LHR Dave Posted January 11, 2020 Share Posted January 11, 2020 I am looking into building a db sport and scale piper cub. It is 7 foot wing span and weighs around 7 pound. Would a 91 four stroke be over powered? Quote Link to comment Share on other sites More sharing options...
Jon H Posted January 11, 2020 Share Posted January 11, 2020 It would fly on something as small as a 50 4 stroke to be fair. I used to fly a slightly smaller goldberg cub on an OS48 and it was quite happy at under half throttle. I also flew a customers 94 inch cub with a laser 100 and it was well over powered for scale. Cubs fly with their wings not their props so its best not to go mad. All things considered, i would use a 70 in it and throw something like a 15x5 prop to keep the thrust high and the speed down. Quote Link to comment Share on other sites More sharing options...
LHR Dave Posted January 11, 2020 Author Share Posted January 11, 2020 Thanks Jon for the great advice it sounds then that the fs91 I was considering would be a way over kill. Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted January 11, 2020 Share Posted January 11, 2020 On their website they say 60 to 90 fourstroke, so if you have a 91 fourstroke then I'd use it and just go lightly on the throttle. Maybe select a larger dia prop with a finer pitch to keep the speed down. If you are buying a new engine then Jon's recommendation of a 70 sounds spot on. I'm flying a Ben Buckle Majestic Major (88" span) on a Laser 62 and 15 x 4 prop and it's lovely. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted January 11, 2020 Share Posted January 11, 2020 I had a very similar sized on with an O.S 90 in, too much, even careful throttle use never made it enjoyable, open the taps and the nose reared up, much more fun replaced with a 70. Quote Link to comment Share on other sites More sharing options...
Martin Dance 1 Posted January 11, 2020 Share Posted January 11, 2020 I have a DB Piper Cub. I fitted an OS 61 FS, pre surpass, and it's too powerful, unless you think a 60 degree angle of climb at full throttle is scale like. I agree with John Stones that even with careful throttle use it isn't pleasant to fly. I reckon a motor in the 48 to 52 range would be best. Also that vintage of OS four stroke wasn't that reliable on low throttle with the motor fitted inverted. Quote Link to comment Share on other sites More sharing options...
Caveman Posted January 11, 2020 Share Posted January 11, 2020 I fitted my Super Cub, 80.5" wingspan with the recommended 91fs and it was ridiculously overpowered. Now powered with an ASP 61fs and it's just right. It flies in a scale manner on half throttle or less, but with a bit of extra power when needed. Cheers GDB PS The undercarriage is not the right one and has also been replaced with something more appropriate! Quote Link to comment Share on other sites More sharing options...
LHR Dave Posted January 11, 2020 Author Share Posted January 11, 2020 How much does your super cub weigh Caveman? Quote Link to comment Share on other sites More sharing options...
Caveman Posted January 11, 2020 Share Posted January 11, 2020 Hi Dave, I'm not sure what it weighs, but if you can wait until tomorrow I'll put it in the scales and report back! GDB Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted January 11, 2020 Share Posted January 11, 2020 Posted by LHR Dave on 11/01/2020 19:42:57: How much does your super cub weigh Caveman? Just seen this Dave, and list my 3 Cubs for comparison for what you have in mind 5 foot, at 5lb OS 48 surpass 6 foot, at 6lb OS 52 surpass 7 foot, at 7lb Saito 62 I do not think there is any science in 1lb per foot of wing, maybe just a Cub thing Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 11, 2020 Share Posted January 11, 2020 Certainly doesn't extrapolate to my 1/4 scale [just under 9 foot] one which weighs around 18 lbs and flies with more than scale performance on a 160 twin... Quote Link to comment Share on other sites More sharing options...
