Finished modifying new snorkel
I finally finished modifying the new snorkel.
As mentioned in the earlier post, the most important step in starting to modify the snorkel for the FM-200 throttle body is first mounting the snorkel to a Bendix style throttle body and taking note of the clearances to the starter, a few pics, and diagrams.
The next steps depend mostly on your artistic/technical savy and fiberglas modelling skills. In all the modifying, adjusting, trimming, mounting, and redoing all steps over again over a period of about a week finally resulted in finishing up. The modifying/adjusting/reglassing the snorkel had to be done in lots of small steps. I tried a bit of modelling with blue foam (Styrofoam) and also with soft filler material covered with spackling paste - these did not work that good for me. The thing that worked best for me was to build up the reglassing first with 0.90" stainless rods and narrow strips of fiberglass trimmings, and then laying patches of fiberglas cloth over the ribbing in 'patches' of area. The 'patching' allowed me to get to the interior surfaces of the patches to smooth and form. It also let me position the snorkel so that the wetted glas patches hung to form the patches in gentle curves (gravity assist) between the ribbing. If you are much more experienced with forming glas using foam molds that may be the way to go to do the glas work in fewer steps.
The resource available for me was being 16 miles from Airflow Performance at KSPA. I was able to take the snorkel and throttle body to Don Rivera and mount it on their air flow test equipment and measure all the operational specs. Everything was well within specs according to Don and his 30 minutes of explaining it all. I understood some of it, but parts of the explanation went a bit over my head.
The things that Don advised as I got more into the modifying was to avoid any air dams in the snorkel, especially at the >90 degree turn into the throttle body, and keeping the tunnel as smooth as possible.
My own vision of how the air was flowing at the bottom knuckel at the last turn seems to suggest that the air needs the extra bit of space to get around that greater than 90 degree turn. So I let the 'bulb' space be as large as I could let it be using the original snorkel form; you have to keep refitting it to the plane to make sure that everything stays compact an within the cowing space. That tight corner bend on the small radius needs a ramp and smooth bend around it into the throttle body.
In the next few days I will post a few of the pics that I took at the earlier stages.
Don Rivera says that there are more than a few aircraft out there using the FM-200 on 360 and 390 size engines and likely enough RV's that have modified the snorkel to fit. His installation manual has a few photos of RV snorkels using the FM-200. In my experience with it, it was accomplished and it does work properly and fits in the cowling and around the engine parts - took some time and a bit of effort.
Simpsonville, SC (SC47)
1946 Bellanca Cruisair 14-13-2 (71 YRS OLD 8/15/17)
RV14A (N14ZT), Ser#140195
IO-390 Lyc Tbolt / CS Hartzell - Currently FWF Kit
Dues paid 11/11/16 (USA 2/67-2/70)
Last edited by jeffw@sc47 : Yesterday at 05:27 AM.