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» 2019 Llanfair TH Village Fete
Can you Guess what it is yet? - Page 2 Empty2019-07-12, 18:53 by Rich

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Saturday 7/7/18

2018-07-07, 21:07 by Gary M Jones

I was at the field today between 14:00 & 15:00 all on my own , good flying too. There is a dead sheep along the fence line towards the gate from the pits, I saw the farmer so reported this to her. I hope no one had plans for a BBQ Smile .

Farmer …

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Post by Guest on 2010-07-30, 12:18

BUILD THREAD!!!
BUILD IT ANDY BUILD IT!!!
Very Happy Very Happy Very Happy Very Happy

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Post by Brian Colclough on 2010-07-30, 12:22

Had a good blimp at this last night and it will pass the "elf and safety " checks. It may seem expensive to some but it's one of those cases where "less is more" and the workmanship in it is little short of exquisite, nice Andy I'm No with envy but if I spend any more wonga at the moment the old bank manager's going to be outta the wardrobe for sure Rolling Eyes

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Post by Andy Sayle on 2010-08-03, 10:58

Elf and safety, man that's a bad joke! Anyway, on with the build. I didn't get as much time as I had hoped on Sunday to start assembling, but I managed an hour or so. The accessory bag has pretty much everything needed in it, the Stabiliser V mount, 3 little tube/wire pushrod ends, an L shape pushrod end for the V-mount, a little carbon rudder horn, wing retaining screws, two carbon launch blades and a pair of screws I don't know what to do with at the moment Smile

The first job, is to fit the V-mount to the horizontal stabiliser. All I did was cut a 16mm line just aft of the carbon spar in the stab (centred of course!) with a scalpel. I only went through the lower glass surface. I then smeared the contact faces of the V mount (it has a little blade that is inserted into the slot) with some thick CA, Zap's finest btw, before inserting it into the slot. A bit of pressure to ensure it is seated correctly, and all is done. You do have to be careful not to get any CA in the hinge, I found using a cocktail stick to apply the CA worked great.

Can you Guess what it is yet? - Page 2 04-acc10

Can you Guess what it is yet? - Page 2 05-slo10

Next up is to cut a slot in the rudder to accept the little carbon horn. This is marked out as per the instructions (50mm from lower edge) and again one glass surface is cut with a scalpel. Thick CA was used on this part again, but I did give the horn a light sand to remove and release agents that my affect the bond. I was also careful to ensure the horn was butted up against the inside of the opposite skin, to ensure a nice rigid joint. At this point, I am going to deviate fro the instructions a bit. The rudder is designed to be actuated by a carbon pushrod. I'm a big fan of spring/pull linkages, so that's what I am going to do instead. I made a spring up by bending two 90° bends in a 50mm length of 0.4mm diameter spring steel wire. Bending them into a "C" shape, allows one prong to be inserted in the rudder, and one in the fin. The rudder will then automatically be pulled one way by the spring, and the idea is that a pull cord actuates it the other way. The picturs explain this better than words. I used some CA to bond the spring in place. The foam core is not the strongest material when a spring is acting on it, so I wicked a TINY bit of thin CA around the spring prongs to bridge the glass skins, and ensure it can take the loads without falling apart.

Can you Guess what it is yet? - Page 2 06-bon10

Can you Guess what it is yet? - Page 2 07-rud10

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With the fin complete, it's time to bond that in place. I almost forgot to slide the pod on, which would have been a nightmare to remedy, but luckily I stopped to double check everything before applying glue! Lining everything up is dead easy, and I used more thick CA to bond the fin to the slot in the boom. When this has cured properly, I'll put a few wraps of kevlar around the boom at the LE of the fin. This is always a weak point on DLG's, and the weight is well worth the increase in strength/toughness.

Can you Guess what it is yet? - Page 2 11-bon10

More inna bit Smile
Andy

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Post by Guest on 2010-08-03, 11:01

Ohh very nice!!!
I dont really get what you have done with the rudder with the springs, sounds complicated!!!
Well ive got something new to!
My exaust deflector arrived!! woop
Its floresent yellow Very Happy

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Post by Andy Sayle on 2010-08-03, 11:16

With a normla pushrod, it pulls to move the rudder in one direction, and pushes to move it in the other direction. Simple. But, you need a stiff, or well guided/supported pushrod to ensure it doesn't buckle when pushing.

