Peter Jenkins

Today, the 14x12 APC props arrived. So, after balancing and drilling out the hub to 8 mm, one was bolted onto the front of the ST90. My colleague who had one had said I'd need 22 1/2 inches from piston centre to the pipe baffle so, having measured this distance twice(!) I cut a slightly smaller than measured amount off the manifold. I also took the opportunity of installing a gasket made from an old business card(!) between the engine and manifold to try and staunch the oil leak from there. With the manifold bolted back into place, I put the wing on and then mounted the pipe and pushed it so that it was almost touching the end of the manifold pipe. This should reduce the amount of silicon tube that can pulse and alter the effect of the shock wave travelling up and down the pipe. So, I'm all set for a final run with the target prop. I'm told I should be looking for around 7,800 to 8,000 revs. We shall see.

Oh, I meant to add that the standard of dress on the flying field was considerably higher than you find today! But that reflects society in 1951 I guess.

Posted by Percy Verance on 08/02/2019 06:49:15: Surely that would be the SMAE Peter? The BMFA didn't exist in the 50's. Unless of course the reference is to the organisation in today's context....... I still have my SMAE lapel badge. Former SMAE members have BMFA membership numbers beginning with zero........     Edited By Percy Verance on 08/02/2019 06:58:05 Hi Percy, I was referring to the final line in the Mail on line's report which referred to the BMFA. Clearly in today's environment that is the correct reference although as Stu Knowles points out the SMAE is still the official name of the body which trades as the BMFA.  As regards former SMAE members having a 0 at the front of their number, I'm not aware that was how it worked but rather when the number of members who join exceeded 100,000 the extra 0 was added, probably for data validation?  I might be wrong!   Edited By Peter Jenkins on 08/02/2019 09:05:13

Hmm, difficult choice between the Amethyst or the Citrin although calling them Sport Bipes might not be fair!

Having started in the 60s, missed out the 70s/80s/90s and returned in the noughties, I would say now is the best time. All very well looking back to flying my Early Bird combat wing on my own in the late 60s - enjoyable but not as enjoyable as flying one of today's electric aerobatic machines in a competition. I still have, and like to fly, IC scale and non-scale models, build kits but also assemble ARTFs.

I was amazed to read this article on the Mail on-line on Aeromodelling in the 50s. There is a passing reference to the BMFA https://www.dailymail.co.uk/news/article-6678867/amp/Model-airplane-fans-work-1951-day-nostalgic-photos.html. Edited By Peter Jenkins on 08/02/2019 00:33:23 Edited By Peter Jenkins on 08/02/2019 00:35:02

It's moving the CG that changes the static margin. However, the only real way to check correct CG position is to fly the aircraft and then adjust the CG to suit how you wish to fly. A calculated CG is helpful to avoid a woopsie on the maiden though.

OOh! That looks nice Chris! The pipe clamp is from a US supplier, Ohio Superstar - follow this link. Jon - the lead comes into the wing bay so is out of the elements. The normal switch harness has the usual plug in port for charging and checking battery voltage of course. As the wing needs to be off to transport the model, the balance lead is easily accessible and terminates close to the charge plug. I'll stick in a photo in due course.

How accurate have you found that calculator to be in the past Cymaz?

This afternoon, I completed the running in process on the ST90. It produced an interesting situation when I started to throttle back to half throttle with the engine being reluctant to run and showing all the signs of excessively rich mixture which was at odds with the full throttle running. So, I guessed this might be the slow running jet set far too rich at the factory and checked it. It was 4 1/2 turns to fully closed so I re-opened it and closed it by 1/2 turn. The result was that the engine would now run at half throttle. I leaned it a bit more and gradually got the slow running to improve significantly. To cut to the quick, I managed to get a slow and reliable idle of 1,800 rpm with an instant response to snapping open the throttle. Holding the model vertically with the engine idling at 1,800 rpm resulted in .... a nice even idle! The pump is clearly doing its work. I didn't have enough hands to open the throttle and check the engine accelerated but will do that as part of my pre-maiden checks. Yesterday, I noticed there was a significant oil leak from the engine/manifold junction, so I tried cutting some greaseproof paper gaskets and the oil residue reduced. So, I shall make a proper gasket and that might make the join oil tight. I had also run the pipe without the final exhaust pipe section and that had resulted in a lot of mess on the model. Today, I fitted the final pipe and arranged it to point to the left of the model. This resulted in a much cleaner model. I will turn this ejector pipe to pointing vertically downwards before I fly the model in the hope that will keep almost all the oil off the model. My 2S LiFe balance extension leads turned up today, so after de-rigging the model I removed the battery hatch, drilled and shaped a hole to take the balance plug through the wing mount bulkhead and can now balance charge the 2S Life Rx battery without removing the hatch. Finally, I re-fitted the cowlings and now am waiting for delivery of a pair of 14x12 props. Once they arrive, I'll re-check the needle settings and then set about optimising the pipe length. The picture below shows the cowlings in place. Note that the engine is mounted as per Mr Reeve's instruction on the centre line of the engine mount bulkhead. That's why there is such a downward curve on the top cowling. Oh yes, it looks like my pilot has decided to become unglued at the back of his head. He was glued to the "head rest" with canopy glue. The join with the cockpit floor also looks like it is not too far away from giving up! So, while the wind blows and the rain rains, I shall have to have the canopy off and re-fix the bally pilot!

