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Dec 03, 2019, 04:58 AM
Design is everything.
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Latest model : Durandal jet fighter. Colored using color pencils, but poster paints are best, and will actually not wash off in the rain.

Flies well, with nose up attitude, and is a little heavy at 16 grammes, but very strong and damage resistant: will have to test and see a little more.

Would make a nice RC model, with its simple nose inlet. More info:

https://www.militaryfactory.com/airc...rcraft_id=1512

http://www.jfrteam-neufgrange.fr/pag...-durandal.html
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Dec 24, 2019, 05:07 AM
Design is everything.
Thread OP

Mig 21 Dec 2019 Model


The latest Mig 21 (picture attached) was actually build using a wing of a previous Mig 21 that was left out in the rain, a testament to the durability of the model. I think the paint scheme came out quite well. Note the masking tape on the tail!

The model flies very well, long flights of over 20 metres, but inaccuracies in the wing make it turn left. Rudder trim also needs to be applied. The model seems to be unstable in yaw, then I noticed that I had left out the under fuselage strake. Hope to add it later. The nose cone again suffered damage, not as much as before, since it is made out of hard cardboard, but eventually I will have to settle for rubber piping, which I have tried before.

Overall a really great model, fun to fly, weighing in at 18 grammes total with the paint. Centre of gravity is at 5cm/10.5 cm of root chord which works out to 48% of root chord, and is just stable in pitch.
Last edited by Designer2010; Dec 24, 2019 at 05:14 AM.
Jan 03, 2020, 10:33 AM
Design is everything.
Thread OP
I am looking at building a model of the YE-2 next. The Ye-2 was one of the options explored for the Mig 21 fighter, with swept wings instead of a delta wing. The problem here is how to maintain strength of the swept wing, and keep the weight down. Drag should be less, due to the higher aspect ratio.

A 3D model created in Wings 3D is shown.
Jan 05, 2020, 07:42 PM
Design is everything.
Thread OP
Update: One of the videos that inspired these catajets: see F-16 video - it turns inside a living room!

The initial video that inspired much of this

Catapult launch glider (4 min 33 sec)


- he is flying in a football field, and I have less than a basketball court with trees in it to fly in, so it is really a different scenario altogether.

Durability vs weight issues still have to be resolved - I will address these in another thread.

See his latest videos - aparently he was an air force pilot in South Korea, judging from the profile picture.


https://www.youtube.com/user/swimjim100/videos
Jan 07, 2020, 01:06 AM
Design is everything.
Thread OP
Most of the models display a structural weakness behind the canopy area, within the first 10 centimetres of the fuselage. Adding an internal strengthening cylinder is expected to correct this problem, I have been experimenting with paper-cardboard-paper laminated fuselage rolls.

The other problem of deformation and abrasion of the nose cone can be adressed by fixing a rubber nose cone or nose section, using part of a rubber tube.

Repairing an existing Mig 21 model to incorporate hard cardboard (cereal box type) in the first 10 cm of the nose and also adding a .5 cm section of rubber hose increased the overall weight of the model (from the previous iteration) by 1g, at most it will increase to 2 g when completed with canopy section.
Jan 07, 2020, 01:31 AM
Design is everything.
Thread OP
So another look at the competition:

https://www.arrowmodels.com/dpr-gnat...l-aircraft-kit

https://www.aliexpress.com/item/32914785027.html

Nice, but expensive.
Jan 08, 2020, 02:07 AM
B for Bruce
BMatthews's Avatar
If you are still finding that you have bad weak spots I'd suggest that you're still not using the materials in the best possible manner. Perhaps you need to go with double layering or an internal keel in the nose or some other option.

You might try some designs that are other than delta wing as well. Some modern jets have swept but otherwise good normal looking wings that might help you out with getting a little more air time. Or transition to some light private aviation designs.
Jan 08, 2020, 08:28 AM
Design is everything.
Thread OP
Quote:
Originally Posted by BMatthews
If you are still finding that you have bad weak spots I'd suggest that you're still not using the materials in the best possible manner.
Yes you are right. As mentioned, the rubber tube section at the front plus 10 cm of cereal box cardboard (CBC) is what I have tried out on a Mig-21 that I repaired. Flies very well, but CG is about 2 mm ahead of the previous CG point. Apparently the CG position is very critical. The model aircraft should climb with the slightest of up - elevator, maybe a degree or so, not readily visible. It is interesting that in an air display put on by a Mig 21, the Mig hardly shows any up elevator.

