Aviation

Messerschmitt: Bf109 Ordinates

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Messerschmitt: Bf109 Ordinates:

I recently received an inquiry from a museum regarding ordinate datasets for the Bf109. As I previously mentioned in this earlier post the archive I have has a lot of data that was done by others…so I figured it was quite comprehensively covered.

Anyway, I decided to have a closer look and see what was actually documented and how well it aligned with known data. It turns out to be a bit of a muddle. Although the data is quite well presented I have uncovered a number of inconsistencies and anomalies which I will need to resolve.

8-109.000 G-2 Flugzeug Zuss 2

What I thought would be a quick response to an inquiry has initiated a much more intensive study which admittedly I had not planned for. I will go back to basics with this one, using the existing data as a reference and develop a new set of ordinate data for the Bf109 similar to how I approached the Mustang P-51 project.

I have already started with the Horizontal Stabiliser and part of the way through the Vertical. The tables will essentially be a reconstruction from the Messerschmitt drawings and then compiled to develop the X, Y, Z ordinates for transfer to CAD.

bf109

 

Grumman F4F Wildcat: Aileron:

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Grumman F4F Wildcat: Aileron:

Having made good progress on the ordinate set for the Grumman F4F/FM2 I decided to put the spreadsheets to one side and do some modeling to verify the dataset. Normally this would not be required to such an extent but I needed to do this to check the relationship between the components and aircraft datums.

I was spoiled with the P-39 project where virtually every component has reference dimensions to the ship center line or thrust lines so positioning was a breeze. However, the F4F drawings sadly lack this reference information on many of the key drawings so developing the 3d cad model is the only sure way to ascertain this data.

F4F Aileron Render

The above model is the left-hand Aileron modeled in Inventor and rendered in Keyshot. Keyshot is a very good renderer, even for a novice like myself; in which you can generate acceptable renderings very quickly. The real-time rendering is very good and will continue without glitches even on a modestly specced system (unlike some of the alternative products). The user interface is logically set out with a good library of materials and textures. I would highly recommend this product.

Getting back on subject; the Aileron ordinates took a long time to complete for various reasons; requiring constant checking and verifying. Once this was done, the modeling was reasonably straightforward except for the small trimming tab. The drawing dimensions are slightly out, so I extracted the neighboring rib profiles to create the template for a finished model.

I also decided to create a few scrap drawing views as a matter of record that will be useful when I eventually move onto modeling the wings themselves.

F4F Aileron 4

For reference; the following image shows the Ailerons attached to the wing assembly. Hinge positions checked and verified with hinge brackets (orange) fitted achieving a planar variation of less than 0.04mm.

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There are still a few items required to complete this model but this is not a priority for me right now. My next objective is to develop the ordinates and perhaps some modeling for the vertical and horizontal stabilizers.

Horizontal Stabiliser & Elevator:

Grumman F4F-FM2 Horiz Stabiliser

F4F Stabiliser

f4f rear fuselage

Tail Fin & Rudder:

F4F FIN RUDDER

F4F FIN RUDDER 01

Fuselage Frame 3:

F4F Wildcat Frame 3a

If you are interested in obtaining my research data for this aircraft then please send me an email. At the moment this is an unfinished project but the available drawings (12) are fully dimensioned which will help you with establishing correct datums and station frame associations along with a few spreadsheets. HughTechnotes@gmail.com

 

Grumman F6F Hellcat: Wing Ordinates

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Grumman F6F Hellcat: Wing Ordinates

I wrote an earlier article on my work with the F6F fuselage ordinates which I have recently updated. Whilst revisiting the archive I also came across the Grumman wing ordinate drawings and decided to develop those as well. I was reluctant to do this as the original drawings were not that great.

Thankfully it was not as bad as I first suspected, though it has taken me over 7 hours to painstakingly enter each ordinate manually to tabulate the ordinates in Excel.

F6F Wings

I still have to interpolate the data to generate the appropriate X, Y, Z coordinates; set out from the 35% chord; which I will endeavor to do over the next few days.

F6F wings 2

To verify the ordinate dimensions the following equations are applied. The chord length is for any wing chord whilst the LER is only applicable from station 75 to station 252.

f6f calcs2

To be honest the F6F Hellcat was not even on my to-do-list but a conversation with a colleague about the F6F performance characteristics prompted me to have a closer look at the archive. Surprisingly it is very possible that this archive may have sufficient information to generate an entire aircraft ordinate set, which is quite rare.

f6f

I will update this post when the wing model is complete, so come back soon.

Update August 23:

 

I have checked the Centre section profile for accuracy and noticed one point out of alignment by 2mm towards the leading edge. Removing this point allowed the natural curvature of the spline to define an acceptable profile as shown. The curvature check shows that this curve now matches the Leading Edge Radius.

