http://faa-engineers.com/~mjgundry/blog/index.php Copyright 2012, Matt Gundry Matt Gundry en-US SPHPBLOG 0.5.1 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry100826-112950
Surface preparation Your wall needs to be very flat. This plaster mix won't fill gaps, so make sure the wall is at a finish quality of level 4 or 5 as understood by drywall and plaster contractors. If you try to level an area by applying a thick coat of this mix, you will spend the rest of the evening babysitting the area, frequently recompressing it to prevent cracking.

Mist the wall with water before applying the plaster. If you don't, the water will immediately be wicked out of the wet plaster, causing it to stick to the trowel on the smoothing pass seconds later. The moisture in the wall also aids adhesion.

Don't apply the lime plaster directly over gypsum drywall. It will crack and chip off in a few days. You will need to apply a quartz primer first, and ideally a skim coat of gauged lime plaster over the whole wall. I know this because I tried various types of wall board as test panels.

Application technique Basically the plaster is troweled on in very thin coats. Think heavy-paint thin. It is the variation in trowel techniques and aggregates that produces the varied finish effects. Since the permutations of techniques are endless, consider the mechanics of the process to guide you to your desired finish. Ultimately, though, this is an art that requires practice. If you are easily discouraged, spend the money on an experienced professional applying a proven product.

My observation is that controlling the finish is all about controlling imperfections. When you trowel on the plaster, the resulting surface has minor imperfections in the surface height. Subsequent applications of plaster will fill in the low areas and may even leave high areas exposed. The variation of exposed layers and tapering of thicknesses creates variation in tone in the finished surface. Burnishing creates the variation because higher burnishing pressure deepens the tone. Higher points in the fluctuating surface get more burnishing pressure and deeper color, even if you used only one tint in a perfectly mixed plaster for all the layers.

We can affect the imperfections by controlling how we use the trowel, and also by the aggregate in the plaster. The length of trowel passes changes the size of the area of similar imperfections, so it changes the density of tonal variation. The angle of the trowel changes the pressure at the working edge - higher angles have higher pressure thereby exposing more of the underlying layers. A flatter trowel will float more wet material aver the surface. The stiffness and size of the trowel used controls pressure as well. The direction of the trowel pass will affect how that layer reflects light - almost as if it changes the orientation of the marble particles. Larger aggregate creates larger variations in the finished surface, and also increases the abruptness of those variations. Abrupt variations lead to more contrast and even the illusion of lines and hard edges.

Use short, crossing strokes with a fine aggregate plaster, and the result will be a dense but subtle variation in tone. From a distance the color will look uniform, but will come alive like paint cannot. Use fine aggregate layers over a course aggregate base coat along with pigment changes, and you can achieve high contrast like that from the exposed sedimentary layers in a slate or shale.

Do be careful to not overwork the underlying layers. As the moisture evaporates and wicks out of the plaster, it will begin to burnish with the trowel. That will adversely affect adhesion of subsequent layers.

Burnishing This is when the surface comes to life. Referring to the photos in my previous post, that wall was a pretty uniform light drab brown before burnishing. Almost all of the tonal variation appeared during burnishing. Regarding pressure, one pass with a few pounds of force on the trowel results in 50%-75% of the surface taking on a sheen. The task is tedious, not strenuous.

I use a flexible pool trowel that allows me to work in a circular motion. A stiffer trowel dictates that it be dragged in one direction per pass, otherwise it digs into the plaster. Either way, I start with a very light pressure to knock down the high spots, then increase pressure until I get the desired depth. If the surface has a low spot that defies burnishing, use a little 600 grit paper to level the area first.

Perhaps it is the type of lime, use of sharp sand, or lack of finesse, but I have a little difficulty burnishing before the surface is completely dry. Most of an area will burnish fine, but then the trowel will stick or catch, pulling off a small area of plaster. Patching is easy, but I prefer to burnish the dry plaster. The main drawback to burnishing dry is that the high spots are much harder to work down, so sanding will occasionally be required to get a uniform burnish.

