The Building of the BebBit

[Chris Bott - Moderator]

Nice one BEB well done.

[Biggles' Elder Brother - Moderator]

Sad Tidings to Report...

 

I'm working at home today. Its raining here now. But before, at lunchtime. there was a nice break in the showers - so I thought I'd chuck the BebBit in the car with couple of batteries and take a quick run to the field. How I wish I hadn't had that idea

 

I'd removed one small piece of lead from the nose - couldn't really decern any movement in the balance point - 1/8" back at the very most.

 

Pre-flight checks OK - so off we go. The take-off was perfectly normal, as was the first 3-5 secs of flight in the climb out. Then the model suddenly reared its nose up at 60 degrees. It was under full power and climbing rapidly, I tried some down trim - zip. I throttled back to induce a stall. It stalled, recovered I eased the power back in - straight nose up again. By now I desperately needed to turn right - but any attempt at a turn was resisted or, if I was heavy handed, threatened the mother and father of a stall.

 

I powered down again, forced a turn whilst nose down, but as soon as I fed in any up elevator the nose just soared. It was like the model was increadably tail heavy - really massively so. I was now a long way to my left and heading away from myself - I needed another 90 degree right turn to get onto a downwing leg. The model was at about 200 feet by this point I would guess. Fed in right aileron - just a lot of wallowing. Added a touch of right rudder to try to encourage her round. The model immediately flicked onto its back then entered a near vertical spin. Interesting, I thought. Centred all controls, no recovery. Left rudder, no recovery. Left rudder and left aileron, no recovery. Thump! In she went, hard, nose first.

 

It repairable - but not without some major surgery

 

The obvious question is what the hell happened? It wasn't radio failure - control inputs were working. The only way I can decribe it is that it felt very tail heavy all of a sudden. It was unstable, wouldn't respond to aileron properly, pitching up, elevator sensitive. Its unlikely to be engine or wing incidence - they were OK yesterday - and symptomes persisted power on and off - though were less aggressive with the power off. The fact that I couldn't recover from the spin also suggests extreme tail heaviness.

 

But I swear I'd only removed about 1/2oz of lead out of about 5oz. The difference in balance point was miniscule.

 

When I recoved the wreakage the batterry was out of it compartment. It had been fixed in by a strip of velcro and a velco belt - there was no added packing/padding around it. It could have come free in the crash - though I would have thought that would tend to throw it forward into the battery compartment not out.

 

Has it broken loose on take off then slid backwards on climb out? I dunno - I just know I've now got a rather broken BebBit.

 

And to think, I was boasting the other day that I haven't had a major crash in over 12 months . Little bumps and the odd over heavy landing yes - but not a really scrunch job like this. Seems I spoke too soon.

 

BEB

 

[Wingman]

Seems to me like it was probably the battery moving backwards because you say the battery was out but velcro usually has such a good grip, especially when it's wrapped round the battery like your strap, that a crash like that would tend to tear out the battery shelf and yours looks in perfect condition to me.

 

Anyway, looks like nice wintertime repair job

Edited By Wingman on 15/06/2011 16:35:58

[Geoff Smith 1]

Oh dear mate, what can I say except hard luck with the Webbit. Will it be ready for Greenacres? It would be interesting to find out what exactly happened so that the rest of us Webbiteers can watch out for similar symptoms. Cheers mate

 

Geoff

 

Nearly finished Webbit Builder No 20

[Chris Bott - Moderator]

What rotten luck BEB. Your flight description certainly sounds like the battery shifted.

 

It does look repairable though like you say.

 

One thing to check now is the motor shaft, give it a run up with the prop off to make sure it still runs true.

[David Gilder]

Very Bad Luck BEB

 

I agree, it sounds like a major shift in C of G (battery movement!).

 

I think I will be adding an Anti Battery Slip Plate to the rear of my battery tray!!

 

Hope it will be fixed in time for Greenacres!!

 

Dave

 

[Big Bandit]

Dave, what can I say but bad luck mate.

 

I've taken to sticking some hook and loop to the under side of my lipo's (with double sided tape) and the battery plate. stops em moving about with the hook and loop tie down straps over the top of the lipo. I've started doing it to all of my models now, since I stuffed my Easy Cub. Can't imagine any other reason for the CG shift. Still trying to make it to Green Acres, but it's in the lap of the gods now.

 

Cheers,

 

Chris.

[Tim Mackey]

Oh dear, bad luck Dave

I concur with the slipped battery theory - almost certainly it would have shoved forward in the crash you described. I assume there was enough lead length though to allow it to move back without disconnection - otherwise you would have had nothing power or radio.

For battery installation such as this one, I recommend you use a "proper" velcro strap such as that shown in the picture. It loops over the battery, and through the buckle - like a proper belt, and then back on itself to really grip very well indeed.

This - coupled with some velcro on the battery and tray should mean nothing shifts unless you want it to..

Bad luck mate.... now get the glue out....youve got a week and a half

[Tim Mackey]

Heres a belt and braces version on my large PC9 - two straps for this big battery - and velcro on the tray / battery too

[Big Bandit]

Hi Tim, Where are they on sale, I've been using the stuff from Asda.

 

Cheers,

 

Chris.

[Lindsay Todd]

BEB get the glue out, no excuses we all expect to see it there!

ps Will this form the basis of a future article?

