I received a few questions about my gas to electric conversion of the Kyosho F-86 Sabre,

http://www.kyosho.co.jp/web/products...f_sabre-e.html

(specs are listed above).

I found the kit at a LHS (Ultimate) about six months ago - at a very good price, it did not seem to sell very well. I had seen the gas one (OS .15 CV-DF) fly and it flew ok - but boringly slow ... :

Kyosho F-86 Sabre video with OS .15 CV-DF

I heard people had just swapped the 90mm Kyosho icdf fan for a WeMoTec MidiFan, but that option I found unappealing because of the lack of any ducting. So I carefully made my own ducting plug out of blue foam, covered it and glassed it. After reinforcing it with carbon tow, I found it fitted quite well.

The intake area (around 37 cm^2) determined the fan size: I needed to get (from warbirds-rc.com) a WeMotec 620, 85 mm diameter, with an eff. fsa of about 43 cm^2. The Sabre intake is a bit bigger than my K&A MiG-15 (33 cm^2) which flies very well on the smaller HW-609 fan (eff fsa 32.2 cm^2).

In any case the 90mm Midi is just too big to allow space for both ducting and batteries (unless you cool the batteries in the ducting ).

Here's the finished product, after the maiden (actually two flights), last Saturday Oct. 15 :

https://www.rcgroups.com/gallery/sho...cat=509&page=1


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The setup right now is a WeMotec HW-620 fan (85mm) w/o motor cone & large spinner gap for cooling,

http://www.wemotec.com/2_1_6.html

a Hacker B50-18S (three years old, 100+ flights), a Jeti-Hacker Master 77A controller and 6S (3S+3S) Kokam 3200 HD pack. Also a separate receiver battery (350 mAh), three HS-85MG servos and fixed (stock & removable) gear.

It's very cramped inside and the Kokams & ducting just barely fit .

Looks great Herb! Fixed gear?

I comes with a very nice and light one piece fuselage. And avery nice decal set. The tail is slightly enlarged, which I don't mind as it probably flies better.


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It took me a looong time to do the ducting, a lot of patience first doing the plugs and then making the ducts themselves. Straighforward but tedious.

Here's some pictures of the duct work (fiberglass, carbon tow reinforced):


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Thanks Chris ! Yes fixed gear, for now.


Mylar tube for exhaust, choked down quite a bit to around 65mm (I think).

Elevator servo was re-positioned out of the way, with silver soldered y-linkage. Receiver is positioned in cockpit, batteries are sitting left (3S) and right (3S) of the duct, resting on the wing.

The cooling intakes, which I had thought initially of removing, are in fact just in the right position to blow air on the Kokams and the ESC.


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Herb,
That looks sharp! Tell us how it flew.........speed? rog? Stuff like that. How much does it weigh ready to fly? Size (in inches please) for us that don't do the conversions very well. Oh yes and your mothers maiden name... Just kidding about that last one. Seems like I am always getting asked that question for some reason or another.

Kerry

For now I have used the (fixed) landing gear that comes with it, it's simple to install and seems to work. The nose gear is fixed (no steering) and a bit weak - in the original the strut went all the way to the top of the fuse theorugh a ply plate (now removed to save weight).

If I really like a lot the way it flies, I might think about Springairs 602's. The retractable nose gear + steering would be a really tight fit ...


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This is a very lightweight kit (that's the reason I liked it in the first place .

Out of the box the empty plane weighs 29.9 oz (850 g) without servos, electronics, motor, fan, cables, batts, esc.

The wings are 4.3 oz (left) and 4.5 oz (right). The fg fuse is 11.5 oz.

My weight ready to fly came out at 69 oz (4.3 lbs, 1960 g) , which means it should fly well on as little as 700+ Watts. In which case a 3S setup might be more appropriate.

The Sabre's power setup on 6S Kokam 3200's HD delivers around 1380 Watts full throttle (cold batteries), which seems enough for a brisk takeoff in less than 80 feet or so.

The Sabre cruises along nicely at 1/2 throttle. Low drag and low weight means a whistling 100mph is erached quickly. The airframe (tail surfaces) seem a bit flimsy so this one's not designed for breaking speed records.

The maiden was last Saturday, the wind was blowing at 20+ knots. CG was at 175mm according to (latest) instructions. Throws were as per instructions (5mm ail, 10mm ele).

This is the first plane I have ever built that did not require any trim inputs to fly straight and level hands off on the maiden !

The CG seems a bit foward (fast landings), the elevator throw was too low (having a hard time pulling the nose up on landing) , the ailerons throws were a bit too much, and were reduced after the first flight.

As I said, it cruises along nicely at 100mph at half throttle or so, it's the quitest and smoothest edf yet, perhaps because the fan mount I made is really strong but the silicone really smooths out the vibrations & resonances.

