JordanGrant

JordanGrant

Well Known Member
A question for those with Airflow Performance fuel injectors.
My wife is flying off the test hours back home (I'm deployed right now) and had a bit of a scare last week. After flying 2 hrs in the morning and 2 hrs in the afternoon with absolutely no problems, she was on her way back to the home drome when the engine started to lose power and eventually die (windmilling rpm). She executed the engine failure checklist (switch tanks, boost pump on, full rich, etc), with no success. As she picked out a field and set up for best glide, she also went to idle on the throttle, then back to full power. The engine came back to life for a few seconds before dying again. So she did the same thing over again, same result. This procedure gave her enough extra power to make it to the field and execute a semi-deadstick landing.
Upon taking the cowl off on the ground, she discovered that the air filter assembly had fallen off the throttle body and was resting on the bottom of the cowl, partially blocking air from the throttle body. At full power, the engine was probably flooding (not enough air) and that's why it lost power. As she pushed the throttle out and back in, the engine found a balance where it could run, giving some power back.

My question is thus: Has anyone else had (or heard of) having the air filter assembly come loose or come off? On the AFP, it is held on only by the tension of that round retainer ring. I thought mine was secured tightly, but obviously it was not. If this is the only case anyone knows of, then clearly our procedures are at fault. If its happened to others, then maybe we should pursue a way to better secure that thing.

Be careful out there,

Jordan Grant
RV-6 N198G
In testing while I roast in the desert
 
Good work!

Jordan, I can't help with the air filter, but just want to say congratulations to your wife for getting back to the airfield safely. Great job!
 
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Loss of AFP Air Filter

Such a failure has occurred at least once previously. The in-flight symptoms were similar as was the outcome. We later surmised the ring separated from the air induction tube because of the installation procedure.

In this case, the ring was fastened (and tightened) to the airbox plate prior to being clamped to the air induction tube. This prevented the ring from closing tightly around the induction tube. Installing the ring to the tube first (followed by the installation of the airbox plate) has allowed the air filter housing to remain attached for several years.

Of course, I have no idea if this is the same issue you experienced...

Good luck,

Dean
 
JordanGrant said:
My question is thus: Has anyone else had (or heard of) having the air filter assembly come loose or come off? On the AFP, it is held on only by the tension of that round retainer ring. I thought mine was secured tightly, but obviously it was not. If this is the only case anyone knows of, then clearly our procedures are at fault. If its happened to others, then maybe we should pursue a way to better secure that thing.

Jordan Grant
RV-6 N198G
In testing while I roast in the desert
Click to expand...

Not sure exactly what your talking about but if the securing device is a standard retaining/snap ring (the kind with the two holes for the pliers that get "pried" apart for installation), you should have lockwired it. Maybe you did or maybe you can't.
 
Retaining ring

I cleaned the Allen bolt and the threaded hole with acetone. Then used the blue (removable) loctite.
As mentioned above, tighten the allen screw BEFORE the 4 airbox screws. And make sure the holes in the airbox mounting plate are large enough so they don't prevent the ring from locking on the throttle body.

PS - Drill and safety wire the airbox bolt heads per the service letter.
I don't think you will be able to drill the allen bolt though.

Mark
Flying 06
 
Jordan,
Yes this has happened to me as well though it was only a reduction in power. I also noticed higher than normal CHT's and more heat coming through the firewall to my feet. This was caused by the airbox blocking the flow of the exiting air.

Part of my oil change checklist (25 hours) is to check the security of the airbos. Get that allen bolt as tight as possible! I have had no problems in the 200 or so hours since I started these regular checks.

Scott A. Jordan
N733JJ
560 hours
 
Sounds like a tightened-up retaining ring should really be all that's required. That's what I'm going to recommend to the frau.

I didn't know about a service letter for drilling/safety wiring the bolts. With self-locking nutplates there, I'm surprised it would be necessary. There should be very little stress on those bolts and it would take a heck of lot of vibration to work them loose enough to cause a problem.
 
Re: Air filter Enginee failure

This has nothing to to with an RV but when I was on my last hour of night flying for my private ticket back in 1989, I had a 152 go to no more than 1100 rpm on takeoff about 400 feet agl about halfway into a upwind turn off the end of the runway.

