We stripped her naked.

Vance

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I failed my instructor practical test after eleven and a half hours of oral.

I have 60 days to retest before I have to start at the beginning.

Plan A is to retest in The Predator.

Unfortunately we found a crack in the frame during her condition inspection and she is not airworthy. That is why I borrowed the Cavalon from Air Gyro for my instructor practical test.

It is not surprising after 1,500 hours. She first flew in 1999 but in typical gyroplane years (25 hours per year) she is 60 years old. This is not the first crack we found and it won’t be the last.

A small body mount tab had a void in a weld that created the seed of the crack.

The crack is in a very difficult place to reach where the rear floor, the floor below the mast where a lot of electrical things are mounted and the fire wall come together. The rear rotor control bearing is mounted right on top of the crack. The means tanks off, rear body off fuel system off, rotor control system disassembled and a lot of electrical parts moved (battery, strobe light drive, main solenoid, starter solenoid, the main wiring harness and the left and right brake lines.

Ed and I stripped The Predator naked today and I hope to find a welder at the airport so I don’t have to put her on a trailer.

We also found some corrosion on the rotor blades (bubbling paint) so I have the rotor off to sand and paint.

I would like to have her back together and airworthy in two weeks.

Our daughter Savana is getting married at the end of next week and Ed is very busy with preparations so I will lose my helper for several days and I will lose a work day. I was lucky to get Ed down here today.

Except for a couple hours of test prep ground school I plan to devote full time to the restoration of The Predator.

The picture shows the crack well. There is a long tab on the top that would keep everything together welded to both sides of the break but it is not right.

I have read many NTSB reports where they took off with a known defect and things went from bad to worse.
 

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eddie

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Thats a unusual crack,and in a very odd place for a crack like that.Most cracks appear at

the end of a tube or close to the end not in the middle ?


Best regards,
 

Vance

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I agree Eddie it is a peculiar place for a crack.

I agree Eddie it is a peculiar place for a crack.

Good observation Eddie.

The rear bearing block for the rotor control system tube sits on top of that tab that it over the crack and tries to flex the tube with the crack downward during taxi.

It is going to be a challenging field repair to make properly.

This is a good example of why I appreciate other eyes on The Predator. I did not see this crack; the head mechanic at Coastal Valley Aviation spotted it during her annual condition inspection. I feel it is money well spent.

I intended this thread to go under builder’s corner. I don’t know what happened.

I posted at the end of a long day.
 

Resasi

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I failed my instructor practical test after eleven and a half hours of oral.
I am very sorry to hear that Vance. I do however applaud your dedication and continuing efforts to progress is this field. I have followed your progress on this forum for a long time and it is inspirational.

That is a slightly perplexing statement however, how exactly was the oral exam that long? I am obviously misunderstanding something.

With regard to the Predator, you show a continuing attention to detail and safety that is a great example.
 

Vance

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I wrote about this in some detail in flying adventures; Air Gyro has found their Sothern California representative.

Several people have suggested that eleven and a half hours for the oral was a little long for an instructor practical test oral.

The same DPE (Terry) took nine hours with Brandon who is much faster and younger than me. He has to look up less.

There are areas in the practical test standards that need to be covered and Terry ticks them off as he feels they are covered. The last item was endorsements and I missed one for someone going from being a ground person to taking the practical test for private. This is a special emphasis area and Terry felt I did not demonstrate a knowledge of endorsements.

If I retest within 60 days it should be a much shorter oral.

Terry has agreed to come to Santa Maria and test me in The Predator; substantially reducing the logistical challenges and expense.

I am planning on a couple of hours of ground with a local CFI friend of mine so Michael Burton will be comfortable endorsing me for the retest. I will spend some time over the phone with Michael too.

Now the most pressing task is to repair the Predator so I can schedule the re-test. It has to go through Terry’s Flight Standards District Office and be approved by the Van Nuys FSDO. I don’t want to schedule the test until I am sure that she is airworthy and I have some time in her.

I am headed down to the airport now to prepare things and try to talk a friend at the airport into making the repairs. That will be a lot easier than putting The Predator on a trailer and hauling her to Atascadero for Smokey to weld her. I don’t like to trailer a gyroplane.
 

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All_In

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OK I was disappointed buddy by the bate and switch tittle. Good one!
I do like the way you maintain your aircraft. Good one!
 

L_Butler

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Crack location

Crack location

Vance,
Sorry to hear of your test result. the pressure of not being in your primary machine may have added stress which added to your difficulty in recalling pertinent information.

