Building for F3P

[racerxky]

This thread is about building ideas and techniques as they apply to F3P. I just built an F3Ai Troll (http://www.amjd.ch/troll.html) as an F3P practice model.

Plans are available in DXF (for those of you with Auto CAD) and in PDF. The site with the plans is down at the moment but hopefully it will go back up.

I saw the Troll and was really taken with its lines. It looks like an airplane. Some of these F3P designs look a bit too too cartoonish for me. From the videos on the website it seems to fly well. It also has a full fuse and I like that. Its meant to be a heavier model than what would now be considered ideal for F3P but its a good starting point

I'm not claiming that anything I am doing here is original. I'm also not claiming that the results are anything better than what others are doing. Finally I'm not claiming that the airplane is as light as it could be. I got a lot of useful information on RC Groups and elsewhere.

If your building for F3P then you should definitely check out Blucor Basher's Equalizer build thread (http://www.rcgroups.com/forums/showthread.php?t=388378) .

If you build models period than you should read Paul K. Johnson's Airfield Models (http://airfieldmodels.com). I got the idea for using Balsa Play from there. Much of his advice for working balsa can be transfered to Depron.

'Nuff said, on with the gritty details.

[racerxky]

Reading this forum its clear that there isn't much hard data on what the parts of an F3P ship weigh. People are tossing out the carbon fiber and running magnet wire all over the place. Is this the best way to go about it? To find out I weighed every component and material that went into my Troll, separately, before it was assembled. Then after assembly I weighed it again. The difference should be the weight of any glue, tape, Velcro and "other" stuff.

The PDF has all the raw numbers and the char has the percentages.

The thing that shocked me was that all the carbon fiber parts weighed less than the ESC! Eliminating carbon spars from your wings probably isn't a good trade off.

The airplane is mostly Depron so its weight is mostly from Depron. Some Depron is structural and some is aerodynamic. Where the parts are stiff it should be possible to eliminate some real weight by replacing some of the Depron with a covering film or tissue. On a boxed fuse there are lots of places to do this.

Tape is heavy stuff. I pulled the tape off the spars so I could get the glue to dry and the weight went down quite a bit so I kept it off. I don't see the tape wrapping of the carbon as necessary. The only tape in that weight is from double sided foam tape for the servo mounts.

[racerxky]

These worked out amazingly well. I got the inspiration foam the way Stevens Aero does the landing gear on their kits. The idea is to absorb all the crash energy in the gear and save the rest of the airplane.

They are basically idiot proof to make, light and super strong. Just make sure you use the right gauge of carbon rod. You want the gear to flex on impact. If they don't flex they will transmit all the crash energy into some other part of the airplane and probably break it. Up to 230 grams 1.5mm carbon rod is probably enough.

My gear have already survived several nose ins and a drop from about 3 meters when the airplane matched wits with a basket ball goal. No damage to the fuse or the gear yet.

[fwilly]

The thing that shocked me was that all the carbon fiber parts weighed less than the ESC! Eliminating carbon spars from your wings probably isn't a good trade off.

My esc weighs around 2g after I've replaced all the wires. If you get a plane light enough, you don't need as much carbon, so why fly with more than what you need?

[wevets]

So many questions...


In your weight analysis, you omit the battery. How would the analysis look with the battery included? What the analysis tells me now is that the biggest opportunity for weight loss is in minimizing the amount of depron.

Also, what are the details of a pull-pull control system?

wevets

[racerxky]

I'll post about the pull-pull tonight, I need to take more photos.

I have a 3S 620mah pack and a 2S 730mah pack. They are both a little heavy for competition. If all you have to fly is a 2 minute routine (and assuming the battery puts out enough amps) you could fly with a 2S 340mah. If you look at Jurgen's numbers a lot of the flyers in Europe are doing just that. So battery weights are all over the place and you can choose what you like.

The other reason for leaving it out is that i dont build battery packs. I dont have any control over their weight other than to go buy a lighter pack.

I think the lightest battery i have access to would be a Thunder Power 2S 430mah at 23g. That makes an all up weight of 171g + 23g = 194g. Thats very close to the competition bipes. They average 180g to 185g according to Jergens specs.

Mono planes need to be lighter, around 160g.

[Aio_1]

While this sort of analysis is interesting I don't think you can really extract quite as much from it as it may seem.
Total weight is not the single most important factor. Without considering the wing area and proportions of the plane you could draw some very odd conclusions. For example in your plane depron accounts for much of the mass and it would seem that this is where savings can be made. However the only opportunities to reduce depron weight is to use thinner depron, less dense depron or less of it. 2mm depron weighs nearly as much as 3mm (presumably most of the mass is at the surface not in the core of the sheet) and is much less rigid so it's unlikely to pay off as you'd need to frame many of the flying surfaces in wood or carbon or go nuts with thread bracing. There is a slightly less dense material which I think some of the builders in Germany anf France are using but I think the savings are relatively small.
Unless you entirely change the construction method (say an open structure with film covering) the only way you can use less depron without reducing surface area is to eliminate areas where it's laminated. On a cruciform fuselage design almost all of the depron constitutes an aerodynamically relevent surface. So for most designs the only way to significantly and easily reduce depron mass is to reduce the size of the plane or stop using depron as the surface material altogether. If you reduce the size of the airframe the wingloading will almost certainly become less favourable and there's no point.

So I agree that there are probably some weight savings that can be made in many designs but I think that the most practical weight savings are by choice of hardware and perhaps some modification with case removal and re-wiring. Most competition setups seem to use something like the following:
12g motor
20g of cells
15g of servos
5g ESC
5g receiver

That's ~57g + prop + linkages + airframe + decoration

Apparently some people are even adding ballast to get the handling they want because this sort of setup is sometimes too light.

I'm not sure what my point is but I've gone to the trouble of writing this so I suppose I'll post it! :D

Aidan

[3dflyindan]

lol

you like gettin your point across :D

dan

[racerxky]

Yes thats exactly the kind of things I wanted to hear back from people.

I'm thinking about many of those things. Im just better and building than I am at soldering.

More Ideas == Better Airplanes

[racerxky]

As promised.

Those 'Barn Door' hinges work great for pull-pull controls. I find them less work than the tape strip hinges. They are easier to get right when you can't lay the surface flat on your workbench. They have almost symetrical movement which is great for a pull-pull setup. I'm a convert.

