Steve in MT

Hello all. I realize that this is the scratch build section but this is the closest to a plans built section that there is. Not only is this my first biplane but its also my first plans only build as well. I learned pretty quick that this hobby is definitely a “Crawl, walk, run” type of experience. I started out with a couple of ARF’s (may they rest in pieces), built a couple of kits, copied a few kits and am now trying my hand at plans only. If I mess around with this stuff long enough, then maybe someday I can design and build a model of my design. The BIPLUM was designed for a 3 channel set up but I decided that I needed more punishment and built in some ailerons as I went along. It originally had 5/8 dihedral under each tip on the lower wing and 1-½ on the upper wing. I went with 5/8 dihedral for both wings because of the aileron addition. Nowhere on the plan sheet or the build article was there any mention of wing incidence. Careful measurement showed that both wings were at the same angle without any differential between the two. After it was built, I put the incidence meter to it and both wings came out to 1-1./2 degrees positive incidence. What I couldn’t find anywhere, was what point do I balance this thing at. I couldn’t balance it under the lower wing because it was way top heavy and hanging it under the top wing didn’t seem right. So, I flipped it upside down and balanced it on top of the lower wing (see picture) What I would like to know, is if this is the correct way to suspend a biplane for balancing. I have also set it for just a tad bit nose heavy to start using this balancing set up. I’m not sure if this means anything or not, but the upper wing is staggered rear ward ½in of the lower wing . The BIPLUM is modeled after a French ultra light built in the mid �80s. There is very precious info anywhere but if ya get bored, then google “BIPLUM MG-302“. So, where is the best place to balance a biplane? Is there anything wrong with doing it this way? Thanks for your time. Steve in MT

All Day Dan

My Feedback: (5)

An easy way to balance a biplane is to find the 30% point of the MAC of the top wing and the 30% point of the MAC of the bottom wing and balance the plane between the two using the bottom wing as the fulcrum. There are other ways but this balance point will be good for the first flight. Another way is to take the vertical projection of both wings on a horizontal surface and use the outline to calculate the MAC. Use 30% of that outline MAC. Both your wings are of a constant chord. That’s real easy. I’ll assume that the chord is 10 inches and the stagger is ½ inch. The vertical projection of both wings is 10.5 inches. The MAC is 10.5 inches. 30% of that is 3.15 inches. The CG should be at 3.15 inches behind the leading edge of the top wing. Dan.

FlyerInOKC

My Feedback: (6)

The purpose of having th top wing forward is to control when the two wings stall. In this case the bottom wing should stall first but not by much. Now you take a plane like the Beechcraft Staggerwing the top wing stalls first making for an interesting landing as you approach touch down.

Steve in MT

All day Dan. I don’t recognize your model, is that one that you designed yourself? I see that the top wing is staggered rearward as well. Did you balance it the same as you would a low wing with the model suspended upside down? Or did you balance it right side up with the model suspended under the top wing? You were pretty close on the wing size. Both wings have a 48” span with an 8” chord with a typical Clark Y airfoil. The plans showed a CG of 2-5/8” on the bottom of the wing, but no reference on how to balance it.

FlyerinOKC. Weird and unusual ? Yep, that’s part of the reason that I bought the plans for this one. I was also looking for something that wasn’t real big and hopefully an easy flyer as well. This one is sort of a test bed experiment before I start building a PT-17. Every thing that I read about biplanes usually stated that the wing incidence was different between the two. There was no mention of this in the build article or on the plan sheet so I left both wings at 1-½ degrees. The upper wing will be real easy to change incidence on should someone tell me that I need to or not. I’ve not built nor flown a biplane before so I’m not sure what to expect when I take it out for a maiden. So, anything new, weird and unusual on your build board?
Steve

FlyerInOKC

My Feedback: (6)

Steve how do these look (if they uploaded). The black and white photos are of a 1937 Ryan SC-M prototype. I am also building the 1938 SC-W production model. The Ryans will be 1/5th scale. The color photo is a 1946 Globe Swift GC-1B the picture is from 1964. I have plans for the Swift in 14 scale but I may reduce them to 1/5th scale.

FlyerInOKC

My Feedback: (6)

Here is the 1938 Ryan SC-W production model only 15 airplanes were built production was stopped because of WWII. I trade emails occasionally with the owner. The second photo is a the Drnier D-1 I have cut out but not started yet. Now you know what is wierd on my workbench. The Dornier was so ugly with that big radiator up front, I just had to build it. Only 5 were ever built before WWI none saw battle.

All Day Dan

My Feedback: (5)

Steve, that's my own design. I used negative stagger because all the other biplanes have positive stagger. For modelling purposes it makes no difference. You always balance a plane in its least stable configuration to avoid a false indication. For a biplane it is right side up using the bottom wing. An eight inch chord with a .5 inch stagger should balance 2.55 inches behind the leading edge of the top wing for a 30%MAC point. That would be 2.05 inches behind the LE of the bottom wing. 2 5/8 should work as well. Dan.

Steve in MT

All day Dan, Thanks for the tips and advice. Im assuming that you built your biplane some time ago? Did you use a model airplane engine or did you convert a “weed whacker” type engine? I couldn’t see enough of the engine to tell.
Flyer In OKC, I researched the Ryan SC-M a bit. It looks to be an interesting airplane. The wing reminds me of a De Havilland Mosquito, minus the engines of course. It also appears to have a lot of dihedral to it but with such a sharp taper I’m assuming that it would be a fairly fast flyer?? . Any time you feel like sharing your build pictures, please feel free to do so. BTW, where did you find plans for the swift? Thanks for your response guys.
Steve in MT.

All Day Dan

My Feedback: (5)

Steve, that's a Brison 3.2. The greatest gas engine ever made. Unfortunately they are not being made any more. Dan.

FlyerInOKC

My Feedback: (6)

Steve I bought plans for the 1/4 scale Globe Swift designed/drawn/built by Charles Richard in 1992. Charles was an owner of a 1946 Swift and recreated it in 1/4 scale. He even designed his own scale retracts! The drawings are a work of art and are prettty enough to frame if it weren't for the fact you can pin balsa through the glass.
The copywrited plans are available from Erik Richard Charles' son and I can provide his email address should you wish to purchase them. The plans are 7 pages including a 3 view and all part details for the airplane and the custom gear. The price is very reasonable and will including shipping. Erik also owns his dad's mold for the original slotted cowling. The mold has some condition issues and he is going to attempt to make a cowling or two and then use them as a guide to replace the mold if there is a demand for the matching cowling. You can get additional details from Erik directly. I don't always get to email during the weekend but I will respond as quick as possible to a PM or email request for Erik's contact information.

Mike