Monday, 31 December 2012

The prop is installed!

Having decided that with the vile weather I wasn't going to get any more flying done in 2012, I instead had a very successful day at the airport today messing around with the new prop.

It was a strange feeling removing the existing fixed pitch propeller from JONL. After all, it has propelled JONL and its self loading freight for over 200 hours of fun flying. It's an interesting question what to do with it - I think I will keep it, in case it ever becomes necessary to revert.

Anyway, it was simple enough to remove the old prop and I took the opportunity to give the flange and surrounding metalwork a good clean. I paid particular attention to the hollow power shaft, as this has to provide a good hydraulic fluid seal at each end for the prop pitch control system.

The next task was to install the rotating hydraulic joint, carefully oiling the rubber seals and pushing the joint fully home. This seal is extremely important as any leak will reduce the efficiency of the prop pitch controller and, annoyingly, cover the engine in hydraulic oil! The rotating joint was completed at the propeller end by a cap with holes for the hydraulic fluid and a nylock nut.

Fitting the propeller came next. Firstly the spinner flange was attached to the propeller. It was then necessary to install six bushes in the power flange. These bushes provide two functions: firstly they ensure extremely accurate registration of the propeller as the bushes interlock with milled recesses in the propeller faceplate. They also reduce the size of the hole in the engine power flange to the correct dimensions for the captive propeller bolts. They were a very tight fit in the power flange! It took several attempts to get them all fully home, assisted by a little lubricant.

With the the bushes installed, it was finally time to fit the prop! There is an oil seal on the propeller that sits on the engine power flange and this was carefully cleaned and oiled. A leak here would be less problematic than at the rotating joint but it would still be a nuisance, so I did everything I could to ensure a good seal, cleaning the flange and lubricating it well.

The prop fitted easily and perfectly on the power flange, engaging with the six bushes, which held it firmly in place whilst the prop nylock nuts and washers were attached. The nuts were torqued up to the required tightness and there we were, propeller installed!

Not quite though! Now to sort out the hydraulics.I connected the hydraulic line from the electro-hydraulic pump to the rotating joint easily enough. Now to fill it with hydraulic oil.

Received wisdom is that the way to do this is using an empty sealant cartridge as an oil reservoir. The applicator is a perfect fit in the filler hole and it provides a small head of oil pressure to help drive out the air. It's also generally agreed that it helps to lift the nose of the aircraft so as to get a greater head, so I did that as well.

I poured a small amount of hydraulic oil into the cartridge and watched with satisfaction as it slowly drained into the system. More oil! Now, exercising the electro-hydraulic pump the oil gradually filled the hydraulic pipe and started running into the pump. It took a while but eventually all the air had bubbled out and the system was full of hydraulic fluid. Removing the cartridge reservoir without getting oil all over the prop was a challenge. I was only partly successful!
The screw cap that closes the filler hole turned out to be a bit of a challenge. It needs to be screwed down very tight otherwise hydraulic fluid seeps out when the system is put under pressure. Eventually I had a oil-tight system and could now play with the pitch control.

It works! In manual mode I was able to adjust the propeller pitch from the Flybox controller, demonstrating the range from fully fine to fully coarse. It seems like such a simple thing but it is the culmination of several months of planning and quite a lot of engineering work, so it was extremely satisfying.


By now it was getting dark, so it was too late to do any ground runs. I spoke with Tom, my inspector and he will come down on Wednesday (two days from now) to check out my handiwork and, hopefully sign everything off. I can then get on with the ground runs and flight testing as time and weather permit.

Not a bad note to end 2012 on. Happy New Year to all my followers and see you in 2013 for an update on the flight trials!

Thursday, 27 December 2012

Just need to fit the prop now...

With the lousy weather, Christmas and all that, progress has been slow but nevertheless I am now ready to fit my new VP propeller. All the preparatory work is completed and I have a permit to test fly the new prop that is valid until 17-Jan-2013, which hopefully should be long enough for me to get the prop fitted, inspected, released for test flying and, at long last, flying.

The last preparatory item to be completed was the installation and testing of the propeller speed control. I spent a lot of time trying to find a way to incorporate a quadrant-style control lever, in the belief that this would be more consistent with the existing throttle layout and also more intuitive in use. However, the mechanics, given the space available and the position of the throttle and (especially) choke controls eluded me in the end.

I have therefore reverted to the original plan, which was to use a linear (slider) pot and mount it alongside the throttle/choke levers. There is plenty of space for this and the end result looks fine. More to the point it also feels fine from an ergonomic point of view.

The blue throttle control knob posed an interesting challenge. Firstly, where to get one? This turns out to be difficult and ridiculously expensive, in the way that parts for C of A aircraft usually are. In the end, I decided to obtain a cheap flight simulator control quadrant and steal the blue knob from that.

I then had to fabricate a metal collet to fit onto the slider pot control lever and create a snug fit into the much larger mounting slot on the blue knob. A bit of work with some rectangular aluminium rod soon yielded a very satisfactory, robust solution.

The result looks pretty good, I think. As required by the LAA, the lever is fully labelled and the picture shows the finished article installed installed in G-JONL.

With the wiring completed I was then able to calibrate the controller to set the max/min speed ranges that the control can select. The maximum is a known quantity, 5800PRM and, in fact, that is actually the limit set in the Flybox controller, since that is the specification for the Rotax engine. For the time being I have set the minimum as 4600RPM, although I don't think I will ever want to select such a low speed cruise RPM. This will, of course, all be sorted out in the test flying programme.

So, I'm ready to go with fitting the prop. The weather is wet but mild over the next few days, so that seems like an ideal time to get moving!

Friday, 21 December 2012

LED landing light

I've always envisaged fitting a landing light to JONL, not so much in anticipation of night flying, which is, of course, not permitted in permit aircraft, but rather as an aid to visibility.

To that end I installed the necessary wiring, switch and contact breaker as part of the original build. However, when it came to installation, back in early 2010 I was unable to find a suitable LED light that combined high output with small size and reasonable cost, so I left it as an installation option for later.

At this year's LAA rally I came across a new vendor, Bailey Strobes, who had just what I wanted. An LED that is compact yet very bright and with a mounting that would be suitable for attaching to the underside on the engine cowling. A unit was immediately purchased and about three weeks later arrived at home, where it has waited patiently for me to get round to fitting it.

The time has come! Last week I installed the LED housing on JONL and then set about mounting and aligning the LED. The result is very satisfactory. A quick test flight followed and ATC reported that the light is bright and has good beam width.

Another little job completed! Now all we need is for permit aircraft to be allowed to fly at night.

Tuesday, 11 December 2012

Slow progress

It's really been too cold to get much work done on the new propeller.

Nevertheless, I did spend some time yesterday on a revised mounting arrangement for the propeller speed control. This is slightly awkward as there isn't a lot of room in the area around the throttle. An earlier design turned out to be no good, as it put the new prop control lever too close to the throttle/choke levers.

Anyway, it looks as if the new mounting arrangement will be OK, so today I am doing the associated electrical wiring. The prop control is actually a 5kΩ linear potentiometer to which I will attach a lever with a friction device to stop it flopping around too much. The controller can be configured for any range of movement, so although it is a 270° potentiometer, there is no problem with only using around 80° of arc as the control range.

Meanwhile, I've put the spinner in for painting at my local shop and should have that back some time in the next week to ten days.

It's starting to look like fitting the propeller will have to wait until the new year now. Not really a problem - the aeroplane is flyable as it is with the current propeller, so there is no real imperative to rush things.