RobertV

It can happen to anyone ant any time.....I was having a great time at Superman flying my Kingcat for three days straight with no problems. Then on Saturday afternoon with a big crowd of spectators and a sky full of jets, I started my Jetcat P120 for another flight. My jet was idling on the taxiway near the flight line with the nose pointed into the light breeze as I began to attach the canopy. Suddenly, I saw something float over my wing and accelerate right into the turbine! An instant later it came to a screeching halt as a flame trickled out of the nozzle. My helper, Jamie Snipes, quickly shot some CO2 at the flame to put it out and then grabbed a leaf blower that was fortunately nearby (thanks Jeff Foley!) to cool the engine (since the ECU now wasn't able to to that with a locked up turbine). It all happened so fast!

With the big crowd comes debris and apparently someone dropped a clear candy wrapper that made it's way to my compressor! A few helpful folks had a look and I then plunked my 120 into the waiting hands of John Redman, who disassembled it as I watched in the Jetcat tent. I was real lucky! The plastic simple wrapped around the compressor inductor and there was no damage to anything. John did notice that the inlet ring appeared to be rubbing some upon reassembly so he replaced that. About 45 minutes after the incident, the great guys at Jetcat had me ready to go again. I walked straight from their tent to the BVM tent and purchased a FOD screen.

We all know the impact that debris can have on our turbines. These things are vacuum cleaners when it comes to sucking in air and anything that happens to be floating around. So look around before you run your jet. I know that will be part of my routine from now on!

Here's a couple of pics of my jet that lived to fly another day..............

Robert Vess

Chris Smith

My Feedback: (2)

Robert,

I watched that happen to you at Superman, and was hoping it didn't hurt your engine. I'm really glad to hear you got it back in service. Kudos to JetCat. I've purchased my first turbine this year so I am new to the jet world. In the three jet meets I've attended this year, my informal count of guys using FOD screens is less than 10%. My experience is with full size helicopters and we would never think of running them with no FOD screens or inlet filters.

Is there a reason more jet models don't use them?

CJ

jetflyer

My Feedback: (5)

CJ,

I think the reason some don't use them is because there is no "manufactured" FOD screen available for our turbines. Most FOD screens were designed for something entirely different then for turbine use. But because we do have some viable FOD screen type devices that have been adapted well, it still leaves quite a lot of people looking for one which will fit their turbine easily. For instance, I purchased several strainers of various sizes before I found one that was a good fit. I still had to glue it on to attach it. My turbine is an air start version, which does not have the motor in front for starting that tends to allow for easier mounting of a FOD screen.

I also fly off grass and at times at another location which does have a lot of rocks around. Most nice "jet friendly" fields have pavement and a limited amount of debris which could damage the turbine. So for some a FOD screen would not be necessary. It all depends on ones liking as to whether or not to use a FOD screen. I myself would like to see turbine manufacturers include a FOD screen with every turbine purchase that has been clearly designed to fit their specific turbine model.

JR Gautreaux

Vincent

My Feedback: (61)

A FOD screen is $20, i wouldn`t leave home with out one.

V..

seanreit

My Feedback: (60)

Tell me about it. Buck had a neat one on his oly at Waco, it looked like it was just mesh attached directly to the engine with some sort of adhesive. It looked unremovable.

RobertV

CJ,

Thanks for the supportive words...

I actually must confess that I'm an aero engineer so I approached the reasoning for not using a FOD screen by judging it as a potential performance degradation. In fact, I have flown my jet since this episode and I didn't use the screen I just bought! It is common knowledge in my circles that there is a total pressure drop across a screen. And the thrust is dependent on the pressure rise across the inlet and compressor stage. So a screen must impart some level of performance loss. The question is just how large that loss is and how does it trade off with the operational safety benefits that the screen provides. Has anyone ever quantitatively measured this? I have access to a fully instrumented model turbine thrust stand at N.C. State University so maybe this winter I'll actually do such a test and report on the results.

Whether you choose to use a screen or not, just be sure to clear the area around your jet when operating it.

