REFLECTOR: Do Plans include Carbon Fiber "Y"?

Sat Oct 10 08:28:43 CDT 2009

I'm attaching 3 low res pictures that I hope go thru the reflector.  Someone asked about the naca ducts and the Y.  Just alter the Y to accomade the ducts but try to maintain the the basic structure to distribute the forces to high strength areas.  

Jim

James F. Agnew
Jim_Agnew_2 at Yahoo.Com
Tampa, FL
Velocity 173 Elite Aircraft Completed & Flying

________________________________
From: Al Gietzen <ALVentures at cox.net>
To: Jim Agnew <Jim_Agnew_2 at yahoo.com>; Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Fri, October 9, 2009 11:01:20 AM
Subject: RE: REFLECTOR: Do Plans include Carbon Fiber "Y"?

Jim;

Thanks for the clarification.  That sounds much better than just the “Y”
Al

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Jim Agnew
Sent: Thursday, October 08, 2009 6:56 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Do Plans include Carbon Fiber "Y"?

To Al & Dennis,

I have a carbon fiber roll cage12" wide that runs down the overhead  from a Y about 18" in front of the engine bulkhead  that connects to the very heavy triax layups for the engine mounts to the overhead of the front window and down into the lower fuselage along the front of the door beams and is tied across the middle between the door rear carbon beams.  I covered all of the overhead carbon with a wider strip of Kevlar containment in case the cage is over stressed and shatters into the sharp carbon pieces.  Mounting the engine did not in any way alter the shape of my fuselage that I can detect.

Jim

James F. Agnew
Jim_Agnew_2 at Yahoo.Com
Tampa, FL
Velocity 173 Elite Aircraft Completed & Flying

________________________________

From:Al Gietzen <ALVentures at cox.net>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Thu, October 8, 2009 8:20:51 PM
Subject: Re: REFLECTOR: Do Plans include Carbon Fiber "Y"?
Dennis;

I’d assume that the increase in difficulty of latching your doors is still a result of distortion in the fuselage.

Some reinforcement helps; although hard to know how to reinforce without knowing what the stress distribution is.  My best guess is that the forces on the firewall (and carried into the spar and strakes from the engine, and further, from the swept back wings); create a distortion of the cross-section of the fuselage forward in the area of the doors, as well as pulling back on the top.  That’s why when you put the jacks under the wings the doors latch more easily.

My approach to strengthening was to continue the carbon side beams across the top (I think this may now be standard), reinforce the small beam at the front of the door and across the over head panel.  I then added foam core beams across the top of the doors, and down the center from the mid cross beam back to the firewall.  The center beam is in place of the V channel that has become standard.  I’m also guessing that more circumferential rigidity at the front of the door would reduce the distortion.

It added a few pounds, and I wouldn’t say it’s necessary, but it added strength and rigidity.  When the engine and wings were added, not much notable change in the door fit, but it did take more force to latch the door.

Terry makes a good point – keep the doors closed, when the plane is sitting around.  In the few months that mine sat without the left door, the right door became more difficult to latch.  The doors are part of the load carrying structure.  Composites are very strong and light, but they are subject to viscoelastic creep at much lower temperatures than metals.  (Don’t ya just love that “viscoelastic creep”.  Sounds like something that should only happen on Halloween J.  I did a lot of finite-element, viscoelastic creep analysis of high temperature metals way back when).

Al

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Dennis Martin
Sent: Thursday, October 08, 2009 7:08 AM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: Do Plans include Carbon Fiber "Y"?

Al Gietzen mentioned this geometry issue in a post yesterday, and Jim Agnew advised me to install carbon reinforcement back in the late 90s. Here's the thing. The entire fuselage will distort after you hang the engine on - and doors may no longer fit properly. Physical forces from engine weight will change all of the geometry.

Jim advised laying up a 2-bid carbon fiber "Y" on the top of the fuselage (inside cabin). I don't know if it's in the plans by now, but I think it should be a standard part of the build. I did this about 6 years ago before installing the engine. I laid up a 12" wide carbon fiber "Y" on the ceiling of the fuselage. The two branches of the Y go to the firewall, and attach about 3 inches down onto the wall to add extra strength where firewall and cabin intersect. The two branches of the Y meet about in the middle of the cabin, then the trunk of the Y runs all the way to the front windscreen.

Added benefit is a stronger "egg" in case you ever end up in a ground loop.

My engine weighs 450 pounds, and my cabin is true to the original. Doors fit same as when I first installed them. Door pins are tight, so there might be minor distortion. But that should be easy to fix. 

-- 
All the best,
Dennis
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20091010/b0cb3f44/attachment-0001.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: BPRollCage1-LR Front View Upside down.jpg
Type: image/jpeg
Size: 74716 bytes
Desc: not available
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20091010/b0cb3f44/attachment-0003.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: BPRollCage2-LR Rear View Upside down.jpg
Type: image/jpeg
Size: 80226 bytes
Desc: not available
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20091010/b0cb3f44/attachment-0004.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: BPRollCage3-LR Door Carbon beam tie in with kevlar overlay View Upside down.jpg
Type: image/jpeg
Size: 65041 bytes
Desc: not available
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20091010/b0cb3f44/attachment-0005.jpg>