Stupid! Lean condition => forced landing.

[pgkevet]

And all my own fault..

This is my Blitz Avro. It's got a 90sx modded to crank pressure with a cline carb feed and has automated mixture control too but no governor. It was being a pig to start..it's mixture is a bit rich by default so i clamped the fuel line, got it going and happily flew a quarter tank. Nothing spectacular since I haven't flown blitz for a few weeks so sports stuff getting to feel it again. Then i got a bit more aggressive and during one fast descent whe it was a few feet above ground the engine suddenly ran super lean. I hit throttle hold but cracked a skid bow on the landing (too much inertia)

It turned out that i'd forgotten to open up the fuel clamp.. the crank pressure is high enough to have forced fuel past it and the cline fuel metering and mixture control happily kept it running and sounding fine until that the first extreme manoeuver.

Still..better a skid bow than an engine!

[trillian]

Just saw this thread. That Sunday the 18th I took out my Robbe Futura and Dyna-X with the main purpose of starting from scratch and tuning both engines because I suspected the Futura (OS70SZ) had a lean idle setting and I think the Dyna-X (OS91SZ) had a lean top needle. Sure enough both things were true and now they're both running properly. What surprised me is that the idle mix on the OS91SZ carb has a big effect on the other needles as well, not so with the OS70.

I had one (thankfully) short lean run with the Dyna-X the weekend before due just to me being daft with the high needle.

I'm a bit paranoid about engines running lean now after my YS91 cooked (but actually that was not due to the needle settings).

I'll have my Avro back in the air soon with a trusty old OS91HZ. It probably won't be as smooth as the YS but will make up for it in just not giving me so much grief!

[pgkevet]

with it#s first stage belt drive smoothness isn't going to be an issue. A 105 would be cool with some scott grey 720 blades...but that's a tad much on £££

[trillian]

with it#s first stage belt drive smoothness isn't going to be an issue. A 105 would be cool with some scott grey 720 blades...but that's a tad much on £££

I'm pretty sure there is someone on RR with a YS120 in an Avro. The airframe is certainly sturdy enough. One thing about blade sizes, I started thinking about this a while back when Laurence was talking about the spacing of the grips on the Raptor G4. The rotorhead on the Avro is very wide, so the where the blade bolts are is even a bit farther apart than the Trex 700 and much wider than the Rave ENV and some other .90/700 heads.

So if you run 710s on the Avro it's like running 720s or maybe a bit more on the Rave or the Century Predator where the spacing is narrower.

The Avro is a bit heavy, even a bit heavier than I thought. Mine comes to 5.52KG ready to fly without fuel, which means with a full tank it's gonna be 6kg! So here's a scary thought - the Predator gasser weighs 6kg. (I will say though, the Avro dos not feel heavy in the air, it's very nimble)

Anyway, I know some guys are running the SG 720s on the Avro but I'm inclined to try 690s even, just to see how it feels with a bit more disc loading.

The Predator used to auto really well with 710s and I was just listening to a podcast with Curtis Youngblood about the Rave 630 and how the higher disc loading allows it actually auto very well because it's easier to recover headspeed.

[pgkevet]

I'm pretty sure there is someone on RR with a YS120 in an Avro. The airframe is certainly sturdy enough.

I'm pretty sure there's an aussie who did a gasser conversion too and the fbl one's are cool. it's a shame that Blitz just haven;t bothered producing and fbl head as such..although the head design allows of a simple conversion if you don't mind the unneccessary fb hole left behind. On day on my to-do list will be a DIY fbl head (when i finally own my lathe and mill) - heck with enough patience one can hand make such things.

If you ever get back to croydon and meet Gordon (the plank guy who flies pattern electric planks so superbly).. he used to be a toolmaker and hand filed a clock out of metals. He tld me he could only file two cog teeth a day or risk losing quality. But then he's about the most anal obsessive/compulsive you could meet..albeit a lovely chap.

[trillian]

I've never seen a gasser conversion, I'd like to see that.

It's a shame that Neil did not make a FBL head because he definitely could have sold them. What would be ideal is a new hub that uses the same design but also sits lower (being mindful obviously of the clearance of the blades over the boom). It could use the same grips with different arms. Someone could make a new hub now and probably sell a few but it really needed to be done a couple years ago because I'd imagine by now most Avro owners desiring to go FBL have already done it one way or another.

[pgkevet]

by now most Avro owners desiring to go FBL have already done it one way or another.

I was goign to..the obvious choice was an rjx 90 size head for 10m shaft...but it just doesn't look right that shiney on the rest of blitz

[trillian]

I was goign to..the obvious choice was an rjx 90 size head for 10m shaft...but it just doesn't look right that shiney on the rest of blitz

Yeah, I have also seen an Align 700 FBL head on a Predator using a sleeve to adapt it to the 10mm shaft.

The thought in my brain about it is that all those subtle things about the Avro rotorhead, the way it stays in phase with the plastic inserts, the damping etc. Those things affect the way it flies in FB mode but maybe that stuff wouldn't really matter for going FBL?

Anyway, when I get both of mine going I might convert one to FBL. I'll send a PM to the guy on RR that has two and see what his experience was with the converted stock head vs whatever else (I think he started with converting the stock head then went with an RJX or something).

[pgkevet]

My understanding is that the phase adjustment is the collar with the swash driver pins? The rjx head has the driver built into the headblock which might be a disadvantage although it'd be difficult to know with fbl control - why it'd probably be better to just pull the fb system and make a direct conversion onto the current grip arms which (as you know) are beautifully centred. The neatest version was one where neil supplied a stock head without the fb hole milled through but seems unwilling to do that again. I'm not sure about lowering the head...implies a shorter mainshaft which perhaps would stop the driver pins being able to disengage when switched off?

[trillian]

My understanding is that the phase adjustment is the collar with the swash driver pins? The rjx head has the driver built into the headblock which might be a disadvantage although it'd be difficult to know with fbl control - why it'd probably be better to just pull the fb system and make a direct conversion onto the current grip arms which (as you know) are beautifully centred. The neatest version was one where neil supplied a stock head without the fb hole milled through but seems unwilling to do that again. I'm not sure about lowering the head...implies a shorter mainshaft which perhaps would stop the driver pins being able to disengage when switched off?

You have the adjustable collar that holds the washout guides which lets you adjust the phasing, but what I'm talking about are the plastic inserts that let the feathering shaft teeter vertically but not twist horizontally, the idea of it being to keep the grips themselves from leading and lagging. But maybe it doesn't matter with a FBL system. (maybe it doesn't matter full stop).

You could lower the head where the grips are without shortening the main shaft or changing anything below the hub, it would just mean having a different hub with the height of the grips lower (and obviously you'd need different length pushrods from the swash to the grips.

If enough Avro owners wanted one it's possible that Quick UK might be persuaded to make a new hub.

That possibility of the washout base coming off the guides bothered me at first but apparently some other helis can do that as well and it doesn't seem to be an issue in practise. I think one fairly easy way to prevent it would be to put some kind of tubing over the main shaft just above the bearing block in a length that brings it where it stops the swash going low enough for that to happen.