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Member postings for Peter Christy

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

Thread: Peter Valentine's experimental helis
16/04/2020 16:01:20

Here's some pix of the Lark-E, currently under construction:

Haven't fitted the tail-rotor servo yet as I haven't decided how to route the linkage. As it won't have a throttle servo, I have a bit more flexibility in how to mount the servo and route the linkage. I should be able to make it a bit more direct.

Still quite a bit to do, and a few things to undo and redo properly! wink

I renovated John Haytree's old Schluter Cobra a while back and converted it to electric. It flies much better like that than it ever did i/c! I'm hoping the Lark will be the same!




16/04/2020 14:58:07

Hi Barrie,

Yes, its the colour of the plastic housing that's confusing me! I have a TeeDee.049 and a TeeDee.09 - both black. I used to have a Medallion 09 (red), but the medallions didn't have a screw-in venturi. It was moulded into the housing, with a conventional spray-bar.

So this is either a TeeDee 051, or a Medallion 049 fitted with a TeeDee housing to take the Tarno carb! Your guess is as good as mine! wink

I think with LiPos and a brushless motor, the Lark should fly OK. I'm hoping to get it airborne on 3S, but I can use 4S if needs be. In the latter case, I may change the gearing slightly to draw more power from the motor for 3s operation.

Martin Briggs has made one like this, but his needed 4S. I think he used different gearing to me, though. So far he's only hopped it in the garden because of the lockdown.

Mine was a present from my son! He found it on ebay, part built. Unfortunately the builder has made a bit of a dog's dinner of the tail-rotor gearbox, which I will have to dismantle and rebuild. I'm also going to have to make some tail blades and recover some of the other wooden bits. I hope to have it ready for preliminary testing in a couple of weeks time.



Thread: RC IC Engines, you've probably never heard of.
16/04/2020 11:58:40

Barrie: To avoid hijacking this thread, I've started a fresh one, with details and pix of some of the bits I inherited from Peter Valentine.

I've also got his electric "MayFly" - which didn't due to the nicad battery pack and brushed motor of the time. It might be possible to retro fit it with a brushless setup, although that won't be easy as the brushed motor had a reduction gearbox fitted!

I'm currently building an electric Lark Mk2, and hope to have it ready to run up in the garden in a couple of weeks....



Thread: Peter Valentine's experimental helis
16/04/2020 11:52:34

In another thread **LINK** , Barrie Lever was asking about Peter Valentine's Cox .049 powered "MayFly".

That model flew very successfully, although in pre-gyro days, the tail was more than a little twitchy!

It was eventually donated to the Goosedale museum, and disappeared when Goosedale closed.

Shortly before he died, Peter had started work on another 049 powered model, and I have the chassis in my collection:

Power is a Cox Medallion .049 fitted with a Tarno carb (It may be a TeeDee .049 - haven't had a look inside to see!)

It should be possible to finish the model off, if i can persuade a metal-working friend to make all the bits, but it will be a long job!

Peter also made an 020 powered heli:

Because of the difficulty in throttling such a small engine, it was designed to run flat out all the time and be flown on collective pitch. The collective system is pure Bell (no Hiller mixing).

Alas, it proved impossible to build a centrifugal clutch that small, that wouldn't slip. When he tried direct drive (no clutch) it proved impossible to start the engine, due to the inertia in the rotor system.

An interesting experiment, though!

He also built an electric "MayFly", which survives in good condition. Alas, the combination of Nicad batteries and the brushed motor proved inadequate for lift off. However, it should be possible to retro fit a brushless motor, though it will require a bit of re-engineering! (The brushed motor had a built in gearbox).

My present project is a Lark Mk2, converted to electric. I'm hoping this will be ready for preliminary run-ups in the garden in a couple of weeks. Full test flying will have to await the end of the lockdown....




Edited By Peter Christy on 16/04/2020 11:52:48

Edited By Peter Christy on 16/04/2020 11:54:21

Thread: RC IC Engines, you've probably never heard of.
16/04/2020 08:08:14
Posted by Barrie Lever on 15/04/2020 21:05:59:
Posted by Peter Christy on 15/04/2020 19:04:58:

My first MicroMold Lark flew with a Veco 19!





At around that time I seem to have memories of seeing a chap flying a heli with power by a Cox 049, his name might have been Peter Valentine, do you remember that?


