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Discussion Starter #1
Hello All!

I'm starting trike build #6 officially tomorrow with the arrival of a couple of hundred in steel and a Karman Ghia disc frond end.

Heres what I'm thinking:

I'm looking for 100 mile range. I live in an area of Florida where anything worthwhile is 40 miles away.

I'm looking for 70mph top speed.

Design goal for the trike is 850 pounds with 24 100ah thunderskys

2f1r rear wheel drive.

alltrax 7245 (unpurchased, but fairly certain of the choice.)

D&D ES-15-6 Series Motor (comments on motor / controller choice?)

Heres my first question. Ive included a primitive sketch of the body design, very clean and spartan, the only compound curve on the whole trike is the massive canopy itself. I found a canopy guy who can do a 55" wide x 96" long canopy so the idea is to slope it downward at the nose and use the "bottom" 6 to 8" as the headlight and directional lenses.

I only know enough about aerodynamics to be truly dangerous and realize that (in my mind) the sharpish slope of the rear as seen in the top view looks good, but is it too sharp to adequately fair the air, would I be better off aerodynamically with a wider tail?

Ive settled on the balance issues, know where the batteries will go to get optimum balance irrespective of how heavy / how many riders. Outer dimensions:

108" overall length
55" overall width at front wheels
76" wheelbase
6" ground clearance
42" overall height (I need to make a new pencil sketch, ive subsequently moved the seat down and divided the batts to one bank ahead of the riders feet and one bank behind the seat.

Anyone here want to do a "mercy drawing" on cad so I can save the forum from these hideous drawings? :)
 

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What speed do you hope to achieve this range? Your pack will probably be too small; you might get that range to 100% DoD at 45 mph, but not at realistic highway speeds. I'd recommend going with a higher AH battery of that chemistry. Keep in mind that you will want to have a battery pack that is sized to where your 100 miles range will not discharge it past 80% if you decide not to use a BMS.

Judging from your drawing, your vehicle will be 49" tall(assuming the drawing is to scale). With your given width, this will be about a 15.2 sq ft frontal area. It seems awfully large for a trike, especially given my Triumph GT6 has a frontal area of 14.9 sq ft, on 4 wheels no less. I'd recommend designing it to be thinner(perhaps a tandem two seater with a 42" height, or if 49" height is desired, no wider than 50", to cut down on frontal area; I know you stated the desired height is 42", but the proportions on your drawing don't match, and I am making assumption that it is drawn to scale and the measurement you gave on the side is the wheelbase).

Your aerodynamics seem a little bit off on the top slope(see attached image). Remember, you want a 6:1 fineness ratio. I’d also use a Kamm extension on the roof going as far back as possible; if you want the rear ‘bumper’ to stick out a certain length, then you want the roof to trail back at least as far following that tear drop shape in the image below. If you correct that and end up with a 0.25 Cd, 100 miles range at 45 mph might be achievable with ease. This assumes your tires have a Crr of around 0.007.

Now a little basic math. I do not know the efficiency of the motor you are using(I will assume ~83% efficient during ‘normal’ operating conditions) and assume you will be using a two speed tranny(~95% efficient) and assume your controller is 95% efficient with 200W of accessory loads(lights, ect). This gives a combined motor/controller efficiency of 79%.

Mass(W)- 450 kilograms (assumes you didn't include the weight of the driver in the 850 lbs)

Drag Coefficient(Cd)- 0.25
Frontal Area(A)- 1.41 square meters
Rolling Resistance Coefficient(Cr)- .007
Transmission Efficiency(TE)- .95
Motor/Controller combined Efficiency(ME)- .79
Battery Capacity(C)- 6912 Wh (7680 Wh pack with assumes 90% deliverable capacity)

Velocity(V)- expressed in meters per second
Force Drag(FD)- expressed in newtons
Force Rolling(FR)- expressed in newtons
Wheel Power(WP)- expressed in watts
Motor Power(MP)- expressed in watts
Battery Power(P)- expressed in watts
Accessory Load(L)- expressed in watts

Run Time(T)- expressed in hours
Air Density(Rho)- 1.25 kg/m^3
Gravitational Constant(G)- 9.8 N/kg
FD = .5 * Rho * Cd * A * V^2
FR = Cr * W * G
WP = (FD + FR) * V
MP = WP / TE
P = MP / ME + L

T = C / P






Results(45 mph)-
At 20.1 m/s;
FD = 89.0
FR = 30.9
WP = 2410

MP = 2537

P = 3257

T= 2.12


This means you have a range of 95.4 miles at 45 mph to 100% discharge.



Results(60 mph)-
At 26.8 m/s;
FD = 158.2
FR = 30.9
WP = 5069
MP = 5336
P = 6629
T= 1.04


This means you will have a range of 62.6 miles at 60 mph to 100% DoD.



***edit***

If you are intent on having front wheel farings that move with the wheels as you steer, a Cd in the 0.15-0.18 range is possible, if you get the proportions of the body correct. THAT would have some serious range...
 

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I look forward to how this will develop.

For my trike I calculated that I would need, at best, 30 x 100ah cells running to 80%DoD for my 70mile, 70mph range. I am planning on finding space for 45 x 100ah cells just to be sure due to the hills on my commute.

Your design has an all enveloping body that does increase frontal area a great deal. I think the trick maybe to go wide and low or tall and thin.
I have chosen the tall and thin route with my body work being only around 700mm wide and overall height being 1100mm tall. The overall width will be around 1500mm with a front track of 1320mm IIRC.

I am not aiming for as much aero as you are as I will most probably have an open top with cycle wings on the front tyres. That will probably use up my extra 15 cells pushing that through the air.
 

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Discussion Starter #5
Thanks for the input guys! I did a new drawing illustrating the drop to now 41" at its highest point, just gotta scan it and send it in a little bit.

Ok, this might seem shallow but there are three things that are important to me as far as personal taste:

That the trike is short (for comparison, an original mini cooper is 120")
I want 108" (Really want 96 but I think the wheelbase would need to be too short to acheive that)

That its low (an Elise is 45.2")
That its light (a fully dressed Goldwing is 908 pounds)

Given the design goal to keep it short, Im wondering from an aero perspective if the "tail tip" being 8" across is the way to go or bring it out to say 24" or has the slopey aft started so much turbulence that it doesn't matter?
 

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Ok, this might seem shallow but there are three things that are important to me as far as personal taste:

That the trike is short (for comparison, an original mini cooper is 120")
I want 108" (Really want 96 but I think the wheelbase would need to be too short to acheive that)

That its low (an Elise is 45.2")
That its light (a fully dressed Goldwing is 908 pounds)

Given the design goal to keep it short, Im wondering from an aero perspective if the "tail tip" being 8" across is the way to go or bring it out to say 24" or has the slopey aft started so much turbulence that it doesn't matter?
Shallow?

My requirements are wire wheels, electric windows and mirrors, leather seats, big stereo and reversing camera!:eek:
That's shallow!

Good aero goes a little hand in hand with a large length vs frontal area ratio. A short but curvy body has more drag then a bluff fronted but very long body. The essence is in the way the air leaves the back of the body so you would be better with a long tapering body but a Kamm back, long and at the best angle, with a sharp cut off seems to work ok too.
 
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