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Old Dec 20, 2009, 05:40 AM
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Quote:
Originally Posted by RENATOA View Post
First serious design flaw revealed. A fellow Xeno engine axis broke at second launch, due to excessive acceleration.
He expected this thing, because there is a * known fact * that carbon fibers does not handle well longitudinal torsion, so he had ready the replacement: a brass tube same diameter, with a 2mm carbon rod glued inside.
The brass will provide anti torsion strength, while carbon will keep it straight.
While a carbon shaft is probably not the ideal solution to transfer torsional loads, it has to be a viable option, as there are even companies producing solid shafts from 4-12mm:

http://www.cg-tec.de/uploads/media/Welle_de_web.pdf

Did the failure occur with the original Xeno Drive Set? Any previous damage due to turning the motor on, while the model was on the ground?

Jürgen
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Old Dec 20, 2009, 06:18 AM
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> Did the failure occur with the original Xeno Drive Set?
Yes

> Any previous damage due to turning the motor on, while the model was on the ground?
None that I know. As I wrote, it happened at second launch.
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Old Dec 20, 2009, 06:33 AM
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I can't imagine that the drive system hasn't been tested thoroughly by Multiplex.

So far I have not read about any shaft failures in the German forums.

Jürgen
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Old Dec 20, 2009, 10:04 AM
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Just another quick look at the drive system:

With the battery approx. 10% discharged, I measured:

9.51V - 19.71A - 9677rpm (static figures).

Jürgen
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Old Dec 20, 2009, 02:12 PM
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Well, a likely scenario is if the prop hits the ground at full rpm this could definitely splinter the shaft, torque on it will be substantial. This however goes for any shaft material type, and could result in failure. I've seen this happen on thin wall brass and aluminum shafts before as well.

Cheers,

Sander.
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Old Dec 20, 2009, 02:34 PM
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Hi.
Although i was silently monitoring this thread for days it was only yesterday that i bought one Xeno kit.
Today it had it's maiden flight.
Everything was perfect, the Xeno is a very stable wing indeed.
There are some things that are not designed correctly though.
Here they are:
1) the airplane has nothing to protect it during landings from scratches (fixed by me)

2) When folded the control surfaces horns are pressing one another and they keep the Xeno from fully folding because they are too long.

3) The control horns are too long and during landing they touch the ground first taking all the impact. I can't understand why they didn't mounted the control horns on the upper wing area in order to avoid any contact with the ground.

4) It is a known fact from early helicopters when they tried to use carbon rods for the flybar that they can't handle longitudinal torsion stress so i can't understand why they chose a carbon shaft instead of a titanium one which i use in my helicopters.
It is light enough, very strong and the cost would be minimal for multiplex.
I know that i would pay some more for a titanium shaft.

My conclusion is that the Xeno is a fantastic flying wing with crappy not well
balanced moving parts (the spinner was malformed in my case), fragile shaft, overpriced motor kit and that the folding feature is not that attractive to me at least as i can fit the wing easily to a Toyota Yaris unfolded.
I bought the standard motor drive because i was in a harry to fly it the next day ( i finished the plane in 6 hours at 05:00 am and flew it at 09:00 am)
and i can say from years of experience that the motor included with the standard kit is useless (50W), they could just not include it at all (maybe they had a stock)
There should be only one motor kit offered, the Tuning kit which can do the job very well
Anyway i fitted a Hyperion Z2213-24 (850 Kv) that i had with a 10 x 8 aeronaut folding prop and the Xeno has unlimited vertical and low power consumption.
At full throttle it produces over 1Kg of thrust (static of course) @ 16.5A but the shaft will not hold i am sure as the inertial shock during acceleration from the 10 inch propeller is high.
Luckily i have a MC4000 so i programmed some delay for the throttle channel.
If i get another one which is very likely i will make it non folding and i will put a motor/ESC combination of my choice at the back of the plastic middle section using bolts.
I hope i wasn't that bad to Multiplex, i merely expressed my opinion.
Chris
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Old Dec 20, 2009, 03:00 PM
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Jurgen ..... any chance you could post photos showing the underside of the wing i.e. to show the control linkage/horns .......
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Old Dec 20, 2009, 03:11 PM
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Quote:
Originally Posted by hendrix View Post
...
There are some things that are not designed correctly though.
Here they are:
1) the airplane has nothing to protect it during landings from scratches (fixed by me)

2) When folded the control surfaces horns are pressing one another and they keep the Xeno from fully folding because they are too long.

3) The control horns are too long and during landing they touch the ground first taking all the impact. I can't understand why they didn't mounted the control horns on the upper wing area in order to avoid any contact with the ground.

4) It is a known fact from early helicopters when they tried to use carbon rods for the flybar that they can't handle longitudinal torsion stress so i can't understand why they chose a carbon shaft instead of a titanium one which i use in my helicopters.
...
My conclusion is that the Xeno is a fantastic flying wing with crappy not well
balanced moving parts (the spinner was malformed in my case), fragile shaft, overpriced motor kit and that the folding feature is not that attractive to me at least as i can fit the wing easily to a Toyota Yaris unfolded.
I bought the standard motor drive because i was in a harry to fly it the next day ( i finished the plane in 6 hours at 05:00 am and flew it at 09:00 am)
and i can say from years of experience that the motor included with the standard kit is useless (50W), they could just not include it at all (maybe they had a stock)
Anyway i fitted a Hyperion Z2213-24 (850 Kv) with a 10 x 8 aeronaut folding prop and the Xeno has unlimited vertical and low power consumption.
At full throttle it produces over 1Kg of thrust (static of course) @ 16.5A but the shaft will not hold i am sure as the inertial shock during acceleration from the 10 inch propeller is high.
...
Hi Chris,

1): Elapor is pretty tough without any additional protection.

