Skymaster Viper ..... unexplained crash??
 

Hi guys,

Maybe one of you can suggest what happened here:

http://www.youtube.com/watch?v=LZpv0O1ubMs

.... to end up looking like this:

http://www.youtube.com/watch?v=D3MGph6-6XY

Cheers

Jan

RE: Skymaster Viper ..... unexplained crash??
 

Did he snap?

RE: Skymaster Viper ..... unexplained crash??
 

Viedo comments suggest radio problems.....

Ugly crash that's for sure!

RE: Skymaster Viper ..... unexplained crash??
 

Snapped it right out on the bottom end of the loop. That sucks. I remember when this plane was first built. Beautiful paint job.

Sorry for your loss.

RE: Skymaster Viper ..... unexplained crash??
 

Something induced the spin, looks like lockout or flight control failure. I wonder what the ECU said. It would tell you if it was lockout with a failsafe count.

RE: Skymaster Viper ..... unexplained crash??
 

My first reaction was a snap/spin since it had all those earmarks...dirty, slow, high angle of attack 30+ lbs. and right at the point in the loop that the wing is really loading up. But when I replay it, the speed with which it was rotating would make me take a close look at elevator servo/linkage on both sides. Absent a failure there...it would appear to be a snap/spin.

It was a beautiful ship...bummer on steroids.

RE: Skymaster Viper ..... unexplained crash??
 

o nonononoooo not this one:( my favorite viper

sorry for the loss Mark..hope your new one is on the way

RE: Skymaster Viper ..... unexplained crash??
 

Tip stall?

marcs

RE: Skymaster Viper ..... unexplained crash??
 

George, thankfully it wasn't mine [X(] but is really sad to see nonetheless as I know how much the owner was looking forward to the model/doing this scheme!!

Personally, I think the model is flying too fast for any sort of tip stall and the pull out looks fine for it not to be a high speed stall. I if I had to make a guess I would say one side of the elevators or flap failed and returned to neutral resulting is an slow type aileron roll. The roll rate looked slower than an 'aileron' roll and slightly 'barrelly' which would support that thinking???

What servos/linkages were used on the elevators/flaps?

Rgds,
Mark

RE: Skymaster Viper ..... unexplained crash??
 

sorry mark:D
..still is such a shame[&o]

RE: Skymaster Viper ..... unexplained crash??
 

Same thing happened to my 2m Skymaster Viper. Did a loop, it snapped & went into a terminal spiral. Maybe not the perfect jet it was made out to be in all the hype.

RE: Skymaster Viper ..... unexplained crash??
 

Between 47/48 seconds (freece the frame), you can see atleast the right hand flap is down.
Maybe this induce the spiral stall?
It's hard to see if the left hand flap is also down though.

RE: Skymaster Viper ..... unexplained crash??
 

Sorry if I am going to upset anyone here, but that was clear pilot error.
Too slow, too low and too much elevator. To me it looks as if the loop was started too low and with too little speed. As the ground is rapidly approaching on the 3rd quarter of the loop the pilot heaves on the elevator to arrest the decent. At the speed he was going, and with the drag he had in the gear being out all this did was cause an aggressive stall. This leads to a departure ( Wing drop ) and the ensuing spin.
Other factors to consider are the weight of the model at the time of the crash. I see a beautiful paint job, smoke. Both things which will add to the overall weight of the model, thus increasing the wing loading and stall speed.
Lastly. Where it was flown. I know from flying in South Africa a few years ago, that the altitude and heat can dramatically change the way the model performed. I will always remember my first loop with my Airworld L-39. A ***** cat of a model back in the UK, but it nearly met its end in SA when it was starting to "Bite" all the way around the bottom part of a big loop.
Sorry if thats not want some of you want to hear but thats how I see it.
Jim. Why does there always have to be some sort of "Issue" or conspiracy with your posts? Your right. The viper is not the "Perfect" jet. I have yet to find one that is. If you are looking for a jet that wont snap out the bottom of a tightened loop which was entered too low, gear down and with too little speed, may I suggest you look for something made out of depron, and that has the wing loading of thermal soarer.
Regards Al.

RE: Skymaster Viper ..... unexplained crash??
 

very well sed Ali

RE: Skymaster Viper ..... unexplained crash??
 

