500 Size EC135 with Fenestron.

[dannyhough]

Hi

This build has been going on a while and so far has been documented on Heliguy and RCGroups forums, as i'm new around here thought i'd share the details and the progress.

The Tail is a six blade alloy unit made by a German guy by the name of Roland Kreamer (heliroland) and as far as i know it's only the second one to have been made, the first being his own. The tail units are available for 450 and 500 size with the only differences being the blade length and the boom clamp diameter.

The Fenestron is limited to a max speed of 15,000 rpm so with a 7:1 ratio that means a max HS of 1800, i'm currently at 1750 with Scorp 1210 kv motor with 12t pinion with a flat 80% TC.

I also have a 4 blade CX flapping hinge head with TF model unweighted scale blades and although the floating hinge head is said to be flyable with no estab i will be using BeastX to keep the flying relaxing.

At the moment i just recieved the new blades as the last set were all over the place after a test hover so the video shows the first test hover with 4 blade head and fenestron, as far as i know the first time the 500 size has been tried with 4 blade head.

[ame=http://www.youtube.com/watch?v=Obq-pluN_1c]YouTube - dan new heli.wmv[/ame]

Sorry about the quality i forgot to charge and take the video glasses so paul kindly captured it on his phone.

The heli had a tendency to drift back and left so i'm thinking a phasing issue, the phasing is currently mechanically set 90 deg advanced but i'm thinking 92 or 93 deg might just cure it.

The tail is controled by a GY401 and S9254 and did loose authority on a couple of occasions, this could well be down to having too much pitch for right yaw and the blades stalling and the 10 - 15 mph winds weren't helping either.

Next is to install the estab and use the gyro to limit the pitch individually and tweak and tweak untill it's perfect. I am very confident that the unit is upto the job as my trusty windometer (hand) detected far more thrust from 3 deg pitch on the fen than the stock 2 blade tail.

By the way the fuse is in the paint shop becomming yellow ready to become the North West Air Ambulance.

That's all for now but i'll post updates as and when they happen.

[dannyhough]

Tiny bit of progress

As the weather has been too poor for flight tests i decided to install the BeastX Man that manual could be somewhat simpler the actual setup and install is a doddle when you get through all the excessive wording.

It's all done now and everything is acting as it should only flying will tell, i left the gains at a touch under default for the maiden hover and the tail limits are now set individually in an attempt to avoid excess pitch and subsequent stalling. At least the BeastX allows me far more parameters to play with as far as the gyro goes.

Quick piccie of the installation....



New issue has popped up now in that one of the MG930 cyclic servos will not power up on first connection of the bty, if i dissconnect and then reconnect with the Radio still on the servo comes to life but when the Tx is switched off as well as the Rx then all is restarted the servo doesn't respond Sure i have another MG930 lying around somewhere.

I tested it with a spare MG90 plugged into the beast and it came to life no problem on 5 seperate occasions with no failures so it must be the servo

With luck if the weather breaks i can get some test flights in, gotta hurry the offshore season is starting
_________________

[dannyhough]

Fixed the servo issue with a replacement and then....




Booo Hooo Twas a muddy field

Had a play with the tail pitch trying to find the max pitch before stall, few hops in the garden gradually increasing the gyro enpoint for right yaw. After 3 packs all was looking good so i recharged and headed for an open field.

First 3 packs at the field went well and the BeastX worked very well, as expected. Did a few steady circuits and fig 8's with no problems.

On the fourth pack things started well with more circuits, still nice and slow. Then went a little higher and tried a few slow piros, again no problem. Next i went for a full left piro and the heli spun as commanded and stopped well without any bounce back confirming the gyro gain was good, Next a right piro (full stick) immeadiatley the heli started to right piro then went into full left with right rudder having no effect.

The spin quickly became unrecoverable, i tried increasing pitch to gain height and time but to no avail so defeat was admitted and throttle hold hit. She came down on her side and at first glance it looked totalled.

Inspection on the bench showed the following damage...
Bent main shaft and lower jesus bolt
Broken left aieleron servo arm
Bust both horizontal and vert stabs
Heavily disfigured boom
Stripped teeth on main gear

The fenestron came out of it pretty well thank god..

2 broken tail blades, 1 split the other missing.
Twisted vert stab mount

So all in all a bit of a result

Oh yeah forgot the bent feathering spindles x2 on the head, i have spares that i got at the same time as the head but can't figure out how to get the flamin things out.



There is a grub screw on each one but when removed the shaft still wont budge There is also a small 1mm hole opposite the grub screw but no idea what that's for.

The only thing i don't have spares of are the tail blades so an email to Roland requesting spares has been sent.

Pretty sure that the tail blades stalled due to over pitching so i will build my self a seriously heavy duty turntable to get the rate pitch and max pitch nailed once and for all.

Anyone suggest a good source for a big smoth running bearing that will take a 500 heli trying to lift it up?

[Boggy]

not good Dan!

i have no experience with your rotor head but could the grub screw be hiding a pin that you can tap out via the opposing hole?

[Streetluge Chris]

That's bad Dan do you know what the cause was.

[Adrian]

ouch thats a real shame, im sure it will be back up and looking good soon

[dannyhough]

not good Dan!

i have no experience with your rotor head but could the grub screw be hiding a pin that you can tap out via the opposing hole?

I thought that aswell but there seems to be a sleeve that the spindle fits into and the grub screw sqeezes on, have ordered a new main rotor hub (only $20) just incase i get too heavy handed getting it out.

@Chris

Pretty confident the tail blades hit stall pitch and with the gyro in HH mode it just continued going full right to try and compenstae, if i had thought to flick briefly to rate it may have saved the day....but...i didn't

Still it's pushed me on to build a suitable turntable for testing with pitch on the mains.

