Super Cub Modified

[bluemax1962]

Here is the start. Wings set for flaperons and tail feathers stick built instead of the slabs in the kit.

[bluemax1962]

Here is another shot of the laminated/stick constuction of the tail feathers.

[bluemax1962]

Here is a shot of the modified wing. Note the new rear aileron spar and rib lightening. I added one rib at the end of the aileron and one crutch rib next to where each wing servo (digital) will be. I can't decide how I want to frame the ailerons. Slabs would be too heavy. Stick framing I fear will twist. I may use a sheet (lightened) and stick const. to stiffen this.

Any thoughts out there on this?

[bluemax1962]

Another angle on the wing construction.

[bluemax1962]

Oops. Here is the pic.

[miraclesailor]

bluemax1962:

Pretty job and nice lamination on the tailfeathers. It looks as though it is coming together nicely.

I cannot tell how big the wingspan is and how light you are trying to keep this plane.

An idea for the ailerons is to use 1/32 balsa for the skins and build up the ailron like you did the wing. That is to say by using rib build-up technique. You are obviously good at this technology judging from the pictures. You would then have an aileron that is fairly rigid and not the weight of a solid piece of bolsa. This has to be about as good as it gets or there would be other ways and materials for making the fuselages of the indoor flyers...there are, but...If you have looked at the plans for the Pixel and the new plan of the month that Dave R. presented in this months (Feb) RCMicroflier you have to understand that sheeting with 1/32 has to be good if it works so well on those. Hope this spurs some ideas. Keep posting pictures.

Later,
Dan

[bluemax1962]

The Wingspan is 46.5 inches. They quote a weight of 21oz. I am shooting for a weight of 11oz ready to fly. Currently each wing half (without aileron) is .75 oz. Tail feathers are at .5 oz and the fuselage is at 1.5oz (without cowling). The darn cowl weight is almost an oz!:( So total so far I am at 3.5 oz. I figure the center wing panel and ailerons should not exceed .5 oz so that would bring me to 4oz! Not too bad for a 46 inch wing spanned plane.


I am fighting to cut weight in the power plant area. The Olympic gear unit and a speed 400 weight 3.5oz. Saw an article on a GWS "A" power unit that reportedly weighs 1oz! Do you think that unit would pull a 11oz plane on a 9/5 or 9/7 prop? The 2oz difference.

Pictures of the completed fuselage coming soon.

Perry

[bluemax1962]

Off and running

[bluemax1962]

What do you know the side match!:p

[bluemax1962]

Still worling on the fuselage details, but couldn't resist seeing the over all shape of things

[genovia]

Hi Blue,

You have a nice looking bird:) Make sure to beef up the wings, it will fold:( ... But aside from that, I am drolling, the Piper looks great, even without her dress on.

genovia

[Dr Kiwi]

Dear bluemax1962 - If your all up weight is going to be about 11-12oz or so an IPS EPU [a.k.a. IPS-DX] motor probably hasn't got enough power for the purpose. However, yesterday in another thread http://www.radiocontrolzone.com/forums/showthread.php?s=&threadid=112149 I touted the idea of using one of the GWS dual motors [IPSD RXC 1 is the 4.1:1 geared version]. With a 9x4.7 prop, one of those only weighs in at 48g (the single motor IPS EPU 4 weighs 36g with prop) - so for a 12g (1/2oz) weight penalty you'll get twice the power. You could even go for a lot more power if you use a 7-cell or even 8-cell battery pack, but your motor life (not great, apparently, even at 7.2v) might be very drastically shortened!
Another possibility is a Speed 300 geared 5:1 (weight with g/box, prop, wires and Deans Ultraplug etc. is 72g). I was playing around today with one of mine and found that on 8.4v with a 9x4.7 prop I was drawing 7amps (45W) at 5400rpm. Half throttle [3amp draw] gave 24W and 4000rpm. This should be more than enough to keep a 12oz aircraft in the air. Now for the frightening experiment - I fitted a GWS 3-blade 9x7 prop to it and with a 9.6v 600Ae battery attached it draw 15amps (my Whattmeter recorded 124W in the few seconds I dared to run it!!!!). I didn't have the tach on it but, by extrapolation, this would suggest a prop speed of 10,000 plus and a motor speed of 50,000. Surely not?
Cheers, Phil

