Official Freewing 90mm F-4 Phantom II Thread

[Elbee]

Question for all, Are there ideas out there for improvements in the actual ducting of the Freewing F-4 or any other EDF airframe with dual inlets and split outlets? I am a novice with this, but I am all about the efficiency of the airflow. Dynamics are different with scale and I do not want to discuss at lot theory unless that can be translated easily into 3DP designed parts. I had a JHH F-4 with bifurcated ducting and as I remember that ductwork was tighter and closer to the fan itself. Any assistance here would be greatly appreciated. Best, LB

[TMoyer]

I am just about finished with my F4 and I was wondering does anyone have any recommendations for an overall flat clear coat that won’t attack my Callie graphics? It would be nice to a) protect the graphics and b) knock some of the shine off them at the same time.
Thanks, Travis

[Bobaroo]

Straight Pipes with long Runs are 'Optimal'. This airframe with Twin70mm or Twin 80mm would be pretty close to 'Optimal' by running things clean and uninterrupted through the Jet.
When looking at our Exit Geometry we see that the direct Line to our Fan from the Exhaust Exit is roughly 10° or so. That has the Bulk of our Efflux Air, if you will, exiting 10° off center. There are losses accrued there as well as at the Bifurcation Origin directly behind the Fan. Lotta Air rushing around in there trying to find a way out. An unavoidable consequence of the Bifurcation due to the close proximity of the EDF to the exit.

I'm working on a Twin70mm for one of mine. It should perform well !!

[TMoyer]

What did you guys do about mounting the switch for the UBEC? Not quite sure I understand the reasoning behind having the switch as the power system is energized as soon at the battery is plugged in and the switch just controls the radio power. That switch somehow gets turned off in flight, you are SOL....I primarily use the power safe receivers that have the fail on switches.

[Bobaroo]

I am just about finished with my F4 and I was wondering does anyone have any recommendations for an overall flat clear coat that won’t attack my Callie graphics? It would be nice to a) protect the graphics and b) knock some of the shine off them at the same time.
Thanks, Travis

WBPU comes in a Satin finish. UltraFine SteelWool gives a great DullCoat after if gently rubbed onto the Graphics and Jet. Shiny Vinyl has to go !! GL

[OV10]

Straight Pipes with long Runs are 'Optimal'.

That's what I said for all my Harley's;)

[Hardway]

NO BIKERS!!!!!!!!!!!! LOL LOL Straight pipes are the order of the day Bro!!!! :Cool:

[Hardway]

That is why I don't wear the colors Jack.... ;) "Wild Hogs" movie

[Elbee]

Straight Pipes with long Runs are 'Optimal'.

BBR, I agree, but that doesn't help with what we currently have. How about the influx of air. There is quite a cubic area fwd of the EDF when compared to the JHH which as I recall came aft as a bifurcated duct right to the fan. All I can figure with the efflux air is make certain the walls are smooth. Is there a penalty at the tips with the added scale nozzles? Mine stick beyond the foam duct by 3/8" or so. Does that create drag turbulence and thrust loss? I understand drag theory and some aerodynamics of lift, though this is not the same, is it? :Thinking: Inquisitively, LB

[Bobaroo]

The Science of it in simplified terms equates to this: We take a given Volume of Air and Redirect it into a Fan, Acc elerate it and then Redirect it out the back !!! Hopefully, all this is done as efficiently as possible with very little disturbances at each end. It's a 'Volume' management problem really. Unlike a FSA, we're not Producing more Volume, we're simply accelerating and redirecting our available air.

Everything about our Single EDF Design is working Against that effort to some degree. Twins will generate twice the Fan Disturbances (Disruption at the Fan) but their combined Degradations don't equal the Bifurcation Losses we get with a single at both ends of the Jet.

These Conditions/Degradations change values drastically when going from a 'Static' state to a Energized State where the Jet is Airborne and the Incoming Air is being routed down an inlet.

Drag at your Exhaust Exits is there because of the Turbulence Region at the Boundary Layer where the Air around the Jet meets your out-flowing Accelerated air as they combine. It's similar to that Disruption occurring at the trailing edges of your Wings and Stabs !! That 1/8" Thick Trailing Edge on everything is Slowing You Down a bit. A thrust Tube or Mylar extension for your Exhaust would help with that, as would shaving/shaping the Trailing Edges on all of your Flying Surfaces into Razor Sharp Edges !! Jepe Mods are all about Cleaning up the Jet, straightening out the 'Flow' if you will. And these things work.