I made my control horns out of balsa ply (http://www.airfieldmodels.com/information_source/how_to_articles_for_model_builders/construction/make_balsa_wood_plywood/index.htm) but they turned out to be too weak. I poped the eyelet out of one as I was rigging. Plastic or carbon plate would be tougher/stronger. I don't see a good source of cheap pull-pull control horns out there for this size model. If someone makes them I'll take a dozen.

I didnt know what to use to make those tiny pulleys, so I kluged it. Plastic sewing bobbins was all I could find. Don't worry about making them spin either just glue them straight to the wing. The friction isnt that big of a deal. The they come in packs of 4 and cost less than a dollar.

The white bits are called bowsies (http://www.ec12.info/Rigging%20Tips.htm) (yea, I couldn't make that up if I tried) and are used in model sailboats. I used the end of a small control horn, just the last 3 holes, to make my bowsies. You snake the line through two of the holes. Then pass the end of the line through the servo arm hole. Then put the end through the third hole in the bowsie and tie a stop knot. Do this for both leads and you can adjust both the trim and the overall tension on the surface. My lines are 'snug' and they help hold the surface close in to the stab/wing.

For the rigging I would go with stop knots and skip the loops. You can tie a loop in kevlar thread but I don't recommend it. I had some of the loops slip on me in flight (I used the wrong knot). Stop knots are easier to tie and wont slip. If you want you can hit the bowsie with a drop of CA to lock the setup in place. So far I haven't needed to.

For the ailerons the servo connects the two control surfaces under the wing. A single return line mirrors this on the top of the wing, passing through a hole in the fuse. The three lines have bowsies so they can be tweaked for trim and tension.

[Trisquire]

Great info racerxky. Thanks for posting all this.

Regards,
Tom

[racerxky]

Hey, no problem.

I would love to see some close up shots of the Manta. I got inspired by that to try the pull pull ailerons. Post them if you have them.

The plans for the Troll are back online (http://www.amjd.ch/troll.html) for those of you that want them. I guess Aéromodélisme Jurassien Delémont got their web hosting sorted out. The instructions up there are very helpfull, just run them through google translate, French to English.

[matchlessaero]

Aidan, I'd have to disagree with you about the usefulness of this analysis. Actually, I think it has a great amount of validity. When it comes down to it, this (analysis) is a big part of what I do for a living. As such, I think it offers a great 'picture' of where to begin trying to save weight, and where you would get very little return. I agree however, that I would like to see the battery as part of the analysis.

I think something that would help even more would be a pareto chart of the individual components, IE a pareto chart of how much Depron is 'flying' vs how much is dead weight (like sprung weight vs unsprung weight in a car). One particularly interesting chart for me would be how much of a servo is the case, wiring and connectors. My own personal observations show that the connectors on the servos are very small in weight, while the wiring can vary greatly.....

My own personal read of the pie chart tells me there is more to be saved in Depron than anywhere else. A 10% reduction in Depron will yield a much greater weight savings than a 10% reduction in Servo weight or Carbon weight.

Fwilly mentions the idea that as weight comes down for nonstructural components, the weight for structural components can come down as well. Its this idea that I'm using currently to develop my own F3P mono....

[Aio_1]

....a pareto chart of how much Depron is 'flying' vs how much is dead weight (like sprung weight vs unsprung weight in a car). One particularly interesting chart for me would be how much of a servo is the case, wiring and connectors. My own personal observations show that the connectors on the servos are very small in weight, while the wiring can vary greatly.....

My own personal read of the pie chart tells me there is more to be saved in Depron than anywhere else. A 10% reduction in Depron will yield a much greater weight savings than a 10% reduction in Servo weight or Carbon weight.

Fwilly mentions the idea that as weight comes down for nonstructural components, the weight for structural components can come down as well. Its this idea that I'm using currently to develop my own F3P mono....
Using a chart showing % depron used as aerodynamic surface versus structural would go a long way to making this analysis more relevant. When I designed mine I originally planned to use a full fuselage made from 2mm depron instead of the usual 3mm cruciform structure however I looked at the weights of 2mm and 3mm depron and the extra material required for the full fuselage (only one side of the material is used as an aerodynamic component) and decided against it. You're right abouty the fact that the lighter the non-structural components the less structural strength is needed and the importance of remembering this in any aircraft design.

Aidan

[racerxky]

I see, a chart of the weight of the wings and surfaces vs the weight of the fuse. I didn't make the measurments that detailed. Next time however...

The box fuslage is very stiff and I like the look of the airplanes with full fuses. I want to see if I can build a full fuse airplane with the same weight as a profile but more strength.

Fuslage side area is critical for good knife edge performance. So part of the fuslage is necessary as structure and part for aerodynamics. In my next build I will try cutting a truss shape out of the fuse and cover the holes with some sort of film or tissue (will dope disolve depron?). Weigh the cut-outs and you have your weight saved/areodynamic depron weight.

One of you guys with the ninja soldering skills let us know what the weight breakdown is for the servo parts etc. And use a sub gram accurate scale ;). My gear is very heavy so I would like to know what is the best way to make it lighter. I never listed the exact gear used and weighed:


Motor: Hyperion Z2205-46 (http://www.aircraft-world.com/prod_datasheets/hp/z22/z2205spec.htm) (46 turn)
ESC: Castle Creations Thunderbird 9 (http://www.castlecreations.com/products/thunderbird-9.html)
Servos: three Hitec HS-50 (http://www.hitecrcd.com/Servos/hs50.htm) + a single 3" servo extension
Reciver: Spektrum AR6000 (http://www.spektrumrc.com/Products/Default.aspx?ProdID=SPM6000)


I'm in flux over the aileron servo. Right now I have a S75 in there because I stripped an HS-50 in a crash (thats what you see in the photos). I havn't found them to be reliable so I may go to a Futaba 3110.

[Aio_1]

Switching from the Thunderbird 9 to a Phoenix 10 or any other very light ESC would only save a couple of grams so may not be worth it. The HS-50 servos are ideal. The very smallest servos apparently don't have adequate centering and resolution so 5g and 6g servos are most common in competition. The Hyperion motor is much heavier than used on the lightest planes. Mine's also a little overweight but I wanted the slightly bigger motor (MicroREX 220/6 = 21g, MicroREX 220/3 = 12g). You could save ~17g there if the 12g motors are sufficient for the particular plane in question. Your receiver is a little overweight but not much. My ACT Pico 4 weighs about 4.5g and I think the Penta weighs about 3g.

I'm looking for somewhere convenient to get some more SD-100 servos (same as Dymond D47). These weigh 4.7g and are very smooth and precise. Their numbers seem to be growing on Jurgens lists.

Isn't the Futaba 3110 a bit big?

