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Author Topic: Mick Reeves Lightning build  (Read 60503 times)

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Offline selleri

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Re: Mick Reeves Lightning build
« Reply #40 on: September 06, 2010, 11:50:57 AM »
Harry Savox makes the Spektrum servos.
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Offline Alex48

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Re: Mick Reeves Lightning build
« Reply #41 on: September 06, 2010, 14:40:55 PM »
I think Als Hobbies are doing a special on 8411's £60 when I last looked 

Offline Mole Hunter

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Re: Mick Reeves Lightning build
« Reply #42 on: September 06, 2010, 14:43:14 PM »
Is that spreadsheet available? It looks very interesting.

Watching this build with great interest. If you decide against silver in the end I have some photos I took at the Museum of Flight last week that may be of interest.
Formerly known as BB-Q


Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #43 on: September 06, 2010, 14:58:32 PM »
I think Als Hobbies are doing a special on 8411's £60 when I last looked 

£120 for the pair or £68 for the Futabas!  No need to install and pay for something as powerful as the 8411s when not needed.  Also, as standard now they come with plastic not metal gears.

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #44 on: September 06, 2010, 15:04:34 PM »
Is that spreadsheet available? It looks very interesting.


In order to understand it you really need to read the article from RC Jet International mag, and this thread, links to the spreeadsheet are in post #12
http://www.rcuniverse.com/forum/m_9638239/mpage_1/key_/tm.htm


Quote
If you decide against silver .....

I will, when Ian Paisley goes to Mass!  I love bare metal finishes.


Offline Pat Barnes

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Re: Mick Reeves Lightning build
« Reply #45 on: September 06, 2010, 17:11:43 PM »
... 8411s .... as standard now they come with plastic not metal gears.

Interesting! I was not aware of that - thanks for the info Harry.  I'm quite keen on the SAVOX range - their servos have some impressive specs, and the feedback (albeit limited...) I've seen is positive.

Offline STORM

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Re: Mick Reeves Lightning build
« Reply #46 on: September 06, 2010, 18:01:07 PM »
I've been thrashing a pair of Savox in the tail of my Elan and am happy enough to install in my new 1:5 L39 all round.
As Sverrir rightly says the new Spektrum servo's are made by Savox.  Standard Savox servo's are Titanium geared.
Gary.


Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #47 on: September 06, 2010, 18:02:08 PM »
It surprised me too Pat, it used to be a metal gear servo, although it gained some criticism for wearing rapidly maybe that's why they changed it, or maybe to make people who want a metal gear pay extra for the 8511, see the following for the latest spec
http://www.macgregor.co.uk/jrpropo/DS8411.htm

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #48 on: September 06, 2010, 18:07:18 PM »
lozza has some hyperions, he took the top off one a few weeks ago, we were well impressed by how chunky the gears are.  I just want to see hyperion and savox get more widespread use in critical controls on high value models for a longer period before I will feel comfy using them, and even then I will start them on non-critical items like brake valves and chute releases.  I got badly burned with Hitec and I will not allow a repeat of that, so until then I stick to Multiplex, JR and Futaba.


Offline Alex48

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Re: Mick Reeves Lightning build
« Reply #49 on: September 06, 2010, 18:58:58 PM »
didn't know that, the last lot I had a few months ago, 14 in total had metal gears....

what about a 579 good solid servo although not digital.

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #50 on: September 06, 2010, 19:13:39 PM »
Of course, MacG's site could be wrong.  But the USA importer has had a plastic gear version of the 8411 for many years so it is not inconceivable that it should have been changed to plastic

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #51 on: September 06, 2010, 21:15:25 PM »
what about a 579 good solid servo although not digital.

A good thought, I found a couple of the 579s when I inventoried my drawer of servos last night, have pencilled them in for the flaps.  They are the same price as the Futaba digi, or by allowing analogue then it brings in the similarly priced Multiplex tiger MG.  Choices choices!

Offline Alan Smithie

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Re: Mick Reeves Lightning build
« Reply #52 on: September 06, 2010, 22:41:03 PM »
...and the feedback (albeit limited...) I've seen is positive.

