Author Topic: NACA 66 Special A/BGS  (Read 596487 times)

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Blue

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Re: NACA 66 Special A/BGS
« Reply #45 on: September 26, 2010, 02:50:16 PM »
Rob:

Ref. Your reply #30 - Updated chassis tube layout

Your overall vehicle concept seems to be quite well conceived and mercifully would appear to be aero stable which is a significant advantage.  However, since you are still in the early stages of frame/roll structure layout and are open to comments, here are a few more for your consideration.

...  You need to prevail upon Blue to allow a generous fillet, or better yet, a straight line tangent to the fuselage side and the canopy, so that the kinks can be eliminated.  ...
Thanks for the advice, and it is being followed.  After seeing the indirect load paths, I recommended we go to a more classical top fuel style cage.  Specifically the later generation with the diagonal upper bracing from the shoulder area across the top of the steering wheel to the forward bulkhead.  It also gives us easier entry and exit.  The Fossett LSR assistant crew chief is a AA fuel licence holder and is helping with the re-design.  I have a little bit of experience with truss structures and firmly believe that every good idea is worth copying:

http://www.bmeltd.com/Dragster/braced.html

vs.

http://www.bmeltd.com/Dragster/current.html

"mercifully" stable?  Thanks, there some here that don't believe in the advantage of un-coupling the downforce and weight trade.  Decades ago, it was thought that we needed weight for all that power.  Remember "leading down" the front and rear?  Then someone went light and went faster.  Now we have weight minimums in almost every motorsport to keep the wanton use of carbon from making formula cars into feathers.

As far as the aero goes, we'll get a good cage design re-done and bump the aero to fit.  While fillets are not preferred, the better course may be to simply increase the width of the canopy and possibly the "shoulder" lines of the OML (outer mold line).  As Brandon points out, this is why the whole thing is in cad first.  We appreciate all of the comments.

The earlier see-through rendering shows how everything fits, the biggest volume items are the coolant tanks for the engine and intercooler.  Chute tubes are above the tranny, forward of the diff.  The doors will be hinged at the front and open with a standard pull cable just like the flaps of a chute pack.  The tubes are short and fat, easing packing and giving us a nice quick deployment.  Pull point is inside the tube, so there's no exposed riser.  All of this is oriented up and aft so that the chutes go into clean air, the risers don't crease the bodywork or chute tube lips, and they pull straight through the CG at the flying height of the chute.

The axle is tied to the wing section (since the wing can generate so much downforce, it has to be) and the wing loads the axle and wheel fairings.  There's a lot of structure back there, it's mostly carbon.  I'm putting plenty of design margin into these areas, since I'm the one fabricating the bodywork and aerostructures.  If I can find the budget, I'm also building one for myself. 

Offline Rex Schimmer

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Re: NACA 66 Special A/BGS
« Reply #46 on: September 26, 2010, 06:53:08 PM »
I am not so sure that I would go away from the "hex section" concept for the driver area is a good idea. Yes it still needs some "tune up" related to eliminating some of the "indirect load paths" as Blue calls them and all of the tube bays need to be crossed with a diagonal but once this is done the hex shape is a pretty good representation of a thick wall tube of very large diameter. A structure similar to a top fuel car is a box and is strong in vertical bending and somewhat less strong in side bending and probably indeterminate across the corners. The hex design will be very strong regardless of what the load direction is. Obviously going with a box cross section will be certainly much easier to build but there are some potential advantages to the hex design. Looks like an FEA of the two structures should be ran.

Also regarding the "kink" that you have designed into the main roll cage structure, this joint can easily be made much stronger than a bend (which would be legal) by making this a bulk head joint.

