nevster

Hello gents
I have decided to finally finish an arrow pattern ship which I have been working on and off for the past 5 years.
The engine I have installed is an OPS 60 goldhead Super SPA RCA which I bought about 25 years ago but have
only run a few times. Unfortunatey I don't have any instructions for this motor. I have also purchased an OPS pipe
from the United States to suit the engine.

I'm relatively inexperienced with motors other than OS and Saito fourstrokes and have no experience with tuned pipes but have
read a lot of info from the very experienced modellers which contribute to this great website.

For initial testing I set the pipe length at 380mm (15 inches) from the glow plug, used an APC 11x9 prop and 10% nitro fuel.
The motor seems to run quite well although quite rich. At this pipe length I'm getting 11,300 RPM. The strange thing is that the needlevalve seems to do
nothing - I can wind it several turns either way with no difference to the rpm.

When I hold the model vertically the engine richens by a few hundred rpm. If the fuel tank is below half the motor
will stop when held vertically.

Would anyone have the instructions for this motor or be able to offer some advice on the use of the needle valve and recommended prop/tuned pipe length combinations ?

Many Thanks
Neville

doxilia

My Feedback: (3)

Neville,

Did you tach the engine at low? What plug are you using? Fuel (brand, oil)?

Does the engine shut down when the needle is closed? Does it transition smoothly? I don't see a pressure line, do you have one going to the header or pipe?

I'd suggest taking the prop down to an 11x7 to 11x8 for a starters if the engine is newish and bring the rpm up by tuning the exhaust. You ought to be able to get it in the 14K+ rpm on an 11x7 when tuned.

I'm going to look for my instructions.

David

PS Nice Arrow by the way! MK kit?

TFF

What kind of setup do you have? It does not look like you are using muffler pressure. Most guys used a pump with these engines to keep the fuel flowing. With out being able to adjust the needles, the pipe needs to be tuned too. If the engine can not "get on the pipe" the carb will not adjust right. Like above the prop size has to be right.

woodie

I ran an OPS Gold Head 'back in the day' when I lived in the Denver area. Also used an OPS pipe. The engine will turn a 11x7 size prop in the 14K+ range but you have to be very careful with carb adjustments. It is very easy to get too lean with that carb due to it's large intake area. The thinner air at the 5000ft elevation certainly contributed to the marginal fuel draw capability of the carb. I eventually went to a ST carb with a smaller intake area to increase fuel draw capability and the engine ran much more consistently with that setup. However, if you are at a much lower altitude, the stock carb might be just fine.

The Gold Head is designed for high rpms and probably won't be too happy with props larger than the 11x7 if you want to run in the 14K rpm range. The engine was very robust, I never had any mechanical issues with it and ran it for several years. Well built and will certainly 'howl' when set up correctly.

Woodie

jetmech43

My Feedback: (9)

The 11-9 is to much prop I believe

daggets

try to increase nitromethane percentage...
if the combustion is not good, then your needle valve will be not very effective...
clean up the carb..and check the fuel line and the tank...

nevster

gents
thanks for all the good advice. I will take off the carby, clean it and inspect the fuel tank.
I was running muffler pressure - just didn't show up on the photos.

I will also try an APC 11x7 prop. The fuel I'm using is 10% cool power.

At idle the motor is doing slightly under 5000 RPM.

David - the model started out as a polyester fuselage which I "inherited" (see attached photo) - can't remember how exactly,
and then I scratch built wings and tailplane from plans off the net. I'm also trying e-flite electric retracts.


I have considered an OPS pump - I don't think I could actually fit it in however - I'm struggling to fit in the battery
and leads for ailerons, flaps, retracts etc etc


I will let everyone know once I've tried a few modifications
Thanks again

jetmech43

My Feedback: (9)

arrow is an awesome airplane, wish I still had mine

doxilia

My Feedback: (3)

Neville,

I was able to take some snaps of the paperwork that came with my engine (see below). As you can see, the length of the pipe (plug to max diameter) is correct at 38-40 cm. If yours is set at 38 cm (to high point not total length), that should be ok although it might be best to lengthen it to 40 cm to start with - it looks a tad short.

Is that an OPS speed or nitro pipe?

A few further thoughts came to mind: First, I'm not sure your fuel contains any castor oil (unless you've added some) and European engines (especially Italian engines) always recommend the use of a good 50% of castor. You might want to try Omega 10% if Morgan is the fuel you can source as it has 30% castor lubrication which should be just enough to keep the engine happy. Otherwise, Morgan 4-stroke (Cool Power or Omega) contains 50/50 lubrication and is a 15% nitro blend. Could turn out to be a good fuel for it.

As mentioned by others, the 11x9 prop is too much. These engines are designed for high rpm on an 11x7 prop. Max torque is achieved very close to max rpm unlike later design long stroke engines. An idle of 5000 rpm sounds like definitely too much. You should be able to get it down. Also, check the high speed needle for leaks as the carbs had a rather "loose" needle/o-ring fit that could leak if the o-ring wasn't in good shape. You might also want to try a cold plug like a Rossi R4 and R5 if you keep your fuel at 10% nitro or less.

BTW, that looks like an 8 mm carb but given the black needle valve, I'm not so sure - it could be a 9 mm carb. Please confirm which one. Whatever the carb, if you can get a pump on it, it will behave better. it shouldn't be necessary with an 8 mm carb though. I'd get it running right on an 8 mm carb first and then go from there.

Let us know how it goes!

David