The trailing edge extends beyond the 100% Chord by 5/8th inch on the centre section (Station 0) which tapers to zero at Station 252. Drawing a straight line segment from the Trailing Edge Radius results in perfect alignment with the spline.

Centre Section Stations:

f6f ctr section

Outer Panel Stations:

F6F outer wing

It is not unusual to have a few rogue points from the tabulated ordinate data which is why it is important for a detailed analysis like this.

And here, at last, the complete wing assembly:

f6f wing assembly

Vought F4U Corsair: Ordinate Data

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Vought F4U Corsair: Ordinate Data;

About 6 months ago I received an ordinate dataset from a good friend Gary Henry for information purposes. It is a very comprehensive set for the fuselage comprising over 2800 points to define in excess of 1930 individual ordinates.

Vought_F4U_Corsair_(USMC)

I have recently updated my data processing procedure utilizing new features in MS Excel particularly the “TEXTJOIN” command which makes it a lot easier to extrapolate the X,Y,Z ordinates from large datasets. This dataset was ideal to work with the new process.

F4U Corsair Ordinates

The Textjoin function allows you to predefine a delimiter and then select either an array of data or individual cells using the Control/Mouse combination. You can see I have locked in the selected column and the top row. The units shown are inches but can easily be converted to millimeters.

F4U Corsair RevB

Due to the nature of the dataset, there is a very distinct central plane on the zero vertical plane, which of course I would filter out if I decided to progress this further as a CAD model. I don’t have enough of the manufacturers’ original drawings to develop this aircraft at this time but it sure is interesting working with other datasets.

F4u-1 sideview

The dataset is actually very good only 3 points not quite in alignment. I profiled the top and bottom contours and the contours either side of the fuselage centerline; all 4 curvatures were very smooth.

Update Oct 2018:

Recently received some new data that has allowed me to progress this project with the development of the Cabin ordinates as shown below.

F4U Cabin

F4U Corsair2

Restoration Project: Corsair F4U-1

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Restoration Project: Corsair F4U-1

This is great news; a good friend of mine has just acquired the wreckage remains of a Corsair F4u-1.

IMAG1368

The long-term plan is to restore this Corsair to its original specification as a standing exhibit. It would be wonderful to restore to flying condition but the projected cost as it stands is quite overwhelming and to achieve flight status would probably double that.

 

IMG_4038.JPG

P1060200.JPG

We will be setting up a dedicated blog and website to record progress on this restoration. Part one of the project is to develop a master lines plan which will be used to design the jigs required to rebuild the fuselage and wings.

Any contributions to the project, regardless of how small will be greatly appreciated.

Technote: Inventor Sketch Datum

Hugh2 Comments

Technote: Inventor Sketch Datum Point.

This is one of those instances where you do something on a regular basis and don’t really appreciate the significance of the process. What I am referring to is when you create a sketch Plane using the option “Parallel to Plane Through Point”.

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It transpires that this selected point becomes the datum for the particular sketch created on this plane. For this example, for a P-39 wing rib, we have selected a point for the Plane location along the wing leading edge as shown.

P39 wing1

The Bell P-39 and similarly for the P-51 Mustang the wing ordinates are set out from the leading edge of the wing so it makes sense that the rib sketch is setup with a suitable datum point. You can tell the location of the temporary datum in the sketch applied to this plane by the position of the main axis.

This is the really interesting part, when you now import a set of points from the Ordinate spreadsheets it will recognize this sketch datum and import the points relative to this point irrespective of the model origin.

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This is very useful particularly for these aircraft projects as we tend to use a lot of ordinate data for the outline geometry.

Another Quick Tip:

To automatically apply a tangent constraint to a sketch line just select and drag the line from an existing line and the tangent constraint will be applied.

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Technote: P-39 Inventor Facedraft

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Technote: Bell P-39, Inventor FaceDraft

Draft angles is actually a common requirement when working with aircraft components, particularly forgings, and it is surprising that I haven’t written an article on this before now.

Facedraft in Inventor is a feature that allows adjusting the face or faces of an object to a specified angle. A more detailed overview is described in this Autodesk article Face Draft feature

Occasionally the implementation is not quite so straightforward as noted therein and some outside the box thinking is necessary. Thus was the case when I was building the forging component for the P-39 Landing Gear Nosewheel Scissor.

To build this component I created 2 separate solid bodies, one for the cylinder item and one for the fork. The fork is split about the X,Y plane with only the outline of the top half being modeled to facilitate the initial face draft.

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For the first option, I selected the X,Y plane and then for the Faces I selected the automatic face chain option and placed the cursor close to the top edge as shown. If you required the face angle to originate from the bottom edge then you would select the faces close to this edge.

I then trimmed out the inside profile of the fork and applied a face draft as above.

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Now it was only a matter of mirroring the fork solid to complete this portion. Notice the solids are still separate items which will be combined as one after inclusion of the central web component.

