dieFluggeister

Hey guys,
Received my plans from AMA on a potential addition to my hanger. Plans call for a 0.15 O.S. Max with a low profile Tatone manifold mounted inverted and fully enclosed in a cowl.

Not familiar with this size of engine, do you guys have any recommendations for this or a different engine? Plans are from about '84 so I'm sure there are a few new choices in engines. Being a seaplane I could appreciate all the power for weight and don't mind stepping up to a .20 if the weight is comparable.

Thanks for your thoughts.

jwren00

Maybe this - http://www2.towerhobbies.com/cgi-bin...?&I=LXXD72&P=0

but the "max" sounds like it refers to a car engine. Check out the .12 and .15 OS car engines on tower. I have no idea

mike50

The OS MAX .15 was an airplane engine. I have two of these; they have been very nice running, reliable engines.

combatpigg

My Feedback: (3)

It's been awhile since I shopped the RCU engine review section for .15s, but the one that got my attention was the K&B .18. It had an excellent power rating and was one of the least expensive. The OS CVA .15 is a sure bet, but twice the price. The old MAX term really meant nothing, kind of like MAGNUM when talking about MOPARS. It's all about marketing and sales appeal. I guess you could say that to distinguish a bypass port engine from a new line of Schnuerle port engines, O.S. needed to stick the MAX in there. By the time I got into the hobby, those MAX engines weren't exactly lighting up the score boards anywhere.

The other .15 that can really put out is the RJL CONQUEST, but it is heavier than the other 2 engines already mentioned. Try out that RCU feature forum, it is a quick way to at least get some leads on what you are looking for.

piper_chuck

My Feedback: (12)

The K&B .18 would be a great choice, great power in a small package. Two other good choices are the OS .15 LA, and Thunder Tiger GP-15.

Andrew

Here are some comparative figures -- manufacturers data -- so they should be taken with a grain of salt. Prices are near market.

OS LA .15
Wt. 6.5 oz
BHP .41 @ 17000
~ $57.00

Thunder Tiger .15
Wt. 6.34 oz
BHP .40 @ 17000
~ $50.00

NORVEL Big Mig .15
Wt. 5.7 oz
BHP .50 @ 15700
~ $58.00

NORVEL AME .15 BB
Wt. 6.4 oz
BHP .55 @ 15700
~ $85.00

MAGNUM XL .15 BB
Wt. 5.8 oz
BHP .45
~ $55.00

MAGNUM has a bit of a reputation for spotty quality control and lack of consistancy. Reports I've read indicate that some are pretty good and some are awful.

The power ratings for the OS and TT are both at 17000 -- this may be a little optimistic. The BHP figures for the NORVELs are at RPMs that are more realistic.

johnvb-RCU

My Feedback: (1)

I have a few different .15s - Thunder Tiger, PAW, Enya, HB, Magnum, OS.

Out of them I like the PAW best of all, but if it has to be a glow then the Enya plain bearing is the one. Both these engines may not be high in the max power specs race but they make torque and can happily turn an inch larger prop than others. The PAW will turn 10" props, not fast, but without strain, while the Enya turns a 9*4 very well after it's run in. The TT .15 is quite a sweet little donk with a Bolly 8.5*4 prop, but not a lot of power. The Magnum and HB are revvers and seem to prefer 8" and 7" props. The OS I have is an old Max 3 which went okay on an 8" prop.

Reading the K&B .18 specs in the review section, wow! 1.15bhp from a .15, but then notice the 19,000rpm you have to listen to [X(] while it's making it. I have a K&B .20 Sportster which seems a very willing engine on the little running I have done on it, probably 1,000rpm more on the same prop than an Enya .19 for example.

Choosing an engine for the job is hard if you haven't done much of it. Going for one size bigger to the .20s or .18s might be the safest course. On the other the plan is an old one and engines have increased a lot in power since then so a modern .15 might fine....

Helpful bugger aren't I.

combatpigg

My Feedback: (3)

I wonder what sort of "VOODOO" NORVEL is using to obtain more horsepower at a lower rpm than those other engines? The only difference is the amount of combustion force that is being produced per unit rpm. The equation for combustion force has something to do with cylinder filling, compression, and chamber design. Or maybe they're just stretching the truth? Those HP numbers would seem more believable if the given rpm numbers were higher.

piper_chuck

My Feedback: (12)

Someone in the 1/2 A forum complaining about an engine that's only turning 19,000 rpm? Sheesh, now I've "heard" everything!!!

Andrew

I went back to double check the figures just to make sure my lesdyxia hadn't kicked in and I had typed 15700 instead of 17500. I got the numbers in correctly, but perhaps the webperson flipped them -- . Well, maybe instead of a grain of salt, it should be a spoon of salt.

