Align Engineering

[jwatts007]

At 3.03 you can see 2 blades pointing forwards...then a boom strike and the tail box comes off.....great vid...

[waveydavey]

I know it's not ally but if you think about it the thickness Ie the thread length of a 3mm nut is just over 3mm so as a minimum that's required. Take into consideration it's ally then is a simple equation, change them for the longest ones you can get in there without fouling. Poor design IMO

[Geek]

Both Dfc boom strikes.

[Tim Procter]

Both Dfc boom strikes.

Inclined to share the same thoughts TBH.

[coolice]

There was connor sloan at the last charmouth took of he rolled the heli and it jus self distruct and then there was alex hawtin at spring charmouth the video says it all!! I guess align jus didn't pay enough attention to this!!

Hey buddy.

The crashes you are referring to were not related to these bolts holding the blade grip change arms onto the grips.
Alex's crash was caused by too loose blades in the grips, which then lead/lagged and boom struck. He'd just fitted the new Align blades and they were too loose. During the unloading section of the manoeuvre the blades moved in the grips and hit the boom.
Connors I think came down to a damaged plastic ball link that got missed from a previous crash, again nothing to do with the bolts in question.

Let's be honest here, the likes of Duncan, Stu M, Jamie R, Ben Storick etc all push their 700's much harder than any of us do and not one has experienced a failure in this area. I am sure there may have been one or two crashes blamed on this point, but following a previous hard crash that has damaged the threads in the softer aluminium.

I think if there was a major problem here then we would have seen forum posts stating it, but to date I have not read any.
.

[waveydavey]

Maybe not Ian but the general rule of thumb for thread depth in ally is twice the diameter of the screw, I can put the calcs up as Gixxer has if you want, 2.5mm is nowhere near enough thread and I'd be surprised if Wayne hasn't replaced these for longer ones.

Don't need to be honest just sensible engineering, impossible to say whether they are responsible for crashes, thats not what the OP is saying.

[Gixxer]

Maybe not Ian but the general rule of thumb for thread depth in ally is twice the diameter of the screw, I can put the calcs up as Gixxer has if you want, 2.5mm is nowhere near enough thread and I'd be surprised if Wayne hasn't replaced these for longer ones.

Don't need to be honest just sensible engineering, impossible to say whether they are responsible for crashes, thats not what the OP is saying.

Correct... I have no idea whether or not this has been the cause of any crashes, nor am I implying it will be (although I am surprised it hasn't been, if it hasn't).

Whether or not this joint has failed on anyone is immaterial. There are rules in engineering and as Davey points out, 2X the screw diameter is the norm when screwing into aluminium. This depth can be shortened, depending on the grade of the alloy, but even if Align had used 7075 (which I think they should have done on such a critical part), the thread depth still wouldn't be deep enough.

This area is possibly the most important area on the heli, and as such, it should be over engineered but it looks like an inevitable failure point to me, so as far as I'm concerned, it's very bad engineering.

[electricsceadu]

the very early test dfc head had a problem with the arm mounting which was corrected before
the head went into its full production run
but the later head hasn't failed with the pilot i fly with

[Chris Boughton]

Hey buddy.

The crashes you are referring to were not related to these bolts holding the blade grip change arms onto the grips.
Alex's crash was caused by too loose blades in the grips, which then lead/lagged and boom struck. He'd just fitted the new Align blades and they were too loose. During the unloading section of the manoeuvre the blades moved in the grips and hit the boom.
Connors I think came down to a damaged plastic ball link that got missed from a previous crash, again nothing to do with the bolts in question.

Let's be honest here, the likes of Duncan, Stu M, Jamie R, Ben Storick etc all push their 700's much harder than any of us do and not one has experienced a failure in this area. I am sure there may have been one or two crashes blamed on this point, but following a previous hard crash that has damaged the threads in the softer aluminium.

I think if there was a major problem here then we would have seen forum posts stating it, but to date I have not read any.
.

Well tbh none of us will know the exact cause of these crashes and its literally impossible to know. I understand what you are saying but id rather change these bolts to give me peace of mind from a mid flight self destruction. Id rather change them knowing my blade control isn't all hanging on 2mm of thread!!

[Chris Boughton]

Correct... I have no idea whether or not this has been the cause of any crashes, nor am I implying it will be (although I am surprised it hasn't been, if it hasn't).

Whether or not this joint has failed on anyone is immaterial. There are rules in engineering and as Davey points out, 2X the screw diameter is the norm when screwing into aluminium. This depth can be shortened, depending on the grade of the alloy, but even if Align had used 7075 (which I think they should have done on such a critical part), the thread depth still wouldn't be deep enough.

This area is possibly the most important area on the heli, and as such, it should be over engineered but it looks like an inevitable failure point to me, so as far as I'm concerned, it's very bad engineering.

I agree with you 100% The amount of force put onto these short threads is incredible! Regardless of how good a pilot you are im pretty sure a pilot tht has bad collective management that is constantly bogging and loading the head would be able to push the mechanics stress near the level of that of a top pilot, for this reason I changed my bolts, we all know align bolts don't have the greatest track records and tbh im pretty sure the likes of Duncan and jaimie would have changed these bolts.

[coolice]

Hey All.

All good points and I appreciate your concerns/theories behind it and while I don't doubt your reasons for debating it, I'm still not sure it's something to be worried about. Not to the degree talked about here at least.

