esc

Hi Guys,

I have just taken out my new P.A. electric shock on it's maiden flight. Everything went well for the first flight - she flew straight off the board with only one click of right aileron needed for level flight. I flew a few low G maneuvres, loops, rolls, etc., and then brought her in to land. No problems there at all. Actually I never got off the low rates setting on the Tx.

After a couple of minutes to settle down I took off again, it was only a few seconds into this 2nd flight that the motor, an Extreme Flight Torque 22T930, tore itself off the front of the plane, landing on a nearby factory roof - well out of reach. See the atached photograhs. It's one thing you never expect to happen - certainly in the 30+ years I have been flying it's never happened to me before. I will never forget the site of that motor spinning away and clunking on the roof as long as I live!

I thought it was the end for the plane at that point, with such a large CofG shift I thought she would be uncontrollable and come down tail first - not so. I managed to bring her down reasonably smoothly from a height of about 80ft in a series of controlled stalls (at last the designers got something right!).

To say I was stunned would be an understatement, I still have not come to terms with the experience 2 hours after it happend. It's also going to be an expensive repair due to the loss of the motor.

Has anyone else out there experienced this problem?

For those unfamiliar with this plane, the motor is mounted on a carbon fibre plate similar in shape to a banjo with two opposing necks. The nose of the model has two blocks which are filed to 2 degrees of right side thrust. The carbon fibre plate and motor are then secured to these blocks using two supplied srews which go into pre-piloted holes.

Beware anyone about to fly one of these planes. I would recommend a much stronger method of securing the motor - possibly the way Hyperion do on their Yak55 SP Profile. Failing that I would advise a goodly amount of CA soaked into the engine mounting blocks where they fix to the rest of the fuselage.

Would anyone from Presicision Aerobatics care to comment?

Regards all,

Dave

esc

Sorry, here are the photographs:

Dave

esc

This is a "before" shot:


Dave

esc

I have been thinking about how I will replair my plane.

One thing I am going to do, and I recommend this to anyone about to fly one of these planes, is to remove the covering from the sides of the motor mount block and along the fuselage and then CA some liteply strips in place. This will spread the motor loading over a much bigger area and help prevent the blocks from dislodging themselves.

Regards,

Dave

Precision Aerobatics

Hi Dave,

Thanks for your feedback and sorry to hear about your mishap

With powerful motors used on the ES it is important to secure the mounting plate in place properly

It is important to drill the hard point carefully and slowly with appropriate drill bit on the correct diameter to fit the mounting drill (also keep the drills in the center of the hard wood blocks). The reason I emphasis this point is because:
1. Too small diameter drill bit may cause the hard wooden block to crack and later on to fail under the motor’s thrust especially when using those big diameter props we use on the ES.

2. Oversize diameter drill bit will harm the integrity of the mounting since the screws’ thread will not hold up under loads (pull out under loads).

I recommend using some thick CA or even epoxy on those mounting screws.
Also please inspect the integrity of the wooden blocks and if you see any gap between the balsa and the hard wood simply fill it up with epoxy.

Please email us your shipping address so will send you some covering, screws and bits and pieces to get you up in the air fast.

Thanks

Shaun

Precision Aerobatics

www.precisionaerobatics.com

esc

Hi Shaun,

Thanks for the reply.

I followed the build instructions carefully, right down to the application of CA to harden the threads in the motor blocks. If you look closely at the photographs of the nose of my model you will see that the whole of the mounting blocks have disappeared along with the motor, which suggests to me that they weren't fractured by the mounting screws.

The Torque 22T930 outputs a maximum of 908 grams of thrust, which is as nearly an exact equivalent to your own PA Thrust 10 motor as it's possible to get.

Which wood material are the blocks made from?

The range of hole sizes specified for the motor mounting screws is quite large ranging from 1.2 -1.5mm. Would you care to make a suggestion as to which size would be best?

I removed the covering from the nose section upto the "cockpit" area last night and discovered the damage was more extensive than I had feared. As the motor departed, the advancing prop blade must have clunked the top of the fuselage where it is broken away and the shock wave broke free several joints along the fuselage up to the wing leading edge. I have fixed these with CA and am proceeding with the rest of the repairs.

Thank you for the offer of the resplacement bits and pieces, I will email you ASAP.

Regards,

Dave

esc

Please note that I have had an email today from Precision Aerobatics telling me that the bits I require for the repair are packed and will ship ASAP.

How's that for service!

Well done PA and thank you.

Regards,

Dave

dashunde

I cant hold my pie hole shut any longer. (I'm still going to order a ES, so dont flame upon me)

Its a 4-screw-mount motor swinging a large prop (read: large gyroscopic forces) mounted to the plane through wood using two screws...
Up and down things are leveraged tightly, left and right... well, no mounting leverage whatsoever.
And notice that his mount appears to have blown out to the left side on the bottom with the blade hitting the top of the fuse.
Really... a four-screw motor mount to aluminum, being held to WOOD using two screws - where is the logic?

One of two things is going here... either esc messed up his mount job and tossed his own motor onto the roof, or PA shipped a naturally flawed/split/weak mount. Flip a coin...

Regardless... this narrow, two-screw mount thing is very questionable... something I will certainly be modifying during my build.

I'm thinking that a double-ended version of this [link=http://www.hobby-lobby.com/motor-mount.htm]AMM010[/link] would do the trick. (halfway down the page).

