Peter Philp Posted September 21, 2022 Share Posted September 21, 2022 Thanks Jon, good to know. I have found your comments on these threads very informative. And appreciate your response. I best get building then! Pete Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted September 21, 2022 Share Posted September 21, 2022 Just to add to Jon's comment, one of the issues with over size engine installations is the additional weight. Normally compounded by the need to add lead in the tail to get C of G. This becomes apparent with the faster arrival airspeed for landing and the complaint that the UC keeps breaking (never broke my wots wot or Acrowot UC), IMO it makes the stall more abrupt so people just land faster, hence more stress on the UC. Let us know how you get on please Quote Link to comment Share on other sites More sharing options...
Peter Philp Posted October 6, 2022 Share Posted October 6, 2022 So had a bit of change in direction. I’ve managed to pick up a Ripmax kit that’s like new. Hasn’t been flown and had an asp65 fitted which I think is toast/ removed. Looks like I’m going to have to modify it a bit to get the 70 in. Have done a bit of a search which suggests a carb scoop may overcome the lack of space. And may need to adjust the height of the tank. Can anyone anticipate any other problems. Thanks Pete Quote Link to comment Share on other sites More sharing options...
Jon H Posted October 6, 2022 Share Posted October 6, 2022 43 minutes ago, Peter Philp said: Its not a 70, I spy a laser 80 Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted October 6, 2022 Share Posted October 6, 2022 My scoop is less pronounced with just a U shape cut out of the cowl and less nibbled out of the bulkhead. I added lead to get the forward C of g and then removed it so it was on the rear mark. Position the RX battery as far forward as possible (mine is just behind the bulkhead). Other than that it should all be straight forward so good luck and keep posting the photos. PS when I spun mine (3 mistakes high) it did so very flat, so power up, nose down on the elevator and then into the usual spin recovery! Quote Link to comment Share on other sites More sharing options...
Peter Philp Posted October 6, 2022 Share Posted October 6, 2022 22 minutes ago, Jon - Laser Engines said: Its not a 70, I spy a laser 80 Thanks for the heads up Jon. I suppose that answers my earlier questions concerning power. Not knowing anything about lasers I bought 2nd hand as a 70. Thanks for your comments Chris, I will keep posting as I go. I have a week off coming up so should make a bit of progress soon. I would appreciate any photos you have for pointers. Pete Quote Link to comment Share on other sites More sharing options...
Graff Posted October 6, 2022 Share Posted October 6, 2022 On 16/05/2021 at 22:59, Jon - Laser Engines said: A friend had a 70 inch cub with a laser 70 fitted. It was awful to fly, 2 clicks off idle and the thing was breaking the sound barrier. There comes a point where you just cant throttle back Well, I fly a DB 1/5 Cub with a Saito 72 running a 14/5 prop. It flies rather well on that setup. My other Cub is getting a Laser 70 that will have the same size prop. I noticed that the speed is not an issue, and the throttle almost only changes how much I want to climb.... Quote Link to comment Share on other sites More sharing options...
Mike Mc Posted October 6, 2022 Share Posted October 6, 2022 I will be building a sport airplane (SIG 4-star 60) this winter with a Laser 70. What's a good prop to start with and what RPM should I be looking at on the ground? Quote Link to comment Share on other sites More sharing options...
Paul De Tourtoulon Posted October 6, 2022 Share Posted October 6, 2022 (edited) I don't leave my rev counter on the ground, someone is sure to tread on it,,,😆 Ps any good?. http://sceptreflight.com/Model Engine Tests/Laser 70.html Edited October 6, 2022 by Paul De Tourtoulon Ps Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted October 6, 2022 Share Posted October 6, 2022 49 minutes ago, Mike Mc said: I will be building a sport airplane (SIG 4-star 60) this winter with a Laser 70. What's a good prop to start with and what RPM should I be looking at on the ground? IIRC I have a 12x7 APC and it revs out beyond 9K, but it will pull a 12x8 NP. Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted October 6, 2022 Share Posted October 6, 2022 34 minutes ago, Paul De Tourtoulon said: I don't leave my rev counter on the ground, someone is sure to tread on it,,,😆 Ps any good?. http://sceptreflight.com/Model Engine Tests/Laser 70.html Wow where did you find that! I have not seen Neil with that little hair in a long time 🤣 Laser web site is more up to date Laser 70 | Laser Engines Quote Link to comment Share on other sites More sharing options...
