Prop Decisions HOBBS 1233.0 hrs

Yesterday I swapped quite a few emails with Jeremy Sutch at Whirl Wind Aviation. Jeremy was great answering my multitude of questions about their props. When buying big ticket items like the prop, engine, paint, avionics...customer service must be impeccable for me to even consider spending my money there. So far, Whirl Wind has been exactly that, and they have the reputation to back that up.

Picking a prop is probably pretty easy for most builders. I, on the other hand, cant seem to do anything the easy way. ;) So, here is my thought process for your benefit. I will tell you, in advance, it is not a standard thought process and I expect many people will not agree with it...I'm ok with that, its my plane and my money, not theirs. I can say I am leaning away from the "conventional wisdom" in my prop choice. My path may not be the best choice for you and I am not in any way trying to sway anyone to follow me down this path. In its simplest form, for me, the heart wants what the heart wants.

The first fundamental decision when choosing a prop...fixed pitch or constant speed? I decided long ago I wanted CS...it just gives you so many more options when flying your airplane, plus added aerodynamic braking and acceleration were key factors for me. Is it worth the money, added maintenance and weight?...I cant argue that it is, but its what I want in my plane...end of discussion for me.

Aluminum or composite blades? Again, this one was easy for me...composite was the choice. Lighter, quieter and ramp appearance were factors in this decision. They are considerably more expensive however and are harder to maintain. You can't just file a nick out of a composite blade like you can aluminum.

Two blade or three? Well, all along I wanted the three blade setup, almost exclusively because of, again, the "ramp appearance"...see a pattern here?...they just look so cool to me. I knew I would sacrifice some top end speed and it wasn't as efficient as a two blade setup but it would run quieter/smoother, and although debatable, should have better climb performance. For about a year now, I had my heart set on the Whirl Wind 151 prop...until I found out it was only rated up to 165 hp (limited to the IO/O-320). That left me considering the MT propeller line as an alternative, which Van's now sells directly for a reasonable price. For some reason, not sure why, I just didn't feel as comfortable with them as I did with Whirl Wind. Whirl Wind makes some darn nice props and guys rave about them on their RV's.

http://www.whirlwindaviation.com/index.asp

At this point, I know I want a CS, composite prop that looks nice. With those parameters, and also the desire for an RV-friendly company with good customer service, it led me directly to Whirl Wind. And gosh, if you are going to go with Whirl Wind...you may as well go with the prop that they designed especially for the RV line--the 200RV prop. A prop that everyone that has installed one, loves flying behind. Decision made, right? Well...not so fast. I usually don't follow the herd so I thought let me look at other options.

http://www.whirlwindaviation.com/index.asp

http://www.whirlwindaviation.com/index.asp

Next I looked at the aerobatic prop that Whirl Wind offers...the 200C (2 blade) model...400C (3 blade). Its a counter-weighted prop which means it takes oil pressure to decrease pitch. If you lose oil pressure to the governor, the prop will increase pitch to help prevent overspeeding. I liked that feature to protect my prop and engine, if needed. Although for gentlemen aerobatics its probably overkill so I could let that go. It also has great aerodynamic braking beacause of its wider chord, which is handy during aerobatics for speed control on downlines. The wider chord also gives better takeoff acceleration. And again, it looks good...I like the "beefy" look of the blades compared to the smaller blades on the 200RV.

The downside of this prop is a recommended one year (or 250 hr) teardown inspection schedule. Jeremy says that isn't a hard and fast rule and is left to the discretion of the owner, it was intended for owners that are flying their props in hard aerobatics so "gentlemen" aerobatics may not need that frequent inspection time. At the end of the day, I just wasn't comfortable cutting corners by stretching that inspection time, no matter how I was flying it.

Although I decided against this prop, I did like the blades...so I continue to look at other options.

http://www.whirlwindaviation.com/index.asp

And voila...I come across the 200G-CS prop. Same blades as the 200C, but the main difference being it is not a counterweighted version and has the same maintenance specs as the 200RV. It was designed specifically for high performance bush planes...they call it a "utility" prop, but list it as an option for RV's as well. The acceleration and deceleration are supposedly outstanding, making it a great STOL performer.

Now of course, the RV line of aircraft are not "bush" planes. When I first started building I swapped several emails with Dan Checkoway and he was sure to point out this fact to me. They can handle well maintained grass and gravel strips, but make no mistake, they are not a Super Cub.

Beyond the great STOL characteristics, lets remember the blade was originally designed for the 200C, so its an aerobatic blade by design, which I like. So, I am intrigued by this prop and want to know more.

With prop design, as with any aircraft design, there are always trade-offs. This prop, with its superior STOL characteristics, will surely trade performance in cruise. And it does...but I'm thinking, not as much as you might think. Randy Lervold, an RV builder, did a very nice test writeup comparing several props including the 200RV and the 200C, you can read it here. 

You will notice that the cruise speed between the 200RV and the 200C is almost identical (1-2 mph). Of course, that's not the 200G-CS...but remember, its the same blade. I would expect that the cruise speed numbers will be essentially the same as the 200C.

Ok, I am liking this option more and more...or should I say, I'm talking myself into it. ;)

There is one other option that you can get from Whirl Wind that they don't publish very well, you gotta read the fine print to find it. Its a "swept tip" option. Here is Jeremy's description of the swept tip... 

"The swept tip is a little more efficient (a little less drag) and if you are operating out of unimproved fields, a little more durable because the nickel leading edge wraps all the way around the end of the blade to the trailing edge. With the swept tip you lose a little bit of area. We have found that this loss of area does not harm thrust much, but it does affect braking a bit. Depending on the type of maneuvers you will be doing, you may want all the braking that the prop can provide. There is no extra charge for the swept tip version of the blade."

So now, I am adding up the scorecard in my head. If I go with the 200G-CS prop:

• Better acceleration on takeoff roll
• Better aerodynamic braking
• An aerobatic designed blade for downline speed control
• Better STOL performance
• Less efficient in cruise than the 200RV
• With a swept tip version, I can close the "efficiency gap" with the 200RV in cruise because of less drag
• Lose 2-3 kts cruise speed over the 200RV
• Looks cooler on the ramp (subjective I realize...both props are works of art)
• Costs ~$800 more than the 200RV (but still less than the money I had budgeted for a 3 blade)
  
  

As you can see, this isn't as crazy as you might think. Does it fit my mission better than the 200RV...probably not, the all around performance of the 200RV is the best choice for most builders. This prop combination has only been around for about a 1-1/2 yrs and Jeremy cant remember anyone putting it in an RV...yet. I would be the first from what I can tell...and thats kind of cool too.

Bottom line for me...I like the "suck you back in the seat" feel from the takeoff roll. I want to fly it to unimproved airstrips so the added STOL characteristics would be handy, even if rarely used. I want to fly aerobatics. And lastly, I just think it is a "bad ass" looking prop. Go look at any high performance airshow plane (Rob Holland flies behind a Whirl Wind prop that looks a lot like the 400C) on the ramp...they don't have wimpy looking props...or engines for that matter! I don't have their plane or engine, but I can pretend with my prop. :) And quite frankly, I just don't feel like I am giving up much to have all that. ~$800 and 2-3 kts in cruise is not that important to me to have exactly what I want hanging on the nose. 

Anyway, that's what I have been doing lately...lots of prop research. Its enough to make my head hurt! I am not 100% on this prop yet, but probably 95% in favor...still pondering it. Anyway, hope some of my legwork on Whirl Wind props helps, good luck with your choice.

http://www.whirlwindaviation.com/index.asp