One more note about materials - did you know that the marking "chalk" used on sports fields is many times actually marble dust. I've found 50 lb bags of Imery's marking powder (marble) for under $10.
]]> 1896 Victorian Restoration http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry100826-112950 Matt Gundry Thu, 26 Aug 2010 16:29:50 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=10&m=08&entry=entry100826-112950 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry100825-223304
Here is a picture of the results from my homemade venetian plaster:



The base layer uses 1/2 part masons sand in place of 1/2 part of the marble dust. In retrospect, course marble dust would probably work better if I'd had it. The sharp silica sand tends to get grabbed by the burnishing trowel, and can "pop" or scratch the surface if too much pressure is applied while burnishing. You can also see the vertical lines caused by the wet trowel chattering over the sand grains. The lines are coloration only, and can't be felt by touch. We like the effect.

The color is "BROWN" liquid integral concrete pigment from Menards. I added the pigment last after everything else was well mixed. I did not fully mix in the pigment, but left a little variation in the bucket. The base layer was textured slightly with a natural sponge roller.

The second and third layers used all marble dust for the aggregate. I tweaked the pigment levels about 50% up and down in the top layers to get contrasting shades. I mixed the pigment well for these layers.

As the following picture shows, the homemade VP burnishes easily. I used a thin stainless steel pool trowel for burnishing. This trowel is very flexible, and does a better job of burnishing low areas. I only spent a minute to work this 2'x2' area into a nice shine. As you can see, some areas are a touch low, and don't get burnished right away. A few passes with 600 grit sandpaper will smooth things out enough so burnishing has better coverage.



Enough with that, here is the recipe:

Lime Putty (1 part) Make this by sifting hydrated lime powder into distilled water until it won't accept any more (dry powder floats on the surface for more than a minute). Cover the container and leave it sit overnight. The next day, the lime will have settled, so add more dry powder to refusal. Repeat until a rest overnight no longer results in appreciable water on the surface (maybe 3-4 repetitions). Now let it sit for a few weeks covered airtight in a cool place. Water and a thin floating crust will form on top of the putty. Pour this off and mix the putty well. Either use the putty immediately, or replace the 1" of water on top of the putty and reseal the container for long term storage. It only improves with age. (Basic method described to me by The Plasterers Arms over at FauxForum)

I used Western Miracle Lime. Yes, it is high magnesium dolomitic lime. No, it doesn't appear to detrimentally affect the plaster.

Marble Dust (1 part) I use Imery's, which is available from various distributors nationwide (they make cultured marble sinks with it). It is also sold as pool aggregate. Get a variety of gradations from medium sand (0.5 mm or so) down to the finest sold. $50 should get you several 50-100 lb bags.

Linseed Oil (~1/10th part) Just plain old boiled linseed oil from the paint store will do fine.

Olive Oil Soap (a smidge) I use Kiss My Face brand from the local natural foods store. Prepare the soap by shaving it and combining with an equal part of distilled water. Melt over a double boiler. The consistency after cooling should be like grease. A smidge is two tablespoons per gallon of plaster. (Method described by Eli Lucero at FauxForum)