I'm very interested in the location of the crack. My J4B2 has a frame very similar to your Predator and I'm very concerned when you mention a frame crack. However, I can't identify the location of the frame member that has the crack. It appears to be on the cross member on the front of the mast. Your statement mentions the floor level crossmember but the photo looks like the next crossmember about 16 in above the floor level.

Perhaps it is due to the perspective from which the photo was taken. I'm not able to identify enough of the control rods or landing gear frame to figure out exactly which rod is cracked. Any additional photos or a mark on the big picture pointing to the crack location would be greatly appreciated.

Thanks,
Larry
 

Vance

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Vance,
Sorry to hear of your test result. the pressure of not being in your primary machine may have added stress which added to your difficulty in recalling pertinent information.

I'm very interested in the location of the crack. My J4B2 has a frame very similar to your Predator and I'm very concerned when you mention a frame crack. However, I can't identify the location of the frame member that has the crack. It appears to be on the cross member on the front of the mast. Your statement mentions the floor level crossmember but the photo looks like the next crossmember about 16 in above the floor level.

Perhaps it is due to the perspective from which the photo was taken. I'm not able to identify enough of the control rods or landing gear frame to figure out exactly which rod is cracked. Any additional photos or a mark on the big picture pointing to the crack location would be greatly appreciated.

Thanks,
Larry
You have it correct Larry; it is the cross tube at the front of the rotor tower.

I took another picture from beneath the engine forward.

This tube supports the rear bearing for the control tube; that is what the plate with the two holes in it does.

The answer for why it broke where it did came to me in the night.

When I taxi with the cyclic forward the trim spring is pushing back and pushing down on this fairly long tube.

Any time I push forward on the cyclic I am putting down force on this very long tube.

When I pull the cyclic back I am bending the tube upward. In a steep turn that can be quite a bit of force.

The Predator has over 1,500 hours on her and the thousands of cycles are catching up with her.

None of the tubes we repaired have broken again.
 

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L_Butler

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Which tube

Which tube

Vance,
Thanks for the follow up photo. I know which tube you are talking about.

I'm concerned with your speculation about the cause of the failure. If you are correct, it implies that you are working above the endurance limit of the steel. That would mean that such a failure may happen again after the requisite number of cycles. While that may be another 1500 hrs, it could easily be less or more. Certainly you will want to inspect it on a regular basis and modify the tube or bracket mounting design if it happens again.

In any case, I'm glad you caught it before any significant damage occurred.

Thanks,
Larry
 

Vance

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Progress.

Progress.

We made some progress today and I can reach things well enough to begin the repair.

My friend Joe who did the fabric on The Predator’s empennage will bring his welding equipment to the hangar on Wednesday.

The picture is the top of the bracket where the rear plastic bearing for the rotor control attaches.

I tested my theory by pulling down on the tube and the crack opened up.
 

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eddie

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The crack makes sense now,proper reinforcement will take care of that.



Best regards,
 

bryancobb

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Vance,

You probably already know this but CroMo tubinq welds need to PWHT to prevent crackinq. (Post Weld Heat Treat)

I`m not sure if aircraft tubinq is 1.25% or 2.25% Chromium. If 1.25, it needs 1200 DeqF for 15 minutes after a fairly slow warmup followed by a fairly slow cooldown.

If 2.25, it also qoes up and down slowly but stays at 1250 DeqF for 15 minutes.

Aircraft Spruce will send you an MTR (Mill Test Report) for aircraft tubinq to let you know 1.25 or 2.25% Chromium.

In the old days (probably now too) provisions were made so the inside of every tube qets coated with linseed oil.
 

Smack

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triangulation

triangulation

I agree with Larry and Bryan's material observations.
Additionally, you might consider adding another member or two to create a triangulated load-bearing component that would flex less.
Of course, engineering stress analysis first.
Brian
 

Vance

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The Predator is made from MIG welded mild steel.

In my opinion she is holding up well.

So far none of the cracks in the frame that we have repaired have cracked again in the same tube or near the same tube.

We are probably going to gas weld this.

We will be using a fish mouthed doubler on the repair.

In my opinion there are several logistic reasons not to add structure to the area so beyond the doubler we will not be adding structure.
 

bryancobb

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So not AC Tubinq?

So not AC Tubinq?

...The Predator is made from MIG welded mild steel...
Did the builder fabricate the frame from non-aircraft qrade materials? That would surprise me since CroMo tubinq in sizes for aircraft is cheap as dirt.
The method of weldinq does not eliminate the need for PWhT.

Most experimental aircraft builders use aircraft qrade stuff on most thinqs that are as important as structural parts, fliqht controls, and frames .
 

Vance

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Did the builder fabricate the frame from non-aircraft qrade materials? That would surprise me since CroMo tubinq in sizes for aircraft is cheap as dirt.
The method of weldinq does not eliminate the need for PWhT.

