Tail blew out -> crash. Why?

[Jotto]

A friend of mine with a T-Rex 500EFL PRO/3GX had a crash today. He uses an 8FG Super and S-Bus. I'm trying to help him find out why.

What happened was that he did a high-speed backwards loop. All of a sudden, when giving more forward cyclic input in order to complete the loop quickly, the tail blew out and he crashed. It happened so fast he is not 100% certain whether he had any control on the way down or not.

I think there may be two possible reasons for this:

1) The tail simply blew out because it couldn't hold anymore in the backwards maneuver. The 500EFL has a bit low tail gearing, doesn't it? Would bigger tail blades help?

2) The 3GX somehow totally failed. Reset, static, who knows. If that is the case, it may be time for a V-Bar.

[tomd27858]

The EFL tail is geared for running above a 2800 rpm head speed. If the head speed is below that the tail can blow out during very aggressive maneuvers. In response to that, people are running 90 flat with a 12t or 100 flat throttle curves with the 11t and getting pretty good performance.

People that are on the edge and needing the last bit of performance out of the tail are using Edge tail blades that have a larger surface area.

No comment on the 3GX.

[hamstar78]

yeah run it wide open for best tail performance, never had an issue with a 100 flat curve even beating on it really hard

[tomd27858]

I agree. If you check out the EFL videos, there is one of my son that has NO collective management skills and the tail holds great at 100 flat on an 11t.

[GT86]

Most of the tail problems people have with the Pro seem to be due to low headspeed. It's geared differently than the ESP and trying to use ESP headspeeds won't work well. I ran into this trying to use the CC governor. The headspeeds I could get in gov mode resulted in both a bob on the elevator axis and a tail that didn't hold well. I ended up going to fixed endpoints at 100%, which cured the problems although it does make for shorter flight times. But that headspeed makes for a fun 4 minutes or so :)

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[hamstar78]

Most of the tail problems people have with the Pro seem to be due to low headspeed. It's geared differently than the ESP and trying to use ESP headspeeds won't work well. I ran into this trying to use the CC governor. The headspeeds I could get in gov mode resulted in both a bob on the elevator axis and a tail that didn't hold well. I ended up going to fixed endpoints at 100%, which cured the problems although it does make for shorter flight times. But that headspeed makes for a fun 4 minutes or so :)

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agree 4 minutes of insanity:lol:

[GT86]

agree 4 minutes of insanity:lol:

Yeah, to me the shorter flight times are worth it because the heli is so much fun to fly. Scary at times because it has so much pop, but that's part of the fun :D

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[tomd27858]

Yeah, to me the shorter flight times are worth it because the heli is so much fun to fly. Scary at times because it has so much pop, but that's part of the fun :D

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To above +100. It is the best 4 minute ride out there.

[Jotto]

Thanks everyone.

If one does not want 4 minutes insane flight, it seems like bigger tail blades is the way to go.

Which ones do you recommend? Are these good? http://www.flying-hobby.com/shop/edge-72mm-premium-cf-tail-rotor-blades-p-6848.html

[hndaluvr]

Yep... great blades, but they WON'T solve your tail issue if you keep your head speed low.

[Steemo]

+1 on 100% Thr curve.

But lets not just blame our tools here guys...
Tail blowouts happen in backward flight when we are too heavy handed with collective and cyclic. Almost any heli will struggle to hold the tail if you do a high speed tail slide and punch the elevator and collective too hard on the exit. suddenly tightening a backward inward loop on exiting at high speed can have the same effect.

Collective management is key.

Not professing to be the master of this but just sharing from experience seeing more experienced guys do backward flight manoeuvres perfectly with my heli that I've asked them to test the tail on, where I will have tail blowouts almost every time I try the same trick on that heli :dontknow

[simon1980]

mine is doing exactly the same, its like flying my mcpx at times needing good pitch control :). I love the heli though, im running at flat 95 throttle in idle up so will try 100 to see if that works, dont trust the tail at the min tbh.

[tomd27858]

This is with an 11t pinion at 100 flat. My son has not learned collective management and the tail holds pretty well using the 520 at 6v with stock blades. He has really enjoyed learning to fly but to him it isn't fun unless the blades make noise.

http://www.youtube.com/watch?v=iowUHbfK0nI&feature=youtube_gdata_player

[Steemo]

Great flight, love the commentary :lol: Saw a couple of backward loops, and yes he's got a little to learn when it comes to collective management but he's doing a really great job of not abusing the collective (more so than me :oops:)

That's my point though, if he were to have tightened the loop and/or fed the collective on too quickly too heavy on exit you could easily get a sudden weathervane happening. his loops were reasonably smooth.

But your son's flight just goes to show the stock setup is more than capable of holding the tail if you fly it right.

[tomd27858]

We have enjoyed the 500 so much I actually picked up a second one since the one he is flying is his. He had done really well since his instructor - me is a 20 year plane pilot whose reflexes are not quite as sharp as his. I am blessed with both of my sons enjoying the hobby with me. We always have a little ribbing going on. It keeps things light and fun like it is supposed to be.


We havent had any problems with the tail but learned very quickly here that the efl was designed for 90 or above throttle curves period.

Thank you for your kind words regarding his flight.

[tomd27858]

Speaking of collective and cyclic management. We are using 12 degrees collective and have limited our cyclic on the beast to 12 degrees as well to match the set up in the manual. Crazy idea but has anyone tried to drop to 11 and see how it works. With the head speed...shucks 10 should be plenty!

[hamstar78]

Thanks everyone.

If one does not want 4 minutes insane flight, it seems like bigger tail blades is the way to go.

Which ones do you recommend? Are these good? http://www.flying-hobby.com/shop/edge-72mm-premium-cf-tail-rotor-blades-p-6848.html
you can run a full size servo too but i think that is too much but some guys like it

[hamstar78]

Speaking of collective and cyclic management. We are using 12 degrees collective and have limited our cyclic on the beast to 12 degrees as well to match the set up in the manual. Crazy idea but has anyone tried to drop to 11 and see how it works. With the head speed...shucks 10 should be plenty!
haha drop to 11 hell no i upped it to 13 lol, i only had one blowout with my tail and that was a transition from a really high speed inverted hurricane to funnel, that is supposedly the torture test for how well the tail will hold. but i was at full collective too so it was screaming

[simon1980]

im using stock pinion which i think is a 12? so run a flat 100 on that? that would be a bit fast ? :) I have to say its only blew out when I have really punched the throttle.

oh im on 3gx by the way, I have noticed alot of you are on beastx, if that makes much difference?

[Steemo]

im using stock pinion which i think is a 12? so run a flat 100 on that? that would be a bit fast ? :) I have to say its only blew out when I have really punched the throttle.

oh im on 3gx by the way, I have noticed alot of you are on beastx, if that makes much difference?

nah not too fast :thumbup:
3GX: Flies well. You have to tinker with it lots to get it to fly great.
BeastX: Flies GREAT! You have to tinker very little to get it to fly perfect.

[tomd27858]

haha drop to 11 hell no i upped it to 13 lol, i only had one blowout with my tail and that was a transition from a really high speed inverted hurricane to funnel, that is supposedly the torture test for how well the tail will hold. but i was at full collective too so it was screaming

It was a thought...lol! I bet it was moving!!