[Dr Kiwi]

"Surely not?" in my last post was indeed correct. I tried the experiment again, and this time used my Hobbico tachometer [set for the 3-blade prop]: - 6v Speed 300 with 5:1 MP Jet g/box, 3-blade 9x7 GWS prop, 9.6v 600AE NiCd, Castle Creations 20amp ESC - current draw 15.2amps and 131W on the Whattmeter - 5500rpm! Now that's a more realistic figure, but it still means the motor is turning at 27,500rpm - impressive! Cheers, Phil

[genovia]

How about SP400 6.v, 2.3:1 Mini Olympus?

-genovia

[Dr Kiwi]

Hey Antonio, You must have overlooked a piece in one of bluemax's earlier posts - he is trying to avoid the use of a 400 and Mini-Olympus because they are too heavy. Perry suggests 3.5oz (99g) for it, but I've just weighed a 400 motor + wires, g/box, prop and adapter, and they come to 4.15oz (118g). That's why I think that saving 2.46oz (70g) by using a GWS Dual (RXC) motor (48g) ought to work.
By the way Antonio (and Dave if you see this), have you tried correlating MotoCalc or similarly derived (e.g. http://brantuas.com/ezcalc/dma.asp) performance figures with those you actually measure on your planes? While I was playing with my 300 today I tried just a few basic comparisons, and not surprisingly, I found some significant discrepancies. Using different combos of prop and cell count I took measurements with Whattmeter and tach, then ran the data through ezcalc and MotoCalc. Though 'n' was too small for any real tests of significance, in every case the "measured" figures for the peak amp draw were much higher by 27-54% and the peak prop RPM's were lower by 7-12% [it follows that since thrust is proportional to RPM then it would be reduced by an equal amount]. I figured that one simplistic way to measure "efficiency" was to determine the number of prop RPM's for each amp of input current, and again the "measured" figures fell far short of the "calculated" ones (from 26-41% less). My take on this is that raw data for MotoCalc et al is obtained by assuming essentially ideal conditions - perfect battery condition, very short wires, zero loss connections, no loss in the motor brushes, no friction in the drive train ........... Obviously our set-ups, with long wires, imperfect plugs, and somewhat worn and imperfectly lubed motors, cannot equal this "ideal" scenario. However, it is something to think about, and if we could obtain good data from a much greater sample size, perhaps we could come up with a "correction factor" which we could apply to our systems [if these few figures of mine are typical, it seems that one could expect one's full throttle flight times might average about 30-35% less than MotoCalc/ezcalc predict, and that "static thrust" might be 10% less]. Sorry for this long ramble. The inquisitive scientist in me has emerged. Cheers, Phil

[genovia]

You know, I'm a fan of yours, when it comes to reading your review and opinions. Doc.

--- Thanks for the link, I was looking around for, that link for quite some time now.

Apologize to the thread author, I jump too quickly in my suggestions. I was caught up, appreciating his nicely built Super Cub:) I don't have any knowledge in smaller motors, as of yet, but by reading your replies Doctor Phil. It sounds good to me:)

Mahalo,
Antonio

[Dr Kiwi]

Dear Antonio - Yes, that link became elusive a short time ago - I lost it too when it wouldn't come up on that weird
"?custompaintjob...." URL. I found it again, by chance, at DMA (Diversity Model Aircraft).

There must be a significant difference in the calculation procedures used for MotoCalc and ezcalc. For the few scenarios I tried MotoCalc tended to come up with even lower current draws than did ezcalc. An example: Speed 300 5:1 7-cell 350 9x4.7 prop - (a) ezcalc: current draw 6.1A, prop RPM 6360 (b) MotoCalc: 5.1A, 5530RPM (c) actual figures from my Scrappy set-up 7.7A, 5800RPM. My set-up's efficiency (RPM/A) turns out to be 28% worse than MotoCalc predicted, and 30% worse than ezcalc predicted. The bottom line is that I'm putting in a lot more but getting less out (bit like my retirement fund!).

