I have recently had an interesting exchange with Martin Pike, who has previously flown Rapier powered models.
Martin writes: Dear Roger,
I often read your articles and consider jet-scale models, but I am not too keen on rockets (not really suitable for my young children). However, I was interested in the 18mm EDF unit, having flown a few D. Knight powered prop planes.
Do you know of anyone that has had success with this EDF unit in a Jetex design - if so who, and which one? Any suggestions? You did mention a Leduc 022 in your article.
I am largely interested in FF scale models. The only Jetex powered kit I have is a 13 1/2" KK Hawker Hunter by Albert Hatfull - often looked at, but never started - I supect it is too small and compex for a first EDF model. Would it be worth enlarging? ? Would you still dangle the motor underneath, or make a 'jet tube' with an exit in the scale position?
these are all good questions, and need a longer reply than I am able to give at the moment. Derek Knight has had some success with his 18 mm EDF unit in Jetex 50 size models - a Mirage and a Swift, where the EDF unit goes into the trough.
SAMS Models now sell an ' 18mm EDF package' so give Kevin a ring. I'm visiting him this PM to discuss options.
One of the problems with EDF is the weight - thrust does not seem to be an issue - and typically a 'Jetex 50' size model with EDF weighs about twice the equivalent Rapier powered model. The ones I've seen fly, but not with any gusto (yet). That said, I think EDF is the way to go as Rapiers are so ... er .... unpredictable!
I think a FF EDF model needs less weight and lots of area, and I'm experimenting with an 'Arbalete' foamy. As my indoor version flies well an EDF version is worth trying I think. Expect an article about all this in the autumn, if my health allows. The Leduc lacks area, as does the Hunter, so (to start with) I would try a delta. That being said, I have a very nice EDF Vampire plan!
Has anyone tried putting an 18mm KP fan inside a fuselage, where the jet engine would have been? I could not see this on the net, although there have been larger rc planes done this way. I presume that the fan needs to be fed air through a duct, in contrast to the Jetex rocket that only needed an exit.
Which delta model did you have in mind?
Which needed a longer reply:
Kevin of SAMS Models has put an internal 18mm KP EDF unit in his 'take' on Richard Crossley's Skyrocket:
It weighs about 50g; thrust (according to Kevin)30g. It is as yet unflown.
As to deltas, I was thinking of a unit in a modified (open at the front) 'Jetex' trough. One problem here is that the EDF ingests dirt and grass etc on an aborted flight. Here's my Arbalete delta for indoors:
The EDF unit for a more robust fast flying outdoor model will be in the body of the fus. An Avro 707 is also a good candidate.
Another possibility is a Cutlass, below is my 'semi profile version for Rapier L-2:
There is plenty of area and the elevons allow flexible trimming. The EDF will be semi-buried in the fuselage and the intakes will be operational.
I'm at the moment trying to put my 'power train' together. Here is Rob Smith's:
Derek Knight has now combined the timer and ESC in a single unit to simplify instillation.