Monday, 30 March 2020

Aerobatics FUUN

The final video that will form part of the TV/Slideshow for Friedrichshafen 2021.


FUUN with friends

Another short video that will form part of my TV/Slideshow at Friedrichshafen 2021.


Tuesday, 24 March 2020

Twister 2.0 - Unlimited Aeros capable?

Could the Twister be modified to be capable of Unlimited Aerobatics competition?

We think so.

So long as endurance is not your prerogative then with an electric motor of 200kW+ and modifications to the control surfaces - specifically the Ailerons - larger and with a horn balance to increase their 'throw' - and a larger elevator, again with horn balance (these act as 'power assistance' to the controls in place of spades) then it's quite possible a Twister could compete at Unlimited level.

Below are three pics.

The first is a 'mild' upgrade with no new molds or major changes to existing layout needed. The flaps are gone and have been replaced with full span Ailerons.

These ailerons also have a horn balance on the outboard section, which is where the mass-balancing weight would now be so that 'throw' is not limited as it currently is by being inside the wing. The outboard hinge is in the same location but on the inboard section of the tip rather than outboard as is normal on a Twister.

The elevators are a little larger in area, also with a horn balance. 

The rudder remains unchanged. The standard rudder in a Twister is already very powerful and overly sensitive compared to the other controls - due to it's too large horn balance - but ideally suited to this more extreme version.

'Mild' version of an Unlimited Twister.

The second version, below, is a more extreme version with a larger aileron surface area - particularly on the outboard area (where it has the most effect). The inboard section of the wing has been left without a control surface (as per the Extra 300SC).

The roll rate for this version would be 400 degrees per second. Roll rate being a function of aileron area and 'throw', coupled to wingspan (wing area ultimately).

The elevators are also larger for more rapid 'Flick rolls' and more control at lower speeds.

More Extreme version with 400 degree per second roll rate and greater speed of flicks.

The final image shows this extreme version overlaid with an Extra 330SC (currently considered to be the ultimate Unlimited aircraft, and with identical wingspan to a Twister at 7.5m). As you can see the ailerons are now of similar size. The elevators don't need to be as big because the Twister is considerably lighter than the Extra (approx half the weight).

Extreme version with Extra 330SC overlay.

Overall the Twister would need to be strengthened considerably so that it could deal with the increased G forces but also the expected higher Va and Vne needed to compete at this level of competition. This will add weight of course but I still don't think it would be as heavy as the steel framed Extra with it's heavy Lycoming 580. The power to weight ratio would be comparable or better than the Extra.

Sunday, 8 March 2020

Building FUUN video

5.5 years and 3,000 workshop hours compressed into about 2 mins of building G-FUUN.


Oshkosh Epic Adventure video

I finally got around to making a short video of my 'Epic Adventure' from 2017.


Monday, 3 February 2020

UL engine work

As explained in my post from August of last year, when I did my 400 hr service, there were a few outstanding maintenance items that I wanted to get done this Winter.

I managed to get organised a couple of weeks ago and flew up to Metal Seagulls (the UK, UL Power Agent) at Sleap airfield to get this done.

The two main items to fix were the leaking exhaust valve on Cyl 3 (with it's loss of compression) and the upgrade of the Throttle Position Sensor to the new 'Hall' Type sensor.

While I was up there, as my annual inspection was almost due, I got that done too. G-FUUN passed again without comment.

Then while we were waiting for parts to arrive back a Service Bulletin was issued regarding the Oil Thermostat failing. Good timing! The issue was the smaller of the two springs inside the Thermostat was breaking. The fix was a new grade of springs and those parts were supplied free in the UK by Metal Seagulls. 

Whilst I was taking the old thermostat springs out it was obvious that the small one had broken yet again - see pic. So that is a total of 3 failures for me with the oil thermostat. Hopefully the new springs will do the job and we won't have it fail again. I am lucky that my engine runs so cool I can actually still fly without the oil cooler working - it's certainly not a problem in the Winter although I would not want to fly without my cooler operating in the Summer.

Onto the two main issues.