RPM w/ 8 x 4 3,500-15,500
RPM w/ 7 x 4 3,800-19,000

Here are the listed figures for the Big Mig -- the 8x4 doesn't even get into the max power band. I would guess that the .15's are designed to turn up, much like the .061's. If NORVEL is getting 15500 on an 8x4, I wonder what the other manufacturers are turning?

combatpigg

My Feedback: (3)

Hi ANDREW, No Sir, I have seen those numbers before, and you punched them in correctly. Maybe they just round up to the next highest .5HP? The NORVEL .15 is supposed to be one of the best $60 .15 for SSC combat. I suppose the AME version is just that much better, though too expensive to be legit for SSC. But they would have to be doing something rather REVOLUTIONARY to be able to put out higher HP with less RPM than these other .15s, which are pretty powerful little dudes in their own right!

dieFluggeister

Wow guys, all great information. I leave for an afternoon and come back to a lot of great reading.

On the subject of torque vs RPMs, the plan on this bird calls for a 7"x4" Graupner prop. In this application I would guess that the high rev engine would be favored if only for the limited space allowed by the pylon atop the wing. Stretching the pylon would really screw things up. So I'm thinking the K&B might be the ticket. On the other hand, I see that the 1.15 BHP is with a tuned pipe and 30% nitro, AND the recommeded prop range is 8x6 to 9x5. My plan won't even fit an 8" prop and of course the tuned pipe is moot. Perhaps the K&B is simply too much engine? (I didnt think I'd ever say that.)

combatpigg

My Feedback: (3)

The K&B has such impressive numbers, but I have never seen one or heard about anyones' firsthand experience with them. It weighs the same as a .15, I figured it is a bored out .15, and should turn a 7x4 with the best of them.

johnvb-RCU

My Feedback: (1)

Yer, I gotta say I prefer lower revs and slower flying. My 1/2a engines tend to be side-ports or diesels. I think the hottest one I have is a Cox Texaco that I run with 7" props. Comes from trying to cap the tinnitus level I have from 35yrs of playing in bands I reckon. Pardon?

dieFluggeister

A few more specs on the plane:
Span - 40"
Weight - 40 oz
Wing Area - 250 sq. in.
Wing ld - 23 oz./ sq. ft
Airfoil E193, E193M
5 channel
flaps 65% span

Seems pretty heavy to only have a 7" prop. Since the K&B seems to have the power, would a three bladed prop be of benefit here?

piper_chuck

My Feedback: (12)

A 3 bladed prop would work, but it would be a little less efficient than a 2 blade. Are you sure an 8 inch prop won't work? I've seen prop size recommendations based on the recommended engine size rather than what the plane can really handle.

flying poodle

I am guessing that the prop limitation is due to the engine pylons location. I have a norvel AME .15 in a sig wonder, which replaced the conquest .15. Both of these are speed type engines as opposed to being a lugger lugger.

I would think that a seaplane would need thrust more than speed, therefore the best solution would be a larger diameter lower pitch prop. Since you are limited to a 7 inch prop, my suggestion is that the lose in efficiency with a three blade prop would be acceptable due to the increase in available thrust.

Good luck.

dieFluggeister

That's my thought too Poodle. With the inability to add more blade area with length, the only other option is to add enother blade. Efficiency would suffer but might be an acceptable trade for thrust. With the K&B the power would be there.

I measured and there is only 1/2" clearance between the prop tip and top of wing. I even brought a pic for show and tell.

ptulmer

My Feedback: (5)

40oz!!! No way dude! You can do better than. Modern radio equipment and choice wood, you could bring it in at 32oz or less. That thing would fly with a .15la anyway. Nice planform and a big wing. The Big Mig would probably be my choice.

There's not much to be gained with a three-bladed prop at our sizes, if you can find one that is 7". Pick your engine based on weight if possible. The lighter, the better. (thus, the big mig)

dieFluggeister

Yeah, its kind of a tub, but the weight is all in the wood and the linkages (of which there is a lot) It calls for Futaba s-33 servos all around which are pretty small and only uses a 2 oz tank. But fully sheeted fuse and wings are the killer with lots of ply throughout.

Finding a 7x4P 3-blade is a pretty tall order too. No makey.

I'm thinking before I build a full size, I might knock off a really stripped version for an .074 for which I have all the equipment.

ptulmer

My Feedback: (5)

Be sure to use Lite ply and not birch for everything but the firewall. That makes a very big difference. Balsa doesn't really weigh squat unless they specify oversized stock. I've seen a .40 size plane that was planked with 3/8 and sanded to shape. It flew ok, but was heavier than my b..ls. If he had just dropped down to 1/4 it would have been a decent plane.

combatpigg

My Feedback: (3)

If I was to attempt this project with a .15, there would have to be some major changes. The plans would be there for outline reference, and to get some ideas from, but that's about it. The best flying planes off the water are the light ones too, the same rules apply as when flying over dirt ! If you were to raise the pylon just a little, you could run a MAS 8x3 prop a this will give the .15 its' best pulling power. I have an OS .15 / 8x3 on a 40 oz SSC plane and it pulls it around real good. Of course we're talking about a 64" flying wing where 80% of the models' weight is dedicated to making lift. After seeing what you were able to accomplish with your contest plane, I'll bet you are easily up to the challenge of building this plane lighter and just as strong.