Robert Vess

seanreit

My Feedback: (60)

Robert, no offense, you're over thinking it. More guys use them than not in my experiance. My jets go very very fast. If I'm losing anything, I don't see it and I've flown both ways.

The question is not performance based on my hundreds of flights. The question is dollars. Does spending 20 bucks to save 1500 repair bill worth it.



You're a smart guy, you'll figure it out.

yeahbaby

My Feedback: (21)

yup just a plain ol' strainer from the kitchen, attached to the removable bullet cowl with shoe goop. works great and it's cheap insurance.

performance drop? I don't notice any on the vertical maneuvers.

c'ya

buck

RobertV

Seanreit,

No offense taken.... I just never heard anyone using a screen state anything about it's performance impact. I do know that I like the thrust I have now and I do know that the screen should reduce it by some level. I'm glad to have a first hand report that the effect is quite negligable. Thanks.

lov2flyrc

My Feedback: (24)

Sure there is.....!

seanreit

My Feedback: (60)

Todd, which one for an OLY?

siclick33

Anybody know of a decent screen for a P80? I thought that a FOD screen would be cheap insurance and bought one but the one I was supplied with was just a mesh that pushes over the starter.

My concern was that where the fuel and gas tubes connect to the engine there were simple holes cut in the mesh. I thought that these were highly likely to chafe and break the fuel and gas lines. I guessed that this was more likely than FOD damage and I therefore decided not to use it.

If anyone knows of a decent screen that fits properly and has 'proper' provision for fuel and gas lines then I may have a rethink.

rhklenke

My Feedback: (24)

Hey Robert,

I have been using a FOD screen on my P-120 for the past year or so, and I have not noticed any difference. I originally got it for the P-120 that will be mounted in my Panther because I didn't want anything from the inside of the fuse to get sucked into the turbine. I'm going to put one on my P-120 that goes into my Eurosport for the same reason.

I had heard from Bob Wilcox that he had tested the FOD screens on the JetCats and it did not effect the performance. However, the shape of the FOD screens he sold went through a major transition - from looking like a round tea strainer to being more form fit to the engine. I also heard that this was done because the round shape could possibly disturb the airflow enough to cause a compressor stall. Obviously, this would be a significant impact on performance

I can't say with scientific certainty what the real story is in either case, so I think the tests you are contemplating would have value. Please let us know what you find. You might also try one of the "tea strainer" shaped FOD screens to see if there is a difference.

BTY, you might be interested that we test flew the twin-engined PCM Models L1011 you saw at NASA Langley at the beginning of the summer. We did the test flights at the NASA Wallops Island Flight facility. The UAV runway there is 750' and surrounded by salt marshes and the Atlantic Ocean. The test flights (3) went well, but we did realise that this model, as well as the 757 "T1" model to come after it, are in a completely different class from what we are currently experienced with!

Bob

RobertV

Bob,

Again, it's good to hear more positive comments about the performance effects (or lack thereof) of the FOD screens. Also, it's easy to see that not all screens would act alike. The engineer in me will probably still require a test this winter just to understand what happens when a screen is installed and what it should look like.

I sent you a PM regarding the L1011 project!

Robert

jetflyer

My Feedback: (5)

Todd,

LOL, Repackaging a $2.99 kitchen strainer under another company's name does not qualify as "manufactured" turbine FOD screen.

$2.99 product reference - Linens-n-Things ( http://www.lnt.com/product/index.jsp?productId=1348592 )
Not sure if you are using this exact one, but it is clearly similar.

JR

PS. No hard feelings man, I just couldn't resist.

Chris Smith

My Feedback: (2)

Robert, and others,

FOD protection was one of the first issues I started asking about for model jets.

