Xfly Model Sirius 80mm Sport Jet

[Turbinefancy]

A new manufacturer Xfly has come onto the scene with a nice looking Sport Jet - Sirius. Length is about the same as the Avanti, span is about 10% smaller. I fell for it's sexy looks and got one!

[Turbinefancy]

It's a good flying model according to the pros!

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Xfly Sirius has decent low speed handling qualities. I like that it has wide main gears that keep it from tipping on the ground. I love doing wheelies with it on landing...

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A little open box review: Super neat packing. Everything looks great out of the box.

All the linkages are connected on outer most holes on servo horn. As a precision flyer, I prefer mine connected closer to the inner holes. That’s about the only change I’d do out of the box. Battery trey has plenty of room to accommodate 6S 6000 mAh pack and then some. Receiver can be placed at a separate platform behind/above the battery tray.

[Turbinefancy]

Plenty of structural reinforcement to make this airframe strong. As small as the stabilizers are, each has two carbon spars running through them. And the wings also has two carbon spars running the full span and a robust wing joiner tube going out to the retracts. No risk of bending this air frame from aggressive maneuvering or over-speeding, that’s for sure.

[Turbinefancy]

First

Consumer Flight Review

Assembly:
Very easy plane to put together. No manual necessary. 4 screws each to secure wings and stabs. But I did a detailed once over, so took about 3 hours:
1. moved the linkages two holes in on all servo horns - need to enlarge holes with 1.25mm drill bit
2. taped wing leading edge with heavy duty packing tape (turned out to be prescient)
3. Tried to correct severe toe out on main wheels. Apparently the wheels were aligned perpendicularly with wing trailing edge - amature hour QC by the factory to allow this to happen. The flat spots on the gear pins are set wrong. I stripped a couple of Allen keys trying to loosen the grub screws. So could not fix it in time before maiden...

Maiden:

Conditions were ideal for test flight. No one at field except me and my flying bud to do some photography. Wind almost calm. But setting sun is blinding at departure end of runway. I placed 6s 5000 HRB battery as far back as I could to get CG 140mm from wing root leading edge. Only took a couple click of trim to fly the plane true. It was super stable and I was already comfortable with it only two circuits in. Here’s the break down:

The Good:
1. Very precise handling in the air; from fast to low speed, no tail wagging, no wondering for level.
2. No coupling when doing knife edge, only need to use rudder to hold nose up.
3. Very slow stall speed. Initial stall is benign nose drop, but if continue to deep stall will drop a wing.
4. Can do extended wheelie on landing - much easier to do then Avanti. Those plastic capped ventral fins are well thought out - protected from scraping. It’s super fun to fly touch and goes using the Sirius
5. Adequate thrust for climb/ loop performance.
6. Wide track landing gear ensure no tipping over during taxi no matter how hard you throw it around. In my case the toed out main gear caused it to wonder wildly on takeoff roll.
7. Great scheme for visibility, even in waning light. Simply looks great in the air.

The bad (what were they thinking?):
1. Hideous intake design with wires and spar right in the middle of the triangular hole. This was acceptable in 2014, not in 2021 though.
2. The nozzle diameter of 75mm which works out to be 108% of fan swept area is outright performance/efficiency robbing. Maiden flight was 3.5 minutes with throttle management, battery had 32% left or about 3.78 per cell.

Verdict: this a fun plane to throw around with low stress flying. I recommend using 5000 packs for optimal performance and easily do wheelies for landing. It flies like a much bigger jet and is docile enough to be used as jet trainer. However, aforementioned design deficiencies means it can not measure up against the top brand sport jets like Avanti or Viper for high speed or efficiency. So for market positioning, Banana Hobby seems just right.

[Turbinefancy]

Since the oversized nozzle was robbing performance and efficiency by actually slowing down air flow after the fan, I made a simple mod by tapping a cut off coffee cup inside the nozzle to reduce diameter to 67mm or about 85% fan swept area. And I see a significant improvement performance wise. Less whoosh sound as well indicating less wasted energy.

I also fitted a head-tracking FPV system inside the cockpit and turned it into a FPV jet trainer. Now I am loving it! It seems to be a decent performer after the simple 15 minute mode!

[killickb]

Added a cut down plastic drink cup to give exactly 65mm outlet as an extension to the exhaust duct i.e. external to the exhaust orifice. Relying on good old eyeball sensors I cannot say that there has been an increase in take off thrust or max speed. Maybe someone will someday do the "math" on this mod ?

[Turbinefancy]

Added a cut down plastic drink cup to give exactly 65mm outlet as an extension to the exhaust duct i.e. external to the exhaust orifice. Relying on good old eyeball sensors I cannot say that there has been an increase in take off thrust or max speed. Maybe someone will someday do the "math" on this mod ?

Some quick math on the sizing the fan nozzle:
stock fan diameter: 80 mm Area: 5027
stock fan hub diameter: 32 mm Area: 804

Fan swept area (FSA): 4223
90% FSA: 3801 Nozzle diameter: 69.6 mm
80% FSA: 3378 Nozzle diameter: 65.6 mm

stock nozzle diameter: 75mm Area: 4413 = 105% FSA
This is way too big to be efficient. It’s slowing the efflux.

So at 65mm nozzle diameter, yours is just slightly lower than 80% FSA. Mine at 67mm is 83% FSA.

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Had a chance to wring it out a little, practicing precision aerobatics from the cockpit. Enjoy!

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Some dogfight action against a Freewing L-39. Outcome depended completely on which pilot was able to see the other first on merge. L-39 pilot had wrong setting in goggles and was not able to see Sirius at all during the engagement.

[Turbinefancy]

Low level aerobatics practice in calm wind at dusk. Enjoy!