Plenum design for the AFP Servo

I'm in the final stages of forming the intake plenum that connects Van's FI
snorkel to the AFP servo. Before I start laying down fiberglass, are there any
areas I should rework from an airflow perspective?





Right now, my concern is the sharp 90 deg turn into the AFP servo. Would it be
better to contour the outside corner a bit or leave as is? I don't have any
clear pictures of the inside corner but it makes an even sharper turn.

Thanks,
/\/elson

What is the difference betweet the AFP throttle body and the bendix?. I assumed my Vans airbox would fit when I get to that point.
Al Grajek

Differences

Hi Allan,

As far as I know, the Bendix has a mounting flange whereas the AFP does not. Also, the AFP servo is quite a bit longer than the Bendix. Combine these two differences and there is some additional work involved.

Regards,
/\/elson

Flow test the duct

David,

Your part looks OK. Actually it?s the inside corner that is important. What flows best here is a larger radius or flat inside radius (like a ?D? port). In any case you can always send us the duct when you get it finished and we can flow it in the airbox to see how it effects the fuel control metering.

?One test is worth a thousand expert opinions?

Don.

Flat inside radius

Hi Don,

Thanks for the feedback. A flat inside radius (like an extruded 'D' bent around corner) ... interesting. I'll see what I can do. Any clues on what I should aim for before I start moulding back into a circle to join to the AFP unit?

Thank you,

Duct design

David,

Just blend the ?D? shaped duct (flat on inside radius of duct) back to round. If you do this within about 2? from the throttle body inlet it should work fine. You can increase the inside radius which would reduce the area in the curved part of the ?D? shaped port by up to 20%, and not hurt the flow into the engine. Send me a picture of the foam before you lay it up.

Don

Got it. Sounds like it might be a pretty tight fit w/ the cowling and all but we'll see how far I can get. I'll work on it this weekend and get some pictures posted.

Thank you,

Don at Airflow said:

David,

Just blend the ?D? shaped duct (flat on inside radius of duct) back to round. If you do this within about 2? from the throttle body inlet it should work fine. You can increase the inside radius which would reduce the area in the curved part of the ?D? shaped port by up to 20%, and not hurt the flow into the engine. Send me a picture of the foam before you lay it up.

Don

Click to expand...

Reworked plenum

Hi Don,

Tackled the plenum this AM. The horizontal line at the end of the snorkel marks the very edge of the AFP's servo inlet. What do you think?



Thank you,

David,

FWIT I wrestled with what you are doing for several weeks and could not create a plenum I thought was worth using. Seemed like the turn into the FM200 was too tight and too restricted in size, but it was never flow checked so it was just my opinion a result of it looking at it. It pitched the device a week or so ago as I got tired of seeing it.

In the end (it was more work) I modified the cowl to accommodate the "Y" adaptor with straight in ram flow and a scat duct up to a filter at the left intake. The filter housing is home made out of aluminum. I know I suffer some take off performance with as the filter is a Brackett designed for the 172 but for now it works. Going to ram air after take off is noticeable as the engine surges up a hundred or so in rpm. What would be perfect is to figure a way to get a large K&N filter installed, an effort I may tackle some day. I have the proper angle ducting and the filter but have not figured a way to incorporate it into the left intake feature. It would work using internal air but that may be worse than with the Brackett filter using external air.

I can not say enough good stuff about direct ram air. The engine seems to really like it.

Explain please

David,

I?m a little confused. The black line is before the inside radius. If the green foam is the ID of the duct, how will that connect to the inlet of the FM-200? The inlet diameter on the FM-200 (3.25? OD) is 5.8? long. If the end of the green foam (round part) is going to be the part that slides over the FM-200 inlet then the part should work fine.


Don

David-aviator said:

David,

FWIT I wrestled with what you are doing for several weeks and could not create a plenum I thought was worth using. Seemed like the turn into the FM200 was too tight and too restricted in size, but it was never flow checked so it was just my opinion a result of it looking at it. It pitched the device a week or so ago as I got tired of seeing it.

Click to expand...

Hi David,

I'd agree that the turn does seem rather sharp and would not work very well. Many moon's ago, I spoke w/ Don at AFP and he was kind enough to forward some pictures of various plenum installations similar to this. I also struggled with the "Should I go with the RAM air?" installation and what method - there's the 'Y' method, the Rod Bower (sp?) method, or something totally different. In the end, I figured that there's enough folks out there doing it with a plenum design and they seem to be working. I'm very curious as to how this design will flow and I'm sure others would be interested, also. Sometimes it feels that every little "diversion from plans" turns out to be not so little. At this stage, I'm trying to minimise those diversions and I _think_ this is the last one.

David-aviator said:

David,
In the end (it was more work) I modified the cowl to accommodate the "Y" adaptor with straight in ram flow and a scat duct up to a filter at the left intake. The filter housing is home made out of aluminum. I know I suffer some take off performance with as the filter is a Brackett designed for the 172 but for now it works. Going to ram air after take off is noticeable as the engine surges up a hundred or so in rpm. What would be perfect is to figure a way to get a large K&N filter installed, an effort I may tackle some day. I have the proper angle ducting and the filter but have not figured a way to incorporate it into the left intake feature. It would work using internal air but that may be worse than with the Brackett filter using external air.

I can not say enough good stuff about direct ram air. The engine seems to really like it.

Click to expand...

Right now, it's a "build the plenum" job and see how it performs. If the results from Don are average, I may just stick with that. If poor, then I'll take a step back and reconsider my options. Of course, I'm really hoping they'll be "good" so I can move on to the remaining 90% with a big grin on my face.

Take care,

/\/elson

1000 word explanation...

Hi Don,

Sorry for the confusion. Does this clear things up?



A little bit of the foam is wedged into the servo's opening to keep it in place. I've also made efforts to protect the internal parts of the servo from any foam FOD. It's my intention to prepare the foam and the servo's machined OD with mold release, etc and then glassing everything in place.

Thank you,

Continue

Looks good to me. Glass it up then send it to us. We'll flow it for you.

Don

Thank you, Don...

Will do. I'll give you a call to discuss details.

/\/elson