Rex
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Offline basher13

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Re: NACA 66 Special A/BGS
« Reply #47 on: September 26, 2010, 07:59:06 PM »
Looks cool, nice to see differant shapes being used on the streamliners. What are your estimates for the length and rear width? Tryin to learn what I can on the aero side of things, can you explain the reference to "fillets"? That's a hard word to google and get a reasonable answer :|
The CAD stuff is neat,do you expect to work out the bugs on the computer or will a scale model be made and also tested?
Good luck, this'll be a good one to watch.
 :cheers:
Dan
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saltfever

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Re: NACA 66 Special A/BGS
« Reply #48 on: September 26, 2010, 09:28:18 PM »
Eric, I looked at both links (thanks!) and they are vibration analysis, not structural FEA. I can easily see how the extra tubing has stiffened the problem area. That raises the natural frequency of the tubing and solves the vibration problem. Knowing how violent tire-shake is in Top fuel I can certainly see the need for the analysis. However, I thought the current discussion was about a stronger cage for Rob not vibration analysis. Are they just examples of some consulting you did for McKinney?

Some of the down force numbers I am seeing are significant. It might be useful to remember that LSR tires are load rated. I don’t know about the MT’s are but the Goodyears are 3,700 lbs each. 10,000 lbs of down-force plus the static car weight should be interesting.

Offline bbarn

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Re: NACA 66 Special A/BGS
« Reply #49 on: September 26, 2010, 10:29:34 PM »
Eric, I looked at both links (thanks!) and they are vibration analysis, not structural FEA. I can easily see how the extra tubing has stiffened the problem area. That raises the natural frequency of the tubing and solves the vibration problem. Knowing how violent tire-shake is in Top fuel I can certainly see the need for the analysis. However, I thought the current discussion was about a stronger cage for Rob not vibration analysis. Are they just examples of some consulting you did for McKinney?

Some of the down force numbers I am seeing are significant. It might be useful to remember that LSR tires are load rated. I don’t know about the MT’s are but the Goodyears are 3,700 lbs each. 10,000 lbs of down-force plus the static car weight should be interesting.

The MTs are have no load rating. The information that we have received on the tires is that the centrifugal forces the tire is subject to at 7000+ RPMs is actually shedding the weight. There is an issue with heat buildup if you overload or from slipping (present in all tires) that needs to be taken into account, but no load rating.

I doubt very much that we will be close to approaching the 10k numbers, that was just a statement as to what could be made, not what we are expecting to need.
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Offline Rex Schimmer

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Re: NACA 66 Special A/BGS
« Reply #50 on: September 26, 2010, 10:59:35 PM »
Blue, (Eric)

"since I'm the one fabricating the bodywork and aerostructures.  If I can find the budget, I'm also building one for myself. "

I see that your money is moving toward your mouth!!! Great to hear you are so involved with this project. I assume that you will be making a plug and then a mold so that you can make several of these.


Rex
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Offline Rex Schimmer

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Re: NACA 66 Special A/BGS
« Reply #51 on: September 26, 2010, 11:24:16 PM »
Rob,
Go to this web site to see some truly unbelievable tube structure weldments.    http://www.race-dezert.com/forum/showthread.php?t=31417

Rex
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Offline robfrey

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Re: NACA 66 Special A/BGS
« Reply #52 on: September 26, 2010, 11:38:44 PM »
Yes Rex, I've seen this before. There is some awesome weldments here.
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Offline interested bystander

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Re: NACA 66 Special A/BGS
« Reply #53 on: September 26, 2010, 11:52:16 PM »
Good welds??? You vant to see good welds????

Look at Project 550's pics  reeel close.

And, I  was recently informed Jim Hume ain't the only awesum welder on the premises.
5 mph in pit area (clothed)

Blue

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Re: NACA 66 Special A/BGS
« Reply #54 on: September 27, 2010, 02:12:10 AM »
Eric, I looked at both links (thanks!) and they are vibration analysis, not structural FEA. I can easily see how the extra tubing has stiffened the problem area. That raises the natural frequency of the tubing and solves the vibration problem. Knowing how violent tire-shake is in Top fuel I can certainly see the need for the analysis. However, I thought the current discussion was about a stronger cage for Rob not vibration analysis. Are they just examples of some consulting you did for McKinney?

