A Future Pilot
New Member
Hello everyone!
So for a long time I've been considering building a small airplane to just punch holes in the skies, and the other day I finally decided to get started. I've been reading some of Aircraft Design: A Conceptual Approach, and I've ordered a copy of Simplified Aircraft Design for Homebuilders.
So far I've been following along in Topaz's excellent thread as he designed his Motorglider: https://www.homebuiltairplanes.com/...gn-inexpensive-single-seat-motorglider-1.html
First I'll give y'all a general idea of the plane. My plan is for it to be an almost-ultralight Bleriot XI that's been highly modified. It's going to have a steel tube fuselage, a cowling similar to a Fokker DR1, landing gear like a Curtiss Jenny, tailfeathers similar to a Sopwith Pup, fewer bracing wires (in slightly different locations), a Clark Y airfoil, and be powered by a Polini Thor 250 (Unless I can find a 4-stroke that would be better). I plan on releasing the plans when I'm done, and I want it to be build-able as an ultralight, though my choice of engine means mine will be registered as Experimental.
I'm really bad at drawings, but I have a friend sketching up some rough drafts that I'll post when they're done.
Following along in Topaz's thread, here's the preliminary performance I'm shooting for (Overall I want the performance to be close to a Mini-Max):
PAYLOAD
Design Pilot
Height: 5’ 6” to 6’ 1”
Weight: Up to 230# (Without baggage, 200# with baggage)
Baggage
Size: 1 tent and 1 bag clothing. About 30” x 20” x 10”. 30#.
PERFORMANCE
Cruise Speed: 65 MPH
Stall Speed: 30 MPH
Cruising Altitude: 5,500’
G-Loading: -1.5g to +3.8g (Normal Category)
Range: 150 Statute Miles
Takeoff Distance: Less than 300’
Landing Distance: Less than 500’
Glide Sink Rate: -500 FPM (this is optional, but I'd really like decent glide performance if I lose an engine)
Crosswind Component: 15 MPH
Climb Rate: 1000 FPM
W0 (Guess) is 254# (Ultralight) + 230# (Pilot) + 30# (Fuel) = 514#
W0 (Calculated) = 512
W0/HP = 14.25 (With the Polini Thor 250).
Now I'm at the point of dealing with Stall Speed and Wing Loading, and the figures aren't making sense at all.
The formula is W/S (Which is wing loading right?) = 1/2P * Vstall2 * CL Where P is the air density.
Now, I don't have any hard way of calculating the lift coefficient, but I can use the Mini-Max's since it's a very similar airplane. To calculate it I do:
(560 (gross) / 112.5 (wing area) ) / (0.00238 (air density) * 0.5 * 30 (stall speed)^2) which gives me a lift coefficient of 4.65. But the book says a plane with no flaps will have a lift coefficient between 1.2 and 1.5 usually. 4.65 seems CRAZY high.
So...what am I missing?
Thanks!
So for a long time I've been considering building a small airplane to just punch holes in the skies, and the other day I finally decided to get started. I've been reading some of Aircraft Design: A Conceptual Approach, and I've ordered a copy of Simplified Aircraft Design for Homebuilders.
So far I've been following along in Topaz's excellent thread as he designed his Motorglider: https://www.homebuiltairplanes.com/...gn-inexpensive-single-seat-motorglider-1.html
First I'll give y'all a general idea of the plane. My plan is for it to be an almost-ultralight Bleriot XI that's been highly modified. It's going to have a steel tube fuselage, a cowling similar to a Fokker DR1, landing gear like a Curtiss Jenny, tailfeathers similar to a Sopwith Pup, fewer bracing wires (in slightly different locations), a Clark Y airfoil, and be powered by a Polini Thor 250 (Unless I can find a 4-stroke that would be better). I plan on releasing the plans when I'm done, and I want it to be build-able as an ultralight, though my choice of engine means mine will be registered as Experimental.
I'm really bad at drawings, but I have a friend sketching up some rough drafts that I'll post when they're done.
Following along in Topaz's thread, here's the preliminary performance I'm shooting for (Overall I want the performance to be close to a Mini-Max):
PAYLOAD
Design Pilot
Height: 5’ 6” to 6’ 1”
Weight: Up to 230# (Without baggage, 200# with baggage)
Baggage
Size: 1 tent and 1 bag clothing. About 30” x 20” x 10”. 30#.
PERFORMANCE
Cruise Speed: 65 MPH
Stall Speed: 30 MPH
Cruising Altitude: 5,500’
G-Loading: -1.5g to +3.8g (Normal Category)
Range: 150 Statute Miles
Takeoff Distance: Less than 300’
Landing Distance: Less than 500’
Glide Sink Rate: -500 FPM (this is optional, but I'd really like decent glide performance if I lose an engine)
Crosswind Component: 15 MPH
Climb Rate: 1000 FPM
W0 (Guess) is 254# (Ultralight) + 230# (Pilot) + 30# (Fuel) = 514#
W0 (Calculated) = 512
W0/HP = 14.25 (With the Polini Thor 250).
Now I'm at the point of dealing with Stall Speed and Wing Loading, and the figures aren't making sense at all.
The formula is W/S (Which is wing loading right?) = 1/2P * Vstall2 * CL Where P is the air density.
Now, I don't have any hard way of calculating the lift coefficient, but I can use the Mini-Max's since it's a very similar airplane. To calculate it I do:
(560 (gross) / 112.5 (wing area) ) / (0.00238 (air density) * 0.5 * 30 (stall speed)^2) which gives me a lift coefficient of 4.65. But the book says a plane with no flaps will have a lift coefficient between 1.2 and 1.5 usually. 4.65 seems CRAZY high.
So...what am I missing?
Thanks!
