shade tree engine mount repair

Putting legality (or lack of it) aside for a moment, I see no buckling in those tube halves, and no elongation in the mounting holes.
I wonder if whoever did the repair actually understood how the loads were distributed in the mount (lack of buckling would make me think the main load through that tube was in tension, not compression) and that bodge held together through a lot more than sheer (shear??) luck.
 
AV8R_87 said:
Putting legality (or lack of it) aside for a moment, I see no buckling in those tube halves, and no elongation in the mounting holes.
I wonder if whoever did the repair actually understood how the loads were distributed in the mount (lack of buckling would make me think the main load through that tube was in tension, not compression) and that bodge held together through a lot more than sheer (shear??) luck.
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An engine mount is designed to take 9G vertically and forward/aft, if I remember right. 3G sideways. Now, a bolt through that tubing cannot carry nearly the load as a tube in good condition. The wall of that tubing is typically only about .035" thick; that's the thickness of ten sheets of printer paper. A bolt through that will soon rip out of the tubing when the mount experiences severe loading that is still well within its design limits. Get into some rough air, or crash into the trees, and the engine comes off and who knows where it goes? Into the cabin, with its prop whirling, maybe. In any case, things get ugly.
 
Omalley1537 said:
I believe so. I recall a Biplane, sport, or F1 (can’t recall which) landing at Reno with the engine hanging from cables.

There was also Relentless (sport) having the prop come from together. Not a full engine falling off, but still…
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that was 1981 on saturday, chuck wentwort in formula 1 race 69 flexi-flyer. it had thrown a prop blade and the engine was hanging under the airplane by the safety cables. which were mandated by rule because of the number of thrown prop blades. If i remember correctly, after this incident, re-pitched metal props were banned after that in the formula class.

in kevins case, a new light weight prop they were testing exploded and fractured the crank. it departed the airframe doing considerable damage to the engine in the process. if i remember right, and i have pictures somewhere, it broke three of the four mounting lugs off the case, even with the loss weight from the prop, kevin was able to get in on the ground.

a lanceair 4 threw a prop blade while trying to qualify for the unlimited class (before sport was a thing) luckily the engine mount did not fail and he was able to land it safely.
 
Dan Thomas said:
An engine mount is designed to take 9G vertically and forward/aft, if I remember right. 3G sideways. Now, a bolt through that tubing cannot carry nearly the load as a tube in good condition. The wall of that tubing is typically only about .035" thick; that's the thickness of ten sheets of printer paper. A bolt through that will soon rip out of the tubing when the mount experiences severe loading that is still well within its design limits. Get into some rough air, or crash into the trees, and the engine comes off and who knows where it goes? Into the cabin, with its prop whirling, maybe. In any case, things get ugly.
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My thoughts exactly. Not nearly as strong. The bolt can tear through that tube long before a welded tube would fail. And that connection is not rigid enough anyway - All the load is going through the rest of the mount structure.
 
Did Earl Scheib do the paint job?
 
We have the legality, we have the engineering….. what really interests me is the mindset; the thoughts of the person who designed and performed that repair (attempt).
Only that will help us address & possibly prevent future such findings.

Was it money?
Did the person come from another type of mechanicking background where that was acceptable?
Was it done just prior to a sale, to hide a problem?
A simple FAA hazardous attitude problem?
 
Early T-18s were built with supposedly safe cut down props - after a couple fatal accidents where imbalance from a thrown blade ripped the engines out of the aircraft, it was determined that failure was inevitable with the modified props.

A safety cable is cheap insurance.
 
Where are safety cables attached? I realize it must depend on the aircraft model but; some examples?
I'd think to structure ie tubular steel behind the firewall.
Would this be 1/4" steel cable?
Possibly two cables, two attach points?
 
Let'sgoflying! said:
Was it money?
Did the person come from another type of mechanicking background where that was acceptable?
Was it done just prior to a sale, to hide a problem?
A simple FAA hazardous attitude problem?
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Based on what I've seen and heard over the years, in general, its a combination of all the above except the "sale" item and subjective to the person. Fortunately or unfortunately, aircraft are not fragile machines and can handle a lot of abuse. Stories from the old days prove that as well just as people today justify their actions when it comes to what they personally believe is acceptable on their aircraft regardless if "legal" or not.
 
Every time I see my plane decoweled, I think those 4 little bolts that hold the engine on don't look sufficient, and I wish I had cables in case they fall off.

Then I look at how the engine mount attaches to the rest of the airframe and I don't feel so bad about the engine mounts anymore.

Maybe a parachute? :biggrin:
 
Jim K said:
Every time I see my plane decoweled, I think those 4 little bolts that hold the engine on don't look sufficient, and I wish I had cables in case they fall off.
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Your engine mount bolts are probably AN7 or AN8, so each bolt has a working load of at least 18,000 pounds. Four bolts is pretty strong.
 
IIRC Mooney aircraft have AN 4 ( 1/4 inch ) in shear!


A pilot of a 182 stated he was unable to reduce RPM unless he reduced MAP

a LOT.. With Engine stopped there no issue with movement.

Closer examination revealed the Governor Arm had worn a hole in the

Lower Cowl and the Arm would protrude and lock in place at high power.

This prevented the Governor from moving to reduce RPM.

Reason? There are rubber bushings where the Mount attaches to

to Firewall. These were deteriorated and allowed the lower mount to

swing forward and produce the worn hole.


On floatplanes this bushing is aluminum and I believe that was the fix.

My belief if this area is not evaluated properly at inspections.
 
Dan Thomas said:
Doing it right means taking the engine off the mount, then removing the mount from the airplane, and getting it welded up by a trained and competent welder.

Engine mounts are not something to take lightly. What would happen to your CG if that mount failed and the engine fell off the front of the airplane? Would the airplane be able to glide?
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On an Arrow? No, the airplane would not glide.
 