Aidan

[3dflyindan]

i would say the 3110 is a bit big IMO

dan

[Mister UHU]

At last someone doing some sort of rational model analysis !

Lightweight is important, but some heavier planes fly nicer,
and aren't so "fluttery" in flight.

It also matters WHERE the weight is,
the further from the CG, the bigger the effect.

As for servos, it depends on the size of the control surface you are trying to move.
2 large ailerons need a bigger servo, than smaller rudder or elevator.

My own personal selection preferences are determined by practicality,
and availibility of parts.

[Aio_1]

As for servos, it depends on the size of the control surface you are trying to move.
2 large ailerons need a bigger servo, than smaller rudder or elevator.

My own personal selection preferences are determined by practicality,
and availibility of parts.
On a sub 200g indoor precision aerobatic plane I don't think torque is a major consideration. I've seen no comments regarding insufficient torque from any size servo (4g+, I'm not talking Wes-Technik servos!). The servo issues all seem to revolve around resolution and centering at this size so that the smallest servo with sufficiently good centering and resolution is the one to use.
The low speeds mean the aerodynamic loads are reasonable even though the surfaces tend to be large.

Aidan

[Bryan Davison]

I can tell you from my experiences....the super small BMS-303's have insufficent torque for use as a aileron servo. In the early days, I stripped two of them in this use. I will never use another super micro for the ailerons. I've got a good scale now...down to the gram...Ill weigh the 3110's tonight and let you know the weights.

[Aio_1]

I didn't check the spec on the 3110s but I think I remember them being ~8g which I would regard as a little overweight. Maybe okay for just one aileron servo but would start adding up if you put in 3.

[Bryan Davison]

Ok, the entire futaba 3110 with servo arm weighs 7.7g or .27oz

The 4axis extended control arm that comes with the servo weighs .3g

Individual parts.
Cable and plug weighs .5g
Bottom of servo case .4 g
All screws .2g
Top of servo case .6g

The Bluebird BMS-306 with servo arm weighs 6.8g
The Bluebird BMS-303 with servo arm weighs 4.4g


Here's some killer info for you
A bluebird 4ch rx minus crystal weighs 6.0g
By simply removing the paper case, the weight drops down to 4.4g

[racerxky]

I was looking for one solid servo for the ailerons. The HS-50's are working great on the rudder and elevator. As soon as I can get some gear sets in to repair the one I busted its going back on.

I am taking the pull-pull setup off the ailerons and going back to pushrods. I had two different problems that are making me do this;

The first was not enough hinge points. This was causing the aileron to flex and not transmit its motion to the opposit aileron through the return cable. I fixed this with a few more hinge points. One on each side of the control horn is critical.

After that the surfaces would deflect symetrically but they would not re-center. Specifically the return line side would remain deflected slightly. I never did find the source of this problem. It might have been the wings themselves deforming under the load. This could be part of the reason that the leading edge of the Manta's wings are doubled.

Either way it was a good experiment and the pull pull is working well on the tail so thats a keeper.

I was at the Pattern competition this weekend and saw some very cool pull-pull setups on the 2 meter ships. One had a single elevator servo with four wires. One pair went to either half of the elevator. This would reduce or eliminate the amount of torsion in the elevator joiner.

[Jerry Combs]

I can tell you from my experiences....the super small BMS-303's have insufficent torque for use as a aileron servo. In the early days, I stripped two of them in this use. I will never use another super micro for the ailerons. I've got a good scale now...down to the gram...Ill weigh the 3110's tonight and let you know the weights.

Interesting as this is the servo that I am using on the ailerons of my bipes. So far I have not had a problem but then I haven't stripped a servo of any kind in many years.

Jerry

[signflyer]

racerxky - thanks for the info on bowsies! i've used alum tubing to crimp the ends of pull-pull cables in the past, which is a real pain in the neck. i tried the bowsies last night, how simple and effective!

-scott

[Bryan Davison]

Jerry, are you using two BMS-303's or only one 303? If your using two,that explains it...if your using one, your lucky.

[Jerry Combs]

Bryan,

I am just using 1 servo. I do admit that the bipe is on the small side being about 300 square inches and weighing about 126 grams.

Jerry

[racerxky]

Servos...


Servo|Torque (oz-in0|Weight (g)|Speed sec/60°

Hitec HS-55|15.0|8.0|0.17
Futaba 3110|22.00|7.7|0.10
E-flite S75|17.2|7.5|0.12
Blue Bird BMS-306BB|15.0|6.6|0.01
Hitec HS-50|8.3|6.1|0.09
Dymond D47|20.0|4.7|0.10
Dymond D44|15.0|4.4|0.12
Blue Bird BMS 303|11.0|3.4|0.11
Blue Bird BMS 306|11.0|3.4|0.11

Other things to consider: quality, reliability, avalability, cost, centering, lead length. Any of those factors could easily keep you from buying a servo with good numbers. Also consider that these are manufacturers specs and not independant test results. Measuring with the same methods and equipment would give more compareable results.

Servo lead length is all over the place. The Hitec's have long leads and you probably wont need extenders. The Futaba has short leads, the E-Flight is somewhere in the middle. The others I don't know about.

I don't have any of the Dymonds but the D47 looks promising, availability is a problem there. I have HS50's on my bird based on their good reputation here and so far they are working just fine.

[racerxky]

Esprit Model has a line of fiberglass, CNC cut control horns and motor mounts, including pull-pull horns. The parts are cut from 1mm board and come in packs of 5:

http://www.espritmodel.com/accesories_hw_cb.html

[Bryan Davison]

Well, Ive decided on a platform for my new ultralight F3Ai plane.

Here's the set-up I plan on using

Himax HC22081260
CC Thunderbird9
VampPowerBatts 2cell 620mah lipos
Futaba 3110 for ailerons
Bluebird BMS-303's for rudder and elevator.
Berg Rx

Im going to be packing all this into a Dan Landis ICE biplane, a very spectacular machine I saw in memphis. Ive managed to snag one of the very rare kits. :D

Ill keep you guys updated.

http://static.rcgroups.com/forums/attachments/7/8/1/1/0/760747.attach?

[Aio_1]

Well, Ive decided on a platform for my new ultralight F3Ai plane......
That'll be pretty light but not by F3P (F3Ai) standards!
Competitive F3P planes typically use motors less than half the weight of the Himax and 2s packs of cells around 300mAh.

[Bryan Davison]

Uh....The Himax is 19-21g ....thats pretty light.
all that on a 40" wingspan plane.