Some of the down force numbers I am seeing are significant. It might be useful to remember that LSR tires are load rated. I don’t know about the MT’s are but the Goodyears are 3,700 lbs each. 10,000 lbs of down-force plus the static car weight should be interesting.
I did not consult on the project, it was just a convenient link.  The lesson I drew from the design was more on the lines of load path from front corner to shoulder:  the diagonally braced design was far superior to the "classic" design when we consider the worst case of an end-over-end flip and roll.

The biggest difference is in the use of a vertical rise and triangle above the knees.  This provides for diagonals that transmit force from the front corners to the opposite shoulder bar without over-loading the cross bar.  Coincidentally, changing from a cross bar arrangement to the diagonally braced design provides for easier entry/exit/rescue.

On the downforce, we are going to use whatever is necessary within the limits of the tires available.  I expect the downforce to be only a few thousand pounds, equivalent to the ballast and weight we do not plan on carrying vs. other 400 mph cars.  The downforce and weight required for traction is proportional to the drag, we have a low drag design, we expect to use less load on our tires than comparable streamliners with higher drag.  
« Last Edit: September 27, 2010, 03:20:46 AM by Blue »

saltfever

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Re: NACA 66 Special A/BGS
« Reply #55 on: September 27, 2010, 03:26:28 AM »
Eric: I have been looking at your links again. That cage is kind of interesting. When you look at it there is a manifest difference in the structural bracing from the diagonal you mention and below. But the upper body and helmet area lacks complete triangulation. Also note the rear end attach points. I wondering if all of the structure we see is more there to react the 4-6G thrust from the launch than roll-over safety. The helmet area looks weak compared to what it is attached to. LSR doesn't have to worry about launch thrust and maybe some of what we see on the dragster cage is not needed for rollover protection since it is there for thrust reaction. The diagonal is obviously a good idea though.

Rob: I have heard that about centrifugal force on the tires but always wondered why Goodyear has a load limit. BTW, your 30" tire at 7,000 rpm is in the 625 mph range.










Offline robfrey

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Re: NACA 66 Special A/BGS
« Reply #56 on: September 27, 2010, 09:18:40 AM »


Rob: I have heard that about centrifugal force on the tires but always wondered why Goodyear has a load limit. BTW, your 30" tire at 7,000 rpm is in the 625 mph range.

That for the front tire at 16" and it's faster than 7000 rpm









[/quote]
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Blue

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Re: NACA 66 Special A/BGS
« Reply #57 on: September 28, 2010, 12:37:41 PM »
Eric: I have been looking at your links again. That cage is kind of interesting. When you look at it there is a manifest difference in the structural bracing from the diagonal you mention and below. But the upper body and helmet area lacks complete triangulation. Also note the rear end attach points. I wondering if all of the structure we see is more there to react the 4-6G thrust from the launch than roll-over safety. The helmet area looks weak compared to what it is attached to. LSR doesn't have to worry about launch thrust and maybe some of what we see on the dragster cage is not needed for rollover protection since it is there for thrust reaction. The diagonal is obviously a good idea though.
All good points that I saw as issues too.  I came up with a concept using the diagonals and adding two more direct cross members while fully triangulating the rollover area.  Fewer tubes and much stronger, it also addresses the comments everyone has made to us so far.  Rob's putting it in cad and we will post it for comment and more revisions.  We need to make sure that all the tech people know exactly what we are doing and how we are doing it from a safety and rules compliance standpoint before metal is cut.  As a former tech inspector, I always liked it when people fixed things before they got into line.

saltfever

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Re: NACA 66 Special A/BGS
« Reply #58 on: October 03, 2010, 05:01:56 AM »
Blue, Rob? . . . how are you comming with the latest CAD drawing?

Offline robfrey

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Re: NACA 66 Special A/BGS
« Reply #59 on: October 03, 2010, 03:07:21 PM »
We might be back to the old drawing board. Not related to cage design.
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