Some You Win, Some You Loose

Took the two repaired bows out to where we shoot near Chelmsford.
The bamboo repair failed, starting to lift with a bit of a cracking sound as my mate JT neared full draw... never mind, I'll take the back off and re-back it.

The re-repaired yew faired better, I'd left a little extra thickness on the new patch and it looked fine at full draw, it's good to keep the old work horse going.
It was very hot over there and my bow seemed to have relaxed a fair bit in the heat. I'd made up a flight arrow from one of my early ones with the front end tapered a lot more and a lighter brass point from a broken flight arrow fitted, and that flew nicely a good 30 yards or so further than the other arrows.

Not my Best work

The repair is done, but doesn't look great. When I strung the bow there were signs of it lifting at the node end. I'll have to see if it survives being shot, it it lifts I'll take off the entire back and do a new bamboo back. Must remember to take some thickness measurements first!

Hmmm the blogger has been updated to make it less user friendly but supposedly better for viewing on a smart phone or tablet. I couldn't find the "new post" button initially (nor could anyone else!) I'm not even sure what I did to create this new post!
Ah, found it... there's a round orange circle bottom right with a + in it . Presumably some one thinks this is better than having "New Post" top left at the head of the main menu? (Sigh)
Can't seem to adjust the size of the pics either. Hey ho, pretty typical really, I expect the bugs will get ironed out..

A Couple of Repair Jobs

We've got back to some shooting, just roving on a big open field, we can keep well apart whilst getting some fresh air and lobbing arrows into the sky.
I went with 2 bows and came back with 3! I gave my mate JT the latest flight warbow to try, he wasn't getting it back to full draw but it seemed promising.

 He showed me some chrysals that had appeared on one of his old stalwart Yew bows. I'd already done an extensive and complex repair on it a good while back as it had a weak point in one limb with very very deep chrysals. Well the same area was still a tad weak and the chrysals were reappearing, they hadn't gone right through the repair patch yet so maybe a shallower patch may do the job, I'll try to leave it a little thicker this time, but that's surprisingly hard to do without creating a weak point either end of the patch.

He was then showing someone the Boo Yew primitive style heavy bow to demonstrate it's performance and shape when I noticed a crack on the boo backing. I've pretty much always touted boo' as being bomb proof, so this was a shock to me... mind TBF it is a 120# bow.
The bow had some previous repair work where the grip was starting to crack. And this shows when it was first being shot.
It's an interesting repair job and it's good to tackle new stuff. The best and obvious repair would be to strip off the whole back and re-back it. However it's interesting to look at the anatomy of the crack, I've noticed the fibres peel up to the node, so I'm hoping to inlay a narrow strip of boo running from the noe almost to the tip, with it fading out at either end. If this fails I'll strip off the whole back and re-do it.

Messing About.

I've been messing about with the wind tunnel a bit more... the fundamental problem is that I need a wind tunnel to test the wind tunnel! If I dangle a thread down the tube I can see it is being pulled straight, but as I lower it further in it starts to waggle and then thrash around, further down it settles again, the implication is that there is maybe a standing wave or surface effect giving nodes and antinodes of smooth and turbulent flow. I remembered reading that in supersonic wind tunnels they have holes in the inner wall to stop the shock waves bouncing back off the walls, so I thought maybe a pattern of holes would allow some air to be sucked in at the walls breaking up any slow surface layer of air... you can see why I need a wind tunnel to test the wind tunnel!
Anyhow, another effect is that if I dangle my length of wooden arrow shaft in there it will be stable for a while and then after about 10 seconds oscillations will build and the end of the shaft will swing round just inside the wall. I noticed that the arm from which the shaft is suspended on its thread, is prone to waggle slightly sideways and this is probably helping to initiate the oscillation. I have ideas for a more stable arm, but I feel I'm in danger of getting sucked into a time consuming and fairly pointless exercise in trying to produce something better with very limited resources (and knowledge).
Another project, that's what I need... but then projects need to jump out and grab your attention, so I'll just fiddle about until something appears.


meanwhile the garage needs a really good tidy, however the council tip (or "recycling centre" in modern parlance) isn't open to the public yet due to Covid19 precautions, so I've a lot of scrap timber and garden rubbish lying about.
I'll probably glue up some billets and have a bit of a sort out to keep me busy... there's only so much, online bridge, youtube and harmonica practice a man can take!

