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Nov 05, 2008, 10:53 PM
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Some thoughts on the build so far.

As I have been working on this build I have been making small changes here and there wherever I find issues or believe that there could be improvements. As I go I have also been updating the CAD file with these changes. Most of these changes have been small things like missing alignment tabs, incorrect hole locations and such.

Today I came across the first major issue that will require an actual geometry or conceptual change to the design but first some history:

As mentioned in the first post this plane was originally designed to be a profile foamy. I had modeled this profile on my existing plane which had a serious tail heavy condition and ended up having the battery tucked up right by the motor making me a little nervous. My solution for that plane was to swap out the motor and ESC for a larger system; not because the plane needed the extra power but because I needed the extra nose weight and I might as well make that extra weight work for me. In order to avoid this with the MXS I had stretched the nose out to put the original motor slightly farther forward and thus help with the balance of the plane.

Well it turns out that when I changed the design plans for this plane from profile to boxed fuse I made many attempts to lighten the airframe to keep it in the same weight range as the profile version. with lighter tail feathers it turns out that the plane is considerably nose heavy. With the current setup and a 3S-1320mAh TP I need to mount the battery a short distance behind the wing spar to achieve the desired maiden CG.

In and of itself this is not that big a deal, I have space to mount the battery there by placing it above the crutch assembly. The problem is an access issue, this places the battery below the canopy (which is fixed and can't open) so getting the battery in and out and most importantly, safely fastened, will be a chore.

As for the next build I will shorten the nose back to the original dimensions which should correct the CG issue. Of curse this change will have to be made and tested and the second prototype will have to be built to see what the outcome is. I may also consider moving the rudder and elevator servos more towards the rear of the plane, possibly mounted directly to the crutch (as opposed to the servo tray). I may just push them as far back on the servo tray as possible and leave the rest to the shortening of the nose.

For now I will do the best I can to lighten the front on the first prototype, (move the ESC and the receiver as far back as possible). I will then find a way to mount the battery wherever it needs to be. Of course, as a last move I will add a little weight to the tail to achieve the correct balance.

Live and learn.

- Birger
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Nov 06, 2008, 11:14 AM
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So you finally decided to go with a 3S LiPo?
Nov 06, 2008, 11:17 AM
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Yes, one fell into my basket last time I was at my local hobby store. I will now have to find another project to use the other batteries I have in. At the end of the day I'm hoping to get 12-15 minutes out of a 1320mAh cell, let's see how it goes.
Last edited by bdelapen; Nov 06, 2008 at 11:17 AM. Reason: Typo
Nov 06, 2008, 11:43 PM
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Build Progress, 11/07/08

It's really getting close now.

Tonight I first tackled some small changes to the components to try to help my nose heavy condition. The changes were small but hopefully it will be at least a little help. I relocated the ESC as far rearward as the wires allowed. I also removed some small nylon stand-offs that I had between the motor and the firewall moving it a little rearward. At the same time I removed some washers and shortened up the motor mount screws to eliminate surplus length. Finally I relocated the receiver to the battery compartment and moved it as far rearward as I could without interfering with the battery placement. This also allowed me to eliminate two servo extensions and to eliminate the lower hatch which has now been glued in permanently.

From here I moved onto gluing in the aileron control horns and fabricating the aileron control linkages. Once these were installed I moved on to gluing in the last two pieces of the airframe which are the front top and front bottom.

Finally for today I moved on to shaping the wheel pants and mounting them together with the front wheels.

Left to do (hopefully tomorrow night):
  • Create battery hatch and release mechanism.
  • Create a battery attachment mechanism that can be used effectively in the confined space under the canopy.
  • Apply remaining decals (activate glue on decals and all tape joints with a hot iron).

Now on a negative note. I will not be able to make the field Saturday due to a family engagement so the maiden will have to wait till at least Sunday. Currently the weather forecast for Sunday does not seem to promising however, probably being influenced heavily and negatively by hurricane Paloma but I will see how it goes. If I can't get the maiden in on Sunday it will have to wait till next weekend .

More to come tomorrow,

- Birger
Nov 08, 2008, 12:28 AM
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Build Progress, 11/08/08

A quick update:

I designed and built a latch system for the battery hatch; pictures below. Left to do is the battery strap and decals.

More to come tomorrow...
Nov 08, 2008, 05:05 PM
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Build Complete. Ready for Maiden!!!

