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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: Irvine 61 new bearings
18/09/2019 19:33:27

While it certainly works with forged steel components under a small amount of tension (although the ball joint I separated earlier this afternoon on my Series 1 Land Rover that hasn't been disturbed in at least 35 years refused to yield and needed an extractor) I'm not so sure that there isn't a risk of distorting the soft aluminium of a typical prop driver.

Thread: Ageing lipos!
18/09/2019 11:27:30

While old NiMH cells are fine, I would be wary of using old LiPos around the home due to the fire risk.

Thread: Irvine 61 new bearings
17/09/2019 22:48:28

This thread may be your friend...

As far as I'm aware, the 61 will use the same tapered collet system as the 53, 46, 40, 25 etc.

Edited By Martin Harris on 17/09/2019 22:52:58

Thread: Laser Engines - Technical questions
17/09/2019 16:30:53
Posted by tigerman on 17/09/2019 16:05:47:

Now reset the idle jet to 7 turns out then done some fine adjustment to get the tick over and pick up just right then reset the main jet and the Laser is working fine again .Lesson 1 DO NOT MESS WITH JON SETTING .Leave well alone and the Lasser will be fine !!!!!!!!!!!!!!!!!!

Sounds like you've got a result.

As a general rule of thumb on an unknown engine, I always start deliberately rich on both top and bottom ends (a rich engine runs badly and cool, lean may not start and may run too hot if it does) and tune the top end first (remember that the feed to the idle jet is influenced by the main needle setting) then tune the idle and recheck the top end as the idle setting has a small(er) influence over the top end. Recheck until neither need further adjustment.

Thread: push
17/09/2019 14:07:16

If "push" in the thread title refers to the engine, be very cautious with an Irvine. The needle valve is extremely close to the propeller arc - Irvine users regularly get a slap on the knuckles while making adjustments to engines fitted with conventional props. If you try this with a pusher prop it will almost certainly inflict serious injury due to the blade coming at you at a chopping angle which pulls the blade into whatever it contacts.

I was bitten (twice in one day) back in the 70s by a pusher driven by a little Veco .19 - I still have the scars to remind me. I shudder to think what an Irvine 53 would be capable of.

Edit: Just spotted your last post after posting this and it seems to confirm it's a pusher.  I would seriously advise against the Irvine unless you can arrange a remote needle adjustment.

Edited By Martin Harris on 17/09/2019 14:17:05

Thread: Laser Engines - Technical questions
16/09/2019 22:50:50

The idle needle setting is significant to probably 3/4 throttle and works in conjunction with the main jet throughout its range. It looks like Andrew has hit the nail on the head...

You may have (or have had) a partial obstruction inside the carb. If I suspect this and can coax the engine to run at full throttle (judicious finger on the exhaust or air inlet if no pressure is being used) once running at WOT, that finger gets used to choke the engine momentarily and draw the obstruction through. If you do try this, be extremely careful though.

Alternatively, a wide open needle valve and my u/c pressurising bicycle pump applied to the fuel inlet performs a similar function - cycling between that and removing the needle and pumping with the magic finger over the carb throat a couple of times usually works wonders...

Thread: Glenns models cap 232
16/09/2019 18:23:57

Re. dual batteries, it might be worth bearing in mind that some smart chargers may not sense the correct cut-off point when attempting to charge NiXX batteries simultaneously from the same power supply while connected to a common negative - i.e. using charging sockets in the model. Using separate power supplies allows safe simultaneous charging.

I'm not sure if LiFe cells are similarly affected.

Thread: Defibrillator?
16/09/2019 14:30:14

Watching with interest as it's something that could be worthwhile at any club...we did try to find out some info a year or two back but like you, found conflicting advice.

Edited By Martin Harris on 16/09/2019 14:31:33

Thread: Autumn is here...you been flying ?
16/09/2019 00:42:16

Sneaking through FRZs?

Thread: Petrol Engine for a Toot Sweet
15/09/2019 23:59:35

I thought the OP did!

"or should I just put a 9cc in and have almost unlimited performance?"

However, the thread has moved on to discussing conversions.

Edited By Martin Harris on 16/09/2019 00:06:08

15/09/2019 12:54:45

I believe the main problems with running small engines on petrol revolve around carburation and cooling.

