|Aug 17, 2003, 10:56 AM|
I finally got around to flying my Alpha Jet.
MF480/S480BB, HS81 servos, Hitec 555 rx, Jeti 35 amp ESC. With a 8XCP1300 pack, AUW is 31 oz @ 20 oz/sq.ft.
The 1st HL resulted in a powered glide into the grass.
Swapped the 8 cell pack with a 9XCP1300, AUW is now 29 oz @ 19 oz./sq.ft. Checked the CofG, all was well.
The 2nd HL resulted in a powered glide into the grass. Not a hint of flight.
Reluctantly I added a launch hook to the alpha jet. I say reluctantly as a bungee launch gone bad is not a pretty sight. Anyway, I stretched the cord to 9# and hit the release. Off it went on a very flat trajectory, no more than 4 feet of altitude as the AJ past the anchor and dropped the line.
Too much aileron throw, even at low rate as the AJ was very twitchy in roll. A couple of clicks left aileron, about the same for the elevator, brought some semblance of control. Eased back on the throttle and put it into a gentle turn. Flew left and right patterns, nothing daring. Fed in elevator until it stalled; the AJ dropped like a rock but I managed to recover.
The timer went off at 6 minutes, lined up for a non-event landing. The pack still had a lot of energy, maybe another minute.
Before I fly it again I will reduce the aileron throws. Do any of you Alpha Jet flyers know what the recommended throws are? My kit came without a complete instruction set so I just guessed.
The MF480 is installed without the inlet lip. I will add it in the hope I can get away from the bungee launch.
The AJ seems to be faster than my Ky T33 with better duration and I suspect it will be much more of an aerobat. But the T33 looks much better in flight.
From what I've read here, no one else has trouble with hand launching the Alpha jet so I'm perplexed.
|Aug 17, 2003, 11:40 AM|
I am flying an Alpha Jet with:
Speed 480 Race
10 x cp1300's
3 x HS-55's
Jeti 18 ESC
I have hand launched it a few tmes and had no problems. There is a drop after launch but within a few feet it was able to pull out and gain altitude.
The control throws as per the manual are:
Elevator: 5 - 7mm on both sides
Rudder: 7 - 10mm on both sides
Ailerons: "The smalest defelection should be 3 - 4mm on both sides."
I think I have my ailerons set to about 5mm each way, with no exponential.
One thing you could check is the thrust line of your fan unit. It should be set to 0 degrees. I know when mounting mine I could move it a few mm each way, which could adversely affect the flight characteristics if not set properly.
Hope this helps.
|Aug 18, 2003, 12:28 PM|
thanks for your input.
I measured the original aileron throws at 19 mm. No wonder is was wild. Reset the lo rate to 6 mm so that should take care of the twitch.
Still have to mount the inlet lip.
My Alpha jet is an older model, specifically designed for the MF480. The mounting holes were pre-drilled - very little to go wrong there.
Do you have a weight for yours?
Why 3 servos?
I'm impressed with the fact you can get by with an 18 amp ESC. The MF480/S480BB combo draws about 15 amps on 8 cells
Again, thanks for the input.
|Aug 18, 2003, 12:49 PM|
Larry, that works out to be about 70 watts per pound, your not gonna get very much perfomance out of that, esp using a brushed motor, You may want to up the cell count some.
|Aug 19, 2003, 12:34 PM|
I flew the Alpha jet this morning with the reduced aileron throws. Misplaced the inlet lip so that was going to be a project for another day.
Using the bungee, off it went. Big difference in the way the plane handled. The reduced ailerons were a vast improvment over the first flight. Timer goes at 6 minutes, bring it down for a smooth landing.
The Alpha is sliding through the dewey grass when it hits something, perhaps a clump of recently mown grass. This causes the plane to yaw, breaking the fuse into three pieces.
The portion of the fuse which holds the battery broke off, the pack still connected. The portion of the fuse above the battery snaps off, back to the start of the "windshield". The elevator servo mounting area cracked, as well.
I was absolutely stunned that a little bit of wet grass could do this much damage to the plane.
Needless to say I was really p*****d about this. My first instinct was to strip out the radio and fan then head for the trash can. But I put the whole broken mess in the trunk and headed off to work.
Now that I have had some time to reflect about this I don't think I will repair the Alpha. I'll return the radio and ESC to the T33 and
resume flying it.
This was my first, and probably my last, 'profile' fuse plane.
|Aug 19, 2003, 12:40 PM|
yea I hear you about the profile fuse, they tend to snap right behind the wing, you need a CF tube or something IMHO to strenghen that area.
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