OK, so I have finally finished the build. Had a few difficult moments right at the end (primarily with the CG problem and the battery location) but I've pushed through them and am ready for the maiden.

As mentioned above, I had to come up with a battery attachment mechanism. I initially tried a Velcro strap which is what I like to use on my planes but there just wasn't enough space under the canopy to do-up and undo the strap so I had to find an alternative. I ended up with Velcro on the crutch and on the bottom of the battery and a piece of foam sandwiched between the canopy bottom and the battery top to hold it down against the Velcro. I need to make sure that I don't have an overheating problem so I will have to monitor the battery closely during the first few flights.

As mentioned before, I am working on changing the geometry of the plane slightly and the location of the components so that the battery can sit farther forward and avoid this particular problem in future iterations.

Finally I attached the remaining decals and ironed them all down (as well as all the hinge tape).

A quick check of the CG and it is spot on (according to the calculator) without having to add any weight to the tail so I'm happy about that. I will probably shift the battery slightly forward for the maiden to gain a little stability but I know that I can reach what I want.

Here are the final specifications:
Wingspan: 37"
Length: 33 3/4"
Wing Area: 332 sqin
AUW: 15.6 oz
Wing Loading: 6.77 oz/sqft
Motor: Hacker A20-20L (~200W)
ESC: Atlas 20A
Battery: TP 3S 1320mAh
Propeller: APC 10X4.7SF

Looks like Paloma has stalled and the weather tomorrow will be flyable after all so I'm hoping for the maiden tomorrow, will post a maiden report (and hopefully video) here.


- Birger
Nov 10, 2008, 11:20 PM
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Maiden Report

It is with mixed feelings that I post this maiden report. Although things could definitely have gone much worse they could have been better as well.

It turns out that the day was much windier than predicted by the weather forecast. Not only was the wind pretty strong (8-12 MPH) and gusty but it was going over the strip and then down the hill (opposite of slope soaring) creating a pretty difficult wind situation.

Early in the morning I put up my profile foamy to get the feel for the weather and had a decent flight but a rough landing. I split the fuselage on one side behind the wing joint and I broke loose the firewall. Nothing that can't be easily fixed but because the firewall came loose I didn't want to do it at the field and opted to take it home to fix. I wanted to get a few flights in before I took up the MXS since I hadn't flown in two weeks but that was not to be.

I waited for several hours (over 3) just chatting with the guys at the field hoping for the wind to calm down but it never happened. Since I had to leave that same afternoon on a business trip impatience got the better of me and against my better judgment I maidened the MXS with the horrible winds (at least for a light weight foamy).

The following is the raw, unedited video of the flight. The flight was between 8-10 minutes but since the video tape in the camera was running out we cut out the last 1/3 of the flight to make sure we could get the landing on tape (which we did).

MXS Maiden Video

I wasn't able to push the envelope due to the wind but towards the end of the flight I did try some things that did not show up on the video. My initial thoughts on the plane are:
  • The whole flight was flown with low rates due to the wind conditions (except for a couple of snap rolls and a wall).
  • Pitch control is crisp and I believe that the plane will be very pitch stable and reactive in good wind conditions.
  • Calculated CG is a little off. I maidened with the CG 1/4" forward from where I thought (calculated) it should be and it was very close to where I would like it.
  • I was not able to get a good sense of the turning ability since the plane was being pushed every which way by the wind.
  • Knife edge was easy, very little rudder input to maintain level flight. There was a little bit of coupling but it was easy to cancel out (possibly just conditioned reflex).
  • Was excellent in inverted flight, there was minimal input once the plane was trimmed out for level upright flight. Due to the winds there was some porpoising but I believe that will go away in calm conditions.
  • I'm not the best at 3D, still learning and the weather was not the best to try anything to fancy but I never went over 60% throttle, even on the crisp upwind passes so it should be very capable. I did fly around most of the time at 30% - 40% throttle.
  • The battery ended up a little warmer that I would have liked after the flight but it was by no means hot. This can easily be addressed with some better ventilation of the battery compartment.
As you can see from the video I had what you could qualify at the least as a rough landing (or to put it bluntly a crash). I was a little tense, the wind was unpredictable and my approach was way to close to the end of the hill (and the corresponding turbulence) and too slow. A gust of wind caught it too close to the ground and I was just not quick enough to react to the dropped wing. I'm still not sure if the damage was worse than the hit looked or the hit was worse than the damage it created but here is a quick summary of the damage (nothing that can't be fixed).
  • The two things that I was concerned for the most survived without damage, the right wing and the firewall are intact.
  • The second bulkhead split at the landing gear mount effectively breaking the left landing gear loose.
  • The fuselage creased behind the wing (same place as the foamy which had a very similar "landing"). The fuselage skin de-laminated from the crutch assembly which has a small split at one of the lightening holes and the two skins separated just behind the cockpit filler piece.
  • The rudder control horn broke loose from the rudder without any real damage to the rudder (just a little torn foam proving that the glue is stronger than the foam).
I will take some pictures of the damage when I get back home before I repair it all but the short version is that I will definitely have it up again next weekend to get a better feel for the plane. I did learn a few things that I will integrate into the next design,

