Here is a list of all the postings Dizz has made in our forums. Click on a thread name to jump to the thread.
|Thread: Eflux Tubes?|
Generally speaking, for max speed exhaust area will be around 85-87% FSA and for max static thrust around 100%FSA (although the Phase 3 Fantom is approx 110%FSA to help had launching). Everything with DFs is a trade off with airframe factors and intake geometry also playing a part.
An eflux tube (also known as a thrust tube) is a usually tapered cylinder of suitable material which joins the rear of the fan to the exhaust opening. Used to ensure a smooth exhaust airflow (minimise losses) and to bring the exit area down to the desired % of the fan swept area.
I'm afraid that there is alot more to getting a fast DF model than just adding more power: what are you starting with?
|Thread: Reverse EDF?|
They mean reverse rotation so that in a twin EDF the gyroscopic forces cancel each other.
|Thread: Inrunner? or Outrunner?|
Google is your friend:
|Thread: DX18 Firmware Update|
I assume that you used the correct tx serial number when you retgistered (no typos): the firmware upgrade download is bespoke to that serial number.
I would use a new SD card and down load the upgrade again, then give it another go. If no joy with that then contact Horizon.
Edited By Dizz on 06/08/2013 08:17:57
|Thread: Tx Upgrade and Spektrum Reliability|
From what you describe Mike I would say something must be trasmitting when the car radio or ignition is on.
MikeS - Does your car radio have Blue Tooth? If it does it will be transmitting in the same ISM 2.4-2.4835GHz band as our radio control transmitters.
BTW, mobile telephones use 2, 3 or 4 of the 850,900, 1800 &1900 MHz frequency bands available depending on what country and what service you have.
Edited By Dizz on 22/07/2013 14:05:10
|Thread: Pod-mounted EDF|
(Forgive me if I am teaching to suck eggs, I will use cm and 1 decimal place))
Area of a circle= pi x radius squared
FSA = Area of the shroud - area of the motor
So for your fan FSA = pi ( (3.3x3.3) - (1.65x1.65)) = 25.7sq cm and a radius of 2.9cm (100% FSA).
Which then gives the following:
110% FSA 28.3sq cm radius 3.0cm
90% 23.1sq cm 2.7cm
85% 21.8sq cm 2.6cm
80% 20.6sq cm 2.5cm
To get a template for whatever exhaust duct you decide on do a search for "cone layout" and you will find plenty of online calculators and free download software available (I actually use a programme called Cone Layout v2.0.4 from Pulse Rate Software).
Google "Phase3 Fantom" and take a look at the pod on that for imspiration
I have a photo of my Fantom here:
Actually the efflux area is approx 105%FSA with this one - they have done that to help hand launching as it was sold as an intro to EDF. If you post the 2 diameter measurements of your unit (motor and inernal shroud) I can show the workings on here to explain if that would help. Admit that making an intake lip for your fan would be "challenging", but because the impeller is so close to the front edge it would be worth the effort. Lots of EF units come with a plastic intake ring though, so maybe you already have one.
Edited By Dizz on 20/07/2013 08:20:54
Edited By Dizz on 20/07/2013 08:27:01
Edited By Dizz on 20/07/2013 08:29:09
Difficult to be specific without pictures or knowing what performance you want, but you will definitely gain benefit of a higher static thrust (easier to hand launch) from a rounded intake lip (2 - 3mm radius). With the efflux it is a case of trading exit velocity for static thrust: up to a point, smaller the outlet area = higher exhaust velocity (higher potential top speed) but lower static thrust. Generally a good place to start is to add a cone to make the exhaust area between 85 and 90% of the fan swept area (FSA) (FSA = total area of the fan shroud - area of the motor housing). For more thrust increase the exhaust area to 95-100% FSA, for more speed reduce the area but never less than 75% FSA.
|Thread: Revalidating A & B Certificates (and examiners certificates)|
The point you raise is a valid one. I know Examiner "currency" has been the subject of discussion at many Area and Full Council meetings over the last few years and I believe the National Achievement Scheme Co-ordinator is considering how this could be implimented.
