Martin Harris - Moderator
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Posts posted by Martin Harris - Moderator
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Very cunning.
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4 hours ago, Albert Ace said:
Sorry, that's Undercambered wings.
Title and OP corrected.
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Painting.
I never seem to be able to organise myself to start - my Tempest airframe has been in primer for over a year! I've had a lot of distractions this winter so haven't even touched the model since I created the panel lines with masking tape/primer and pencilled in the camouflage pattern last autumn.
My radio installs are planned during the build process so it's not a one off task. It does take a lot of thinking through on more complex models. We had a club member once who claimed that his radio installations took "half an hour". He was one of the most prolific crashers I've ever known - I wonder if there's any connection!
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I'm very tempted to follow this advice the next time I dig mine out...it will be interesting...hopefully not too interesting! My FW190 has excellent ground handling (but it does have nice big wheels) so perhaps Black Horse followed this principle when they specified the CofG?
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A not so obvious reason why (jet) engines on wings are set away from the fuselage is that the mass of the engines opposes bending moments due to lift and consequent G effects (e.g. the engines get "heavier" while the wings are generating more lift in a turn) so the centre section doesn't experience as much stress.
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22 hours ago, Martin Harris - Moderator said:
Like all Hurricanes, a pain on the runway but if you can keep the spinner off the grass then once airborne it should be a delight to fly. I can’t tell you the weight offhand but with air retracts (now electric) and a 90FS it is no lightweight although the builder (I bought it when it was already quite elderly at the Watford Swapmeet in 2003) had taken the trouble to fabricate a built up tailplane. It still has a large slug of lead in the nose though.
As far as I can recall, I went with the plan CofG.
I've weighed it this morning and it comes out at a rather porky 9.62 lbs (or 4.36kg for Paul) without fuel. I can't see any guidelines on the Galaxy site but it flies fine at this weight.
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Spoilers and airbrakes are actually quite different so make sure you're searching for the right thing.
Spoilers normally lie flat on the wing surface and were fitted to many earlier gliders. They work by spoiling that part of the wings lift but only contribute a limited amount of drag. Airbrakes are blades which come out of the wings vertically, both spoiling lift and contributing significant drag. They can be provided on the top surface only, or far more effectively, top and bottom surface with deliberate air leakage through the housing. Learning to sideslip on the approach was a very useful skill on vintage gliders!
As the T31M was a conversion, essentially just sawing off the nose section to mount the engine and adding an undercarriage, I would think you can safely assume that the spoilers would be in the same place as the original glider.
I've had success with using ailerons mixed to deflect upwards on several non-braked or flapped model gliders - including a 4 metre Fly-Fly Discus. Not scale of course but fairly unnoticeable except by the pickiest purist...
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Dunno. 11 years on, the original battery (more correctly, cell) in my DS16 is still performing well.
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Really? I’d be quite happy to be asked to pass either side - this reflects a choice whereas both is an instruction!
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On 30/03/2024 at 19:39, Futura57 said:
Maidened my new xfly F22 Raptor EDF today. Two words: Gutless & Disappointing. Not me, the model 🤣
It's nearly 100g heavier than my Strange Quark prototype, has less grunt and speed and only flys for 4 mins versus 4.5 mins on the same 4S 2200 (leaving around 25%).
To be fair, I did have the u/c fitted. It is awkward to hold for a hand launch.
Well, I’ve just maidened mine and I don’t recognise your description, Futura. I didn’t fit the undercarriage though so perhaps it makes a significant difference?
I found it very responsive on the recommended first flight high rates and switched to low where it was still quite lively. It got away steadily and as soon as the speed built up performance was excellent with big loops, both positive and negative coupled with benign high alpha flying.
This was with a new GNB 2600 4S (120C claimed) - perhaps your battery is past its best? I flew for 6 minutes but will probably standardise on 5 minutes to allow a good margin as I landed with 14% remaining.
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2 hours ago, Cuban8 said:
Not something that I've given too much thought to, but the nature of the glow ignition system precludes any seperate ignition timing system that you will find on spark ignition systems. Usually highly critical, especially on high performance two stroke motor bike engines (still have my Mitutoyo dial gauge and spark plug adapter from back in the day) a mis-set engine would blow a piston crown very quickly. Points just open at 1.8mm BTDC IIRC on my Yamahas. Auto advance weights would take care of the advance from the basic static timing point.
How do our glow ignition (and I suppose compression ignition diesels) cope with the timing change requirements across the rev range? Presumably ignition has to advance as revs increase? With no mechanical or electronic advance - what's occuring?
