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Wind screen

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Graeme Toft

Joined: 09 Jan 2006
Posts: 123

Posted: Sun Mar 12, 2006 2:33 pm Post subject: Wind screen

Hi guys, Iv'e noticed this thread a couple of times now on wind screens and their thickness but didnt realise that this issue is related to VNE. I will be replacing mine as a last task before getting airborne again. Why is the thickness an issue with VNE. I assume it is because of possible distortion and the potential for failure. Is this correct and what thickness should I order if I want to increase VNE. The current windscreen is 3/16th and I believe it is from the factory.



Cheers



Graeme

wingsdown(at)comcast.net
Guest

Posted: Sun Mar 12, 2006 2:50 pm Post subject: Wind screen

The windshield alone is only one small factor in Vne. I would be more

concerned with control surfaces and aileron flutter. No doubt a better

windsheild is better. Still some debate on materials and thickness. Not

good to try to intall any of the non lexan in cold temps. Hot days and

patients are the best if possible.



Rick



--

ddsyverson(at)comcast.net
Guest

Posted: Sun Mar 12, 2006 3:31 pm Post subject: Wind screen

Graem,



I don't know that I can contribute much to the windscreen vs Vne issue. Vne is 

a design parameter which is defined by whatever becomes a problem first when 

adding speed. I don't know enough about the design limits of our airplanes to 

even guess if a thicker windshield would get you out there further or not. I 

don't think my engine will push me to Vne anyway on 100hp.



The wind screen I paid for twice (once to Skystar & once to John Mc Bean who 

got the job done for me) is the 3/16" thick version.  I would always 

gravitate towards the thickest one available simply because thicker provides 

more resistance to object penetration - whatever that object may be which 

chooses to get in front of my windshield - rocks on takeoff, golf balls, June 

bugs (which make a pretty good snap on the window at 100MPH) or English 

weaver finch. I realize that with the operational speeds of a Kitfox - birds 

have at least half a chance of getting out of our way - but if they don't 

it's not good. I have seen a Cessna 172 which ruined a Canada goose's day on 

the Cessna's short final and a Bellanca which took a mallard through the 

windscreen at cruise speed and the mallard parts didn't stop till the pink 

mist coagulated in the end of the tail cone - you just can't get a thick 

enough windscreen to keep those things out so the object penetration thing is 

sort of relative rather than absolute. Obviously, resistance to object 

penetration is a function of materials too (polycarbonate holds up much 

better than acrylic - everything else being the same) - but that is my main 

reason to avoid a lighter windscreen.



Sincerely,



Dave S

St Paul, MN



Do Not Archive



On Sunday 12 March 2006 4:29 pm, Graeme Toft wrote:

 	  Quote: 	
		   



 Hi guys, Iv'e noticed this thread a couple of times now on wind screens and

 their thickness but didnt realise that this issue is related to VNE.

Clem Nichols

Joined: 10 Jan 2006
Posts: 88
Location: Munfordville, Ky

Posted: Sun Mar 12, 2006 4:29 pm Post subject: Wind screen

With the crazing on my present windscreen, I realize it's just a matter of 

time before I'll be forced to replace it.  If I remember previous posts, the 

acrylic is more resistant to scratches, etc., than the polycarbonate, and 

obviously the acrylic can be ordered preformed whereas the polycarbonate 

(lexan?) comes in a flat sheet and requires a good deal of work to make it 

fit.  Moreover, the polycarbonate is not tinted (can it be ordered that 

way?), whereas apparently the acrylic can be.  In the summertime when I do 

most of my flying I sometimes find myself wishing I had a little shade over 

my head.  If I remember correctly the polycarbonate can be damaged by 

glue-on sun screens, and I've had no luck with the screens that are held on 

by static electricity.  Thanks in advance.



Clem Nichols

---

lcfitt(at)sbcglobal.net
Guest

Posted: Sun Mar 12, 2006 5:24 pm Post subject: Wind screen

Hi Greame,



I think a little clarification here is in order.



With the Model IV the kits came with two thicknesses of the Lexan 

(Polycarbonate) wind sheild (screen for you, i guess).   This was a flat 

sheet that was cut to shape and bent over the front area and actoss the wing 

root area and then back to cover the skylight.



The two thicknesses were .060 and .093 inches. The .060 was used on the 

standard long wing IV -VNE 125 and the short wing speedster - VNE 135. 

