Fei-Bao Mirage 2000

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Harry Curzon
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Re: Fei-Bao Mirage 2000

Postby Harry Curzon » Tue Aug 18, 2009 10:05 pm

jbrown wrote:Mirage Fans,

But I have yet to see a picture with one deploying any 'flaps'?

Anyone else curious about this?

Hi Jim, "flaps" on a tailless aircraft are elevators! So putting down the "flaps" is simply putting in down elevator.
Harry

Keith Whiddett

Re: Fei-Bao Mirage 2000

Postby Keith Whiddett » Wed Aug 19, 2009 9:30 am

Hi All i have lost my Mirage do to flutter,the surfaces are to big for one servo even a 8711 and i would fit four servos,two each side, this is a must do,also fit new CARBON hinges in between the factory ones to double up, the factory fitted hinges do not have enough meat around them,i have enformed the factory who are changing things regards Keith

jbrown
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Re: Fei-Bao Mirage 2000

Postby jbrown » Thu Aug 27, 2009 9:17 pm

Hi Dick,

Thanks for your reply. I think there's more interest in our beloved Mirage on your side of the pond. I don't see much activity on any build threads over here, and have yet to see one (turbine powered) at any of the fields I fly at?

After seeing Harry's post on the loss of his Mirage, it's two 8711s per side for me. Sorry Harry.

Thanks to all for the answer on why no flaps, that makes perfect sense now. One less channel to use.....LOL

Let's keep this post alive for all of us Mirage addicts.

Best reqards, Jim

jbrown
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Re: Fei-Bao Mirage 2000

Postby jbrown » Thu Aug 27, 2009 9:22 pm

Harry, sorry, I meant to say Keith.

Keith, sorry for the loss of your Mirage.

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Dick Spreadbury
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Re: Fei-Bao Mirage 2000

Postby Dick Spreadbury » Fri Aug 28, 2009 12:03 am

jbrown wrote:Hi Dick,

Thanks for your reply. I think there's more interest in our beloved Mirage on your side of the pond. I don't see much activity on any build threads over here, and have yet to see one (turbine powered) at any of the fields I fly at?

After seeing Harry's post on the loss of his Mirage, it's two 8711s per side for me. Sorry Harry.

Thanks to all for the answer on why no flaps, that makes perfect sense now. One less channel to use.....LOL

Let's keep this post alive for all of us Mirage addicts.

Best reqards, Jim



Hi Jim,

Not really surprised that the Mirage isn't overly popular there...I think that mainstream jet modellers there tend to stick to American prototypes...just a few seem to find interest outside!

Anyway, having spoken to Keith about the demise of his Mirage, it seems he suffered elevon flutter. Even though he had top end powerful servos fitted, he mentioned that there was some slop in the hinges of his elevons - which, incidentally, I have absolutely none on mine - and a little bit in the linkage. He surmises that, together, these may have had a contributory effect.

What also bothered Keith was the fact that the elevon detached from the model, taking the hinge pin with it - in other words, the hinge points mounted in the false trailing edge of the wing didn't have enough 'meat' on them 'behind' the hinge pin, and the pin broke loose. I believe Keith's been in contact with Fei-Bao about this last point.

Before Keith's incident, I had been thinking about splitting the elevon and putting in another servo...I was uncomfortable that there was no redundancy there...and this incident has cemented my thoughts. The issue being where to put the second servo box. I need to know what the wing internal structure's like to help make that decision and, fortunately, Keith has kept a portion of wing from his Mirage which he's letting me have so I can get a look inside. The only assumption I'll have to make is that all the Mirage wings are jig-built and, therefore, the same inside.

There is a 'scale' split point on the elevons that's just outboard of the model's horn position, so I'll probably split it there and insert a couple of closing ribs in the ends of the 2 parts.

One thing I have done with my model is to make and install 2 new elevon control horns per surface - they sandwich a ball-link - which are much longer than the kit supplied parts (surface of elevon to hole in horn = 28mm...this gives much greater mechanical advantage and much more servo movement, with the clevis at the servo end on an inner hole). I'll post details and pics of that shortly, to show how I did it. I'll also post pictures of the structure of the wing Keith's giving me, just in case anybody else wants to go the 2-servo route.

Cheers,

Dick

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Re: Fei-Bao Mirage 2000

Postby Dick Spreadbury » Wed Oct 21, 2009 8:39 pm

It's been a while...too busy with other things! Anyway, I've done a bit more to the wings of late...