The throttle sensor replacement was fairly straightforward. The biggest pain was removing my ECU as I have it located up under the footwell area of the safety cell so it's out with the instrument panel and then an awkward reach to undo the bolts. No matter, it is only the first time it's been out since it was put there and I don't envisage having to take it out ever again.

The ECU has to be removed because it has to be sent to Belgium to have it's firmware upgraded to 'talk' to the new throttle sensor type.

The whole throttle body was removed and replaced with the new body and sensor. There is also an intermediary connector to fit which converts the round plug of the new sensor into the 3 pin plug of the old connector. 

Of course the idle then needed adjusting once the engine was warmed up.

All seems well with it, although I did notice a hesitation from the engine when the throttle is moved rapidly. Slower movements are better. There was always a hesitation with the old style throttle when going from high idle to full power at take off but this new throttle seems to suffer from the brief hesitation at any setting change if done too rapidly.

Finally onto the Exhaust valve for Cyl number 3. There was a discussion with Jonathan about whether to repair or replace. In the end we decided to replace the whole head as the amount of labour involved to fix it ends up being almost the same as a new head. Also there was the problem of the leaking gasket on this head which had been there from new so it became a 'no-brainer' to replace the head to fix this issue at the same time.

All seems well so far. I need to fly it a bit more to let the head settle down but it seems to run well so far.

Hopefully we will have a good season of flying without any more issues. Fingers crossed.

At Metal Seagulls hangar for the work.
New Throttle Position Sensor, Made in the UK!
New parts. Throttle body and Hall type position sensor and the Oil Thermostat springs
The broken smaller spring from the Oil Thermostat

Detail view of the area where the leaking head gasket let combustion byproducts seep out.
General view of the old cylinder head from Number 3. 

Detail view of the Exhaust valve seat. It seems it was the valve rather than the seat that was damaged.

Exhaust valve showing evidence of damage and leak.
Jonathan cleaning up the gasket area before installing the new head.

General view of the piston and cylinder before the new head goes on.
New Cylinder head in place. Torqued down very carefully and progressively to ensure the gasket seals well and evenly.

The Metal Seagull...

Saturday, 21 December 2019

French Twister article from 2013

For some reason this article had slipped by me until recently. I bought a copy of the magazine and share the article here.

Whilst my French is non-existent I get the impression the author was very impressed with the Twister.

Sunday, 17 November 2019

Trim fail

I had a bit of a scare last week.

Just after take off I heard a 'bang' and had to use more back pressure on the stick than normal to keep the climb attitude the same.

I decided to continue to climb up to a safe altitude - 3,000 ft - before investigating what had gone wrong.

After thinking about it for a little while I concluded that one of the trim springs must have either broken or come loose.

The rest of the flight continued without incident and I made a normal landing. The stick forces were not much more than normal - thankfully the Twister does not really need a trim in the first place as the forces are so light.

That evening I investigated and sure enough the rear spring securing bolt had come right out. 

This explains the stick forward bias as only the front spring was acting against the elevator push rod tube - requiring a constant rearward force to overcome it.

I noticed that the bolt thread did not have evidence of Loctite on it so that is a failure on my part. It's taken just over 400 hours for this to happen.

I've used Loctite this time! And also added TorqueSeal to the outside so that at each annual it can be inspected for movement.

Something to be aware of if you have not used Loctite - but certainly an inspection item (with the TorqueSeal) to add to the Annual if you have already not done so.

After removing the baggage tray it was instantly obvious what had happened. The bolt holding the rear spring had worked loose and come completely out.

Closer view.

After fixing with Loctite on the thread of the bolts and also now with TorqueSeal (in Blue) which will aid inspection.

Saturday, 9 November 2019

New spinner

It has taken me many months but I have finally finished getting a new spinner installed after the old one 'departed company' in May.

In my usual fashion it has been 'modded'. I always found the original design of spinner to be a bit blunt looking compared to the rest of the aircraft, so this was my opportunity to change it's shape.

My boss loaned me an old spinner from his plane and I used that to make a 'splash mold' part off the front of it. I then combined that part with a replacement spinner that was kindly sent by Matthias.