Discussion in the past has suggested that the windshield thickness, was at 

least in part, a VNE design issue - a tendency for the thinner material 

diforming at high speeds.  I have the .060, and have replaced it once about 

200 hours ago.  The first windshield was in use over 500 hours and the 

reason for the replacement was the large scratch that appeared in the 

building process - I just got tired of looking at it.  I have flown at near 

VNE - my airspeed indicatoronly goes to 120 and I try to limit my speed to 

that - and I doubt anyone could convince me of the need for the .093.  I do 

see some wind effects on the Lexan at high speeds and some prop pulse 

effects, but it doesn't bother me.



I think the thicker windshields mentioned in the inch fraction range are the 

ones from LP Aeroplastics and they are not Lexan, but Acrylic.  Acrylic does 

have some advantages relating to ease of polishing out minor scratches, but 

the stuff is very brittle and extremely unforgiving and must be handled very 

carefully.  For strength it has to be a quantum leap thicker or what will 

merely deform the lexan for an immediate bounce back will break the acrylic.



I run (fly) with a group of "light" airplanes - mine is the heaviest and I 

sometimes wonder why the bigger and heavier seems to often get the nod even 

where there is no demonstrated benefit.  I recall of one Lexan windshield 

splitting from top to bottom for some reason.  It was cleverly field 

repaired and the flight went on.  That one incident was not reason enough 

for me to go thicker or heavier and definitely not more expensive.



Keep in mind that this is for a fairly quick Model IV and I have no opinions 

on the subject regarding the heavier airplanes.



regards,



Lowell



---

lcfitt(at)sbcglobal.net
Guest

Posted: Sun Mar 12, 2006 6:22 pm Post subject: Wind screen

Clem,

For Summer shade, I use one of the smaller spring loaded hoop-like 

alumanized auto dashboard protectors.  It fits very well overhead between 

the tubing and the skylight.



Lowell



---

clint_bazzill(at)hotmail.
Guest

Posted: Sun Mar 12, 2006 9:39 pm Post subject: Wind screen

The standard long wing model IV came with the .093.  The speedster was .250, 

a friend had a speedster and had trouble with bending it.  I used it and had 

no problem.  Does increase the Vne to 140 as the .093 would flex in at 

higher speeds.  Clint with .250 now.

From: "Lowell Fitt" <lcfitt(at)sbcglobal.net>

Reply-To: kitfox-list(at)matronics.com

To: <kitfox-list(at)matronics.com>

Subject: Re: Wind screen

Date: Sun, 12 Mar 2006 17:22:51 -0800






Hi Greame,



I think a little clarification here is in order.



With the Model IV the kits came with two thicknesses of the Lexan

(Polycarbonate) wind sheild (screen for you, i guess).   This was a flat

sheet that was cut to shape and bent over the front area and actoss the wing

root area and then back to cover the skylight.



The two thicknesses were .060 and .093 inches. The .060 was used on the

standard long wing IV -VNE 125 and the short wing speedster - VNE 135.

Discussion in the past has suggested that the windshield thickness, was at

least in part, a VNE design issue - a tendency for the thinner material

diforming at high speeds.  I have the .060, and have replaced it once about

200 hours ago.  The first windshield was in use over 500 hours and the

reason for the replacement was the large scratch that appeared in the

building process - I just got tired of looking at it.  I have flown at near

VNE - my airspeed indicatoronly goes to 120 and I try to limit my speed to

that - and I doubt anyone could convince me of the need for the .093.  I do

see some wind effects on the Lexan at high speeds and some prop pulse

effects, but it doesn't bother me.



I think the thicker windshields mentioned in the inch fraction range are the

ones from LP Aeroplastics and they are not Lexan, but Acrylic.  Acrylic does

have some advantages relating to ease of polishing out minor scratches, but

the stuff is very brittle and extremely unforgiving and must be handled very

carefully.  For strength it has to be a quantum leap thicker or what will

merely deform the lexan for an immediate bounce back will break the acrylic.



I run (fly) with a group of "light" airplanes - mine is the heaviest and I

sometimes wonder why the bigger and heavier seems to often get the nod even

where there is no demonstrated benefit.  I recall of one Lexan windshield

splitting from top to bottom for some reason.  It was cleverly field

repaired and the flight went on.  That one incident was not reason enough

for me to go thicker or heavier and definitely not more expensive.



