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I'm building a 72-inches wingspan (about 800 sq. in) Scale PBY-5 Catalina (flying boat version, no wheels) http://pages.infinit.net/heliweb/pby5.htm and I'm planning to use two .25 engines with a small 2oz round tank (header tank) in each nacelle connected to a bigger 10 oz tank (main tank) in the fuselage. I'm looking for slow scale-like flying so high performance is not an issue here.

My first choice was to use OS .25 FX engines (length of 3" from backplate to front washer) but after doing some measurements I found that the nacelles are quite small, and the only engine that will fit without major cosmetic modification of the nacelles are TT .25 GP (2.65" from back plate to drive washer). Maximum propeller diameter is 8-inches.

My questions are :

1) Is the TT .25 GP bushed engine coupled with a 3-blade 8X6 propellers is a reliable setup to use in this plane or do I need to use a higher performance ball bearing engine ?

2) Should I expect any problem with the headers and main tank setup. Assuming a standard muffler-pressurized main tank (no pump) in the fuselage (under the pylon) connected with long fuel lines to the 2 oz header in each nacelles just behind the engines firewall. The two engines will share the main 10 oz tank.

Thanks for help

http://pages.infinit.net/heliweb/pby5.htm

UkerDuker

My Feedback: (3)

I am working on solving the same fuel plumbing issue. I am building an E-2C Hawkeye and the engine nacelles are very tight after installing the engine and retracts. I will be experimenting with 2 header type tanks first, because its the cheaper option. If that doesn't work, I will have to decide whether to buy a Cline or IronBay fuel regulator. After measuring, I will have about 12-15 inches of fuel line between the main tank and the engine. I don't know if the header tank will work in this situation. Plus, another thought, if one engine flamesout, will that engine be flooded with fuel from the operational engine still pressurizing the fuel system?

There are several postings on this site explaining these fuel plumbing issue. Just search for fuel regulators or fuel pumps. Another option is the perry pump, but I have no working knowledge of these pumps.

Mike

William Robison

My Feedback: (3)

You are indeed doing a high roll with this one. I have serious doubts about a six foot flying boat getting off the water with a pair of 0.25 engines. With a long enough runway it would probably rise off ground, but the water is a lot more drag to overcome. Give it a try, you can always put bigger engines in it.

A common belief about header tanks is that the engine only needs to have enough suction to pull the fuel from the header tank. This is not true. The engine has to pull the fuel from the header tank, yes, but at the same time it has to pull the fuel from the main tank to the header tank. Hydraulically, the engine sees only the draw from the main tank.

If your main tank was up in the wing, your proposed system might work very well, but having to lift from the fuselage up into the wing probably will not. Muffler pressure is not adequate.

Using wither the Iron Bay or Cline regulators will work, but you may have to go to crankcase pressure to get the feed. Fuel will not run from a dead engine, the regulator will cut it off. You will need a regulator on each engine, of course.

I am not a fan of pressure beyond that from the muffler, any leak will fill the fuselage, the wing, or both with whatever fuel you have on board. the 0.25 engines are big enough to use Perry VP-30 pumps, and they are less expensive than either of the regulator systems as well.

With either the high pressure or the pump system the header tanks are redundant. just an extra complication, and another several connections that could leak. If you need their capacity to get the fuel volume you want you can use them, a larger main tank is the better way to go.

Also with either system, install two clunks in the main tank, one for each engine.

I went through all this with my C-3/10 twin, the main tank, header tanks, for the last eight years or so it has had a VP-30 Perry pump on each engine, no header tanks, and a single tank in the fuselage. With two clunks and a vent to the atmosphere.

Just one additional note: the clunk for the right engine is about 1/4" shorter than the one for the left - this way the right engine will die first if I overstay my welcome, right engine out is easier to fly than left engine out.

Bill.

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If I remove the header tank I gain engine space in the nacelle so I can install OS .32 SX or even a OS .40LA. But the problem is the propeller diameter, which cannot be more than 8" and I'm not sure this size will work with an engine bigger than .25.

I will use the Perry pumps with a single main tank in the fuselage without header tanks so it should work fine as you explained.

William Robison

My Feedback: (3)

HR:

That means it's time to consider athree bladed prop.

Bill.

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So Bill, do you think a 3-blade 8X6 could give enough load on an OS .40 LA ? Any suggestions ?

William Robison

My Feedback: (3)

HR:

I think I would be tempted to cheat and move the nacelles out a little bit. With a 72" span who's going to notice that 3/4" error from the centerline of the plane to the engines?