[dannyhough]

Hey Ron

Seems you were spot on ....

Got the spindle out at last, foud a 0.9mm allen key and with a bit of force managed to push out the cross pin Easy when you know how.



Simple matter of inserting the allen key in the small hole and pushing the securing pin out, thanks for making me look closer

So now it's just the tail blades and we are ready to rock.

[dannyhough]

Howdy

Little later than promised but here's the update

Took the heli with 4 b;lade head and stock 2 blade tail to the club yesterday and it flew great had a play around with the expo for aieleron and elevator as it was a little twitchy to begin with and settled on 28% for both.

Was a lttle windy for a first real test of the microbeast but it came home in one piece so i'm happy.

The dampers in the head are worn already after only 3 flights so i need to find some silicone tube with 5mm ID and 7mm OD. Anyone ?

Fitted the fenestron this morning and tried it all out on the turntable, by some miracle the pitch i initially set at mid stick rudder was almost spot on for holding heading in rate one turn out on the servo rod got it close to perfect, it does start a slow left spin when pitch comes on to the mains but an extra turn on the rod sends it the other way so it's staying as is.

First picture is the pitch for rate hold..



The next is full right yaw pitch....



Not a whole lot of difference, i gradually increased the right yaw pitch through the beastX untill the blades stalled on full right input then backed off a touch, it was also nesseccary to reduce a little more as the blades were on the verge of stall stopping from full left piro.

The pitch shown gives plenty of authority for right yaw and i tested it with around 4 deg pitch on the main blades, there is a little bounce back when stopping but that can be sorted i think with tweaking the delay.

When i said earlier that there seems to be a very fine line between full authority and stall i had no idea just how fine.

Looking at the pic i measured the distance between the tip of a marked blade (blade to left of pic) and the boom mount bracket at 3.2mm for rate hold and max pitch is now at 5.15mm. If i increase the max pitch so the gap is 5.5mm (smallest increase i could manage) the blades stall at full input and stopping from left piro. If i decrease to 4.8mm gap then there is barley any authority for right yaw with the heli taking an age to stop comming out of left piro with occasional left piro comming back in.

This is the only way i could think of to measure the pitch with any reasonable accuracy.

The wind is set to drop a little in the next hour or 2 so with luck i'll get out for a test flight, fingers crossed.

[dannyhough]

Alas no test flights, bummer as the weather could not have been better. Ho Hum at least the Pro got a thrashing

Replaced the bearing blocks and main shaft bearings but the gear wobble remains i don't think that this is causing the vibes though, looking at the head from above with only the hub and swash in situ there is a definate wobble and nothing to do with the shaft.

Ran out of time yesterday and today is gonna be spent making sure i don't forget anything for work

I have a spare centre hub so will put that on without blades etc and see if the wobble persists, if that doesn't cure things i'll have to go back and strip the whole thing down when i get back onshore

We will get there in the end Also still need to find some silicone tube for dampers, the only stuff i can find with the correct ID and OD comes in 30 - 50m rolls for £35 - £50 No way i'm spending that when i only need 20mm of the stuff.

By the way i posted the wrong sizes, should be 5mm ID and 8mm OD (1.5mm wall thickness. So if anyone knows where i can buy a meter let me know PLEASE!

I'll spend a few hours in the engine room onboard sweet talking the chief to see what he's got

[pchristy]

Pretty confident the tail blades hit stall pitch and with the gyro in HH mode it just continued going full right to try and compenstae, if i had thought to flick briefly to rate it may have saved the day....but...i didn't

That would be my analysis as well! I ran onto this exact problem in 1974 with my first heli! It had completely flat tail blades, and the main blades I used were a bit thicker and heavier than the design called for, so it needed a lot of left t/r to keep it straight (it was a left-hooker!). If you applied more than about half left tail-rotor, the blades would stall, leaving the heli pirouetting uncontrollably to the right! Of course, back then we didn't have any gyros to aggravate the situation, but it was still a pretty untenable position for someone with no previous heli experience, and it took me a while (and several crashes!) to figure out what was happening!

Full size Gazelles are prone to what is known as a "Fenestron stall" - particularly when hovering cross wind - so I suspect your analysis of what went wrong is 100% correct!

[dannyhough]

Cheers for the info Pete, seem to have the Fenestron sorted now just gotta figure what's causing the vibes and should be good to go.

Hats off to you guys flying the old school way.

Back off to work offshore tomorrow with no idea how long for so it'll all have to wait till i return.

[mole hunter]

Hi Folks,
Looks like you're getting somewhere at last with this build Dan. It looks and sounds great, even in pod and boom form.
YouTube - RC Heli test flight

2nd test
http://www.youtube.com/watch?v=0Ae65aVe3r0


Should be fantastic in the fuse.
Onward and upward

[dannyhough]

Thanks for posting the vids Marty and yes it's gonna look awesome when it's done. Still some more testing to do first though, i need to test fly the mechs with added ballast to simulate the fus.

At the minute the max collective is 7 degreess (ish) set via the pitch curve and i need to see if that's gonna be ample to lift the helis AUW, adding more pos pitch could cause issues with tail authority.

Think it will be ok though as on the videos i barley got above 3/4 stick (about 5 deg) and there was plenty of lift although you can see the tail blow a little on the mini pitch pumps i tried.

More testing with fingers crossed and a nappy on and we shall see

[dannyhough]

Little update, been working away and as this is the busy period time will be limited untill the end of the work season (September ish) so progress is a little slow. Hoping to get a couple more test flights in today then next time i'm home i'll install the mechs into the fuse before doing the detail work and if it all works i can get the finishing touches done when i get back home in the middle of July.

4 weeks on and 2 off relly eats up the time.