Carbon Cub makeover: the Ultimate Amphib

[randylervold]

Jim Richmond and I were doing some planning for 2015 recently and we were pining about not having a way to demo the new Aerocet amphibs once we get into the nice spring weather next year. The Carbon Cub on those floats is just cool beyond words, we just know that more pilots would want to buy them if they could experience it for themselves, after all there's only so much you can get from pictures and videos. Yet dedicating a company aircraft to that is a bit expensive given that floats are a relatively narrow market. What to do? Well, we just happen to have an aircraft in our company fleet that we thought of... N56XC, hmm.

N56XC background
N56XC was built from Carbon Cub EX kit #0009 in 2011, so it has the EX tail feathers and so on. The reason for the original project was Jim's: "what would a Carbon Cub do with an even bigger engine on it?" So, Jim bartered a deal with Bart Lalonde at Aero Sport Power for an O-375, and as long as he was going big he went all the way, "let's put 10.0:1 pistons in it too". And, "as long as we're going big let's try a constant speed prop on it too, we've got an extra MT around here somewhere". And so the plane was built with this big-assed engine, constant speed prop, and a few other tweaks we were curious about as well. What would happen, how would it perform?

Turns out that an engine like that with high compression and electronic ignition creates a combustion event, and associated pulses and harmonics, that simply aren't compatible with some props. In fact N56XC caused at least partial failures of two MT constant speed props and one Catto fixed pitch prop before the first year was out -- it quickly became known around here as the engine that eats props, and got to where we weren't sure it was even safe to fly. Bart offered to swap for 8.5:1 pistons, which eventually we did. Craig Catto then made yet another prop for it and it has now been stable with no damage for over 150 hours now. That's not the end of the story though.

Now you'd think this plane would just strut around boasting a superiority complex to all the normal Carbon Cubs with it's big-assed engine and all. Turns out that's not the case. I've personally flown N56XC several times now in a tight formation flight missions including takeoff, full power climb, and flat out level run with new Carbon Cubs just off the production line. No kidding, the stock Carbon Cubs will usually out gun me in climb and top speed both by a small margin. Go figure.

N56XC has been used in the intervening years for various other tests of course, but we can't use it for many things we want to try because it isn't a conforming LSA Carbon Cub. It is commonly a camera ship or a chase plane, and Jim typically loads a couple of kegs of his home-brewed beer in it each year and flies it to the Johnson Creek fly-in, but otherwise it sits on the ramp outside a lot. Well, I remember how freakishly fast it was for those few short hours I flew it with the constant speed prop, and it does have lower compression pistons it in now, so maybe... we'll you get the idea, the project was forming.

The makeover project
Now that you have the background on this aircraft let's talk about the makeover project. The idea here is to give a "refresh" to good 'ol N56XC to include the following:

• Install new Whirl Wind carbon fiber constant speed prop
• Refresh the weathered Poly Tone portion of the paint and clean up the cosmetics a bit
• Update the Dynon Skyview to the latest touch screen offering, and install their autopilot to complete the Dynon suite
• Put it on a new set of Aerocet 1500 amphibious floats
• Collect performance data and see what it'll do!

The point of all this is to create a showcase airplane to show just what a builder can do with an EX-based aircraft and a little creativity. We know from the regular Carbon Cub float installs we've done that floats don't slow the plane down in cruise, and with the c/s prop I'm hoping to see cruise speeds significantly higher than what a normal Carbon Cub will provide. That speed, and with the big tanks, should extend the cross country capability of this plane to a hopefully impressive level. Add to it the fact that you can land on the water or the land once you get there and you see why I'm inclined to call it "the ultimate amphib".

The plan is to start on this list of upgrades immediately and work on them over the winter as time allows, then fly the plane to Florida in April for Sun-N-Fun 2015 to show it off and do some demo flights for those interested. We're busy around here and this list will take some time to complete so we're starting today on it, in fact the prop install starts tomorrow. As a two time aircraft builder I've been without a project for quite some time now, so Jim and I agreed that I'd take this on as my personal project. Cool, I'm stoked!