All I have done, is added a spring to the rudder, to replace the need for a pushrod to push. The spring deflects the rudder one way, and a pull cord (a bit of kite line probably) will pull the rudder the other way. The advantages are that the pull cord is much lighter, needs much less support, and can be routed all over the place with no problems. The idea is to try and save a little bit of weight Smile

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Post by Guest on 2010-08-03, 11:17

ahh ok, now I get it!!!!

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Post by Andy Sayle on 2010-08-03, 11:19

Good stuff. The other benefit to it, is that the spring effectively removes any slop or play in the linkage/geartrain from the servo, by preloading it. No slop = more precise controls Smile

Andy

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Post by Guest on 2010-08-03, 11:22

Ahh ye so it does!!!
I take it the spring isnt very strong?
If it was I presume it would be putting quite a load on a micro servo

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Post by Andy Sayle on 2010-08-03, 12:17

The spring tension is strong enough to overcome the aerodynamic loads on the control surface (otherwise it wouldn't deflect one way!) but not so strong that it places a huge load on the servo. I used a similar method on the elevator of my Mini-Fireworks, and found that it hardly affected the current draw of the servo.

On a bigger model, a spring linkage would probably be a non starter, because of the larger spring force required, and therefore more load on the servo (which results in a larger current draw, and heating of the servo).

Andy

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Post by Marty on 2010-08-03, 13:33

Andy, I'm curious about this sprung control surface. Knowing your appetite for things going really fast is there not a danger of the spring giving a little when you have the "pull string" (for want of a better word) slack and the surface pulled to the spring side? surely it would cause flutter? I'm not try to be obtuse just interested.
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Post by Andy Sayle on 2010-08-03, 13:39

Me? Liking things that are fast? I have no idea where you have got that impression from... Twisted Evil

On a fast model, or a highly loaded model, or a big model, I would have my doubts over the sprung control. Flutter may be a possibility, as would the spring not having enough force to overcome the force applied due to aerodynamic loading.

However, this model is rather small (1m span) and incredibly light (95g estimated all up weight, approx 3.5 ounces in old money). The wingloading is incredibly low, and this model will not be going particularly fast. it is designed to go veeery slow, and catch the slightest updraft. For that reason, I have no doubts the spring/pull system will work great Smile

Incidentally, I have a feeling that this model will make my Blaster 2, seem like a rocket ship!

Andy

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Post by Marty on 2010-08-03, 13:50

Just 2 points Andy,
1) Thanks for the "Old money" equivelent, at some stage someone will have to drag me screaming and kicking into the 21st centry!
2) I have no doubt in my mind that you will get bored pootiling round the sky at snail speed and you'll do some sort of mod just to make that tad faster! (it's in yer genes mate! lol)
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Post by Andy Sayle on 2010-08-03, 14:09

I've actually just had a look at the aerofoil polars (data relating to the performance of an aerofoil section at various angles of attack, reynolds number etc, loads of stuff noone really needs to know) to see what the wing is going to be capable of, and it is quite remarkable.

The aerofoils used on the ELF are the AG series, designed by Dr Drela. (a rather well known bloke in aerodynamics circles). He has somehow managed to come up with an aerofoil that will be capable of being really rather floaty, without a nasty cutoff at the maximum lift coefficient (by cutoff, I mean a vicious stall!). To do this would normally require sacrificing a lot of high speed capability (e.g. make the thickness of the section, er thick). The AG series seem to have remarkably low drag at higher speeds though, indicating that the aerofoil is going to be just as happy zipping around quickly, as it will be floating around slowly.

Anyway, I digress. It's only got a rudder and an elevator, and everyone knows you can't go fast without ailerons....

