L-39 64mm 6cell, Flyfans. (This has to be the best value in an EDF)

[Konrad]

When looking over my stable of EDF jets I was shocked to see how many 64mm models I've acquired over the last year.

This can be traced to the advent of the 6cell 64mm fan power systems. Most of these are twins (Arrows Mig 29, Flyfans Su-27 & Freewing F-14) but I also have one single 64mm EDF the Flyfans L-39 on 6cells. 

 

I'm really impressed with the performance from all these 64mm models. I think the key to their performance can be traced to the new series of batteries now on the market. I fly my 6cell 64mm EDF on the HV 4.35v cell batteries. Other than the Freewing F-14, I'm using the SMC 4400mAh HV v1, 6cell battery in all my new 64mm EDF. The Freewing F-14 is set up for the 5900 mAh HV v2 battery. This is an inrunner set up and draws a lot more power than the other outrunners.

 

I admit that in a moment of weakness I purchased the Flyfans L-39 Baltic Bee. I was very pleasantly surprised by the product I received and the performance from this single 64mm EDF. This is even more astonishing when you realize I'm flying at 6K feet altitude in the Denver area (USA).

 

What caught my eye/wallet was that this little model has everything! First it has controls on all three axises. It has flaps, retractable landing gear and lights! And last a livery I can see in the air. This is rare with EDF jets as far too many are painted in low visibility gray! All for $210USD street price delivered to my door.

 

When I first opened the box I was hit by how closely this looks like what we got with the old 70mm Habu or 70mm Meteor. I was dubious that the 64mm EDF could perform at the level we saw with the 4 cell 70mm EDF units of old. Well, not only did the Flyfans L-39 perform as well as the afore mentioned 70mm model, but she has a lot longer flight time.

 

Looking at the model in detail I saw a few issues. First, the the ball joints for the surface linkage is far too tight. This can lead to centering issues with the flight controls. Second, the trailing link main gears are using tension springs rather than compression springs. These are easily distorted on a hard landing. The ball joints can be fixed with a light sanding of the mold part line with a few swipes of some 600 grit sandpaper followed by some dry film lock lube. The landing gear springs are easily replaced with spares (order 3 or more sets when ordering the L-39).

 

I was shocked at the high rate of climb. I loved the speed on the flat and level runs. The flaps really allowed the model to slow down and drop in on small runways. And the flight times where phenomenal like over 5 minutes with about 50% left in the batteries!

 

I was starting to think there was little that could be improved straight out of the box. Then I started to try some aileron rolls. Yikes, she does huge barrel rolls! It was impossible to do level axial rolls. I kept moving the CG aft and getting better rolls but at some point the rest of the flight envelope was starting to suffer. I then started to look at the thrust line. Yikes, when I slammed the throttle to idle the little L-39 would jump into a climb and if allowed to keep going would stall. This is a classic indication of far too much down thrust. I had to use a lot of up elevator trim to get level high speed and full power flybys. Cutting the throttle removed this down thrust allowing elevator trim to raise the nose into a stall.

 

This became an issue with landings as I like to land in a high alpha stance with the nose high and carrying 30% plus power. As I get lower (below knee hight) I'd cut the throttle and modulate the flair. The problem was that when I cut the throttle the nose would jump up and stall the wing. On my 5th landing this stall/snap resulted in the cartwheel severely damaging the airframe. 

 

So since I had the spackle out, I reworked the trust tube to gain some up thrust. This worked well, I still need to unload the elevator a bit when performing rolls but my landings are much more predictable.

 

I think the root cause of my thrust line issues was that the EDF unit is placed far too high in the fuselage to align with the intakes. I think the EDF unit should be mounted much lower in the belly to allow the thrust tube to point upwards in the rear.

 

A pet annoyance of mine is the use of "Y" leads! Wiith the 10ch & 12ch RX being so cheap, I think just about every servo should have its own channel assigned to it. This opens up a lot of programing options with the jet. It can solve the elevator induced roll we often see with these dual elevator servo models!

 

Wow, for $210 and a bit of spackel I don't think there is anything in the EDF market that offers this high a value with performance to match. Don't let the term 64mm fool you. This EDF jet performs!

 

 

[ArtB]

I have the Olive Green version of this Flyfans L-39.  Agree with this great writeup, however I didn't have the barrel roll issue.  Mine rolls very tight and fast.  Perhaps there's a QA issue with their motor mounting process?   Anyway, the landing gear must be discussed further.  With a really nice runway, ordering extra springs might be a viable solution if you never land hard.  But with a less than optimum runway, those springs get stretched far too quickly, and if you don't notice it and fly again, the landing gear can bottom out at which point it can "pogo-stick" the runway and rip the retract out.  Ordering spares isn't an option, because 9 outta 10 times I check, they are out of stock.  Tried looking for OEM source, not much luck.  I did, however, discover that replacing the springs with a half inch long narrow chunk of truck-tire inner-tube rubber, works fantastic and doesn't lose its tension with hard landings!!!    For $210 this is a GREAT buy!   But I'd replace those main gear springs with rubber, and install actual hinges on the flaps and ailerons if I buy another!  

[Konrad]

Thank you for your input!

 

My fan is seated well, but as they are using only 2 screws it might be an issue.  

 

Oh, I land hard! That is why I have spares of springs! I'll look into the rubber dampeners. As it is it can cost at least $2.39 a landing if I need to replace the springs!

[GBG]

Hello, I have a Baltic Bee ready to go and would be grateful for your thoughts on CG position.

[Konrad]

The 90mm in the maual is fine (no further forward!). I think I'm now setting around 94mm aft of the mannal's LE reference. I also moved the aileron and elevator push rods one hole closer to the servo output shaft to gain much better servo resolution. The manual throws are a bit much on high rate for a maiden!

Edited October 28, 2024 by Konrad

[Jake Bullit]

I've also got the Baltic Bees L39, had it a couple of months now and absolutely love it. 

I also use the SMC HV batteries and get great flight times with mixed throttle. 

It's not super fast, but it will slow right down with flaps deployed. 

My starboard main great must have stretched a spring also as it can get stuck. I've put some rubber O rings around to help it a bit. 

Great value for around £200.

 

[Konrad]

Looking a lot better than mine! Will she fly off that sod? And what can you report about the rolls and thrust lines?

[Jake Bullit]

 

[Jake Bullit]

She`s OK off the grass in the summer when its dry and short.

 

In the winter I take off the back hard packed paddock ,then walk back to the main field for flying and landing.

 

Of course the beach is ideal(our second site).

 

No problems at all with the rolls,shes very locked in.

[GBG]

Hi Konrad, thanks for the reply. It will be taken on board especially the control throws.

[Konrad]

Jake, it looks like your video is private. Well, I can't see it.

[Jake Bullit]

14 hours ago, Konrad said:

Jake, it looks like your video is private. Well, I can't see it.

Sorry, try it  now.

[Konrad]

Thank You.

 

I loved the slow fly by!

[Jake Bullit]

Yes she slows down really well.🙂