More to come.
Nov 12, 2008, 02:58 AM
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Hi Birger,
If you check my blog you'll notice that I had a similar experience during my first flight of the Owl-RT (except for the crash; I crashed it later! ).
One thing I was taught by Kaos2 (Rich, great guy, wise and experienced), who designed the Regal and Regal Bipe 3D models, and he is sooo right, is that it's useless to fly your maiden flight in windy conditions, specially for a new model, and a new design.
Your MXS looked great in flight though and I am sure it has a lot of potential. I guess it's normal to revise a design after the first prototype. I am on my no. 4 Owl-RT and still making design changes! That's why foam planes are fun to build and fly (and crash).
I am sure that after you have a few hours flying on the MXS (in calm air) you'll be able to figure out lots of things that are already perfect in the design and whatever needs improving.
Good luck!
Nov 17, 2008, 09:22 AM
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Detailed Damage Report

Some pictures of the damage after the maiden. As mentioned above the damage was located in 3 main areas:
  • Fuselage buckling rear of the wing
  • Landing gear mount failure
  • Rudder control horn failure
For more details see the pictures.

There was one piece of damage I couldn't get a picture of due to the location and that was the de-bonding of the crutch assembly and the crack in it. All damage was taken care off with some glue and a small strip of carbon to reinforce the crack in the crutch assembly.

- Birger
Nov 17, 2008, 10:24 AM
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Flight Report, 11/16/08

Got to take the MXS out for another spin yesterday.
I only have one pack right now so I only got two flights in with a charge in between but they were both good flights.

First flight was in calm weather early in the morning and it flew very well. It has endless vertical with the current set-up and fast snaps. It will fly much faster then my profile foamy and I did a couple of what I would consider "high speed" passes to get a feel. It will slow down a fair amount though I haven't pushed the envelope to see how slow it will go. It flies just as well inverted as it does upright, just a little down elevator to keep it level. Inside and outside loops both normal and inverted were a breeze. Roll rate is a little slow for my taste and I will try to make some changes there. I did some flat "rudder only" turns and they were nice and crisp, just a little opposite aileron to keep the wings perfectly level. Came down for the landing nice and slow, does need a little more speed than my foamy to land (more like a real plane), I keep some throttle in it until just before touchdown.

My second flight was a couple of hours later with 5-8 Mph winds. This was my first take off from the deck. The roll-out was straight and short, itjumped into the air at half throttle within 10-15ft. It handled the wind very well but due to it's light weight it was being pushed around some, you definitely need to be on top of it in the wind (like any foamy). Again, still getting a feel for it but it flies nicely. I did a few knife edge passes and they did require a little bit of aileron and elevator to keep straight but in general I was very happy since they require very little rudder to keep the plane flying level. This time I landed with more speed to avoid any mishaps in the wind and had to come around 3 times before I could get the right approach angle, speed and altitude for a beautiful landing, taxied back to the pits on the grass runway and taxiway! One thing I noticed is that at faster landing speeds it definitely wants to stay up there in a brisk head-wind, you need to start you approach lower/farther and "help" it down a little.