Andy

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Post by Marty on 2010-08-03, 14:17

so when you modifying the wings for ailerons then Wink
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Post by Andy Sayle on 2010-08-04, 09:27

That might be an option, although it wouldn't be easy, without adding shedloads of weight. There is next to no structure at the back end of the wing you see.

Anyway, I'm trying this really slow R/E type flying to see how I get on with it. I've always been dead set against any models without Ailerons, partly because they don't go fast, and partly because it is just wrong!

More build time yesterday evening. A bit of careful alignment and checking saw the horizontal stab in position, and a wee bit of thin CA (Zap's pink finest) wicked into the V mount where it contacts the boom, saw it locked in place. There does seem to be a bit of flex in this mount, primarily in the plastic v mount (the carbon blaster one was rock solid). This may prove useful in the event of a botched landing. Hopefully Vladimir has got the amount just right though, and it doesn't cause any issues on the launch.

Can you Guess what it is yet? - Page 2 12-bon10

With the back end all bonded in place, it was time to move onto the pod. This was aligned with the wing in place to make sure everything was square. Once it was, Zap's finest pink CA came out again (the thin stuff) and it was wicked into the join between the pod and boom. With it tacked in place, the wing was removed, and more CA used to make sure the bond is good. Incidentally, I did roughen the contact surfaces with a bit of sandpaper, to remove mould release/and provide a bit of a key for the bond. I'm not 100% sure of using CA on flexible plastic, because it can crack (the adhesive), but I'll see how it goes.

Can you Guess what it is yet? - Page 2 13-bon10

More in a mo...

Andy


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Post by Andy Sayle on 2010-08-04, 09:44

The next job was to get the horizontal stabiliser pushrod installed. I wanted to use a spring pull on this too, but couldn't see a neat way of getting a spring on the V mount. Had it been a normal hinged surface, it would have been fine, but the all moving aspect makes it really tricky. So, I have followed the instructions, and used a pushrod. This is pretty easy, just CA the L shaped bit of wire to one of the carbon pushrods supplied, and add a bit of heatshrink to secure.

Can you Guess what it is yet? - Page 2 14-pus10

The pushrod is routed down the boom using small (5mm) bits of the supplied guide, bonded to the boom. A continous bit of guide is used to enter the pod, and route the pushrod to the nose section where the servo will be.

Can you Guess what it is yet? - Page 2 15-sta10

Now, onto the rudder pullcord. I used some kevlar thread for this, nice and hard wearing, and minimal stretch. A length of it was tied to the rudder horn (half blood knot and a dab of CA), and threaded down the boom. I drilled a couple of 0.7mm holes in the boom, one in frotn of the stab V mount, and one just in front of the pod for this. Threading it down the boom wsa a pain, but a bit of fine wire helped out.

Can you Guess what it is yet? - Page 2 16-rud10

Can you Guess what it is yet? - Page 2 17-nos10

I now prepared a couple of ripmax SD100 servos by centring the horns, and trimming the case lugs off. These were then bonded to the boom (on the nicely flattened section) using some thick CA. I did think about taping the servos up, but the CA will release from the cases pretty easy, so I don't see the point. I also did the same to the Smart Lipo, and warning sounder. I shall probably go around the servos/smart lipo with either some kevlar thread, or tape, to secure them good and proper.

Can you Guess what it is yet? - Page 2 18-nos10

Concious that CA sometimes takes a while to set, I put the fuselage down now, and decided to do the launching blades for the wing. These were sanded to a rough oval shape, and then the edges were rounded off. I used a combination of a dremel (anding drum) and 400 grint sandpaper. I also used a light smear of thin CA on sanded edges, to ensure they stay sealed. The blades are bonded into precut slots in the wingtips using thick CA. I did spend a bit of time making sure the wing was balanced laterally by adding a bit more CA to the light wingtip.

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Can you Guess what it is yet? - Page 2 21-win10

That's it for now. All that is left to do, is set the linkages up at the servo ends, get the rx installed, and set the balance/throws up before giving it a chuck Smile

Cheers
Andy

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Post by Brian Colclough on 2010-08-04, 09:49

Be careful where you're chucking up Suspect tends to make a mess on the carpet, specially shagpile Wink

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Post by Andy Sayle on 2010-08-04, 10:17

I always find that a good stretch, and taking it easy for the first couple of chucks, helps prevent any injury Wink

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Post by Andy Sayle on 2010-08-04, 22:33

Evening all.

