Hi, all. I picked up "Simplified Aircraft Design for Homebuilders" by Dan Raymer a couple weeks ago at the suggestion of the good mr.Topaz, and started running through the calculations to try my hand at it. I went through a few ideas before I settled on a concept I'd like to explore and do some quick drawings of, etc.: what happens if you took something the size of an RV-8 (or similar -number) and made it a composite single seater?
In the initial sizing I played with power loading and range bit to get the (gross weight)/(pwr loading) to coincide with the IO-360, and let the performance work itself out from there. The most notable design decisions are a low wing (no spar/carry through in the cockpit+space for retracts+sexiness), side bulges in the cowling to fit the engine (I prefer the mustachioed look to a squared-off nose), and use of the NASA NLF foil for GA, requiring full-span flaperons to exploit the full effect.
In case the HBA uploader butchered the resolution of the pictures here's the cliffnotes version of the figures:
As drawn it has a wingspan just a hair over 25', wing area of 79ft^2 and an aspect of 8. Fuse is 20' long, 2.5' wide, and 2.75' deep. Tail areas are calculated using the recommended coefficients of 0.04 vertical, 0.5 horizontal. Taper ratio is 0.5 (not counting the tip shaping) and stall speed is predicted at 58kts.
The goal gross weight is 1375lbs, with a fuel fraction of 0.185 and an empty weight fraction of 0.61. Predicted performance is 230kts max level speed and 2700fpm max climb at 5000' ASL.
(note that everything is sized to fit my unusual requirements for a 225lb, 6.5' tall guy)
Thing is when I did the weights estimation, it came out 25lbs over budget without fuel. The obvious solution is to find avgas with a density of about negative 5lbs/ft^3, but iterating again might be an easier option. I wanted to ask, since I don't have any practical experience to reality-check my numbers, if the weights seem reasonable (tell me if the chart in pic. 3 is illegible, I'll transcribe it). Also, if I'm doing anything that unnecessarily increases weight, e.g. I'm worried that I chose a tail boom too large in the name of tail efficiency, big picture stuff like that. Before running through a second iteration and a second drawing and all that, I'd like to know why it didn't work out the first time.
(sorry about pics 2 and 3 being sideways, somewhere along the line everything was changed to landscape)
In the initial sizing I played with power loading and range bit to get the (gross weight)/(pwr loading) to coincide with the IO-360, and let the performance work itself out from there. The most notable design decisions are a low wing (no spar/carry through in the cockpit+space for retracts+sexiness), side bulges in the cowling to fit the engine (I prefer the mustachioed look to a squared-off nose), and use of the NASA NLF foil for GA, requiring full-span flaperons to exploit the full effect.
In case the HBA uploader butchered the resolution of the pictures here's the cliffnotes version of the figures:
As drawn it has a wingspan just a hair over 25', wing area of 79ft^2 and an aspect of 8. Fuse is 20' long, 2.5' wide, and 2.75' deep. Tail areas are calculated using the recommended coefficients of 0.04 vertical, 0.5 horizontal. Taper ratio is 0.5 (not counting the tip shaping) and stall speed is predicted at 58kts.
The goal gross weight is 1375lbs, with a fuel fraction of 0.185 and an empty weight fraction of 0.61. Predicted performance is 230kts max level speed and 2700fpm max climb at 5000' ASL.
(note that everything is sized to fit my unusual requirements for a 225lb, 6.5' tall guy)
Thing is when I did the weights estimation, it came out 25lbs over budget without fuel. The obvious solution is to find avgas with a density of about negative 5lbs/ft^3, but iterating again might be an easier option. I wanted to ask, since I don't have any practical experience to reality-check my numbers, if the weights seem reasonable (tell me if the chart in pic. 3 is illegible, I'll transcribe it). Also, if I'm doing anything that unnecessarily increases weight, e.g. I'm worried that I chose a tail boom too large in the name of tail efficiency, big picture stuff like that. Before running through a second iteration and a second drawing and all that, I'd like to know why it didn't work out the first time.
(sorry about pics 2 and 3 being sideways, somewhere along the line everything was changed to landscape)