I feel the issue may deserve more study. I'm particularly interested in the effects of the relationship between inlet area of the engine and various shaped screens. During the developement of the Army helicopter I've been working on, we spent considerable time measuring the differential pressures between the outside and inside of the plenum chamber area around the engine intake. The resulting data led our engineers to the actual filter/screen area chosen, and what electronics we ended up installing around the intake that might disrupt flow. In flight, we gained power and 30 degree cooler EGTs. Something like a 6% increase in horsepower, even with new pleated K&N type inlet screens. Gone are the screen wire mesh because they don't do anything against Iraqi sand.

rhklenke is right, there is also much to be said for protecting the turbine blades from a small loose screw or washer inside the fuselage.
I wonder if a screen that was larger than the inlet area like half of a football shape would eliminate any potential flow disturbance.

I'd love to hear from more pilots using FOD screens. Maybe the power loss is so small we don't need to be so scientific.

Thanks,
CJ
FTE-T500
building Baby Boomerang
New member of the Nashville band/gang

unknown

The best way to test FOD screen is to try it with the older engine with CP pressure reading. Your compressor pressure reading will tell the before and after reading.

Wren Turbines USA

My Feedback: (39)

A buck ninety-five from Kmart. Held on with an o-ring... No performance loss here.............

Gordon Mc

My Feedback: (11)

I originally didn't have one on my Bobcat, for two reasons:

1) The available FOD screens at the time did not fit in the space available.

2) Most debris comes from below; The deflector plates etc on the Bobcat, combined with the engine position, was supposed to make it pretty hard for foreign objects to be able to get into the engine.

I ended up with some FOD after about 150 flights on my Bobcat. Cost $414 & change to get it repaired, so I went in hunt of a solution and ended up with a FOD screen from Tam.

Gordon

J. Campbell

My Feedback: (31)

When i bought my simjet it had a fod screen in it. Do all simjets come with one or was i the exeption?? Russ

MAX EFFFORT

2.99 at bed ,bath ,and beyond.. marine sealant holds it on, fuel line around starter

Wayne22

My Feedback: (2)

Reasons for a FOD screen:
a) know of a guy who had his hand sucked in a running turbine. He lost the tip of a finger and bent the compressor

b) saw an insect flying over top of our running engine, and get sucked right in. It must have gone right through, and got spit out the back end...the turbine never noticed - fortunately!! ( but it could have just as easily been a candy wrapper with a different end result!! )

c) saw an F-86 land with no nose gear. Touchdown was perfect, but with no steering, the two wheel sabre veered off the concrete runway and scooped up an hand full of dirt in the inlet. The pilot killed the turbine on landing, so hopefully nothing got anywhere near the engine, or was left in the duct work for the next start up.....

I installed a kitchen strainer type FOD screen and honestly have not noticed any change in performance at all.

MAX EFFFORT

oops,, delete plz

Chris Smith

My Feedback: (2)

Robert,

Sorry to hijack your thread, but you've strarted an important discussion. I'm hearing from the posts here that there is a lot of good reasons to use a screen.

I want to find a way to install mine without using sealant on my beautiful chrome inlet.

CJ
FTE-T500
building Baby Boomerang

tomcatman

My Feedback: (2)

In my opinion, I think what you have to ask yourself with regards to an FOD screen affecting performance is.....is the amount of air being fed to the engine thru the inlets equal to or much more than the amount of air REQUIRED for maximum performance of that particular engine? My guess is, the engines are getting a lot more air than they actually need, so I really don't see an FOD screen as something to worry about. Now, on the other hand, and of course this only applies to models with inlets and ducting....if you choose to use a larger engine than the model calls for, then this may be an issue. Inlet and ducting designs deliver X amount of air to the engine area, even worse so with a fully bypassed engine. I'm tempted to say that most designs deliver much more than adequate amount of air, which may be the case. However, even on something like a ducted fan which certainly doesn't compare to a turbine where air consumption is concerned, cheater holes have been known to improve performance. So what does that say about turbines which require so much more air? I think we have to consider the possibility that perhaps turbine engines operating within an enclosed environment (inlet, ducting, bypass, etc..) are NOT getting the excess air supply we might think they are and we SHOULD be a little weary of the design of the FOD screens we choose to use. I for one am not much for engineering and I wouldn't even know where to begin with calculating air intake and consumption and how one affects the other, but the results of such tests, would certainly be interesting to say the least.