The result is a sharper look - more Mark 9 Spitfire than the old rounded Mark 1 looking spinner.

The other modification is the addition of a front plate. This has added a great deal of rigidity and security to the attachment of the spinner, I feel quite confident it will not come off again!

The front plate is made using the same schedule as the back plate. A 3mm thick sheet of carbon is cut out and drilled to match the bolt holes in the crush plate. Then an angled flange of carbon is added to the edge, projecting forward, giving a large area of contact with the inner front of the spinner.

The spinner was fitted and aligned using a laser level before all the holes were drilled. Then nut plates were fitted to the inside of the front and back plate flanges. 12 on the back plate and 4 on the front plate. I've gone for metric anchor nuts this time round and button head Allen screws with fibre washers underneath for security as I found the Tinnermans with the sprung plate to be unreliable over time.

Everything runs very smoothly now. However I will still do a dynamic balance to see what the vibration levels are and if they can be improved at all.

Regarding the old spinner - the conclusion was that it was a substandard part. 

It was not made by the factory but supplied to me by Hercules propellors using their own mold. They had not followed the same layup schedule as the factory spinner. They only put carbon on the back inch or so where the fasteners go for the backplate - the factory made spinners have carbon all the way up to and beyond the cut outs for the propellor. Therefore the old spinner was vulnerable to cracking in the prop cut out area. 

I believe this is what must have happened, a crack formed and then quickly propagated on the fateful flight, the spinner ripping open once the high pressure air got inside and popped it off, wrenching the fasteners as it went. We will never know for sure exactly what happened as the spinner was disintegrated but the above seems to be the most likely cause. Please check your spinner if you believe it was made by Hercules as they are not fit for purpose.

Original and new shapes compared.
Front plate for added security, micro on the edge was done to form fit to the inside of the spinner.

Side view of front and back plates

All done and looking good

I think this shape of spinner suits the Twister better

Button headed Allen screws with fibre washers underneath with a front plate. This is the same standard used on certified aerobatic aircraft

Sunday, 20 October 2019

First take off of a D-Motor engined Twister

Great news from Germany as the first D-Motor engined Twister takes to the skies for the first time.

Video on this link:

Reports are that all engine parameters stay in the green and with a climb prop they are seeing 1,000 fpm climb rate at 75 knots and 100 knots in level flight at 2,800 rpm (max continuous).

Next test flights will be with a cruise prop.

Monday, 19 August 2019

400 hour service on UL Power engine

For the second 200 hr service I decided to visit the UK UL Power agents, Metal Seagulls, based at Sleap airfield.

Mostly because I wanted Jonathan Porter to look over the engine and also because I do not have the facility to do a compression test on the cylinders, which is called for as part of the 200hr scheduled service.

Jonathan is very knowledgeable and accommodating, readily sharing his wealth of knowledge in an open manner. We are really fortunate to have such a person as the agent for UL Power here in the UK.

We had also planned to look at the cylinder head gasket on number 3 as I had long suspected a slight leak from the head gasket and this certainly had evidence of it throughout its life with a 'spattering' of 'black stuff' (sticky by product of combustion) that continually leaked out and was spattered against the pushrod tubes and inner cowling since the very first 15 hour service up until now. As it turns out the 'black stuff' has reduced quite a lot recently and almost certainly has the effect over time of gumming up any leak to the point where it becomes a non-issue. So Jonathans conclusion was to leave it be.

The service went smoothly with only two issues.

The oil thermostat has failed again (stuck in the closed position so the oil cooler was not being used as part of the oil circuit). It last failed at 278 hours and was replaced with a new part. It failed this time after just another 100 hours at approx 380 hours. I noticed the oil temps again were not coming down as per usual in the cruise and stayed at 103 degrees. I noticed this about 10 hours ago. The oil thermostat has been replaced again (as a warranty item) and oil temps are back to their usual 90-92 degrees in the cruise which is optimal.

The second issue and a more major one is a leaking exhaust valve/seat on Cylinder number 3.

The compression test (done hot) gave these results:

Cylinder 1 - 78/80
Cylinder 2 - 78/80
Cylinder 3 - 69/80 (leaking exhaust valve/seat)
Cylinder 4 - 78/80

For comparison at 200 hrs they were all between 78 - 80 over 80.

