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First heli! Trex 450

F106DeltaDart

Well-known member
#21
I finally received my battery today so I charged it and slapped the training gear on my heli and went to do the blade tracking check.

It was super scary and my camera was too low so I don't know if blade tracking is right but I guess it should be.
Is there anything obviously wrong in there?
Tracking looks good to me, don’t see any variation in the tip path plane, and hardly any vibration on startup. Nice work! I would highly recommend securing the aircraft to the ground for tracking checks. Usually I set something on top of the training gear or the skids so that it can’t go anywhere when you are trying to perform these checks.

The only items left before flight that I can think of are checking the CG and controllability. Balance at the rotor mast, and on a ground run, check that the rotor disk responds correctly to your inputs; fwd stick tilts disk fwd, yaw control is correct, etc. I know you’ve double checked these by now a few times in the setup, but one last check is always worth it. Good luck, and I can’t wait to see it take to the air!
 

tamuct01

Active member
#22
This thread is great! I just assembled a KDS 450, and it is my first 450-sized heli as well. I have smaller ones: Blade 180 CFX, Nano CPX, and MSR, but those are tiny in comparison. I think I have everything ready to fly, but I need to go through these tracking tests as well. Thanks for sharing!
 

Fluburtur

Cardboard Boy
#23
I checked CG before and after putting the training gear on and the swashplate moves in the right directions, I also reduced the controls to have about 10° of pitch on cyclic. Tail rotor seems to respond correctly but I still have to check it while the heli is running.

The only problem I had is that the blade grips are very tight so I can't really move the blades by shaking the heli but I tried to align them as good as I could.
 

F106DeltaDart

Well-known member
#24
I checked CG before and after putting the training gear on and the swashplate moves in the right directions, I also reduced the controls to have about 10° of pitch on cyclic. Tail rotor seems to respond correctly but I still have to check it while the heli is running.

The only problem I had is that the blade grips are very tight so I can't really move the blades by shaking the heli but I tried to align them as good as I could.
That’s fine if you can’t get them any more free by loosening the blade bolts. My old 450 had a similar issue. The alignment will more or less fix itself (as long as they aren’t super-duper-unmovably stuck) upon achieving full RPM. The inertial forces there will align the blades correctly, and let them lead and lag as required. If you see a weird vibration in flight (not gyro oscillation) then you need to mess more with blade grip friction.
 

F106DeltaDart

Well-known member
#25
This thread is great! I just assembled a KDS 450, and it is my first 450-sized heli as well. I have smaller ones: Blade 180 CFX, Nano CPX, and MSR, but those are tiny in comparison. I think I have everything ready to fly, but I need to go through these tracking tests as well. Thanks for sharing!
Awesome! Glad this thread can help others out as well! Is this the flybar version or the FBL?
 

tamuct01

Active member
#26
Awesome! Glad this thread can help others out as well! Is this the flybar version or the FBL?
It's the FBL version with belt drive. So far I have everything built and the surfaces all go the way they're supposed to when they're supposed to. I'm using a FrSky X4R receiver with S-Bus to the FBL unit. I've leveled the swashplate with a 3d printed tool I designed (https://www.thingiverse.com/thing:2776658). I couldn't find an existing version for 450-sized heli. I setup the collective pitch using a 3d printed pitch gauge and iPhone 4. I have a few more ground tests to do before I take to the skies.
 

Fluburtur

Cardboard Boy
#27
I just came back from flying my canadair and while my friend was here I had him film my heli a bit.


The rotor disc tilts in the right direction and it is very light on the skids at 0 pitch so I guess that is good but it's not less scary running the heli in such a small place.
 

F106DeltaDart

Well-known member
#28
I just came back from flying my canadair and while my friend was here I had him film my heli a bit.

The rotor disc tilts in the right direction and it is very light on the skids at 0 pitch so I guess that is good but it's not less scary running the heli in such a small place.
Looks like it wants to fly! I think you're all set for a maiden flight. I know what you mean about the enclosed space. I maiden my 450 in parents driveway when I was starting and quickly realized that wasn’t a great idea.
 

F106DeltaDart

Well-known member
#29
It's the FBL version with belt drive. So far I have everything built and the surfaces all go the way they're supposed to when they're supposed to. I'm using a FrSky X4R receiver with S-Bus to the FBL unit. I've leveled the swashplate with a 3d printed tool I designed (https://www.thingiverse.com/thing:2776658). I couldn't find an existing version for 450-sized heli. I setup the collective pitch using a 3d printed pitch gauge and iPhone 4. I have a few more ground tests to do before I take to the skies.
Very nice! Interesting to see the use of all the 3D printed tools there. I would have never thought of that!
 