The pucker factor was way high because at KMOR on 23, there is no options for a landing out in the industrial park off the end of the runway. I know you are not suppose to attempt to turn a 180, but I did and survived. I turned 45 degrees at a time to see if I could make it. The 1100 rpm was just enough to get me across the threshold. Thank God there was little to no wind that night.

The problem was the filter screen that covers the air inlet sucked into the carb and choked it off.

We had to push the airplane back to the hangar because it would not develop enough power to taxi back.
 
Service letter

JordanGrant said:
Sounds like a tightened-up retaining ring should really be all that's required. That's what I'm going to recommend to the frau.

I didn't know about a service letter for drilling/safety wiring the bolts. With self-locking nutplates there, I'm surprised it would be necessary. There should be very little stress on those bolts and it would take a heck of lot of vibration to work them loose enough to cause a problem.
Click to expand...

The service letter is ONLY for the four 1/4 - 20 bolts that hold the top plate of the air box to the anodozed aluminum "dougnut" with the allen screw in it.

If these bolts come loose they will go through the intake.......

Mark
Flying -6 (with AFP fuel injection)
 
JordanGrant said:
My question is thus: Has anyone else had (or heard of) having the air filter assembly come loose or come off? On the AFP, it is held on only by the tension of that round retainer ring. I thought mine was secured tightly, but obviously it was not. If this is the only case anyone knows of, then clearly our procedures are at fault. If its happened to others, then maybe we should pursue a way to better secure that thing.
Click to expand...

Yes 2 that I know of have come off, but not with the results you saw.
My self, and the other pilot drilled holes in the ring and the flow meter and safety wired it on.
 
markscogg said:
The service letter is ONLY for the four 1/4 - 20 bolts that hold the top plate of the air box to the anodozed aluminum "dougnut" with the allen screw in it.

If these bolts come loose they will go through the intake.......

Mark
Flying -6 (with AFP fuel injection)
Click to expand...

If those bolts come loose and go through the intake with AFP fuel injection, you have put them on wrong. They come from the top and thread down into the ring (unless this design has changed).

The only bolt inside the filter is the socket head cap screw which tightens the split ring down, and that should be locktited.
 
Jordan:

Yes, this happened to me also. The engine was running rich and slow to come up on power for takeoff. Fortunately, in my case it did not fail.

Upon investigation, I found the the four bolts that go into the AFP supplied doughnut ring were not allowing the allen bolt clamp to securely tighten the ring around the servo body. The solution was to open up the holes a bit on the airbox mounting plate to ensure that the clamping action of the allen bolt would not be impeded. The airbox mounting bolts are secured last during installation. After 160 hours, no further problems, but it remains an area of inspection.

The preflight check on my airplane now includes a look inside the indiction scoop to ensure that the airbox and the inlet are properly aligned vertically. This is especially important on quick turns while away from home base. Of course, this will not be possible if you do not have vertical induction.

Fellow NERV'er Scott Jordan had the same experience as I did when the airbox fell off inflight. We performed the same fix on his airplane and as you can see by his post, no further problems so far.

Does that test pilot wife of yours buck rivets, paint and otherwise fabricate airplane parts too? Does she have any sisters? :)

Hope this helps.
Jon Ross
RV-8 N207RV
 
My advice for RV builders - marry an aviatrix

She bucks rivets, drives rivets, fabricates, paints (!), sands (!!), changes oil, changes spark plugs, and performs general maintenance. Lately, she has been an RV-6 test pilot. And oh, by the way, she's a qualified F-15E Strike Eagle fighter pilot with over 1300 hours in high performance jets.

What a woman, huh? Unfortunately for you guys, she is an only child. After they made her, they broke the mold...

Its good to be me,

Jordan
 
Common Occurrence?

Guys,
I just counted 7 known incidents from the replies on this thread alone. I can't help but compare this potential problem to the fuel tank service bulletin. A lot of guys are out there digging into their fuel tanks to correct a possible problem that has manifested itself exactly once (as far as I know of).

I'm beginning to think that AFP (or we, as a community) should come up with a better way to ensure that the air filter assembly can be safely secured. For such a flight-critical part, there is no current provision to "safety-wire" it on, although I like the suggestion about drilling through the retaining ring into the throttle body - at least that's a positive safety wiring method. It would be best for the experts (i.e. the manufacturer) to endorse that kind of thing, though - or point out why its a bad idea. Or maybe they can come up with an even better way to secure it.