Let'sgoflying! said:
We have the legality, we have the engineering….. what really interests me is the mindset; the thoughts of the person who designed and performed that repair (attempt).
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Older pilot - 80+. At some point he just quit caring about legality because the consequences were no longer a deterrent. Stopped getting annuals and just fixed it himself. Finally decided to sell and realized backyard repairs were going to cost him money that he needed.

He was 100% hoping the A&P would not spot that repair. When informed, his response was "good catch."

The harsh reality is that age effects us all differently. Some people remain mentally sharp. Others become increasingly rigid in their thinking, lose interest in learning, and may become defiant or paranoid.
 
Ed Haywood said:
Your engine mount bolts are probably AN7 or AN8, so each bolt has a working load of at least 18,000 pounds. Four bolts is pretty strong.
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Cessna often uses AN6 at the firewall. Even on the 185.
 
unsafervguy said:
for the formula class here is everything you need to know.

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Thanks, that's perfect info.
3/16" minimum.
I like the 'wrap around the cluster including behind the firewall method - seems foolproof.
Method A), however says it attaches to a bracket under the head of the engine mount-to-firewall bolt....so if the bolt fails, the cable isn't going to help you. I guess they know from experience this is 'gutenuff'.
 
Let'sgoflying! said:
Thanks, that's perfect info.
3/16" minimum.
I like the 'wrap around the cluster including behind the firewall method - seems foolproof.
Method A), however says it attaches to a bracket under the head of the engine mount-to-firewall bolt....so if the bolt fails, the cable isn't going to help you. I guess they know from experience this is 'gutenuff'.
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Bolts are hardened solid steel. The aircraft frame and engine mount are hollow thin-walled tube. The bolt is by far the strongest component of that structure. It is not going to fail.
 
Let'sgoflying! said:
I cannot think of a single airplane part where I would be comfortable making such a prediction.
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Not really pertinent to the thread, but we engineer several weak links into all sorts of aviation components. The weak link is the part that is designed to fail first, thus, there are parts that we can assure with conviction will not fail.

I believe Ed was saying that the tube would fail long before the bolt.
 
aterry1067 said:
The weak link is the part that is designed to fail first, thus, there are parts that we can assure with conviction will not fail.
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Exactly.

Such as the Piper wing spar failing in order to make sure that the luggage compartment coat hook will never be able to reach failure.
 
Ed Haywood said:
Older pilot - 80+. At some point he just quit caring about legality because the consequences were no longer a deterrent. Stopped getting annuals and just fixed it himself. Finally decided to sell and realized backyard repairs were going to cost him money that he needed.

He was 100% hoping the A&P would not spot that repair. When informed, his response was "good catch."

The harsh reality is that age effects us all differently. Some people remain mentally sharp. Others become increasingly rigid in their thinking, lose interest in learning, and may become defiant or paranoid.
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Not that I would condone his repair, but this is probably the best reasoning I could think of for the condition of the plane. I'd venture a guess that if the guy lived in rural Alaska rather than (I'm assuming) suburban FL, his repair would probably be less shocking.
 
Let'sgoflying! said:
I cannot think of a single airplane part where I would be comfortable making such a prediction.
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Then perhaps you may want to steer away from a career as a mechanic. They tend to make predictions on aircraft every day and sign their names to it. But don't give much credence to what those engineers say as most are simply failed mechanics who don't like to get dirty.;)
 
Bell206 said:
Then perhaps you may want to steer away from a career as a mechanic. They tend to make predictions on aircraft every day and sign their names to it. But don't give much credence to what those engineers say as most are simply failed mechanics who don't like to get dirty.;)
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True. But some of those mechanics could be failed engineers who couldn't drink enough coffee to get through a day of staring at a 4-screen display of CAD drawings designing L brackets and submitting a 120 page Spec Control Document for each one, that a GA mechanic would make in his shop with tin snips and a 1940's brake in about 15 minutes...if he has to hunt for some 2024 T-4.

:stirpot:
 
Ed Haywood said:
Older pilot - 80+. At some point he just quit caring about legality because the consequences were no longer a deterrent. Stopped getting annuals and just fixed it himself. Finally decided to sell and realized backyard repairs were going to cost him money that he needed.

He was 100% hoping the A&P would not spot that repair. When informed, his response was "good catch."

The harsh reality is that age effects us all differently. Some people remain mentally sharp. Others become increasingly rigid in their thinking, lose interest in learning, and may become defiant or paranoid.
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I can understand being old enough to take personal risks that to others seem crazy. But I can't understand not giving a damn about potentially having your plane spin in into someone's occupied home. If he's only flying over farmland and forests, then his logic makes sense.
 
As stated in above post, the entire plane is suspect. An AI would be hesitant to sign off on that IMHO. So high of a chance that something is going to be missed by virtue that there are just so many things wrong.

Sounds like a good candidate for a part out.
 
I have an OLD textbook that shows some type of split sleeve reinforcement

using CLAMPS. I don’t recall the application or conditions. Presume not for

things like engine mounts.

Might have been something that was in CAM 18 along with woven

Cable splices.
 
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aterry1067 said:
But some of those mechanics could be failed engineers who couldn't drink enough coffee to get through a day
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Ha. But I don't think its because they couldn't drink enough coffee. Regardless I hold both pilots and engineers very dear to me as it always equates to endless job security as a mechanic.;)

WDD said:
An AI would be hesitant to sign off on that IMHO.
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Not really. Depends on a number of factors. But this aircraft appears to be a prime candidate for one of those $10k annuals you hear about. Now whether it is economical to annual or repair is a different matter.
 
Hurricane Milton may resolve this issue. Right now we are in the crosshairs.
 
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