Dave Cooper 3

Hi E.D. That price sounds more than reasonable if it's a good unit. Just been on Jet Hangar's site (jethangar.com) and they advise 80-100% of Fan Swept Area (FSA) for inlets and 70-80% for outlet. They do warn about cheap Chinese clones of their product, a number of which have failed in service....You pays your money....etc. There's a formula for calculating FSA under the "EDF Rules" heading. It does look like it's a compromise between take-off power and top speed. As I'll have 2 inlets and one outlet I'll have to get the calculator out ! Hope to get bench testing soon...one or two other projects to finish first. Dave

Good to hear the thrust should be OK. The "Banggood" 12 blader looks good - couldn't see a price on the ad' though. As my model is EPP I was just wondering if this would have some sound absorbing qualities. Presumably, I'll have to conjure up some form of thrust pipe as well ? Rolled ply /balsa sheet ? I'll have a look at the Youtube videos on balancing as well... Dave

Yes, thanks for that John - quite a few of our sites are noise-sensitive. I will test the unit and see if the neighbours complain first ! A '12-blader' may be more appropriate anyway - more efficient ? extra thrust perhaps ? A real learning curve for me... Dave

Thanks for the reply E.D. A trip to the workshop has now revealed : Fan: 6 Blades - 75mm diameter Motor - 3500KV (QF 2827) Fuselage width - 70mm and depth 100mm. (measured at approx. C of G). Width could be made wider with air intakes to accommodate the fan unit Weight : approx. 2lbs (without LiPo and without fan unit). I would imagine a 6s may be needed to give reasonable flight times ? The model was designed as a PSS glider, so, an EDF version would need some mods ! I will bench test the fan soon to see how it sounds /performs... Dave

Hi, I have recently acquired a brushless EDF fan unit and a PSS Aermachi model at an auction. I think the fan unit is an '8-blader' and the jet model is about 51" span. I was intending to fly it PSS to start with and, later, convert it to EDF. What data would we need to decide whether it was suitable for conversion or not ? I have in mind : Model weight, KV rating of the motor, fan diameter, fuselage width /depth at the CG for starters.....anything else ? Thanks for any assistance (only previous 'jet' experience is with "Jetex" models as a young lad !) Dave

Castor Oil - the word superceded should be spelt "superseded" (from the word supersession)...I got 'picked-up' on this whilst at Airbus, by the Quality Assurance Team, writing the requirements spec' for the A350's wing ! Compliments of the season everyone... Dave

All very mysterious....status, profiles, public, friends, clicking etc etc. Tutorial anyone ? (I'm not volunteering by the way !). Thanks to all the contributors so far... Dave (for testing purposes 'status' = "Improver Mark 1" sadly, no 'friends' as yet)

I don't think I've ever seen a member "On Line" notification on this forum, but, will pay more attention in future ! We live and learn it seems.... Dave

OK thanks eflightray - I'll try something....

If there's a Moderator around, the posts are now repeating whilst the 'post counter' does not seem to be incrementing Even more confused of Wiltshire.....(sorry to be a pain everyone !)

Ron - such as what exactly ? Do I just make something up, or, are there 'standard' status's (stati ?). Where else does it appear on the forum once set ? Confused of Wiltshire...!

Just found the blank "Edit" box....but, really, none the wiser ! Allowable settings ??? Dave

Under "My Friends" on the Forum home page it tells me to 'set a status'... How does one actually do this ? I can't find any relevant help anywhere on the forum or am I becoming myopic ? Dave

Hi All - a quick update : Having just finished working with the builders to level my garage floor and applied the (very expensive floor paint !), I can now get my modelling projects back on track... (Andy mentioned an interest in motorsport in an earlier post - so, the level floor is for my 10% wind tunnel. This to give me key lift /drag data for a Le-Mans style sportscar that I'm building. Also, it now gives me reliable 'datums' to take chassis measurements from). So, finally dug out the plan for the JP and it's a Roger Howells' design for a 40-size power model. About 47" span, and, prettymuch-true-to-scale. If I can keep the wing loading to a reasonable level, it might just work as a PSS job. Wing section looks OK(ish), but, yet to verify the actual section. Will probably need some tip washout to make it nicer nearer the stall plus some lead up front in lieu of motor /fuel etc. Anybody tackled anything similar ??? Dave