We've all seen crashed DFC models and the majority of damage is sustained by the blade grip control arm bolt, which bends and damages the blade control arm as a result. I have only seen one or two actually ripping these two screws out of the blade grips along with the arms.

The original point of failure on the early DFC design was as the thread of the blade grip control arm screw stopped inline with the control arm, thus all the stresses of flight were breaking the bolt at the weakest point. Align fixed this by adding a longer plain shank part to enter the grip control arm.

However, going by the engineering practices don't we also need to look at how much thread is actually available to us in the blade cuff for these screws to go into? It's no good fitting longer screws if the thread depth isn't long enough to make full use of this extra security.
It's been a while since I've built a DFC head, but I can't imagine more than 4mm of thread length in there before you hit the bore of the grip.

The bolts are there to secure the control arm to the blade cuff, the recess into which the arm fits also takes some of the loading imposed on the blade grip in flight as the blade is wanting to twist the blade grip against the servos and the arms recess guides the blade pitch arm.

In any case as proven if there was a problem here, publically we'd know about it quite quickly.
The previously mentioned crashes are not caused by these screws failing, but by lead/lag problems inducing a boom strike for Alex (and a poor chap over on HF) and in Connors case a duff link.

If it was me, I'd be more worried about the short connecting rod between the DFC control arm and plastic ball link, as this is subject to side loads on a small thread diameter.
.

[Chris Boughton]

Hey All.

All good points and I appreciate your concerns/theories behind it and while I don't doubt your reasons for debating it, I'm still not sure it's something to be worried about. Not to the degree talked about here at least.

We've all seen crashed DFC models and the majority of damage is sustained by the blade grip control arm bolt, which bends and damages the blade control arm as a result. I have only seen one or two actually ripping these two screws out of the blade grips along with the arms.

The original point of failure on the early DFC design was as the thread of the blade grip control arm screw stopped inline with the control arm, thus all the stresses of flight were breaking the bolt at the weakest point. Align fixed this by adding a longer plain shank part to enter the grip control arm.

However, going by the engineering practices don't we also need to look at how much thread is actually available to us in the blade cuff for these screws to go into? It's no good fitting longer screws if the thread depth isn't long enough to make full use of this extra security.
It's been a while since I've built a DFC head, but I can't imagine more than 4mm of thread length in there before you hit the bore of the grip.

The bolts are there to secure the control arm to the blade cuff, the recess into which the arm fits also takes some of the loading imposed on the blade grip in flight as the blade is wanting to twist the blade grip against the servos and the arms recess guides the blade pitch arm.

In any case as proven if there was a problem here, publically we'd know about it quite quickly.
The previously mentioned crashes are not caused by these screws failing, but by lead/lag problems inducing a boom strike for Alex (and a poor chap over on HF) and in Connors case a duff link.

If it was me, I'd be more worried about the short connecting rod between the DFC control arm and plastic ball link, as this is subject to side loads on a small thread diameter.
.

Jus saying I landed and upon checking my model one of the blades had come slightly loose (dude to going from a warm to cold environment) to the extent it would fold under its own weight, so if it was a lead/lag problem surely I would have seen this happen in my last flight I was flying it pretty hard yet no problems. Not trying to contradict anything just saying. In my opinion I still see the bolts being too short to be safe in prolonged use.

[waveydavey]

Ian you're looking too deep, Gixxers point was that he thought the bolts are too short, they are and he replaced them with longer ones. Fixed

The posts referring to boom strikes are meandering from the original point, 2.5mm is no where near enough thread to secure anything in aluminium

[coolice]

Jus saying I landed and upon checking my model one of the blades had come slightly loose (dude to going from a warm to cold environment) to the extent it would fold under its own weight, so if it was a lead/lag problem surely I would have seen this happen in my last flight I was flying it pretty hard yet no problems. Not trying to contradict anything just saying. In my opinion I still see the bolts being too short to be safe in prolonged use.

Hello mate.

Depends on what blades you're flying as well as the type of maneuvers flown, constant load can be ok as it keeps the blades inline. In Alexs case hed switched to the longer ones and left them loose.

Ian you're looking too deep, Gixxers point was that he thought the bolts are too short, they are and he replaced them with longer ones. Fixed

The posts referring to boom strikes are meandering from the original point, 2.5mm is no where near enough thread to secure anything in aluminium

Evening mate.

Sorry dude I'm just looking at the topic from all angles, if we're increasing thread length to avoid problems we need thread depth to make full use of the longer screws surely.

Unfortunately I felt I had to speak up about the boom strikes as it was thought these could have been caused by the bolts talked about here, thus scaring DFC owners for no reason as they are not to blame in these instances.

I'm keen to find out how much thread is in the DFC blade cuff, so we know for sure if adding longer screws will have a marked impact on security or not as they contact more surface area.

Another thought, the screws being used to replace existing, if they have the screw thread going to the underside of the head of the screw, is this point now weaker than the shouldered screws?
Thread cutting weakens the screw and we're now putting a weaker point in a different position.
.

[Chris Boughton]

Hello mate.

Depends on what blades you're flying as well as the type of maneuvers flown, constant load can be ok as it keeps the blades inline. In Alexs case hed switched to the longer ones and left them loose.

.

Im useind the exact same longer align blades as alex was using and I don't constantly load the model when I fly (in fact I put a mid flight blades stop into that flight aswell) I fly loading and unloading. So I don't think blades folding slightly will cause this!! Well I guess we all hav our own opinions, jus don't wanna see someone have a failure due to not using a longer bolt that could have easily been swapped out. That's all I have to say