Its possible we could have lost our airplane (or worse) due to that thing coming off. Now granted, most of the blame lies with me since I probably could have checked the security of the airbox more closely. But its happened to others, and although no one mentioned any bad outcomes, someone could eventually get hurt because of that. In fact, I just re-read Greg Young's account of the first (and last) flight of his AFP equipped RV-6 (from the Matronics RV-List). I don't think Greg ever determined the cause of his engine failure and crash, but the symptoms were very similar to what my wife experienced. You never know - might've been the same thing.

Overall, I think the AFP system is awesome and I've been very happy with it, but I think there has to be a way to make it better and safer in this regard. And whatever that is, it should be standard procedure for future (and current?) AFP installations.

Thoughts? Anybody think that's just a dumb, knee-jerk reaction?
 
JordanGrant said:
Guys,
I just counted 7 known incidents from the replies on this thread alone. I can't help but compare this potential problem to the fuel tank service bulletin. A lot of guys are out there digging into their fuel tanks to correct a possible problem that has manifested itself exactly once (as far as I know of).
Click to expand...
There have been at least three engine failures reported on the RV-List due to fuel pickups coming undone. Two ended up with successful forced landings, one ended up with the aircraft totaled, but the pilot survived.

JordanGrant said:
Guys,
Thoughts? Anybody think that's just a dumb, knee-jerk reaction?
Click to expand...
I agree that the AFP filter problem is happening way too often, and it could lead to an accident in the wrong circumstances. AFP should proactively make users aware of the problem, so they can be more careful, and be sure to inspect the filter regularly. A fix should be found, and AFP should encourage owners to install the fix.

Let's not be complacent, just because we don't know of any accidents yet.
 
AFP Mounting Ring Clamping force

Ok, before we ground all the planes again, let's have a look at the clamping force on the AFP ring which secures to the fuel servo. For those who haven't seen one, it is an aluminum ring about 4" in diameter, and about 3/4" in cross section. It is split in one place, and a bolt (I'm guessing it is about a 1/4-20 or 1/4-28 socket head cap screw) clamps across the split.

This size bolt will clamp between 1500 and 2800 pounds when torqued properly, and I would really be surprised if any rings have come off when properly tightened. Additionally, IIRC the designer recommends that loctite be used on this bolt, preventing any loosening of the bolt itself.

The bottom line is that anything can come apart if improperly put together, and there are alarmingly few fasteners in the whole plane which aren't important.

The procedure which should be followed is to torque a bolt, then mark it with inspection lacquer, then torque another, mark it, and so forth. It is tempting to tighten a row of bolts, and then mark them all with inspection lacquer, but you are asking for trouble by doing that.

Let's be careful and diligent!
 
Jordan:

I agree with Alex. If you do the math the clamping force should be adequate; but this is not to say that it could not be redesigned. When I look back at my own experience with this, I can see where I should have been more careful with respect to the mounting plate.

Note that with earlier Van's designs the four bolts attaching the airbox mounting plate used to be inside the airbox. I'd rather have the airbox attached the way it is than have bolts that could be drawn into the servo.

The magnetic alternate air door is another area that Van's reworked, which was really an accident waiting to happen.

Nice to see your wife so involved with the RV. My better half has a similar amount of air time but it was gained while working in the back of a G-IV or Global Express with yours truly up front. She can't rivet too well, but she does point out poor metalwork on the flightline at Oshkosh every year.:)

Jon Ross
 
AFP problems

Well,

I had the entire airbox depart my RV-6 at 9500 MSL. It spread the exhaust pipes and cracked the lower cowl on its way out.

I'm pretty sure that the ring screw was plenty tight when installed, but it may not have had enough loktite.

In thinking it through later, I'm pretty sure I remember some "give" in the throat of the airbox on preflight, that I didn't pay any attention to at the time. If you want to avoid this interesting and entertaining experience, I suggest paying attention to ANY unusual play in this area on preflight. It's on my list in boldface now...

Miller McPherson
RV-6, Aerosport IO360, 750+ hours
Cascabel, AZ
 
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