Best Engine for Exp PA-12 on Amphibs?

[Gordon Misch]

I'm working with a friend on an Exp -12 and it's getting close to time to decide on an engine. I'm not the owner, just helping with the build. Right now the owner is kinda thinking IO-340, but he's also talked about 375's and maybe even 390's. The fuel supply system is 3/8 tube, good for 200 HP. The engine needs to be mo-gas compatible. We don't know an empty weight yet, but guessing in the mid 1200's on wheels. We'd be grateful for opinions, and importantly, reasons for the opinions.

Thanks!

 

[Hardtailjohn]

If it's Steve, he needs another 390!
John

 

[Gordon Misch]

Ha! Yes, but maybe not the Steve you're thinking of?

 

[Hardtailjohn]

Ruff?

 

[Steve Pierce]

After looking at the complicated fuel system on the recent MOAC build at Legend why not just a good ole O-360 and a carburetor? Nice and simple.

 

[stewartb]

What’s the planned prop? The engine is only that. The prop is what makes it go.

 

[Gordon Misch]

John, yup. Steve, not sure other than weight and he likes FI for its metering and overall efficiency. Stewart, agree but don't know prop yet, other than it's planned to be either fixed or ground adjustable.

What experience is there here with the IO-340? Good, less-than-good, other??

 

[Bill Rusk]

Gordon

My opinion for what it is worth. You are going to be fighting two issues. Max GW and CG. The 12 has a limiting GW (he is experimental and that will certainly help) and the Amphibs are not going to help; coupled with the fact that amphibious floats will push the CG forward. You will want to keep the front end as light as possible. Constant speed props, 0-390 engines, Fuel injection, etc will only exacerbate an already forward CG problem. You may find yourself adding lead to the tail to get the CG in range which could further reduce an already limiting useful load. I would lean towards a 0-360 (it will likely have more torque than the 0-340). But keep everything firewall forward as light as possible. Lightweight alternator, starter, ignition, magnesium sump, magnesium flywheel, Catto prop, lightest exhaust possible, etc.

Dynafocal mount, fuel injection, CS prop, Angle Valve engine, could easily add 50 pounds FWF and you don't want that. Get the max Hp you can for the amphibious floats but watch the weight like a hawk. It is all a trade off.

"Guys that build heavy airplanes don't fly them much". I have seen this a lot. Guys that don't worry about weight, claim that just put a bigger engine on it.......well..... after a few years their airplane has 100 hours on it. The guy that builds light likes the way it flies, and after a few years he has 600 hours on his cub.

Best of luck

Bill

 

[Gordon Misch]

Thanks Bill, very good points. As experimental, the gross will be over 2000 (I never can remember, 2200 or 2300). But I agree, light empty weight and good CG really matter.

 

[stewartb]

If not using a constant speed, I’d stay at or below 200hp. If wanting to run car gas, I’d favor an IO-375 with max 8.5-1 compression. More torque than a 360, better fuel economy than a carb, better fuel and temperature management. Couple it with electronic ignition to get the most out of it.

 

[Paul Heinrich]

I used the lightweight 180hp Cubcrafters CC-340 with a 3-blade Catto for my Exp. 12. Everyone seemed impressed with the performance. If you think 180 hp isn’t enough power for your needs you probably should think about getting into a different airplane model.

A 12 will never be a 180/185. Few, if any, 12s on amphibious floats are legal with a single passenger and full fuel. Piper set the Gross at 1750 lbs. for a reason. Building an Exp. 12 and arbitrarily setting its max. weight at 2300 lbs. makes it look good on paper, but keep in mind that you will have only anecdotal evidence that the wings will be safe to fly at that weight.

Bill Rusk’s “Building a Javron” thread is a must read. The lower the empty weight; the happier you will be.

 

[Gordon Misch]

only anecdotal evidence that the wings will be safe to fly at that weight

In general, I agree. These wings are certified for the up-gross, from Dakota Cub. Relevant fuselage components have been subjected to engineering scrutiny and have been upgraded from Piper's specs.

Thanks for that input - it certainly matters.

 

[DENNY]

13 rib Piper wings on a 18A was good to 2070 lbs. I would not worry a bit about 2300 lbs Gross weight on Dakota wings. But I tend not to worry that much in general.
DENNY

 

[Paul Heinrich]

Sorry, I didn’t see where it said that Dakota Cub components were being used.

As with all my posts, remember that I am frequently, and once again, wrong.