Jon H Posted January 11, 2020 Share Posted January 11, 2020 Posted by Martin Harris on 11/01/2020 22:54:24: Certainly doesn't extrapolate to my 1/4 scale [just under 9 foot] one which weighs around 18 lbs and flies with more than scale performance on a 160 twin... Is that an ASP 160? if sop they perform much like a decent 120 single so should be really nice. 1/4 scale is 105 inch right? In any case, i cant fault any of the comments here. Cubs are great fun and dont need massive power. What they do need however is a good grasp of how to use your rudder. Connecting it to the ailerons on the tx is no good as you often need to use them in opposition! Quote Link to comment Share on other sites More sharing options...
Caveman Posted January 12, 2020 Share Posted January 12, 2020 Morning Dave, just weighed my Super Cub and it comes out at 4030g or 8lb 14oz. ready to fly but with no fuel. Cheers GDB Quote Link to comment Share on other sites More sharing options...
Brian Cooper Posted January 12, 2020 Share Posted January 12, 2020 Cubs are really good fun. . As already stated, they don't need huge amounts of power to keep them airborne, but a Cub can be surprisingly aerobatic, and that is where they need a bit of "grunt in the front", especially in low altitude knife edge flight. Yes, the potter around the sky on a whiff of power, and if that's your thing, then great. . Mine get used for giving goes to kids, and part of the routine (it's a well-trodden path) is to let them do three consecutive loops starting from from straight and level flight. A Cub will struggle to do this without sufficient power, so mine have enough power available for this most basic manoeuvre. Looking forward to summer already. B.C. Edited By Brian Cooper on 12/01/2020 09:53:40 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 12, 2020 Share Posted January 12, 2020 Posted by Jon - Laser Engines on 11/01/2020 23:36:40: Posted by Martin Harris on 11/01/2020 22:54:24: Certainly doesn't extrapolate to my 1/4 scale [just under 9 foot] one which weighs around 18 lbs and flies with more than scale performance on a 160 twin... Is that an ASP 160? if sop they perform much like a decent 120 single so should be really nice. 1/4 scale is 105 inch right? Certainly is an ASP - maybe a "budget" engine but it's soooo smooth...and sounds superb. Span is nominally 106" - exact measurement should be 105.75" so you're pretty close! While I use the rudder a lot with this model, unusually for a model Cub it requires very little, if any, in normal turns. I put this down to it having proper Frise ailerons. There's little more rewarding than a slipping approach and one wheeled touchdown in a crosswind with this sort of model! Quote Link to comment Share on other sites More sharing options...
Paul Marsh Posted January 12, 2020 Share Posted January 12, 2020 I have several Cubs, the Clipped wing 85 inch version also has a 160 twin up front. This model I still got and is now 20 years old. Flew it recently at a scale fly-in. Quote Link to comment Share on other sites More sharing options...
Jon H Posted January 12, 2020 Share Posted January 12, 2020 Posted by Martin Harris on 12/01/2020 10:31:25: Posted by Jon - Laser Engines on 11/01/2020 23:36:40: Certainly is an ASP - maybe a "budget" engine but it's soooo smooth...and sounds superb. I have an ASP 160 twin as well and is is very smooth running. I have to confess though, the noise on the straight pipes is not to my taste at all. I had the same experience with an OS 300 super gemini but once i fitted a muffler to it then i was sold as it purred like a kitten so i suspect the ASP will be a similar story. Admittedly my engine has never flown as i my friend and i both bought cubs and were going to fly them together. Sadly though, he crashed his before i even got mine out of the box so i sold my model. Part of the delay was due to me trying to get the engine to run right. Its compression was always poor and the right cylinder always ran rich below half throttle. I have since modded the engine with pistons and rings from a laser 75 and performance has improved. Its still not brilliant though, i might have to make it twin carb or something to fix the imperfections. Quote Link to comment Share on other sites More sharing options...
Ted Khinsoe Posted January 12, 2020 Share Posted January 12, 2020 My 76” sig 1/6 Cub in Grasshopper mode flies very scale like on an Enya 46 four stoke. Quote Link to comment Share on other sites More sharing options...