Cheers, Phil

[bluemax1962]

Thank you all for the great replies. I must admit I have had to put the cub on hold for the moment.

My wife just gave birth to a 7.8 lb Baby Boy (our first and only) on Friday night at 4:50 PM. He was some 20.5 inches with a head full of blonde hair. I actually got to do more than cut the cord and assisted in the delivery! Well till she some complications and I had to step asside and let the DR do her thing.

All is well in the Bluemax household. Momma and my future flying buddy are doing great.

I will send more on the cub soon. I have an idea on making the gear, more finctional and able to adapt to floats later.

Bluemax aka. Daddy :-))

[Dr Kiwi]

Dear Daddy-Bluemax - Congratulations! But where did you get the idea that you'll have ANY time in the next few years to dabble in model-making!!!!!! My children are 14 and 11 and I only got back into aeromodelling 2yrs ago - and still family commitments take most of my time and money! Good luck with your great new adventure. Cheers, Phil

[genovia]

Bluemax,

Congrats....:) I am trailing you by three months, my wife and I are expecting our first baby this coming April. It's a boy.

*****. I actually got to do more than cut the cord and assisted in the delivery! .****

My wife records a show on TLC, about women delivering babies, she make me watch it, force me to watch it:D .. I have been practicing and teaching Filipino Martial Arts since, I was 15 years old. Fought in competitions in Asia and here in the States, I hold the rank of being the youngest Chief instructor. I am not afraid, not until I saw, that show.

Women laying in hospital bed, some of them screaming, helpless, and sweating... OHHHHHH!!!!! BOY!:( I was watching that show "Maternity Ward", I was turning blue, I felt like, I was going to get sick in my stomach. I found my fear:D what makes it worst, my wife is going to kill me, if I'm not in her side during labor (Go figure, she Italian) Now! I'm really dead:D .. I think, but I will be okay though, because I have been watching each episode of the show, and I totaled 40 hours, I think, I'm good to go:D

Now that time is getting closer, I'm excited, I am ready and I can't wait to hold my son in my arms:)

Good luck with the baby, and congrationalions to you and your wife.

Yours,
Antonio.

PS. If you notice the time stamps in some of my post, some of them I made 3AM:D I have been practicing my night shift:p

[Dave Robelen]

Hi Antonio,
Hang in there buddy, I have been to that birthing room 5 times, and it does get a little less traumatic with the preliminary stuff. By the last trip, I felt almost like I was qualified to teach one of those "Natural Childbirth" classes "Hah".
Phil, I have noticed the same caractarisitic with Motocalc, but it does seem somewhat consistent, and is still mighty handy for comparing "better-worse" cases for the same motor-battery-gear package.
Take care, Dave

[Dr Kiwi]

Dear Dave - Yes, you are, as usual, quite correct. I still find MotoCalc and ezcalc very useful for getting a "ballpark" idea about whether a particular set-up will work - I'm just trying to find some way to estimate exactly how "overly optimistic" their calculations really are! Of course, since we have no way of measuring "in flight" current draws, thrust values, prop speeds inter alia - their estimates are better than nothing and may, in fact, be closer to the truth than we give the programs credit for! In the final analysis - the moment we launch the model, we'll know immediately whether our system works (if it doesn't we just repair the BALSA quickly and easily, modify the faulty system and chuck it into the air again!), and if the model flies okay, who needed all those figures anyway! As Garrison Keillor says " Be well, do good work, and keep in touch". Cheers, Phil

P.S. I just have to say that I continue to be impressed with the quality and workmanship exemplified in every one of your models I see illustrated here or in flying magazines. We are all inspired!

[bluemax1962]

Thank you guys for the congrats and comments, but I don't want to turn our thread into a Baby chat room. I would love to share with all those Dad's or about to be Dad's, but don't want to burden those that may not be as interested.

Phil, I hope to keep having time for modeling by keeping my family involved. Jr already has models with Snoopy in them and a steel persuit petal plane. I have a Herr Starcruiser kit for my wife
that is being converted to electric.


