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Building Tips and technical articles. => Building techniques => Topic started by: Richard Speer on June 06, 2022, 10:10:43 AM
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Ok: I’m just finishing a McFarland Dolphin. It’s going to come out at 33 oz. Is my LA 25 going to be enough, or should I change to a Fox 35?
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Or, conversely, is your 1948-technology Fox 35 enough, or should you change to a 1990-technology 25LA which more than makes up for 40% less displacement with a higher RPM and generally more efficient operation?
For comparison, a 20FP (20, not 25) is more than enough engine for a 32-ounce Ringmaster. I'm not sure how big a Dolphin is, but I suspect that engine would work in it.
Note that OS confused things by making two versions of the 25LA -- the original production run is wimpy compared to later engines. No one's figured out why, but if your 25LA won't pull a 33 ounce aircraft with authority, getting another one may solve your problem better than a Fox 35.
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At That weight your LA 25 should be more than enough power for the Dolphin with the right prop. Also 10% fuel and at least 22% oil 1/2 & 1/2. H^^
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The Dolphin was designed around the Fox.35, and if you are familiar with running a Fox .35 and it's idiosyncrasies, it will do just fine. That means have proper fuel for it and such and some different 10-5 and 10-6 props to experiment with. If you can't get fuel for Fox .35's with the 25 to 29% total oil and in different nitro contents, then use your LA. 25. I used a blue LA.25 on a SIG Primary Force ARF that exceeded 42 ounces if I remember correctly, and it did the job but was right at the ragged edge on power. At 33 ounces ready to fly, you should be just fine there. Again, experiment with props to find the one that pulls it the best and that could be any where from a 9-4 to 10-4, and use fuel in the 20 to 22% range in total oil and 5 to 15% nitro. The Dolphin is kind of an under rated design in my opinion. I haven't built one yet but have seen and flown many others and it should serve you very well.
Type at you later,
Dan McEntee
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Thank you all! I will let you know when I get to fly it!👍