-21) has some good info on the crank flange issue:
OP, I would feel much more comfortable with the Whirlwind prop with your crank than a metal one. 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.
Last edited by RetroAcro; 07-16-2012 at 10:13 AM.
It is good that you only do snaps at the reccomended speeds. My reccollection is that in the '80's there were folks who thought that you could snap a Pitts at any speed and I believe that is where the crank AD originated. Those same folks are responsible for the AD that says you have to inspect the upper longerons where the cabanes are welded on. They broke some airplanes almost in half doing high speed snaps. But that is another story.
The folks at Lyco know a LOT about aerobatics. Their engines own the acro market and have for years. Continental does not make any aerobatic engines. I believe the rep that I spoke with. But your caution will serve you well.
As for composite props, we are talking about two different stresses that will cause the engine to fail. A composite prop puts less load on the crankshaft flange. That is good. But the torsional resonance issues will destroy the engine components on the other end of the crank. In both cases you will find yourself looking at a landing off the airport. I have a friend who ran into this and the engine rebuild was very costly. The engine only flew with the inappropriate lightweight prop for 50 hours or so. The problem was fortunately identified on the ground. A lot of expensive internal parts went into the trash that are normally inspected and reused in an overhaul. An issue that it is not wise to ignore.
Best of luck,
Wes, what are the details on your friend's airplane/engine/prop combo - and how it was flown? I'm aware that this issue has been talked about, but I've only heard of a single reference to it, and details are sketchy. It seems to only apply to Lyc. 360 series engines? I'm just wondering what the difference is for folks who have been running wood/composite props on their Lycoming 360's for years/decades. Composite is becoming almost ubiquitous. RV guys have been running wood props on their 360's for decades...and composite has taken over and been in use for many years. Craig Catto can't build his composite props fast enough for the RV guys. He also builds the props for Cub Crafter's 180 hp Carbon Cub. Lots of S-1 Pitts using them. Every Giles and Extra 200 has a composite prop. There's a huge market (and track record) out there for composite props (FP and CS) on 180-200hp engines. I just haven't heard of any issues outside of the single mention I read about on the Acro Exploder some time back. What do you think the difference is for the people (or person) who had a problem?
Originally Posted by WLIU
Last edited by RetroAcro; 07-17-2012 at 08:15 AM.
The specific problem seems to be lightweight constant speed props that have no counterweights on the blades but instead use an oil accumulator with the prop governor, and that are installed on 4 cylinder engines. That setup is up to half the weight of a propeller that uses counterweights and the reduced inertia provides inadequate damping for the power impulse frequencies specific to the flat 4 cylinder engines. 6 cylinder engines have a different set of power impulse wave forms that have much lower peaks.
I recall that the engine in question was a Lyco IO-360-A1A with one of the original 2 blade (yes 2 blade) Hartzell Claw's that used blades that are un-counter weighted. The engine lasted less than 100 hrs and I believe that the accessory drive gears and some other expensive internal parts were junk at that time. The propeller is very light, but to use it successfully you need to have either and IO-360-A1D, or do what my friend did, throw away the original engine and purchase a new IO-390. The -A1D's and the -390's have the 6th order counterweights on the crank that solves the problem. I did not ask my friend what the bill was as I am sure that the experience was financially painful.
I write this as a guy who knows where one of those Claws is located and for sale and is scheming to convert his IO-360-A1A to the -A1D configuration at the next engine rebuild. Swapping out a 54 lb aluminum Hartzell for the 2 blade Claw would provide a significant CG and empty weight improvement to my airplane. The propeller is approved for my airplane, but putting it on the engine configuration that I have now would be mechanical (and budgetary) suicide.
Oh, the composite props that are rapidly becoming so common all have counterweighted blades and those counterweights are heavy. Those installations won't see the problem we are discussing.
Last edited by WLIU; 07-17-2012 at 12:31 PM.
Good info, thanks for clarifying. In your previous post it sounded as if you were describing a problem purely related to the composite construction of a prop blade.
I really appreciate all the help. If anyone has any more suggestions on things I would appreciate it.
Do we think the problem is caused from snaps being done at a high airspeed or snaps done at high power settings.
High speeds are the issue. In snaps, speed drives G. Most pilots forget that published Va is for max gross weight and Va decreases when you fly at lower weights. You should take your airplane's V-N diagram to heart as it tells you performance for both positive and negative maneuvers. You can break your airplane going either way.
Rotational speed of the snap drives the increase in stress on the crankshaft flange and the crankshaft between the flange and the thrust bearing. Higher speed snaps rotate faster, and folks think that they present better to the judges and the gallery. That's why guys want to do them. But the propeller is a big gyroscope and resists the change in orientation. Lighter propellers resist less, hence our desire to find a way to afford a Hartzel Claw or an MT. But there is no free lunch and if you install an MT and think that you can snap at a higher speed, you are looking at repairing cracks in your upper longerons.
So in my Pitts S-2A for instance, Va is 140mph at max gross. I try to fly lighter than that so I do snaps from 100mph to 130mph. Do them at 160mph and you are asking to crack or break your upper longerons. See the longeron AD.
Last edited by WLIU; 07-18-2012 at 06:55 AM.