Antonio, congrats to you. Please e-mail me privately as I can fill you in on what to expect if you really want a man's perspective. I would love to share what I experienced so that others may benefit. If I could have gotten real (first hand) experience from someone I could have made my son's first day much more pleasurable. When it comes to your child, trust no single opinion (even a Dr.'s).

OK back to the cub....now where did I put it. There it is...under the diaper bag. :-) Just kidding

Thanks all
Perry

[bluemax1962]

Ok, back to the cub.

I scanned everyones replys and I must admit I am a little more confused. You guys are a lot more knowledgeable on elec.'s than I am. I am an old gas flier and have much to learn.

The kit suggests a speed 400 and a Olympic gear reducer and a 800ma Battery. They feel the plane will be about 21oz.

I hope to lighten this where ever practicle. I would like to get at least 8-10 minute of flight time per charge. I would like to have enough power to perform mild aerobatics. I would like some ability to climb, but don't need verticle performance.

Some of you have motocalc? Is it worth investing in?

Now if I have a bare fram that weighs say 6oz and I cut back to say a sp 300 and change the gear ratio and use a smaller battery? I am using a Hitec 555 recv. and 4 HS-55 micro servos. I plan to use a smaller esc but that will be decided by the motor/battery question.

Ok guys here is where I need your help figuring out what to buy.
I would not mind investing in Liploy packs, but chargers are changing daily it seems.

Thanks to all responding to this thread.

Perry

[genovia]

Hello Perry,

I just got 20 LilPolys today, I'm planning of configuring my own, hoping to juice up my Mega motor, I don't have any experience with these new batteries, as of yet, nor have any idea how to configure my cells to draw the amps that I wanted it to draw. I got my Lilpolys at Sheldon's Hobbies, but you can get them directly at http://www.edogfight.com/Catalog_page/BatteriesCells.htm it's cheaper, than If you buy them at a hobby store.

Doc Phil. Dave.

Lilpoly's, I want to power up a 400/480 motor, how would I go about configuring these cells?

Thanks,
Genovia

[Dave Robelen]

Hi Antonio,
There is a neat chart that relates the capacity of the Li-Poly cell to the current draw, and the number of cells required at www. fmadirect.com under the Kokam cell directory.
Rgards, Dave

[Dr Kiwi]

Dear Bluemax - A reading of Quiet Flyer for Feb 2003 (p.30) suggests that Lithium-polymer cells may work but to get 8-10 amps current at 7.2v you are going to need 6-8 950mAh cells wired in three-four strings of two series cells each (this will weigh 4.6-6.2oz and cost you $60-$80 for the cells). I see no great advantage over NiMh or NiCd here. Li-polys are probably good for IPS motors at low current draws but getting the 25amps Antonio wants is going to require 20 or 30 cells [if he needs 10v] (at $200-300) connected together.
As far as the Cub goes it seems the kit estimate of 21oz may have been a bit on the low side, considering the 400 + Olympus + 800mAh (8-cell?). However, looking at your numbers you are not going to get away with much less than 18oz, even with your paring of the frame to 6oz and going to,say, a 300 + g/box. Let's review those numbers:

Frame uncovered - 6oz (say, 7oz covered)
Speed 300 + 5:1 g/box - 2.55oz
555 receiver - 0.75oz
4x HS55's - 1.15oz
ESC - 0.62oz
I'd figure your average current draw might be about 6 amp, so for 8-10 min flights you'll need at least 7-8 cell 600mAh (6min) to 7-8 cell 1000mAh (10min). Whether you use NiMH (remember NiMH 720AAA won't give you enough amps, though HeCell 1000's or the better KAN950's will) or NiCd you're up for a minimum 5-7oz pack weight.

