Tony H Posted January 2, 2022 Share Posted January 2, 2022 Hi All, I have a dilemma, I am building a PB Models Tornado at the moment and have and Irvine 53 and a Irvine 61. The instructions recommend a 60 size engine (probably based on 70s less powerful engines). The 61 engine seems fairly large for the size of the plane being 62" wingspan (wing area 625sq.in) and about 6-6.5lb. I am debating about putting the Irvine 53 in because it would be less thirsty and weighs 168g less. Also from what I have seen the power is pretty much the same. Cloud models say a good 55-60 engine will fly the plane. If I compare the plane to a modern Seagull Models ARTF PT-19 Fairchild which is designed for a 46-52 IC engine, it has a 61.4in wingspan (604.5sq.in wing area) and an overall weight of 6.4lbs. So I would assume the plane will fly quite well on a Irvine 53 and not be underpowered. What do you think? I am building the retract version so it will be on the heavier estimated weight of 6.5lb. Quote Link to comment Share on other sites More sharing options...
kc Posted January 2, 2022 Share Posted January 2, 2022 (edited) I think your assumption that 70's engines were less powerful ( than later engines) is probably wrong for .61 two strokes of the top makes. I would say try to use a decent .61 if possible. As the model was designed for a .61 then the lighter .53 will probably need lead unless you reduce the tail end somehow. Edited January 2, 2022 by kc Quote Link to comment Share on other sites More sharing options...
David Foley Posted January 2, 2022 Share Posted January 2, 2022 Don't forget the Tornado in its day was powered by Webra 61, OS 60 FSR and Rossi 60 all on Tuned pipes. Quote Link to comment Share on other sites More sharing options...
Tony H Posted January 2, 2022 Author Share Posted January 2, 2022 I was wondering about the weight, I don't want to have a add nose weight as that wil make the weight saving void. I am surprised to see that the or Irvine 53 had the same 1.7hp as the 61......can that be right? Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted January 2, 2022 Share Posted January 2, 2022 Tony providing you can keep it down close to 6Lb then the Irvine 53 should be adequate. If you take a period contemporary schnurle-ported engine (to the Tornado) an HP61 this weighed 528g with silencer against the Irvine 53 at 516g with extended quiet silencer. The HP61 was rated at a maximum power of 1.28BHP against the claimed figure of 1.7BHP for the Irvine 53. Quote Link to comment Share on other sites More sharing options...
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