stumax

Hi guys, I'm looking into designing a few multi-purpose kits based on side by side twin jets, specifically the F5E, Mig25 and Voodoo (any other suggestions?). I hope to make them flyable with either twin EDF or a single Wren54 or similar. The twin EDF is simple, but the turbine setup would require a bifurcated tailpipe. Are there any guidelines to stick to when designing a tailpipe such as maximum angle of deflection from centreline, area ruling, max offset distance from centreline etc? The F5E and Voodoo would be fairly simple, I imagine, but I don't know about the Mig25 - would the exits be too far apart? Thanks guys!

Gordon W

Sea Hawk [8D] [8D]

Gordon

stumax

Gordon, you know I'm a sucker for the old jets! Somehow I think I would only make two Sea Hawks, one for me, one for you . I imagine the patent on the bifurcrated tailpipe mentioned in the pic has expired by now, thankfully!

Gordon W

Hi Stu

The Sea Hawk was flown also by the German, Dutch and Indian air services, and also briefly by the Aussies and Canadians though not in full sqn service. So it did get around a bit. Surely anyone who'd build a Venom would be a sucker for a Sea Hawk as well.

Re the patent, a derivative of the bifurcated pipe must still be used in the Harrier

Actually, I don't think that fixing the tailpipe rigidly to the engine will be all that practical at model sizes as an engine mod might be needed and hot gas leaks a serious risk.

From what I've seen and read here and in magazines, there's normally no rigid connection between engine and tailpipe, the latter terminating in a bellmouth at its front end. So judging by the number of replies you've had here, I imagine that most bifurcated pipes for model jets comprise two tailpipes joined at any old angle to a short front cylindrical section which incorporates the bellmouth, without too much science involved

Wren have discovered that letting the tailpipe expand slightly for a short distance aft of the bellmouth, before becoming a parallel tube, enhances thrust a little and there was an article in a recent RCJI, and the tailpipes they market incorporate this feature.

Gordon

stumax

Well I may have to give it some more thought! One thing I always look for is a subject that has a multitude of finishing variations, the F5E is a good example (Mig 25 not, but, hey, it's cool and not been done yet!).

Re the tailpipe, the Wren guys have been in touch (nice chaps!) and they are keen to work with me on it. I'm interested about the thrust being enhanced by expanding the tailpipe a little. Does it then contract again? If it just expands, then it's simply lowering the efflux and raising that static pressure. I'll have a chat to our turbomachinery guru at work about it. I get the feeling it's something to do with getting the timing of the reflected pressure waves which are emmitted (blade passing freq between the EGV blades and turbine blades) correct - perhaps similar to the extraction pulse in a 2 stroke tuned pipe. I wonder if it can be tuned? Interesting.

ShaneUSMC

My Feedback: (1)

EA-6B would be nice. Large scale though for P120. Although an F-5 in Large scale would also be nice. Keep us posted on your progress though.

stumax

Hi Shane, I forgot about the A6 - what's the diff betwen an intruder and a prowler? Nice plane, I saw them when one of your carriers was in Sydney several years ago and dwarfed our bathtub destroyers!

Don't forget I'm designing for a Wren54, so the size won't be that big, I imagine the F5E would be about the same size as my old Cressline F20 (around 1.8m long, I think), an A6 would be quite a bit shorter due to it's larger wings.

uncljoe

My Feedback: (8)

Stumax
intruder A6 2 SEAT... PILOT /BN A FEW A6 BECAME EA6 2 SEAT WITH PILOT AND EWO (USED BY USMC ...VMCJ squardorns )
prowler EA 6 B 4 SEAT... PILOT 3 EWO'S
SEMPER FI
JOE

stumax

Thanks Joe! See you on the dark side! BTW so nice the the Navy to give the Ewos some work after George Lucas finished with them