Timing is self regulating by the amount of heating of the element. As loading with increasing revs increases, the element (a catalyst) reacts with the methanol more readily, effectively advancing the point of ignition.
If an engine such as the magneto equipped Zenoahs has no method of varying the timing, you have to compromise either to easy starting or maximum power. Damage mostly occurs when timing is over advanced, causing detonation, which causes the damage to piston crowns etc. Normal engine running is a controlled burn - not an explosion, which detonation is akin to.
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Like all Hurricanes, a pain on the runway but if you can keep the spinner off the grass then once airborne it should be a delight to fly. I can’t tell you the weight offhand but with air retracts (now electric) and a 90FS it is no lightweight although the builder (I bought it when it was already quite elderly at the Watford Swapmeet in 2003) had taken the trouble to fabricate a built up tailplane. It still has a large slug of lead in the nose though.
As far as I can recall, I went with the plan CofG.
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6 minutes ago, Peter Miller said:
Handy if you’ve got a short sighted hamster.
I often wondered about turning up with a couple of large lorries and putting the statement “everything for a Pound” on the window of a well known high street store to the test!
I’ve also never quite worked out how to comply with road signs before bollards/islands directing you to pass on both sides…
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Absolutely - that’s why I qualified the design aspect. Manufacturers don’t always get it right - I believe at least one had to replace a number of badly designed throttle barrels some years ago where the scroll was wrong and made them horrible to try to tune in mid range.
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I use that as an initial indication that the idle mixture is too rich. Unless massively rich you’ll probably get away with it but a properly designed carb will not give any obvious drop and should work reliably over its whole range if leaned correctly.
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On 07/04/2024 at 16:30, Cuban8 said:
Any glow fourstroke will be a lot less messy than a glow twostroke, just the nature of how they work and how the oil is used. Siting the exhaust in the best position to keep the residue away from the model is also important, so careful planning during construction is to be considered.
Never a truer word. An ASP 180FS that I had in a Miles Atwood Special left barely a trace of oil on the airframe - just a faint (and very scale looking) sooty mark near the exhaust outlet. The same engine, running the same fuel, in a Seagull Yak 54 left the underside like the aftermath of the Torrey Canyon (younger members might prefer to relate to the Exxon Valdez).
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+1 for something like an 18 or 21W lamp - indicator or brake light filament from a failed rear/brake light one.
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JD8's method is easier for a lamp (bulbs are what you plant in the garden, as our storemen at work drummed into me!) with spade connectors - you could solder to them or use a dedicated 3 wire headlight connector from a scrapyard (or Halfords!)
Remember that if you use a halogen headlight lamp, it needs to be kept scrupulously clean (use meths or alcohol) and not handled by the glass or it will fail quickly. It will also get VERY hot.
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Very.
Tin the wires and a spot on the casing, hold the wires onto the terminal and tinned spot and apply the soldering iron.
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We're lucky to be at the top of a chalk hill so our field drains pretty quickly although the downside is we sometimes find the clouds forming at ground level. Last Thursday there were actual puddles on the field and the drag through our well trimmed grass was enough for my Vampire to reach terminal velocity before flying speed was reached but by Saturday it had dried enough to reach flying speed rather more easily...although the "slight" increase in wind speed meant that the ground roll was negligible!
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The concern would be voltage depression with several servos under load or stalled rather than average current draw. However, if the maker's data is to be believed, the plugs and wiring are likely to be the limiting factors.
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That rate would be for the purposes of standardised testing rather than a maximum discharge rate. The voltage will drop as the discharge rate increases and that is the critical factor. The site linked shows a maximum discharge capability of 7.5A - in other terms, 3C.
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Years ago, the BMFA News published a simple to use nomograph which I’ve used successfully on a number of occasions. I don’t know if anyone has an electronic copy?
The published CofG should really be a range of positions within which the handling will be acceptable. Where a point is marked on a plan will be the designer’s best guess at a good starting point (or in the case of some ARTFs an arbitrary guess/error!).
The position of an acceptable CofG depends on many factors - primarily the mean chord (this takes into account wing taper and sweep), the effectiveness of the tail (area and moment arm) and personal taste so there’s no “one fits all” solution although it will often be within the 25-33% range on a trainer/sport/scale type platform.
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I experienced that a little after 9am. I’ll flag it to the IT team. First time for weeks though.
Galaxy/Pegasus Hurricane
in All Things Model Flying
Posted
And I thought mine was weighty!