The plan is to fully document this project and my journey to Florida right here in the forum. Look for additional posts as we make progress, of course complete with pics, maybe even a little video from time to time.

Following along
If you'd like to tag along and monitor my progress you might want to "subscribe" to this thread -- just click the "Thread tools" menu at the top right of this thread and click on "Subscribe to this thread". You'll then receive an email whenever there is an update to this forum thread. For those unfamiliar with this forum software you need to be Registered in order to see the pictures. If you are not registered there's a link to register at the top right. Please note that if you are registering for the first time the system will send you an e-mail with a link in it you'll need to click to validate your account. If you'd like a quick and simple briefing on how we have the forum set up click HERE.

Lastly, I'll leave the thread open so you can let me know what you think if you like.

Stay tuned!

[randylervold]

Let's start with some "before" performance data. As I mentioned above, N56XC very closely matches the performance of a production line Carbon Cub SS with the CC340 in it. Still, let's see what that means. In order to gather some "before" data I took a test hop today and did some screen shots with the Dynon to document things, which is quite a bit easier than manually recording data BTW. I did a Vy climb to 6,000' to attempt to capture climb data, then a cruise that I'll describe below. It was a cold out and so this data probably should be mathematically corrected to standard temps, but let's just take a look and maybe I'll get lucky and be able to test the new prop in cold temps too.

Climb
Three different screen shots below of the climb, all very normal for a Carbon Cub, the VSI is just to the right of the airspeed tape for those unfamiliar with the Skyview display.

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Note that climb is right at 2,000 fpm at 2,400', then decays slightly as I climb, but still is climbing at 1,700 fpm nearing 6,000' when I level off. This is very consistent with what we see in a stock Carbon Cub.

Cruise
For cruise I wanted to establish some sort of standard that I could replicate with the c/s prop, which is a bit hard to do. Here's my test: use a pressure altitude of 6,000' msl, set mixture to 100° ROP and rpm to 2400. Once I get the new prop installed I can use the same altitude, same mixture, same rpm and fuel flow and see if there's any speed difference.
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Again, Carbon Cub drivers will recognize this is pretty normal info with a TAS of around 110 mph at 2400 rpm.


Next report will be once the c/s prop is installed, and I've now figured out how to get rid of the "expired database" warning. ;-)

[randylervold]

Update: 1/9/2015

As expected the course of normal business is getting in the way of progress on my project, but we've made some progress nonetheless. The new prop is here, has been mounted, the governor installed, and work is being done on the controls such that I should be airborne within a week or so for some preliminary testing of the new prop.

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The new prop is a Whirl Wind model 284 which is a new model for them. It features an 84" diameter, all carbon fiber blade construction, and a scimitar-type airfoil. Jim Rust, owner of Whirl Wind Propellers in California, who designs all of the props for both Whirl Wind companies, tells me that even though it looks like a go-fast prop for something like a Lancair or RV, that he designed it for the speed envelope we are operating in. The large diameter should help shorten takeoff roll and climb with the tradeoff being more wetted surface and more parasitic drag. We'll see how this comprise works out.

We have our typical freezing fog here this week but we should be able to get in the air next week. After that it will be on to the panel updates followed by the float install in early February. Expect another update after we've flown it with the new prop.

[randylervold]

Update: 2/25/2015

Progress continues...

New prop
The new Whirl Wind 284 installation got finished and after a few runs to get the governor settings correct for both low pitch and high pitch I took about a 1.5 hr test flight to get to know it and collect some comparative performance figures. These flight tests, as well as the "before" numbers collected and presented above, should not be considered "certification grade" flight test numbers. I think they are however a good representation of relative performance as the most important variables such as altitude and so on, are fairly comparable. I just love being able to do a screen capture with the new EFIS's, all the data is right there. So, let's take a look at few power settings. Note the four power settings below and the TAS as indicated at the bottom of the airspeed tape on the left, then compare with the fixed pitch prop numbers above.