From a professional pilot's point of view, you did what is called an accelerated stall. Do a google search on the term. But, basically, an airplane can stall at any attitude, when the wing's angle of attact exceeds the relative wind over the wings.

RE: Skymaster Viper ..... unexplained crash??
 

I believe that the explanation of Ali is the most successful, aggressive use of elevators, with leads that result. In the video premiere of my Vampire, at 2 min ... There is a similar case, the output of a roll, but had more height and weight was lower.

I encourage the pilot and more luck next time, it is important to know what happened.

Norbert

RE: Skymaster Viper ..... unexplained crash??
 

Yes, it is called an accelerated stall!

Accellerated Stall - The accelerated stall usually surprises a pilot because it occurs at a higher airspeed than a normal stall (in which a wing loading of 1 G is maintained). Remember, a wing can be made to stall at any speed—all that has to happen is for the angle of attack to get high enough. As G-loading increases, so does stall speed. If a wing reaches its critical angle of attack when the wing loading is 2 G, twice normal, the stall will occur at a speed that’s proportional to the square root of the wing loading. The square root of 2 is approximately 1.41, so the stalling speed at 2 G will be 1.41 times what it would be under 1 G conditions. Accelerated stalls are often caused by abrupt or excessive control inputs made during steep turns or pull-ups. If you’re in a dive and pull back with enough suddenness and force to load the airplane to a typical design load factor of 3.8 G’s, you’ll enter an accelerated stall if the airspeed drops below 1.95 times the stall speed at 1 G loading (the square root of 3.8 is approximately 1.95).

RE: Skymaster Viper ..... unexplained crash??
 

Yep, they all bite if you pull hard enough, particularly low & slow. http://www.rcuniverse.com/forum/js/f.../sad_smile.gif

RE: Skymaster Viper ..... unexplained crash??
 

That for sure looks like a accelerate wing stall induced by elevator input. When he hit the ground, just look at the impact splash. He was caring lots of speed all the way into the ground.

RE: Skymaster Viper ..... unexplained crash??
 

Yeah, I couldn't believe how much of the jet was actually left!

RE: Skymaster Viper ..... unexplained crash??
 

As any pilot who has practiced accelerated stalls in a full sized airplane would know, you roll the airplane to a 60 degree bank and pull hard on the elevator. You will feel the buffet. When you release the back pressure the buffet stops and you can fly the airplane away from the stall.

Unfortunately In a model we are not given that second chance as we have no warning of the impending stall. It's over very quick.

I have been flying all kinds of models for many years, three months ago I had my maiden flight on my SM L-39.
Plane flew perfect for two minutes. In a tight bank which I thought was not to slow, I pulled on the elevator to tighten the turn (I set elevator throws to factory specs). It was over very fast. As someone said in a previous post, I stood there in amazement not understanding what could have happened. an Accelerated stall is what happened. Full fuel, 33 lb airplane, 68" wing, to slow, to much elevator in the turn. BAM! Over very quick, was for me.

If possible, keep them light guy's.

Stan

RE: Skymaster Viper ..... unexplained crash??
 

Accelerated stall was my first thought, but ya'll beat me to it !!!! Great explinations !!!! When I learned to fly full scale the instructor showed me this configuration. I did many myself, and the numbers said here are correct. Good rule of thumb for me was 60 degree bank in a level situation, pull into the turn and at 2 g's the stall increases 1.5 times... Ie: 60 kt normal stall speed now becomes 90knts. I've seen it happen many times in modeling and guys just don't understand the concept. It will bite you !!!!!


Danno

RE: Skymaster Viper ..... unexplained crash??
 

Yeap, keep them light. Only delta wings can get away with stalls like that...

RE: Skymaster Viper ..... unexplained crash??
 

Ali. No conspiracy at all. When a new model comes out, it is often hyped up to get sales. Little or nothing is mentioned about vices or bad points. All I am saying is I lost mine in similar circumstances. Others have contacted me to say they have lost theirs & don't want to publish the fact on RCU. There are currently no Vipers left flying in Cyprus. They have all crashed.

RE: Skymaster Viper ..... unexplained crash??
 

It looks as though the left flap is fully down at the 44 sec mark of the video...right before the hard left into the spin.