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Jul 16, 2010, 02:28 PM
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Build Log

Macross Inspired 18" YF-21 Pusher Jet with Plans


I finally gave in and watched Macross Frontier last week. If you're into that sort of thing, its not bad. I personally enjoy those shows more for the interesting aircraft / spacecraft designs they come up with. Some of them are off the wall, others are vanilla. I spotted this one in the background of some of the battle scenes, the standard cannon fodder so to speak, as opposed to being a hero vehicle.

So yesterday I started up the CAD software (a first for me when designing planes,) and went to work on this design. I just loved the Tomhe style of pusher jet, and of course I blatantly stole his style of design with the tabs, and the basic assembly; the design itself is original however. Since yesterday I have built one airframe and revised the design drawings several times. I had to take a significant liberty and design the airframe with proper elevons. The original design is tailess, and I do not think it would have flown that way.

The attached plans will go together without too much trouble, and even include some options. The one in the attached photos has the short and more accurate horizontal stabilizers, but the plans give you the outline for horizontal stabilizers with about twice the surface area. There are also lines for ailerons, if you wish to cut them out. As I complete the prototype for flight testing, I intend to add them. The motor mount area is probably going to need some work. Finally, you will notice the CG is not marked yet. Sorry, but I'm not really sure where it should be, yet. I expect similar to the Tomhe F22, but I will update the drawings when I know.

The plans are designed with 4.5mm ~ 5mm depapered readiboard in mind. The prop slot is sized to accommodate a 6" prop. I am aiming for a 5.5 x 5.5. I intend to run this plane on a 1700kv blue wonder, with a 5.5 x 5.5 prop on a 610 3S battery. This plane is lighter than my 18" Tomhe F22, and this is the power system I use on it. I expect a similar 2500kv motor would really make this plane move along.

I will update as soon as I have performed some flight tests, I'll even try to get some video.

EDIT: Already a quick update to the design. Prop slot has been redesigned to fit a bluewonder with a prop saver correctly. Limited to a 5.5 dia prop. 6" possible, but not without changes to the frame.

EDIT: Added V3 plans after some testing of the V2. Significantly changed the rear, the wing area, and the horizontal stabilizers. Should balance easier, and be more stable. Suggest trying with just the elevons first, as with the ailerons cut out too, the amount of control is way over the top.
Last edited by Ace12GA; Jul 18, 2010 at 01:36 PM.
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Jul 17, 2010, 12:53 PM
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Very interesting Ace. I have found myself more and more inclined to build these profile foamies. I have an F22 18"WS which I have flown the pants off! It is one of my favorite aircraft. BTW, no one should have this much fun for about 3-6 dollars worth of foam! I may give your design a try. I just happen to have a spare 1806N 2500KV motor looking for a home and a couple of foam boards I just bought from the dollar store. Any tips on removing the paper? Also do you have any info/shots of the real one? I need a camo scheme. Thanks, Marty
Jul 17, 2010, 02:22 PM
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Very nice build.

Question, behind the wing area, right behind the slot for the motor, it looks like you have 1/2 inch of foam on each side. Will this be enough to hold the plane together if you do any hard loops?
Jul 17, 2010, 07:15 PM
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I attached the images I based this on to this post. You can see how I took a major amount of liberty with the rear section to add elevons. The fictional version operates in space, and uses thrust vectoring. I suppose the thrust vectoring could be achieved with some clever design, but I went with standard elevons.

The way its built, it should hold up as well as a Tomhe F22, which is pretty well. Mine is a year old, and beat to heck. We'll see how this one holds up however. The prototype is all geared up, and ready for a maiden, just waiting for the wind to drop off. Figures the first day its ready to fly the wind is gusting to 30km/h.
Jul 18, 2010, 09:09 AM
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Corrugated steel roofs suck. Sharp edges you know. Also, tail heavy sucks too. Combine, they eat planes alive.
Jul 18, 2010, 01:36 PM
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Got some testing in today, and updated the plans. The V3 plans have been added to the first post. Should be easier to balance than the V2.
Jul 18, 2010, 11:37 PM
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Gotta Love The Macross Series...I haven't done a profile yet but will need to give this a try.