I decided to make cradles for the elevon servos, instead of using the suggested servo bolted to a piece of angle aluminium and screwed to the two plywood points in the servo box cut-out. As can be seen it's just a 1/16" ply base with vertical side pieces from hardwood. The servo is held down by a piece of thin Proskin (available from Mick Reeves Models) and secured against lateral movement by the lugs sitting in slots formed on the base. The cradle was Aeropoxied to the wing skin, and a slot cut in the box cover for the arm to come through.

Maybe a bit of overkill but I decided that, as I had to make longer elevon control horns (on Keith Whiddet's advice), I'd double up on them and use a ball-joint between them. This would alleviate any twisting tendencies of the horn if just one ball-joint was fitted.

The pictures show the difference in size of horns. Also shown is the slot I made - Fei-Bao place a balsa block where the single horn goes...I routed a fair bit of this out, then closed the 'open' rib with a piece of 1/8" balsa. This left a fair size hole into which I Aeropoxied the new horns (having first got symmetry, spacing and position by fitting them to the ball-joint, and the control rod to the servo with the elevon in the neutral position...just as if finished). I glued a piece of balsa filler between the horns and filled the remaining void with Aeropoxy. Picture shows the final arrangement (not yet properly secured or painted).
Attachments
8 Cradle.jpg
8 Cradle.jpg (195.94 KiB) Viewed 13657 times
7 Servo in cradle.jpg
7 Servo in cradle.jpg (181.39 KiB) Viewed 13657 times
6 Servo in wing.jpg
6 Servo in wing.jpg (156.65 KiB) Viewed 13657 times
5 New & old horns.jpg
5 New & old horns.jpg (202.14 KiB) Viewed 13657 times
4 Horn slots.jpg
4 Horn slots.jpg (281.16 KiB) Viewed 13657 times
3 Horn slot cut-out.jpg
3 Horn slot cut-out.jpg (320.5 KiB) Viewed 13657 times
2 Horn in slot.jpg
2 Horn in slot.jpg (292.75 KiB) Viewed 13657 times
1 Horn, rod, etc.jpg
1 Horn, rod, etc.jpg (244.53 KiB) Viewed 13657 times

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Dick Spreadbury
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Re: Fei-Bao Mirage 2000

Postby Dick Spreadbury » Wed Oct 21, 2009 10:01 pm

As promised, following the demise of his Mirage, Keith Whiddet kindly gave me the largest part of wing he had left so I could de-skin it, have a look at the structure and decide where best to put an additional elevon servo box in.

I'll describe how I did that in the next post but, first, it's worth sharing what I found when I de-skinned Keith's wing (which was a difficult job in itself...it was very securely glued on!).

Not much of a surprise was the relative lack of structure...the composite skin is pretty rigid and stiff and provides a lot of the strength to the overall component. What structure was there, though, was sound and of good materials for the job. I was surprised, though, that Fei-Bao hadn't extended the rear spar right to the root rib and tied it in there (that's not the rear carbon rod-spar, by the way, I'm talking about the rearward diagonal spar).

All the glue joints were very well made - no gaps! - and the structural parts were all capped with carbon-fibre tows that were well wetted and glued to the structure.

The main spars (carbon-fibre rods) were well glued to the structure, as the photo shows, as were all the elevon hinge-points.

The photo of the hinge-points show the relative lack of meat aft of the hinge wire hole - I did test one to destruction (not very scientifically!) by hanging a 28lb weight on the hinge wire, the hanging points one either side of the hinge-point so that it, alone, took the weight. The weight alone didn't pull the wire through...the hinge-point eventually failed (hinge-wire pulled through) when I 'bounced' the weight by up/down movement of the wing/weight and applying instant shock loads.

To see if I could pull the hinge-point out of the wing, I held a single point with a mole-grip and, despite exerting a strong load and my best efforts at twisting/turning/whatever, I couldn't pull the point out...it was there to stay!

When a control surface flutters, loads are exerted on the hinge-points from several directions, at different frequencies and varying amplitudes, so if I do decide to reinforce the hinge-points, it'll be by sandwiching the original point in its entirety between a couple of thin metal shims, Aeropoxied on.