[matchlessaero]

Gotta say I agree with Aio on this one Bryan, the last time I picked up one of those Himaxx's it was not in the weight range you mentioned ready to fly. I seem to remember it being slightly heavier than the Axi 2204.

I'd also suggest going with something lighter than that Vampower.

I need to break down and finish my F3p....

[Bryan Davison]

Ill weigh it tonight just to check...you gotta take that stupid stick mount off.
And if it isnt that light, it will be when I get done with it.

What 620mah lipo would you suggest that is lighter than the VPB battery?

[matchlessaero]

HiMaxx lists the weight of the 2208 as 25 grams with the stick mount. However, I don't believe that includes connectors or prop adapter.

Battery wise, I'd probably suggest something like a 2s 340 kokham or 2s 400 mah "Twenty" pack.

[racerxky]

I see some servo manufacturers rating their weight without the leads so thats something to watch out for with the motors too. Its hard to get an apples to apples comparison.

The Hyperion 2205 is 31g with connectors & adapter by my measurments. The AXI 2204 specs at 26g (well 25.9g) and that includes the prop adapter & cables. The little screamers motors are 23 grams with a molded in prop adapter. The Microrex 220 motos come in 12g and 21g versions, not sure what that includes.

If there is one bit of equipment that I have that could be lighter its the motor. Going to a 20g motor would cut 10-12g out of my setup. There are certainly people flying very succesfully with the AXI, they are expensive though. I don't see any sources for the Flyware products in the US. The Little Screamer looks good, I saw someone fly one at the club here and it performed well. Their ordering is down right now but I don't recall them being that expensive.

Here are some links to the spec pages:
AXI 2204/54 (http://www.modelmotors.cz/index.php?lang=czech&id=en&nc=produkty_vypis&kategorie=m_neodym_ac&id_rady=axi_22&id_produktu=axi_2204_54&nazev_rady=AXI%202204/54%20GOLD%20LINE&hmotnost_rady=(25,9%20g))
Hyperion 2205 (http://www.aircraft-world.com/prod_datasheets/hp/z22/z2205spec.htm)
Flyware Microrex 220/3 (http://lipoly.de/modellbau/motoren/flyware/microrex220/microrex220_3.html)
Flyware Microrex 220/6 (http://lipoly.de/modellbau/motoren/flyware/microrex220/microrex220_6.html)
Little Screamers (http://www.littlescreamers.com/ls1/products.html)

...and with those rambling thoughts I will leave you as I have to get to bed.

[Aio_1]

Uh....The Himax is 19-21g ....thats pretty light.
all that on a 40" wingspan plane.
The thread has been all about weight saving specifically for F3P planes and for those your setup looks to be on the heavy side. The figure I found when I had a look for a weight on Himax was 25g. I didn't realise that included the mount which you'll be getting rid of but that will still leave you much heavier than the typical competitive F3P motors which weigh about 12g with an integral prop adapter. Admittedly at 40" your plane is bigger than usual and may need more power than a 12g motor can supply.

My own setup is probably not much lighter than yours but I wouldn't claim it to be ideal for F3P. I've been slow to get my plane in the air so I can't report on actual performance yet! I'll be using the MicroREX 220/6-1600 (21g) with 3s TP480 (34g) and a Phoenix 10 ESC (~6g).

Incidentally if you want to keep weight to a minimum it doesn't make much sense to use connectors between the ESC and Motor. It really all depends how competitive you want to be and how much work you want to do. There's no F3P competition around here at the moment so the plane will be purely for fun flying. I've already compromised on the power system and I'm certainly not going to bother using magnet wire on servos and soldering them directly to the RX or stripping their cases. I think your gear may be a little heavy for competitive F3P but I'm not saying it's a bad choice.

Aidan

[Bryan Davison]

Well, I weighed it last night 23.8g with no stick mount.
The motor comes with two prop mounting methods, one is a collet, and the other is a prop saver. The collet weighs 1.1g and the prop saver weighs 1.5g.

So total weight is 24.9g....still pretty lightweight. Lighter than the AXI 2204/54.

So far we've only seen one of the miracle sub 20oz motors, and we cant get them over here. So this still seems like a really good option to me.

I can also cut down the case quite a bit to shed a few more grams.

We weighed the lipos last night too.
Vampowerbatts 2cell 620mah = 30.6g
Thunderpower 2cell 730mah = 32.8g
E-tec 2cell 340mah = 28.3g

CastleCreations Thunderbird 9 = 7.8g

All of the above weights are including everything...wires, plugs, and prop adapters...ready to fly

[matchlessaero]

Well, I chunked my new power system on my scale to see what it weighed in at..... I have to admit, right now the motor is somewhat an 'unobtanium' motor, but everything else is easy to get here in the US and the motor will be eventually as well. Total weight of the system was 33.5 grams. Thats the motor, prop, prop adapter, ESC, and 2s battery. Total thrust available from this system is just over 200grams on testing equipment.

While most people are going to a manufacturer of larger (what most people consider normal size) motors and asking for the smallest they sell, I went to the manufacturer of smaller motors and asked for the largest they had. I do the pre-production flight testing for them on their new motors, so I was eager to test this new one.

The ESC is a Thunderbird 9 with lightened wiring. You can do this yourself fairly easily.

The battery I'm using is a 300mah 2s Apache pack that I got from Brian Cooper at Cooper fuels.

Servos will be Blue Arrow 4.3's and the reciever will be a Berg MicroStamp

The motor is one I'm testing for the manufacturer and helping to dial in. I have run a duplicate of this motor with a thinner stator stack extensively and it is impressive, but would not pull an F3P airplane along. This new one should get the job done, but flight testing will be the final word. I'll put more up about this motor when I can.

In all, I'm hoping to build something in the 3.5-4.5oz range (around 110 grams). I have not decided the final wing area, but I'm shooting for a wingloading lower than my current freestyle planes by approx 25-35%.

[Aio_1]

So far we've only seen one of the miracle sub 20oz (20g ?!) motors, and we cant get them over here. So this still seems like a really good option to me...
If you really wanted one what's to stop you buying one?
I buy the vast majority of my motors, cells and ESCs online or by phone. The local shops rarely have what I want. The MicroREX was an exception a local guy ordered one in for me but I could just as easily, quickly and cheaply have bought one from Germany or France.
My cells and ESC are from lightflightrc.com in the US and my receiver is from lipoly.de in Germany. Much of my other stuff is from Aircraft world in Japan, AlleRC in US and Hollein in Germany. You can very easily get what you want from wherever sells it if you really want it!

