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04-22-2013 | 08:55 AM

#19

JackD

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RE: Another Fine Day With FEJ

Quote:

ORIGINAL: Aussie Bart

Dubd

I know your pain and some of your frustration. I too had the FEJ F14 although 1:8.75 scale fitted with 2 x P80's. It flew like a treat but every time I flew it I expected the wings to clap due to all the bad press on this forum however its final demise was my fault!

One day I was on a high speed pass low pass and could see the Stb fin banging side to side about 4 inches from 200 mts away, backed off the noise and dropped the gear and swung onto downwind to set up for landing. We could all still see the fin banging side to side when all of a sudden it departed the fuse when opposite us. The plane just kept flying as though there were no problems so I went through the normal landing procedure onto base and then onto final but I had let it get too slow and the inside wing stalled and she rolled in, total fuse loss but I had time to kill the donks so no fire.

First thoughts were bad flutter issues similar to B1 Bob and straight away started getting dark about FEJ, however some of the boys at the club had gone off and collected the fin while me and a few others were collecting the remains and what I found when the fin came back was a sombre reminder not to cut corners.<o

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>When I built it I decided to change the rudder control by fitting JR DS 168 thin wing servo's into each fin to get a more direct drive onto the rudder which I still believe is a better idea but I got slack and used the plastic servo arm that it came with. Well you guessed it, the servo arm was broken but the servo gears were just fine so the most likely cause of the failure was the arm snapped and the rudder just became an uncontrollable swinging mass.

Next day I went for a drive and held the fin outside the window into the airstream to see if the rudder would oscillate, even at a low speed of 30 kph, it became so violent that I struggled to hold onto it.<o

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>The other things I found on post crash examination were that the wing structure and wing box assembly were actually very strong and were not likely to fail. The amount of force caused by the oscillations was so big that the carbon rods in the fin had actually snapped with the remainder still in the intact clamps in the fuse. The first time I left plastic horns in a jet cost me a bucket of cash.<o

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>I also have a gen 1 1:6.5 FEJ A10 which was one of the very first out of the factory and I had issues with the wings. I had a lot of trouble with the factory trying to get them to review the design and was not the only one but eventually we sorted out the problems.<o

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>As I said earlier, I have experienced a wide selection of the mainstream manufacturers and keep coming back to FEJ simply because I like the big scale military stuff. I have just ordered the 1:4.6 F16 and like I always do, will go over it and modify area’s I personally feel are not right!<o

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>History is littered with these same stories but with different brand names, even BVM and the big Germans had serious issues and unhappy customers in the day, the only difference was there were no forums back then. These guys don’t have problems these days but they also don’t bring out any new planes. <o

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>I am truly sorry for your loss

Bart, not sure I follow. Why was that your fault? you are saying that the rudders will oscillate violently even at 30mph.
Plastic horns are OK. I have no metal horns on any of my planes, including the F100 and Rafale, which are super high performance (speeds similar or higher than sport jets)

I think there is a design issue. a surface should not be kept steady by pure brute force from the servo.

For example, on the BVM sabre, if you don't balance the rudder (like the full scale) it will flutter. So you either do it scale with the mass where is supposed to be (and BV gives you instructions on how to do so). Or you make the rudder smaller (leave the top 3rd fixed). Up to you how to solve it.

We encountered the same situation on the rafale, and also modified (instructed by BVM) the rudder (fixed the top 25%)

So, not sure you should blame yourself for this one.

Just a thought
Jack

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