Thoughts/Improvements for rev. 2
  • I've shortened the nose by 1/2" to improve the nose heavy condition. I have also re-located the elevator and rudder servo to the rear of the fuselage for the same reason. The receiver will be moved to the location where the current elevator and rudder servos are and the ESC will be moved to the space above the crutch (from the space below where it currently is).
  • The battery is coming down warm but nothing that can't be easily controlled with some better ventilation (already designed into the next version).
  • I've modified the control horn design to give some additional moment advantage and more bonding area.
  • The current aileron setup is no good, the barn-door hinges just aren't tight enough. This leads to slightly unpredictable roll response but more importantly it leads to imperfect centering. It just seemed that I was chasing the aileron trim the whole flight. I have re-designed the torque rods to work with traditional tape hinges for the next prototype but since it will be a little while before I start work on it I will have to find an interim solution for this plane (maybe scrap the ailerons and build new ones to the new design).
  • Need faster roll response. I am going to try increasing the endpoints and lowering the expo a little to see what kind of result I get there. If it is not enough however I may need to change the wing to give the ailerons a larger percentage of the wing area.
  • I want to make some changes to the landing gear mount. I need to have a stronger mechanical coupling between the front and read mount elements, maybe kevlar thread wrapped around them through holes in the foam.
  • This one is minor but I want to put one more thin carbon doubler on the rudder, close to the top.
Sorry, I have no pictures or video this time but I will try to take some more next time around.

- Birger
Nov 17, 2008, 10:30 AM
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Waiting on plans or kit once it is out of test flights.
Nov 23, 2008, 10:35 AM
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Update, 11/23/08

A quick update, several things have happened since I last posted:

First of all the plane design:
I thought long and hard about the aileron issue I described earlier and decided to scrap the current ailerons. I went ahead and built a set of the re-designed ailerons (the ones currently in the cad system) and mounted them. In essence they are 1/4" wider (longer chord), I moved from a round tube to a square tube for the torque rod and I moved the torque rod in from the edge a little so that I could bevel the front and use traditional tape hinges. I also brought them in a couple of mm on the inboard side to solve a small clearance issue I had, when the aileron was deflected down it would run into the fuselage. On the radio I dropped the Expo to 45% from 60% but I did not change the end points yet. Some pictures of the new ailerons attached.

Secondly, the flight performance:
I went out to fly today, it was again a little to windy for my taste but I went up anyway. Got a few flights in with some horrible landings (has to do with the way the wind blows down the hill at the end of our runway, I had to come in high to avoid the turbulence and then "drop" out of the sky to make the runway. Flight was much improved with the new ailerons, crisper turns and higher roll rate so overall I'm very happy with that. It was too windy to check on the trim but it's a start. I did learn that my ESC is set to soft start, I had a moment when I gave it full throttle and nothing seemed to happen, I will have to re-program it before next flight .
On my third landing I must have hit a little hard (or hit a pot hole) because I broke off the landing gear. I already knew that the mount needed a re-design but this has convinced me to give it some more attention and stiffen it up even more (beyond the initial measures I had taken). I will have to take apart the lower fuselage skin on the prototype to get in there and fix what I currently have but it should be fine after that. Some pictures of the damage attached.

Thirdly, build manual and plans:
I am working on them, I am very happy with the design over all and just tweaking a few things here and there (e.g. landing gear mount) that I want to incorporate into the first version of the plans. I don't make any promises but I'm hoping to have a set available sometime before Christmas in case anyone wants to give them a try. The first set will probably be with diagrams and descriptions but no pictures since I will have to build the second prototype in order to get all the necessary pictures and I will probably not have time to do that before then. Nonetheless, if you are brave, a patient reader (there will be many instructions) and a good builder you may want to give them a try .


- Birger
Dec 05, 2008, 09:45 AM
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Preliminary Plans


I'm still working on the instruction manual but I have all the parts layout complete. If you are an accomplished scratch builder and you would like a challenging project that flies very well here it is. There are some changes that I have incorporated into the plans but have not built myself yet since I will not be able to start on the second prototype until after Christmas break but I feel very confident this is very close to where I'm going to end up.

As soon as the preliminary manual (diagrams, no pictures) is complete I will post it as well so that you have some more guidance, for now all you have is this build thread.

I will give you one hint, when assembling the crutch and the fuselage sides be mindful, there is a left and a right (servo control horn clearance slots need to match servo positions. Also, all servo cutouts are dimensioned for Futaba S3114 servos, if you have different servos you may have to adjust your cutout sizes.

I will be glad to field any questions, you can either post them here or just PM me.

Happy building

- Birger
Last edited by bdelapen; Jan 13, 2009 at 09:14 PM. Reason: Updated Attachments, added new layout diagram
Dec 07, 2008, 06:37 PM
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thanks for this great job !
Dec 07, 2008, 07:45 PM
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Thanks Marie,

If anyone is building one of these please post pictures here, I would love to see what people are doing.

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