Amateur aerodynamics
- Thread starter Jim Gerwing
- Start date
Jim Gerwing
Well-Known Member
Alas,
the tidy profiling of the grips as pictured vis a vis the reality is due to the flattering perspective of the photo. The Following pic will illustrate that the first exhibit doesn't reveal the whole truth as neither does its horny companion.
the tidy profiling of the grips as pictured vis a vis the reality is due to the flattering perspective of the photo. The Following pic will illustrate that the first exhibit doesn't reveal the whole truth as neither does its horny companion.
Jim Gerwing
Well-Known Member
Horny
.jpg)
snilard
Guru of hot glue gun
Hi Jim.
I also think that
Hi Jim.
I also think that flat rear and narrow profile of your tailbox will cause unwanted pressure drag. Tailbox must have rain drop shape to be efficient. It must be wider than your shoulders in widest point and must go edge or nearly to edge.
I think that your actual tail box will be better than without any tailbox. But I think that there is huge space for improvements.
I also think that
Hi Jim.
I also think that flat rear and narrow profile of your tailbox will cause unwanted pressure drag. Tailbox must have rain drop shape to be efficient. It must be wider than your shoulders in widest point and must go edge or nearly to edge.
I think that your actual tail box will be better than without any tailbox. But I think that there is huge space for improvements.
John Tolhurst
Zen MBB Master
Look at Kammtail.
Look at Kammtail.
Look at Kammtail.
snilard
Guru of hot glue gun
Kamm tail is nice technology.
Kamm tail is nice technology. But it is designed to make profile shorter. True airfoil will have lower drag.
I guess that this tailbox will also have pressure drag on whole surface not only on the end. I guess that there will be flow separation on back of riders shoulders.
Kamm tail is nice technology. But it is designed to make profile shorter. True airfoil will have lower drag.
I guess that this tailbox will also have pressure drag on whole surface not only on the end. I guess that there will be flow separation on back of riders shoulders.
Jim Gerwing
Well-Known Member
Side view
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Jim Gerwing
Well-Known Member
Quarter view front
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Jim Gerwing
Well-Known Member
Commentary:
Major design consideration was laminar flow.
As a general rule of thumb, the length of an airfoil should be about 3X it's chord.
I have followed this except that I cut it off at about 70% which some sources indicate one can get away with without sacrificing significant gains (if, indeed, there are any to be had in my dream come true)
Pressure drag (do you mean parasitic drag?) is always present, I'm taking a macro approach.
My experience is that at low speeds, the kind I'm involved with, there is a lot of forgiveness.
For example airfoils are nice but in the absence of a NACA4867 (I just made that up) a kitchen table will do.
My head, shoulders and torso are covered in the head on profile of the above pictured tailbox.
IMHO, this is my best offering so far. . .
The proof of the pudding will be in the eating, your speculations are welcomed.
And, yes, Eric, the back tire is flat.
Major design consideration was laminar flow.
As a general rule of thumb, the length of an airfoil should be about 3X it's chord.
I have followed this except that I cut it off at about 70% which some sources indicate one can get away with without sacrificing significant gains (if, indeed, there are any to be had in my dream come true)
Pressure drag (do you mean parasitic drag?) is always present, I'm taking a macro approach.
My experience is that at low speeds, the kind I'm involved with, there is a lot of forgiveness.
For example airfoils are nice but in the absence of a NACA4867 (I just made that up) a kitchen table will do.
My head, shoulders and torso are covered in the head on profile of the above pictured tailbox.
IMHO, this is my best offering so far. . .
The proof of the pudding will be in the eating, your speculations are welcomed.
And, yes, Eric, the back tire is flat.
hamishbarker
Well-Known Member
Any plans for filing a smooth
Any plans for filing a smooth bevel and putting in bar end plugs to make the handlebars a bit less "core sample-ish"? Would hate to hear about an injury!
Full marks for effort on the tailbox, hope it makes for some extra speed (and maybe some convenient storage in case you want to carry some stuff on a day /overnight trip.).
Any plans for filing a smooth bevel and putting in bar end plugs to make the handlebars a bit less "core sample-ish"? Would hate to hear about an injury!
Full marks for effort on the tailbox, hope it makes for some extra speed (and maybe some convenient storage in case you want to carry some stuff on a day /overnight trip.).
Jim Gerwing
Well-Known Member
The bar ends
will play a role in stabilizing the front fairing. The hurricane bars are inset so that my hands are in the shadow of my knees. That little bit that sticks out beyond the hurricane bars could play a protective role in a crash. When I crashed with the stock bars (hands on the drops) I put a serious dent in my pinky which took the initial contact with the pavement. Eric posted a picture on this site that shows a wound similar to the one I sustained.
The tailbox weighs about 3lbs and could have been constructed lighter and is IN NO WAY intended for carting impedimenta.
Heh, Hamish, you're in New Zealand aren't you? I'd love to make a low and slow flight the length of NZ someday.
will play a role in stabilizing the front fairing. The hurricane bars are inset so that my hands are in the shadow of my knees. That little bit that sticks out beyond the hurricane bars could play a protective role in a crash. When I crashed with the stock bars (hands on the drops) I put a serious dent in my pinky which took the initial contact with the pavement. Eric posted a picture on this site that shows a wound similar to the one I sustained.
The tailbox weighs about 3lbs and could have been constructed lighter and is IN NO WAY intended for carting impedimenta.
Heh, Hamish, you're in New Zealand aren't you? I'd love to make a low and slow flight the length of NZ someday.
snilard
Guru of hot glue gun
Hi Jim.
By pressure drag I
Hi Jim.
By pressure drag I mean pressure part on drag force. Especially part of drag caused by low pressure on the back flat side of your tailbox. This part of drag is much lower on full airfoil.
Are you sure with laminar flow assumption? I would say that I will not be laminar in speeds like 12 m/s.
But I may be wrong. I don't know aerodynamics as much as It may be seen from my writings and as I would like to. I am numerically optimizing shape of velomobile in my thesis. So I have seen differences between full airfoil and kamm tail in mathematical models (what may be wrong). I have studied mainly mathematics not fluid physics so I have to believe my tutor about credibility of my models.
If you look at tested Dutch tailboxes It is different from yours. Is goes to edge on end as much as possible.
By pressure drag I
Hi Jim.
By pressure drag I mean pressure part on drag force. Especially part of drag caused by low pressure on the back flat side of your tailbox. This part of drag is much lower on full airfoil.
Are you sure with laminar flow assumption? I would say that I will not be laminar in speeds like 12 m/s.
But I may be wrong. I don't know aerodynamics as much as It may be seen from my writings and as I would like to. I am numerically optimizing shape of velomobile in my thesis. So I have seen differences between full airfoil and kamm tail in mathematical models (what may be wrong). I have studied mainly mathematics not fluid physics so I have to believe my tutor about credibility of my models.
If you look at tested Dutch tailboxes It is different from yours. Is goes to edge on end as much as possible.
hamishbarker
Well-Known Member
how is the fairing project coming along Jim? Any performance numbers with both the front and rear fairings fitted?
trplay
Zen MBB Master
I know nothing about air flow but having read enough to still know nothing it seems this design might not be as off base as some of you speculate. I may have misunderstood I thought I've read where the boat tail design works just fine for slower moving objects <less than around 55mph).
super slim
Zen MBB Master
Any news from Jim Gerwing on how his aerodynamic Vendetta is going?
super slim
Zen MBB Master
Any news from Jim Gerwing on how his aerodynamic Vendetta is going?
