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Member postings for John Cole

Here is a list of all the postings John Cole has made in our forums. Click on a thread name to jump to the thread.

Thread: FMS flight sim.
19/12/2008 10:30:00

You don't say which version you have.  If you look in the folder you will see a file with a name like ParEdit.exe - it will definitely end .exe  and then if you choose the correct View (or right-click on it) you can see the file-date and size.  For me these are 23/04/2006 16:11 and 985 KB.

Is that the program / verson you are asking about?

There are two types of program referred to as a PAR editor.  I want one that edits the .PAR files that control how the plane flies.  Although the editor I've referred to gives you a diagram showing how the parts fit together there's another type which edits the .x files that controls how it looks.  These give a very-detailed visual representation.

Thread: Looking after your LiPo cells
18/12/2008 12:24:00
Thanks.  I had a look at the FMA site.  They give a link to Cadex, who recommend storing at 40% capacity and 15 degrees C, saying that this minimises loss of usable capacity.  So i'm going to run all mine down to that point (about 3.75 volts per cell) and leave them like that for the winter until I want to use them again.
Thread: Where should the motor go?
18/12/2008 12:10:00

Yes, but in a Firebird-type config the tail surfaces see the prop-wash (for control) but the propwash doesn't go all down the fuselage (which is where I suspect most of the extra drag comes from).  The theory of props is that both the in-wash (i.e. before the prop) and out-wash (i.e. after the prop) speed up, with the out-wash speeding up more.  Speeding up means also that the flow narrows, so you get a slightly-narrow slightly-speeded in-wash followed by a rather-narrow  rather-speeded out-wash.  It's this narrow speeded-up out-wash that in a conventional layout runs all down the fuselage, creating drag that can be avoided.

I think it's not strictly EDFs that have the control problem: it's those where the "jet" comes out the back. Some have a mid-placed fan unit with the jet exiting immediately.  They should be OK as the jet will at least partially flow over the tail surfaces.

Thread: FMS flight sim.
18/12/2008 10:41:00
Eric: you say there are only two models (each) suppled with FMS. By that you mean FMS 8. All the earlier-version models (in FMS 7) will also work. Jonathon: all the planes I've ever downloaded work for me. Is it possible you are running FMS 7 and trying to run FMS 8 planes? The planes are not transferrable backwards, but they are forwards. Roy: I've just downloaded the pz-28-trojan from the GG site, and it works fine for me. I downloaded the .zip file to a temporary directory and then Extracted the files there. I then copied the seven files to the FMS8\model directory and it flew fine (really rather nicely, if a bit forgiving: I'll look at the .PAR file and "sharpen it up" to suit me). As it's an 8 model it will only run in FMS 8. It's defined as an electric one, so will restart from closed throttle. You should have 7 pz-t28-trojan files with the following extensions: .bmp .mqo .par .wav .x _prv.jpg and _readme.txt Only the first 5 are used "in flight"; the _readme just says who wrote it, and the _prv is just a preview image for when you're selecting a model (Model / Load).
18/12/2008 09:59:00
No. Exactly the same. When I looked at the posting they had smilies embedded in the centre column. I've changed my settings (In My Forum to basic editor and render-smilies-a-text and the smilies have gone. But now I've changed them back and they're still gone!
17/12/2008 15:09:00

Sorry about the Smilies: they are converted from the file-content text by this Forum's text-editor. 

For instance, the third-from-bottom line should read:

0.09     23: She(m^2)    Effective Area of Stab

Except that here I've inserted a SPACE after the colon, but the .PAR file should not contain this.

17/12/2008 14:24:00

Eric: what  you've just described is exactly how i/c models work!  If you stop the engine it doesn't then re-start when you open the throttle! So what you've described is a FEATURE of FMS not a BUG.  If you look "inside" the models you'll find this feature only applies with i/c-engined models.  Electric ones can be stopped and started.  Just like real ones.

 This feature was only introduced in FMS 8 and is only present in models designed for FMS 8.  FMS 7 models that have been transferred to FMS 8 do not use this feature.