All in all, a wondeful kit. But a lot of work to make those ducts !!

Thanks for the report Herb. It sounds like a very nice kit. One of the LHS has a bunch of the Kyosho war plane kits in stock. They all look very nice.
This is the size of plane I like best. I am able to keep them oriented better it seems. It will be interesting to see how your retract set up goes. Keep us posted on that also.
Thanks,
Kerry

Great job Herb. I wondered if anyone was ever going to convert one of these... I know they've been out for a while.

Looks great! Hope to see it fly in person very soon.
I remember you talking about doing this conversion 3 years ago!!!
The advent of LiPo battery technology has really made this type of conversion possible.

glad someone figured that one out, good job Herb

Really nice Herb, I'm wondering how many people out there would like a set of ducts???

Gene

With a proven setup, ducts probably will be in demand.

Looks great Herb, I'm guessing retracts soon.

Thanks for the comments guys.

The Kyosho F-86 electric conversion had been done before a few times, but none with ducting, as far as I am aware.

I think the performance without ducting must have been horrible as soon as you get above 70-80mph. You end up wasting a lot of precious lipo energy heating the air - with all that turbulence inside the fuse .

But doing the ducting yourself is a LOT of work, hopefully somebody (maybe ven Kyosho, why not) will come out with a nice 85mm-90mm F-86 with pre-made ducting.

Originally Posted by kriptonic

Really nice Herb, I'm wondering how many people out there would like a set of ducts???

Gene

Well, I would be interested in a set. I was just to chicken to ask. Now that it has been brought up, if you do offer them count me in.....

Kerry

Originally Posted by kriptonic

Really nice Herb, I'm wondering how many people out there would like a set of ducts???

Gene

That is exactly what I was thinking Gene.
Justin

Sorry no ducting plugs, I used acetone to dissolve the foam.

There hasn't been much interest in the Kysoho F-86 Sabre here for years, I did not think anybody would be really interested, after all the ritual Kyosho bashing by the experts .

I will have Al take a video perhaps on Sunday, tomorrow it's off to a friend's wedding

Great conversion Herb and looking forward to the video

Maybe Kyosho do deserve a bit of ritual "encouragement" now and then - sending them a DVD of your vid might help

Ref the ducting, wouldn't it be possible just to make it from rolled up thin grp sheet, or are the insides configured so that moulding is the easier route?

Cheers

Gordon

Thanks for the comments Gordon

What is grp? The problem with the intake is that it transitions from trapezoidal/squashed-oval at the mouth to round at the fan. Anytime you don't have a perfect fit at the intake, you lose some performance.

After Ron Laden posted his technique with paper & white glue, I had to try it myself when he did. That comes out very strong too if done right, but I think for 1400+ Watts it will need fg and carbon on the outside, otherwise you might get a really loud ka-boom on the first flight

Originally Posted by Herb

What is grp?

Grp is Britspeak for fiberglass - Glass Reinforced Plastic

Herb, do you have a link or some more info on this paper and white glue ducting? Sounds interesting.

Justin

Do a search under Ron Laden in this forum, you will find it I am sure.

Video of the Sabre from yesterday, Alberto took the video with my Sony camera and did an excellent job !

Dougie came out and flew the Sabre (guess no seedy Buttville motels this weekend), so I just stood there and watched the show for once ...

Jon (LittleJon) took some very nice inflight pictures with his bad*ss Canon eos digital camera, which will be posted here later ...

Level flight speed in the video is around 108 mph, fan rpm around 29.8 krpms which gives around 1020 watts in flight wot, or ca 49 Amps. The full flight was about 4 mins.

F-86 Sabre video (17 MB, 2 mins)

Judging from the video, the Sabre takes off of short California grass in about 30 feet.

Awesome Herb!

Dunno how you keep that little 18S together at that power level , didn't sound like he was backing off the throttle much!

Nice video, flies really great Herb.

Beutiful flyer Herb. Good job.

Justin

I KNEW the B50-18S I once had ( and sold on... ) was good for far more than only 10 cells !
DAMMIT !

Herb, that looks almost REAL !
It JUMPS off the ground...

Keven.

[QUOTE=keven64]
Herb, that looks almost REAL !
It JUMPS off the ground... QUOTE]

A slight contradiction in terms there Keven ... the real machine did anything but jump off the ground, the F-86F with 6-3 wing needing a 3320ft (0.62 mile) ground roll, and 4720ft (0,9 miles) to clear a 50ft obstacle The slatted wing version did better (phew!).

That apart, yours sure goes great Herb, and shows Kyosho the direction they really should be going in She does look to land quite slow, with good low-speed stability.

Cheers

Gorodn

Thanks for the comments, it's really a nice flier .

