Thorp Air Command - T18.net

I have about 20 hours on my new engine/prop combo, including a new spinner with screws attaching both the rear and front spinner bulkheads. After my flight today, all the screws were missing from the front (smaller diameter) bulkhead/spinner. There was nothing different about this flight. I felt no new/different vibrations, and I used the same rpm/mixture setting. The flight consisted of a few touch and go's, a few stalls and then about an hour and a half of straight and level.

I am concerned because ALL the screws from the front bulkhead were gone. I would feel better if only one or two screws were missing after the flight, but not all of them. I plan to remove the spinner and recheck prop torque.

Do you guys have any idea what would have caused all the screws to back out of the spinner?

What prop/combo ? Are there nut plates involved ? I can't see how ALL the screws would depart the AC with a nut plate installation ? Must have sounded like a Vulcan Cannon when the screws departed ! Send pics of your prop spinner install so we can evaluate .

RB

You have a real Gatling gun! First T18 ready for action

I see that one time on a new Mc Cauley prop installed on a Cessna. All the front screws except one was lost in flight around 5 hrs after the first run-up.
The clue was easy to found....The last mechanic replace the 10/32 rusted screws by some very similar M6 Metric shinny hardware. I put news 10/32 screws with nylon washer and 500 hrs later the prop and spinner turned happy ever after....The End!

We need to see some photos to understand the assembly. On this critical area it is very important that all these parts has no free-play.

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Thierry
French Canadian T-18
C-FPVE #091

I use the 10-32 also Thierry, these are button head,socket screws, and they are 304 Stainless. I have to keep the threads greased as they will gall in the nut plate if you are not carefull. Stainless is known for this In close tolerance applications such as using them in nut plates, and the nut plates are tight. The button head is wide and grips a good portion of material when it is snugged up, I hate taking these out as they are tough. I can't Imagine even one of these screws getting loose, I don't like nut plates they will mess up threads on the screws or bolts, but they are needed in some places to keep things from moving around and just have to be delt with. Also, being Allen head, they are easier to grip than a Phillips head and the heads are less likely to strip, the Allen wrench don't slip out and ding the spinner as the screwdriver is known to do........Dan

yes, I cant imagine all the screws backing out of those nutplates, but they sure did. There was no play in the spinner and it was a good tight fit. I have an 0-360 with a wood prop from Performance Propellers. I believe Dan has one of these props with the same length and pitch as me. I'll take a few pics and get them posted.

Wow... hard to believe. They didn't just lose their heads, did they? Dan talking about the SS button head screws put that thought in my mind. If they were really tight going in, and (for instance) you were using relatively low-strength screws like that, the screws could have been fractured or over-stressed upon final tightening. I know that's a long shot. If you have the proper combination of screw & nutplate, and the nutplates haven't been completely worn-out or "loosened" by running a tap through them, it would be almost impossible for them to back out. Sure you put them in? (Sorry - I had to ask.)

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

yea john, I agree, its a weird deal. I know I put them in and I tightened them down. I wipe the plane down after every flight, including the spinner. I didn't notice anything unusual about the spinner when I wiped it down after the flight prior to this incident flight. I also didn't notice anything unusual during my walk around before the flight.

So after 20 total hours, the screws were completely gone out of the nutplates, not just sheared heads. I looked down into one of the nutplates and there were still good looking threads in there, so its like they all backed out on the same flight. The screws were only in and out of these nutplates a couple of times during installation. Frank at Performance Propellers installed these nutplates in my spinner bulkheads, so I may reach out to him to see if he used a tap on some of them. I figure that unlikely, but I might as well knock out that question.

Take the spinner off and try threading a screw in and see if it hits the lock portion of the nut plate . Continue to screw the screw in until past the lock portion to see if that part of the equation is OK ? It may not be an issue , but I would inspect the spinner around the screw holes for any small crack(s) that may have developed from this unusual deal .



RB

Hi Ryan Allen!

Are you absolutly shure that all the screws are in place when you do the walk around before the last flight?
I just say that because here at Mascouche Airport we have a real ''Midnight Parts'' super store...
Aircraft miss some parts in the morning. Sometimes big, sometimes just small SS hardware....
I don't know if your Thorp sleep inside or not!

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Thierry
French Canadian T-18
C-FPVE #091

I feel confident the screws were in and tight prior to this flight although, I did not specifically recall looking at these screws prior to this flight. I am in a locked hangar, but everyone knows where everybody else's keys are hidden. I don't think a thief at this point.

I will be heading to the airport today to inspect the spinner and take photos.

Great!!!!!!
Pictures,pictures,pictures

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Thierry
French Canadian T-18
C-FPVE #091

well, it appears the nutplates are my culprit. They all still have good threads in them, but they never grip the screw like a nutplate should. I can screw them all the way down with my fingers. The screws are correct for the nutplate. I called Frank at Performance Propellers, who advised he had not run a tap through them and was surprised by my information. Closer inspection revealed the nutplates on the larger spinner bulkhead were also the same way. I don't know why none of those screws hadn't loosened or come out.

Frank suggested I try and ever so slightly squeeze the nutplates to make them properly grip the screws. Would you guys agree with that course of action?

I find it hard to believe that ALL the nut plates are this way ? Are you sure it is the correct screw ? You should be able to look at the end of the nut plate to see if the locking portion is still there .

RB

Just a thought, these nut plates are somewhat heat treated, if you can squish em in, then they will be soft enough for the screws to spread em out again, these little bugers are supposed to hold their shape, Maybe they never got heat treated and spread open on the first go around when the screws were put in the first time? Dan

Rich, you are right, it is hard to believe. I have a bag of 10-32 and 8-32 screws from ACS. The 10 is too big and the 8 fits just right. Its just that the nut plates don't snug them down like they should. I think I'll buy some new nut plates, drill out the existing ones and replace them.

Dan, that's a good thought. I hadn't considered that. I Just better buy some new nut plates I guess. Its weird that all are this way, but I don't have any other explanation. Its either the screws or the nut plates.