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25" DH Vampire from a Jetex plan

Old 01-29-2015, 04:57 PM
  #1  
quorneng
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Default 25" DH Vampire from a Jetex plan

Although the Canberra is not yet flying properly the current UK weather precludes virtually all flying, even Manchester International Airport so a nice Vampire!

The original plan was from Jetex to be powered, not surprisingly, by a Jetex 100 unit.
The plan as downloaded from Outerzone.
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Fairly simple and really just stand off scale but it looks the part so my challenge is to convert it to an EDF and RC.
After some measuring it looked like a 40mm EDF (I have one spare!) would just about fit in the fuselage. The tail pipe on the plan was close to 85% of the FSA and the inlet area would be just about 100% of the FSA. Good enough!

The next task is to do some modifications to the drawing.
First the non scale dihedral (for Free Flight) needs to be reduced to nearer scale. This alters the wing root geometry a bit as well.
Second the EDF & ducting has to be squeezed in.
The exhaust tube is relatively easy but the big problem is the bifurcated inlet that has to change from two widely spaced low aspect ratio triangles to a circle and over a short relatively distance.
I will not attempt to 'design' it on paper but will actually build it inside the fuselage as I go along. Well that's the plan!
The redrawn plan.
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Not fully detailed by any means but enough to get under way.

Just a word of caution. The down loaded plan has a bit of 'distortion' so that in some case the L&R sides are not exactly the same! I had to resort to quite a biit of 'select/copy/flip/paste' to ensure things were really equal about the centreline.
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Old 01-29-2015, 05:29 PM
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Quarneng,

Take a look at this plan, it's a prototype for a kit that was never produced due to the lack of suitable EDF unit available at the time. The plan was given to me to see if i could modify it to take a newer type fan but i never got around to it.
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Aerographics Vampire.pdf (1.00 MB, 255 views)
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Old 01-29-2015, 09:44 PM
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quorneng
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JPF
That looks very nice and probably rather a better scale outline than the Jetex plan I am using.
As with all the Vampire/Venom the inlet geometry is rather poor for an EDF but then the full size was pretty poor but of course as a turbo jet (and quite a small one) the inlet volume was much smaller.
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Old 01-30-2015, 06:03 AM
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Bill G
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Nice project Quorneng. I'm sure this one should be a success. I have one at a bit over 20" that weighs 4oz with an anemic Feigao powered EDF30. I think the short ducting makes up for the loss in efficiency of the steep angled intake ducting.
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Old 02-01-2015, 06:33 PM
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quorneng
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Default $100 EDF scratch build contest - 25" Vampire

With a bit of luck this could be included in the $100 EDF build. It certainly wont cost that much including everything!
First the fuselage.
With this sort of micro EDF I find it is easiest to build from the EDF itself as it tends to be the strongest single bit.
The 40mm EDF with the first Depron former (actually F6) glued to it.
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The paper thrust tube is next. It is formed over a wooden mandrel (bit of wood turning required!)
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The thrust tube provides support for the two rear formers F7 and F8.
In conjunction with F6 these provide support for the wing root rib.
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This in turn provides support for the two formers ahead of the EDF, F4 & F5.
So far all done in 3mm Depron.
Before the fuselage can go any further the bifurcated inlet duct has to be built in. Far too complicated to draw out (by me anyway!) so it will be built in 2mm Depron 'in situ' piecemeal.

Last edited by quorneng; 02-01-2015 at 08:05 PM.
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Old 02-02-2015, 10:37 PM
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Very fiddly to do but the inlet duct is complete.
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Although the duct is of sufficient area its complex path is probably where most of the duct losses will occur.
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The next issue was how little room there was in the fuselage so I decided to mount the ESC above the inlet duct to leave the nose completely free for the battery box.
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This actually proved to be quite an effective layout as it meant all the fuselage formers were fully supported by a rigid Depron structure before any of the balsa stringers had to be added.
The fuselage is exactly 11" (279mm) long.
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Old 02-05-2015, 02:29 PM
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The slots for the stringers were cut with a 1/32" jewellers diamond file which cuts the Depron very easily. This means the 2x1mm balsa stringers are a 'tight' fit in the soft Depron formers so the stringers stay in place while the POR sets.
All the fuselage stringers in place.
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When tissue covered it will look the same as if it were an all balsa structure.