Terence: the accuracy of FMS was considerably improved (in principle) in FMS 8.  Indeed the three big changes are improved aerodynamics, wind effect and model parameters.  HOWEVER very few "constructors" have used the model-parameters properly.  In fact many provide lots of models whci are really the same one but with a different appearance.  How a model flies is determined by the .PAR file.  FMS 7 planes have small .PAR files (1 to 2 kB) but more-fully-described FMS 8 planes have much larger ones, typically 16 kB.  I'll goive some details in a second note.

.PAR files can be opened and edited using any text editor, but MANY planes are of Japanese origin so the third (descriptive) column is unreadable unless you use an editor that can read and display these characters.

Thread: Where should the motor go?
17/12/2008 10:17:00

If you're designing a model aeroplane with conventional wings and tail, then it's normal to put the engine or motor at the front, driving a tractor propeller.  Most (but not all) single-engine full-size 'planes have the piston-engine up front.  Most models are the same.  It's easier to start the engine of a piston-powered model if it's up front!

 

But quite a lot of the RTF electrics have their motor elsewhere, often in pusher-mode aft of the wing seat like the Hobbyzone Firebird.  Interestingly, other long-duration craft have unconventional layouts: some UAVs like the RQ-1 Shadow follow the Firebird layout.  The long-duration MQ-1 Predator has the engine right at the rear, with a pusher prop behind the tailplanes.  Cruise power from the round-the-world Voyager came from a rear-mounted motor.  The Convair B-36 had 40-hour endurance; its engines drove pusher-propellers mounted behind the wing. 

 

Long-duration planes require efficient propulsion systems, and these need to be energy-efficient right up to the point where power has been turned to thrust (by the airscrew).  The examples above suggest that for efficiency we should be looking at motors fitted with pusher-propellers, located to minimise drag.

 

Electric-powered models have moved beyond the fragile-but-heavy NiCd / brushed motor-powered configuration of a few years ago, but even with today's brushless motors and high-output LiPos we are still energy-limited for long-duration flights.  This is much more true of electric models than piston-engined ones: the weight of the fuel is normally small compared with a LiPo, and the LiPo weight is constant.  For this reason, with the Electric model you will normally need to place the LiPo near the front for balance, but there's much more flexibility in deciding where to put the motor, as it's much lighter than a piston engine of the same power.  So what's the best place to put the motor, and why?

 

The airflow in front of the propeller is accelerated, but this acceleration is only half that behind the propeller.  That's why pusher-props are more efficient, because although their in-wash may travel over the plane, the out-wash generally does not.  The lowest-drag configuration is to have the motor on pylons, like jet airliners do.

 

But a Firebird configuration has the propeller arc just above the fuselage.  If the motor is not fitted much above the wing this limits the diameter.  Small diameter propellers are less efficient than big ones.  So for best results we need a layout with a large-diameter pusher propeller.

 What practical experience do you have that shows a particular configuration to be efficient?  What models or designs have you found to have particularly long duration?  What snags have you found with unusual configurations?
Thread: Parallel charging multi Lipo packs
16/12/2008 19:46:00
Thanks.
Thread: Looking after your LiPo cells
16/12/2008 19:45:00
Thanks. That's exactly what I thought, so at least we're making the same (educated) guesses.  So if we are right then it's OK to keep them charged up, provided they are kept at (relatively) constant temperature. More particularly, there's no real need to part-discharge them for storage.  Mine are kept indoors in a heated area so I would not expect them to get significantly colder over winter.
16/12/2008 15:43:00

I would like to raise a different aspect of LiPo care: does anyone KNOW why we are advised to store LiPos at about 50% charged (that is, not close to either the low or high voltage limits).  I've seen this advice in several places, and my new LiPos always arrive in that state.

 I can make several GUESSES as to why this might be best practice, but I'm after the real gen.