24 squared...
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23 squared...
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22 squared...
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1900 & 18"
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Wow, look at that last one, 107 mph TAS on 5.2 gph! My conclusions from the above is that the plane is about 20-25 mph faster overall, that's a huge increase for a draggy airframe like a Cub, approximately a 23% increase! And what I appreciate perhaps even more is that it gives the pilot the flexibility to customize the power setting for the mode of flight one desires, for example max power & speed, slower with max efficiency, etc. I've found from personal experience in my time with my RVs that rpm is a much larger impact on cruise fuel consumption than does throttle or mixture, therefore the ability adjust prop speed with a constant speed prop is a big tool to use in maximizing cruise efficiency.

Above numbers aside, everything is a tradeoff with an airplane. With this setup we have gained some weight, I'll attempt to quantify that at some point for you, and we've spent more money. I haven't attempted to quantify takeoff performance, that is much more difficult to test accurately. Also, any Carbon Cub takes off so fast that I really don't care if I'm off in 50' instead of 60'. As I fly it more I'll likely develop a feel for whether it takes off any better or worse and report back.

Lastly for this update, I've been told that Whirl Wind Aviation now has this new prop on their web site, details can be found HERE.

[randylervold]

Update: 2/26/2015

I was afraid our rebuild shop would get behind and miss our planned date for float installation, but no, they're right on schedule. It's up on the floats but there's still quite a bit of work to do with the hydraulic gear system, the gear warning system, and all the rigging adjustments.

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I should be able to fly it next week and will make a point of testing speeds at the same power settings as above to check for any difference. I should have mentioned above, the plane was on the new Desser 8.50 x 6" tundra tires.

[randylervold]

Update: 3/12/2015

The E-AB Operating Limitations on N56XC require putting the plane back in Phase I operation if any "major change" is made. Because both the addition of floats and the switch to a c/s prop are considered a "major change" we made a logbook entry putting the plane back in Phase I. As of Monday that period was complete, the W&B info has been updated, and I signed it back into Phase II operation.

We're busy now tweaking little things and getting the plane ready for the big trip to Florida and presentable for booth duty at Sun-N-Fun. Can't wait!

[randylervold]

Update: 4/15/2015

Wow, the past couple of weeks have been a bit frantic, busy with both the normal fray prepping for Sun-N-Fun as well as prep on the amphib project. We've been working through getting the prop governor and cable adjusted correctly, fixing some bugs in the trim that caused it work intermittently, working with Aerocet on an update to the nosegear, and getting the Dynon system tweaked including the autopilot. I think we're there, and we'd better be because I'm out of there tomorrow morning!

Here's what she looks like pre-launch...

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As anyone who's flown VFR cross country in the spring knows the weather can be challenging, so I'm planning various route options with the weather patterns in mind. I'll try to post updates each evening with some pics.

See you in Florida!

[carlconti]

Randy, it is awesome! Can't wait to see it at Sun n Fun. Carl

[randylervold]

Update: 4/16/2015

I am writing this update from Yakima rather than on the road somewhere. Why? When buttoning the plane up late yesterday we discovered some cracks in the gelcoat of the prop...

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We quickly got in touch with Whirl Wind and they concluded that the cracks would likely propagate into the carbon fiber structure at some point, no way to predict when, and it therefore wasn't safe to fly. Mission scrubbed, darn!! Frankly I'd much rather know this now though than find out over the mountains so maybe this is a good thing.

I know there were many folks anxious to take a look at this bird at Sun-N-Fun, and we had a number of demo and press flights already scheduled as well, but safe operation must trump all such plans as I'm sure everyone would agree. I had my O2 system ready and was hoping to see some pretty spectacular groundspeeds by flying high and using the extra speed that this prop provided. I guess that will have to wait.

As yesterday wore on we got to thinking, as often happens around here, and we have hatched an alternate plan for SnF. We had an announcement scheduled for several weeks down the road and we've decided to move it up to Snf. So, stay tuned!

[glickle]

OH NO NO NO! so sorry Randy to hear but still looking forward to flying her one day as sure looks amazing numbers and cool look also . Best Gary