Posted by Peter Jenkins on 28/01/2019 14:39:37: Posted by Nigel R on 28/01/2019 10:45:50: Looking good Peter re: the above, are you looking for a header/pipe joiner? If so, 19mm ID silicon tube is available on ebay, £3.60 for 1/2 metre here: https://www.ebay.co.uk/itm/Silicone-Vacuum-Vac-Hose-Pipe-Tube-3mm-4mm-5mm-6mm-7mm-8mm-9mm-10mm-Available/290742298928?hash=item43b1976930:m:mukwgwKXqWPSCPCt7EqavOw:rk:6f:0 Thank you Nigel, that's very useful. Might just get some of that. And I did! £5.28 for 1 mtr delivered is excellent. I tried it in lieu of the Teflon joiner today. It's a snug bit to both the manifold and slighter tighter on the pipe but I could use the spring clips rather than the small jubilee clip to clamp to the manifold. Unlike with the Teflon joiner, there were no oil leaks from this join! Good call Nigel R!

Two points. I'm surprised there are so many contributors to this post who are able to say with clarity what air fighting looks like from a cockpit. I thought most of us stood on the ground and flew our aircraft. From what I've seen of the snippets of film the camera gun shots seem quite like those I watched when I was shown real camera gun photos of mock combat when I served in the RAF. Yes there are howlers when Spitfires replace Hurricanes but then again how many people these days know the difference plus it is much easier to get air to air shots with Spits as there are so few flying Hurricanes around. Second, I am delighted that 303 Sqn is being given such prominence. They were, after all, the highest scoring squadron in the Battle of Britain despite not being involved until late on. Not many people know that as it is rarely mentioned. I believe that within the Polish Air Force, even during the communist era, the exploits of their countrymen flying in the RAF was something that generated much pride. I know when I took some Polish Air Force Officers around the UK in 1999, the one request they made that was not to do with business, was to visit the Polish Air Force Memorial outside RAF Northolt.

The sunny afternoon tempted me out to give the ST90 a run. So, here's the first photo of the Gangster in flying trim minus the cowlings as I wanted access to the engine and fuel pump at this stage. First problem, which took a while to find, was that the Dubro filling valve had jammed in so no fuel was reaching the engine. Initially, when I choked the engine, I saw a bubble travel up the fuel line. Unfortunately, it took some time to realise that there was nothing other than a bubble! So, defuel, tuned pipe off, wing off, manifold off, old tank hatch opened, battery and packing out, and then Dubro valve out. You can just feel my frustration in those words! I didn't have a spare Dubro valve but did have an old MacGregor valve so installed that. Everything else re-installed and the model fuelled up. The ST manual said needle vavle 3 turns open and go from there. Unfortunately, this resulted in the mixture being too rich so decided to turn the model over, place on the build stand and start the engine upright. It wasn't until I'd closed the needle valve and churned the engine over that it ran! So, open the needle, no choking, apply starter and no go. Choke for 2 flips, and she starts! The running in process is run full throttle for 5 minutes (this is a ringed engine remember) and then gently lean the mixture by 1/8 turn till pinching the fuel tube does not result in an increase in rpm. I had a tach with me so once I had full throttle established, I checked the rpm. I was surprised to see 9,000 rpm. I was using a 14x10 APC as a friend who'd had a similar setup had suggested a 14x12 would be a good match for the pipe and to expect 7,800 rpm. I ran the engine at this speed, lots of oil spewing out, for 5 minutes and then, as I'd not filled the tank more than halfway, the fuel was exhausted. As it was now close to cup of tea time, I packed up but it took an age to clean all the oil off! Things I learned: Most of the noise was coming from the propeller end with hardly any apparently coming from the end of the tuned pipe. The engine held speed without wavering A 14x10 is clearly not big enough for the engine. I have a 15x10 which I will try next time out and by then the 14x12s should have arrived. The pipe must be close to its ideal position as the rpm drop is likely to be around 1,000 with a 2 inch increase in pitch thus putting me in the right ball park for my friend's experience. Oh, and a glow engine running rich is a messy beast! Well I knew that but after flying electric and petrol for so long it has just reminded me why I moved away from glow!

Posted by Don Fry on 02/02/2019 20:30:32: After last year, shut up Peter. Just saying!

A 20C rating should be quite OK. That means it's good for 100 amps and I very much doubt on a 6S that you will pull that. I use 20/25 C packs for my 2 mtr electrics. On a 10S I draw about 80-85 amps on a vertical up line. 20/25C packs are also lighter than 35C or more but you do need to get used to throttle control - one of the more difficult skills to master with precision aerobatics.

Best I've seen an England team play since the World Cup in Oz! The big question is "Can they put in the same performance next time?"

Cymaz, I would have to disagree with the advice about closed loop elevator not being good for aerobatics. The Capiche 140 was a highly successful 3D and precision aerobatic machine and had closed loop elevators. Never fear, 2 mini servos are just as good and a lot easier to set up not having to cope with 6 closed loop wires.

Interesting early refereeing decisions today. Paresee being dumped on his head was just a penalty and an intercept that made no attempt to catch the ball just a knock on. These used to be yellow card offences and penalty respectively. Lucky for Scotland!Edited By Peter Jenkins on 02/02/2019 14:44:34

Well done Wales!

Thank you France! What a howler! Only 2 points in it now.

In truth, that could go either way. The change in fundamental frequency of the structure could help or hinder. I think that most fuselages are stiff enough to resist the forcing frequency of the engine. I've never had a problem but I suppose there is a chance that could occur.