That could be disastrous - servo feedback should of course be negative...

PDR
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Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #53 on: September 07, 2010, 09:07:02 AM »
servo feedback should of course be negative...
Did someone say "hitec"?  ;D

Offline Alan Smithie

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Re: Mick Reeves Lightning build
« Reply #54 on: September 07, 2010, 11:40:44 AM »
Did someone say "hitec"?  ;D

Bless you!

PDR
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Offline Alex48

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Re: Mick Reeves Lightning build
« Reply #55 on: September 07, 2010, 12:01:22 PM »
lol, I was sent this lot the other week from a customer, all was good until I inspected the contents and found a blue box among the white.... ;)

« Last Edit: September 07, 2010, 12:09:42 PM by Alex48 »

Offline selleri

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Re: Mick Reeves Lightning build
« Reply #56 on: September 07, 2010, 12:33:05 PM »
lol, I was sent this lot the other week from a customer, all was good until I inspected the contents and found a blue box among the white.... ;)

I'm sure it was just to keep the other things from moving around in transit.    :''
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Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #57 on: September 07, 2010, 13:04:19 PM »
Anyway, back to the Lightning build...

The bottom bolt joining the fuselage sections is at an angle since it has to be accessed via the underside of the model, through a hole in the belly tank.  Bevelled hardwood points are supplied in the kit to provide a right angled surface for the bolt head and blind nut, I Hysoled them to the formers.

In case you think my Hysoling the wood mounts for the bolts/nuts is unnecessary bling, remember that it is no longer a wood to wood joint.  You will recall that I have reinforced the former to fuselage join with epoxyglass so the surface of the former is now epoxyglass, not bare wood, and therefore the Hysol provides a much better joint.  If it was still wood to wood then I would use Devcon as normal, I don't think Hysol is especially good for wood to wood as it is so viscous I doubt it penetrates into the surface much.  To improve Hysol's adhesion to the wooden parts I either drill 2mm holes into them or scratch them with the tip of a scalpel to give it plenty of mechanical grip.

On the front section, I drilled a 2mm pilot hole facing forwards and downwards through the former at an angle to come out of the bevelled section at right angles, then followed this up with a 3mm drill.  Then through that hole i could feed an exceptionally long 3mm drill bit that I have, about 8 inches long, and score the fuselage to indicate where to drill the access hole, which I did with 6mm drill for the moment.  Then I put the 2 fuz sections together, and fed the extra long 3mm bit through the fuz, through the former just drilled a moment ago, so it now touches the former on the rear section at the correct place and correct angle, and commenced drilling. When done, separate the fuz sections and I drilled out the rear section to 5.5mm to take an M4 blind nut.  Drill out the front section former to 4mm and put the fuz back together, put long M4 bolt into place with a penny washer, slip on the blind nut and tighten it up to pull the blind nut into the wood.

So all three fuselage bolting points are complete.  But thinking about access to the lower bolt through the hole, I think I will install a plastic pipe from the fuz to the former to be a guide for the bolt and driver.

I took a look at the plan for attaching the nose cone to the intake bullet, it shows one dowel floating in space, and one tiny screw, I think I may glue 3 little patches of lite ply inside the bullet and attach the nosecone with 3 tiny screws instead.

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #58 on: September 08, 2010, 22:58:53 PM »
I was intending to install a guide tube for the bottom fuz bolt, between the fuz and the former, but I did not have a tube of sufficient diameter for the M4 bolt head.  So what has happened is actually better, I installed a tube too narrow for the head and cut it short so that the bolt can't fall out, it will always be held there and not go missing, meanwhile the guide tube will point the hex drive to the bolt head, see photo


the noseleg retract has consumed a lot of time.  The main pivot block is free to move side to side by less than 1mm, but since the steering depends on the leg's position relative to the slot in the servo arm that it engages, the leg will be turned a little off centre, or struggle to get the peg in the slot, if it is not consistent.  So I took the unit apart again and installed washers cut from mylar hinge tape, until all the gap was taken up and it can no longer move from side to side.  Then I discovered the T end piece on the pushrod from the piston was coming off, it has a threaded hole to engage the threaded end of the pushrod, but the hole is too large and only at one side does it engage the pushrod for about 1 turn, so I took it apart and cleaned it and put it back together with 30 minute devcon, I do hope it holds against the bang-bang stress of the retract.  Maybe solder and a 100W iron would have been better?

