Montag DP's blog
Posted by Montag DP | Sep 18, 2012 @ 12:18 PM | 2,415 Views
This thread will detail my work on a vortex lattice code intended for optimizing wings. For the final tool, I plan to couple it with XFOIL code subroutines to compute profile drag at each section, which will then be integrated using a strip-theory approach. So the lift and induced drag will be computed via the 3D potential flow approach, and the profile drag will be summed up by a 2D analysis of each section.

The solution process will look like this:
1) Create the geometry using a separate spreadsheet with visual display of the wing as you create it. The spreadsheet will then automatically write the required geometry input files for the vortex lattice code.
2) Set up an input file for the code listing flight condition (specified alpha or specified CL, yaw angle, Reynolds number at the root); root airfoil, tip airfoil, and other airfoils between the root and tip; paneling discretization, and any runtime options.
3) Run the code. The following will happen:
---i) First, airfoil shapes will be interpolated to each panel. These coordinates will be used when running XFOIL to get profile drag.
---ii) From the computed airfoil geometry, create the mean camber line at each panel. The mean camber line is used for the vortex lattice geometry.
---iii) Using the mean camber lines, input geometry, and paneling setup, create wing panels and compute information such as panel areas, collocation points, normal vectors, etc.
---iv) Set up a vortex ring for each panel, where the...Continue Reading

# Images

Posted by Montag DP | Dec 15, 2010 @ 04:37 PM | 4,692 Views
As part of my Master's thesis, I'm going to be investigating unsteady panel codes for flapping-wing micro air vehicles. The plan is to compare with CFD solutions to see under what conditions the panel code gives good predictions, because CFD solutions take a very long time and thus make design work tedious. Panel codes have limitations, though, especially when there's significant separation.

I thought some RCG members might be interested in the development, so I'm posting here. So far I've written a steady panel code and plan to spend the next couple weeks modifying to make it unsteady and able to simulate airfoils in flapping motion. Some details of the panel code:

-Between each set of vertices for the airfoil, a vortex panel is placed. The formulation used allows for linear variation of vortex strength across the panel. There are usually at least 100 panels distributed across the surface of the airfoil.
-As with any panel code, the variation of vortex strength on each panel is calculated so that the summed effect of each vortex panel and the upstream velocity is such that the airfoil is a streamline. That is, on each panel the normal component of velocity is 0.
-Additionally, as with any lifting panel code, the Kutta condition is applied so that flow leaves smoothly at the trailing edge.

Once the vortex strength distributions are calculated, the velocity and pressure at each panel can be computed as well.

Changes required for unsteady panel code:

# Images

Posted by Montag DP | Sep 11, 2010 @ 07:15 PM | 4,155 Views
I got hooked on thermal soaring accidentally this summer when I meant to be slope soaring with my Alula...well before you know it I was looking at getting into discus launch gliders. I didn't want to spend a lot, so the multi-hundred dollar composite kits were out of the question for me. I looked at some of the cheaper built-up kits like the Gambler AG, DL-50 and QFII, but in the end I decided I wanted to design my own.

I have to admit I did borrow heavily from the Gambler design. Allan Wright, who designed and kits the Gambler, provided me with a lot of useful advice and also sold me a set of CF tow, kevlar, and fiberglass from the Gambler kit, along with the plans for reference. By this time I was well into the build. I actually set a personal record though - only 2 weeks from concept to having parts ready for the laser cutter, and then a little less than 2 more weeks to get it built. I had to hustle because Fall is going to be upon us soon.

I couldn't have asked for a nicer day for the first flight, though. After a while practicing my throws, I finally felt like I was consistently getting good height, and at the same time the sky seemed to be getting a bit more active. I started stretching flight times to about 2 minutes. Then, around noon I made only a decent toss but caught a thermal and away it went! I was just kind of putzing around gaining a little bit of height for the first minute or so, but after that the thermal gained strength and it specked out fast....Continue Reading

# Images

Posted by Montag DP | Apr 01, 2010 @ 10:32 PM | 4,240 Views
I had to do a group project for an engineering optimization class this semester. We were allowed to choose our own, so I chose airfoil optimization. I thought the results would be of interest to this forum.

Since the class project I have done a bunch more work with the optimization. I have moved to a particle swarm algorithm and have increased to 26 design variables using cubic b-spline control point curves. Follow the discussion in the Modeling Science forum:

EDIT: You can find the code in its current state, along with a tutorial, attached below.

# Files

Posted by Montag DP | Oct 27, 2009 @ 08:22 PM | 5,503 Views
This CG calculator is meant for airplane design - especially components layout and unusual planform evaluation. If you just want to figure out where to balance a preexisting model, you probably don't need to use all the functionality. However, it will still be very useful for figuring out things like how much nose weight to add, etc.

