what scale should my giant ft Dr1 be?

[Pigfarm1403]

I am making a giant ft dr1 triplane for Flite Fest Ohio and i have a motor in mind but Im not sure what scale I should have the plane. The power pack F produces around 1000 grams of thrust at its best. The motor I'm looking at has about 5,400 grams of thrust. Is this enough to do a 500% scale DR1? The wingspan would be 10ft not for forget three wings. Or would a 300-350% scale be better?

 

[Pigfarm1403]

Should I base my ratio on thrust to weight or thrust to wingspan?

 

[AkimboGlueGuns]

One thing you're going to want to keep in mind is that aerodynamics will not scale. As you increase size lift AND drag will increase exponentially, so you will be looking at a slower airplane as you increase the size. Lower speed means you are flying closer to the critical angle of attack, and have less airspeed to play with before the stall. 350% will probably be your best. You're still looking at about a 7 and 1/2 foot wingspan at that scale, but you should have ample power to overcome the increase in drag. At that size you are just a bit over 1/3 scale, so expect performance to be similar to that of other 1/3 scale DR.1s. You will likely be slower due to the weight of foam being less than most balsa builds. Here's a video of a 1/3 scale.

 

[DamoRC]

350% will probably be your best.

Yep - I'm with AkimboGlueGuns. Also remember that as you scale the plane up the increase in weight will not be a linear correlation. If you were to simply scale a foamboard model up by re-scaling the plans, the weight of foamboard can increase quickly. Take a simple side of a fuselage that's 2 inches tall and 20 inches long, that's 40 square inches area which is directly correlated to the weight of that part in foam. Now double it (200% scale) so that the fuselage side wiall is now 4 inches tall and 40 inches long - the area is 160 square inches (4 times the original size and thus 4 times as heavy). At 300% the same side wall is 9 times the area and would be 9 times heavier. Obviously you can modify the plans to try to mitigate the extra weight but you will also probably be adding extra components to stiffen the wings, tailfeathers, and fuselage, so the weight will pile back on.

All that being said, a 10ft version would be cool!

DamoRC

 

[thenated0g]

Im on my 4th huge plane and one thing i learned pretty early is that you cant simply scale the plans up. The smaller plans are designed with the relative weight of the electronics in mind. Meaning that on a regular flitetest plane or model the motor and battery are a large and significant portion of the total flying weight. As you go up, for me 200%, the motor and battery have a highly noticeable lack of weight compared to the entire plane. So if your doing a pusher and do not make any adjustments the plane will be VERY nose heavy and if your doing a tractor it will be VERY tail heavy. I learned that the hard way on my 200% FT-22. I put the motor in the same place. When i did my 200% guinea pig i made the motors stick out in front of the wing more and i extended the nose by about 4 inches to give my batteries more leverage.

 

[thenated0g]

You could obviously add lead, but i hate useless weight.

 

[Pigfarm1403]

Okay it turns out the motor I'm looking at produces more like 10000 grams of thrust (didn't calculate the fact it swings 4 blades). So would this be like a 700% build?

 

[Pigfarm1403]

I think that a 1/3 or 1/2 scale model would be apropriate. This is the Motor I plane on using with an 80amp esc, and a 5000mah 40c battery
Motor- https://www.motionrc.com/collections/motors/products/flightlinerc-5055-390kv-brushless-motor

 

[FOGeologist]

Okay it turns out the motor I'm looking at produces more like 10000 grams of thrust (didn't calculate the fact it swings 4 blades). So would this be like a 700% build?

Go back and carefully read the responses you were given. There's a lot of good information there. If you are talking about a motor that generates 10 kg of thrust, what is its weight? At what number of cells will this motor generate that thrust? Tell us more about the speed controller you plan on using.

About that speed controller - you better have your act together picking one, or this will happen.

 

[AkimboGlueGuns]

I think that a 1/3 or 1/2 scale model would be apropriate. This is the Motor I plane on using with an 80amp esc, and a 5000mah 40c battery
Motor- https://www.motionrc.com/collections/motors/products/flightlinerc-5055-390kv-brushless-motor

If you want the prop size to scale to the model (which I would highly recommend, as it's the closest way to scale up a plane linearly) that motor would give you a wingspan of about 4 feet with a 2 blade prop. That may seem very small to you, but being a triplane it will really be a very substantial aircraft at that scale. 4' is also a much easier size to work with seeing as structural sag probably won't be a big deal.

 

[Pigfarm1403]

Actually I abandoned this project and switched to a 7ft wingspan t-28 trojan, about halfway done with it.