Aidan

[Alexandre Cruz]

Yesterday I installed the power sistem to my 26" Yak (own design).
I am using a MAE Slo-Fly (they weight 21g but I removed the carbon tube and used a Balsa ply fire-wall, glued to the tube, so weight droped to 18,1g) . The Yak weights 115g and torque rolls at 2,1A on a Ployquest 2S 300. At full throtle it pulls only 3.6A so a 300 HG is enought and thrust seem to be around 170g.
The prop recomended is a 10x6 but that would produce too much torque so I used a 9x4,7. At full throtle it pulls only 3.6A. Maybe on a 10x6 it can provide more than 250g of thrust at 6A on 2S.
I am really happy with this motor and it costs U$ 30,00.

[Trisquire]

MAE offers the same motor in different versions. The 25-turn motor is intended for a 10x6 prop.

Regards,
Tom

[racerxky]

Trisquire & Alexandre Cruz; Those are some light and very practical power systems. Trisquire, can we get a pic of your motor mount with the MAE motor?

Here is a link to the MAE (Model Aeroplane Engineering) motors page (http://m-a-e.com/Sub_Pages/Products/products_Mots.htm).

I have been wondering about the pitch speed on the props. As I understand it for this application we dont need or want the top speed to be too high. So a 10x6 would make a lot of thrust but the airplane would fly nearly twice as fast as a 9x4?

Flying the Troll last night we found that it wanted more speed for maneuvers than for level flight. I see videos where pilots are flying knife edge without a noticable speed change and I drool. We fly in a small gym so slower is better.

[Trisquire]

racerxky,

Unfortunately, I can't help you. I don't own an MAE motor.

The MAE website says that the 25-turn motor (the one intended for a 10x6) is for slow speed, high thrust applications. That is the type of application that interests me.

Regards,
Tom

[racerxky]

Unfortunately, I can't help you. I don't own an MAE motor.
...

Sorry I meant to ask Mr. Cruz for the pic. :o

[Alexandre Cruz]

Sorry for the drawing but my camera is broken...
I attached the prop by drilling 2 holes on its base and using 2 bolts. This is lighter than any other thing I have seen excepting for gluing the prop

[Jerry Combs]

Alexande,

That is a very good idea on lightning the Westport motor! I will have to give that a try.

Jerry

[Alexandre Cruz]

I was thinking on drilling holes to the bell but since the magnets are glued I believe I am going to have problems with them.
The way to attach the prop removed almost 2.5g (prop saver+ o-ring), almost more than changing servo wires, so lets do both! :D

[racerxky]

I attached the prop by drilling 2 holes on its base and using 2 bolts.

Yes, I like your idea for mounting the prop! Its easy to do and it makes it easier to mount the prop. No messing with rubber o-rings or zip ties. Saving a couple of grams is a bonus at that point.

I tried it out last night and I need some slightly longer screws than those that came with my prop saver but it should work great.

[fwilly]

I just glue mine on :D

[racerxky]

I got the fiber glass control horned in from Esprit Model. They are very nice, tough and light. These will be for the next build.

In the Troll's design there is a gap between the keel and the firewall. This means that the firewall is held by the fuselage sides only. The fuse tore under the strain of a nose first crash. I am reworking the design so that the firewall sits on top of the keel. This should send nose first crash loads through the keel which is much stronger.

The last pic is of the plans being re-worked in Sketchup (http://sketchup.google.com/). I can't believe I never used this tool before, its fantastic. It can import DXF, its super easy to use and now Google is releasing a version for free. Once they get PDF export it will be a real boon for the hobby.

[Bryan Davison]

Well, my ICE came in at 5.79oz. Me and racerxky went out last night and flew it around. It flys great. Needs a little work in KE flight, but really flys slow and smooth. Four point rolls are spectacular. Stops dead on the points.

Smooth one roll rolling circles, and nice fast rolling circles. Seems to perform them in both directions exactly alike. Wish I had this plane when I went to Memphis.

I would like a little more power on it, but the little himax with a 2 cell does ok.

[Aio_1]

...I would like a little more power on it, but the little himax with a 2 cell does ok.
Do you know what the current draw is?

[Bryan Davison]

No unfortunatly I dont have a wattmeter. The motor pulls the plane around fairly well. I think its a combination of my rearward CG and the 2cell lipo that's not giving me the power option I need. Im going to move the CG farther forward and try it again. If that doesnt work, Ill be looking for a really light weight 3cell lipo for the extra umph.

It will work fine in a small gym, but in a larger arena like the one in memphis..Ill need a little more power for the good vertical stuff.

Unless something changes, I think Ill be using this plane in the Memphis Freestyle championships next year. I really like it alot. Its one of the best planes Ive ever had. Just flys so smooth. Harriers are incredible with it, it flys easily inverted, and even does inverted harriers so well, you could drag the rudder around on the floor as you do harrier circles. Really incredible plane. Im truly impressed with it. Dan Landis designed it, and flew it in Memphis this past year, thats where I first saw it. Tony Stillman bought the kit from Dan while we were there, I bought it from Tony. I think Scott Anderson at www.rcfoamy.com will be making kits soon. He cut the kits for Dan.

I was curious if it would track well with the short tail...It does just fine. Ive got just a touch of rudder to aileron mixing to do. Its much like the Sypher, very little rudder in KE or even opposite rudder to hold the nose down. I think moving the CG a little might make this better.

Its truly a competition grade airplane. Not like any of the mass-made kits. Very sharp design. Ill try to get some videos of it flying soon and post them.
Im not quite good enough to do the F3Ai sequence(need more practice), but I think I can do some hardcore stuff with it enough to give you an idea of what its capable of.

[Aio_1]

No unfortunatly I dont have a wattmeter. The motor pulls the plane around fairly well. I think its a combination of my rearward CG and the 2cell lipo that's not giving me the power option I need. Im going to move the CG farther forward and try it again. If that doesnt work, Ill be looking for a really light weight 3cell lipo for the extra umph...
A watt meter is well worth getting. Essential really unless you're only using conservative tried and tested motor/cell/prop combinations. For example you could be sure you can't get more power simply by changing the prop rather than increasing cell count.

I don't understand what you mean about the CG position influencing power.

Aidan

[Bryan Davison]

CG influencing power.

If its too tail heavy, it flys around in slight harrier all the time. Which slows it down. So to build up airspeed you hold a little down elevator in it to get it to speed up and level out. Move the CG farther forward until it flys level, and you get a increase in airspeed at level flight. Just a matter of trimming it out right. Sorry for the confusion.

