Hello, I remember watching a video posted on you tube awhile back of a maiden on the 1700 P 51. Everything was going well when BOOM.....that prop separated and the vibration just tore the airplane apart in midair.....I noticed more than one person chime in with the same experience.... Well unfortunately it happened to me with this plane....I only had about eight flights on it previously.....I was operating at about 3/4 throttle doing a low pass when it came apart.....fortunately I was able to get it on the ground but couldn't get gear down in time and will need new retracts....I am pretty sure that this is a design flaw and has not been fixed.....It could have very easily cost me the airplane.....Can anyone else chime in on this.....I had balanced the prop ......one blade just broke off at the hub......it was not overtightened.....
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So the prop blade broke right at the hub? If that is the case it was a casting flaw, not design. I have multiple planes with this same design never had an issue yet in 6 years of owning them. At least none that wasn't my fault with a bad landing where I noses over or something like that. Thats just been by my experience, so as far as blowing props or screw plate failure I cannot comment as I have never had one happen with the 5 planes I own that use this design -
I have seen this happen with the 1700mm FMS Corsair. The YouTube video clearly shows the explosion in mid-air, starting at the front and then blenderizing the first 1/2 of the plane. These 1700mm prop assemblies are quite large and the rotating mass is huge. There could be many reasons why this happens but I doubt it's a design flaw throughout the model line. These propellers that come with 4 distinct blades need some special considerations and any deviation from the "proper" set up can create issues down the road.
1. Some folks feel the need to use Loctite on the screws that hold the blades on to make sure they don't back out. This is a really big mistake as Loctite can destroy the plastic on contact. This can create small fracture lines in the plastic or even dissolve the plastic. The prop can stay together for many flights until one day, the stresses and vibrations just makes one or more blades come apart.
2. There are some who consider that those screws need to be torqued on with "King Kong" force. This will create fractures in the plastic around the screw holes of the blade and the backing plate. Again, time and vibration will make one cut loose.
3. Each blade must be weighed and all of them made to weigh the same.
4. The backing plate and whatever associated paraphernalia should be balanced as you would a one piece propeller and marked so it can be assembled in the same way as it was balanced. Some assemblies are more complex (P-51) than on others (Corsair for eg.). The more complex it is, the more attention must be paid to balance.
5. All motor mount screws must be tightened and periodically checked as any that come loose can accentuate any imbalance and work the complete assembly off.
6. Any ground strikes with the blades need to be checked out thoroughly as these can cause fractures in the blade roots and backing plate.
7. There was a time when FMS sold the wrong blades for these planes where the blade root did not seat perfectly into the backing plate. Nevertheless, owners used them and simply torqued them till they "looked right". Unfortunately, they weren't "right" and sometimes, it took many flights before that became apparent.
Instead of Loctite, it might be better to use a little FoamTac on the screw threads. I've flown my big Corsair for 2 years and many, many flights and although a few things on it has broken and come apart, never has the prop assembly given any cause for alarm. Perhaps this wasn't what happened with yours, but it's still a very frustrating and disappointing occurrence.Comment
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I have never had a FMS prop come apart. They MUST be balanced and the screws tightened properly. DocComment
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Well .... I just had another prop blade fail in the hub.....prop was not tightened excessively, was properly balanced...had not had any ground contact...and flown twice previously with no indication that there might be a problem....third flight and she let go at about half throttle.....managed to get it down with minimal damage....but there is definitely a problem with these blades.....bad design....Comment
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Guess it doesn’t much matter as the airplane is discontinued..
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