█▬█ █ ▀█▀ MiG-21 LanceR - Air Show Radom 2013 - Romanian Air Force (5 min 24 sec)


Neither does this RC model: only the slightest up elevator is needed to make it do a climb. It's really nice to have an airplane set up this way.

Quote:
Originally Posted by BMatthews
Perhaps you need to go with double layering or an internal keel in the nose or some other option.
An internal keel is just what I had in mind for my planned indoor lightweight models.

Quote:
Originally Posted by BMatthews
You might try some designs that are other than delta wing as well. Some modern jets have swept but otherwise good normal looking wings that might help you out with getting a little more air time. Or transition to some light private aviation designs.
I have built a Mig-19, which is quite a large model in comparison, and it flies well, very sensitive to even 1 g ballast in the nose area. It makes such a difference. I wonder if the Mig 19 actually has such a sensitivity to CG.

They key is to be able to be harshly critical of ones own designs and be willing to make drastic changes. Bold designing.
Last edited by Designer2010; Jan 08, 2020 at 08:34 AM. Reason: Added information
Jan 08, 2020, 08:46 AM
Design is everything.
Thread OP
The YE-2 is a nice swept wing model, but I have difficulty fixing the wing rigidly to the fuselage, the answer is a thicker wing and a corner brace with additional bracing at the corner.

https://www.designlaunchers.com/what-is-3d-cad-modeling
Jan 08, 2020, 11:11 PM
B for Bruce
BMatthews's Avatar
The amount of up elevator needed to make any plane pitch up strongly is going to depend on a wide variety of things.

First off never mind the full size craft. Especially in the age of relaxed stability and fly by wire with auto stabilizing included.

Also at higher speeds a slight pitch up can look stronger because the aircraft pitches faster. But in reality the pitch rate for distance traveled might be low. It's the speed of the airplane that makes it seem like it's pitching rapidly for very little input. So again you can't directly compare full size to our model size. Each is it's own thing. Granted there are some similarities. But there are also differences related to the speeds and scaling.
Jan 09, 2020, 04:54 AM
Design is everything.
Thread OP
In connection with elevator settings : most aircraft have elevator travel limited to +15 and - 15 if I remember correctly. For a model aircraft, it would be better to locate the CG so that minimal elevator is required to fly the plane level, and to pitch up into a climb and to turn. This is what I am discovering - it is no point getting the CG too forward or the model too heavy and then trying to compensate with more up elevator.

Also, the L- bracket solution worked fine if the L-Bracket is braced with a brace glued at an angle to the L_bracket.
Jan 09, 2020, 03:36 PM
B for Bruce
BMatthews's Avatar
You'll find that you need to pick the elevator to wing angle to suit the flight style you want. And then to put the CG where it needs to be for that particular wing to tail angle. Or for delta wings as per the elevon angle.

Basically if you want duration and distance you want a low wing to tail angle or a low amount of elvon/reflex on the delta so it glides more efficiently and doesn't just try to loop over and hit us in the head at the launch release.

But if you WANT the model to loop around in tight spaces like the last few videos of the model in the guy's living room at that fellow at the show it needs a higher angle between wing and stabilizer to make it pitch that way. And that same angle will make the model stall repeatedly in the regular glide unless the CG is further ahead to kill the stall.

Mind you those indoor loop around models do not look like they are allowed to glide away normally. And if that is the case you COULD set up the CG and trim for a good long duration or distance setting. Then just for doing the tight loopy thing inside angle the elvons or stabilizer strongly to JUST do the loop around and catch style. The model won't glide normally if you try that but if you're doing this loop around flying you don't care since you'll be catching it every time at the end of one loop around.

