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  #21  
Old 10-02-2020, 05:25 AM
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DanH DanH is offline
 
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An aside for casual readers..

The "RSA-5 class" fuel controls (Bendix RSA-5 and subsequent Precision Silver Hawk, AFP FM-150, and Avstar equivalents) are physically shorter than the FM-200 seen here. The FM200 also has a round, no-flange inlet rather than a 4-bolt flange. The additional length in particular makes good modification of a stock RV-8 snorkel more challenging. Note the very small (actually non-existent) radius where Mickey's snorkel turns into the mouth of the fuel control.

Mickey, this just isn't hard to fix. The minimum effort approach is a simple reshaping of your current snorkel, something like the attached. And as you've no doubt heard, the new IO-390-119 effort for the RV-14 resulted in a good snorkel shape for the FM-200, by test, not guess. It will be an available part eventually, and you may be able to adapt it to the -8 cowl, or the cowl to it.
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  #22  
Old 10-02-2020, 09:58 AM
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rv8ch rv8ch is offline
 
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Default RV-14 snorkel

Quote:
Originally Posted by DanH View Post
...Mickey, this just isn't hard to fix. The minimum effort approach is a simple reshaping of your current snorkel, something like the attached. And as you've no doubt heard, the new IO-390-119 effort for the RV-14 resulted in a good snorkel shape for the FM-200, by test, not guess. It will be an available part eventually, and you may be able to adapt it to the -8 cowl, or the cowl to it.
Thanks Dan - I didn't know about the RV-14 snorkel - will have to keep an eye out for that. You are absolutely right - I need to fix this. I like the idea of buying a solution I can (almost) bolt on - my fiberglass skills are so bad that I can see this taking me months, and I can't stop flying that long!

That said, I need to pull the snorkel off and have a look at what it would take to do what you suggest - might also be possible to safely glass in the flow straightener honeycomb I picked up off of ebay. Rainy weekend here so perfect timing.
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Last edited by rv8ch : 10-02-2020 at 10:08 AM.
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  #23  
Old 10-02-2020, 10:53 AM
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hgerhardt hgerhardt is offline
 
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Here's most of the new RV-14 snorkel:

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  #24  
Old 10-02-2020, 11:04 AM
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Quote:
Originally Posted by hgerhardt View Post
Here's most of the new RV-14 snorkel:

That is a very unique and interesting shape - I wonder if it's fully hollow inside or has some structure there...
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  #25  
Old 10-02-2020, 12:38 PM
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Originally Posted by rv8ch View Post
...my fiberglass skills are so bad that I can see this taking me months, and I can't stop flying that long!
Mickey, this fix should be easy, a few 20 minute work sessions.

Start with a short length of tube, about 1.5" or 2" diameter, and a rectangle of scrap aluminum. Duct tape them together with the scrap tangent to the circumference. Smear a little wax on the duct tape, then lay up three plies of 9 oz plain glass using fast hardener. Set aside to cure.

Make two saw cuts per the black line in the sketch. Remove the light green chunk. Now wrap 80 grit paper around another short length of the same size tube as the previous form, and sand a semicircle per the dark green.

When the fast hardener has the original layup firm enough, pop it off the ad hoc form. It should fit right into the sawed out gap in your snorkel. Reach inside with your fingertip and smear a filet of flox/epoxy in the 90 degree junction all along where the new part meets the snorkel. Again set it aside to cure.

When cured, cut and sand to remove all the excess exterior flange from the new portion. Round off the junction, exposing the flox filet, and lay up one exterior ply over the seam. You can also touch up the inside with some micro if desired. Sand inside and outside smooth after cure. Mount and go test fly.

Will it fix your problem? Can't guarantee it, but I'd bet a cold beer
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Last edited by DanH : 10-02-2020 at 12:41 PM.
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  #26  
Old 10-02-2020, 12:43 PM
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Quote:
Originally Posted by hgerhardt View Post
Here's most of the new RV-14 snorkel:

Actually, I think that one has been discarded in favor of a better one.
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  #27  
Old 10-02-2020, 02:09 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by DanH View Post
Actually, I think that one has been discarded in favor of a better one.
Dan is correct
The snorkel shown in the photo was the early prototype / hybrid made by modifying the original that had been used with the RSA servo that was on the original 390A engine.
It was used for the initial flight testing of the new engine installation until the work was done to tweak the design for making production tooling.

It was at that point things started getting interesting.

We have have a reasonably good understanding of what makes good shapes when efficient movement of air is involved.
Very small tweaks were made to the shape (when compared to the original hybrid version that was used initially) while the final tooling was being made.