A shaped and drilled /14" ply plate is supplied for mounting the retract, along with 1/8" spacers, and 1/4" ply pieces for the servo mount.  To this I added 1/4" ply backing to take the blind nuts.  Although the mount is pre-drilled for these retracts, the retract mounting flange tries to occupy the same space as the steering servo.  I checked some different servos and this one is actually quite shallow at the top i.e. height above the mounting lugs, most servos I have are worse and really conflict badly with the retract.  So I had to file some material off the end of a retract mounting flange to allow both it and the servo to go into place.

I chose a Multiplex digi metal gear servo.  Overkill?  I don't think so.  For example, my F-86 steering is done by a micro Futaba servo, so why have so much power and MG in this application?  Well, the Sabre steering has a straight noseleg, not trailing link.  The tyre's contact point with the ground is straight down below the steering axis.  No matter which way the tyre points, it feels no force trying to centre it or drive it further away - it has neutral stability so the servo has very little force to overcome, and no "blowback" force against it, it won't feel any shocks through the steering.  But the Lightning has a trailing link which has positive stability, so whenever it is moved off centre it will generate "blowback", and it can get shocks back through the steering.  So a metal gear servo seemed right, and the spare one I had was a digi so there it is!  I had intended to use the very thick arms/discs that come as options with Multiplex servos now, but those are for the Hitec derived servos and they have different output shafts compared to this real Multiplex servo, so I screwed together 2 discs to give me the depth to cut a funnel shape into the slot
« Last Edit: September 08, 2010, 23:03:34 PM by Mpx »

Offline lozza

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Re: Mick Reeves Lightning build
« Reply #59 on: September 08, 2010, 23:09:44 PM »
Slot in that horn wants tidying up with a file looking a bit ruff on the edges  ::) ::) BUILDERS, we won't mention the car  :banghead:

lozza

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #60 on: September 08, 2010, 23:24:50 PM »
This photo shows the leg in the down position with the peg in the servo arm slot.  Just to add to the problems, the hole for the peg has not been drilled at right angles to the leg so it is slightly off to one side when the leg is straight, and the trailing link arms seem slightly skewiff putting the wheel slightly at an angle, so getting the nosewheel straight will take some trimming.

Which leads on to a poser of a problem, that of making a centering mechanism so that when the leg comes down, the steering peg goes into the slot in the servo arm.  The pivot block has an M3 hole with a grubscrew deep down inside it, so into this I put an M3 6mm bolt to take the centering spring.  I made the spring from fine piano wire wrapped round 1.5 turns around the bolt

But of course I can't rely on the bolt holding the spring in that orientation, some force from the leg turning could cause it to turn with the leg and then the centering has been lost.  That can be solved easily by drilling a small hole either side of the spring arms and popping in a small peg.  But now comes the real problem.  The location of those pegs will determine the centre that the spring returns to.  But taxi trials always show a need for trimming the steering, and as soon as the leg is retracted the spring will take the leg back to the centre position which is no longer coincident with the position of the servo, so when it comes down the peg will hit the servo arm instead of going into the slot.

I am still not happy about that steering, it just seems too much opportunity for the leg to come down and miss the steering slot.  The result would be a nosewheel way off centre when the Lightning lands, and that would be catastrophic.  Have to say I am still tempted to enquire of Unitracts about a custom made unit with integral steering servo, or just contact Aviation Design and get the unit they use on the F-100.