It's just all about how you want to fly the model.

Kids also really don't care about duration either. For them it's more about the fun of the model performing antics like looping around and narrowly missing them or their friend and then performing some antics in the air before touching down at around 5 to 8 seconds. Later on they might get interested in longer flights. Or maybe not.
Jan 12, 2020, 08:33 AM
Design is everything.
Thread OP
Bruce, you are right of course. I only have to recall that foam model I once saw a child handle at a birthday party - that did loops and turns but glided in a series of dips. Not good for gliding. Most of these planes have a movable wing that shifts the CG to get the desired flight profile.

I agree that kids don't really care about duration and distance. So I have started experimenting with a 'flying triangle' - larger, easier to build and hand launch model. Of course at that size I have to find ways to increase stiffness. Looks like these two paths are diverging - my rubber band launched 'scale' models that need to be trimmed carefully to the hand launched stunters.

Duration and distance: I am not really interested in either. What I am interested in is a high speed launch, in level flight, followed by a sharp pull up or a sharp turn, or a long flight. to gauge how the model 'handles'. I still have a feeling that these models can teach me something about the real aircraft, and it is very intriguing. For example, my model of the Mig -19 is large, and a little heavy at 22g. The Mig 21, however was designed for the lowest frontal area and the smallest possible fuselage, both in cross sectional area as well as wetted area, reducing drag. It is difficult at this scale also to build a long stiff wing, whereas a delta wing made out of a flat sheet of cardboard will fly and take any amount of abuse. The smaller the aircraft also, the greater the acceleration since mass and drag are both low.

When you look at the F-16 with its 10,000 kg thrust engine in that relatively small air frame, and the Mig-21 also being a small airframe, you can see what the designers were thinking. The swept wing prototype I made seemed to have less drag, and from the figures the Ye-2A (swept wing Mig-21 prototype) had greater range (more efficient wing?).

I look forward to completing and flying the Ye-2a, right now the parts weigh in at 13g and I am hopeful it won't get much heavier. The Mig 21 I have weighs in at 19 g or so.

My final goal is an R/C 1/32 or so model, but that is far in the future it seems.

Have a look at some of the Ye-2 and Ye-2 pictures here. To me it is the quintessential 1950s jet fighter.

http://ram-home.com/ram-old/ye-2.html

http://www.aviastar.org/air/russia/mig-e2.php

https://forum.warthunder.com/index.p...and-tech-tree/
Last edited by Designer2010; Jan 12, 2020 at 09:03 AM.
Jan 15, 2020, 01:53 AM
Design is everything.
Thread OP
I really need to post some videos of the models in flight - will visit a nearby park and get this done.
Jan 17, 2020, 01:25 AM
Design is everything.
Thread OP
This project has been divided into two branches - one will be a simple hand launched glider for children to play with, 1/32 scale seems reasonable, and the other will be a continuation of the 1/48 series of even a 1/32 series for my work.

I am forced to resort to an engineering analysis of the structure improve its function. It should be an interesting exercise.

It will be quite an interesting engineering exercise to get the weight down while preserving stiffness, or refining the build and maintain cycle so that the least cost and effort is involved. I have been faced with the continual failure of the forward fuselage under impact loads, and the result is very messy.

The fuselages built so far have been the monoque type. This type of structure is prone to buckling when it encounters off-axis loads, as I now find out.

Quote:
Monocoque is a structural technique in which stresses are reacted by a thin membrane or a shell of material, rather than a collection of beams. Such structures are stiff in bending, and light, and are therefore ideal for weight-sensitive vehicles such as airplanes.
Quote:
A monocoque structure has a great tendency to fail in buckling or crippling, something easily demonstrated by a person standing on top of an empty aluminum beverage can
https://www.sciencedirect.com/topics...ring/monocoque

Some internal bracing therefore is required. This does not have to add a lot of weight, the standard bulkheads and formers may be incorporated here without much added weight and effort.

The wing also may benefit from re-engineering, the use of spars and skins instead of a solid piece of cardboard.
Last edited by Designer2010; Jan 17, 2020 at 01:38 AM.


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