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Member postings for Martin Harris

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

Thread: Battery problem
20/04/2018 23:47:38

That should be fine - it will charge virtually any battery you're likely to use. More importantly, it has the capability of discharging them so that you can do an occasional check on how much they can deliver safely. Far better than finding out that a battery has degraded half way through a flight!

20/04/2018 22:11:34

NiMH batteries are better charged with a "smart" charger but can be charged with a standard "wall-wart" one. The problem is that they don't like being overcharged and it's difficult to avoid it unless you have a very good idea of what has been taken out (or self-discharged).

Suitability also depends on capacity and the charge rate given by the charger. Are these fresh batteries or have they been standing after earlier use? NiMHs don't have a very long service life like good quality NiCds had.

It would be better to invest in a charger that can be set to a suitable rate and detect the fully charged state. There are many available for not too much money.

Thread: Electric Cars.
20/04/2018 20:04:34

From info gleaned in the previous posts, I'd imagine they are referring to Jaguar Land Rover.

Thread: Data protection regs
20/04/2018 15:21:49

Any informed views on this guidance from the BMFA?

If using electronic communications to members gather consent from all existing members and new members when they join. This requires a positive action from the individual.

Does this imply that after the 20th of May, clubs need to cease email communication with any member who hasn't positively elected to receive emails?

 

 

Posted by MattyB on 20/04/2018 11:27:42:
...it is highly unlikely regulators will have the capacity or will to go after clubs and societies who have very small financial resources to pay fines (4% of global turnover isn't much for a model club!)

Matty, while the financial penalties may be small, would there be any criminal liability involved?

Edited By Martin Harris on 20/04/2018 15:26:46

Thread: Laser Engines - Technical questions
19/04/2018 13:32:56
Posted by Jon - Laser Engines on 19/04/2018 09:04:20:

Martin, i understand that the test is being done 'by the book' but that does not mean it is being done correctly. I have seen it at clubs before where meters were set to record peak sound and if a butterfly broke wind nearby you failed the test. Some clubs average all 4 results, others do not. There is no real standardisation. Given that the noise test records of a club offer no protection of any kind against a noise complaint the whole thing is, sadly, pointless. Im not saying that noise is not a consideration as it is very important, but running flat out on the ground is hardly a representative test. I understand why we use it though as sadly a perceived noise test with the model in flight is not really quantifiable so cannot be tested very easily, even if it is perceived noise and nuisance that actually cause complaints.

And i know my phone app isnt offical but its all i have. If i get a reading of 79 for example there is no way the app is that inaccurate. Thats all i was looking for.

In the meanwhile Chris angle the exhaust deflectors back very slightly and see if you can work out which part of the model is resonating and sort it out. As before, double check you dont have a prop out of balance and then as a last resort set some sort of throttle limit. Make sure its easy to turn on and off as you need to be able to open both throttles fully to tune the engines. Were you able to check the rpm of the engines? i assume they were pretty close to eachother? if not this will create more noise. Again i assume they were the 12x7 apc props? If so you cant really do much more. 13x7 would slow them down for sure but ground clearance will be an issue. 3 blade is not an option as they make more noise anyway.

DO you have a video of the model running?

 

I did say it was done to the test specifications - slow response, dBA weighting and common sense when transient noises boost the readings, so no peaks. Noise level not to exceed 82dB in any of the 4 orientations.

Factors which can affect readings include proximity of sound reflective material - even including bystanders...we sometimes resort to standing out in the middle of the field for marginal models!

Very often, increasing pitch rather than diameter will drop the noise level significantly unless you hit resonance of course! RPMs drop and with the lower diameter, there's a double whammy on the speed of the tips, which is where most of the prop noise is generated.

I'm glad you gave such confidence in your phone app - it sounds impressive that all microphones come out of the factory equally calibrated!  Comparisons between our meters and phone apps have been less than impressive when we've tried them.

Edited By Martin Harris on 19/04/2018 13:34:09

19/04/2018 00:22:02

The picture on your other thread suggests that the deflector(s) may be angled towards the propeller(s). I tested a surprisingly noisy Laser a few years ago and the cause was that the owner had the silencer exit pointing slightly forward - repositioning it stopped the interaction between the prop wash and the exhaust gas and reduced the readings dramatically.

