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DLE 35 engine size

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Old 12-11-2018, 05:08 PM
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Default DLE 35 engine size

I have recently purchased a Sig 1/4 scale Piper Cub. I have a DLE 35 that I wish to use in it but after looking at the plans the engine is about 1 inch too long. I can't change the standoffs because they are the shortest for it. I was wondering if I could modify the firewall by moving it back the necessaary distance. I think that this would change the cg and thats something I want to avoid. Otherwise the engine fits inside the cowel ok. I want to use this engine because I'm flying off floats and the extra power would be nice. I also have a Zenoah G26 that appears to fit a little better but is twice as heavy and has half the power. A plane, on floats with a 108 in wing span needs enough power to compensate for the extra drag and weight of the floats. Any help here would be greatly appreciated.
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Old 12-13-2018, 05:35 AM
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I think you're going to have a lot more "extra" power with this engine than you think. That said, moving the firewall back is just part of the game many times. You're likely going to be nose heavy, but installing the rudder servo, and possibly the elevator servo, in back should leave you in pretty good shape. Install the engine, then do a mock up to see what needs to be done (re: servo locations) to get you in range for CG. DO NOT build it per directions, then start adding weight to get it in proper CG range.
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Old 12-14-2018, 04:01 PM
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I agree with ahicks and will add to that . The DLE 35 will be way overpowered for the SIG Cub . I installed Roto 35 in one and was able to easily hover it and pull out with extreme authority. A DLE 20 would be appropriate for this plane even with floats on it . Having said all that the firewall will need to be moved back as I did when installing the Roto 35 . It is not that difficult to modify the firewall position while you are building the plane , if you are experienced at building . It is much more difficult to move the firewall back if it has already been set per plans. Be sure to pin the new firewall in if you are using the DLE35 or you may get an inflight surprise .
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Old 12-14-2018, 04:38 PM
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Agree on the 20cc option. The only way I would use anything bigger is if I already owned it and was looking for a home for it.
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Old 12-18-2018, 04:41 AM
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From Sigs web site: "Nationals Scale Champion Mike Gretz flies his SIG 1/4-scale Piper J-3 Cub, equipped with a set of these 46" floats, off Diamond Lake near Montezuma. An O.S. 1.20 four-stroke engine provides more than enough power." For what it's worth this lake is around an elevation of 1,000 feet.

Since a national champion can fly the Cub with floats on an OS 1.20 (20cc), your thoughts of using a 35 will only cause you a great deal of grief. Your other thread you mention having a 1.60 on hand. Stick with that and save yourself a lot of trouble.
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Old 12-18-2018, 05:02 AM
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I would say it depends on how you intend to fly it. If your goal is to fly in a scale like manner then the 20cc will do that just fine. If you want more spirited flight then go with the 35. Make any nesessary structural improvements to handle the additional stress if nesessary. You can cut a hole in the firewall and run the carb inside the fuselage. Only downside to that is it makes the adjustments a bit more difficult. A couple guide tubes installed in the fuselage side will help greatly. Of course with gassers once adjusted well you usually don't have to adjust again unless changing your fuel mix or prop. Altitude changes of less then 2,000' usually don't require a needle tweak either. Nothing wrong with overpowering, I have a couple Reed Falcons. One was designed for the first production OS 120 4 stroke. It's powered with a YS 140 DZ, the other one is the TOC version that was designed for a 44cc Tartan twin. I have a 3W 70cc twin in that one.
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