Keep in mind that this is for a fairly quick Model IV and I have no opinions

on the subject regarding the heavier airplanes.



regards,



Lowell



---

Graeme Toft

Joined: 09 Jan 2006
Posts: 123

Posted: Sun Mar 12, 2006 9:42 pm Post subject: Wind screen

Thanks for the replies guys. I remember the trouble I had replacing my Model 

1 windscreen and even though it was acrylic (not even sure you can get lexan 

down here) it was one hell of a job bending it to fit the near right angle 

turn from screen to overhead clear view and back to the beginning of the 

turtle deck. Also as many others have found, I ended up with lots of crazing 

around the rivet holes because I didn't make them over size. Experience is a 

great teacher. Has anyone tried some judicial use of a heat gun to make the 

bends?. Could be an expensive mistake but I'm wondering if it would make the 

material pliable enough to bend without experiencing the cracking so many 

have, to their frustration experienced. Anyway I'll stick with the 3/16 as 

advised.



Cheers

Graeme



---

lcfitt(at)sbcglobal.net
Guest

Posted: Mon Mar 13, 2006 7:14 am Post subject: Wind screen

Hey, Clint.  .250 is 1/4".  Are you sure your figures are correct.  I 

measured mine before posting.  And I just remembered I still have the 

original in my shed.  Just measured that and it is .060.   The Lancair has 

.250 (Plexiglass) and it claims to be a 300 mph airplane.



Lowell

---

Richard Rabbers

Joined: 09 Jan 2006
Posts: 114
Location: Benton Harbor, MI - USA

Posted: Mon Mar 13, 2006 8:03 am Post subject: Re: Wind screen

Hello List.



Windshield thickness:

My company makes a film that is used by many to product the surface of materials when thermal forming - customers names are probably not familar to most but one uses our film to shape a laminated sheet for F-18 windshield. I got a hold of a piece (in discussing concerns with our film) 

The laminate is made up of several layers - Clear on both outer sheets - green tinted and an amorphous goo (probably for dampening as one lamination - The total thickness is just under 1 inch! .... I think I may want more !!!!!  I understand the SR-71 has about 3 inch thickness  



Acrylic (or PC) forming:

Back in my college days I used a heat gun to warm then shape some material (probably acrylic) to make a dust cover for my stereo (ie rotating vinyl disk / needle)

I've not done any shaping since but had pretty good luck... with care, heating uniformly just in from the edge (with a shield) to heat where needed - the piece gradually 'fell' over under it's weight and with removal of heat and gentle support I achieved my goal.  I'd do ALOT of practice before I pursued a LARGE piece of material. I purchased a FORMED windshield from Skystar for my model 1 a while back but have not installed it yet. (they had only 2-3 size but said it should fit my M-1 with a bit of tweaking) 



My bill wa$ $imilar to yours  (Rich in Kennebunk)

Good luck with your crack - please wish me luck. It sounds like that'

s what it might take. I read quite a bit from archives on this topic and will wait for summer warmth also.



Regards,

_________________
Richard in SW Michigan
Model 1 / 618 - full-lotus floats (restoration)

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Mon Mar 13, 2006 8:41 am Post subject: Wind screen

Just for kicks, I measured scraps cut from my LP Aeroplastics 

WS/Skylight combo, and the thickness was .115-.135", for what that's 

worth.



Lynn

Kitfox IV...Jabiru 2200



On Monday, March 13, 2006, at 10:12  AM, Lowell Fitt wrote:



 	  Quote: 	
		   



 Hey, Clint.  .250 is 1/4".  Are you sure your figures are correct.  I

 measured mine before posting.  And I just remembered I still have the

 original in my shed.  Just measured that and it is .060.   The Lancair 

 has

 .250 (Plexiglass) and it claims to be a 300 mph airplane.



 Lowell

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

clint_bazzill(at)hotmail.
Guest

Posted: Mon Mar 13, 2006 10:17 am Post subject: Wind screen

Sorry about that.  1/8 inch is what I ment to say. .125 inches the same as 

they put in the Speedster.  Clilnt

From: Lynn Matteson <lynnmatt(at)jps.net>

Reply-To: kitfox-list(at)matronics.com

To: kitfox-list(at)matronics.com

Subject: Re: Wind screen

Date: Mon, 13 Mar 2006 11:40:49 -0500






Just for kicks, I measured scraps cut from my LP Aeroplastics

WS/Skylight combo, and the thickness was .115-.135", for what that's

worth.



Lynn

Kitfox IV...Jabiru 2200



On Monday, March 13, 2006, at 10:12  AM, Lowell Fitt wrote:



 > 

 >

 > Hey, Clint.  .250 is 1/4".  Are you sure your figures are correct.  I

 > measured mine before posting.  And I just remembered I still have the

 > original in my shed.  Just measured that and it is .060.   The Lancair

 > has

 > .250 (Plexiglass) and it claims to be a 300 mph airplane.

 >

 > Lowell

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