450 size HUP Retriever Build

[F106DeltaDart]

For the last several months, I’ve been working on taking a 450 size TwinRex and converting it to fit a HUP retriever fuselage. This mostly involved extending the rear shaft to a greater height. I also fitted Blade 360 Trio heads and used the Rotormast V-22 Swashplates to allow for a 4-servo configuration with V-links.

Components:
Blade 360 Trio 3 blade heads
CopterX thin chord 325mm blades
Rotormast V-22 Swashplates
Garrt 1800kv motor
HobbyWing 60A ESC
2700mah 4S Battery
HC3SX FBL







Video of the first 2 flight below:

During these first 2 flights, I’ve experienced some issues as seen in the video. Multiple times now, I’ve seen a sudden drop in in power, accompanied by a yaw kick. In all cases, the motor was cool to the touch and seemed to work fine, ESC operation was also uninterrupted. I’m really not sure what’s been going on. I am also troubleshooting a building pitch vibration that’s begun building the last few runs. I will be doing some close inspections of the bearings and the gears to see what I can figure out. Any suggestions or feedback from those experienced with tandems is appreciated.

[sfcfury]

What ESC are you running? I'm definitely not expert enough... but if its not heat, perhaps some kinda overdraw of power?

[sfcfury]

Looks hella cool tho man!

[F106DeltaDart]

What ESC are you running? I'm definitely not expert enough... but if its not heat, perhaps some kinda overdraw of power?

I’m running a HobbyWing 60A ESC. The strange thing is when I loose power, I don’t hear the rpm sag. Normally, you can hear the motor roll off if that’s an issue. I’m wondering if it might be the flybarless doing some sort of reset, and letting down on the collective. The Helicommand unit that I purchased was used, so who knows what its been through. Would explain why sometimes it flies great, and sometimes it has issues that clear with a reboot. I just wish I could find a new in box Demon 3SX somewhere to eliminate that possibility.

[PawPaw]

Can a 3X be firmware upgraded to a 3SX?

[F106DeltaDart]

Can a 3X be firmware upgraded to a 3SX?

Unfortunately not. There’s a hardware difference between the two. There has been some chatter about the Axon being updated to support tandems, but not sure it ever happened. Sent an email to the company to ask.

[F106DeltaDart]

Got a new in box Demon 3SX installed in the aircraft now. Looks promising, not seeing any strange twitches like the old unit. Hoping to flight test it soon, but this rain just isn't letting up.

[F106DeltaDart]

Well, the new Demon solved my strange flight controls issues. However, another one has emerged. The cheap 450 motor that I was using is definitely having issues at higher currents. If I let the aircraft hover out of ground effect, after 10 sec or so the motor bogs down and headspeed starts to drop. Once in ground effect, headspeed comes back up. I have a new ego drift 450 motor rated for higher current on the way. A few in flight photos from several weeks ago:

[F106DeltaDart]

I have also heard back from the gentleman building my fuselage. He is making some great progress on the plug! I also decided on my paint scheme. Will be going with the HUP that carried John Glenn after his Mercury capsule flight.

[PawPaw]

Very impressive, F106!

[F106DeltaDart]

A few more updates. First, the fuselage plug was completed. Hopefully I’ll have a fuselage in a month or 2. I ordered 2 just to keep a spare around.



I also played with gain tuning and flew more with the new ego drift motor. Really had to dial down elevator gain, but it’s flying well now. I still have a very small low frequency pitch shimmy, but it doesn’t seem to be affected by gain, and I can’t locate any mechanical issues. Might try playing with different blades and see if that affects it. For the motor, I had to bump down timing on the HobbyWing 60 to 10 deg. Motor is coming down cool and I’m getting 7 min flight times. Huge improvement over the old one.

[F106DeltaDart]

A few more updates on the fuselage. I’m really looking forward to receiving this one.










On the mechanics side, recently I’ve been fighting a sudden sinking on the mechanics. It’s almost like VRS, but not nearly as predictable. One second I’m in a totally stable hover, the next I’m sinking toward the ground and full collective hardly slows it.Going to try switching out the flexible plastic blades for some carbon Align blades and will see if the increased rigidity and area makes a difference.

[PawPaw]

Very nice and unique project, F106! Truly awesome.

[F106DeltaDart]

Merry Christmas all!

Just got a few photos of the finished fuselage. Can’t wait to have it in hand!






I’ve still been fighting the VRS tendency of rear rotor the tandem mechanics. It requires a pretty aggressive nose down input and full collective to recover from, and can be impossible to recover if it happens too low. I’ve switched to the Align blades and there isn’t much of a difference so far. It’s strange to me that this twinrexx tandem seems to be the only one that exhibits this performance.

One of the things that I noticed on most other tandems, is that the forward mast generally has some forward tilt. I may try biasing the swash forward a few degrees to mimic this. Also will try moving the CG farther forward to unload the rear rotor a bit. This will need to be resolved (or at least more livable) before I put on this beautiful fuselage.

[sfcfury]

Wow! Looks fantastic man...

[kiwi_craig]

wow, wow and blipping WOW. what a stunner. custom shell... gads $$$ what a neat build. I have watched your video several times and I'm sure I can see a small lateral yaw occurring in the rear shaft and or the rear chassis ?? the rear shaft bearings are really close together and that super long shaft above is going to be hard to control in flexure . whilst a bucket load of work I'm wondering if a third bearing higher up and lifting the swash might stiffen the whole rear end ?? and have you though about those scale blades with the weighted ends ??

The twin rex - chinook deal is something I'd pay $$ for an RTF........ hats off to you on this custom build !!

[Helikapoter]

Nice project , looks amazing 👍👀

[F106DeltaDart]

Thanks all, I received the fuselage from Buamodel 2 weeks ago. The quality is excellent, but its a bit heavier than I was hoping for (about 1.1 lbs). With that weight in mind, I wanted to do some gross weight buildup on the mechanics before I did anything else. Ended up slinging a 6S 4000 underneath to simulate the fuselage weight. I had to bump up the headspeed a bit, but to my surprise the mechanics handled the extra weight well. It is still prone to the VRS issue, but recovery is actually easier than at empty weight. I also started playing with CG. So far, more forward CGs have been more benign. Lightening the load on the aft rotor definitely helped tame it a bit, but results in some oscillation from the FBL. Might need to look at some more gain tuning there next.

Kiwi, as far as I can tell, this isn't due to longer mast in the rear. Another person is building one in the stock configuration (but with Gaui 3 blade heads and an ikon2 FBL) and has noted the same flight characteristics. From a loads perspective, I agree that another bearing block would be beneficial though. I do actually have a set of the weighted blades on the table, and may try them next. So far, the Align blades have had the best characteristics though.

[kiwi_craig]

What does VRS mean - involve - result in flight wise ? it looks like it is oscillates on the rear mast - rotor head ?

[F106DeltaDart]

What does VRS mean - involve - result in flight wise ? it looks like it is oscillates on the rear mast - rotor head ?

VRS stands for Vortex Ring State, also known as settling with power. It is when a helicopter descends into its own rotor wake and starts re ingesting it. This video shows it well:

How this manifests on the tandem model is a bit different. Basically, it flies well in hover and forward flight, but particularly when slowing from forward flight to a hover, you can hear the rear rotor get noisy and the model starts to loose altitude. Although the front rotor is still in clean air, the FBL prioritizes attitude over altitude (as it should) so it reduces the front rotor pitch to bleed altitude as the rear rotor looses lift.

The only recovery that’s worked well for me is to quickly lower the nose. This seems to get the rear rotor back in clean air and then you can fly out of the condition.