CorradoMatt

Thanks for the replies. As a starting point I made the outlets the same diameter as the original silencer. I have a couple of those pepperpot add on inserts which might be worth a try.

Took the Mystic to the field today to test the mk2 silencer design with the additional baffle and stainless steel wadding. The noise level has now dropped from around 86 to 84db so I am pretty close now to the 82db club limit. The engine has certainly lost the typical 2 stroke petrol engine exhaust pop and bark. I'm now going to change from the wooden Menz 17x8 prop to an APC prop. I'm not sure whether to try a 17x8 APC, 17x10 APC or 18x8 APC. Props at this size are starting to get a bit pricey so I don't really want to buy a few different ones to try! I think i'm going to try an APC 18x8 unless anyone recommends anything else. I've also been looking for alternative silencer designs and saw some threads on the LMA forum about a Sid King silencer design that is based on a gun silencer. I've registered for the LMA forum and will ask for more information. Does anyone here have experience of this design? Matt

Fitted now - I was pleased to see that i have clearance for the ht plug! I'll take reading with the new setup before I change anything else. I am currently running a wooden Menz 17x8 prop. I understand that using an APC prop may help reduce the noise and i could also experiment with the size. I am not sure whether to increase the diameter or pitch (or both) to reduce the noise. Does anyone have any advice on this?

Photos of the new silencer below. I've added a baffle around the exhaust port that will also stop the stainless steel scourer entering the engine. The baffle also adds support to stop the silencer being crushed when the bolts are tightened. Just need to fit and seal it on to the engine and carry out some testing. If this doesn't work i'm not quite sure what to do next other than experimenting with props or possibly fitting a header and cannister.

Thought I should post an update on this. I took the Mystic to the field today and ran the engine with the new silencer. We took sound level readings using the club meter and achieved an average of around 86db which was 2 to 3db less than the standard silencer (Club limit is the usual 82db at 7m). I was allowed to fly it to see how it sounded in flight and although the bark had certainly reduced, it still sounded pretty loud. I'm now going to make a mark 2 version with an added baffle around the exhaust port and fill the inside with a stainless steel pan scourer. I can also adjust the dimensions for better clearance on the ht lead and change how the parts are joined for a stronger joint. I'll post some pictures once i start making it.

Thanks for the replies. I've run the engine with it fitted but haven't taken any db readings yet as i need to do it at the field where there are no obstructions etc. I suspect that the heat of the exhaust may crack the joints as the parts are only butt jointed and then aluminium brazed over the top (not much thickness to the braze material). I think next time I will extend the end plates past the edge of the box section and then run a fillet of braze along the joint. I didn't fit anti-crush tubes to this one but I will with the new version. I have bolted it using Norlock washers and high temp silicone. The alternative is to have larger access holes opposite the exhaust port that i can pass the bolt heads through and only bolt up on the exhaust mating face. I'll then have to fit some kind of blanking plate to cover the access holes. I've got a few ideas about fitting extra baffle plates either side of the exhaust port or fitting another perforated tube that the exhaust feeds into first.

Evening all, I recently finished an old Galaxy Models Mystic that I have powered with an RCGF Stinger 26cc rear exhaust engine. The model has had 2 flights and performs well but unsurprisingly the engine is rather loud with the standard silencer. I have made a new silencer from aluminium using Durafix Easyweld to join the parts together. The new silencer is twice the volume of the standard silencer and uses "stinger tubes" to act as baffles. I have run the engine with the new silencer but have not taken dB readings yet. There are a few things that need modifying (plug cap is just touching the surface of the silencer for one) so i will need to make an improved mk2 version. I have found loads of information with regard to effective canister silencer design but there appears to be very little for the pitts style of box silencers. I was wondering if anyone has any good advice with regard to effective silencer design or could recommend something that has worked well for them? I was wondering if fitting a couple of perforated baffle plates between the exhaust inlet and stinger tubes would make a big difference? I've attached a few photos of the model with the standard silencer and home made item. Thanks, Matt