Yes indeed! Peter Valentine was a fellow club member at the Watford Wayfarers, and a very good friend of mine!

When I first met him, he was flying an OS10 (1.5cc) powered version of the "MayFly" - slightly larger than the .049 powered one. At the time, the only helicopter kits available were the Schluter, Kavan and Graupner ones, all German, all for 61 power and all huge! Many experts didn't believe that smaller machines were possible!

The smaller .049 powered one followed the OS 10 version. There were no gyros back then, so they were quite twitchy on the tail! He eventually donated it to the Goosedale museum, and it disappeared when that closed. He was working on another set of .049 mechanics when he died, and I have the central chassis of it in my collection.

He also made one powered by a Cox .020, but never managed to get it to fly. He couldn't make a clutch small enough that wouldn't slip! He did try a direct drive version, without a clutch, but it proved impossible to start!

Around 8'50" into this video is some fairly blurry footage of the .049 powered heli at RAF Odiham:

I've recently re-digitised some of that 8mm film in better quality, and really ought to get round to re-making those videos!
Meanwhile, back on topic, down in my garage I have a Veron Colt control-line trainer, built to teach my kids to fly nearly 40 years ago! Its powered by a KingCat diesel. A very pretty little engine in appearance, but couldn't pull the skin off a rice pudding! Just about adequate for the Colt trainer, though......

Edited By Peter Christy on 16/04/2020 08:10:34

15/04/2020 19:04:58

My first MicroMold Lark flew with a Veco 19!



Thread: Aerial positioning
15/04/2020 10:21:03

Re: Single wire aerials...

Because these aerials are a "resonant length", and also more rigid than the "dangly wires" of old, the dead spots off the end tend to be sharper and deeper than 35 MHz receivers.

Having said that, they are much more efficient. Also the rate of data transmission is much higher than the old PPM / PCM systems, so any drop-outs tend to be of shorter duration. The way the data is transmitted is also much more robust than even PCM could achieve, so any drop-outs will be easier to disguise.

They may still happen, but you are unlikely to notice them - unless you scrutinise the RSSI logs carefully! wink



Thread: RC IC Engines, you've probably never heard of.
14/04/2020 19:02:06

A few years back, I had an "AirSupply" .40 engine in a helicopter. I believe it was made in Japan.

I tried it on my usual 16% nitro heli fuel, and it didn't like it at all! Switched to straight (no nitro), and it ran like a turbine! Unusual, as Japanese engines usually like their nitro....!



Thread: Aerial positioning
14/04/2020 14:47:13

I don't normally have mine poking outside the airframe. Balsa and fibreglass are pretty transparent to RF! I usually have a couple of plastic tubes, or even drinking straws, glued somewhere convenient inside the fuselage, and poke 'em down those.

Having them "out in the breeze" makes them more prone to unnecessary bending and damage. Keeping them inside the fuselage protects them, and won't have any significant impact on range.

The one caveat to the above statement is where carbon fibre, or any other kind of electrically conductive material (sheet aluminium, even silver foil) is present. These can make a very effective screen against RF, and aerials should not be placed nearby.



14/04/2020 08:41:13

I agree with leccyflyer about drilling a small hole and putting one pointing vertically downwards.

Its difficult to tell from the picture, but it looks as if the other aerial ought to be short enough to go transverse across the fuselage, between the receiver and servos.

Alternatively, again, poke one down vertically and move the one alongside the battery back so its alongside the receiver.

The whole point of having two aerials is so that if one is either screened or poorly orientated wrt the transmitter, the other will take over. In any model, this is bound to happen at some stage of the flight, so don't worry too much about it.

These systems typically have an in-the-air range of a few kilometers, so even with a relatively poor installation, you should have range beyond the limits of your ability to see it adequately!

Its always worth removing the prop and doing a ground range check with the motor running if you have any worries, but I'll be surprised if you have any problems.



13/04/2020 22:27:54

Ideally, a monopole aerial (usually 1/4 wavelength) should be mounted vertically over a ground plane (a large area of metal, relative to a wavelength). The metal ground plane acts as a reflector, so that the monopole looks like a dipole, in the same way that standing a pencil on a mirror looks like two pencils end to end.

The more usual "bare-wire" aerials use the braid as the reflector, which is not terribly efficient. The sleeve dipole is a neat way of providing a genuine dipole aerial with a minimum of problems feeding it.

