Variation on a FOD screen
 

Since the statrer motor on my BMT 120 is inside a polished aluminium case, I didn't really want to get it all scratched up by using the same kind of FOD screen as I have on myu Jetcats (where the black plastic starter case won't show minor scratches from the ends of any cut-off wire, I decided to come up with a slight variation on the usual theme. In case it's of any interest to anyone, I'll post some pics here.

A trip to my local Ace Hardware store yielded all the necessary components - a sink strainer of the appropriate diameter, a sheet of rubber for me to make a rear-gasket with (for between the FOD screen and the cowl), and a nice big grommet whose inside diameter exactly matches the diameter of the starter case. As you can see, the grommet has a nice deep channel in it where the cut ends of the strainer will go. (I lost several f the pics I took, so hopefully descriptions of some steps are enough.

RE: Variation on a FOD screen
 

A circle cutting tool was used to cut a suitably sized ring out of the rubber sheet, to act as the gasket between the FOD screen and the cowl.

RE: Variation on a FOD screen
 

I measured the outer diameter of the grommet, subtracted twice the depth of the groove, and cut the appropriate size of circle out of the strainer center ; the grommet was then fed into the hole, and a small bead of glue used to help secure the wires in place inside the groove. The smaller holes for access to the Festos were also made. at this time. Then I glued the rubber gasket to the rear face of the strainer & let everything set.

RE: Variation on a FOD screen
 

The finished item in place. Now all I need is a working engine so that I can test whether the FOD screen does what it is supposed to...

RE: Variation on a FOD screen
 

Looks good Gordon!!!.......

Not all screens are created equal...:D You could have saved yourself some time as the FOD screens from Todd Witkoff at Dreamworks RC have a rubber ring permanently glued to the front of the screen. The cut off wires are trimmed back as to not ever touch the starter motor and the adhesive that bonds the rubber ring to the screen also serves to encapsulate the cut off wires preventing them from possibly becoming FOD themselves. [sm=thumbup.gif]--Just a little heads up for those that want a quality pre-made screen.

..But, half of this hobby is all about doing somethings yourself----Your screen looks fantastic!!!!

Kevin

RE: Variation on a FOD screen
 

I forgot one thing....The outer stainless steel ring aound this type of screen is just crimped to the screen material....It can work loose if the crimp is not done properly at the factory, possibly exposing stray wires that can become FOD. You might want to run a bead of glue around the perimeter of the screen where the screen material meets the stainless steel outer ring to seal it all up as a precaution. Just a suggestion.:D

Kevin

RE: Variation on a FOD screen
 

Didn't know that - thanks for the info. There again, I made this one for less than I would probably have paid for the shipping alone, if I'd bought one ;), plus as you siad half the fun can be in making stuff yourself (I've just finished making my own fuel tanks too - had a blast doing them.)

RE: Variation on a FOD screen
 

Gordon

Looks great and I feel much better using them especially if you happen to leave the runway and start into the grass.

Have you ever measured the Thrust loss or Temperature increase with these screens in place I imagine it's fairly small?
What plane is this going in?

Ian

RE: Variation on a FOD screen
 

I've run engines on test stands with and without fod screen and my thrust o fish weigher indicates no measurable change. EGT no measureable change either.

RE: Variation on a FOD screen
 

I haven't checked the thrust loss, though I could do so once I get the engine running.

The intention is for this to go into my venerable Bobcat ... I needed another turbine for my Hunter, and I've long wanted a BMT to see if it's as good as several reports suggest, but I didn't want two unknowns togeher - so I elected to pull one of my trusty P120's out of my Bobcat, then "split the odds" by putting the known engine in the unknown airframe and vice-versa.

RE: Variation on a FOD screen
 

Hi Gordon,
It would be interesting to measure fuel consumption with and w/o the FOD by placing the fuel tank on a scale when you are running the turbine and calculate the consumption as weight/min.

In some cases the FOD will generate a pressure drop in the compressor inlet. Even a marginal pressure drop will have significant effect of the efficiency and fuel consumption. In general the FOD should have as large area as possible and be as far away from the compressor inlet as possible. The size of the grid is of course also a critical factor. If it is large enough the distance and area may not be so critical. The speed of the air increases exponentially the closer to the compressor you get. The higher airspeed over the FOD the greater pressure drop in generates.

I tested once a custom made FOD and the fuel consumption increased by almost 0,75 litre in 5 minutes flying. This is my safety margin when I land but this time (twice) I had to dead stick after 5 min because of no fuel left. In this case the FOD had a grid that was too fine.

I also find it quite amazing that the FOD distributed by a world known turbine manufacturer has a price of 45Euro when anyone can se that is a conventional tee strainer made in China and some Festo connectors. A total value of less then 10Euro!

/Johan

RE: Variation on a FOD screen
 

:eek:;)

This is my made home in Brazil.

Hiran

RE: Variation on a FOD screen
 

:)

RE: Variation on a FOD screen
 

Yeah - there's definitley profit in it for the manufacturers, but ya know - if there wasn't, they wouldn't be doing it !

Between the time I spent shoping for the parts, and the time spent measuring, cutting, fitting, gluing etc ... I probably have almost an hour's time in my FOD screen - and since I earn $70+ per hour base... ;)

Wonder how much profit festo makes on those connectors ?

RE: Variation on a FOD screen
 

Hi Gordon, this FOD screen fits in a P-120 and you save to cut the hole for the starter.

BR

Jesus

RE: Variation on a FOD screen
 

Indeed - though in this particular case it won't fit on a Bobcat. I need the concave shape of the sink strainer in order to fit the screen within the confines of the wing centre-section with it's carbon fibre deflector plates etc. Depending on the target model, the FOD screen sometimes just has to be reworked a bit.

I imagine that where size constraints are not an issue, your system could potentially be more efficient in certain cases, since the amount of area for the air to get through the mesh to the turbine is more substantial.

Cheers,
Gordon

RE: Variation on a FOD screen
 

Gordon,
Nice work.
I have the problem running around to find the FOD screen that will work for P-60 and P-70. So far nothing can be found.
Not only that. The time to make a FOD screen ready to be resale cost me at least $13.
So last trip in china. I went to plastic mold injected factory and make my own design FOD for P-60 and P70-P160.
It cost me a fortune for the tooling and large quanlity order. But is way cheaper to make one by one here in the U.S.
Next year I'll have enough FOD screen will last a life time.

RE: Variation on a FOD screen
 

Thanks to your information I fited a TAM's FOD screen to my BobCat w.o. destroying the T.E.:D:D

BR

Jesus

RE: Variation on a FOD screen
 

I currently sell a FOD screen to fit the P-60/70's