I ditched the idea of 3 screws to hold the nose cone to the bullet, and followed the concept shown on the plan, though a dowel floating in space doesn't help much!  I used sliding fit carbon tubes and balsa blocks to make this fitting at the top of the cone , there will then be just the one screw at the bottom
« Last Edit: September 08, 2010, 23:29:00 PM by Mpx »

Offline Alan Smithie

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Re: Mick Reeves Lightning build
« Reply #61 on: September 08, 2010, 23:36:52 PM »
1. Can you fit a longer steering pin, and grind a taper onto it to improve the chances of engagement?

2. [assuming you'll be driving this with a proper Tx] Could you set up a logic switch that removes the rudder (and trim) input from a nosewheel steering servo mixer when the gearswitch widget = "up"? Then you could have another input (probably a fixed numeric value) to keep the pin aligned regardless of any nosewheel trim that is found to be necessary.

PDR
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Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #62 on: September 08, 2010, 23:43:03 PM »
1. Can you fit a longer steering pin, and grind a taper onto it to improve the chances of engagement?

2. [assuming you'll be driving this with a proper Tx] Could you set up a logic switch that removes the rudder (and trim) input from a nosewheel steering servo mixer when the gearswitch widget = "up"? Then you could have another input (probably a fixed numeric value) to keep the pin aligned regardless of any nosewheel trim that is found to be necessary.

PDR

1. No, it has already been ground down to the minimum by MR, the socket head defines the minimum size at the end.

2.  The leg and the servo can do what they like when "up" is selected, one can go hard left and the other hard right for all we care.  The problem arises when "down" is selected since in that configuration the steering servo needs to be in the trimmed position and the leg will be coming down to engage the peg into it.

Offline STORM

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Re: Mick Reeves Lightning build
« Reply #63 on: September 09, 2010, 08:29:53 AM »
Harry, the simple solution would be to taper the servo arm into a v shape, that way even if the leg drops off centre it will still be guided into the arm.

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #64 on: September 09, 2010, 08:44:21 AM »
Harry, the simple solution would be to taper the servo arm into a v shape, that way even if the leg drops off centre it will still be guided into the arm.
Won't work Gary, the peg is coming at the disc from "above" rather than from the side so it could be a hole in the disc, doesn't need to be a slot all the way in from the side.  That's why I added a second disc, to give some depth, the top disc slot is cut in a V shape to give a funnel entry for the peg.  The peg doesn't go near the edge of the disc.

Offline STORM

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Re: Mick Reeves Lightning build
« Reply #65 on: September 09, 2010, 08:52:54 AM »
Understood,  sorry.

Offline nmacwarbirds

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Re: Mick Reeves Lightning build
« Reply #66 on: September 09, 2010, 19:45:26 PM »
Harry,
If I get a chance I will take a picture of ours at Tibenham tomorrow.

Regards Phil G.
Never in the field of human conflict was so much owed by so many to so few.
Coltishall Memorial Flight. 242 Sqn.

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #67 on: September 10, 2010, 09:17:22 AM »
That would be great, thanks Phil.  All ideas welcomed.  Have a good time at Tibenham, Lozza and Trebor from over here are on their way to join you.

I decided to put the fuz aside for a little while and make a start on the wings, so last night I got the starboard wing dry assembled and ready for gluing, photos to follow soon.

Offline Alex48

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Re: Mick Reeves Lightning build
« Reply #68 on: September 10, 2010, 20:38:58 PM »
Can you make a stainless servo plate that would be clamped between the oleo and the retract?  This would mean the servo would retract and extend with the gear allowing you to have a more traditional linkage set up.  Obviously from the pictures I cannot tell if this would be suitable but just in case....




Offline Alan Smithie

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Re: Mick Reeves Lightning build
« Reply #69 on: September 10, 2010, 21:23:07 PM »
Hmmm....

Well I've had a thought which involves a completely different linkage system.  Add some flat "pads" on each side of the rotating part of the leg. Add a belcrank to the mount which has rollers on each side in a position such that the pads just contact the rollers when the leg is locked down. Drive the belcrank with the steering servo (mounted in any convenient location). When the leg retracts the pads move away from the rollers and the steering is disengaged.

