Mar 04, 2012, 11:11 AM Registered User San Diego, California Joined Dec 2004 3,159 Posts To add to the problems, beyond (or in addition to) the aerodynamics, are the physical limitations on how strong a spar you can acheive in a low profile cross section. Clark Y gives you the meat where you need it. Les
 Mar 04, 2012, 12:54 PM Registered User USA, NH, Manchester Joined May 2010 269 Posts Thank you all for the incredible info. I must admit I'm going to need to give these a few reads through. Sound like i may need a cf spar if the wing is too thin. One good thing is I'm not planning on making an aerobat. Slow gentle flyer is my hope, like the full scale one was.
 Mar 04, 2012, 01:19 PM Registered User United States, OH, Bradford Joined Jun 2005 3,672 Posts You don't need to resort to the aerodynamics of a telephone pole to get a decent spar, and you don't have to use huge amounts of carbon, either. If you use the right materials to their best advantage, even balsa can make a surprisingly strong wing. The first thing you need to do is determine your "mission profile", i.e.: what you expect the plane to be able to do. How big, how much endurance, how fast and/or how slow, then make a realistic estimate of weight, power required, etc.. , and then revise your weight based on those. You may need a few iterations to converge on an estimate that includes enough weight to cover the requirements of the power system, radio gear, structure, etc. Once you know the approximate weight and span, you can look at what sort of spar you need to carry that weight, and so on. We already know you want it to be a scale model of a Mig 8. How big, and do you want to have "scale visual speed" (same fuselage lengths per second as the full-scale airplane, in which case you'd better design it to be feather-light, and a serious "floater"), or are you planning to fly it in 40 knot winds, with enough top speed to come back home from downwind? Just nailing down the size and required flying speed will nail down many of the other parameters. Don't worry about airfoils yet, that's actually one of the last things you will need to define in the preliminary design process. Last edited by Don Stackhouse; Mar 04, 2012 at 03:10 PM.
 Mar 04, 2012, 03:08 PM Entropy Happens! Bellingen NSW Australia Joined Aug 2008 5,547 Posts I agree with everything Don has said. So if you read his posts along with Captain Canardly's and a couple of others, you should be headed in the right direction. Jim, over and out!
 Mar 04, 2012, 04:52 PM Registered User st. paul, mn. Joined Jan 2007 2,855 Posts seems I'll have plenty time to dig for my Tiger's projects!- Great assistance! Thanks (Don!)
Mar 04, 2012, 10:46 PM
Registered User
USA, NH, Manchester
Joined May 2010
269 Posts
Yes an excellent amount of info, and I'll have some reading /video watching to do. Captain Canardly, I will be looking at your vids soon, I think I'll learn a lot from your experience.

Quote:
 The first thing you need to do is determine your "mission profile", i.e.: what you expect the plane to be able to do. How big, how much endurance, how fast and/or how slow, then make a realistic estimate of weight, power required, etc.. , and then revise your weight based on those. You may need a few iterations to converge on an estimate that includes enough weight to cover the requirements of the power system, radio gear, structure, etc.
My intention is to have a scale 'ish' appearance on ground. I'm sure adjustments may be needed and I'm fine with that. I'm not going for any competitions, so as long as someone who saw a mig-8 can look at is and say that looks like a mig-8, I'll be happy. As far as scale flight, I do not care at all. I would prefer a slower plane that is also stable. Our club has a short field, and thinking about it, along with advice here, the .25 powerplant makes a lot of sence considering my understanding of canard aircraft, along with a long talk with the crew of a Beechcraft starship, indicates they like a lot of runway.

Quote:
 We already know you want it to be a scale model of a Mig 8. How big, and do you want to have "scale visual speed" (same fuselage lengths per second as the full-scale airplane, in which case you'd better design it to be feather-light, and a serious "floater"), or are you planning to fly it in 40 knot winds, with enough top speed to come back home from downwind? Just nailing down the size and required flying speed will nail down many of the other parameters.
Definately not scale visual speed. Also unless she surprises me, I'm thinking this will be a fair weather flyer. I think Captain Canardly nailed it with a .25 glow engine and 60 inch span. I know the mig-8 had flaps on the front canard, those I do not intend to include on the model.

well, time to start looking into those youtube vids and other things presented. Thank you all again, Your help is invaluable to me and I think I may actually pull off a prototype
Mar 05, 2012, 03:35 PM
B for Bruce
Joined Oct 2002
10,094 Posts
Quote:
 Originally Posted by ryokox3 ...... I think Captain Canardly nailed it with a .25 glow engine and 60 inch span........
I like that combo as well. But it will require some light building techniques to work with that size and power in a nice way. You'll basically need to look at designing and building the airframe along the lines of the old timer free flight models with lots of sticks and formers and only minimal sheeting. The goal being to build the shape using most air.....

From this image for fuselage sections I pulled off the web;

Note that the fuselage cross sections are more or less rectangular with only a little curving at the corners. This would lend itself to a "stick build" similar to the old gas powered old timers very nicely. Then some small upper and lower formers with a few stringers to get the rounded corners and wind screen areas and you'd be away. Similarly using light techniques for the wing surfaces would produce a light structure.

With this methodology I don't see any issues at all at producing what could well be a sub 4 lb model. At that weight the .25 would fly it in great form with a good but not "jet like" climb and generally nice "light plane" like flying charactaristics. It would be a model which would be at its best on moderate wind to calm days. At least until you get to know it's strong and weak points. But I don't see it being a "fun" strong wind day model by any stretch.

And when you consider that from my quick calculations a 60 inch span version of the Mig 8 would have a cross section under the wing of roughly 8.5 x 6 inches you REALLY want to build up the fusleage with something light. And the old timer style of sticks would be the way to go IMHO. Note that this does not mean that the model would be fragile. With the proper wood grades and use of diagonal uprights that form a Warren truss like structure similar to seen on heavy lift cranes a stick built structure can achieve high levels of strength and rigidity with surprisingly little material. Yes it's a little more work and fuss to build but when done you'd be rewarded with a great flying model.

Quote:
 Originally Posted by ryokox3 ...... I know the mig-8 had flaps on the front canard, those I do not intend to include on the model.......
The "flaps" on the canard surface are actually the elevators. Or are you talking about not including the smaller trim tabs?

Due to the distance away from the CG the fore plane is the better spot to place the elevators. By fortunate happenstance the downward deflection for "up elevator" acts to increase the camber of the foreplane making it a little less prone to stalling from the added lift. So all in all I'd suggest you stick with "the plan" and use the foreplane flaps for the elevator function as per the original.

And CURSE YOU! From looking at the Mig 8 3 view plan attached I'm getting the urge to open up my CAD program and start tracing over the image .....
Mar 06, 2012, 12:40 AM
Registered User
USA, NH, Manchester
Joined May 2010
269 Posts
Hmm, you might be right about those being the trim tabs. I thought I read something about them being flaps, but looking at the drawing it does seem like they would be too small for flaps and likely trim tabs.

Quote:
 And CURSE YOU! From looking at the Mig 8 3 view plan attached I'm getting the urge to open up my CAD program and start tracing over the image
hehe, she does have something intriguing about her
 Mar 10, 2012, 08:15 AM Registered User United States, OH, Bradford Joined Jun 2005 3,672 Posts Yes, those are trim tabs, used for pitch trim. The larger movable surfaces they are attaced to are the elevators. The trim tabs are not necessary for an R/C model, but you definitely need the elevators!