Guten Morgen Miteinander
Nachdem ich von Chrigi den Forum Tipp bekommen habe, nahm ich kurzentschlossen mit John kontakt auf und bekamm nur kurze Zeit später schon antwort. Wirklich ein super Typ und danke noch an Chrigi für den Tipp. Die Antwort von John möchte ich Euch nicht vorenthalten.
Mail von John:
Hi Thomas,
In 2010 I did fit a PHT2 into the Hirobo ec120 but it was not completely successful, so I will not be published the story. However you are not the first person to ask about it, so I have pasted in my other reply below.
I hope this helps... If I can help further please contact me...
Here is the reply, it includes a response from Hirobo about the problems I had with the Fenestron
All the best
Jon
(PS I think the problem with the Fenestron is that the gearbox is supported by the plastic vanes and when working very hard, it twists resulting in the blades hitting the casing.)
I started this project last year and the model has flown several times but is not yet, and may never be, a complete success. The problem is that my finished model with fuel is about 19 lb, which for this size rotor disc is very heavy. I am using the Hirobo 3-blade rotor head, which carries the weight OK but the increased torque reaction means the Fenestron tail has to work to its maximum and even then is on the limit. So you have been warned!
The Hirobo 3-blade rotor head has a target rpm of 1500 and using the stock mechanics, gives a Fenestron tail rpm of 15,000 rpm. So these were the targets.
Re the PHT 2, I have one that I can choose to run at 1488 rpm main shaft speed, which gives a tail rotor rpm of 6949, so I chose that. As I understand it, later software versions offer different rpm, ie 1394 or 1617.
I reversed the main shaft rotation (to right) but putting the main gear below the pinions.
I then had a simple speed up gearbox made that increases the tail output speed to close to the target of 15,000 (I think it's 25:12, = 14,447 rpm). The output shaft was 5mm and so I could fit the Hirobo drive coupling to it. The intermediate tail drive shaft needed shortening.
I had a plywood chassis assembly made to raise the mechanics so the servos in the PHT-2 are just inside the top cowl. I used the Hirobo swashplate anti-rotation arm, which fitted easily with some shim washers. The Hirobo swashplate and rotor head then fitted in an ideal position. I used 3 servo eCCPM, - the photo shows how the servos were fitted (the PHT-2 is designed for 4 servos eCCPM). I also used the top stays that came with the ec120 kit to secure the PHT-2.
I used 2 saddle tanks (Sullivan S390) and a 3rd header tank inside the plywood 'chassis' - it sits on the fuselage floor. This gives about 1.2 litre of fuel, which weighs about 1.2 kg... The PHT-2 is thirsty - it will burn about 1 litre in 6 minutes.
The exhaust was difficult - I used a trade contact who got a tube made for me, but is wasn't to the dimensions I specified so I had to modify it. I then found an old Wren exhaust with a taper on it, I cut this so it would fit the tube, lined it up and silver soldered it together (Badly!). I could not support the exhaust and so tack soldered it to the turbine.
I protected the top cowl from the heat using ceramic paint by (Heat Shield by BVM).
I switched from the Kero start to gas.
The whole job is not difficult but I did need help with the wood chassis and gearbox and exhaust. It is a VERY tight fit in the model and as I say it really is too heavy for the model size, so it will never fly that well. But it shows what can be done...
Finally the Fenestron is now causing problems and in fact has failed in some way, the blades touched the housing, so I have to strip it down to see....
Finally, would I do it again, I'm glad I did and have not given up, but an electric conversion is a lot more practical!
I contacted Hirobo about problems with the Fenestron:
I have recently been flying the model with a small turbine engine in it (JetCat PHT-2) and I now have trouble with the Fenestron tail.
I am sure this is because the flying weight is higher than it should be but it is such an interesting model I hope to make it fly well.
The model ready to fly is now about 18.5 lb (8.4 kg).
The problem is that the Fenestron tail has to work very hard and the housing (0414-053) has flexed so the blades have hit the case. Also the housing has been rubbing against the plastic of the casing. I think the bearing that carries the 0414-055 shaft is now loose in the case and this has caused the problem. See Photos
Are there upgraded parts for the Fenestron?
Do you think this can be made to work, or is the model too heavy?
The reply was that the Fenestron was made for 60-size models and there are no upgrades to it.
I believe the bottom line is that the Fenestron is OK for models it was designed for but is not capable of reliably producing the thrust needs for anything heavier/needing more torque compensation. It may have handled using the 2-blade rotor head as I believe it produced less torque... but that was not the idea.
I did not explore improving the Fenestron, although I did look at the Cinescale unit (now owned by Vario) but it fits a to a boom, which would mean major changes to the fuselage.
I have seen electric conversions of the Hirobo models including the ec120 and they work fine. I have also seen a ec120 with a much lower rotorhead speed (1200) and the tail worked fine. This all leads me to beilief my first conclusion is right, the 3 blade head with ic /electric power is OK but anything heavier is not going to be reliable...
I hope this helps and will be interested to hear how you get on...
Wieder etwas gescheiter
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Hirobo ec120 mit Turbine
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