The "pads" could be a machined part that screws to the leg with a bolt in the hole your current steering peg is in, or it could be a bent steel sheet item (also screwed on in the same way).

Well it's an option...

PDR
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Offline STORM

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Re: Mick Reeves Lightning build
« Reply #70 on: September 10, 2010, 21:46:12 PM »
Don't know why things are getting so damn complex, this works fine, can't be that much different on the Lightening, or can it?

Offline nmacwarbirds

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Re: Mick Reeves Lightning build
« Reply #71 on: September 11, 2010, 17:31:55 PM »
Dear Harry
I had a look at our set up for the Lightning steering
and it is exactly as you have it with the double disk.
When the nose wheel retracts it sits in for want of a better word(s)
a plastic piece (supplied with the kit) which keeps it straight,
76 flights later and we have never had a problem with it.

The wheel can become misaligned if the model is pushed backwards,
the steering piece will flip out of the wire guide.
If you include a visual check of the wire and make sure it is engaged correctly
when you do your walk round and as a preflight check, everything will be fine.

Regards Phil G.
Never in the field of human conflict was so much owed by so many to so few.
Coltishall Memorial Flight. 242 Sqn.

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #72 on: September 11, 2010, 20:33:03 PM »
I don't suppose you have a photo of the plastic part Phil?

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #73 on: September 13, 2010, 22:27:53 PM »
The wing parts are mainly made of routed 1/8" ply (might be a form of lite-ply) - the front and rear spars and all ribs.  Pre-cut and slotted leading edge and false trailing edges for the flaps and ailerons are from balsa.  On first putting the leading edge on the plan, it seemed that the notches for the front of the ribs were cut wrong, being too far apart so that if the root rib notch is in the correct place, the notches by mid way were wrong and by the tip they are miles out

As it turns out, the leading edge is correct, the plan is smaller than all the parts (or all the parts are bigger than the plan!) so this will have to be factored in when cutting wood for the ailerons and flaps.
The two spars and the leading edge all come in two parts, with an S shaped cut as the joint to be glued, for which I used epoxy.  Note the leading edges are not straight, the leading edge kinks downwards towards the root between ribs 4 and 5, and the ribs towards the root have an increasing undercamber at the nose, so this seems to be fairly scale and replicates the complex change in sections and shifts in thicknesses along the wing, rather than take the easy option of a simple section and constant taper all the way from root to tip.

The ribs slide flat into position in the spars and are then rotated upright, the fit is very good.  The two aluminium tubes slide into place, again the holes in the ribs for these were accurately cut, the false trailing edges slot into place, and the massive root rib slots into place.  When happy that all is aligned, it can be glued but for this the leading edge near the root needs to hang off the edge of the board because it hangs below the tabs on the main spar.  I pinned the spars down hard to their tabs to ensure correct alignment then flooded every rib to spar joint with thin Zap.  Most held well, some didn't due to slight gaps so I flooded again and hit with kicker, that locked it all.  The backs of the ribs don't align perfectly straight, so when attaching the false trailing edges I used big dollops of pva, put the wood into place and used a ruler to ensure they are straight and just have to accept the glue filling some big gaps.  Now it has all been left to cure until my next session some days from now, when I will glue on the root rib, again using a ruler to ensure straightness, the balsa leading edge, and a couple of other minor parts.  The wing tubes are left in but not glued at this stage
So here is something you see less and less of these days, especially in a jet - a fully built up wing.  It's a shame to have to cover it up!
« Last Edit: September 13, 2010, 22:35:25 PM by Mpx »

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #74 on: September 13, 2010, 23:00:49 PM »
Some points for discussion -

The plan shows the ailerons being top hinged with leaf and pin hinges, by cutting slight rebates into the surface of the wing skin for the leaf to sit in.  Something I liked with my glow motor models is a hinge I think is from M&M developments, which is two pieces of solartex stitched together, the stitch forming the hinge.  It is applied along the entire length so it has massive gluing area, a very long hinging to take the strains, and being so flexible offers no reistance to moving, and seals the joint line. Some models, e.g. Glens CAP use iron on film, single piece, as the hinge.  How about using just one piece of solartex ironed onto the wing and aileron as a hinge before glassing over?  Lots of small holes could be cut in the 'tex to allow resin to flow through to the wood below and secure it very well.  Good idea or bad idea?

