Cool running Part II

Saturday 22nd

Another clear day , temp about 10′ and as per usual around 7-8 knots varying NE/E

Start up fine again and the 7-8 mins to get oil up to around 35′ so good to start the taxi as it’s the opposite end of the runway for 08 from the aero club

Brakes holding well now on power checks .. Was creeping a little before .. Maybe the newish pads are bedding in.

Continue reading “Cool running Part II”

Cool running

Following some great input and advice from Paul HS at TLAC and Danny’s feedback I re shaped the input holes and also scaled up the exit.

Having a long frustrating wait for both workload – which included a pop from Jersey to Fairoaks and back – such a friendly team at Fairoaks and so helpful .. Where else can you order a taxi 5 miles out ! … Workload AND weather ! Been pretty breezy in Jersey over recent weeks and just too much for early flights.

Friday 21st October .. Planned to finish work early and get up to the hangar … Of course that didn’t work and got stuck in meetings meaning I didn’t get up until pretty late. By the time I had the wings out and pegged (that’s getting easier each time as the pegs bed in) and then climbed aboard after the full walk around check .. Air Traffic advise me that it was 2 minutes to sunset !

It was certainly feeling cool and moist …

I used both carb heat elements on start up and this was pretty un eventful .. And sat .. Whilst negotiating a slot – which Jersey ATC give without hesitation ..

Outside temp was about 10′ so it would be interesting to see how long the engine oil temp takes to come up to 50′ .. Used to be about 5 mins .. Has now extended to 10 mins which is absolutely fine … But THIS evening I hadn’t got too long .. Don’t have lights (yet !)

Started the roll and it was def starting to look dark as the effect of 100’s of runway lights made the sky look pretty gloomy

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Pulled away and straight up to 3,200 rpm … And all fine temp wise. Kept a fairly tight (bad weather) right hand circuit off 08 runway at Jersey which put me close to but south of tower… First touch and go .. Waited for tail to settle and speed to come down then up again … The oil temp was now settled at 90′ and stayed put all the way around , regardless of throttle .. HAPPY DAYS … As Paul says .. Don’t get cocky 😄 As if !

seriously though .. This means I can take the next steady step … And run a few more circuits like this and then plan for another over the runway power climb test .. See next blog entry …

On landing the tower very kindly said “Looking great” which is nice .. I then slowed her down and managed to mess up breaking again … Done this twice now .. So she suddenly starting heading left as I couldn’t get right breaking.. Managed a full ground loop .. Embarrassing but calm, settle .. Turn her around and get off the active runway back to base

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Good shared knowledge – Danny Baker

Many thanks to another Sherwood builder (Danny) for sharing these pictures with me …

Shows I’ve got a few more hours work to perfect the re-modelling of the top cowl.

Looking at these – Danny has made a great job of modelling the intakes and make a very smooth entry … I now realise what’s involved to ensure a SMOOTH intake flow rather than the abrupt angles I have which I guess cause turbulence under differing in line speeds !

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I can also see, from Danny’s measurements that I am about 5-6cm smaller in BOTH height AND width !

I was feeling that I shouldn’t ingress into the part where the top and bottom overlap but Danny has made an excellent job of re-shaping that.

Time for some careful dremel work and tape up tests … then off with the cowl for filling and smoothing and re-painting once my temps are back where they should be under power.

Cheers Danny 🙂

One hour test flights and circuits

Sunday 2nd saw some good weather .. Crosswind of course but used to that by now ..

Nice photos captured by the local Jersey photographer Mike Illian .. He’s got a real eye for a photo

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Noticed I am still flying with a couple of under tail access holes open as I await the painting of the alloy circular discs

Cooling – First steps

OK .. So it looks like my first stab at cooling was way too conservative … My start up and warm up are pretty short term affairs .. Getting up to temps (50 ‘ oil temp) in about 5 mins of taxiing

The cooling however, is not brilliant after my first (tentative) hole cut

The problem at the moment is that initial climb out power at around 3200 is fine on first run .. Subsequent circuits it starts to get hot.

As Paul HS advised .. Do small things in steps so that you can monitor the effect of each change in a controlled way.