I think the worst-case scenario is late cut-off of the BEC. This happened to myself and a friend when we built the HobbyKing Phoenix 1600 electric glider (this is our club's chosen one-make competition machine). The motor is a modern brushless with a programmable ESC and a 2s LiPo. His model crashed (fortunately without too much damage) when he ran out of radio contact and he immediately phoned me to check mine. The motor and ESC are supplied with the kit. I tested mine on the bench and had a max.of two or three control movements just as the motor was running down. None of the other kits had this problem and came from an earlier shipping 'batch'. After some more bench testing, HobbyKing supplied a replacement ESC...the first job was to 'calibrate' the ESC to the motor, the second was to set the prop brake (using their instructions). Next, I took a LiPo that was down to about 50% capacity and timed a 'dummy' last flight until I was satisfied that I had enough range and control movement to safely land the glider. The moral of the story, IMHO, is to know the limitations of each model /installation and use planned flight duration times if there is any doubt...Happy flying everyone ! Dave

Thanks for the advice Andy, as a PSS beginner I'll try and do a light build on this one.... ( for some reason my tails often come out a little over-weight !). The main local slopes are about 600' high and, for PSS, the experienced guys tend to fly in winds of 10-20+ mph. As you say 'brick-lifters'. Nevertheless, I think 15-16 oz/sq ft is a good target for me to aim at. BTW Andy / Phil I'd like to have a look at Ron Collins's plan - any idea of size and where I could get one from ? Cheers for now, Dave

Hi both - thanks for replying : Phil - Yep, a straight scale-up is very tempting. We've got the builders in at the moment and all my modelling stuff is up in the loft for safe keeping ! But, I was thinking around 4 foot span and about an 8" median chord. I'm not a very efficient soarer yet and I was thinking that the extra wing area might help me to stay aloft in more marginal conditions. Andy - yes, I have a Capstan model (E205) of around 6' span and, from memory, it has about 1-2 deg's of tip washout. Not maiden'd it yet but others report that it flies nicely rudder /elevator and very well with ailerons (I've just finished the conversion). I was wondering if the washout on the JP could be 'blended' into the tip tanks to make it look more scale-like ? I don't think the plan is 'Ron Collins' but, it is a Mark 5. Target weight was around 3-4 lbs if I remember the magazine article correctly. Does this seem ok for wing loading ? Some of our club members have built yours and speak very highly of it's performance. Dave

Hi All Quite fancy a PSS Jet Provost design /build for this winter. Had a look at the Andy Blackburn design (subject of the Mass Build ?) but this is rather small at around 36" span. Have now sourced another plan plus some scale drawings which look rather promising....not sure about the plan's wing section though which seems to be a member of the NACA semi-symmetrical family. On the slope, I'm wondering about a Selig 7055 or Eppler 205 /374 section ? I'm after a fast(ish) model with good penetration and energy retention. Probably 'stand-off' scale in terms of detail - light, but strong airframe which can be ballasted up for different wind strengths. I have some carbon, Kevlar, grp and Liteply available (plus good-old balsa !). Thanks for any assistance from the PSS experts... Dave

Hello Timo - you are making great progress ! I read Harold Penrose's biography many years ago....did you know that he designed his own glider ? There was a Nexus /Traplet plan available at one time. I was interested in building it as a future project (I like unusual scale gliders for slope soaring). A couple of questions if you don't mind :- 1. Where did you get the 'Japanese Saw' ? It looks really useful. I haven't seen one advertised by anyone in the UK. 2. What radio are you planning to use ? Will there be a special arrangement to synchronise the motors /props to resolve any adverse yaw tendency ? Special ESC(s) linked to micro-controllers ? Looking forward to seeing a possible video of the early flights maybe... Dave

Hi again Eric - just a few final comments from me. I'm basically a Futaba man (35 MHz) and I think their '2.4' spec's are very impressive. The problem for me is I will have 5+ models on the go next year, so, Rx cost comes into it very strongly and I don't want to disturb each installation to swap out a trusted Rx every time. I read a tech' review on Aurora 9 the other day and it seems there may have been an issue with 'dead-spots' at the extremities of stick travel. This may have been fixed now, but, worth checking out. (potentiometer mis-alignment ?) Taranis - this is most likely my new route for 2019 - a 3-metre, vintage, scale glider. I can put you in touch with an "Open TX" expert who will talk you through a complete set-up over the phone. BTW their Limited Edition Tx now has 'hall-effect' sticks - beautifully smooth when I tried them last week ! Dave

