Phoenix 1st flight dilemna...

[KevinM]

Greetings all,

I've got a first flight question with respect to the Aerotech Phoenix, I'm hoping someone with experience flying them could chime in with their thoughts...

I picked up an original Phoenix kit a little more than a month ago and I've nearly completed building it. It's come out straight as an arrow and weighs in at 20oz. (No covering, but radio equipment installed.) I ordered some RMS reloads in advance of finishing it so I'd have them in hand by the time it was ready to fly. My plan was to start as recommended with some flights on F13's, then take a crack at the G12's and F23-W's so I ordered a couple of each. My motors were delivered today, and so with great eagerness I went through the contents of the box:
-2x G12's, check.
-2x F23-W, check.
-2x F16-J??? :jaw: Those were supposed to be F13... So now I'm pondering what to do. I know the F13 is the recommeded first flight motor, but would an F16-J's be a really poor alternative for a first flight? I've only got about a week-end's worth of work left to complete the Phoenix and needless to say I'm itching to give it a try but I cetainly don't want to duff it on the first outing.

I'm assuming that recommending the F13 for first flight is two-fold, first to give an opportunity to ensure that Pheonix is well trimmed before moving on to higher powered motors, but also to give the pilot a chance to get used the ascent and flying characteristics of the Phoenix before moving on to higher powered motors. In that respect, I should qualify that I've been building and flying RC planes for more than 15 years (including turbine powered jets) so I don't think I'll be in for anything I can't handle, but I defer to the wisdom of those who've actually done this before. Is the F13 the only way to go for a first flight?

Thanks in advance,
KMc

 

[georgegassaway]

Given the launch mass of a Phoenix, and that you are a VERY experienced pilot of fast-moving planes, I think in this case you will be OK using an F16 for your first boost.

If this were someone who did not have a lot of R/C experience before, I would highly recommend waiting to get hold of some F13’s for a first flight.

When it takes off, try to get it into a “climb zone” of between 45 degrees and 60 degrees climb angle. What I mean by that is if on liftoff from a 45 degree angle it pitches nose down from 45, give it some up elevator to bring it up towards 45 degrees. If it starts to pitch up from 45, you can let it “drift” up to about a 60 degree climb angle, but if it is going to exceed that, then give some down, to try to get it back into the 45 to 60 degree zone.

When you do a G12 boost, since the thrust is lower, you may want to hold closer to the 45 degree climb angle since the steeper the climb angle the slower the model will get.

If this was a different kind of model, like an S8E type (Cuda Stingray, etc.) weighing say 8-9 ounces using an E6, it would be different. With those, they are best flown at a climb angle of 70 to 80 degrees. Of course those have about a 2:1 thrust to weight ratio so they can do vertical with a lot of airspeed, while the Phoenix weight can be close to the thrust of a G12, or a 1:1 thrust to weight ratio, so the Phoenix needs to climb at an angle like 45 degrees.

BTW - F13 is exactly the same thrust as a G12, but simply does not burn as long (see the thrust curve plot on the G12 instructions).

Now, I have never built a Phoenix, and only have made 2-3 flights of someone else’s using a G12, to “test fly” it for them and work out the trims. But I’ve seen a lot of others fly them, have had the instruction manual, and know a pretty good bit about them (I actually own an unbuilt kit that was given to me for helping out in a university project, same project where test-flew one). When I was boosting it, my biggest concern was to NOT let it drop the nose down much below 45 degrees, and if it pitched up from 45 degrees I did not make a big correction unless it was going to go past 60, since I knew it would slow down a pretty good bit due to the 1:1 thrust to weight ratio using a G12.

Oh, I should also say I used to fly an R/C X-1 model that weighed about as much as a Phoenix, mostly using G12 reloads. I boosted it at 45 degrees, and climbed it at 45 to 60 degrees. Anytime I let it get more than 60 degrees, it slowed down to the point that it did not end up as high as it did when I kept it at no more than 60.

One of the things different from doing a normal R/C model is this. Aim the launcher facing into the wind. If you were to orient the launcher with a club runway, or for any other reason aim it so there is a cross-wind, the model may yaw (and possibly also roll) badly on liftoff out of the tower. Sort of why when someone flies a hand-thrown powered “park flyer”, they face into the wind and not a crosswind when they throw it.

As a pilot for an R/C RBG, I like to be about 100 to 150 feet away, and standing at a 3/4 view from the model’s back and side. So, about an equal distance downwind of the model, and to the side of it. That view helps provide a good view of the pitch orientation at liftoff, and the model as a whole as it climbs and starts to get smaller in the distance. Some prefer to be a little closer than that, but it is never good to be close to the pad

- George Gassaway

 

[JoeG]

Not much to add to George's comments.

Yes, launch into the wind.

I have launched my Phoenix on lots of different motors. There was a time when the 32mm reloads were not available and I used a lot of different motors. Some worked better than others.

With 15 years experience I think you will find even the boost phase pretty tame.
You should be good with about any of the motors you have. Follow the instructions. (I know, I know.)

Load an empty case and test glide it if you are nervous. Once you have the model gliding well from a shoulder high hand launch then load it up with a motor and add a little down trim for boost or it will probably pitch up.

It is easy to control on boost just don't over control. I use low rates on boost. you may want to do so if you have that option. Then switch back to high rates and move your elevator trim back to where it was for a good glide.

This airplane is very clean and so it is pretty fast. Make sure you have lots of overrun on the landing because it will probably end up much further down the field than you expect.

I like the F23 because it gives you quick getaway but the G12 will really get you up there. The first time you fly a G12 you wonder if it is ever going to stop burning. So does everyone else. It's way cool. 9 seconds is a long time.

Have fun and good luck.

 

[KevinM]

Hi George, Joe,

Thanks to both for chiming in, I appreciate it. "Launch corridor" straight into wind and between 45 and 60 deg climb are noted, as well as pilot's position relative to the launcher. I've not decided yet if I'll do my first flight at my regular flying field, depending on the pattern direction it's rather unforgiving of overrunning the landing area on one end. (But the other way's clear so it may just come down to choosing the right day on which to do it.) Radio setups are a non-issue, I have the luxury of one of those fancy computer radios that will even do the dishes and take out the trash. I was going to set it up so that activating elevator down trim and low rates (for launch), and crow mix (for landing) are all done from a single 3-pos "flight mode" switch.

I'm covering today, I'll get some photos up as soon as that's done. (Hopefully tonight.)

KMc