I am putting together a scratch built mid-winger that has a w.s. of 35" and a length of 28". It has a basic "boxey" fuse with ailerons. I had considered going brushless, but due to weight, I figured on using a Norvel .074 that was in my collection. My question is: will this engine provide enough thrust? I have asked several guys in the club and they are clueless as to how much weight a Norvel .074 can pull. I believe the model should weigh approximately 24-26oz. Any feedback would be helpful. Tim in Tacoma

It will probably fly it but I really think you would want a .15 if you want good verticle performance.
This question will probably get a lot more answers if you post it in the 1/2A forum.

Moved to this new home....

That size and weight with a Norvel 074 will be a hotrod. No need for a 15 unless you're looking for a real rocket. I personally would like to see it come out a little lighter for that span or perhaps keep the same weight but with a 40 inch span but I like my stuff lighter as I find it enhances all the performance aspects.

You're not going to get good vertical at 24 to 26oz with an .074, if you even care about that. At that wingspan, try to drop the weight to 20oz.

Tim, watcha basing your weight estimate on? How many square inches are we talking about? (span x average chord)

Bear in mind that these engines are much lighter than the .15 and up cousins, so when scratch building with 1/2A or 3/4A power, you need to move the wing further back than what you would see for wing placement on a model with a ".15 on up" engine.

OK, I will concede that this plane won't need a .15 . I was thinking about a 2/3 scale model of a .40 size pattern plane that I built that I used a OS .15 FP in. The plane was a Zenith 40, RCM Plan 1212. Wingspan is 37 inches and weight about 32 oz. I had a copy place make a 66% copy of the original blueprint and proceeded to build a plane from that plan.
Nick Ziroli's "Mini Sukoi" had a 34 inch wingspan. I used a Cox .09 RC with throttle and that plane was definitely not underpowered.

B.L.E., it's all about weight and area. And, of course, the desired performance level! Tim pm'd me his wing measurements and we're dealing with 210 squares. With a .15 it'd glide like a brick. There's other stuff to consider, but I've got a 36" span airplane that's underpowered with a .15! A .25 is more like it. Of course, it's got about 400 sq in's due to a long chord.

Yikes! Only 210 square inches of wing area. Now that I'm aware of that fact, I'm in full agreement that a .15 is too much. At 24 ounces, this plane is going to have a wing loading of 16.5 ounces/square ft. I would move mountains to get that figure lower on a plane this small.

I agree. I think you need to shoot for 20oz or less.

For anyone who isn't familiar with 1/2A building techniques, and typical wood sizes, have a look at the "DAS NOT UGLY" and similar build threads to see how lightness and adequate strength is acheived. If all a guy has ever been exposed to is .40 sized kits, then it takes quite a shifting of gears mentally to know when enough is enough for 1/2A planes. After seeing even the most extremely stressed 1/2A planes hold up to engineering that omits doublers, formers, braces, and sometimes even spars, it's safe to say that it is way more difficult to build too light than visa-versa. Having access to select grade [4 to 6 pound] wood is essential. A 210 sq" model with a simple design will easily come in at 14 ozs with 1/2A power. The HALFWIT is another design to glean ideas from, even though it is a profile, it is a great example of how to build in generous wing area, run 4 channels and have the whole thing weigh 13 ozs.