That snorkel was installed and everything was great, until we discovered a specific power range/flight condition where the engine was not happy at all.
This shape had very little difference from the current part that everyone is flying on the RSA style injection systems, but it was not working with the AFP.

Don and engineering at Lycoming worked hard to help but but were sure we had some type of ignition problem based on how it was acting. Long story short, we eventually came around to the realization that it was the snorkel. Don tested if for us on his flow bench and said it was horrible

Here is the interesting part..... at some point I discovered that if the (new) cowl flap was open, the engine ran fine. Close the cowl flap and the engine would start its die, run, die, run, cycle.
So just the small amount of pressure change across the inlet filter because of the change in upper plenum pressure with the cowl flap movement, was apparently having a noticeable effect on the inlet flow to the servo.
Redesigned the snorkel to have a very generous turn radius in the inlet run to the servo, and the problem was solved. We had Don test the final version as well and he said it flows very efficiently.

A side note top this (that I almost hate to mention so keep in mind it is just a single data point that was obtained during some other flight testing without any structured test plan).
While doing some flight testing at a dry lake bed (think miles and miles of smooth flat landing area) we did an impromptu test of the induction system by noting the MP value on the EFIS at ground level and then doing a flat out WOT run over the desert at 10 ' AGL. The in flight MP indication was a delta of +0.9 inches (0.9 " of ram air MP boost).
We are not prepared to officially promote this as part of the new design and we have no data for the old version to compare it too, but it is conceivable that closing down the outlet flow on the cowl in high speed flight will help with induction pressure since the inlet filter is inside the pressure plenum.

Here is a couple of photos of the final version prototype of the AFP snorkel.
Note the generous turn radius (about the same radius as the inlet to the servo). It may be difficult to copy this because the new RV-14 bottom cowl was reshaped ahead of the servo to give some additional room, but you should try and copy this to what every degree is possible. Note the photos are of the snorkel taped together after it had been cut in two to use it as a tool for making production tooling. Hopefully they will be useful.
The first is a view straight down from above showing the turn radius. The second looking directly fwd. from the servo side (but upside down). Hopefully they will be useful to those that are doing a DIY snorkel.
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Van's Aircraft Engineering Prototype Shop Manager
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RV-6A (aka "Junkyard Special ")
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  #28  
Old 10-02-2020, 02:38 PM
Mitch757 Mitch757 is offline
 
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I have a snorkel that I purchased from Vans a couple months ago and in checking it out found the outlet flange diameter to be 2 1/2 inches. My Superior IO360 has the FM 150 servo with forward facing cold air sump.

I spoke with Don at AFP when ordering another item and he mentioned that I needed a 3 inch opening mated to the FM 150 or I would lose around 5 hp.

Is there another version of the snorkel that Vans sells or do I have to do surgery on this one?
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  #29  
Old 10-02-2020, 02:51 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Mitch757 View Post
I have a snorkel that I purchased from Vans a couple months ago and in checking it out found the outlet flange diameter to be 2 1/2 inches. My Superior IO360 has the FM 150 servo with forward facing cold air sump.

I spoke with Don at AFP when ordering another item and he mentioned that I needed a 3 inch opening mated to the FM 150 or I would lose around 5 hp.

Is there another version of the snorkel that Vans sells or do I have to do surgery on this one?
The one you have as all that is currently available from Van's (that is why all of the discussion about DIY snorkels).
There will be a AFP version available soon but it will be of no help to you because it is for the 200 series servo which is larger in diameter than the 150 series.
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Hubbard, Oregon
Van's Aircraft Engineering Prototype Shop Manager
FAA/DAR
RV-6A (aka "Junkyard Special ")
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  #30  
Old 10-09-2020, 01:19 PM
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rv8ch rv8ch is offline
 
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Default snorkel

Quote:
Originally Posted by rvbuilder2002 View Post
The one you have as all that is currently available from Van's (that is why all of the discussion about DIY snorkels).
There will be a AFP version available soon but it will be of no help to you because it is for the 200 series servo which is larger in diameter than the 150 series.
Do you think this snorkel will work on an RV-8? I modified mine to add the airflow straightener, and it had a dramatic effect. The idle is very smooth down to about 600 RPM. Everything feels much smoother. I believe I have an induction leak, which I hope to address with Ross's kit which I ordered, but will need to get the induction tubes welded since I have the Superior cold air induction which has fatter induction tubes.

Here's a picture while the epoxy/flox was drying, before cleanup.

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