First step was to open my neat but woefully small cheek inlets (cheeky .. But hey .. It has to be done !)

image Started to widen this out proportionally

image Good old gaffa tape comes into play as a temporary air dam

image Not particularly elegant … YET … Plan to open it out and neaten the entry duct .. Also investigate NACA

If these are being opened I should enlarge the lower exit hole which was largely blocked by the oil cooler matrix and pipe work.

 

Cooling – a hot subject !

Cooling is clearly a tricky subject that is not really open to novices … Like me ….

Having reviewed the back section of the Jabiru 2200 engine manual it is very useful BUT it refers to the 2200 engine going into a Jabiru aircraft ! clearly they can’t put all scenarios but it does provide useful overview and pointers.

I elected to call the oracle .. Paul H S … And this has opened up a fascinating subject

Clearly no definite right answers as each design, build, tweak could mean and drive a different result.

The initial summary for now is

  • my dinky neat looking ‘eyelet’ type intakes on the cowl cheeks are probably too small
  • i have fitted internal cylinder head shrouds and rubbers
  • these mate nicely with the cowl so no air bleed BUT the small openings mean a reasonable (significant) amount is shrouded
  • plan is to Dremel out these BUT still stay within rubbers to preserve ram air effect
  • trimming these out will probably increase INPUT flow by around 20%
  • the fun part of all this is the dynamics that will leave in the cowl in terms of pressure and exit capability
  • i love engineering !
  • so as well as enlarging these I plan to tape up the lower pre moulded hole in the cowl which is there for those designs where you place the oil cooler matrix up front .. And mine is in a scoop underneath
  • this means that I have an open hole in the front, albeit blowing onto the sump – which in my MGB engineering mind was good .. But in an enclosed aero cowl that works on pressures isn’t particularly good !
  • blocking this up may help that ‘equation’ and I at least know from the 10 circuits I have done I can prove this in probably 2 circuits !
  • next steps will be to review me air exit path and how large that needs to be ..
  • small steps .. Small steps … But all POSITIVE !

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This ‘plane keeps on giving … So much to learn .. So much interesting stuff !

 

Test flying continued – Hot

Sunday 2nd October finally brought some lovely calm clear weather .. The 30+ westerlies of the previous day were met with a F2 albeit from the North .. So yet another cross wind sequence if flying tests !

initial runway was 08 then switched to 26 (over the cliff and bay)

Having now cracked the RPM gauge and battery charging – located to one mislocated wire on my part ! this was going to be a good test day.

Start up was its usual burst into life and taxi out fine and line up. Straight off, getting the ball in the centre … Nice and straight climb out catering for the 8-10kt from 90′ left.

Felt brave enough to do my first wing over left turn into the bad weather close circuit .. And sailed downwind for a nice wide normal approach and touch and go over the cliff. Around for a second as soon as I had let the tail come down and settle true and straight.

Powered away and checked pressure and temps as temp looked a little high .. Around 110 … I noticed as I eased off the temp went back down but when I applied 2600 or more it went up proportionally … Eased back and levelled off at around 700′ and then downwind and fine .. Offered to orbit right a couple of times to let other traffic away and 2 departed .. Then back for landing.

Short stop for coffee and cool down and check everything. All looked fine so up and away again. This time the engine was already warm so went through 70, 80, 90 in the climb quite quickly, then onwards.

Called the tower and said I would make this one a shorter .. And they said ok call final .. And I opted for no .. Like really shorter and they asked if I wanted to declare an emergency !

As she was still clearly flying and on pulling throttle back she instantly cooled I declined the emergency but landed on a tight left turn with no drama …

Back at the club, cowls off and started to check .. No loose pipes, no oil signs, level fine … One pipe to matrix hot, the other quite cool .. So checked the temps on a static ground run for 20 mins and all fine .. So maybe this is the first time the TOCA oil thermostat has opened ?

Back for another run and this time flew for around 30 mins watching the temps and pressure like a hawk !

The temps would climb rapidly as soon as I put in a chunk of power but stabilises when around 2,500

Elected to do 2 bad weather circuits then a wider around the bay and back. I felt I was nursing a heat problem so elected to land and investigate further.

 

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