Trex 500 Throttle Curve

[ChrisOlson]

Since I crashed my Trex 700 Nitro when the engine quit in flight and pretty much bent or broke everything on the helicopter, I been looking for another one - electric this time. I found a Trex 500E with a flybar head on craigslist for $125 that had been crashed. Damage was fairly light and got it about ready to fly again for $75 in parts. It was nosed into blacktop, blew the blades off, but the mainshaft didn't get bent. The rest of the parts on the head need to be flight tested before I'll trust them.

What are you guys running for headspeed and throttle curve on a 500 with the stock 425mm blades in Normal mode? I want to fly it scale at first until I make sure everything works properly after being rebuilt. The PO put a Turnigy Typhoon 500H motor in it on 6S, so it can run insane headspeed. I know it will fly decent at 2,500 but I was thinking more along the lines of 2,000 rpm for hover tests and scale flight. Wondered if anybody has experience with these, as to whether or not it will be stable at that low of a headspeed on a 500? I just don't want to push it hard at first until I make sure nothing in the equalizer, swashplate or linkages got damaged in the PO's crash that I can't see, or without replacing the whole head or dye penetrate checking the arms for non-visible cracks.

 

[ChrisOlson]

Kind of an update on my Trex 500 low headspeed project. I initially got it flying, flew it for a total of about 35 minutes and the elevator link broke and crashed it. But I found out it will fly perfectly fine at 1,900 rpm headspeed.

So after a second rebuild, this time with a new DFC head and Pixhawk flight controller, custom landing gear with a cradle to hold the big battery, and using a 10,000 4S MultiStar, got it flying again. Running 1,900 rpm it flies for 29 minutes. Takeoff weight is right on 6lbs.

Tried flying it at 1,800 rpm and it gets a bit slushy with the hover collective at 7.5 degrees. At 1,900 rpm it will hover at 6 degrees of collective and 19 amps. Top speed is about 40 mph with no problem with retreating blade stall, but it runs of power and collective in the turns on 4S at that speed. Not suitable at all for even sport aerobatics, but really fun to fly scale with it.

 

[F106DeltaDart]

Wow! That is some crazy flight time! I am running a 5 blade head on my trex 500 and getting similar headspeeds (1800) with about 6-7 minutes of flight time. Granted, it is loaded down with a scale fuselage as well. Nice work on a cool project!

 

[ChrisOlson]

I would think that with a five blade head you should be able to get down around 1,500 rpm and save some power moving blades. A two-blade head will always beat a three-blade at the same headspeed and takeoff weight. A three blade will be better than four. And so on.

What you gain with more blades is rotor disc solidity, and potentially much higher payload capabiilty. But the power requirement goes up to spin more blades unless you can save power by spinning the head slower. I'm sure with the scale fuselage, the five blade head is required for the scale look too. So that is likely a moot point.

Any time you can trade weight in a scale fuselage for more fuel capacity, you'll get more flight time.

I've wanted to do a low headspeed 500 for awhile, was happy to get this one cheap, and I was pleasantly surprised at the results. It is more common to convert 600's and 700's, where a 700 can run down to 1,000 rpm with no problems. But a lot of people claim you can't do a 500 with a stock rotor using 425 blades at less than 2,300 rpm. They are wrong. I'm using the stock 162T main gear, stock tail drive ratio, stock autorotation gear, 13T pinion with a 1800kV motor. And it works great. Plenty of tail authority. No problem with roll with forward cyclic, and no problem with RBS up to 40 mph.

So it works.

This was the first hover test with it, before I tuned the PID's in the FC, just testing it in Acro flight mode with the controller set to flybar so I could fly it with straight-thru signals from the RC and not have to worry about PID tuning.

 

[F106DeltaDart]

Completely agree with what you said. But everything in my model is a sacrifice to make it look more scale, which is the goal for me. Still got a 500 sized Huey and Apache on the bench as well. Same goes for my fixed wing models with 4-5 blade props. I am also running some very thin chord scale blades, so it really needs about 1700 to get it to lift at a reasonable pitch. The vertical fin also impinges on my tail authority, so between that and the 5 blade head I had to run 600 size tail blades to get enough tail authority.

It is very cool to see this done though, and the performance looks great! Congrats on a very cool project.

 

[ChrisOlson]

Oh yeah, that's a nice looking scale model. Where is a good source for 500 size scale fuselages of different types? And where did you get the head?

I like the 500 size for an electric because it doesn't take insane amounts of batteries to fly it. My opinion is that once you get to 600 size and above you really should be looking at a piston engine, or a Wren turbine or similar, to make it practical.

 

[F106DeltaDart]

Thanks! I agree on the size as well, although for me it's more of a cost issue. As you start going up to 700 and above there are more scale options available though. The sources for scale parts for 500s are pretty mixed. RC Aerodyne: http://www.scaleflying.com/500-Size-Fuselages_c_25-1-4.html is more or less the only source for fuselages, and are mixed in price from reasonable to ridiculous. The MD500 fuselages tend to go on sale pretty often, and I snagged a Huey on clearance from them for $70. Others, like the Apache fuselage are discontinued, and I found one in the Rcgroups classifieds. I have actually changed heads/blades since that photo and currently run this head: http://www.ebay.com/itm/5-Blades-Sc...elicopter-Flybarless-Rotor-Head-/332039504126 with these blades: http://www.ehirobo.com/copterx-mult...fiber-main-blades-for-4-blade-main-rotor.html. The TF model head is also a very nice product, but I haven't tried it out yet. You can see why a said it gets expensive fast... But, totally worth it to have at least one scale heli in the collection!

 

[ChrisOlson]

Wow, cool, thanks! Yeah, I've seen quite a few 700's refitted with a Wren 44i with scale fuselages of different types. Even seen a 600 with a Wren MW-54 in it with a Bell 220 (I think it was) fuselage once.

But the cost of those is so prohibitive. It's supposed to be a hobby and when your RC heli costs more than your pickup it kinda takes the fun out of it. The 500 is just as much fun to fly as the 700 was, and I got enough parts left over from the 700 crash to build up another one, but I probably won't put 700 blades on it. When I build up another one I'll likely use 525 blades from a 550.

 

[F106DeltaDart]

Completely agree there. There is a point when I would start saving up for a real one, especially once you get into turbine birds! I'd have a significant savings into a fund for a used Enstrom F-28C by then.. I may get a 700 someday, but it would be built piece by piece over a long period of time to make it less painful. For the moment, I'm perfectly happy with my 500s though, and intend to stick with them. Let me know if you ever do a scale build though, they are really something to see in the air, and worth a bit of cost in the performance!

 

[ChrisOlson]

I think you'd better stick with the RC turbine heli. The last thing you want is a full-size manned one. I work on 'em all the time and you can't even get an annual done for it what it costs to build a RC turbine one

 

[F106DeltaDart]

Naaa... Totally worth it to me! I've grown up flying in my Dad's Enstrom, and loved every minute of it. And the Enstrom piston birds aren't the worst on maintenance either. Unlimited life blades, and they are built quite well. It's had one or two expensive annuals, but it's never been terrible. And besides, as much as I like RC, full scale Helis will always be my first love. Someday...

 

[ChrisOlson]

Well, at least you know what to expect from a full-sized heli

I wouldn't actually mind getting a Micron coax heli imported from Russia. My wife and I were there in January on business, toured the Russian Helicopters Factory in Moscow, and looked over the Micron heli's in St. Petersburg. I don't know that they've received FAA cert yet in the US, and are a little too heavy for UltraLite. But it is a very well designed machine compared to a Mosquito.