Thread: Parallel charging multi Lipo packs
16/12/2008 15:35:00
Where did you buy the "sockets"?
Thread: Battery chargers demystified
06/12/2008 18:26:00

What's the hurry?  If anything's old hat it's buying a Leisure battery to take to the field.  Necessary when you used NiCds as these needed a charge-boost to top them off, and power / weight ratio meant you needed every scrap of charge.  Or when you could only afford 1 LiPo and needed to field-charge it to fly twice in one day.  Now that's all in the past.  Good LiPos hold their charge very well, and when I've used mine there's loads of time to recharge them at home.  If I'm using c. 2000 mAH packs they will recharge in 1 hour each.  And while LiPos not cheap they're sufficiently affordable for you to buy a day-out's worth.  If the article was aimed at beginners or near-beginners then they are probably just using 3S (and probably not A123s either!) so a simple inexpensive set-up like mine is probably quite adequate for them.

You will see such (4A or 5A) power-packs offered by some of the EF webstores, without indicating their original purpose.  But these are priced a bit higher than £4 each!

06/12/2008 14:00:00
My 12V-input charger has a max output charge rate of just 2A, and for this it takes a maximum of 3.7A input - well within the 5A capacity power supply capacity.  Now that LiPos are relatively inexpensive, the idea of field-charging them seems a bit out of date. You can buy quite a few LiPos for the cost of a Leisure battery.  And if you're going to charge them in advance at home, charging at a low rate will likely increase their life (and be safer).  So it all works for me, and so I don't find it too limiting at all.
06/12/2008 11:13:00
In my opinion, if you have a 12V input charger there's a cheaper and nicer (and lighter) solution to powering it than a £85 Leisure Battery:  buy a mass-produced powerpack intended to drive a computer screen.  You see these advertised as TFT powerpacks on Ebay.  I bought one (new) from China for £4.  It's rated at 5A and is stabilised and smoothed.  Search ebay.co.uk on TFT Power 5A, sorted price + carriage lowest and you'll find them.  Mine was from
http://pics.ebaystatic.com/aw/pics/uk/s.gif

allforlaptop
Thread: Li-Po battery balance plugs
30/11/2008 18:52:00
If the two packs are at significantly different stages of charge, the initial current flow will be from one pack to the other - and might make the wires glow!
Thread: Looking after your LiPo cells
21/11/2008 18:46:00
If you want them full to capacity, charge to the 4.2V per cell limit.  Use a balancer to make sure no cell exceeds 4.2V.  If you're only coming down to 3.86V you are only taking 30% or so out of them.
Thread: Li-Po battery balance plugs
19/11/2008 15:20:00

David (Ashby) : So most contributors are just converting to XH.  As I said in an Email to you some time ago, I still think some JST XH connectors would make an excellent free gift to go with the magazine.  Lots of people would appreciate them, and soldering-on a bare lead or crimping to make up a connector are both easy tasks (though I agree that crimping is a bit fiddly, but no more so that lots of other modelling taks).  As the majority of LiPos are 3-S (I believe) you could just give those.  The delivered cost to me of a 4-way housing and 4 crimp terminals (ex. VAT) is 12p for the terminals and 6p for the housing; 18p altogether.  If RCM&E bought them in bulk from China you would of course pay much less.

 Who (else) thinks this would be a welcome idea?

18/11/2008 16:23:00

Erfolg: Here's a direct link via the JST UK website:

http://www.jst.co.uk/productSeries.php?pid=136&cat=30

Look at the entry and the downloads for detail, not to buy - they're high volume guys.

You can buy club-size quantities from http://uk.farnell.com/ - £20 lot gets you free delivery.

Search on XH for the header and connector housing and on 1516301 for the contacts.

17/11/2008 19:35:00

There's a comment above about needing a heat-sink for JST connectors.  JST stands for Japan Solderless Terminal.  You are supposed to CRIMP them not solder them.

 JST-XH connectors are available 2-way to 16-way.  Look at www.jst.com and then under wire-to-board crimp-style connectors (listed in pitch order) then look at the 2.5 mm ones.  For me they come up as item 41 on page 3.

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