Once I get deeper into the Twin I'll be able to make straight runs into and out of the Jet with pretty much equal values of uninterrupted air entering and exiting the Fan without the Penalties imposed by the Bifurcation. Shaping the Trailing Edges won't necessarily help enough for me to worry about on this F-4 because as we know,... I fly my Jets 'Dirty'

[Elbee]

BBR, I understand that, but in the Freewing F-4 there is a large gap between where the 2 inlet ducts end and where the fan unit begins, call it 3" and I wonder why that is. Shouldn't the 2 inlets come all the way back to the fan face even if those are still split? I would think there would be turbulence in front of the fan caused by this where if the 2 ducts simply meet at the fan face and that should be avoided. I understand that the exiting air is forced and that it should extend to the point where there is no outer air influencing or redirecting its flow. I might be overthinking this, but the inlet ducts seem clunky to me and with some 3DP assist, could be improved, though I am asking about something that isn't even an issue. Best, LB

[Bobaroo]

Ahhhhhh, I hear ya... That Plenum or Chamber in front of the fan. I know that there is Violence at the Fan Face with the Air Swirling to get into the Blades. As far as the necessity of having that Volume of Space there at the Fan Face, I do not know. It would be interesting to make a Splitter for that, install it and Try it out !! I don't know how you could accurately measure the Effectiveness of something like that !! Or, how you'd get it in there !!

[EA-6B Geek]

I am just about finished with my F4 and I was wondering does anyone have any recommendations for an overall flat clear coat that won’t attack my Callie graphics? It would be nice to a) protect the graphics and b) knock some of the shine off them at the same time.
Thanks, Travis

I use Testors dull cote. Works well. Doesn't attack the stock finish or Callie's graphics. Pictures when you're done!!

[Elbee]

A simple design, I think, and as far getting in there, even if one had to remove the fan, it should be easy. Mount it to the rectangle slot at the trailing edge of the union where the ducts join. Sketch me what you envision something like that should look like. A simple vertical splitter was my thought. :Thinking:What do you think? I'd send you a test proto. Best, LB

[Bobaroo]

A simple design, I think, and as far getting in there, even if one had to remove the fan, it should be easy. Mount it to the rectangle slot at the trailing edge of the union where the ducts join. Sketch me what you envision something like that should look like. A simple vertical splitter was my thought. :Thinking:What do you think? I'd send you a test proto. Best, LB

Sounds Good, I'll be getting in there soon since my Dual GoonieBurner is due to arrive this week !! That Rectangular Slot allows for some evacuation of the Battery Bay !! That Ventilation will need to be incorporated into the Plenum Wedge !!

[TMoyer]

I use Testors dull cote. Works well. Doesn't attack the stock finish or Callie's graphics. Pictures when you're done!!

Thanks, I was wondering if that would work. With it being a laquer I wasn’t sure if it would attack either the stock paint or the graphics.

[Bobaroo]

I've had problems with some of those Aerosols 'Yellowing' over time !! Especially on light surfaces. WBPU and the Tamiya ClearCoats... Not So Much ! Tamiya's are Lacquers also, but when applied in very thin Mist Coats, they work Great !!!

[TMoyer]

No problems with the WBPU yellowing? I remember from many moons ago, Pactra had Formula U for the nitro stuff. It was a urethane. I used the clear a few times and after a while in the sun it yellowed like crazy. Really looked bad after a while.

[TMoyer]

Do you spray or brush on the WBPU?

[Bobaroo]

Do you spray or brush on the WBPU?

Comes in either form !! I use spray if my Surfaces are already pretty smooth and I just need a light Coat ! Brush it on if I'm trying to smooth out a rough GatorJet finish or need a heavier finish !! Either way, it flows out Nicely if you don't go too crazy heavy with it !!

I prefer these Tamiya's for delicate work. I'll Mist a coat of Flat over the Gloss and get a great Sun Bleached look on the Top Surfaces of the jet , Intakes, Dorsal Spine, etc...!! GL

Once you've WBPU' the Jet, Lacquers can be applied lightly with more confidence !!