However, bear in mind that even the basic, wire ended aerial is still much more efficient than the dangly bit of wire which we used on 27 / 35 MHz! And on those frequencies we were also limited to 100mW ERP transmitted output. So any of the current crop of 2.4 GHz aerials will provide much superior performance to that achieved in days of yore, when we rarely had any range issues!

Sometimes it doesn't pay to worry too much over these things! wink



13/04/2020 15:42:55

Bob is right. That looks like a centre-fed dipole to me, with one of the two elements "sleeving" the co-ax feeder.

Ideally the two should be at 90 degrees, but its not super-critical. Anything better than 60 degrees will usually do in practice, but the nearer 90, the better.

I usually try and get one of them vertical in the fuselage somewhere, and the other either length-wise down the fuselage or across it. This is usually possible in even quite small models.

Hope this helps!



Thread: Taurus retro aerobatic build
09/04/2020 16:10:37

Here's some tank bay detail on mine:

The hatch is held in place (very securely!) by 3 magnets, two at the back and one at the front, making access a doddle!

The hatch itself is part block, part built up:

I built it square initially, installed the magnets, and then carved it to shape once it could be "installed".

The floor of the tank bay is screwed to bearers for access to the steerable nosewheel linkage:

My nosewheel is bolted to the rear of the firewall (just visible at the front of the tank bay), with the linkage under the floor and out of sight.

I use the rudder servo for the nosewheel too:

(topmost in the frame)

The linkage has a large Z-bend under the tank, which takes the piano-wire pushrod from one side of the fuselage to the other. This provides the necessary springiness to protect the servo, but still provides surprisingly accurate steering control on the ground.




Edited By Peter Christy on 09/04/2020 16:12:14

Thread: Liability of Open Source radios
08/04/2020 11:43:09

Whilst it may (in theory) be possible to increase the power output of any system (even 35 MHz!), the extra output available at 2.4 GHz is trivial.

Going from 100 to 200 mW may sound a lot, but a more accurate way of perceiving it is by the dBm figure. 100mW=20dBm, 200mW=23dBm. The dBm figure is a far more realistic way of imagining the increase.

You will get a similar increase just by replacing the standard antenna (2dB gain) with a "high gain" one (typically 5dB gain - a similar 3dB increase!), without ever having to adjust the Tx at all. And that applies to ANY transmitter, Open Source or not.

All the transmitters I have looked at have a typical output of 60mW. The 2dB gain of the antenna raises this to 100mW erp (Effective Radiated Power). It does this by concentrating the RF output in a specific direction, a bit like a torch bulb being "brightened" by placing a reflector behind it - but only in a specific direction.

The higher the gain of the antenna, the more directional it becomes, so higher gains do not necessarily improve performance in our application.

Note: What I am talking about here is "squishing" the doughnut shaped radiation pattern of a typical RC antenna, ie: making the "dead spot" off the tip deeper and wider.

In practice, yes, increasing the output of the transmitter by either a firmware tweak (not trivial!) or using a higher gain antenna (simple!) does break the regulations.

The likely impact of a 3dB increase in power on other users in a typical model club environment approximates to - er - zero! The likely advantage of such an increase to the user approximates to - er - zero! In the case of high gain antennas, the narrower beam of the signal may well prove detrimental!

Note that I am NOT recommending modifying the RF output of our transmitters. 100mW / 20dBm is more than adequate for our purposes, and increasing it does not do our reputation with the powers-that-be any good, at a time when we need all the friends that we can get!

The only system I know of that actually offers 200 mW is (or was?) Spektrum - which is NOT open source! The US versions do - or certainly did at one time - use 200mW, as permitted by FCC regulations. EU versions are restricted to 100mW, but of course if someone grey imports a US spec set........



Thread: Taurus retro aerobatic build
08/04/2020 08:45:46

My KingPin follows a very similar method of construction for the fuselage. I made the decking over the tank detachable, held in place by magnets, rather than cut a hole in the bulkhead for rank access. This meant I could seal the tank bay from the rest of the fuselage. I've had tanks leak in the past, and soak the radio gear in fuel!

This made it a lot easier to hollow out that bit for tank clearance! In fact, IIRC, I built it up.

I also got the linkage for the steerable nosewheel to go internally, under the floor of the tank bay. The floor is removable for access if required.