Hi Rich, Thanks for the advice. I read your message at the flying field so I widened the U/C as suggested and made sure that i wasn't going too fast. This certainly seemed to help as the next take off was much better! Unfortunately it was also my last battery for the day so i'll have to wait until tomorrow to try it again (plus a few minor tailplane repairs to carry out this evening!). The Gyroo has certainly received a lot of attention at the club and a couple of members are now thinking about building their own. Thanks again for all your help and advice! Matt

Hi Rich, I’ve now had 5 successful flights but I am still struggling with take offs! Once airborne I am fairly happy flying circuits etc but it is hit or miss if I am able to take off or do the classic roll to the left and end up in a heap! I’ve taken your advice and stand downwind of the model whilst getting the blades up to speed but I do find that the model starts to pull up on its own and then roll over. I’m wondering if I have too much rear tilt at the neutral position? It seem fairly well trimmed in flight. Matt

Thanks Rich. I found it easier to get the rotors up to speed when there was more of a breeze and holding rearward tilt with the model stationary. This gave me confidence that the rotors would be going fast enough (and making the swishing noise) before taking off. If there is little or no wind, is it just a case of having a longer take off run to get the rotors spinning?

Hi Rich, Had another chance to fly the Gyroo today following the not so successful maiden flight! I took your advice and tried test hops to get it trimmed before finally committing to flight. After a wobbly start I managed to do a circuit and land it successfully on it's wheels. I think I just need plenty of practice now to get used to it and build my confidence. Photos and video attached. Thanks again for your help and advice! WhatsApp Video 2023-05-23 at 16.04.10.mp4

Hi Rich, Tried maidening the Gyroo today without much success! It took off and then rolled steeply to the left and got blown downwind on to the ground resulting in a broken mast and boom. Full right aileron had no effect. I think it was a combination of things: probably not enough rotor speed, too fast take off, a little too windy and a lack of (zero!) autogyro experience! It's an easy repair due to your design and fortunately the rotor blades and head are ok. I'm determined to master it so will hopefully give it another try this week. I totally forgot to take a photo of the finished model so once it is back together I'll take a few snaps. I noticed on your videos that your take offs are very slow. Am I correct in thinking that you use full up pitch to get the rotors up to speed and then slowly open the throttle until the tail lifts? It feels like learning to fly all over again! Matt

Hi Rich, Thanks for the advice. I've done as you suggested and managed to balance the blades and move the cg rearwards. Hopefully it will be ok! Fuse and tail are now covered - just got the blades to do now. I'll post some more photos when it is finished. Thanks again, Matt

Hi Richard, Having always fancied flying an autogyro, I decided to give your Gyroo a go. The fuse build went well and is now ready for covering (photo attached). Today I have been working on the blades. I have finished shaping them and have glued the lower and upper blade mounts in position. I am not sure if it is a problem but the blades currently weigh 43.6g, 39.4g and 36g. When I worked out the chordwise cg position for each blade, the lightest blade has a cg 2mm further forward than the other blades. Will this be a problem? Also when I come to balance the blades, I will need approx 7.6g of extra weight adding to the lightest blade to balance with the heaviest blade. I understand the weight must be added at the lengthwise cg position. Will it be ok if I cut a slot in the balsa and epoxy in a piece of lead? Looking at a 7g piece of lead, it looks pretty large! Cheers, Matt

That's great - thank you. I'll give them a ring to see if they have details of a magazine feature and whether the cowl and canopy are still available. Cheers, Matt

Hi Robin, Thanks for the message. In my search for possible models, I did find this design but it appears that the plans are for a 37" and 49" version of the Ultimate where as mine is a 55". Link to a description of the magazine here: https://www.magazineexchange.co.uk/cw/scale-aircraft-magazine-june-july-1994-issue.html Thanks for the link to Vortex Vacforms - I will give them a try. I did see the Ultimate on Ebay but it is the other side of the country from me! Cheers, Matt

Evening all, I have recently picked up a used Ultimate 10-300 that I intend to restore and convert to electric. It was originally thought that it was a Carl Goldberg model but since examining it and looking at plans online, I believe that it is the 55" Ultimate by David Boddington. I've bought the plans from Ebay but I was wondering if anyone has any further information on this design? The model is missing the canopy and the cowling has been cut for the old engine so I would be interested if these parts were still available? There is nothing on the DB website. Thanks in advance, Matt