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Radio Control Forum => Jets => Topic started by: Konrad on June 05, 2017, 11:45:15 PM

Title: Freewing F-5 Tiger II (Your Dance Partner!)
Post by: Konrad on June 05, 2017, 11:45:15 PM
As I hinted earlier, here are some of my impressions of Freewing F-5 Tiger II.

Some background is in order. I received this model as a hand me down after the original owner crashed it on the maiden flight performing a classic rendition of the “Saber Dance”. While the model is an honest flier she is a handful and not suited for low time flyer or even intermediate flyers. One needs to have a lot of experience with models that have high wing loading to have success with the Freewing F-5.

First lets get some of the construction out of the way. In the stock form the nose (battery tub) is far too weak. While Freewing does have some carbon tubes across the nose part line this really isn’t sufficient. I found that one really needs to add some additional support in the way of .014" x 0.25” carbon blades imbedded into the upper sides of battery tub. This added support kept the maiden crash damage to a minimum. As the damage was basically limited to the cosmetic damage to the bottom of the plane. Actual damage was 2 destroyed retract units, a torn off elevator and the loss of two blue sidewinders.

Staying with the battery tub, the battery tray as positioned by Freewing limits the practical size of the battery to 3300-4000 mAh to maintain the center of gravity. While these lighter batteries do allow for better vertical performance on the rather weak stock outrunner EDF unit, the run time really is insufficient. One should move the battery hold down tray aft about 30mm. This allows reasonable sized batteries to be used while maintaining the proper center of gravity. Also it places the tray over the nose part line offering more support on this joint. You will have to cut some shallow channels into the main fuselage and add some balsa support to the nose of the tray. All are very easy to do. I like to fly with 4600- 5000 mAh 6 cell batteries. This gives me great flight performance and flight duration with the upgraded EDF systems (Freewing and others). (Note; That as shown the tray is too far aft, I placed the tray for use with 6000 mAh cells, this results in an aircraft that is too heavy to fly nice at 6000 foot altitude)

The other major issue with the model, besides the weak nose, is that the main landing gear retract pockets are misplaced. That is they are molded so that the retract mounting pads are parallel to the bottom of the wing. As a result of the wing's dihedral from the airfoil taper the landing gear will sit about 6mm proud, sticking out of the fuselage if one glues the plastic retract mounts down flush with the wing pockets. To get around this issue one should assemble the wings onto the the fuselage. Mount the retract unit to the plastic retract mounts. Then with the retract in the retracted position (up) glue the plastic retract mounts with the retract units into the wing retract pockets. Use a lot of very thick CA glue to fill the inevitable gap that will form at the outboard area of the mounting pocket, as you keep the wheels pushed up into their respective pockets in the fuselage. With the use of very thick CA I also like to use an accelerator on the plastic retract mount.

The last issue is that Freewing doesn’t seem to understand the concept of servo resolution. To get the best performance from the servo one needs to use the full range of motion while getting the desired amount of control surface deflection. To that end move the aileron push rod as close to the center of the servo while maintaining the desired control throw at high rate. The servo should be allowed to move 100 to 110% (90° plus). The control deflection given in the manual are decent but rather high for a maiden. So be aware of this on your maiden flight.

With the above modification the Freewing F-5 is a fine flying and durable model as long as one respects the high wing loading and limited power from the stock EDF unit.

I know the last statement is faint praise. But all is not lost, the F-5 does respond well to some simple upgrades! The first is that Freewing offers an inrunner upgrade to the EDF unit. The use of an upgraded inrunner motor should not be thought of as a option but rather a mandatory upgrade. As such I think one should only buy the ARF Plus version of the model as the stock outrunner* really is inadequate and rather inefficient! I also have found the 12 bladed rotor found on the Freewing 80mm EDF unit to be grossly inefficient. I like to use the Jetfan 80mm rotor. I go into detail on these EDF units here: http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=21998.0

Now while I blame the designer in making a mistake with the main retract mounts I need to place the blame for the poor flap hinging on the MBAs (Bean Counters). The designer has made the flaps with close to a proper Leading Edge (LE). But to save 50 cents on the manufacturing cost of the model the bean counters (MBAs) did not want to pay for a new set of molds to make stand off hinges. Without the offset hinge line the flaps don’t work to near their potential. I’ve added some photos showing how, with large Robart hinges one can correct this MBA induced crippling.

It is my finding that high blade count fans (actually it's placing the rotor farther away from the stators) don’t tolerate low SFA outlets. So the last modification I did was to open up the exhaust outlets from 44.5 mm nominal diameter, from a very constrictive 78% of Swept Fan Area (SFA) to 87% SFA (46mm nominal diameters). I then used Beacon Foam Finisher to smooth out the outlet walls. http://alofthobbies.com/foam-finish.html

All the best,

* The new 80mm Freewing jets are coming with a more powerful 1800Kv outrunner. This might make the power available adequate but still suffer the inefficiencies (power in vs power out) of an outrunner motor.

Title: Re: Freewing F-5 Tiger II (Your Dance Partner)
Post by: Konrad on June 05, 2017, 11:53:55 PM
I'm also showing where I place the RX with proper sized batteries. With the large heavy 6000mAh battery I had to place the RX in the dead space just ahead of the cheater hole. This gave me concerns with wires working their way into the rotor. While the F-5 did fly with the weight of the 6000mAh it wasn't fun to fly at 6000 feet altitude! The best performance I have seen is with the 6 cell Revo 4600 mAh 435 series battery.

Reading over the first post I see that I failed to mention the cause for the Saber Dance. The root cause of the maiden crash can be traced to two issues. First and foremost is that the manual did not state which way the model will pitch as the flaps are deployed. Depending on the placement of the flaps and stabilizer, some planes will pitch up or pitch down when the flaps are deployed.

On the Freewing F-5 there is a mild pitch up when the flaps are deployed. This is disconcerting on landing as one is forced to hold forward stick on the landing approach (opposite of what you normally do). If one does not hold enough down the model will get into a deep stall and no amount of throttle (power from the weak EDF system) or down elevator (no prop wash) will result in a recovery.

On the Freewing F-5 one needs to mix in about 6% down elevator with the deployment of the flaps. Also the shape of the mixing curve should be asymptotic (more at the beginning) rather than exponential in shape.

The total amount of mix is highly dependent on the placement of the center of gravity.

The second reason was alluded to, lack of power from the weak outrunner motor. This was expected, in that all ducted fans show a marked loss of performance at the higher altitudes. So I can't really blame that on Freewing or MotionRC as much as I'd like to!

Looking at the MotionRC site it looks like the manual has been updated to reflect this needed down mix with the extension of the flaps.
Version No.:FJ208-V01, this looks to have been done sometime after or near the introduction of the Swiss livery. I did not see any mention of how to properly install the retract torque boxes (mounting plates).

All the best,


I see that on Hobby Squawk Pilot Ryan said he didn't need any mix.

Title: Re: Freewing F-5 Tiger II (Your Dance Partner!)
Post by: Konrad on June 06, 2017, 02:31:14 PM
To the moderation staff.
Thank you for straightening out my mess.

All the best,