Lime-safe Pigment I use the liquid integral concrete pigments. These won't fade in the presence of lime. You can add up to 15% by weight of lime, or 5% of the overall plaster batch weight. Fresco pigments should work as well.]]> 1896 Victorian Restoration http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry100825-223304 Matt Gundry Thu, 26 Aug 2010 03:33:04 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=10&m=08&entry=entry100825-223304 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090820-221012 Airframe Audit http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090820-221012 Matt Gundry Fri, 21 Aug 2009 03:10:12 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=09&m=08&entry=entry090820-221012 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090803-200517
]]> Ragwing RW-11 Construction http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090803-200517 Matt Gundry Tue, 04 Aug 2009 01:05:17 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=09&m=08&entry=entry090803-200517 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090802-205522
]]> Wings http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090802-205522 Matt Gundry Mon, 03 Aug 2009 01:55:22 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=09&m=08&entry=entry090802-205522 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090731-163842 Ragwing RW-11 Construction, Falconar F11A Project http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090731-163842 Matt Gundry Fri, 31 Jul 2009 21:38:42 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=09&m=07&entry=entry090731-163842 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090726-220029
I am trying a new (actually old) adhesive - Weldwood Plastic Resin. I really like T-88, but it isn't available locally. I can get it in St. Paul, MN at Rockler, but they only carry the very expensive 8-oz. kit. I can currently get WPR at the local Ace Hardware store, and it is MUCH cheaper. I think the plastic resin works fine, though I can see where it would be unforgiving of gaps.

Speaking of locally (well, kind of local) available products, I stopped at McCormick's Lumber in Madison, WI this weekend to get some 1/16" birch plywood. They were out of the plywood, but they did have a very nice selection of Sitka Spruce. The quarter-sawn rough-cut boards were 1"x9" in lengths from 14' to 18'. I didn't have to go into the stack more than a few boards to find one that will make some nice longerons.

Yes, the spruce is more expensive than the lumber at the local lumber yard (we do still have a lumber yard in Eau Claire, in addition to Menards) - but I haven't had much luck finding wood that I would make a spar or longeron out of. The structural grade douglas fir at Lyman Lumber was one exception - I found a few 2x10s that I could have used. Each timber could have yielded a couple one-piece longerons or caps, maybe double that with scarfing and laminating. That douglas fir was better than half the cost of the nearly perfect spruce - not worth my time to save so little.]]> Wings http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090726-220029 Matt Gundry Mon, 27 Jul 2009 03:00:29 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=09&m=07&entry=entry090726-220029 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090720-224835


The radius is pretty sharp for the 1/16" bias-ply birch. It took a fair amount of coaxing to get the skin tight to the ribs, especially from 2" to 6" back from the nose on the top. In the image above you can see where I needed to use some oak boards under the straps for extra pressure in that area.

On the strut-braced wing with two struts per wing, the leading edge is not normally load carrying - the chordwise moment is directly carried by the struts. So why use the expensive 45-degree plywood? The primary reason is because the bias-ply holds shape better between the ribs with less tendency for warpage. The other reason is that it does offer some degree of structural redundancy. Even though the skin cannot resist the moment from all the design flight loads, there is a good chance that it would be sufficient to resist 1G loads in the event of a rear strut failure.

1 hr.]]> Wings http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090720-224835 Matt Gundry Tue, 21 Jul 2009 03:48:35 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=09&m=07&entry=entry090720-224835 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090719-182040
I also ripped the 45-degree birch ply into wide strips for the leading edge. These strips were scarfed end-to-end to make one large piece for the leading edge skin. The plans call for two butt joints in the leading edge skin over heavier nose ribs with cap strips. Aside from the PITA scarf joints, I feel that the one piece leading edge skin will be easier to build and will form a smoother leading edge.

It is interesting to note that the 45-degree birch ply has a very pronounced sheen that the 90-degree ply does not. The 45-degree ply is mil-spec, whereas the 90-degree stuff is GL-2. I'd wager that the mil-spec material is more sensitive to needing the surface scuffed. Testing that I did with the GL-2 ply and epoxy didn't show much difference in bond between scuffed and un-scuffed.

2 hr]]> Wings http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090719-182040 Matt Gundry Sun, 19 Jul 2009 23:20:40 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=09&m=07&entry=entry090719-182040 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090718-194004


I am now able to access the trim actuator. It is a simple powered lead nut salvaged from something. The linkage to the trim horn consists of a leadscrew on one end that threads into the actuator. My problem with this setup is that there is no limit to the motion. In a trim runaway situation, the actuator would keep going until something broke - I'm fairly certain the motor has sufficient torque. This will be replaced with a standard MAC servo or equivalent.