Ted Khinsoe Posted January 12, 2020 Share Posted January 12, 2020 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 12, 2020 Share Posted January 12, 2020 Posted by Jon - Laser Engines on 12/01/2020 12:23:27: Posted by Martin Harris on 12/01/2020 10:31:25: Posted by Jon - Laser Engines on 11/01/2020 23:36:40: Certainly is an ASP - maybe a "budget" engine but it's soooo smooth...and sounds superb. I have an ASP 160 twin as well and is is very smooth running. I have to confess though, the noise on the straight pipes is not to my taste at all. I had the same experience with an OS 300 super gemini but once i fitted a muffler to it then i was sold as it purred like a kitten so i suspect the ASP will be a similar story. I made a siamesed silencer for mine from a stainless steel salt and pepper set found for the purpose at a car boot sale and using the open pipes for headers so except for some initial test bench running I've not had any experience of the bare pipe sound. At tickover it's barely audible and prop noise is the dominant sound at higher revs. It may be a little over restrictive as I found the engine very needle sensitive when running with exhaust pressure so I simply blanked off the silencer and run vented to atmosphere now. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 12, 2020 Share Posted January 12, 2020 Posted by Martin Harris on 12/01/2020 13:57:32: Posted by Jon - Laser Engines on 12/01/2020 12:23:27: Posted by Martin Harris on 12/01/2020 10:31:25: Posted by Jon - Laser Engines on 11/01/2020 23:36:40: Certainly is an ASP - maybe a "budget" engine but it's soooo smooth...and sounds superb. I have an ASP 160 twin as well and is is very smooth running. I have to confess though, the noise on the straight pipes is not to my taste at all. I had the same experience with an OS 300 super gemini but once i fitted a muffler to it then i was sold as it purred like a kitten so i suspect the ASP will be a similar story. I made a siamesed silencer for mine from a stainless steel salt and pepper set found for the purpose at a car boot sale and using the open pipes for headers so except for some initial test bench running I've not had any experience of the bare pipe sound. At tickover it's barely audible and prop noise is the dominant sound at higher revs. It may be a little over restrictive as I found the engine very needle sensitive when running with exhaust pressure so I simply blanked off the silencer and run vented to atmosphere now. ...and at just past 3 minutes was the last occasion I ran pressure! Edited By Martin Harris on 12/01/2020 14:19:09 Quote Link to comment Share on other sites More sharing options...
Jon H Posted January 12, 2020 Share Posted January 12, 2020 I like that exhaust. I am trying to decide what type to make for the OS300 as well as the 160 and that is a type i have considered so knowing it works well is good to know. As for muffler pressure i didnt use it on the 300 when i flew it and dont use it on the OS FF240 either. most of my lasers run without it (one exception), my Enya's dont need it and neither does my magnum 240 twin. I definitely think its importance exaggerated and its mostly a bandage to cover up poor tank placement Quote Link to comment Share on other sites More sharing options...
LHR Dave Posted January 12, 2020 Author Share Posted January 12, 2020 Thanks for all the replies guys, the general opinion seems to be no need to over power. I am now thinking in the region of a Saito 62fs. To me this seems a good compromise. Quote Link to comment Share on other sites More sharing options...
Jon H Posted January 12, 2020 Share Posted January 12, 2020 Posted by LHR Dave on 12/01/2020 19:40:32: Thanks for all the replies guys, the general opinion seems to be no need to over power. I am now thinking in the region of a Saito 62fs. To me this seems a good compromise. yep, if you have one already its a good choice. If not and you are shopping anything 60-70 would work well. Quote Link to comment Share on other sites More sharing options...
LHR Dave Posted January 13, 2020 Author Share Posted January 13, 2020 Dont own one but always fancied a saito. Will be looking around to see if I can get any good deals , no rush though as I still need to order the cub from db sport and scale. Quote Link to comment Share on other sites More sharing options...
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