Jump to content

Pull cord getting sucked into prop mid flight


Recommended Posts

I am back......

Yes the polini strikes again..

OK so I have been flying nearly as much as possible since I managed to fix my motor..

My pull cord is getting sucked into the prop..

I have had two brown pants moments in the last week, first time same thing smashed a prop, managed to land.

Next up quick flight after work this evening, carbon prop bang!! not as bad as wooden prop repairable.

After the first incident I modified the pull cord so It would happen again (failed)

My pull cord is getting sucked into the prop..

I have a flash starter on my polini thor 100.

Pull start is connected to the frame for overhead start..

Is super easy to start maybe too easy, It happened mid flight when I applied mass power it appears the pull cord comes lose..

Has anyone experienced this before.

in the video look for the pull cord, its dangling about and then gets smashed.

Ideas or thoughts??


Link to comment
Share on other sites

Looks like it's basically too long. When the return spring retracts the cord it should retract right up to the 'stop' or pulley.

If it really needs to be the length it is I'd fit some sort of clip/clamp/bungee to hold it solidly.

Cheers, Alan

Link to comment
Share on other sites

  • 4 months later...

The pulley unwinds at full throttle,I have taken the entire flash starter apart about 20 times now checked all the bits, had it without grease, with grease, cleaned it, tensioned the spring as far as it will go, spent about 6 hours trying to sort it, can NOT understand whats going on :(

Any ideas would be helpful!

The bungee cord is one idea, but doesnt really solve the problem as sometimes when it fully unwound itself it can still go into the prop .....

HELP ! :)

Link to comment
Share on other sites

Its extremely odd, theres nothing in contact with the starter itself, theres no reason for this to happen, looks like theres many other occurances of this :-



We even tried adding a bungie cord inside the starter to rewind the shoes that move out to engage the engine to no avail.... we thought perhaps the air coming into the engine via the housing perhaps as theres no contact with anything else . HELP :)

Not sure on hours or starts unfortunately, its the 110 cc, no mods.

I have recently replaced the inners of the flash starter with brand new ones and it worked fine for 5 hours and then the starter snagged and shredded.....again..... :(



Link to comment
Share on other sites

Hello from Australia...

Hey Phil as you know this happened to me, I tried a few things (3 props later) I ended up buying a new flash starter as my old one was beyond repair.

All was cool for about 5hours with the new one then yesterday during a 2 hour flight they bloody same thing happened..

I saw the pull starter handle fly past me and get stuck on the net.. I managed to grab it (mid flight) from the net and some how tie it up..

But now confidence is back to zero with the motor. no long flights for me.

I am thinking about adding spacers 2mm again to increase the distance from the motor to the flash starter. Was flying with another pilot who has the same motor thor 100 and he said he got rid of his and put back on the stock starter!!

If you figure out how to stop this please let me know. Not even going to waste my time asking polini!!



Link to comment
Share on other sites


thanks for the reply, I am just in the process of putting a little bolt sticking out of the starter so after I start the engine I can tie the flash starter off to stop it moving, a temporary fix for now so I can actually fly !

I cant believe there hasnt been more occurrences of this, as I have like you bought another starter and its done the same thing, waste of £130 unfortunately we cant see a cure as we originally thought the dogs on the starter were vibrating out but we added a bit of bungie to hold them in and it still does it, the only thing I can think of us either vibration or air from the fan..... but neither seem likely as the return spring is really strong !?

I have tried the spacer idea as you say, no use.

Will keep trying !


Link to comment
Share on other sites

Just sorted it, I think :)

Ran the engine for full for 1 minute with lots of pressure in the recoil still, happy days !

Basically the problem is, as the starter wears a little, in the recoil spring area , the whole assembly is too tight up together.

As the engine reaches a natural frequency the recoil spring vibrates against the metal back plate of the starter, thus uncoiling the spring, its a very strange one but thats the problem it seems.

I have put a small fibre washer between the backplate and the recoil spring and then 2 lock washers between the bolt and the backplate, pics attached, the whole assembly is now spaced away from the back plate so the spring can not touch, I would think machining some washers to fit would more suitable but its all I had at the time and I want to go flying now ! :)

This works for me, hope it works for someone else, anyone using a Flash started should perhaps check this and think about making the mod before your starter ends up in the prop, seems to me a bit of a design fault.... !



Link to comment
Share on other sites

Excellent.. That's tomorrow's job lined up.

If the weather is good in the morning may have to get in a sneaky flight and hope it doesn't happen if its rubbish weather I am going to try this mod (will let you know how I get on )..

Are you suggesting that polini put a product to market which had a design fault. Surely not!

Cheers guys if it works i will be a v.happy!!!


Link to comment
Share on other sites

Hey Guys,

Just finished the mod and it did not fix mine. I just tried it under full power and had the same effect as before!!

Quite frustrating, if I need to fly i think I will lock in the starter with a removable cable tie.

Q. What thickness was the fiber washer plus the two washers / spacers you used???

Tempted to get the old starter back in.

Link to comment
Share on other sites

What a pity, can you post a pic of the inside of the flash starter back plate, on mine you can see all the paints come off, are your clutch dogs ( pawls ) worn at all , we originally thought it was these engaging on the steel starter plate on the back of the engine but its definitely not that on mine.

Washers where all about 1mm thick.

Also I took the c ring off the end of the starter and compressed it far beyond what it was before.

Looking at the unit, theres only 3 places it can bind and vibrate out, the dogs can vibrate outwards and touch the starter cage ( try putting white paint on the dogs and see if this ), the spring on the back plate ( that happened with mine ) or the outer ring of the recoil housing touching the back plate, also put white paint on and see where its catching ?

Edited by Guest
Link to comment
Share on other sites

I once had a lawnmower which had exactly the same problem. At a certain engine RPM, orbital vibration drives the starter pulley to rotate against the spring tension, allowing the starter cord to run out.

The fibre washer fix adds friction to the system, absorbing some of the vibration energy.

Unfortunately, friction is affected by heat, oil, humidity etc. so it might work one day and not the next.

The usual fix for resonant vibration problems is to change the resonant frequency of the part. The objective is to increase the frequency to one higher than the engine frequency. In practise this means either making the pulley lighter or making the spring stiffer. Note that 'stiffer' is not the same as more preload. The spring would need to be made from thicker material.

An alternative fix might be to fit a collar to the cord where it passes into the pulley housing, with a magnet to latch the cord in place there. This won't prevent the pulley from unwinding as described above, but it would keep the loose cord contained and out of the prop.

Link to comment
Share on other sites

I will open my starter again tomorrow and try a few different things in the hope of resolving it.

Here is the thing, surely we cant be the only one's out there having this issue with thor motor's.

The only other pilot I know who fly's the thor 100 had a flash starter but got rid of it for due to the pull cord getting pulled out mid flight!!!

My temp fix was a removable cable tie in the starter once started, not ideal but will save my prop!!

Link to comment
Share on other sites

It's not any special ability, just the product of:

1) A healthy curiosity coupled with an inate desire to pull things apart to see how they work.

2) Age, providing decades of opportunity to indulge (1).

3) The good luck to get away with (1) over the course of (2)

Working in engineering manufacture and design for 30 years has also offered opportunity to pick up the odd thing or two.

Link to comment
Share on other sites

  • 11 months later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...