I removed the light and associated wiring. I plan to use an LED tail light, but I haven't decided which one to use yet.

I also removed the sharp leading edge piece. Once the new skins are in place, the plan-specified rounded leading edge will be shaped. The rest of the workmanship appears above average.]]> Airframe Audit http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090718-194004 Matt Gundry Sun, 19 Jul 2009 00:40:04 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=09&m=07&entry=entry090718-194004 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090714-205510


I am checking this part against Falconar drawing 119A 83 Iss. 5, sheets 1 and 2. Status of the components by callout number are as follows:

-1 - 1/4"x1/2" strips and 1/16" birch ply OK
-2 - 1/4"x1/2" strips and 1/16" birch ply OK
-3 - 1/4"x1/2" strips and 1/16" birch ply OK
-4 - 1/4"x1/2" strips and 1/16" birch ply OK
-5 - 1/4"x1/2" strips and 1/16" birch ply OK
-6 - 1/4"x1/2" strips and 1/16" birch ply OK
-7 - Obscured
-8 - Partly obscured, 1/16" ply OK
-9 - 1/16" ply, ash blocks, ply doublers, and 1/8"x5/16" strips OK
-10 - Upper nose ribs made from 3/8" pine block instead of 1/4" ply. This part is not subject to significant loads, OK
-11 - Starboard skin is delaminated from the ribs in numerous places. Skin extends further than necessary. Remove and replace skin and trim to plans shape.
-12 - 1/16" ply OK, though face grain isn't oriented as shown in plan
-13 - 1/16" ply OK
-14 - Cover not present. Will be made after rudder is fit to fuselage
-15 - Trim tab not to plans. A larger tab has been made that is hinged to allow for electric trim. A servo and linkage are present as well. Although the tab is OK, the linkage is unacceptable and the servo is suspect. The linkage contains a double link to "turn the corner", but is insufficiently constrained, so the flexibility of the pushrod allows uncommanded movement of the tab with only slight sideways pressure. A longer horn on the tab will solve the linkage geometry issues, but the servo will still need to be checked out.




-16 - Skin in radius area OK
-17 - Hinge plates not present
-18 - Eye bolt is homemade, not specified AN hardware. Finish is poor, with cut threads, no cad-plate. Replace with appropriate AN hardware.



-19 - Nut is not appropriate AN hardware. Replace.
-20 - Washers not present or not appropriate AN hardware. Replace.
-21 - Clevis pin not present
-22 - Washer not present
-23 - Cotter pin not present
-24 - Rudder control horn has poor finish with rough edges, insufficient hole-edge clearances, and sharp internal radii that are prone to cracking. Not attached with AN hardware. Make new part and attach with appropriate AN hardware.

Other issues not related to a part callout:

* The leading edge of the rudder has a rather sharp radius made by the addition of an additional wood strip. This will be removed and the leading edge reshaped to plans. In addition to adding unnecessary weight, this could change stall characteristics of the rudder.
* The light attached to the top of the rudder is not the correct nav light. Also, the wiring is not teflon. Replace the light and wiring.



When removing and replacing the rudder skin, I will have a chance to better view the internal components and give the inside a good coat of epoxy varnish.]]> Airframe Audit http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090714-205510 Matt Gundry Wed, 15 Jul 2009 01:55:10 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=09&m=07&entry=entry090714-205510 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090712-080146
Some of the differences of the Falconar from the Jodel are as follows:

1) The kink in the cranked wing is moved inboard
2) The washout is reduced in the end wing panel
3) The spar is simplified - washout is by rib geometry, not spar twist
4) The landing gear is spring instead of rubber puck

The project I acquired has the airframe largely complete. However, many items will need to be revisited. Here are some pictures of the project provided by the previous owner:

















As you can see, a lot has been done. Most of the craftsmanship is good, some is excellent, and some will simply need to be redone. In general, the woodworking is fine but the hardware and control linkages are not.