Most peoples solution is "put a bigger motor on it". Phooey on that.
I tend to use kinetic energy more than raw power when Im flying, which probably explains why I can get incredible flight times out of batteries. Ive come to the realization that Im really conservative on throttle. I dont really plan to be, thats just how I fly.

Now I do have barnstormer airplanes that are WAY overpowered, and I designed them for ballistic verticals and rapid violent maneuvering, but I dont like my indoor birds like that.

I have considered the prop thing, Im running a 8x4 now. I had planned on trying a SF prop next instead of the DD prop. Then start looking at different sizes.

[matchlessaero]

Good job getting your Ice that light Bryan. Sounds like it was worth the effort.


I'm interested in hearing from some of the guys flying in the current F3P comps about how much power they actually have. As it sits, I've been working towards having enough for strong uplines, but nothing like the power to weight ratios of my freestyle planes(well over 2 to 1 T2WR) . Watching all the videos of the European F3P comps, it appears that they are essentially at, or near, full throttle when on an upline.

I finished CAD'ing out my new indoor pattern plane and hope to cut it out tonite....

[Bryan Davison]

Yeah I think so too. It doesnt look like their planes are like most 3D planes and overpowered. Honestly for indoor flying, I dont think you really need all that power. I was doing just about all the maneuvers in the book last night with the ICE and its certainly not over powered. It will hover though. In all reality for indoor F3A, all you need is enough power to get it to climb vertical 20ft, beyond that is the ceiling.

I was flying it outdoors last night in a zero wind environment, because we couldnt get in the gym (high school graduation cermony). I cant wait to get it indoors and see what it will do.

I used to have a 4.5oz shocky superstar, and it flew good as well. Weight is key for indoor flying.

I have to agree with racerxky. I eliminated carbon on some planes thinking I could save weight with that. Not so. Carbon barely weighs anything. I used TONS of carbon on the ICE, and still got it light weight. After weighing each individual part on the plane...I have to agree with him. Most of the weight is in the foam. So the trick is going to be eliminating foam as much as possible and using more carbon instead of less. The entire carbon for the ICE only weighed 10g...in comparison, the foam weighed over 2 oz. I cut holes in the fuselage stiffeners and weighed the holes. They only weighed .13g...so cutting holes isnt enough. There has to be another way. 2mm vs 3mm doesnt save that much weight either. So it really comes down to design, and build.

Profile planes end up lighter, but theres not enough drag on them, which means speed brakes. I also used plenty of kevlar thread on the ICE as a stiffener. I think thread could be used to induce drag.

Ive got some serious thinking to do now. How do we reduce weight of foam componants, introduce drag through means other than increased fuselage sizes and speed brakes. Hmmm

[Aio_1]

...Ive got some serious thinking to do now. How do we reduce weight of foam componants, introduce drag through means other than increased fuselage sizes and speed brakes. Hmmm
You could use a router to remove most of the material from the foam surfaces. For example cut a 2mm deep recess in one side of the 3mm depron so there's only 1mm of depron for most of the surface. You could use carbon for LE and TE and leave some unrouted strips as ribs so the central area doesn't get too floppy.
The airflow over the ridges will create vortices which will increase drag. If the material was just removed from one side of the surface there could be some asymetric effects since both the drag and flow attachment would be effected only on the routed side. I don't know if you could successfully remove material from both sides but you could try a few experiments on scrap to see.

I know someone posted a picture of a plane which used this routing method. Probably one of Jurgens pictures. If I can find it I'll add it to this post.

Found the pictures!

Aidan

[fwilly]

Yeah I think so too. It doesnt look like their planes are like most 3D planes and overpowered. Honestly for indoor flying, I dont think you really need all that power. I was doing just about all the maneuvers in the book last night with the ICE and its certainly not over powered. It will hover though. In all reality for indoor F3A, all you need is enough power to get it to climb vertical 20ft, beyond that is the ceiling.

I was flying it outdoors last night in a zero wind environment, because we couldnt get in the gym (high school graduation cermony). I cant wait to get it indoors and see what it will do.

I used to have a 4.5oz shocky superstar, and it flew good as well. Weight is key for indoor flying.

I have to agree with racerxky. I eliminated carbon on some planes thinking I could save weight with that. Not so. Carbon barely weighs anything. I used TONS of carbon on the ICE, and still got it light weight. After weighing each individual part on the plane...I have to agree with him. Most of the weight is in the foam. So the trick is going to be eliminating foam as much as possible and using more carbon instead of less. The entire carbon for the ICE only weighed 10g...in comparison, the foam weighed over 2 oz. I cut holes in the fuselage stiffeners and weighed the holes. They only weighed .13g...so cutting holes isnt enough. There has to be another way. 2mm vs 3mm doesnt save that much weight either. So it really comes down to design, and build.

Profile planes end up lighter, but theres not enough drag on them, which means speed brakes. I also used plenty of kevlar thread on the ICE as a stiffener. I think thread could be used to induce drag.

Ive got some serious thinking to do now. How do we reduce weight of foam componants, introduce drag through means other than increased fuselage sizes and speed brakes. Hmmm

My 3.75oz shocky sized plane has a single flat carbon spar that weighs around 2g. That was about it for structural carbon. I used little squares of thin carbon to reinforce where the thread went through, which probably adds up to less than a gram. Had I used 10g of carbon, my AUW would have been 4oz, and all of the sudden my motor starts to struggle on the uplines.

The best way to get your AUW down is to use as little as you have to for EVERYTHING.

If you are dead set on redistributing some of your foam weight into carbon weight, check out EPP or EPS. a 6mm thick sheet of EPP weighs less than a 3mm sheet of depron, but will need some carbon to make it stiff enough.

[fwilly]

depron weighs .08g per square inch

The average density of 3mm depron is 2.65 lb/cubic ft.

EPS is available in 1lb/cubic ft.

Contest balsa is 4-6 lb/cubic ft.

Using the .08g/sq in, and the total area for the depron in a given design (easy to get with CAD) you can figure out the total depron weight for that design. My design has 42g worth of depron.

[matchlessaero]

Thanks for putting up those dims Fwilly! You're not as dumb as I look.... LOL

I just got word that one of my local clubs has gotten an indoor site on a semipermanent basis. They are looking at having flying from 6-10 pm every 3 weeks or so. Much better than not having anything at all! I can't wait.

[Bryan Davison]

Something else to look at is the motor and battery. We cant do much about the batteries. But the motor is something we can change. According to the chart at the beginning of this thread, the motor accounts for a large percentage of the weight too.

