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Member postings for Mark Powell 2

Here is a list of all the postings Mark Powell 2 has made in our forums. Click on a thread name to jump to the thread.

Thread: My Son`s Trainer
03/08/2012 20:23:00

Stephen

That looks a really good trainer, and your son is pretty good at keeping it in view on the video.

It's so nice to see people actually building aircraft rather than just buying these ARTF toys from the far east. Making things for your children is what good parentage is all about, rather than just buying them things. About 50 years ago my father built me a Skyleada Auster and a 2ft long boat. Still got the boat! Love the colour scheme, and the contrast between the camouflage top and the yellow underside is good for vision and orientation.

Thread: E-flite electric retract discussion
01/08/2012 21:06:57

Idris

Thank you for your reports on these legs. I recently purchased a pair to install in a TopFlite Spitfire, replacing a pair of 20 year plus old servo operated BVM retracts with plastic trunnions which were not really up to the job.

I have not so far installed them, but prompted by your posts and links I have measured the current draw of mine and by modifying/adjusting them in the ways you suggest I have halved the current draw. The removal of the sharp points in the transition from the locking to the curved track was particularly effective. I also lubricated the pivot pin with motor oil and the leadscrew and guide tracks with moly grease. It is curious that the allen grub screws holding the legs in place are only half as long as they should be. I replaced these.

I do however take minor issue with two of your points. I believe the fact that the brass pivot bearings are not flush with the outer plates is intentional. It prevents the trunnions from actually contacting the outer plates, so the surface finish of these parts need not be mirror smooth. Even when screwed down tight there seems to be sufficient clearance on both my legs.

Also, while I am not disputing your '6% efficiency' figure, I would draw your attention that such leadscrew operated legs are (or were) common in many full size aircraft. The DH88 Comet racer comes to mind (admittedly De Havilland's first try at a retractable undercarriage, and manually operated by winding a handle) and also the Douglas DC3.

Overall though, I am constantly disappointed by the quality of so many model aircraft accessories. We should not have to fiddle with these fairly expensive legs to get them to work reliably. It is not just Horizon - every single screw on a recently purchased OS 46 AX was, I found, little more than hand tight, even before running the engine. And they are hardly inexpensive.

Best wishes.

Thread: Which Mobile Phone
01/08/2012 17:48:43

You mention texting. Typing on a phone-sized touch screen is a nightmare.

Thread: This picture shows everything that is wrong with civil aviation
01/08/2012 16:21:25

Yes, its somewhere about 8 percent I believe. Don't think 20 Concordes were in service. mabe ten or twelve.

Almost all airline professionals, talk about 'good safety records' and 'aircraft geing safer than a car'. It is actually all nonsense, because they use 'passenger miles' as their base, so 200 people going safely to Australia adds 2.million plus to their their 'safety' figure.

If they want to compare like with like (which of course they don't) they should use 'deaths per journey.', when you will probably find that that cars come out MUCH safer than aircraft.

The way the airline industry does it actually means the figures look better if you are killed on the landing rather than the takeoff, as they can then still add the 2 million plus above (less half a mile or so) to their safety figure.

"If God had meant man to fly he would have given us more money"

01/08/2012 15:29:02
Posted by ConcordeSpeedbird on 01/08/2012 13:57:18:

"...Concorde also had the best safety record,...."

No it didn't. It had an awful safety record. About 15 percent of them crashed fatally

Thread: BMFA and failsafes
31/07/2012 18:16:50

Personally I always set the so-called failsafe. Throttle low, slight up elevator in the hope of a slowish descent, if fitted flaps and undercarriage up to reduce damage to them. Always have since I started to use Multiplex 'IPD' receivers some years ago, now also do it on 2.4 GHz.

However, while I strongly support the BMFA, I am getting fed up with Manny Williamson's constant nannying. Every issue of their (generally excellent) magazine has got our universal nanny telling us what we should or should not do.

They need to remember that neither the CAA nor the BMFA 'govern' aeromodelling (or toy planes if you prefer) in any way whatsoever, provided you stay under 7Kg. They just like to think they do. Many model flyers have not heard of either the BMFA or the CAA.