Some obvious things I noticed were the wood stains on the rudder, red automotive-type light on the rudder, foam and fiberglass leading edges on control surfaces and wings, and more body filler than I like to see on the tail. These and and any other problems I see will be addressed as I audit the project against the plans.]]> Falconar F11A Project http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry090712-080146 Matt Gundry Sun, 12 Jul 2009 13:01:46 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=09&m=07&entry=entry090712-080146 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry081102-111946


I've been asked how to find the field. It is hard to find unless you know where to look. I don't have any markers up for it yet. Below is an aerial photo of our place. This is a half mile east of Fall Creek, looking north. Our place is the one on the south side of the road (CTH D). The airstrip is about three hundred feet south of the large red pole building. It runs east-west (right-left). On the west end there is a barbed wire fence across the end.



My wife asked if a Cessna could land here. I told her the runway was too short. I guess I was wrong. A couple friends stopped by with a 182 this weekend. Here they are on the way out - I think he used less than 400 feet taking off.



Stop by when you get a chance.]]> General http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry081102-111946 Matt Gundry Sun, 02 Nov 2008 17:19:46 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=08&m=11&entry=entry081102-111946 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080920-205856


The east-west runway is just a little under 700 feet long. The Taylorcraft was down and stopped in about 400 feet. It used just a little more getting out. The approaches are clear to the east, and only a fence and cornfield is on the west.]]> General http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080920-205856 Matt Gundry Sun, 21 Sep 2008 01:58:56 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=08&m=09&entry=entry080920-205856 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080902-174005
1 hr]]> Wings http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080902-174005 Matt Gundry Tue, 02 Sep 2008 22:40:05 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=08&m=09&entry=entry080902-174005 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080902-101923
Condition A represents Va, the design maneuvering speed. From the previous posts, the load factor, n, is +3.8, and the airspeed is 85 kts. The aircraft weight is 1200 lbs. One new piece of information we need today is that the wing weight is estimated at 220 lbs. This acts at the wing CG which I've estimated at 26.6% of the chord length back from the leading edge. This weight includes 90 lbs of fuel (7.25 gallons per side), the tanks and fittings and half of the strut weight in addition to the basic airframe and covering.

To get the loads on the front spar, we add all the twisting forces acting around the rear spar, and divide by the distance between the front and rear spars to find the force required by the front spar to keep things in equilibrium. There are four forces/moments at work in our simplified (CAM 04 Appx IV) analysis:

1) Force of lift acting at 25% of the chord
2) Force of drag acting at 25% of the chord
3) Pitching moment of the airfoil
4) Weight of the wing acting at the wing CG



The lift force is defined as follows:



...where Cl_local is the local coefficient of lift, A is the wing planform area, and q is the dynamic pressure:



...which works out to 24 psf for this speed at sea level. FAR 23, Appendix A in paragraph A23.7(e)(1) states that we need to increase the positive loads by 5%. We also need to account for the angle of attack, as the diagram above illustrates. Multiplying the resulting lift force by the moment arm (distance from the rear spar to the aerodynamic center) gives us the moment about the rear spar due to lift. Using the chord length instead of the area in the equation above, and dividing the result by the moment arm of the front spar gives the force per unit length in the front spar. The equation looks like this, where rac and rfrontspar are the moment arms for the aerodynamic center and the front spar, respectively, about the rear spar:



Drag is made up two components, form drag and induced drag. The equation for the combined drag coefficient for our example looks like this:



AR is the aspect ratio of the wing, Cd0 is the zero-lift drag coefficient from the airfoil data (0.011), and Cl is the wing coefficient of lift. Coefficient of lift can be calculated using the following equation:



S is the gross wing area (135 sf), Wgross is the max gross weight of the aircraft (1200 lbf). This Cl computes to 1.4 which should, and does, come out pretty close to the max wing coefficient of lift of 1.38. Substituting that result into our drag coefficient equation gives a Cd of 0.105.