Does anyone have long-term experience of either Flite-metal or the aluminium sheeting that Mick sells?  Flite-metal looks incredible but has a reputation for being damaged if you sneeze near it, I would like to know if it is just too soft to cope with everyday flying and handling in car and house?


Offline Maximum maxage

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Re: Mick Reeves Lightning build
« Reply #75 on: September 14, 2010, 01:53:55 AM »
The tailplanes will probably work fine with plastic gear standard servo but in case of flutter I think a metal geared, ball raced, digi will be best.  Each tailplane has its own servo so it doesnít need to be super powerful. It must be from a brand with a history of reliability.  I am considering 3 types of servo that fit that, they are:
Multiplex Tiger MG digi 4  about £52
Futaba S3050 about £34
Spektrum S6020 about £27

Thoughts or suggestions anyone?  I include the Spektrum since afaik it is made by JR?  and it is a good cost saving.  But does it have any history yet, good or bad?  Please donít suggest Hitec, I wonít touch them, no exceptions, no ifs or buts, I wonít even let them in the house!  I am curious about Hyperion and Savox but am not aware of them being around for long enough under their own brand name, in use in valuable models, to trust them yet on a primary flight control.



How about a set of these beasts
A few people including myself love them

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6221&Product_Name=Towerpro_MG996R_10kg_Servo_55g_/_10kg_/_.20sec


chocks away

Neil B :af
Set a man a fire and he'll be warm for a day, set a man on fire, he'll be warm for the rest of his l

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #76 on: September 25, 2010, 09:40:32 AM »
No-one with experience of flite metal, or thoughts on solartex hinging of the ailerons?

The second wing is now mostly built.  Taking experience from the first wing I thought I could make a better job of it but the parts just aren't accurate so both wings have the same problems.  In particular the very long root rib is not straight, it wavers in and out a great amount.  It is attached to the rear edge of many main ribs and their rear edges are nowhere near a straight line, so the root rib waves in and out in order to be attached to them.  You could not butt the root up against the fuselage, there will be huge gaps, which is no doubt why the instructions say to leave an overhang in the wing sheeting.  This will be shaped to fit the fuz and hide the gaps.  Also the profile of the root rib does not match the rest of the wing.  It's trailing edge should meet one end of the false t/e that the flaps are mounted to, the position of the false t/e is set by all the ribs it is attached to, but the root rib t/e is about 4mm higher than them.  This occurred on both wings.  To get it to match I had to make two saw cuts from the bottom of the rib almost all the way up to the top, crack/bend the rear of the rib downwards thus closing the saw cut, and re-glue.  The leading edge should overhang the end of the root rib or at least reach it, but it doesn't quite so there is a small gap to be filled with spare block balsa or light filler.

The retracts are a fraction too deep for the wing, the top edge on one side just rest on the top sheeting about 1mm before the retract flanges reach their mount, so I will have to file/grind some material off the retract sides.

Mick shows an interesting idea for operating and sequencing the undercarriage doors.  Drive them by small servos.  Open the servo and cut one of the power wires to the motor.  (Big problem with many modern servos being soldered onto the pcb and having no wires to cut!)  Attach long wires taken outside the servo and fit a diode and micro switch in parallel.  Fit the micro switch so that when the leg reaches the up position it will push and close the switch.  When up is selected, the servo tries to close the door but power to the motor is blocked by the diode and open switch.  When the leg gets up it closes the switch and the servo can then close the door.  When down is selected the power to the motor is reversed so it can get to the motor through the diode and it doesn't matter that the switch will open as the leg moves.  Advantages?  Each door depends on its own leg being up so won't try to close and jam a leg that isn't up.  No chance of an air leak from the doors emptying the air tank.  No expensive electronic sequencer required.  Disadvantages? 2 mains and 2 noseleg doors needs 4 servos which for many people is a lot of daisychain Y leads and that is likely to cause problems for the servos.  Not a problem for me with 22 programmable outputs on the Rx to drive each servo totally independently!  Can't say I would normally bother with the mods to the servo, my tx or Rx can handle all the sequencing, though it will be time controlled rather than individual leg control as per Mick's idea so it loses the failsafe of the door not closing against a slow leg.