I'm glad PA is paying attention and helping out... excellent PA!

Precision Aerobatics

Dashunde,
I do understand what you are saying but we didn’t have many cases of motor mount failures and we tested our planes hard.

I had a case of motor detached from one of my test planes but that was my fault after many small crashes I had and after I saw the motor mount which was loose on the fuselage I still flow the plane. I didn’t care at that point since I was at my final stages of testing the ES. I landed safely without the motor/prop/prop adaptor and no other damage to the fuselage. In fact I took the motor and reinstalled it with the same prop and flow it the next day.

Even with the prop forces you need to engineer the construction in a way that will withstand the loads during flight and as long as it does, it’s fine. One thing you can’t see from photos is the construction underneath the fuselage balsa sheeting. There are some reinforcements there. In other word it is not just two balsa sticks that you probably have seen on other profiles before.

So the important points are to drill those two hard points properly and to make sure there is no gap between the balsa and the hard points and if so fill this gap with epoxy just in case.

Don’t get me wrong we never ignore feedbacks, in fact I already modified the CAD drawings so the hard points will be a little longer from now on to have more gluing surface, but we still all flies our ES very hard with the same configuration, no mods.

Hope this helps,

Thanks

Shaun
Precision Aerobatics Team

dashunde

Shaun... good to hear your thoughts.
I am convinced that it is a sound mount that will stand up to flight stress, if:
a) The wood used has no flaws
b) The motor is mounted correctly.
Its been around awhile and this is the first I've heard of a motor coming off of a ES, so... it seems to work.

However, I'd still like to see alternative mount options.... I'm going to crash... a lot.
I'd gladly pay a small weight penalty for a unquestionably sound mount.

I might suggest you guys pre-drill and supply a couple of 1-2" studs that epoxy deep into the wood structure, using nylock nuts on the ends sticking out to hold the mount on.

Precision Aerobatics

Yes, you’ve got some good ideas

In fact I did thought about a few different motor mountings but I gave up after I realized how many configurations you have for different motors

I guess for some customers who prefer a little different mounting a small mod will be quit easy to do.

Anyway thanks for the feedback

Shaun
Precision Aerobatics Team

esc

Hi Guys,

Shaun's comment "and to make sure there is no gap between the balsa and the hard points and if so fill this gap with epoxy just in case. " has only come to light since my post. The build pamphlet carries no such instructions. I don't really feel that it should be necessary either if the factory has done it's job properly. I also note that he mentions some engine mount failures over and above his own self-abused prototype, so mine is not just a one off. Was each failure carefully autopsied?

Dashunde, I won't take offence at the suggestion that I might have got it wrong, but I will say that I am no begginer at this lark. I will also reiterate that I mounted the motor exactly to spec. - with one exception, I countersunk the carbon fibre plate for the 4 motor fixing screws. The drill I used to pilot the hard wood blocks was 1.4mm Dia., well within the manual recommendations of 1.2-1.5mm Dia. Thin Cyanoacrylate was then applied to the threads to "harden" them.

As far as I am concerned the Electric Shock is a good plane, but I would not have designed the motor mount the way that it is. The fuselage shows no signs of the blocks being torn from the surrounding structure as there is no collateral damage, rather a complete and catastrophic seperation due to the lack of/or an appropriate adhesive and insufficient contact area. What surprises me is that any of them stay put at all.

A simple and untraumatic way to strengthen this mount would be to remove some covering from the side of the blocks and along the fuselage. Then adhere 4 strips of 0.8 or 1.5mm Birch ply 3/8" x1.5in. using a goodly amount of adhesive, either CA or epoxy, ensuring good contact between the surfaces. Having said that I have already designed a more sophisticated ply mount that I may use instead. If I do, I will post details on this site.

These are my final comments on the matter so I will just wish you all good luck with your PA Electric Shocks.

Regards,

Dave

5150flyer

Looks like a poor design to me no matter how you mount the engine. Rear mounting is much stronger and less prone to flexing. IMO...PA should replace your engine and prop.

Precision Aerobatics

Just for your information this is not true at all.

In fact we tested that thoroughly and we found that rear mounting is by far weaker than firewall mounting of any kind.
That is why our Thrust motors series are all firewall mounting.

Just giving you some of our valuable experience but you can decide which method you like the best and use it. It will still work fine

Shaun
Precision Aerobatics Team

aerofundan

I hope you get it back in the air soon, its kind of surprising to me, as i have flown mine and crashed it a lot and i never had any time the motor coming out of the plane like that... and i fly it really hard. I hope you get it back in the air soon! remember, with glue you can fix anything

esc

Daniel,

Thanks for your good wishes. The repair has temporarily ground to a halt due to a failure in supply from an LHS and the unavailability of the Torque motor for 3 weeks. I have opted for a Hacker instead, hopefully the new motor should be with me some time next week.

Smooth loops,

Dave

RichardGee

My Feedback: (156)

I am itching to order a PA Electric Shock, but am a bit unsure of my power package suitability... I have a Hacker A20-26M which produces up to 27 oz. of thrust with an APC 9x4.7 prop and 11.1v battery. My 15 oz. Charger CR-1 foamie has unlimited vertical and hovers easily.
Can I use this combo on the Electric Shock with similar results?
Thank you.

aerofundan

Yes, the ES AUW is around 14-16 oz, so you should have unlimited vertical in this one too!

RichardGee

My Feedback: (156)

Thanks for the info!