I'll see if I can get some pix and put them up later.



Thread: Pink and Purple Super Sixty
08/04/2020 08:37:15
Posted by kevin b on 07/04/2020 19:00:33:
Posted by Peter Christy on 07/04/2020 17:25:21:

I would hesitate to cover a Super 60 in film! Nylon or Solartex (if you can find any) would be much more suitable. I had a nylon covered one for many years. It was only a high-speed argument with a barbed-wire fence that finally destroyed it! blush



Super 60 - High speed ?

Isn't that a contradiction ?

Did the wing come off and it plummeted to the ground (followed by the wing, several minutes later).

This was back in the days of reed equipment (pre-proportional control). Unbeknownst to me, I had an iffy DEAC pack powering the receiver. I lost contact with the model and it started to fly away. When it was a LONG way away, I regained control and managed to shut the throttle. I also applied full rudder and put it in a tight and fast spiral dive. When I guessed it was about 50ft or so up, I applied opposite rudder and full up elevator. It actually pulled out about two or three feet of the ground, doing some considerable speed, and went straight through a barbed wire fence! Not a lot left, though the Merco 35, receiver and servos were completely undamaged!

After replacing all the battery packs (one for the receiver and one for the servos), the radio never gave any further trouble, but it was too late for my poor old Super 60!

Its amazing how fast they can go in a spiral dive! surprise



07/04/2020 17:25:21

I would hesitate to cover a Super 60 in film! Nylon or Solartex (if you can find any) would be much more suitable. I had a nylon covered one for many years. It was only a high-speed argument with a barbed-wire fence that finally destroyed it! blush



Thread: Vertigo
06/04/2020 14:57:41

I remember seeing Frank Van Den Bergh fly the original Vertigo in aerobatics at the nationals in the late 60s. It was the first time I'd ever seen a model *accelerate* vertically upwards!

He didn't win (IIRC!), but he did leave a lasting impression on a teenage me!




Thread: Liability of Open Source radios
06/04/2020 14:53:32

I'm not sure what the difference is between Open Source and proprietary code in this case. I can't think of a single instance being reported where Futaba, Jr or any other manufacturer has been held responsible for an accident involving RC gear.

Hardware failure is a far more likely scenario than software failure, and in the past its proven almost impossible to claim for incurred losses even when a demonstrable hardware failure has occurred. When such cases have occurred, the manufacturer has offered to repair the radio gear (usually FOC), but the loss of the model or any other damages is down to the owner and his/her insurance where appropriate.

One of the beauties of open source is that far many more eyes are examining the code than is the case with proprietary software, and when faults are found, they are usually fixed much more rapidly.



Thread: Cox 0,49 vs PAW 80
06/04/2020 09:26:03

I've got loads of Coxs and a PAW 80. My observations: The PAW is heavier and doesn't have an integral tank, as many Coxs do. It doesn't lose as much power when silenced, and is much quieter either silenced or not. Special piston and liners are available for Coxs with an extra transfer port (like the TeeDee) and no sub-piston induction, which brings the power back to (almost) un-silenced levels.

Although the PAW 80 will swing a bigger prop (7x4), it is much happier on a 6x4 - same as the Cox.

But the real killer is starting! The Cox is MUCH easier to start! My PAW 80 is a little brute to get going! I can be there flipping it for ages, without a pop or a bang from it, and priming it is just asking for a painful back-fire! The tiny size of the prop makes it difficult to use any kind of finger protection, and I have received more (and deeper!) cuts from the PAW than I have ever got from a Cox!

It also flatly refuses to start on D-1000 (so-called "easy start" fuel!). It is much better on D-2000, and even better on D-3000, though that isn't recommended for plain bearing engines. (Any comments on this Jon-Laser?)

The easiest way to start it is with some kind of electric starter, but you need to be VERY careful doing this! Most electric starters are way too powerful, and will bend the conrod (at least) if you flood it!

Its a shame no-one makes an electric starter for small engines (based on a 540 or smaller motor, perhaps?), as this would solve many of the problems.

Don't think I'm anti-diesel - I'm not - at least not in model aeroplanes! (Cars are another matter!) I've got quite a few diesels, AM15s, a KingCat, and several PAW 149s. In contrast to the 80, the PAW 149s are little jewels of engines! Easy to start (as long as you don't use D-1000!), quiet and they throttle extremely well.



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