I still think the lightweight CC O-340 and a 3-blade Catto is an ideal setup for a 12. IMO.

 

[Gordon Misch]

Not wrong at all! I hadn't included enough info re the gross weight. Thanks for your comments.

 

[stewartb]

I recently saw pics of Kirk Ellis’ latest 4-place, with an O-540 on the front. I’ll be interested in its performance.

 

[The Kid]

An 18 on wheels has a gross weight (1750) stall of 43. Seems like Cub Crafters gross weight like 2000 or 2200 lbs years ago was like 55? If that's true, it ain't a cub anymore. So, of course, it starts with your empty weight.

 

[stewartb]

Hmm. I must not have a Cub! ��

 

[mvivion]

13 rib Piper wings on a 18A was good to 2070 lbs. I would not worry a bit about 2300 lbs Gross weight on Dakota wings. But I tend not to worry that much in general.
DENNY

Not in the normal category. Read up on what was required to meet Restricted category criteria.

MTV

 

[stewartb]

PA-12 gross increase never had any work in the wings. They can carry the weight. I wouldn’t want to test it at dive speeds, though.

 

[stewartb]

This topic is comical. Build it light. Grams make ounces, ounces make pounds. Then put it on Amphibs. Or 35s. Those mods add weight and drag and CG. And change the airplane. So we chase a return to the performance of an empty plane on 600 tires. Not very useful but it’s light and flies good. We all accept compromises that increase performance and usually add some weight. As long as the benefit is greater than the penalty the compromise works well. I have a Cub that at 2200# lands at 20 mph. It’s over 1400# empty and I don’t care. It works. If a guy is really frugal with weight he won’t deviate from a 320 or close variant. Yet they do. What they’ll tell you is their level of compromise is the golden line. Less isn’t good and more is worse. Fraid not. More is more.

 

[cubdriver2]

My 2¢
Those that have never flown a truly lite cub will never understand what it is all about.
The E2 at 37HP and 554 that I got to fly a few times was sooooo sweet. It hopped rides at LHV in 90F heat all day long. The Top Cub on amphibs with a 2300lb gross was such a pig it was not even enjoyable.
Bill always say build for 90% of your flying, not the 10% you hope to do

Glenn

 

[stewartb]

My dog weighs 75# and I wouldn’t leave him behind for anything. Maybe I should get one of those mini dogs to save weight? Pass. I’ll add wing and power and smile all the way there.

My 90% is heavy. 10% is light because I’m making freight trips. My planes are built to perform loaded, not light.

To the thread, a guy with Amphibs isn’t flying light.

 

[Gordon Misch]

The owner has decided - he bought a first-run run-out O-320 and will have it overhauled and converted to O-340, 180+ HP with magnesium sump electronic ignition, etc. Should be a dandy. Thanks to all for your inputs.

 

[Gordon Misch]

Next related question: Best prop? Fixed or ground adjustable - -

 

[Bill Rusk]

I will only add that it seems most folks do not change the prop pitch once they find what works, so in effect they have a fixed pitch prop. It adds about 10 pounds over a Catto. But there may be some evidence (I am not entirely sure a good pull test has been done, at this point all evidence appears to be empirical) that the Sensenich prop "may" pull harder than the Catto. Until we have some good apples to apples test, take it with a grain of salt.

Bill

 

[Gordon Misch]

Thanks Bill. Is there any experience here with Whirlwind ground adjustable ? Comparison to Catto fixed?

 

[skywagon8a]

Definitely use a ground adjustable. You have too many unknowns to consider a fixed pitch. What pitch will you order? Will it be the correct pitch? Will it be the correct pitch if you decide to fly without the floats? How many different props do you want to buy before you find the perfect pitch for your circumstances?
Your question should be, "Shall I buy a Sensenich or Whirlwind" ground adjustable?

I have the Whirlwind 200G and have tried many different blade settings before I settled on the one which seems to be the best for my airplane's configuration.

 

[RaisedByWolves]

The ga sensnich pulls better than a Catto. Only downfall so far is how long it takes to get one. I thought the weight was pretty close to the Catto.


Sent from my iPhone using Tapatalk

 

[Steve Pierce]

My Sensenich ground adjustable prop weighs 19 lbs. I changed the pitch quite often. Cruise when I go cross country, middle for daily flying and low for STOL contests. I really like the ability to go 104 mph on a trip or get off really really short in 10-15 minutes.