|Dec 07, 2013, 05:08 PM|
Australia, VIC, Bendigo
Joined Jan 2012
Andy..It was work that sent me to Oz and to be honest the winters here are a lot better than your summers ,,lol Im still on my training wheels learning on the HK Club Trainer but my fly buddy took up my SV using the 5s...She looked great flying in the setting sun..There was a little tail waggle but he thinks that with some Tx mixing it can be tamed.
Is the Scimitar a "scrachy" too..I havnt seen them in "foam"
|Today, 07:41 AM|
Australia, VIC, Melbourne
Joined Nov 2006
Sea Vixen Down..... DOH
After a rainy/drizzly day the evening turned to sunshine a very light wind - even dead calm at times. So off to the airfield for some Vixen testing!!
With the CofG at the front edge of the main wheel bays, I still needed quite bit of up elevator trim. About 5deg or so. A notable amount 'too much' really.
To come more rearwards just 5mm in CofG would need 40g of weight on the tailplane!! So I did start making up a weight system the night before to add 50g, and be variable higher or lower too. But I didn't get that finished.....
Seeing I wanted to record the tests, I achieved 30g on the tailplane with the 808#16 camera there... BUT with battery on board (2650 45C) it still only balanced at the wheel bay front edge. Oh well, that is what it typically flies with....
Take-off... all fine.... it needed even more UP trim added to fly level.
50% master gain on all three of the Roll, Pitch and Yaw gyros was not enough to erase waggle.
100% was very close to all gone! So it was a pretty good result - acceptable, adequate, and it was flying nicely.
Not thinking at all about the CofG, and less so the notable UP elevator trim, I decided to do a slow roll as it came towards me and overhead at about 30feet. It always was a BIT scarey process (in the past too), as UP trim means DESCENT as it goes over towards, and through inverted... which I knew of, but this time totally forgot about!! eg start a slight climb before a long slow roll.
So level flight, into the slowish roll.... which of course was already losing height as it went through 90deg.... I wasn't really worried as I would correct that from 100deg onwards, via DOWN elevator.
I think I did quickly begin to be worried.....!!! Because as it went through 100deg and I was adding DOWN elevator, it was just coming down sharper and sharper anyway!
In that split second when you recognise "This is not good!!" you only get that split second, and one chance to CHOOSE what to do! My decision was to go to FULL DOWN elevator and "mess up" having a nice roll, in the interest of survival!!
In hindsight a different choice MIGHT have been better.....
For eg, a hard reversal of roll to go back UPRIGHT possibly would have been a better outcome....
Full down elevator hardly helped... because the UP TRIM offset was so much, it limited the down side of elevator travel !! I normally adjust end-points to fix up a direction of travel being limited by trim offset, but I have never done it on the Vixen at all (forgot to).... and dialling in more UP trim this flight just made things worse than ever!
So my committed choice to use DOWN Elevator to save the day - which it could not actually achieve - was a fatal choice....
Down it went into the ground at about a 45deg angle... bamm !!!!
I have Hatcam and Tailplane camera video, but have not slow-motioned the crash to see how it hit exactly. But it must have been the BEST way you could crash a Vixen!
The nose snapped off, due the the battery wanting to "get out"... and that impact angle on the nose. Then flipping the stress longitudally to rear down to hit the tail booms, so they both snapped off.
The wings are perfect.....
A few bits and pieces (fuel probe, antenna, strake etc) broke off.
All in all it looks like it will be the easiest possible fix, for such a big crash. And should also come out in very good shape/condition too.
One rudder servo stripped and that was it for electronics issues.
All major breaks are already repaired even now..... a few hours later....
The pics are after turning it over... it hit inverted and ended up lying inverted, almost 20metres from the impact crater!
As I said.... it must have hit at the BEST possible angle and manner possible! This was dong over 100 kph all the way into the ground!
|Today, 08:12 AM|
Sorry Peter. Never like to see that but certainly can't say we haven't all been there before (me more than my share). As you said, it looks very repairable so I'm sure you'll have her flying in no time. Not sure I understand why you needed more up trim than usual for your standard CG location. Seems like something changed since you last flew it; like maybe a boom was loose or tailplane incidence change (loosening glue joint maybe)
|Today, 08:29 AM|
Australia, VIC, Melbourne
Joined Nov 2006
I had just been checking CofG/trim things over the weekend, not liking the up trim it had/needed.
I didn't want to add weight but it flies very stable so I figured it could cope with even 10mm more rearwards CofG... if I could work out HOW to get it to that. To move rearwards just 10mm needed 100g right at the elevator!
But the AIM was to have a neutral elevator.
I made up some screw in 50g lead weights, which were going to have mounts into the rear top end tailplane boom roundish end bits. Thus 50g cylinders sticking out rearwards about 25mm.
But I was not thinking about the inverted issues specifically, that would just have been another resultant showing it was really CofG that needed moving rearwards, not for eg a tailplane incidence change.
I just didn't think about doing the roll at all.... no pre-planning, just that instant decided to do that. Thus no thought at all about the inverted issue of even more up trim, and no slight climb for entry. Just a blonde-moment.... LOL
At least it was the 'best' high speed jet crash I have had!! Just one hour to have the main breaks all re-joined.
I decided to do "just straight foam" joins, with Epoxy - no rails/skewers etc - and will add carbon fiber rods etc afterwards, after assessing what strengths each joint needs.
If I had started as soon as getting home it would probably be flying tomorrow again. But now another day required Not that it is a rush....
Maybe the fact I need UP trim, even with the manual's CofG, shows there is some difference in alignments from one Vixen to another? And any requiring up trim have a greater waggle resultant(?).
The 'inverted descent' result shows it is nose heavy, in those terms at least.... so X amount more rearwards would bring the up trim to neutral AND inverted become level flight still too. It is so docile and stable (as it was) that it probably would not even care about 10mm more rearwards CofG. So I will make sure of that change too, before resuming flights.
YouTube keeps only doing 240p for my uploads since about a week or two ago!
|Today, 11:31 AM|
You really weren't very high when you started the roll IMHO so you didn't have much time to how to bail out
My Vixen balances at the front edge of the wheelwells also and I do have a little up trim (~1/16") for level flight. I also have max elev travel to give me enough pitch control to do rolls w/o loosing altitude. I do have to push pretty hard inverted to keep the nose up and not decend but it works. Haven't tried to add tail weight to move the CG back because I hate adding weight to the plane. I do think it would be more maneuverable & fly better with the CG shifted back. That said, it flies pretty darn go as-is; maybe after I finish my powerplant upgrade experiments I'll fiddle with the CG
|Today, 11:44 AM|
I still need to do the fillet work to complete the OEM restoration and will refly one more time. Then I have a 12blade CS fan to try (currently has a 10blade). Will be doing each mod separately and then fly to gauge how much better, if at all, things go. After this, I will probably try necking down the exhaust further to see if there's any increase in top end speed. I know it goes against the ~90%*FSA rule, but my earlier results clearly showed opening the exhausts to that area was in the direction of 'badness'.
Will report back after fillet work and 12blade mods fly.
Oh, and I still love those fast, low strifing runs In fact, this is my first EDF and has been so much fun that I bought this
Suppose to be a rocket; at least it looks like it just sitting on the bench. I've got it all together and hope to fly it next weekend. I guess I'm hooked on the 'need for speed'
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