Add all those up and you have a ready to fly weight of 17-19oz. You'll certainly need every bit of power the 300 can supply! A GWS R4-P receiver (6g) and Pico Servos (5.6g each) would help a bit, but there are things you are stuck with! Hope it continues to progress, Cheers, Phil

[Dave Robelen]

Hi,
Antonio, if you can find out what sort of Li-Poly cells David Hsu used in his A-10, they would work fo your glider, and this Cub. The A-10 fans draw around 8-9 amps static and in flight.
Phil, I have an 18 ounce ARF (Lil Luscomb Sport) that has really strong performance with a sp300 geared 3.75-1 driving a 9-6 APC Slow Flight blade on a 7-cell ni-cd pack. The gearbox is the MP Jett sold by Hobby Lobby. My Scale Bristol Brownie with a 6V sp400 and Mini Olympus running on 8 cells does fine at 27 ounces. The wing loading of all three of these (including the Cub) is pretty similar. The sp300 might be a very good candidate at the lower weight.
Regards, Dave

[Dr Kiwi]

Dear Dave - Sorry I sounded a bit pessimistic over the 300. I had touted it in an earlier post (at 16oz or so) but I started to get concerned when the numbers began to climb to possibly 18oz or so. Perry was originally hoping for 11-12oz, but that is clearly unobtainable. I'm sure that a Speed 300, esp. geared 5:1, should provide plenty of thrust at a not unreasonable current draw. My Nanognat is 15oz and Scrappy is 14oz and they both do well with 300's on 4.5:1 and 5:1 respectively. However, each has 315 sq. in. of wing area [and Nanognat's is undercambered at that], and thus they both have much lighter wing-loading than this Cub will have. Cheers, Phil

I just received from Fedex my Mini AC1215/20 with 6:1 planetary - perhaps we should drop that into Perry's Cub and see if THAT can get it airborne!

[genovia]

Dave,

I emailed David, he did not power the A-10's test flight with Poly's, instead he used:

Antonio,

Final setup for A-10 is:

6 x HECELL 1100
3 GWS Pico servo
1 Berg 4DSP receiver
1 Pixie 7

David Hsu

The Lil Poly's will be flown on the A-10's second flight. ( Will retract my statement)

[bluemax1962]

Doc/Phil/Dave,

I am leaning toward Lith/Poly's, but am concerned the rate of drain from a speed 400 will be too much for the packs. This is part of my thinking that a 300/280 motor will serve better as well as be lighter. I read too thata special speed controller may be ness. as well. Thoughts on all this?

Here is a pic of the start of the gear. This has prooved to take longer than the fuselage to make! I plan on splitting the gear in the center and feading the ends into aluminum tubes that will be buried in the lower portion of the fuselage. Elastic will hold the two halfs from pulling out of these new sockets. This will flex like the real cub gear and allow me to install the gear without binding with thread from the underside (as per plans). Also I can change the gear to floats when I am sure it flies :-)

Perry

[Dave Robelen]

Hi Perry,
A few words about the Li-poly situation. You can get a lot of information from the enginering data chart for the Kokam brand cells on the site www.fmadirect.com . If you do not already have the Motocalc program downloaded, you might want to this one www.motocalc.com will show the range of currents likely with these different motor/gear/prop combos.
The special ESC has become an issue with the Li-Poly cells to avoid draining them below the critical voltage. FMADirect is stating that they will have this feature available shortly. Meanwhile, when I am flying wih a Li-Poly, I land at the first sign of reduced power. The literature says that permanent damage may result from too deep a discharge voltage.
Regards, Dave

[bluemax1962]

My last pic was too much for sending to the thread sorry. I will have to take another.

[Dr Kiwi]

Dear Perry - Tried to post this this afternoon but the site was "down". You shouldn't need to TAKE another photo. I don't know if you are trying to post a digital image or a scanned photo, but if you have something like Adobe PhotoDeluxe you simply need to open your photo in that, then go to "adjust PhotoSize" and {using pixels, not inches] adjust your photo to less than 640x480 pixels - that will bring your file size down below the 61.4kb limit for posting.
As Dave says - you can download "MotoCalc" on a free 30-day trial, or you use "ezcalc" absolutely free from DMA (Diversity Model Aircraft's site - http://brantuas.com/ezcalc ).
If you are tossing up between 280 and 300, for me it is 300 all the way. With 7-cells and a 9x4.7 on 5:1 you can be revving at 4000 on only 3amps. That should be plenty, and if you need it you'll have a lot in reserve when you throttle up - my bench tests show you may max out at about 5800 revs at 7.7amps. Cheers, Phil

[bluemax1962]

Thanks Doc for the photo hint. I will try that.