Hello Eric I'm in a similar position to you. If budget comes into it, then I think Taranis (FrSky) is worth a look. Good range of Tx and Rx and you could still go with Hitec servos, hence, a minimal mix. Not sure about service though - with 2.4 GHz gear most components are 'surface mount' ie non-serviceable (at least for me). So, it's straight-forward replacement if it goes wrong I suspect. Probably best to check on warranty for the Tx though. Most of the flyers at my club use Taranis and report no known problems....I guess time will tell ! You can use something called "OpenTx" (firmware) which is fairly easy to set-up on your PC with a little familiarity. Plenty of help available on-line also. Good luck Dave

I wonder if anyone has investigated the number of fan blades and the rigidity of the fan housing as key variables to efficiency ? I'm looking at installing one in a Jet Provost model next year (about 46" span), and, one supplier suggests that a twelve-bladed fan in a metal housing would be best. I think the recommended O/D was 80mm. On asking about the cheaper plastic Chinese fans, the advice was to walk away... On reflection though, if the fan housing is tightly constrained by the duct walls - would it actually 'flex' that much ? Dave

I wonder if a possible approach for clubs would be to operate a 'risk-assessment /planned progression' approach :- 1. A new member wanting to fly turbines would first have to demonstrate safe, competent flying on a fast(ish) EDF model. Either their own, or, possibly owned and operated by the club. Main benefit - no (or little) fire risk. Failsafe(s), installation checks etc to be regularly carried out by a competent club examiner. 'B' cert to be encouraged, but, let 'A' cert's progress to this on EDF first. 2. Existing members will be known to others. If they are 'top-notch' fliers then let them go the turbine route if they want to but with compulsory technical checks as above. If they refuse - what are they hiding ? 'Progressing' members - EDF first. It only needs one bad accident to lose a site (or, heaven forbid, a life).... My own planned progression here for your comments :- Year 1 Airfix kit /scale drawings of a jet provost Year 2 PSS model jet slope soarer Year 3 EDF Jet Provost or similar 'straight-wing' jet Year 4 Professional turbine flying lessons / Jet build Year 5 Maiden jet with professional / v.experienced club member on buddy box Overkill ? Dave

cymaz - I only have very limited theory on this but I did look into it last year for a turbine-powered LMA Westland Wyvern (reduction gearbox with contra-rotation props). Hardly an SE5 I know, but if using a simple 'toothed belt' drive we calculated a power-consumption loss of about 10-15% of quoted 'driveshaft' bhp. Whereas the full 'planetary' gearbox was soaking up some 25% with spur gears (noisy, but efficient !) and anything up to 35% for helical gears. Prop's also vary enormously in efficiency (we were planning on variable pitch to help with this), so, I would advocate the simple test rig approach - perhaps 2 or 3 props of the same diameter but with sensible pitch spacing. Take thrust measurements at a set rpm (spring extension /Hooke's law). Repeat test with different tooth ratios on the belt set-up (driven over driver gives the gearing ratio....) You may find you need a different engine or a change to a more efficient prop design. I think I would stay with two-blader's as 3's and 4's add complexity (as well as cost !). BTW those are BIG prop's so take care near the test rig ! Also, have a close look at torque /bmep figures /curves when choosing an engine - these may be more critical than quoted bhp figures especially if going the bigger pitch route. Good luck Dave

Just a thought :- When designing the radiators on my Le-Mans style sportscar, I went for a 'tight fit' between the radiator edges and the duct wall thinking that this would give the best result (it's a ram-air duct design). However, one day in the model wind-tunnel (10% scale), one of the radiators detached on one side and suddenly we were getting better mass-flow figures from the duct exit. Next experiment was to fit smaller radiators with a small air gap between the rad's and the duct walls - result even better mass flow. No heat input to the rad's as all measurements were cold. This could, of course, just be reduced drag. Maybe a simple experiment with an EDF fan in a larger duct O/D to I/D could yield an optimal gap between the fan casing and the duct wall ? Dave