I wouldn't use the LA engines. Similar price, power, and weight can be had with the K&B 4011 engines. The LAs are ABN and a plain bearing crank, the 4011s are ball bearing crank with a ringed piston. Outlast three or four LAs. For more power, again with similar weight, go for the Magnum XLS 40 or 46 engines. Again, same price range. The XLS 46 spins a Zinger 10x6 three blade very nicely.

The C-3/10 I mentioned before has the Magnum XL 46 engines with the Zinger 10x6 3b props, I'm happy with it.

Bill.

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Thank you for the infos !

teemto

A fellow modeller put two .40LA's in a ~70" Kyosho Catalina, and soon they appeared way too strong. Now his Catalina flies with regular OS 15 LA's and it has enough power for water takeoffs. Of course it's not a speed demon but the real Catalina wasn't either...

I'm currently working on my Catalina (the same Kyosho ARF) and I put two Magnums XL15A in. The same weight as OS15LA, slightly more power (I hope...), ball bearings, and "normal" carburetor with two needles (not an "air bleed" like OS LA's).

jaka

Hi!
I have flown the Kyosho Catalina (174cm in span) with two OS .15 LA engines for 5 years now and they are certainly proving to be just perfect for this airplane. I'm using 8x5 APC props and 15% all synthetic fuel (Motul "Micro" ) and 5% nitro.
I only use full power at take off, as soon as the Catalina leaves water it cruises at half power or slightly less than half throttle. No water rudder is necessary on this bird. It steers fine using just side rudder.


Regards!
Jan K
Sweden

teemto

Hello Jaka !!!

Greetings across the Baltic Sea!

I have chosen Magnums (except that they have ball bearings and better carb) mostly because all the world here flies with OS Max (I have some OS-es too)

But I have another question - as far as I remember You have altered the angle of attack of the wing in Your Catalina ??? Am I right? Have You changed both wing and horizontal stabiliser or the wing only ?

jaka

Hello!
Yes! I altered the wing incident to make it look more like the full scale PBY Catalina.
I repositioned the wing 6mm higher up at front. Did no alternation to the stabposition but made a new elevator linkage inside the fuselage with internal wire steering.
I don't think any other 2,5cc (.15) engine is lighter than the OS LA .15 or throttle as good ...I used Magnum .15 prior to using the OS LA and those did not throttle as well.

Regards!
Jan K
Sweden

teemto

Hello Jan!

6mm is a significant change... Don't You have problems with e.g. "pumping" or different behavior with slow and high speed??? Should fly slower at all...

With the Magnums - for now only couple of runs on a test stand - perfect behavior, no problems, stable low RPM-s, good power, good transition from low to high - I can say nothing bad about those engines...

BillS

My experience is that two wing engines sharing a single fuselage tank will represent a problem, which can easily be solved by using two fuselage tanks. In my case mixing the muffler pressures from two engines resulted in an 800-RPM loss on one engine and finicky needle adjustment on both engines.

Single 6oz tanks per engine were being used successfully for 25 or so flights. Wanted more capacity so a single fuselage tank was added to feed the 6oz tanks. Thirty minutes of ground testing and adjustment proved very disappointing. After a day and a half of thought the single fuselage tank was replaced with two fuselage tanks. During ground testing it was immediately apparent that the engines were back to original operation.

The fuselage tanks are approximately the same height of the outboard tanks but the fuel lines are 21” to 22” long. The four tank setup has been in use during the last forty or so flights. The engines start easier by hand priming because it does take a few moments after starting for the lines to come up to muffler pressure.

Pictures were posted earlier in the forum.

Another approach to consider is oval tanks in the wing one bay over from the engine, which will shorten the fuel lines. I am working on two current projects with oval wing tanks and plan to omit the header tanks unless they prove to be necessary. Simplicity is sometimes better for me.

Bill

jaka

Hi!
My Catalina behaves just as any other plane, no different trim when flying at slow speed compared to full speed. As normal I trim my airplanes so that at full speed they fly straight and level.
The Kyosho Catalina is light in weight and behaves like a 2m sailplane in flight. Slow and gentle flight is possible with the engines spinning at just over idle speed. Large Loops and stall turns are easily done at full speed. It also does nice rolls and flies inverted quiet good.
As for fueltanks in a 182cm (72 inch) span Catalina I would definitely go with a Tettra "Bubbleless" fueltank as these are rather long and slim. 85-110cc is enough for a Kyosho Catalina powered with a 2,5cc engine and 150cc would be OK for a little larger engine like the .20-.25 in a little larger Catalina...OS .15 LA engines might work in a 72inch span Catalina but it all depends on the weight/wing loading.
I don't think that fuselage mounted tanks are any good in any twin engined airplane but provided a pump is used it naturally could be done.
Keeping things simple is what I strive for.

Regards!
Jan K
Sweden