Jon - tests at Chris's club are done to the stipulations of the DoE noise test - unfortunately they include a front on reading with a calibrated tester - a phone app isn't compliant.  Although I follow your logic and appreciate the limitations of the test which was probably designed around mid range 2 strokes, compliance is seen as a primary defence against malicious complaints, of acting responsibly.  A full-blown noise nuisance investigation would concentrate on the actual raising of ambient noise but is a costly exercise so anything that could help environmental health make an early rejection is seen as worthwhile, however flawed the DoE test may be.

Edited By Martin Harris on 19/04/2018 00:38:30

Thread: Wing dropping
18/04/2018 17:04:25
Posted by Piers Bowlan on 18/04/2018 08:29:23:

Even with laterally balanced models, not only torque but also slip-stream effect will cause the aircraft to roll in opposition to the rotation of the propeller. The prop slip-stream rotates around the fuselage and impinges onto the rudder asymmetrically, causing a sideways force and a yaw to the left. Since roll is the further effect of yaw, this in turn causes a roll to the left. How large the rudder, the tail moment length, the power of the engine and importantly, how much dihedral the wings have, will all influence how large the slipstream effect is. The greater the dihedral the greater the yaw/roll couple.

Like torque, engine offset will counteract torque and slip stream to some degree or at least improve things. Also rudder trim will counteract the yaw but both torque and slipstream will be at a maximum at full power (during take off/ go-around). Mixing a bit of rudder with throttle might improve handling during these phases of flight if thought necessary.

Edited By Piers Bowlan on 18/04/2018 08:47:00

I wonder how much slipstream effect there would be at idle during a stall test, though. My (very empirical) guess would be that it wouldn't contribute enough yaw to cause a significant wing drop as the airflow over the fin at the stall should still be providing significant weathercock stability. Unlike the very significant effect at high power, low airspeed, during take off...

18/04/2018 00:37:24

It might be worth considering gyroscopic precession effects caused by the nose dropping during the stall - possibly more likely than side thrust issues which I don't believe would cause wing dropping. Did you try an inverted stall - the results could add some light to the discussion...

I have to say that the picture above suggests that the right wing is heavy - was this taken after adding weight?i

Trevor, wouldn't a yaw to the right tend to induce the right wing to drop?

Edited By Martin Harris on 18/04/2018 00:39:46

Thread: How did that happen?
17/04/2018 19:13:25

 

Posted by Geoff Sleath on 17/04/2018 17:30:10:

Posted by Biggles' Elder Brother - Moderator on 17/04/2018 13:35:58:

Remember - aeroplanes don't stall because they are flying too slowly - they stall because the AoA is too high!

BEB

Isn't it actually a combination of the two? Too low a speed for the AoA? eg if you slow a plane up too much even in straight and level flight (ie virtually zero AoA) it will stall but will recover (hopefully) if you apply a negative AoA.

Geoff

How do you slow an aircraft by reducing the angle of attack? The only way it would slow down is when it hit the ground at high speed!

I suspect that BEB's point was trying to emphasise that angle of attack governs speed rather than airspeed having any direct relationship to stalling. If the elevator is powerful enough, stalling is possible at any speed up to the point that the airframe fails.

Edited By Martin Harris on 17/04/2018 19:30:45

Thread: Wing dropping
17/04/2018 19:03:45

Assuming the lateral balance is OK, then it's most likely due to torque reaction - the propeller turns clockwise from the cockpit's point of view, so torque is opposite to this, causing the port wing to drop.

 

Edited By Martin Harris on 17/04/2018 19:04:25

Thread: Electric Cars.
15/04/2018 21:53:16
Posted by J D 8 on 15/04/2018 10:36:37:

That makes my hard worked but well cared for 1990 Land Rover 90 well green then.smiley

I don't think I know that shade but my 86 was bronze green when it came out of Lode Lane in 1954/5 (but it was blue when I bought it in 1979.) It's now green and natural aluminium...

I wonder how its energy/pollution debt per year stacks up against a 3 year old car which will probably be scrapped within 10 years when faults in the engine management and anti-pollution systems become too expensive to justify replacement?