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There is an option for the Facedraft feature to Draft using a parting line, either a 2d or 3d sketch. The draft is normally applied above and below this parting line. In most circumstances, the Parting Line option works well but occasionally the model may be too complex to achieve the desired result thus the solution described here provides an alternative approach.

Forgings or castings commonly have a draft angle on all faces which is normally 7 degrees and occasionally 5 degrees. The Face Draft feature is ideal for applying the drafts with an extensive range of options. The model of the forging would then be derived into a separate part file and then machined according to the finishing requirements similar to the process described here Derived Parts.

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For more information on the Bell P-39 Airacobra project: Bell P-39: Project

Technote: Inventor Export Sketches

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Technote: Export Sketches

The Inventor product has an option to export part Sketches to either an Autocad DWG or DXF format directly from the model environment. This is very useful if you are needing to share development information with someone else who is working with a different CAD product.

It is simply a case of highlighting the sketch as shown in the example below and selecting the “Export Sketch as…” option.

Inventor export sketch

A dialogue box pops up asking for the file format DWG or DXF and location for saving. I would recommend the DWG for the format as this replicates the Splines more accurately.

 

In this example the left image is for the Mustang P-51 rear fuselage, showing the outer profile for the P-51 B/C and the inner profile is for the P-51D. The image on the right is the fuselage tail-end.

I plan on extracting all the fuselage curves that include P-51D data to DWG format as a reference until such time as I can add the point data to the already comprehensive set of ordinates available here.

Mustang P-51 B/C Ordinates

 

Technote: Complex Surface Hole Location

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Technote: Positioning Holes in Complex Surfaces

When detailing the skin panels for aircraft it can be quite daunting trying to locate a series of holes accurately at a specified distance from the edge of the panel. Typically fillets to wings and horizontal stabilizers and transition pieces to vertical stabilizers are all complex surfaces.

In this example, we need a series of holes located 17.5 mm from the top and bottom edges. As you can see the surface at the top and the flange angle at the base varies.

The location of the first hole, top and bottom, is aligned vertically so we first create a workplane to determine the horizontal position of the first hole. Ultimately we will use a 3d intersection curve for the centre line of the holes which must first be determined by sweeping a circle profile sketch along the edge as a surface with the radius set to the required edge distance. Using a circular profile for the sweep ensures that any intersection point on the surface will be at the specified edge distance.

This swept surface is then trimmed to the first work plane to define the start point of the 3d surface intersection curve as shown.

The resulting 3d spline represents the line of the hole centres at 17.5mm from any point along the edge of the fillet.

We then apply a point and an axis (perpendicular to the surface) at this point to determine the hole direction. I suspect because it is not a regular surface the hole feature will not allow me to select the surface for direction. Use “Extend Start” when creating hole.

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To pattern the hole along the spline and be perpendicular to the surface create the array as shown below. Be sure to select the extended options for “Direction 1” and “Adjust”.

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Do the same for the top array of holes, resulting in 2 sets of holes aligned with the surface at 17.5 mm from the edge.

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This works for the vast majority of riveted panel connections where locally there is a degreee of flatness between the matching parts. In instances, where there is extreme curvature of the connecting faces the radius of the extruded circle would have to be adjusted accordingly.

Grumman F6F Hellcat: Ordinates

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Grumman F6F Hellcat: Ordinates

I am without access to a Cad system for a few weeks so I decided to spend time reviewing my archive collection. Whilst looking through the many aircraft in the archives I came across some interesting information for the Grumman F6F Hellcat.

F6F-3_Hellcat_11_of_VF-2_on_the_catapult_on_board_the_carrier_USS_Hornet_CV-12_May_6_1944

The archive consists of a substantial number of the Grumman drawings, varying in quality from very good to very poor, though I should clarify the latter relates to only a small number of drawings. This archive includes ordinate tables for the wings and fuselage so I figured it might be a worthwhile project to attempt to decipher and create a set of ordinate spreadsheets as I have done previously for the Mustang P-51.

Hellcat ordinates

Though I rather like this aircraft it was not a priority project on my to-do-list, but having spent today studying the Grumman drawings this could turn out to be a rather challenging project.

Fuselage Work in progress:

hellcat ords 2

Update:

hellcat prelim 2I have managed to obtain a trial copy of the Inventor LT so I can now move ahead with this project. This first interpretation of the fuselage profiles is actually not bad at all. A few macro adjustments will be required to get the profiles correct, mainly due to the quality of the archive where roughly 10% of the values are very difficult to read.

Each point represents the ordinate of the longitudinal stringers which I will profile to assess the alignment and curvature as an aid to finalizing the frame ordinates. Perfecting the frame ordinates can become quite tricky at this stage, requiring constant referencing of the original drawings including the frame structures themselves which often provide additional information that can assist with this process.