2): That has been noticed before. Those who want to fold the wing further, could move servo and control horn by approx. Th8mm on one side.

3): I think it has purely to do with the looks. Servos and linkages on top of a wing don't look so good.

4): The prototypes used different materials. Anything but carbon fibre rod will be heavier - even titanium.

50W was probably OK before the models weight went up. A low kV motor in conection with a bigger prop will increase the loads on the drive shaft by quite a margin, i.e. not a good idea.

I did not notice any crappy plastic parts.

The folding mechanism is great for taking your model on holidays. You may even take it on board of a plane as hand luggage?!

Jürgen
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Old Dec 20, 2009, 03:15 PM
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Quote:
Originally Posted by hobie14 View Post
Jurgen ..... any chance you could post photos showing the underside of the wing i.e. to show the control linkage/horns .......
Sure - nothing unusual here:
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Old Dec 20, 2009, 03:26 PM
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Hi Jurgen.
I agree with you on all (many mentioned by me problems can be alleviated) except for the control horns.
The risk of damaging the servos or ripping an elevon from the wing is there.
I know that a 10 inch propeller will brake the shaft but this is what i had laying around at the time.
My spinner was malformed (maybe i was unlucky) and subsequently it wobbles producing vibrations.
About the motor of the standard kit i think 30 more grams for the bigger motor is not that bad for a wing area like the Xeno has.
200W instead of 50w for 30g is i think a good deal.
Chris
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Old Dec 20, 2009, 03:40 PM
Failure is an option !
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Jürgen, I appreciate your analysis but sometimes I wonder how close you are to Multiplex .... as you always defend them even on obvious issues.
I personnaly love the Multiplex - German quality build and enginering. I own a Gemini, a Parkmaster , an Easy glider and now a Xeno. Now, even the bests do mistakes especially on first release of a model. This is nothing unforgivable.

So, let me tell everybody that the Xeno is not perfect.
I bet my shirt (I only have one, it is a big deal) that the carbon shaft issue will soon be a major issue if Mpx does not release a fix about it. On top of the torsional load transfer issue of the carbon shaft, I witnessed another major issue.
The driver and the hexagon collet that are supposed to compress the shaft end to transfer the torque can easily damage it. The torque is transferred through pressure on less than 1 cm length on the shaft leading to mating of the carbon fibers. So that the result was just impressive, on my 5th minute of first flight I simply lost my whole spinner and blades that went loose on the damaged shaft ! Maybe I made something wrong but I simply think it is mechanics and Darwin at work ... Luckily in winter, no crop in my field and I found the prop in less than 20 minutes searching. By the way the Xeno is a great glider which I checked the worst way

Anyone can forward my post to MPX I am sure they will understand what I mean and prepare for massive claims from customers ... let me do another bet :
MPX will soon release a replacement Shaft (stainless, titanium anything that can be trusted) for unsatisfied customers. The weight is not an issue as the Xeno has not been designed to be super light (check the weight of the Tuning set up, it is anything but super light)
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Old Dec 20, 2009, 03:58 PM
Failure is an option !
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Hobie 14 thank you very much for the tip on safety barrier tape. How long would you typically put ? the target is to do combat with this : does it break easily in combat when a prop gets into it ? thanks
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Old Dec 20, 2009, 11:16 PM
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Quote:
Originally Posted by austin13 View Post
Jürgen, I appreciate your analysis but sometimes I wonder how close you are to Multiplex .... as you always defend them even on obvious issues.
...
I bet my shirt (I only have one, it is a big deal) that the carbon shaft issue will soon be a major issue if Mpx does not release a fix about it. On top of the torsional load transfer issue of the carbon shaft, I witnessed another major issue.
...
The driver and the hexagon collet that are supposed to compress the shaft end to transfer the torque can easily damage it. The torque is transferred through pressure on less than 1 cm length on the shaft leading to mating of the carbon fibers. So that the result was just impressive, on my 5th minute of first flight I simply lost my whole spinner and blades that went loose on the damaged shaft ! Maybe I made something wrong but I simply think it is mechanics and Darwin at work ... Luckily in winter, no crop in my field and I found the prop in less than 20 minutes searching. By the way the Xeno is a great glider which I checked the worst way

Anyone can forward my post to MPX I am sure they will understand what I mean and prepare for massive claims from customers ... let me do another bet :
MPX will soon release a replacement Shaft (stainless, titanium anything that can be trusted) for unsatisfied customers. The weight is not an issue as the Xeno has not been designed to be super light (check the weight of the Tuning set up, it is anything but super light)
Where do you think I am defending Multiplex on obvious issues?

I can see potential issues with the drive system too. I had the prop adapter come lose on me too. Luckily it happened during testing on the ground and I just needed to tighten it more. Wondered whether I should use some glue on the adapter, but we will see how it performs after x flights.

Changing the shaft should be no fun either, as you need to remove and reinstall the motor. It may be a bit tricky to get to the screws and get all the epoxy out of the shaft adapter.

I am not too worried about the linkages at the bottom. This is one of the few models were I have servos with metal gear installed - as recommended.

The canopy of the motorized version has a nice NACA air inlet, but where is the air supposed to go to?

Jürgen
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Old Dec 21, 2009, 12:29 AM
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how do you guys start the XENO? are you throwing it with engine running overhead or are you letting it go by releasing it by throwing it like a DLG?
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Old Dec 21, 2009, 01:03 AM
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Hi Guys,
A very interesting thread, with good information. I am sure Multiplex is reading this, and will make it better,
Joe Pierson
USA
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