Next the wing. The ribs, leading and trailing edges are Depron.
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The wing spar itself is a 'composite' with 3x1mm balsa flanges over a 2mm Depron shear web between the ribs.
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Despite the wing looking much like the original construction there is now remarkably little balsa in it!
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Old 02-07-2015, 02:33 AM
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As Depron is rather more flexible than balsa the leading and trailing edges need additional support to resist the shrink forces of the tissue.
Rather than gussets I have used diagonal 'braces' in 2x2mm Depron.
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The diagonal bracing ahead of the spar not only supports the LE but also provides significant drag stiffness.
The braces for the rather weaker trailing edge provides support at 1/3 and 2/3 the distance between the ribs.
The bracing adds just under one gm to the weight.

The wing root inlet in next.
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Old 02-08-2015, 08:11 AM
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Looks good. You probably have more than enough ESC, but it's never a bad idea to face the heatsink into the ducting wall with a small cutout for cooling. Personally cooling hasn't proven to be an issue with amply sized ESCs, but a small cutout would create some air exchange, unless of course the fuse bottom is to remain open.
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Old 02-08-2015, 10:11 PM
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The ESC is actually a 'spare' from the original set I used in my Concorde that also used the same 40mm EDF. It is rated at 20A but did get noticeably warm which is why it had the heat shrink removed and the heat sink held down by the nylon tie to allow air contact directly to the aluminium.
It always seems odd to me that although positive air flow over the ESC is recommended the actual heat transfer through the thick heat shrink is very limited. Even bare aluminium is not brilliant which is why in cases where the ESC is being worked hard I exchange it for a 'fingered' heat sink which has many times the heat dissipation rate.

The wing root inlet fabricated in 2mm Depron.
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It also adds considerable rigidity to the inner wing.
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The next problem is to build the other wing the same!

Last edited by quorneng; 02-09-2015 at 12:35 PM.
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Old 02-10-2015, 12:09 PM
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The wings complete.
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The exreme bracing does look add compared to conventional all balsa construction but it is required to support the edges, adds significant rigidity yet weighs very little. All the wing bracing adds just 1g!
The tail booms are next. Depron with a 2x1mm balsa spar inset top and bottom.
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The booms are actually made as a hollow square tube and then sanded to the required shape. Difficult to photograph.
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Each boom weighs just 0.07oz (2g). It is plenty strong enough but it won't have much (any?) crash resistance.
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Old 02-12-2015, 12:13 PM
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The booms and tail feathers.
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The tiny 2.5g servo mounted in the middle of the tailplane.
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To give a smooth surface close to the fan slip stream the elevator will be bottom tape hinged with the horns on the top.
The elevator servo wire will run inside the hollow RH boom.
The fin and tailplane will have to be covered before they can be assembled as indeed will the wings before the boom can be fixed on.
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Old 02-14-2015, 02:26 PM
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With the tail feathers covered and glued in place the tail booms can be temporarily slotted onto the wing to give the first impression of what it will look like.
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The aileron servo just fits within the wing.
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The servo will be in contact with the tissue top and bottom!
The Lemon 'Featherlite' 4ch radio is simply glued to the back face of the spar. The domestic 13A fuse gives a comparison of size.
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Strictly a 'shockie' radio but the Vampire is so small you wont be able to see it if it gets any sort of distance away!
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Old 02-15-2015, 07:05 PM
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I bought one of those receivers from a fellow hobbyist and have had a number of flights with it. Never had any problems with it. The light weight factor is a good thing. Probably weighs less than that 13A fuse. Looks like you'll be all covered up soon and ready to fly. Wish I had your UK weather, with it 0 F at the moment. It would be like Florida, compared with here.
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Old 02-17-2015, 12:26 AM
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With the wings covered, apart from the panel over the radio, the booms can be glued in place.
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The radio fully installed and tested.
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The radio can now be 'tissued in' - If it need re binding the tissue panel will have to be cut away and replaced.
The aileron tape hinged.
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Now for the canopy/battery hatch.
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Old 02-18-2015, 05:21 PM
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When I started to make the battery hatch I realised I had a problem. I had simply made the battery box too small. The battery fitted ok but then of course you have to find somewhere for the connectors to go!
The only practical solution was to make the box deeper but to do this the whole fuselage area under the box had to be carefully cut away to expose the bottom of the box. Cut off the bottom, extend the sides, replace the box bottom and then modify and replace the formers. Finally replace the stringers.