Fluburtur

Cardboard Boy
#30
I was still unsure about setting things up in the radio so I asked directly on the vstabi forum

Short answer: collective pitch curve in the radio, cyclic is done by the gyro depending on the programmed flight style.
 

tamuct01

Active member
#32
I don't want to hijack the thread, but I took my new KDS 450 out into the driveway and did a test run up. I presently have a Nano CPX and Blade 180 CFX. This thing is scary! Everything looks good so far. I may play with the ESC start parameters a little bit. The ESC it came with doesn't have a governor mode, so I have to play with throttle curves in the Tx.

 
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F106DeltaDart

Well-known member
#33
I don't want to hijack the thread, but I took my new KDS 450 out into the driveway and did a test run up. I presently have a Nano CPX and Blade 180 CFX. This thing is scary! Everything looks good so far. I may play with the ESC start parameters a little bit. The ESC it came with doesn't have a governor mode, so I have to play with throttle curves in the Tx.
Nice! Sounds ready to go. Planning on training gear or just normal skids? I know that scared feeling on ground runs. My 500 was absolutely terrifying running for the first time, and now I’ve got a 700 on the bench that is going to be swinging 5 blades. I’ll be backed up pretty far when those rotors get turning.
 

PsyBorg

Wake up! Time to fly!
#34
I think I remember reading or seeing a video back when I was trying nitro helis that its a really bad idea to try and hold your heli down when the blades are turning. If I remember correctly it was something about ground resonance can exponentially progress without have the freedom to buffer itself. The cure for real helis is to lift off and get out of ground effect I think was said. Same thing with having a free floating head on a run up stand to allow for that to work itself out.

Has that train of thought changed since then? If not it might be a topic to put out for the many beginners setting up their first helis.
 

F106DeltaDart

Well-known member
#35
I think I remember reading or seeing a video back when I was trying nitro helis that its a really bad idea to try and hold your heli down when the blades are turning. If I remember correctly it was something about ground resonance can exponentially progress without have the freedom to buffer itself. The cure for real helis is to lift off and get out of ground effect I think was said. Same thing with having a free floating head on a run up stand to allow for that to work itself out.

Has that train of thought changed since then? If not it might be a topic to put out for the many beginners setting up their first helis.
It really depends on the number of blades and head design. If you are running a multiblade heli, then you can get ground resonance, especially if have a fully articulated rotor head (independent vertical blade flapping and lead-lag hinges), that is solved by finely tuning strut and tire pressures to damp out any oscillations. This is why most RC multiblade heads are either rigid or semi-rigid designs. We actually regularly do restrained ground runs on the full scale birds to test out components, and it is fine with proper precautions. And yes, in normal operation if the oscillation does begin to develop, lifting off the ground will immediately get you out of that situation and give a chance for the rotor oscillations to damp out.

Fundamentally, ground resonance happens because the rotor system gets out of balance. Picture you are looking down at a 3 blade head. Each blade can lead and lag pivoting about their blade bolt. In ground resonance, you end up in a situation where 2 blades are lagging and one is leading or vice-versa. In flight, this would damp out and equalize. However, feedback from the ground can cause this condition to worsen. Now, you have an out of balance rotating system that has to release of all that rotating energy and can shake apart the aircraft. If you look up videos of ground resonance on youtube, it can be pretty devasting. This doesn't happen to a teetering 2 blade heli, where the blades are linked by a feathering shaft, like our RC birds.

Where RC Helis get in trouble is one of 2 situations. Running negative pitch on the ground can get you in a near ground resonance state, and cause a lot of vibration quickly. The other issue is older FBL units having trouble dealing with feedback from the ground. The align 3G in particular really hated running on the ground, but would calm down after liftoff. Most modern FBL controllers deal with that without a hitch now.
 
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Fluburtur

Cardboard Boy
#37
WOOOOOOOOO

I got it flying!


It isn't as hard as I imagined, but I was super scared and happy :cool:

Guess now I only have to fly it every day until I get good!
 

F106DeltaDart

Well-known member
#40
Yeah, will have to get into figure 8 stuff and such.

Too bad I only have a single battery, I can only fly for like 4 minutes at a time.
4 minutes isn’t great, but it should improve when your not lugging the training gear around. You can also turn down the headspeed a bit, which will buy you more flight time and a bit less pitch sensitive. That’s what most scale guys do to get longer flight times for relaxed flying.