Why do we not have carbon fiber outrunners. Everything is metal on these things. Metal bells, metal mounts, etc. Why not make the entire case out of carbon fiber. Bell, housing etc.

Congradulations matchless....You'll like having a indoor place to fly. Ours isnt perfect, but its sure nice to have.

[fwilly]

I use carbon output shafts and bearing tubes. In the past I have used a plastic faceplate on the bell. A carbon bell would be awsome, but it would be hard to make. You'd still need a metal fluxring.

I like the etec 300s for a light weight pack. They are a good match for a 20mm GB cdrom.

[matchlessaero]

Fwilly, when you flew your Etec 300 fed 2S foamy at OKC this winter, you convinced me. I have a few of them myself now.....

[Jerry Combs]

FWILLY,

Have you tried the polyquest 20 series 300s yet? I like mine a lot better than the etec300s.

Jerry

[fwilly]

I haven't tried them. The specs say they are about 4g heavier for a 2s pack, which puts them pretty close in weight to the kokam 340. Wish they had individual cell weights posted, since its hard to tell with heat shrink and connectors.

[Alexandre Cruz]

I am flying Polyquest 300 XP (20C) 2S, the wheight with JST plug is 18.3g, with shorted wires to 2in. However I don´t think they can dicharge at real 6A, but 5A.
Kokan 2S 340 wheights 26g on my scale....

[fwilly]

18.3 is closer to my etec packs. IIRC my 340s weighed 22g with no shrink and short leads. My etec 300s weigh 17g for a hand made pack.

[Mister UHU]

Something else to look at is the motor and battery.
We can't do much about the batteries.
But the motor is something we can change.

According to the chart at the beginning of this thread,
the motor accounts for a large percentage of the weight too.

Why do we not have carbon fiber outrunners.

Everything is metal on these things.
Metal bells, metal mounts, etc.

Why not make the entire case out of carbon fiber. Bell, housing etc.




Hacker already make some motors with some carbon parts.

It makes motors for F5D,F5F,and F5B pylon racing with carbon housings.

They weigh between 144 grams and 307 grams,
and need ESCs of between 90 Amps and 195 Amps.

I guess they won't be cheap.

[Malves]

They weigh between 144 grams and 307 grams,
and need ESCs of between 90 Amps and 195 Amps.

LOL...144g is the weight of a F3P plane. :p

[racerxky]

I have been waiting to do this because I honestly didn't like the way the Troll flew. It was getting pretty frustrating and I could fell that it wasn't trimmed or balanced correctly. It took three weeks, three different props, two different batteries, one major crash and one seriously lacerated finger to get it right. Last night it finally flew like what I expected.

With the setup I flew last night it finally clicked. The Hyperion 46 wind likes that 9"x4.7" prop on 2S cells (TP Prolite 730mah). It has unlimited verticle with that setup without straining. It will hang at about 3/4 throttle and cruise around at 1/2.

Inverted and upright are about neutral when the CG is right. Knife edge needs more prower and some rudder. There is still some altitude drop in fast rolls. This might relate to the KE issue or to the CG.

It is pretty stable in a hover. I dont really have the skills to do a good hover yet but this plane make me look good :D. Its a blast to fly. I gave Bryan the sticks and he put it through some stuff I can't do, like rolling circles, K.E. turns and snaps. Judging by the big grin on his face it flies well.

The next version will have more side area, larger wingspan, longer tail and should be easier to cut and construct. Plans will be made available when I get it how I want it.

[bergfalke4]

Something else to look at is the motor and battery. We cant do much about the batteries. But the motor is something we can change. According to the chart at the beginning of this thread, the motor accounts for a large percentage of the weight too.


You can save at least 2 grams from a 2 cell Etec 700mAh battery pack by removing the shrinkwrap and shortening the leads. Notice that there's wire along the entire length of the pack inside that shrinkwrap. When you remove the shrinkwrap it's therefore possible to reduce the leads by up to 50mm without actually making them shorter.

2 grams might not sound significant but everything adds up and this is like 6% of the total weight of the battery pack.

- David

[fwilly]

The same applies to the etec 300s. They also use a lot of solder. Some desolder braid will suck up the excess solder. Not sure how much it saves, but it makes me feel better:D

[matchlessaero]

There is still some altitude drop in fast rolls.

Glad to hear you persevered and got it to fly more like you wanted it to.

I'm not sure I understand your statement above though....

[racerxky]

Glad to hear you persevered and got it to fly more like you wanted it to.

I'm not sure I understand your statement above though....

It performs a fast axial roll (full aileron deflection, no correction on elevator or rudder) but on exit the airplane is in a nose down attitude and the altitude is lower that on entry. So it flys in an arc instead of a straight line.

I tried adding some power on entry and this helps a little bit. I think this is related to knife edge performance/side area. More side are will give you more constant lift through a roll. Also my CG might be a little forward of the neutral point. I'm not sure what it is yet. Maybe I just need to correct with rudder and this is normal?

[matchlessaero]

Racer, I'm thinking your last sentence sums it up. Even a properly trimmed airplane will lose altitude and exit with its nose down if you don't correct the roll to keep the plane on the same trajectory.

Remember also what you are trimming this airplane for - F3P. No where in the F3P pattern is there a series of fast axial rolls. Trim the airplane to fly the routine correctly.

[Bryan Davison]

His troll is set up good. Flys great. I popped his 9x4 prop on my ICE, and it made a big difference in pull. I think Im gonna switch to that one too.

I finally figured out KE on my ICE. NO rudder input, and it KE's pretty nice. no push so thats one problem worked out.

[jskrebs]

Working on smaller motors

[Alexandre Cruz]

jskrebs, this motor is the one I asked you.
As you can see in this forum there is a compulsory investiment on tryiong to remove unnecessary weight (even if power is decreased).
Please tell us more about this motor. Prop, thrust, Amps, maybe a kit?

Thanks

[jskrebs]

My wife has me on asignment to cut the grass at the moment.

But,

the motor as shown weighs about 12 grams and provides 5 3/8 oz of thrust on 2S with a 5x5 prop. I am making more this afternoon to try different winding and magnet arrangments.

I will kit this as well as offer pre made units. Currently I am almost maxed out making the larger ones.

[Alexandre Cruz]

After getting your grass cut, please try to wind some for bigger props like the 6x3 or better the 7x3,5. It would be good if you could get at least 6-7oz under 5Amps

[jskrebs]

Slight rain delay in grass cutting so I cut down 5 more can/shaft assemblies on my lathe. I made them .03 taller so I can put some additional windings on without rubbing.

