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The Fairey Delta 2 - an EDF in Depron.


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In general an EDF model of a conventional turbojet has to have oversize inlets and exhausts.
My idea was that if it could be built big & light with a small enough EDF scale ducts could be used.
The FD2 was a super sonic research delta that first flew in 1954. In 1957 it held the world speed record at 1132mph.
From my point of view it made a good subject because
a. A delta is strong and light for the wing area.
b. The exhaust had a distinct nozzle for supersonic flight so the total inlet area was actually bigger.
c. The fuselage was circular in section.
A nice 3 view to work from.
With a 55mm EDF it would come out at 32" span. Could I build it light enough to fly?
I don't see why not. It's not the best example but HK makes a EDF trainer called the Dolphin. At 1010mm, aerodynamically inefficient and a very weak stock 55mm EdF it flies pretty darn well and that's not even mentioning your build would be lighter. A few things to consider, I have a feeling any scaled model of that plane is going to be tipsy without some good speed. That will mean a good high kv Edf capable of speed required, that being said launches may be interesting with a plane prone to tip stalling and a high speed low torque edf. Check ratio on nozzle, it almost looks a tad to tapered for an edf application which will mean widening up a bit.


Yup, I think it will work. You know how to build light, so I'm sure you can come in with a reasonable wing loading. I think she will be a "hot" plane for sure.
Looks suspiciously like a B-58.
Answer: yes. You can build anything and it will fly.
The Hustler was a mad sexy beast! All those gen 1 supersonic craft were just plain hot.

Found this in my old Windows backgrounds file.....needless to say it is now back up, replacing my Volocity XL at sunset pic.



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From the Brit point of view the sad part is it is despite its very high performance it was only a research exercise and was even banned from super sonic flights over land. As it only had a flight endurance of about 30 minutes Fairey had to take it to Dassault's airfield in France (super sonic over land was allowed there) for much of the high speed testing.
I bet Dassault were only too happy to have their calculations confirmed for the up and coming Mirage!

To keep weight down this was going to use extreme monocoque construction with all the stresses taken by the 2mm Depron skin with no reinforcement of any sort!

To do this the wings and fuselage have to be considered as an integrated structure with no 'strong' points.
The wings are attached along their entire root directly to the duct wall and the fuselage formers and skin built around it. Once the structure is fully complete the forces in the wing skin will be uniformly distributed to the inner and outer fuselage skins - hopefully!
The wings have no spar just closely spaced triangular shear webs.
Although flat to start with it is lifted from the board and the top skin added 'freehand' so drawing the wing into a fully symmetrical section. Needs good 'eyeball' to ensure it all remains true.
A wing attached to the inner duct skin which is supported on a piece of plastic rainwater down pipe.
With both wings attached the fuselage formers can be added.
Each fuselage former position coincides to a wing shear web.
Initially for simplicity the duct is too long so has to be cut back to start to form the bifurcated inlet duct.
A fiddly and delicate process using the first of a great many carefully shaped planks!

The actual fan swept area (FSA) of the 55mm fan is 1760 sqmm. The main part of the duct is 70mm diam (3849 sqmm) as is the area of the inlets. It thus seemed logical to place the fan right at the back to keep the overall duct losses as low as possible.
The fuselage tail cone under construction.
The duct tapers gently from 70mm diam to 55mm over its length.
The EDF unit perched on the end.
For the sake of appearance the EDF duct body has been extended aft by 2cm simply to match the length of the outrunner bell.

With an 1800mAh 3s the aim is to keep the total weight to 20oz and a static thrust of 16oz. With 2.5sqft of wing area the loading comes out at a modest 8oz/sqft.


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The intakes were about the hardest to do.
Splitting the single circular (and rigid) duct into two creates a definite weak point in the fuselage structure.
The nose section with the battery compartment in the cockpit.
The original had separate elevators and ailerons. To save weight I decided to make them as one piece elevons and use just two servos.
They are huge and add considerable area to the wing.
The basic structure complete including that long pointy nose.
A rough balance check indicated the battery would have to be further back so its compartment had to be rebuilt behind the cockpit .
The top surface skinning was left off to install the electrics.
To save the substantial weight of the silicone insulation solid conductors are used to connect the ESC to the motor.
The radio is positioned to give the minimum cable lengths from the servos and the ESC.
A rear view of the EDF showing its FSA size annular 'nozzle' with its 3 blade fan.
With the electrics all in and tested the skinning is completed.

It may only be a relatively low power EDF (250W) but with the fan mounted right at the back and the lightweight hollow Depron structure making a wonderful sounding board, quiet it is not!
I normally test fly before painting but bad weather prevents this.
The question is what colour? As built they were left natural aluminium. Very difficult to achieve anything like realistic on Depron.
The record holder was later painted Royal Blue and other Mauve! Ultimately this one was converted into the 'ogee wing' BAC221 which was first black and then blue.
So blue overall it is, although not an ideal colour over white Depron.
About the only benefit is with careful masking the white roundel borders and nose cheat line can be left white Depron.
The Vinyl decals can wait. It weighs just a fraction under 20oz.
Now it is just a case of the right weather.
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WAAAAAAAAA......I was expecting to check in with this thread every week or so to check on progress.....scratch that....how do you go from concept to fully operational painted model in 2 days!?:eek: Especially with your building style, even small models take tons of precision measurements and cuts.....how I say....HOW. Simply amazing.....I have spend weeks on projects that turn out ugly as sin and fly even worse.
To be honest only now is progress more or less in real time.
To get to this point actually took 3 weeks but I am retired so it is almost a full time job!

With this type of moncoque construction things tend to start slowly but as the skinning progresses it get stronger and things speed up.
In addition having built 5 previous planes in a similar way does help a bit too! ;)
The maiden did not go that well! :(
Just a few seconds 'staggering' with a stall followed by a firm impact that split the fuselage almost in half at the intakes
and put crease in than long nose.
I diagnosed the problem as the CofG a bit too far back coupled with those immensely powerful elevons.

The existing battery compartment is big enough to move the battery forward to bring the Cofg forward about 1/2".

To reduce elevator authority they have been cut back to the scale aileron size but they still work as elevons. Fortunately I had anticipated this might be required so had placed the servos far enough out along the wing allow this.
The inboard portions are fixed but set with a small amount of reflex.
I can only hope the next flight is better as this is not nor was it ever intended to be a crash resistant plane!
With the reduced elevons, a bit of reflex and a slightly forward Cofg it does fly.
Note that much of the flight was on reduced power and it glides remarkably well.
Fairly late in the winter afternoon so a low sun thus the landing area was in shadow which confused the camera.