Well that was quick, the Elf is ready to fly! Another hour or so this evening, and it's job done. I've fitted the RX inbetween the wingmounting posts on the pod moulding (there is a cutout in the underside of the wing, which is most useful here), and I have connected up the servo ends of the control linkages. The elevator one uses a tube/rod part that was supplied, bent to a Z link, and bonded tot he pushrod. The rudder pullcord is simply tied to the servo horn, and a drop of CA locks it in place. Obviously I set the servo centres and checked the travels before finalising everything Smile

Can you Guess what it is yet? - Page 2 22-jet10

Can you Guess what it is yet? - Page 2 23-ele10

Can you Guess what it is yet? - Page 2 24-rud10

Now on to the nosecone. I have made a little cutout in the upper surface, to allow the jumper/charge connector accessible on the Smartlipo, without needing to remove the nosecone. All it takes is a little cutout about 12mm by 6mm, and it works great. The nosecone is held on by friction for now, but I have a feeling it may require a small bit of tape to stop it moving.

Can you Guess what it is yet? - Page 2 25-con10

Can you Guess what it is yet? - Page 2 26-con10

And with that, the model is done! The centre of gravity is recommended to be placed between 80mm and 85mm from the leading edge of the wing. I assume this is measured at the wing root, as it has a swept leading edge. With no additional weight added, my balance point is at 79mm. This will do for now, but it is obviously caused by the weight saving at the back end from using a spring/pull linkage on the rudder). The all up weight has come to 96 grams as measured, 1g over the recommended weight.

Can you Guess what it is yet? - Page 2 28-top10

Can you Guess what it is yet? - Page 2 29-bot10

All that is left to do now, is set the control throws, and give it a chuck. If the wind drops a bit tomorrow evening, I'll be maidening it at our club night. I expect I will need to tweak the CG to get it flying nicely, which will probably mean adding weight at the tail. If you do build one of these, and use a spring pull linkage, make sure you mount the servos as far aft as you can to compensate Smile

I'm really impressed with this model anyway. It has taken me harldy any time to get it built, and the standard of build on the parts is just outstanding. The only thing that looks a little out of place, is the translucent plastic nosecone. It looks great on its own though, and would really benefit from a coat of paint, or even better, it being supplied coloured.

Cheers
Andy

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Post by Guest on 2010-08-04, 22:40

very nice!!!!

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Post by Mark Barnes on 2010-08-05, 08:40

Nice one Andy, good little build thread aswell (helps with the discount im sure Wink )

Dont think i really understand that sping link method so will have a look tonight

C ya later

M

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Post by Andy Sayle on 2010-08-05, 09:34

To be fair, I would have done a build thread on this anyway, there isn't really one out there yet.

The spring link is dead simple, It's so simple, I reckon even you can understand it Twisted Evil You've seen it before on the elevator of my Mini-Fireworks, it's exactly the same as that.

The wind is currently at around 14mph according to my mk1 calibrated wet finger, but is forecast to drop this evening, so it looks like we are good to go for a maiden tonight!

I'm amzed how light this thing is too. If it doesn't catch the hot air from all the chatting going on in the pits, I'll eat my hat*

Andy

*well, I might just chew it a bit, but not swallow....

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Post by Mark Barnes on 2010-08-05, 09:42

if it dose catch the hot air from the pits, then your clearly breaking club rules and should be punished!

Havent realy taken any notice of the mini FW but will do once i own it!

M

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Post by Andy Sayle on 2010-08-05, 10:02

AH, but if the thermal is drifiting downwind, and the wind is in the direction of the strip from the pits, that would be acceptable right? Twisted Evil

I was going to ask for £200 for the MF, but as it is you, £165 and it's yours, ready to go, just add RX.

Andy

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Post by Mark Barnes on 2010-08-06, 07:44



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