Alexandre,

I was putting out 5 3/8 @ around 3 amps. I'll try the 7x7.3 in a minute and report back.

[jskrebs]

Just put the 7x3.5 HD on the 12 gram motor.

Used a 2S Etec 400 battery

Spun @ 8040 RPM @6.7 volts and 4.74 amps according to E-meter

Ran at extended WOT and the windings got pretty warm, not smoking, and the mags were cool. On a plane so I could not direct measure thrust.

Edit: According to TPE_Calc thrust is 135G @ 11W with 26.6 mph pitch speed

[Bryan Davison]

Well, here's my Dan Landis ICE biplane all painted and finished up....now if I could just learn that F3Ai sequence. :D

http://image.rcuniverse.com/forum/upfiles/121828/Zx69823.jpg

[Jerry Combs]

Bryan,

Very nice looking Ice and a good looking model inspector too.

Jerry

[Bryan Davison]

Heh..that's my blue russian cat named "Shiloh". I dont put her in the pics, she just likes to get in them for some reason. Never fails, when I go to take a pic of a plane....she hops up next to it like......"Im ready for my close up Mr Deville"

Younger folks probably dont remember that line. Its from an old classic movie.

[racerxky]

Here's a movie quote: "How does it feel to be frozen? Yea! Ice is Nice!"

[Bryan Davison]

You cant tell it in the pics but the blue is lightly speckled to really give it a frosted look, and its more blue than the pic shows. Ill try to get some video of it flying tonight.

[fro540]

bryan.... can post a side profile pic of your bipe... looks really good.... inspector looks fiesty?

[racerxky]

Any novel ideas for mounting the motor to the firewall?

I am using 3mm metal screws now but they weigh a few grams. You could glue the motor on but the thought of putting CA on a band new AXI makes me squirm.

It would be particularly useful if the mount was adjustable so you could set the thrust angle too.

So any ideas/cool installs you want to show off? Zip ties? Rubber bands? Vibration Isolators (http://www.performance-pcs.com/catalog/index.php?main_page=product_info&products_id=3294)?

[racerxky]

Not to really drag the discussion away from that last post but I found this cool pic of the guts of a Donuts Models Phaser with what looks like the 12g MicroRex on the nose. Notice the innards are basically empty. My new design currently has two bulkheads but this may change. Anyone with a gut-shot of an Aito?

OK, back to talking about motor mounts ;)

[matchlessaero]

Racer, check out Microfasteners.com. You can find some pretty good screws there.....

One thought worth mentioning...... Don't do any thing on mounting the motor you'll regret. At the EAC Indoor in Memphis, a large number of the pilots had the motor come loose during practice or during their final round routine (Luckily, I was not one of them... : )

For my stuff, I use a 1/16" ply firewall. On shocky style fuses, I mount the firewall to a carbon tube and glue the tube into the fuse. The tube quadruples the gluing area and makes the nose stiff. For adjusting thrust on the Axi, I use 1/64" ply shims to make final thrust adjustments.

[Aio_1]

I believe the motor in the picture is in fact a Micro Cyclon (27g and <65W)

[Aio_1]

I think the suggestion of a carbon tube or rod extended behind the motor mount on profile type fuselages has a lot to recommend it. One of the things depron is NOT good at is providing hardpoints. Any nose impact tends to risk crunching the material behind the motor causing structural damage and knocking things out of alignment. You need to spread the load and I think a carbon rod/tube extending partway down the fuselage is among the simplest, neatest and lightest. I've tried doublers and others have tried small patches of glass cloth etc.. but the tube method seems preferable to me (or it could be used in combination with the others if necessary).

[Bryan Davison]

Aio,

I completely agree with you there. I stumbled across this after I mounted a rimfire on carbon. During smack-ups which normally would have torn the nose off, the motor and nose stayed intact. Mounting the motor on any kind of carbon stick that runs parellel with the fuselage is a great idea.

[Trisquire]

How about an expendable balsa stick mount? Rigid, but fragile enough to break away on impact. The objective would be to localize the damage to the mount itself and leave the rest of the plane intact.

Tom.

[racerxky]

For the box fuslage I find that it works best to mount the firewall up against the depron as opposed to inside it. In my design im using some sheering blocks to carry the load of the firewall. Also it seems inportant to reinforce the 'chin' of the airplane. It would be best if the the chin hit first in a crash and not the motor.

Also for the firewall I will make a composit of light ply (1/32) and 3mm depron. A sandwich of that should be nigh on indestructable.

My real problem is mating the motor to the firewall in a matter that is adjustable, removable, light weight and secure.

Tube mounts for CDROM type motors are a natural because all you need is a set screw. The tube disapates the shock loads intot he fuse nicely too, a very good idea.

I like the idea of the vibration isolators but they may not be secure. Here is a better link (http://www.acoustiproducts.com/en/ultra_soft_fan_mounts.asp) and a pic:

http://www.acoustiproducts.com/images/products/fan_mounts/afm02_fan_mount_design_550x209.jpg

The 4mm gap goes through the firewall, the 'head' end sits up against the motor. I don't know if it would hold 15oz of thrust but it might be worth a try. As a plus the mounts should absorb some energy in a crash and the airplane would be quieter :D

[matchlessaero]

Racer, I think I'd stick with good old screws...... and staying away from anything that could introduce flexing into the motor mount area. In order to reduce flex in my birds, I go so far as to use zip ties to attach my props to the wobbly adapter of an Axi 2204. Mount it as solid as possible.

I also don't like the idea of doing anything to the front of the bird that improves crash survivability if it adds weight. On my Freestyle and fun airplanes, I do several things that improve crash survivability because weight is not as big of a concern, but for my competition birds, I think its just dead weight in the air, and if I crash--- then my day is probably over anyway with that airplane.

Here is one thought however that might be useful in your bird. It would be light, simple and might help a tiny bit in a crash.... Use nylon 4-40 bolts to attach the motor to the firewall. If memory serves me right, the mounting ears on a 2204 might be big enough to be drilled out a tiny bit to accept the bolts. Your sandwich firewall should be plenty stout enough to thread well.

Remember Colin Chapman's mantra "Just Add Lightness".

[Trisquire]

...............or, you could cut your firewall to have "ears" that correspond to the 2204's mounting ears. You could slip small "rubber bands" (thin cross sections of fuel tubing) over both sets ears to hold the motor in place; a "motor saver."

It's the type of thing that's easier to make than to describe.

Tom