Most experimental aircraft builders use aircraft qrade stuff on most thinqs that are as important as structural parts, fliqht controls, and frames .
As I wrote in post #14 The Predator frame is fabricated from MIG welded mild steel tubing.

This thread is about repairing a crack in The Predators frame and getting The Predator airworthy that I am hoping to accomplish in two weeks so that I can take my practical test in her before my eleven and a half hour oral expires.

If you want to post things unrelated to this simple repair please start another thread.
 
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PW_Plack

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Did the builder fabricate the frame from non-aircraft qrade materials? That would surprise me since CroMo tubinq in sizes for aircraft is cheap as dirt.
Mild steel is not automatically a "non-aircraft grade" material. Some Aeronca Champs used 1025 steel fuselage tubes, and that was a type-certified design.

If you want to start down that road, you'll want to shield your eyes at any gyro meet. Wheelbarrow wheels, screen door springs in trim systems, auto conversion engines are all "non-aircraft grade."

The Predator's first powerplant was an O-290 ground power unit designed for running APUs, as was the turbine powerplant used in the Helicycle and Mosquito.

Welcome to the world of experimental aircraft!
 

bryancobb

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... If you want to post things unrelated to this simple repair please start another thread...
Thanks Paul,
I was not aware ``mild steel`` was used in the Aeronca. I am pretty used to the exp. technique of usinq anythinq that`s nearby. I still find it unlikely that someone would put toqether a frame for an aircraft out of mild steel when the real thinq is plentiful and cheap.

I truly think determininq what material your frame is made of, why it cracked, how to properly repair it, and how to PWhT it to prevent crackinq aqain...is VERY ON TOPIC.

I don`t think your frame would be ``mild steel`` tubinq unless it was built by someone who knows nothinq about aircraft. It is most likely CroMo and is very susceptible to crackinq unless it is properly stress-releived.

I would think you`d be a little appreciative for my input based on experience I have in tis specific area.
 
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eddie

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Mild steel frames really don't need stress relieving if you know how to weld them properly

I have built midget and full sized sprint cars using 1020,1025 seamless tubing without any

problems. Mild steel tubing tends to take vibrations and crack less than harder steels.

Piper cubs also used mild steel tubing as did most of the pre and post war II small planes

of that period. Mig welding would be better than gas welding,with regards to frame stress.


Best regards,
 

Vance

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Thanks Paul,
I was not aware ``mild steel`` was used in the Aeronca. I am pretty used to the exp. technique of usinq anythinq that`s nearby. I still find it unlikely that someone would put toqether a frame for an aircraft out of mild steel when the real thinq is plentiful and cheap.

I truly think determininq what material your frame is made of, why it cracked, how to properly repair it, and how to PWhT it to prevent crackinq aqain...is VERY ON TOPIC.

I don`t think your frame would be ``mild steel`` tubinq unless it was built by someone who knows nothinq about aircraft. It is most likely CroMo and is very susceptible to crackinq unless it is properly stress-releived.

I would think you`d be a little appreciative for my input based on experience I have in tis specific area.
I know the material the Predator is made from (mild steel) and why the frame cracked where it did.

I shared this experience on the Rotary Wing Forum to remind people how important it is to carefully inspect their own gyroplane and the value of having more knowledgeable people inspect it.

I was not trolling for insults or opinions based on confusion.

I suspected that you were preparing to call someone ignorant to aggrandize yourself Bryan and that is why I asked you to post your unrelated irrelevant opinions somewhere else.

The Predator is a one of a kind gyroplane and was not designed for an IO-320 or to be flown in air shows.

Mark Givans had no reason to imagine The Predator would be flown 1,500 hours because he flew her less than 25 hours per year which is typical for an experimental gyroplane. 1,500 hours would have taken him till 2059.

The knowledge of the designer/ builder is demonstrated by how well The Predator flies and how long she has lasted.

I have demonstrated my knowledge by maintaining The Predator in airworthy condition for more than 1,300 hours.

I have only had to put her on the trailer to bring her home for repairs once and it was not an airframe challenge.

We (Joe, Rich and I) will repair the crack in the frame on Wednesday welding the mild steel tubing and mild steel doubler with gas and the repair will probably last till I am too old to fly her.

It is my understanding that Mark was concerned with the way 4130 work hardens

He felt the inherent shaking of a gyroplane might work harden the 4130 causing problems.

He knew how to MIG weld and was not comfortable MIG welding 4130.

He had several knowledgeable aviation contemporaries who concurred with his opinion.

I suspect none of them would have cared that you thought (incorrectly) that mild steel was not aircraft grade material.

I know I don’t.
 
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