MalaysianFlyer

I am about to install the MVVS 45cc in the H9 extra 260, and am wondering if the following steps I plan to take are correct.

1. 45mm standoffs
2. Maximise open area on bottom of cowl for air cooling of the cylinder head [am not so bothered about the aesthetics at this area since its under the plane.
3. Create air dams/baffles to force air into the engine mount box to ensure the carb has sufficent air. [Box is not sealed, and is open to the fuse interior

I am particularly concerned about items 2&3, hope to hear what you experts out there have to say

Thanks

DarZeelon

Suntharesan,


Your concerns are valid and is you do take care of these issues, your possible problems will be fewer.

MVVS have their own stand-offs (#3361/I, #3362/I), but their deepness is 120, or 140 mm, which may be more than you want.

If you install internal baffling, to route the air around the head and cylinder, the exit must be 1.5 times the area of the entry hole(s).
A huge hole in the bottom of the cowl is not necessary. See how it is done in full-size engines.

You may want to block the unused entry hole, so only cooling air will flow through the cowl.

MalaysianFlyer

Dar Zeelon,

Thank you for responding. I was wondering if I was going to end up with "overkill", thanks for putting my mind to rest. I plan to seal the engine box, so that no contaminants from the fues [wood dust, etc] , then make a set of fibreglass "air-guides" to force air into the box for the carb to breathe adequately. Then add another hole at below the spinner line to allow for cooling air over the cylinder head, with a proper exit, based on your advice. I had a look around, and its definitely very workable and should be really effective.

I have seen suggestions of using the velocity stack on the carb and routing it to face forward to "supercharge" the carb [slightly anyway]. Any opinions on this?

Thanks again for the tips, Dar, its greatly appreciated

DarZeelon

Suntharesan,


Theories of aerodynamics often discuss this... Ram-air compression really has any effect only when air is forced in at trans-sonic, or higher speeds... An Extra flying 3-D is a bit slow for this (typical British understatement...).

If, however, you route cool air that has not passed through the cooling fins into the carburettor, it would marginally add to the power.

Use the unused entrance for induction air.

I remind you there are two 'standard' holes at the front of the cowl, to either side of the spinner; so there may not be a need to add another hole below the spinner.

MalaysianFlyer

Dar,

Thanks for the tips

pe reivers

Be sure to guide the airflow through these powerful engines by baffling. Like Dar said, no hole underneath the spinner.
general principle:
guide the cool air up over the engine, and let the only exit be downward through the engine's cooling fins. Try to keep the ignition and carb intake located in the cool air section.
Examples see below

MalaysianFlyer

Pe, thanks for the pictures, looks like I have my work cut out for me.

And also thanks for the prop power calculator you made, it has been amazingly helpful.