That said, setting of a failsafe might reduce the consequences of loss of radio contact with the model, and thus keep insurance costs down. But check your house insurance - you might find that model aircraft flying is NOT specifically excluded from the 'third party' cover. Don't phone your insurer and ask specifically if it is, you might cause them to exclude it when they next re-write their policies. So just ask them what the exclusions are. If it is not excluded, you don't need any other insurance, BMFA or anyone else's.

That said, BMFA membership is well worth having, both for its other functions and for insurance. But, as someone already said, BMFA insurance covers you for accidents that ARE your fault, via lack of failsafe, mis-piloting, and everything else.

Thread: What electric flight battery connectors do you mainly use?
31/07/2012 14:18:23

Deans. Used to use MPX green ones, using three pins per pole, on smaller models but moved to Deans as MPX are not readily obtainable where I live (Southampton).. With care you can solder two Deans plugs and one socket directly together to make a low resistance and compact Y-connector (thanks to BVMJets for this).

The ribs on the later Deans help with disconnecting and filing a small bevel on the plug pins help with connecting.

If you have trouble with melting push a plug and a socket together before soldering.

Shortly after I settled on Deans the XT60 started to appear. Wish they would make up their minds. Not changing now.

Thread: Ducted fan theory and practice
31/07/2012 12:47:31

Having only found this thread a few days ago, and seen Richard flying his foam Tornado yesterday (30 July 2012) at Beaulieu I have a few observations on 'Theory and Practice'.

Theory is essential, we would have discovered/invented very little otherwise. However, I feel we are past needing to worry about the theory too much and should concentrate on the practice. I also wonder how many of the theoreticians (Scharnhorst et al) have actually experimented with these small, high-powered fans.

I have performed many static thrust measurements using two 90mm fans, the Wemotec MidiFan and the Schubeler DS51 Dia 3ph. Interestingly, the static thrust, motor for motor, difference between them is only one or two percent at most. This agrees with what several successful flyers have said - "Any half-decent fan will give much the same performance as any other, matching the motor to the fan is far more important than the make of fan used.". In my results below the Wemotec MidiFan was mainly used, the Schubeler gave very similar results.

MY TESTS (I increase the number of cells until the motor starts to get pretty hot. All cells are Intellect 4 Amp/Hr 25 C)

Kontronik 600, 1700 RPM/Volt. Maximum thrust about 4 lbs. Hopeless. RPM/Volt is far too high. Gets hot with 5 cells, very hot with 6. As a result is working at only about 1000 watts.

Mega 22/30/3,1260 RPM/Volt. Maximum thrust 4.5 lbs on 8 cells. 1150 watts. This motor is simply too small. (short) to give high thrust.

Mega 22/45/3, 860 RPM/Volt. Maximum thrust 5.5 lbs on 11 cells. Really needs 12-14 cells, but I am unable to make up such a pack with my existing cells. Runs stone cold (good) on 11 cells.

Hacker B50 16L 1500 RPM/Volt. Maximum thrust 5.5 lbs on 8 cells, but the motor gets rather too hot for my liking.

Hacker B50 12XL, 1300 RPM/volt. Maximum thrust 8.7lbs on 10 cells. get warm, but not hot. The best motor I have found, but rather expensive.

HEAT.

The motor should only be warm to the touch even after long periods at full throttle. Anything hotter is simply wasting power and over-stressing the motor. Long motors, such as the Mega 22/45 and the Hacker B50 XL are best for both power handling and giving the high torque required.

INLET DUCTING.

1) If you suffer duct collapse (which has been mentioned here) your inlets and ducts are too small, restricting the airflow and lowering the thrust.

2) Try stopping the duct a few inches short of the motor rather than continuing it right up to the fan. This will give you a 'plenum chamber' and also allow you to use an inlet bellmouth (such as the one included with the Wemotec fans) on the fan unit. Schubeler now recommends this. The space between the end of the duct and the fan inlet does not have to be particularly smooth, but do not place deliberate obstructions.

MODEL WEIGHTS

Why are most ducted fan models so heavy? My RBC Panther is 7.5 lbs for its 48 inch span and is not a whole lot of fun to fly. The E-Flite Habu has an even higher wing loading. KEEP THEM LIGHT! One would not be happy with a 40 or 50 inch, eight pound propellor model, don't do it with D/F models either. A lighter model will land slower, fly faster (lower drag due to lower angle of attack to sustain horizontal flight), and will not drop out of thge sky on turns or on a glide.

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