The equation to find the required reaction in the front spar due to the contributing component of the drag force is as follows:



To be continued...]]> Structural Analysis http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080902-101923 Matt Gundry Tue, 02 Sep 2008 15:19:23 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=08&m=09&entry=entry080902-101923 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080901-210018
2 hours

]]> Wings http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080901-210018 Matt Gundry Tue, 02 Sep 2008 02:00:18 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=08&m=09&entry=entry080901-210018 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080831-220602
2 hours]]> Wings http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080831-220602 Matt Gundry Mon, 01 Sep 2008 03:06:02 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=08&m=08&entry=entry080831-220602 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080822-170904 XFoil and JavaFoil and produced two polars. This is a very cambered airfoil capable of producing a lot of lift.

The polars listed above are 2D estimates assuming the wing is infinitely long with no spanwise flow, and give a Cl Max from 1.6 to 1.8 at a Reynolds number of 3x10^6. Wind tunnel data from NACA report 824 indicates the Cl Max for the 4415 to be somewhat lower than that, about 1.3 for similar Re. It has never been clear to me whether I should treat the numbers from the NACA report as 2-D or 3-D. That the data is from an actual airfoil and the values are considerably lower than computer model estimates suggest to me that it is 3D. However, the report does say the data is from the Langley 2-D tunnel.

To be useful, we need the lift coefficient to be corrected for 3D effects. For that, it is again easiest to consult Mr. Wilford's spreadsheets. S405-WindDesign.xls specifically. This uses the Schrenk method to approximate the lift coefficient distribution over the wing, and then the wing coefficient of lift. Using that spreadsheet and the lower computer model 2D Cl from XFoil of 1.6, I arrived at a corrected Cl in the clean condition of 1.38.]]> Structural Analysis http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080822-170904 Matt Gundry Fri, 22 Aug 2008 22:09:04 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=08&m=08&entry=entry080822-170904 http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080822-150745
To do that we need to know what that performance envelope looks like. The easiest way to go about that is to use Neal Wilford's S306-Airloads-FabricWings.xls spreadsheet. The calculations are not in any way difficult, but Neal has gone through all the trouble of sorting through the various load cases in compliance with FAR 23 Appendix A and CAM 04. For the sake of education, we'll work through the calcs here.

Let's outline what operating conditions my RW-11 will be designed for:

Gross Weight (W): 1200 lbs
Maximum Operating Speed: 100 knots
Positive Load Factor (n1): 3.8 (Normal)
Negative Load Factor: -1.9 (Normal)

We also have some values based on the geometry of the wing:

Wing Area (S): 135 S.F.
Flaps up CL Max: 1.38

This gives us the information required to find points A, C, B, E, F, and G on the flight envelope diagram. With the gross weight, load factor, wing area, and CL Max we can calculate the minimum design maneuvering speed (A,G):

or

...and the minimum design dive speed (D,E):



...based on the Simplified Design Load Criteria in Part 23, Appendix A. The minimum design cruise speed:



...is greater or equal to what I expect my RW-11 to actually be capable of, so n3 and n4 are 1.0 and -0.5, hence points C and F have 3.8 and -1.9 as a load factor, respectively. These are the same as the max positive and negative load limits specified above. Using the equations and data above, my V speeds look like this:

Minimum Design Flap Speed: 64 knots
Minimum Design Maneuvering Speed (A,G): 85 knots
Minimum Design Cruising Speed (C,F): 99 knots
Minimum Design Dive Speed (D,E): 139 knots



I've also created a PDF of my calculations.

Up next, we will see how those V speeds translate into flight loads.]]> Structural Analysis http://faa-engineers.com/~mjgundry/blog/index.php?entry=entry080822-150745 Matt Gundry Fri, 22 Aug 2008 20:07:45 GMT http://faa-engineers.com/~mjgundry/blog/comments.php?y=08&m=08&entry=entry080822-150745