It is one of those jobs that seems drastic (particularly when you are still building the plane!) but it all went well enough.
All put back together.
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The battery box is now about 6mm deeper.
The battery in with the JST connector in position on top but still below the hatch line.
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The hatch and canopy windscreen.
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Built just like the fuselage Depron with balsa stringers. The windscreen is simple as it is made up of 'flats' but the 'bubble' canopy will be harder.
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Old 02-20-2015, 01:05 AM
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Nearly there!
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The paint has added 0.22 oz (6.2 g) so it now weighs 4.5 oz (127 g) ready to go. This gives a wing loading of exactly 7 oz/sqft which is rather higher than the 4.5 oz/sqft of the Canberra although the Vampire's 60% thrust to weight ratio is marginally better.
I expect the Vampire will feel rather different in the air.

Hopefully some suitable weather will arrive before the 15th!
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Old 02-21-2015, 01:23 AM
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I think you'll do fine. The little one I have is over 4oz and is quite a floater. Don't want to spam your thread with a YT link, but it's on my WTFLYR channel if you're interested in seeing it. It was much faster when the ancient 10c lipo was new. It's one of the most docile, easiest models I have to fly also. It was probably flying on a T/W of 1/4. I'm convinced the general airframe is a good platform, same as the FW225 which also flies well.

I had the deadline date as Mar2. I hope it is the 15th and that we get some better weather before the 15th. It was -16F here last night. Tomorrow is our first and only warm day, supposedly at 35F. Zeros and sub-zeros for another week.
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Old 02-21-2015, 02:31 AM
  #19  
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If the weather is a factor, I think it's fine to give an extension.
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Old 02-23-2015, 12:58 AM
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The Vampire is now all ready to go.
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Roundels added.
Inside of the jet pipe painted black
Canopy retained with apeg at the front and a tiny magnet at the rear.
3 balsa stringers added over the ESC cut out that follow the line of the fuselage.
Just need some dry (it snowed this morning!) calm weather!
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Old 02-28-2015, 12:11 PM
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On the grounds I had little to loose I did actually manage to maiden the Vampire early this morning before the wind got too strong but it was raining.
Not ideal conditions for a tissue covered plane!

Apologies for the poor video but the grey conditions and light drizzle combined with a small silver plane does not make for good pictures! If you watch the video in 'full screen' you can just about see it.

Plenty of power but it seems to have an 'inbuilt' left roll (not that surprising as the tissue was very slack) which also caused the left wing drop on landing - but it survived.
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Old 02-28-2015, 07:57 PM
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Nice job. Silver and grey sky is challenging to fly in, especially with a small model when it gets a good distance away.
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Old 03-10-2015, 06:48 PM
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A slightly better video of the Vampire although it is still hard to see so it had to be heavily edited to show just the bits where there was anything to see! (Better in full screen)

It seems to roll adequately but the airframe drag (compared to its weight) is so high that it can only manage a very tight loop.
Sufficient power and reasonable endurance (over 6 minutes) but it really doesn't like any turbulence!
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