[Tim Mackey]

I got mine from friend, but a few places seem to have them.

[Richard Harris]

BEB,

Sorry to hear of the 'bump'. I am sure you will get it repaired in time for the fly-in. You wouldn't think 1/8" difference would make so much difference to the flight characteristics.

Better to know now of the CG position issue.

 

 

Rich

[David Ashby - Moderator]

All part of that leccy learning curve BEB.

 

So it's a 'mass repair' for the winter then

 

 

 

 

[David Davis]

Hard Luck BEB.

 

I'm just waiting for the wind to drop before re-maidening the wideline Webbit.

 

Judging by everybody's comments they're hot ships!

[Chris Bott - Moderator]

I think the "Mass repair" might come after the Fly in David

[Biggles' Elder Brother - Moderator]

When I prang one I always find it really hard to get the enthusiasm up to repair it straight away - I usually can't even bring myself to look at it for a while! Then after a couple of weeks I take it out and grasp the nettle.

 

But if I'm going to have this ready (and flown again) before the 25th I'm going to have to knuckle down now. I've only really got tomorrow night and maybe some of Saturday - I'm off to Weston on Sunday. Then I have to hope for at least one flying opportunity before the following weekend - fingers crossed!

 

BEB

[Chris Bott - Moderator]

You can do it BEB, I know what you mean about leaving 'em a while but this has to be the exception You know as well as I do that once you start repairing it nearly always isn't as bad as expected.

 

Good luck with the weather at Weston Park on Sunday. I'm still unsure about going myself due to time pressures, and the forecast isn't helping me decide

[Pete B]

I had a 'dumb-thumbs' with my VMAR Fournier a few months ago - vertically downwards through the trees. Didn't look good - wings snapped in two at joiner, section of l/edge crushed, tail assembly ripped off, flimsy cowling shattered, pilot has broken nose, etc etc - you get the picture...

 

It's been looking at me every time I've walked into the store room - until last week, when I thought, "That's it , you're getting fixed!"

 

Three evenings work later, much less drama than I was expecting and she's now flown four times this week - what would I do without Gorilla Glue? The repairs are stronger than the original now, so get that pot of glue and balsa hatchet out now, BEB, and get cracking!

 

You know you have to.............

 

Pete

[Vecchio Austriaco]

Just foud your thread now BEB, And I have to say I had exactlty the same experience with the plane. 60deg up and almost impossible to control. And I had it more than once. But in my case I am sure the battery didn't move.

My theory was rather that the rubber bands were too loose and so the whole wing moved and was responsible for the behaviour. Unfortunately I saw that your version is using screws to fix the wing - this means the theory is as quickly killed as it was created....

 

don't know if it helps - this is the state of my Webbit - and there is also the engine shaft bent and some problem on the fire wall.

 

Weekend is repair time....

[martin Rowley 1]

Maidened mine yesterday, took a long time to ROG, then shot vertical, used loads of down trim and it still had a tendency to nose up. C of G on the spar, weighs 2 1/2 lb and 300 watts to power it.

Reduced the power and noticed that the plane was more stable, though now had a tendency to dive, so I'm thinking more downthrust is needed. It wasn't too bad on the glide, though I had to keep the nose up to compensate for all the down I'd dialled in under power.

Got the plane down ok, and reset the subtrim on the elevator, tried a second flight, long ROG again, shot vertical into a stall turn at 10'. Vertical arrival. Firewalls gone, but the wing looks ok.

[Biggles' Elder Brother - Moderator]

I'm sorry to hear about that Martin These WebBits certainly do pose a few challenges in flight!

 

300W for that weight is certainly not overpowered - its about the same as mine. The behaviour of yours seems remarkably similar to mine. I'm beginning to think that the WebBit is very sensitive to the exact position of the CoG. The slightest movement around the spar seems to produce disproportionate changes in flying trim. Although Chris's eperience with the CoG 12mm back has me completely baffled!

 

BEB

Edited By Biggles' Elder Brother - Moderator on 21/06/2011 12:39:29

[Lindsay Todd]

Mmh strange, sounds like the incidence meter needs to come out and check. Certainly mine requires some down thrust on the motor, have added a couple of washer behind the mount so that should help. In the glide it was remarkably stable and flew surprisingly slowly wich was a good sign. I did note a tendency to leave the nose high in left hand turns when under power so it may yet need some side thrust as well but seems minor compared to these problems. I have the CG just forward of the spar by 3 to 4 mm and was about to move it back slightly to improve its aerobatic potential as it seemed quite docile but a little stuck until my TX comes back from HH, due later this week, fingers crossed!

Linds

 

[Biggles' Elder Brother - Moderator]

Based on some others (including my own) experiences Linds I would be very cautous in moving that CoG back - although I'll happily watch on Wednesday evening while you do it

 

BEB

[Richard Harris]

When I built mine way back then I took into consideration that the WebBit was designed for IC power. The CG position marked is for an IC engine, for me I always take this CG position as with an empty tank. So as a 'guestimut' I moved my CG position forwards about 6mm to compensate the 'full' tank weight.

I have had no flight issues what so ever with the WebBit ( standard fixed wing), its just everything else after!

 

 

Rich

Edited By Richard Harris on 21/06/2011 22:25:15