Where I'd sliced the top of the flared wooden inlet for the wind tunnel it had left a nice ring of endgrain wood... hmmm, "that would make a nice target" I thought so I pinned it up on the boss and had a go from 10 yards hoping to stick an arrow in the ring. Better than that, it caught the edge and the wood exploded in a most satisfying manner!
Excellent, I had a short off cut of timber lying around so I glued it up and sliced it thinly to make some nice targets, I'll have some fun later today with my son trying to smash them.
I s'pose they could also be used as coasters, and once they get too dirty, they could then be come targets :-)

Wind Tunnel Update

I got the new improved windtunnel running and the tried my reference 9.5" nock test shaft. It started off stable then started to wobble and ended up with the nock end swinging round in circles almost touching the wall of the tube... Hmmm?
I slipped a piece of slit pipe down inside the flared section and the stabilised! I took noted the test figures and the figure for the drag was exactly the same as previous test.
Oh well it looks like the fancy wooden flared inlet will be coming off!

Wind Tunnel

I'm now on the mk2 wind tunnel :-)
The mk1 proved the principle and gave some useful figure for drag. It needed some baffles to help achieve linear air flow as the rotating fan created a vortex, which ironically held the arrow steady in the centre but made it spin V rapidly.
Mk1 arrow wind tunnel

I've reverted to the 65mm drainpipe for the mk 2. I've made a grid of thin sheet metal (from the back of a old scrapped oven) to smooth the airflow, this is pushed up into a cardboard tube. The plastic drainpipe fits down inside the cardboard tube with the slight gap between two blocked off with draught excluder. This arrangement gives a nice clean interface between the grid and allows me to try longer pipes or other arrangements.

I've made a flared wooden inlet for the top end of the pipe, as a further possible improvement, mostly just for the fun of doing it... dunno if it will make any difference.

As a test I made up some 9.5" lengths of 3/8" Ash arrows shaft with different nock styles the other end of the shaft was tapered and had a thread glued to it to allow the shaft to dangle into the pipe.
The results were nicely measurable as were as you might expect with the tapered nock having less drag and the one cut square having most.

Lockdown Ideas and Distractions

Arrrghhh... no pictures!
I've been doing more videos on my Youtube channel "Del Cat"... (it's not monetized, no damned adverts to wait through). I've had some good reaction and even done one video in response to a specific question.

I've been toying with the idea of making a wind tunnel to measure the drag of arrows. It would be a vertical pipe with a fan at the bottom drawing the air through. The arrow would be suspended from its point by a fine thread which would connect via a lever which pressed down onto my digital grain/gram scales. Switching on the airflow should in theory increase the apparent weight of the arrow as the airflow pulls it down due to the drag.
The main problem is getting a fan with sufficient airflow, but then I thought of my dust extractor!
It's spec says 183 cubic metres per hour air flow. Now it's just a matter of some arithmetic to convert that into feet per second (fps) of air flow through a 60mm drain pipe. Unfortunately it comes out to about 52fps which is much slower than a flight arrow (~200fps or more).
On closer examination of the fan assembly from the dust extractor I found the air inlet is only 30mm diameter which is half the diameter of my drain pipe and thus 1/4 of its cross sectional area... ha, now if I make the pipe 30mm diameter, that would increase the air speed to about 200fps.
There are nice commercial dust extractor fans which shift 100 cubic metres an hour, but they are about £90 , rather big and probably noisy... not worth it for something I'll prob' only ever use once... not enough room in the garage for a decent wind tunnel really.... I could doubtless fill a large barn with stuff given half a chance.
Of course this is all rough calculation back of an envelope stuff (other writing surfaces are also available, although backs of fag packets have now been largely superseded).
There are many problems with wind tunnel design, even a crude one, but there is tons of stuff online for anyone interested. One obvious problem is that as the pipe diameter gets smaller the arrow can hit the side and the diameter of the arrow starts to become a bigger factor in blocking the airflow than its genuine drag. Still it may provide useful comparisons between similar diameter arrows with different tapers, points or fletchings... ah, that gives me an idea... a relatively short vesion could just test fletch configurations, drag vs area of fletch!

Anyhow, no rush to leap in doing it yet as I have another distraction... I bought myself a blues harmonica! The rest of the family are V musical but I'm not, I can sing, but if someone harmonises I get immediately phase locked into their notes!
I'd been given one as a kid one Christmas, and we had to call out who had given us what present so that we could all write our "thank you letters " when the excitement had died down. When my Dad asked who gave me the mouthorgan, I gleefully replied "'Our Monica!" (It was from Uncle Morris and Aunty Monica)
I had no idea how to play it and of course in those days, if you wanted to learn it would be from a book or a record if you were lucky. Nowadays with the wonders of Youtube it's easy to find a tutorial that suits your aspirations. Within a few hours of the blues harp arriving (see I already have the lingo!) I could make a reasonable sound and even managed a rather lumpy jam with my Son on his guitar. It took me a good 20 minutes to get the grin off my face.

I hope you are all finding stuff to do, keeping safe and refraining from drinking disinfectant.