The CG calculator is designed to work with almost any airplane configuration, including:
• Standard monoplane and tail configuration
• Biplanes
• Triplanes
• Canards
• V-Tails
• Any combination of the above
Unlike other CG calculators, this one allows you to:
• Include the fuselage contribution to the stability calculations. This is particularly important for wide fuselages that extend well forward of the wing, e.g. jet models.
• Estimate your actual CG location by assigning weights to airplane components and by adding point masses to represent things like batteries, motor, servos, the fuel tank, or any other weight in addition to the airframe's weight.
• Compare your actual CG to the neutral point of the plane, before ever building it.
• Use the "Static Margin Wizard" to move point masses, adjust the weight assigned to point masses, or adjust other quantities to achieve a desired static margin. This is very helpful for deciding where to place components in your plane or for figuring out how much nose weight you need to add, for example.

# Files

Posted by Montag DP | May 25, 2009 @ 01:55 AM | 6,508 Views
Someone made a thread about the Great Planes Electrostreak and I decided it looked cool and I wanted something like it, so I quickly whipped up this. It's got a mid wing and an MH-32 airfoil for speed (I'm open to other suggestions at this point).

It will be my biggest plane yet (I'm planning on building this one before the "Big AP Plane" a few entries down), with a 47" wingspan and 40" length. I'm planning to just make it hand-launch with no landing gear because I think LG is awkward on this type of plane, but it would be easy enough to include removable landing gear too.

I want to prop it for speed with a motor around 300 watts, and a folding prop. If anyone has any suggestions for a motor/prop combo let me know.

It will be laser cut from balsa and ply. The plan right now is to finish the design in the next couple weeks and then build it in August after my internship's over and before classes start again. Wish me luck.

Maiden Flight Video:

 Grandpa Bob's Plane (1 min 36 sec)

Aerial video:

# Images

Posted by Montag DP | Mar 31, 2009 @ 04:46 PM | 5,327 Views
Differential Equation solver spreadsheet. You can also enter a transfer function with inputs and run a simulation! This means, among other things, that you can simulate aircraft responses to control inputs, provided you know the transfer function for its dynamics. See examples below. Let me know if you have questions about using it.

Dan

# Files

Posted by Montag DP | Nov 18, 2008 @ 08:38 PM | 5,507 Views
EDIT: Redesign with some changes from the original concept. Wingspan is now 60 inches instead of 68, I removed the dihedral, switched the inverted V-Tail for a more traditional horizontal / two vertical stabilizers approach, increased the height of the fuselage to help with prop clearance issues, moved the booms closer together. I'm going to hope to get it cut before summer '10 so I can start building.

# Images

Posted by Montag DP | May 03, 2008 @ 11:21 AM | 6,670 Views
Sadly, my Zenith V1 crashed a few weeks ago due to electrical failure, but I have a new and improved version on the way.

This one is about the same size as the old one, and uses the same power system. Wingspan has been reduced a little bit and length has been increased a little bit. It addresses the two main issues I had with the old one: the fuselage is much thinner and the thrust line is more or less in line with the CG, instead of being way above. It should handle nicer and go a little faster.

Parts are laser cut and are actually waiting for me at home right now. The build will start in a few weeks, and I'll post real pictures as it moves along.

EDIT: See finished pictures now attached and the maiden flight video linked to in the fourth post....Continue Reading

# Images

Posted by Montag DP | May 16, 2007 @ 06:22 PM | 6,969 Views

Dan

# Images

Posted by Montag DP | Mar 05, 2007 @ 07:00 PM | 8,015 Views
Some of you may have seen my thread in the Parkflyers forum called "G-Ride Replacement". I ended up going with the Mountain Models Flashback, as I had been leaning the whole time. This will be my build thread. I plan to finish the build this week before I have to go back to college for eleven more weeks.

The G-Ride is now looking beautiful hanging in my room. It is the nicest-looking of three different planes at the moment: A Fokker Dr. I triplane, a Supermarine Spitfire Mk. IX (both of which I built several years ago before I got into radio-control), and of course the G-Ride. It's a shame the G-Ride has been demoted to a static display model. Maybe someday I will build another one.

Dan

Look at 'comments' to see entire build.

# Images

Posted by Montag DP | Jan 30, 2007 @ 05:54 PM | 7,609 Views
I've got a lot of in-flight photos, but not that many good and clear ones. I'll see what I can dig up here.

Thanks to my older brother Nate for taking most of these pictures while I flew.