View Full Version : BH models Extra 300S Conversion

05-09-2006, 12:31 AM

I sart today the conversion of a BH models Extra 300S from IC .46 to a LRK 350-25.

I am planning to use a 4S 3300mAh 20C lipo, a Outrunner LRK 350-25-16 , a Jeti advance plus 70A and a APCE 15x8 If the clearance to the ground allows it.

Since the Flying weight of the IC model should be between 2,8kg to 3kg, I hope to obtain a Flying weight max of 3kg, not sure if the motor is enough to give the extra a decent behaviour in the sky :confused:.

The bigger problem till now was to figure out a way to mount the lipo in the model, I decide to use the "ribs" that sustain the glow fuel tank some use to fix the lipo to the frame.

What you folks think about my solution, it isn't elegant, but I hope it works...


Jeff Boyd 2
05-09-2006, 11:42 AM
Hi Jorge,

It will work OK, providing the mount will handle the intended 'G' forces thrown at it . . and the LiPo's are secure. Bare in mind, that you can subject your LiPo's (and mount) to 10 'G's (more or less) in a 3D aerobatic Extra.

Your LiPo looks like a Flightpower pack which weighs 350g (12.4oz), your mount will need to withstand about 2.5kg (7 3/4lb) force applied in aggressive aerobatics.

I would build the LiPo mount with a reasonable amount of 'engineered' strength with consideration to the way you intend to fly it. PS. A hard landing can subject reasonable force to battery mounts, too !



05-09-2006, 02:40 PM
Hi Jeff,

You're right about the g-forces, that's where is my doubts too.

The problem is that the plane structure is light (which is good), don't have a strong part of the frame to fix the batt tray.

I may go to the "box" solution. I'll post pics when done.


05-11-2006, 02:37 PM
yesterday take de model and weight it.

2660g with all the bits (ready to fly), not bad :D

I'm using Futaba s148 for ailerons and elevator and a Graupner 5077 for rudder.

Have also multiplex MS04BB (half the mass of a Fs148) but they are slow, have to decide what to use.

I'm using also a 4 cell reception pack (80g) not sure If I should use a 5 cell pack (140g) for servo speed and duration, what you guys think?

Maybe the MS04BB with the 5cell pack???

05-13-2006, 02:37 PM
MAiden the BH Extra 300S.

Two things:
1. pitch down tendency, not resolved with up trim
2. the LRK 350-25-16W/APCe15x8/FP3300_4S was not enough to give decent performance

pos-flight analisys:

1. Horizontal stab has positive angle of incidence when the wing has zero degrees --> put a little foam underneath the screws that hold the wing in place

2. Open a hole in the bottom of the cowl, and increase the hole in the bottom of the fuselage, trying to reduce the drag, the model did aerodynamic noise when crusing the sky, the belly pan fall from the model due to internal increased air pressure.

05-13-2006, 08:25 PM
Success at last :)
The "new" BH Extra 300s Fly like a charm with his new settings.

The performance was enough to do some figures in the sky, the air speed was a little for the slow side, but it was enough. The rolls are perfect axial, the looping was very high and very round, the inverted flight was very stable with very little "up" input.

Did a 7 min flight, then decide to land, the motor still as the power but I decide to land anyway. In the second approach, I crash the plane , just bring it Sloooow till a wing tip drop, I (over) correct, then the plane drop to the other side, I (over) correct again and the tip of the wing touch the ground, then tip toc, tip, toc. The plane finally stops with the LG support broken, wing tips with marks and the cowl with several marks without red color.

Have to practice the landing procedure without wind (wind is my friend when landing...)

Conclusion: Magnificent Plane, lousy pilot

05-13-2006, 10:29 PM
Some photos of the model after conversion:

05-17-2006, 10:03 PM
I'm just starting a conversion of the same plane. I'm planning to use an AXI 4120/14 with a 4S2P Polyquest 3100 battery. Can you tell me the amps and watts your power train is taking. Also what is the distance from the firewall to the start of the motor shaft?

It looks as though the batteries do not need to be as far forwards as I thought to balance - I was going to mount them under the cowl. What is the weight of your motor?

Thanks for posting this info - it has helped me start my conversion.


05-17-2006, 11:11 PM
Also what is the distance from the firewall to the start of the motor shaft?

You welcome :)

aprox. 8,5cm from firewall to the front end of the cowl, 9cm to the backplate of the spinner.

the motor is a HT3525/16, so far I use FP3300mAh 4S1p lipo packs.

I use three props with different results:

1. APCe15x8, 36A WOT, 7min flight, 2,6Ah , slow, WOT almost the time
2. APCe14x10, 33A WOT, 8min flight 2,9Ah, slow, WOT almost the time
3. APCe15x10, 46A WOT, ?6?min flight , 1,6Ah, 60~70% throttle

the 3rd prop unleash the potential of the plane, only have 1 flight with it but I like very much of the performance of the plane, not ilimited, but quite adequate, the lipo arrive almost cool to the touch :D


05-18-2006, 10:06 AM
Thanks for that. I expect my power train to take a similar amount of amps but with a smaller prop.

Could I ask another favour - could you post a picture of how you mounted the motor. This is the first time I've converted a glow plane and seeing someone elses efforts on the same plane would help a lot.

Also where did you balance the plane for the first flights?

Many Thanks


05-18-2006, 02:17 PM
How to mount depend of you motor. Mine has 4 holes in the back that I use to fix it to a ply plate then I use the bolts that came with the kit to fix it to the frame. As spacers, I use 4 wheel collar (aprox: 5mm).

You can see also in my avatar the technic I use.

As for the fist flight, I balance at 110mm, now I have it at 120mm (more difficult to land, the plane glide very well).


10-29-2007, 12:09 PM
Well after over a year I finally got this one in the air. After messing around with LiPo options I finally decided on 8 of the A123 batteries from a Dewalt drill pack. So the setup was

8S A123 battery
HXT 50-55 - 500 motor from United Hobbies
APC13x8E prop

This gave about 900W on a 3.2Kg plane (about 130W/lb) which was plenty.

The first flight was late in the evening as the light was fading and right after removing the undercaridge from my other plane by landing in a the field next to the runway! Feeling a bit nervous (these Extras have a bad reputation), I just took her up and round a few times with a fast low pass and then a landing being careful to keep the speed up. It flew beautifully - the takeoff had no ground loop tendancy and the landing was also problem free. In fact it slowed down nicely in the flare at the end of the approach.

I could get bitten next time but I recommend this plane as an electric conversion. With the tank holder removed and a ply plate inserted there is a huge space for batteries. The mounts for the glow engine are about the right space for the backmount of the motor I used and standard inch PCB spacers put the motor just where it should be.

It was well worth the wait.


10-29-2007, 06:45 PM
I am Glad with your success :)

I sell my Extra, don't have it anymore.

Keep on with the good work.

10-30-2007, 09:53 AM
Sorry to hear that Jorge. Thanks for your input and flight reports. My initial attempt at a power system would have been very underpowered. I doubt it would have got off the ground and the LiPos would be ruined after only a few short flights. Your measurements and reports made me redesign the power system for over 700W and it worked.

Definitely the way to go with higher power setups is more voltage and medium amps. LiPos are getting better but they are still so over-rated and degenerate over time. I would never use a LiPo over 10C after my experiences with them. A123 cells seem so much better if you don't mind a 6 minute flight!

Hope you found something better to replace it with.