rmgmag

You've got to check this out!!

This is a pre-production prototype of the Sierra, currently being developed by www.rcxplanes.com. I was lucky enough to get my hands on one to test it out for them. I'm not the most accomplished 3D flier, but I'm probably representative of the average builder and flier. And no, they're not paying me to write this or test their planes.

This thing was very easy to build, took me about 5-6 hours (I'm a notoriously slow builder) with only basic instructions (they're still being worked on). The design lends itself to easy building. It took me longer to get the electronics set up than it did to build the airframe. The graphics are easy to install, and I really like how they look.

I've got to thank Bud Wilkinson for this one, I think he's got a winner here.


Here are the specs:

Set-up:
Custom CDR cool motor
Prop - GWS HD 8x4
Align 10 amp ESC
FMA M5 receiver with one of those mini antenna's
3 HS-55's (they recommend 2 HS-50's and 1 HS-55 for the ailerons)
3S batteries, e-tec 700, TP730, Vampowerpro 620
Transmitter: Futaba 9CAP Super
AUW: 11 oz (but I think my scale is about 1 oz heavy) I also build fairly heavy because I use mostly thick CA, and a lot of it.


Throws:
As much as I could get on each surface without binding.

Expo:
Ailerons - 25% (I'll probably reduce this further)
Elevator - 60% (the elevator is very effective)
Rudder - 30%

Flight Tests - these are based on the first 10 flights

For the first 5 flights, I flew it without having the aileron servo glued in!!! Didn't even notice it until after I looked it over after my first crash.

1. The 1st flight using the recommended CG seemed quite nose heavy to me. Eventually I moved the CG back about an inch from their recommendations.

2. Hovering: It's very stable, probably the most stable plane I've flown. It does torque around a bit if you're off center in your yaw axis, but that's kind of normal for foamy bipes. I could even back it down, which I have trouble doing with all of my other planes

3. Moderate adverse yaw at low airspeeds and high angles of attack. Right aileron doesn't seem to exhibit as much of this as left aileron. I've found that this is pretty normal for foamie bipes, and by my 5th flight, I'd adjusted to it and it's not even an issue for me anymore, but I thought I'd mention it.

4. Great climbing flat spins in both directions. Better than my Allure, and I thought that plane was good. My other planes seem to only like going to the left, but the Sierra goes either way, and does it better than anything else that I've flown.

5. Waterfalls are pretty tight. You need to be very close to vertical or they don't come out right, and you get torqued around a bit, but that could be my thumbs too. You can flip it nose down or nose up. It's pretty quick.

6. Harriers are very nice. Very easy, just bring the nose up, and set the throttle, no muss, no fuss, and no wing rock.

7. Elevators seem to have some wing rock, but I couldn't start off very high as I was flying indoors in a confined space, so there really wasn't any chance to see if it would stabilize itself.

8. Inverted flight, though limited by lack of space, and my lack of skills, it seemed fine. I didn't notice any tendancy to climb or descend.

9. Accelerated torque rolls: seem easier than with anything else I've flown. I was able to torque roll and "fall" into a rolling circle. Didn't even need any rudder or elevator input, it just kept rolling and turning on its own. I've got to see if I can do that intentionally. It was really cool, especially since I've never done a rolling circle before.

10. I think knife edge is going to be fine. I didn't really have enough room for a long run, but it seemed easy. Not much rudder required to set it up.

11. Slow flight: this plane will fly really slow. With the nose up around 10 degrees, you can get it to slow down to a walking pace.

12. I think I built it kind of heavy. You can tell it's a little heavy because it will rock the wings a lot if you try to horse it around a turn at a low airspeed and a high angle of attack. When I used the 620 Vamp battery (12 grams less than the others), it seemed to behave better.

....One hard crash (bad thumbs), based on the loud noise when I hit the ground, I thought I must have cracked something big time. Planted it pretty hard on the nose. No damage to the airframe, but I did crack a gear leg. Took me about 2 minutes to fix it. Also managed to break an aileron control horn. It pulled through the push-rod hole. That took about 5 minutes to fix.

The fuse is really stiff, stiffer than the Allure, probably because the 45 degree support is wider in the tail area than the Allure. There's virtually no noticable flex in the tail area.

The Custom CDR motor is a pretty good match, hovers at a little more than 1/2 throttle and pull out is fine. I might try the Custom CDR hot wind motor and a Cool Running ESC (saves about 10 grams) for better pull out of a hover, but that motor is very peaky, kind of like some of the older Japanese motorcylce engines. Not much low end grunt, but rev it up, and it screams. The Little Screamer PP will probably work well, and I think Bud flew it with the Hacker A20-34S.

Overall, a great little plane. I'm hoping to take it outdoors this weekend (assuming the tempurature makes it above 45) and really wring it out.

Below are a couple of pictures, I left the wheel pants off because with my flying, they end up getting destroyed fairly quickly.

Thanks Bud for all of your help, great plane!

Mike Hill

Looks good Bob. Should have mine finished soon.



Mike

rmgmag

Hi Mike,

Let me know your set-up, control throws, expo, etc... I've reduced my aileron expo to 20%, everything else is as I stated above.

Got a few more flights in today. Still flies great. Tried some snap rolls, and they're really tight and they stop straight too. This might be my new favorite plane.

I was wondering about reducing the size of the ailerons to reduce some of the adverse yaw or maybe changing to a dual aileron set-up and dialing in some differential? Based on how it floats, I think the airframe can easily handle an extra 8 grams or so for the additional servo. It does mean having to use a 5 channel receiver.

I'm going to try to get my daughter to shoot some video this weekend so I can post it.

Bob

Mad_Scientist

I Had a similar yaw problem with my Raptor bipe. Aileron Diff. of less than 20% made a big improvement. You might try replacing the 9gram servo with 2 of the 6gram servos. I'm also a heavy builder but I found 2 things got my raptor down to 9.4 oz including 2 hs55's and 2 Gws pico's.
The biggest weight loss I got from using the new PQ"twenty" 400mah 3S packs from HL, there only 40 grams. I ran them pretty hard with a rimfire 1000 8-4.3 and i'm very happy. The other weight loss came from building mostly with UHU por glue.

rmgmag

I sort of cured the yaw problem, I just use a lot of rudder...The plane will do rolling circles without any control inputs other than aileron! Just crank in full aileron, and it will do about 3 full rolling circles without needing any other control inputs. KE was really good, virtually no rudder is required. Last week I crashed and pretty much destroyed the entire nose area. I'm waiting for Bud to send me a new plane. I'll be keeping it light by using only thin CA and ligher servos. I may even use magnet wire to connect everything. Using minimal amounts of CA will probably help too. That should help reduce some weight. I may also try a smaller battery pack, but I only get about 8-9 minutes on my e-tec 700's, so going down to 400 mah will really put a dent in the duration.