Some more pictures taken by Jon (Canon EOS 10D) on Saturday:


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And I got to do the honors of the maiden!

Balanced F-86 HW-620 fan spool up, after 4+ min flight (22% Kokam 3200 battery left) it still spins at 30.4k rpms, or around 1110 Watts . Thanks Bruce ...

<Testing if I can get these attachments to work >

https://www.rcgroups.com/gallery/sho...cat=500&page=1


Complete flight video here:

https://www.rcgroups.com/forums/show...=438267&pp=100

That was cool Herb, I only held the camera!
I had no idea you could figure out rpm by sound.
We'll have to try that on my 4s mega/2 Alfa!
Bruce

The 30.4k rpms gives you a rough handle on the efficiency of the setup.

The (no-load) kv of the Hacker B50-18S is 2000 rpms/V, so the no-load rpms on 6S is 20V x 2000 =40k rmps. The load rmps at full throttle is therefore 30.4/40 = 76 % of the no-load rpms.

A good rule for efficient (ie low heat generation) two-poles is around 80% of the no-load rpm, so the 76% is quite close to it.

In flight the rpms (at full throttle) increase another 10% or so (applying a spectral analyzer to the F-86 video), bringing the 76% figure close to 84% ...

F-86 Sabre video (17 MB, 2 mins)



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thats just incredible....thanks for sharing!

Herb,You got me building another one and using a full duct. Using HW-620 fan, Hacker B50-15L and 6S2P Lipi pack.
Bob

As I understand it, Hacker is just one of a few motor mfg's that rate their motors Kv stat while it is under load. Most others do it free spinning and when put to use it usually "bogs down" alot more than the Hacker and other high end motor makers do if you use yoru rule of thumb. Have you noticed this much Herb or Bob?

Justin

Thanks guys Bob you'll love it, it's a sweet gentle flier ...

When you make the duct, plan ahead on where you will put the batteries. I think 3S+3S is probably the only way to go.

But 3S2P 2000's end to end, one long stick on each side, might take up less space. It makes a difference on how the duct should be shaped, there's very little space in there. The WeMotec HW-620 is the ticket imho.


Hacker no-load rpm table:

http://www.hacker-motoren.com/deutsch/b50_drehzahl.html

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Herb, Where do you have the fan at?
Thanks,
Bob

The front of the fan (HW-620) is located around where the two wingbolts are, I used the original kyosho ply former to secure it (it needs to be reduced in diameter to accept an 85mm fan). I played around quite a bit with the fan and the batteries to see what the best location was, so that the batteries would be easily accessible, and the CG would come out right.

The picture below shows that the fan is hidden just behind the rear wing mount.

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Originally Posted by Pdemon

Hi, following this discussion in the power system forum:
https://www.rcgroups.com/forums/showthread.php?t=489821
I would ask if anyone has experience in this setup for my Kyosho F86: Hacker B50-15S (or 16S?), Wemotec HW620, 5S lipos. I know Herb made a successful Sabre with 6S lipos and same fan with a B50-18S, but having three new 5S packs, I would like to use them... PG

To get roughly the same power I get on 6S - but on 5S - you will need a motor with a kv of 2000 x 6/5 = 2400, which would roughly correspond to a Hacker B50-15S:

http://www.hacker-motor.com/deutsch/b50_drehzahl.html

... but this might not work as the amps will go through the roof (the battery won't handle it?). So a softer wind might be a wiser choice ...

Herb
I had purchased a B50-16S and have in hand both 4S and 5S packs, so I can play a little trying a correct setup. Thanks for the suggestion, I admire your work. Just a question regarding the ducts diameter: the intake and exaust of the model have a diameter smaller than the fan itself. This inverted "venturi" will slow the airstream in front of the fan: will this cause a loss in performance? Enlarging the intake (out of scale) will improve the fan efficency?
Thanks in advance
Pierluigi

The large exhaust is no problem, you can narrow it down with an appropriately rolled mylar tube.

The intake is indeed too small for a 90mm fan (eg Midifan), but the HW-620 (85mm diam) works fine. Keep in mind that you want to match the F-86 intake area to the fan swept area (fsa), which is defined as the circular area of the fan minus the circular area of the fan hub. Even if the intake is a few percent below the fsa that is still not a problem from an airflow/efficeincy point of view. So, to answer your question, yes the fan looks like it has a bigger area but in fact it does not, as there's no airflow through the hub .

Perhaps the most important aspect of the ducting is to get a nice smooth transition with no bends and abrupt restrictions/enlargements from the intake to the fan.

Thanks a lot, Herb!
you've made it all clear, this was the answer I was looking for . Now I can proceed with my F86. I'll keep you updated...
Pierluigi