What else to say about the wing...well, the pylon securing points are merely a piece of (soft-ish) aluminium angle glued to a balsa block and arranged to sit just beneath the skin - simple but effective. The wing skin itself is a composite of 2 layers of fibreglass sandwiching a dense brown foam that forms a light and stiff component - it can though, as you would expect, be fairly easily crushed/marked if a point load is applied perpendicular to the surface. Particularly worthy of note, given past concerns about some manufacturer's lack of attention to leading edge areas, was the strong and securely glued structure in this area. The Mirage's L/E was formed from a single wood strip, securely glued behind the L/E point and to the skins, forward of which was a very substantial glue fillet giving added security to the skins and forming a very strong L/E. Finally, and answering the question posed by Nick Yuhaz a few posts back, the structure in the undercarriage mounting area is made from substantial ply-wood, well tied to the skins, which are strengthened with the use of carbon-fibre cloth. Apart from the 'short' rear spar, quite an impressive piece of construction, overall!
Attachments
Keith's wing 1.jpg
Keith's wing 1.jpg (251.4 KiB) Viewed 13657 times
Keith's wing - 2.jpg
Keith's wing - 2.jpg (253.26 KiB) Viewed 13657 times
Keith's wing - spar.jpg
Keith's wing - spar.jpg (257.19 KiB) Viewed 13657 times
Keith's wing - hinge point.jpg
Keith's wing - hinge point.jpg (309.66 KiB) Viewed 13657 times
Keith's wing - pylon mount.jpg
Keith's wing - pylon mount.jpg (314.86 KiB) Viewed 13657 times
Keith's wing - skin composite.jpg
Keith's wing - skin composite.jpg (284.09 KiB) Viewed 13657 times
Keith's wing - UC area reinforcement.jpg
Keith's wing - UC area reinforcement.jpg (273.13 KiB) Viewed 13657 times

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Dick Spreadbury
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Re: Fei-Bao Mirage 2000

Postby Dick Spreadbury » Thu Oct 22, 2009 7:00 pm

Putting in the second elevon servo:

Given the info from Keith's wing, I decided the best place to cut the wing bottom skin to allow another elevon servo in was as shown in the picture below.

The initial dimension was taken from the outboard edge of the existing servo opening, and the opening marked from there using the other dimensions as shown.

The skin was cut with a thin dremel cut-off disk and, as the servo was going to protrude a bit outside the surface, which meant I'd need to make a suitable cover to sit on the wing surface, I made the 1/16" ply insert skin reinforcing plate to match the opening - ie., no panel land left.

The reinforcing plate had to be cut to miss the pylon mounting point in the wing which made it easy to insert inside the wing! The plate was made such that its forward edge butted against the diagonal wing spar so that, when it was all aeropoxied in, the plate was secured to the skin and spar, making a good, strong job.

Servo cradles were made and fitted as described before and I made the cover from a couple of pieces of 1/8" balsa for the sides and 0.4mm Proskin for the cover surface.

When I cut the elevon in two parts, I'll probably add another hinge point for added support...when I do it, I'll post details and pictures
Attachments
5  2nd elevon servo box location.jpg
5 2nd elevon servo box location.jpg (177.91 KiB) Viewed 13656 times
4  Servo box marked.jpg
4 Servo box marked.jpg (195.61 KiB) Viewed 13656 times
2  Reinforcing plate - 1.jpg
2 Reinforcing plate - 1.jpg (161.67 KiB) Viewed 13656 times
3  Reinforcing plate 2.jpg
3 Reinforcing plate 2.jpg (261.82 KiB) Viewed 13656 times
1 Servo cover.jpg
1 Servo cover.jpg (99.35 KiB) Viewed 13656 times

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Shaun Chant
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Re: Fei-Bao Mirage 2000

Postby Shaun Chant » Wed May 05, 2010 8:29 pm

Dick, how did this progress?

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Dick Spreadbury
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Re: Fei-Bao Mirage 2000

Postby Dick Spreadbury » Wed May 05, 2010 9:56 pm

Shaun,

No progress for ages...it's still at the stage it was at my last post...other things have got in the way and continue to do so. Aim to get going on it again when I get my workshop back in abt 4 months time.

Cheers,

Dick

Florent Colombet

Re: Fei-Bao Mirage 2000

Postby Florent Colombet » Thu May 06, 2010 5:42 am

Dick,

You know that I can help you make some room in the garage! ;o)

cheers
Florent

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Dick Spreadbury
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Re: Fei-Bao Mirage 2000

Postby Dick Spreadbury » Thu May 06, 2010 7:50 am

LOL!! Nice one Florent...thanks for the offer but the Mirage is a keeper.

Cheers,

Dick

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Re: Fei-Bao Mirage 2000

Postby Dick Spreadbury » Fri Oct 22, 2010 9:20 pm

Just noticed it's a year ago today since I posted anything about the Mirage! Still no progress since then...lots of 'other' stuff going on (incl house alterations...and 'refurbed workshop!) and have done almost no modelling at all save for painting my Foxjet (pic below)! With any luck, that'll change soon - new workshop floor going in tomorrow...then bring everything back out of storage and set the workshop layout from scratch. It's been a looooooong year!

Rgds,

Dick
Attachments
20 June 2010 016a.jpg
Florence the Foxjet!
20 June 2010 016a.jpg (91.02 KiB) Viewed 13330 times


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