Don Fry Posted October 6, 2022 Share Posted October 6, 2022 43 minutes ago, Mike Mc said: I will be building a sport airplane (SIG 4-star 60) this winter with a Laser 70. What's a good prop to start with and what RPM should I be looking at on the ground? Laser engines website, specifications for a 70, gives the range of props. Warning, the props size specified, are the efficient APC sort. 13x6? Second part, don’t own a tachometer. Ground RPM is not a measure of anything. The prop is stalled, so is eating energy, ie drag. How it behaves when working well is demonstrated in flight. But I bet, a 13x6 will get it in the air. After that, more speed, more pitch, less diameter. More grunt, less pitch, less diameter. I confess, my prop collection fills a small suitcase. A lot of aircraft need a bit of adjusting for flight as you like to see it. ie, you might like to fly smooth, high pitch, or hooligan, low pitch. Quote Link to comment Share on other sites More sharing options...
Mike Mc Posted October 6, 2022 Share Posted October 6, 2022 I was thinking of starting with a 13x6. Quote Link to comment Share on other sites More sharing options...
Peter Philp Posted October 11, 2022 Share Posted October 11, 2022 On 06/10/2022 at 14:51, Chris Walby said: My scoop is less pronounced with just a U shape cut out of the cowl and less nibbled out of the bulkhead. I added lead to get the forward C of g and then removed it so it was on the rear mark. Position the RX battery as far forward as possible (mine is just behind the bulkhead). Other than that it should all be straight forward so good luck and keep posting the photos. PS when I spun mine (3 mistakes high) it did so very flat, so power up, nose down on the elevator and then into the usual spin recovery! I have removed as little as possible out of the firewall to clear the carb, needs a bit of finishing/ tidying, But seems far less than other examples I’ve seen. Did you have any issues with heat from the exhaust? I have removed a little bit to clear but wondering how hot this will get and whether I need something more heatproof. I have cut the cowl and considering this had already been cut by the previous owner I think it has come out pretty well. Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted October 11, 2022 Share Posted October 11, 2022 Hi, looks much like mine from an install point of view and yes the exhaust will get hot if you are giving it a good thrashing 🙂 but not had any issues with mine. Perhaps some yoghurt pot or the alike could make a suitable inlet scoop, just make sure its bigger than the carb inlet, just in case it tries to get ingested! Other than that its looking great and how has the C of G turned out? Quote Link to comment Share on other sites More sharing options...
Jon H Posted October 11, 2022 Share Posted October 11, 2022 Make sure you have enough clearance for the engine to move on the mount. Depending on how soft that mount is the engine will move a certain amount as its running and you do not want the exhaust or carb bashing into something as they will break. I would also take a little more out round the carb to make sure you have good airflow. Also 14x6apc is a starter for 10 on the 80. Look for 9000rpm +-200 at full power. Quote Link to comment Share on other sites More sharing options...
Peter Philp Posted October 12, 2022 Share Posted October 12, 2022 23 hours ago, Jon - Laser Engines said: Make sure you have enough clearance for the engine to move on the mount. Depending on how soft that mount is the engine will move a certain amount as its running and you do not want the exhaust or carb bashing into something as they will break. I would also take a little more out round the carb to make sure you have good airflow. Also 14x6apc is a starter for 10 on the 80. Look for 9000rpm +-200 at full power. should be plenty of space now for airflow and movement. Quote Link to comment Share on other sites More sharing options...
Jon H Posted October 12, 2022 Share Posted October 12, 2022 Looks good from here 👍 Quote Link to comment Share on other sites More sharing options...
Peter Philp Posted October 14, 2022 Share Posted October 14, 2022 On 11/10/2022 at 12:32, Chris Walby said: Hi, looks much like mine from an install point of view and yes the exhaust will get hot if you are giving it a good thrashing 🙂 but not had any issues with mine. Perhaps some yoghurt pot or the alike could make a suitable inlet scoop, just make sure its bigger than the carb inlet, just in case it tries to get ingested! Other than that its looking great and how has the C of G turned out? Not sure if I have just been lucky but the centre of gravity has come out pretty much on the money as per the manual with the battery positioned under the tank. May need to be moved slightly but nothing serious and shouldn’t need to add any addition weight. Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted October 14, 2022 Share Posted October 14, 2022 Peter, Mine came out spot on with the battery pack against the bulkhead...added lead for a forward C of G and then took it out after it was flown once! Mine also came out spot on the target weight so has nice low speed performance as well as the superb sound of a Laser being given a jolly good thrashing when required. 🤣 All the best for the maiden. Quote Link to comment Share on other sites More sharing options...
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