Brett
Jul 18, 2010, 11:58 PM
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After I come back from vaca, I will be cutting some foam! Marty
Jul 19, 2010, 06:20 AM
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Thanks for the interest guys. Still some bugs to work out. I have had it flying a few times, but its pretty squirrely, the V2 design is anyway. I think its the small horizontal stabilizers, which on my test version I have more than tripled in size. Going to get a test flight in this morning I hope I before work. If successful I will update the V3 plans, which already have larger horizontal stabilizers.
Jul 19, 2010, 06:41 AM
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Ace do you think the problem could be because she's short coupled? Might want to consider some expo at center say 30%. How about slightly enlarging the WS? Maybe more wing area might help too. I'm excited about the build. But I'll let you work out the bugs first! Marty
Jul 19, 2010, 09:50 AM
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Marty, in the V3 version I have increased the wing area significantly, but the prototype is still the V2 with some heavy modifications. I don't know that I can increase the wing area without some serious problems in weight. I will be building a fresh V3 or, heh, V4 once I am done testing with the current model. I am considering going up from 18.5" WS to 22" WS, just for more wing area.

I don't have expo on my cheap radio, just dual rates. I am playing with that. What I have observed so far is way too much roll, and seemingly not enough pitch at times. At other times its all pitch.

Motor / prop combo have enough power to do limitless vertical at 3/4 throttle, but it seems to lose pitch control at higher speeds. I have managed to fly it reasonably in control, and in the same flight lose complete control and barely get it back. I still think horizontal stabilizers are playing a roll, as the balance seems to be right currently. It glides wonderfully. May be looking at a thrust angle issue too. Motor is mounted such that thrust is parallel to the wing, and in line with the wing as well. That's how I have mounted all my previous setups on this type of plane. If you apply throttle from a glide it has a tendency to go nose down. I can high alpha it nicely at low speeds and low throttle from a gentle hand launch.

As I said, bugs need to be worked out. Heh, this is my first proper scratch build, so its a lot of fun for me.

EDIT: That red tape is tuck tape, its meant for sealing vapour barrier, but it works really well on foam. Too bad its ugly, but I was out of clear packing tape.
Jul 19, 2010, 12:37 PM
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Ace from sounds of it I think you are losing control at high speeds because the control rods are flexing. I had the same problem with an F15 I built. I increased the size(diameter) of the rod and it fixed the poor response at high speeds. Using the vectored controls you should have response with no question at any speed. Nose diving under throttle is definately a thrust angle problem. I'd try a little more positve angle on the motor (shim it). Gee Ace, I feel like I'm right there with you on this project! Does it mean I can claim some credit too? LOL If you'd like I can call you to discuss (no pressure). Gee I always to be an aircraft design engineer! On second thought..... Marty
Jul 19, 2010, 12:46 PM
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A thought


Ace just now taking a second look at the control setup, I wonder if the airlerons are blanking out the elevons and could be the reason she's losing control. Try taking the linkage off the airlerons and lock them neutral. Then try flying her. Enough deflection on the elevons should produce enough/sufficient roll (this is the setup I have on my F22). Let me know your thoughts. Marty
Jul 19, 2010, 01:27 PM
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Quote:
Originally Posted by martys
Ace just now taking a second look at the control setup, I wonder if the airlerons are blanking out the elevons and could be the reason she's losing control. Try taking the linkage off the airlerons and lock them neutral. Then try flying her. Enough deflection on the elevons should produce enough/sufficient roll (this is the setup I have on my F22). Let me know your thoughts. Marty
Marty I don't think control rod flexing is the issue. I use the same wire on a 28" Tomhe Mig 29 with no issues, and that plane has a lot more power, with much larger control surfaces. I have, however, wondered if the aileron surfaces were over kill. I was already thinking of taking them out of the picture, but I want to try the new configuration in flight before I do that.

Its getting there however, I feel it. If the damned wind would just give it a rest. 20km/h outside right now is just too much.

I should mention all of my test flights have been in more wind than I would normally test in. 15km/h on average. Now as a comparison, I have been taking out my F22 at the same time just to make sure its not only the wind. The F22 flies just fine for being blown around some. Hoping to get another test flight in this evening.

Thanks for all the input Marty, its appreciated.

EDIT: attached a shot of my Mig29 beside the YF21 for perspective.
Jul 20, 2010, 08:03 AM
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Success. Marty you were partly right. I reduced the surface area of the ailerons by about 50% by cutting the triangle off of them, and bam, it flies great. Its faster than my F22 by a significant margin, and it handles pretty well, considering all I've done to it.

Do not cut out the ailerons as they are in the plans, you only need the elevons. The larger horizontal stabilizers help as well.

Going to do some more testing, then move on to building the V3 plans myself.

So compared to the 18" F22, its faster, and capable of much tighter loops like my larger Mig 29. The roll rate is insane with the reduced ailerons. No really, its insane. Like my Mig29, has a tendency to pull loops and hard banked turns too tight, and actually stall out for a moment. You can try to power through it, but the change in direction is so quick it stalls anyway. Its easy to recover from, but good to know about. Hopefully vid to come shortly.


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