However having gained Examiner status the individual's lead club has the responsibility of ratifying the qualification in the yearly BMFA return in the New Year, so if someone is no-longer suitable that is where the process should start. Several Areas run Examiner statndarisation sessions during the flying season, but you can't force attendance - one of the issues with an un-paid voluntary scheme. Comparing to a Driving Instructor or OFSTED inspector is comparing apples with pears.
Edited By Dizz on 17/07/2013 00:23:32
Edited By Dizz on 17/07/2013 00:23:46
|Thread: Forum members' new models: Let's see them.|
Re-painted Lander 70mm foamy EDF. I decided not to use retracts to save weight: takes off from a dolly and belly lands on the grass.
PND Sea Vixen. Twin Wemotech 70mm EDFs with HET 2W-25 motors. Now complete but not yet flown.
Edited By Dizz on 07/07/2013 23:48:03
|Thread: Reverse EDF?|
Torque/gyroscopic effects are less, but still pertinent given the higher rotation rates in EDFs.
|Thread: Phase 3 Squall 3cell TOP SPEED???|
Here is the thread I was referring to - all 101 pages! Afraid you won't find a speed set-up based on 3S though.
A prop will always be more efficient than a ducted fan at model sizes and air speeds, its the law
but then it wouldn't be half as challenging/interesting.
Edited By Dizz on 16/01/2013 22:29:28
It is in the right ball park Scott - a stock Phase 3 F16 is good for 65-70mph but the Squall has that massive draggy intake. There are several Speed Squall threads on RC Groups documenting the serious mods required to get it moving.
|Thread: Ebay being flooded with LX Mig 29 rtf kits|
Actually one of the guys who bought one has a China Post tracking number and his box has left Beijing
I saw the buy-it-now £20+£10 listing on Friday. Thought it was too good to be true therefore probably a scam.......................but have protection buying through PayPal so for £30 took a punt, as have several others.
Will report back what arrives idc (if anything).
|Thread: Ducted fan theory and practice|
I have been away and missed the recent posts - all very interesting. As it happens I acquired airspeed telemetry for my DX18 at the Nats this weekend, intending to use it for real time velocity measurements across the duct (the "How Fast" system only gives a single maximum velocity measurement).
On the drive home yesterday it occurred to me that I could use either system to show static pressure in the duct by positioning the static probe in the test region, connecting it to the pitot input on the sensor board (kept clear in still air) and leaving the pitot input open. Any difference detected would only be relative to atmospheric and due to the fan compressing the flow. Output would be in mph, but it is an easy conversion to a pressure. Would not be very accurate, but certainly would show trends.
I have some thrust and power readings taken as the intake lips were fitted during my P1154 build. Unfortunately all the figures are in a spreadsheet and I'm not sure I can post it on here. Will try and generate a table of the relevant information.
With a sealed duct to the fan the bell mouth/rounded lip is on the actual inlet opening, effectively increasing the area by allowing air to enter the duct from larger angles than with a sharp lipped intake. This has the greatest effect on static thrust. With a plenum chamber bell mouth the fan can't draw any more air than is being delivered by the duct infront of it unless of course the chamber is open to the fuselage. If that was the case then you would not have the efficiency gain from the claimed pressure increase ahead of the fan with forward speed (Stumax' explanation for the sealed duct recommend and one I subscribe to given the improved performance over expected of my M52, FD2 and P1091). Maybe the L39 scale intake area is too small wrt fan FSA and that is why Daniel has done it (to allow greater mass to enter the fan?
Anyway, here is another conundrum for you theorists.............what is the prediction for this installation:
The intake will have a large splitter plate standing off the fuselage side and the other 3 sides will have a rounded balsa lip.
Am enjoying the discussion (again).
Edited By Dizz on 11/08/2012 13:26:24
Edited By Dizz on 11/08/2012 13:29:05
An interesting situation and 100% opposite to what Stuart Maxwell of Stumax fans recommends.
I can't see how the Schubler recomend would do anything other than disturb the air flow approaching the fan face, but I guess they must be basing it on something.
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