Glow carbs are extremely simple devices which work acceptably when metering the relatively large volumes of fuel used relative to petrol. As the metering involves tapered needles, you will probably find that the adjustment minimum of one click on the knurled body is too coarse to achieve an accurate mixture setting. Walbro type carbs work well in larger sized engines but aren't really suitable for anything smaller than a .60 - and maybe .90s upwards are better suited and getting something suitable for an engine conversion may involve a large amount of luck as there is so much variety and lack of info from the makers.

Petrol engines also need more cooling as the fuel burns hotter and as the finning on a glow engine is designed to maintain the correct temperature range for methanol fuel, will be far less tolerant of any inadequacies in cooling air flow. I also have an inkling that vapour locking could contribute to problems due to the higher temperatures and higher vapour pressure of petrol vs methanol.

 

Edited By Martin Harris on 15/09/2019 12:55:07

Thread: Well this could get interesting
13/09/2019 16:34:01

So although the specifications are secret, you can confirm that the jamming is focused and targeted?

I don't seriously suspect a connection but it just so happened that on the Thursday afternoon 3 weeks ago when a jamming trial was taking place on the other side of the country in Herefordshire, we had 3 unexplained losses of control at our club. This is an unusual occurrence - most crashes can realistically be put down to human factors.

It might be interesting to collate experiences of that day just on the off chance that there could be some connection - if so, it is a very worrying (if unlikely) situation!

Edited By Martin Harris on 13/09/2019 16:48:04

Thread: Thinking aloud about Spits...
12/09/2019 16:43:31
Posted by Dad_flyer on 07/09/2019 23:26:10:

There was a red one that used to do shows apparently. It was the wings of one spit, and fuse of another. "Red spitfire" search will get you pictures.

Search for G-FIRE and/or the owner, Spencer Flack. You may wish to avoid reproducing the strobe lights in the gun ports given your aversion to its military heritage!

12/09/2019 11:47:25

Good point Pete, the up aileron trick has tamed many a tip staller although I'm not sure about that version with the non scale ailerons...

Edited By Martin Harris on 12/09/2019 11:49:26

12/09/2019 11:23:30
Posted by Foxfan on 12/09/2019 08:15:24:

Was that too slow? Looked pretty fast to me. Maybe he just pulled the wrong stick.

The whole flight was way too fast for my tastes. I've so far not seen anything that quick at our club!

 

Martin

I'm talking about the crash within the first 30 seconds of the video. The model appears to dead stick and while being manouevred, drops a wing and spins. Many models would probably have survived without incident but the more heavily wing loaded and less forgiving wing profile of the Spitfire meant that it was prone to flicking when pulled into the turn. Speed is a simplistic explanation, what actually happened was that the wing exceeded the critical angle of attack. In a 60 degree bank, for example, stalling speed doubles.

The hard turn after the engine cut bled off much of the energy from the model's speed and by the last turn with almost certainly some elevator being applied to hold the nose up (hoping this observation doesn't offend Steve but we've all done it) put the model in a position vulnerable to stalling at that point. You just can't get away with stretching the glide with such a model.

I used to set up my 1/12th scale combat models so that at full throttle, the model just wouldn't flick out of a maximum rate turn - but you had to be careful if you were trailing an opponents streamer as full throttle stalls could then still occur!

Edited By Martin Harris on 12/09/2019 11:45:58

Thread: Ashbourne 2019
12/09/2019 10:54:12

Sadly, I am otherwise engaged this weekend.

12/09/2019 00:48:20

What on earth is oatcake? Sounds like something you'd feed horses!

Thread: Thinking aloud about Spits...
11/09/2019 23:32:33

See Stephen Jones' second video...the consequences of getting too slow while manouevring are demonstrated very well!

Edited By Martin Harris on 11/09/2019 23:34:35

Thread: Alternative servo linkage
11/09/2019 23:03:35

I came up with this solution as a retro fit when it became apparent that my Tony Nijhuis Hawk would need tail weight. It drives the rudder (normally fixed) from below. It's worked well with little or no slop but I don't know that I would recommend it as an aileron or elevator system without a bit more engineering. It might give food for thought?

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Thread: Latest CAA Update
11/09/2019 22:00:43

Aren't we a helpful bunch!

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