But, a device that I am fitting to the Lightning bricks Mick's idea right back into contention.  I am fitting a Tamjets gear failsafe.  This excellent device has already saved my F-100 when it sensed an air leak caused by a ruptured pipe to a door ram and it dropped the u/c about 20 seconds into a flight.  Had it not done so I would have finished the flight with wheels up, selected down and nothing would have happened, the model would then have been very seriously damaged or destroyed on landing.  The device plugs in between the Rx and retract servo/valve, and has an air line to the main u/c air system.  You program a failsafe pressure.  As long as the air pressure is above that value the device just passes your commands through it, but if pressure drops below that value it takes over and commands the servo to the down position.  Disadvantages?  It only has one input and one output, so tx or Rx sequencing of the legs and doors can't be done, because closed doors will probably prevent the legs from coming down.  You would need to fit a device to each channel and they ain't cheap but it can be done.  On my F-100 the gear failsafe outputs to the Jet-tronic sequencer which then outputs to the legs and doors so when the gear failsafe says "down" the sequencer handles the door opening as well as lowering the legs.

The Lightning has simple door sequencing, open or closed, rather than the closed open closed sequence of some planes.  No point in buying an expensive add-on sequencer for that, but, it means the single output from the gear failsafe must operate the doors as well as the legs and that prevents me using tx or Rx sequencing.  I know SM makes a relatively cheap sequencer but the one person I know who had one has put me off it.  I can try Mick's servo technique, or use an air system with an air switch such as my Starfighter originally had.  That proved troublesome because the small spring pressure of the switch acting on the noseleg was just enough to sometimes jam the mechanism against the retract's spring down action.  Air down should be ok for that, and I could go further - rather than one air switch on the noseleg, copy Mick's servo idea and have an air switch for each door at each leg.  Either a servo or air ram with its own switch is appealing due to their independence against the chance of a slow leg, otoh it introduces lots of new components to fail!  Servo set up would be easier as I can give each one its own programmable output from the Rx, thus easily set the travel.  No air lines and connectors and rams to leak precious air.  Sods law is I buy 4 small servos, and their motors are all soldered direct to the pcb!

Discuss!
« Last Edit: September 25, 2010, 09:52:06 AM by Mpx »

Offline HarryC

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Re: Mick Reeves Lightning build
« Reply #77 on: September 25, 2010, 20:22:00 PM »
Photo shows the ailerons mostly built, upside down awaiting ply inserts for hinges and bottom sheeting.  The riblets are supplied but there were 5 of one size, 4 of another and one of another, and none were correct!  I had to re-cut them all.


Offline Gordon W

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Re: Mick Reeves Lightning build
« Reply #78 on: September 25, 2010, 20:43:20 PM »
The Lightning's little nose doors might work with an over-centre spring-locked setup like I have on my Hawk.  The doors are dragged up and pushed down by the noseleg.  My air-up spring down unit has no problems working the door.  One door doesn't close perfectly on my Hawk, most likely because mine is a bit crudely made, but a bit more effort on my part could probably sort that out.

The main gear doors could use a mechanical lever system, similarly opened and closed by the legs.  These diy systems were common on complex scale models years ago and a typical main gear system, which I eventually used on a Spitfire F24, is illustrated in a certain sport scale book   ;)

That way you could use the Tam fail-safe and omit all the servo wiring or pneumatic spaghetti for the doors.

Gordon

Offline STORM

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Re: Mick Reeves Lightning build
« Reply #79 on: September 25, 2010, 21:42:36 PM »
Makes my job look easy Harry.  ;)


 

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