Thread: Anet A8
14/04/2018 21:59:17

Mark Stringer recommended this earlier in the thread - I printed it and it's transformed my filament changing woes...

aprint.jpg

Edited By Martin Harris on 14/04/2018 22:09:24

Thread: Spring 2018 is here...been flying?
14/04/2018 21:52:43

Cracking day - tee shirt and Nieuport (Legionnaire) weather!

Thread: Coffee And Biscuits.
13/04/2018 12:42:52

+1 on that, Geoff - there are those who appreciate good coffee and those that add milk and/or sugar.

As for a double skinny latte americano mocha topped with nuts and chocolate or whatever...disgust

Thread: Military paint supplier.
13/04/2018 12:29:15

Very handy link - for my Land Rover.

If you do spray these paints, be aware of overspray - unlike typical car paints, droplets can carry a long way before drying. Long story but it cost me an afternoon and a can of T-Cut to keep a neighbour happy...

Thread: Safety plug
13/04/2018 00:26:57
Posted by Geoff Sleath on 12/04/2018 14:53:25:The battery lead length still seems to be a dark(ish) issue but I've never seen any esc instructions which actually set a lead length value and batteries come in non-standard lead lengths.

Copied from the Jeti Advance Pro ESC manual:

connection cables to the flight battery can be extended to a maximum length of 20 cm

More specific example from the high end Mezon manual:

 The distance between the motor and the controller should not exceed 10-15 cm . The cable lengths to the flight battery may be lengthened up to an additional 20-25 cm. You can lengthen the battery cables further, if you solder, in parallel to the cables, electrolytic capacitors (so called ESR low internal resistance capacitors with corresponding voltage values and capacities of several hundred microfarads). Add one capacitor for every 25 cm of additional battery cable length.

From the YGE 200 Hotliner FAI manual:

In the FAI types the cables to the motor are usually cut to a minimum and directly soldered. On the other side the total line length, from the controller to the battery, for all types should not exceed 20 cm. If long cables cannot be avoided,  every 20 cm a  330μF / 50V Low ESR capacitor should be soldered into the line, or add our Capacitor Module YGE Cap's Type 7

...and as I've only checked 3 non-far east manufacturers with known reputations (nothing obvious on Castle Creations) I'm sure there are other examples.

Edited By Martin Harris on 13/04/2018 00:43:43

Thread: Coffee And Biscuits.
12/04/2018 14:40:15
Posted by MattyB on 12/04/2018 13:48:06:the only waste is the ground coffee at the end.

...which can be used on the garden as a nutrient for the soil.

Although I normally use a (permanent) filter machine for convenience, the "jug method" is surprisingly effective with no polluting products and good to know in an emergency - just pour almost boiling water onto the grounds in a jug, stir and after brewing for a few minutes, draw the back of the spoon over the floating grounds which then settle quickly - pour off carefully and you get an excellent coffee.

Edited By Martin Harris on 12/04/2018 14:47:53

Thread: Anet A8
12/04/2018 12:28:05
Posted by Geoff Gardiner on 05/04/2018 23:44:03:

Spot on, Martin.

I hadn't done an upgrade but somehow the filament diameter had changed to 2.85mm. I didn't notice because I only keep the drop down menus open for settings I alter, so I can't see how it got changed.

I will know where to look if it happens again.

Don't ask me how I knew...blush

Thread: Coffee And Biscuits.
11/04/2018 21:54:41

Try the Aldi coffee Dave - it's very similar to Costa in flavour and a fraction of the price!

Thread: Help need charging a 12V PB battery
11/04/2018 21:37:57

Rocker, you wrote "I have set the charger for Pb battery and it is charge OK but now it has reached 18 .v"

There's no mention of the cell count...did you set it for 6 cells? I think the display shows something like 12.0V (6P) at the bottom right when set correctly. If it was showing something like 18.0V (9P) or 20.0V (10P) it would explain why the cell appears to have been overcharged.

Don't worry if the display shows 12.0V (6S) or similar - the info above is from the online manual but I can't see any logic in the use of P...

Edited By Martin Harris on 11/04/2018 21:44:40

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