An audible hissing could be heard from the exhaust when Cylinder 3 was being tested and putting your hand over the exhaust pipe you could feel and hear the difference, confirming that it was the exhaust valve/seat that was leaking.

This ties in with what Pete Wells was telling me recently - that the UL 260 cylinders are only good for approx 400 hours then they begin to fail. Especially at the exhaust valve/seat area.

So this is happening to me also despite me using the Decalin additive which helps to break down the lead in AvGas into a powder so it does not stick on the valve and damage the seat.

Lycomings and Continentals do not have this problem as they run much hotter CHT's and also they must have different metallurgy in the valve seats to cope with lead deposits. UL Power have made an aircraft engine which will not run reliably to TBO with AvGas - which is kind of ridiculous really...

There are many (most) places in the world where you have no option but to use AvGas so this is a gotcha for anyone expecting to run their aviation engine to TBO on aviation fuel.

Of the 400 hours that I have run this engine only approx 150 of those have been on AvGas (always using the Decalin additive). The rest on MoGas or UL91.

The other ongoing problem is the Throttle Position Sensor which has failed again. It first failed whilst I was in the USA at approx 120 hours. I replaced it with a new one when I got home at 188 hours. It failed again at 315 hours (approx 120 hours on from replacement - which seems to be the failure region/mode for this part).

This time I took apart the TPS and cleaned out all the Carbon dust from the contact face and also noticed that the ultra thin wires that make the contact were a little bent in places so straightened those out and bent the base of them slightly out so the contact was better. This worked fine for about another 70 hours or so until it started failing again. So I have pulled it apart and done the same procedure and it works ok now but I am looking to get rid of this and go for the Hall Sensor throttle option when I can afford the plane to be out of the air for more than a week. At the moment I am using it to commute to work so it would be a hassle to have it out of the air for so long. 

The problem is that the ECU has to be removed and sent to Belgium for new firmware to be updated so this means at least a week lost to posting their and back not to mention the time fitting the new throttle sensor type and some wiring changes to accommodate it. (Not to mention the approx £600 cost!)

I plan to do this job and also get the valve seat on Cylinder 3 fixed in the Winter sometime when I can afford to be out of the air for a week or two.

The fact that UL Power no longer use this old style TPS and only make engines with a contactless Hall type sensor for the throttle now says it all. This was always a sub-standard component for aircraft use. I know of many other UL Power users that have had their TPS fail as well so it is not something unique to my installation.

I am also now using the UL recommended Teflon additive to the oil for aerobatic engines. See pic. This is UL Powers answer to the 'mysterious' seizure of the engine by oil starvation on G-JINX that Chris Burkett was flying during a display at Abingdon in May of 2017. UL's thinking being that the Teflon will continue to lubricate in the event of oil starvation. I would of course prefer that they got to the bottom of why the oil was not getting around the engine and why it seized in the first place rather than ad a 'sticking plaster' solution such as this. It is not cheap either at £36.40 per bottle! This adds quite a bit to the oil change cost each 50 hours.

At Metal Seagulls for the 400 hour service.

Teflon additive for aerobatic engines.

Throttle Position Sensor - note damage to thin contact wires.

TPS inside. Carbon dust forms on the contact faces so I clean these each time I have it apart.

Saturday, 10 August 2019

National Aerobatic Competition

Last weekend I competed in the National Aerobatics Competition.

My first flight was not up to my best standard (scoring 76.5%) so I was only in 6th place after day one.

Day two went much better with the highest score for the day (scoring 82.7%)for the 1st UnKnown sequence which put me in 2nd place overall and just 0.02% behind the leader.

Day three did not go well for the 2nd UnKnown as I messed up the first of the quarter clovers and ended up getting a hard zero (scoring 70.5%) which put me back to 5th overall from 14 who competed.

Figures flown and videos of each sequence are below.

1st Sequence flown which is the Known for the year.

2nd sequence flown which was the first of two UnKnowns.

3rd sequence flown which was the second of two UnKnowns.