As for the battery delema. Does anyone know where to find a chart that shows different makes of packs (by cell type/count)? What I want to do is find the breakeven point for pack weight and mHa. Example does a 8cell 800 mHa weigh the same as a 8cell 1100 mHa? Obviously I would go 1100 mHa....

Things have slowed on the cub due to the fact that there is NO HOBBY SHOP here. I may have to drive a bit or just order on line. This is why I would like to make the battery choice and make one big order. Without the battery decided on I can not calc the balance point and thusly the servo locations. I am hoping the servos will go under the elevator and leave the fuselage for esc and Battery.

Perry

PS. This is a great site. Everyones info ads a new demention in modeling! Gotta Love it!

[bluemax1962]

Let's Try this again.

Here it is sitting a top the gear. Sure was a pain. It has taken longer to form/solder the gear than the entire fuselage.

Goal is to split the gear in half. Aluminum tubes to be buried in the fuselage. This will negate the need to sew the gear to the bottom/outside. Also will make gear function like the real thing does. Secondly I will be able to switch to floats when I like to.

Perry

[bluemax1962]

Here is another shot of the gear and cowl. I didn't like the kit's openings so I found a site to reference Supercub.org. It's is a great site. Lots of pics/movies. Good color references as well as for details. Noticed a scoop that will help cooling so I drew the cutout you see on the bottom.

If you go to the site, check out the film clips. There is one that shows an attemp at short take off. Full throttle/flaps/brakes locked and it jumps off the ground in about 10ft! Way cool.

Perry

[bluemax1962]

Here is a shot of the Cowl/Firewall fit. Kind of proud of how well it mated up. I chucked the plywood Firewall from the kit due to weight,warpage and very poor fit.

Used two cross grained pieces of hard 1/16 balsa. This is lighter,stiffer and will be easier to attach things to later.

More later.

Perry

[bluemax1962]

Ok, I finally got the cowl roughed out. I am having trouble getting my old styrene to form under heat without cracking :-(

You get the idea.

Anyone know where I can find a scale shape spinner for this bird? I hate to think I will have to form one. I may have to dig out the old vacuform machine.

Perry

[Dr Kiwi]

Some time ago Antonio posted a whole bunch of data on battery sizes [but perhaps not weights] - but you would be best to go to somewhere like www.batteriesamerica.com or radicalrc or indeed any of the better hobby suppliers like aeromicro, balsaproducts or Todds Models - they almost always give pack weights. Most importantly, you need to ascertain, amongst the bewildering range of possibilities, the cell "size" [AAA, AA, 2/3A, 2/3SC...................................]. One of these many battery suppliers will have a chart, at least for individual cells, which will enable you to calculate the pack weight. Cheers, Phil

[bluemax1962]

Just got my Olympic gearbox from Hobby Lobby.

What a disapointment. The unit is covered in flash. Even the bag with setscrews and pinon has flash in it!

OK you might say just clean it up and use it (right?)

Well since the main gear and prop shaft are way out of center it is unusable! The entire shaft assembly rotates around a false center. The resulting vibrations would shake the firewall off the plane!

I am leaning toward a planetary in line gearbox now. Any suggestions out there?

[bluemax1962]

Another shot:mad:

[bluemax1962]

Did I tell you I work for a plastic molding firm?

GM would never buy from me if I sent them this!

[bluemax1962]

I just want to stop anyone else from the disapointment I have endured.

Perry

[Dr Kiwi]

Dear Perry - I am horrified by that lack of quality - Hobby-Lobby needs an earful on this - they must surely have gone to some el cheapo supplier - I'd send it right back to them and demand a refund and replacement with a good quality one. I can't recall what motor you are fitting this to - I thought you were using Speed 300 or the like but it looks as if you are now with a 400. If it is their Mini Olympus for Speed 400, there is a beautifully machined replacement available, and that is a GENUINE Graupner Olympus look-alike GR170303, 2.33:1. Mine cost $28.40 but it is superbly finished (by coincidence I fitted it to my Mini AC 1215/20 this very afternoon). Although it feels a little rough when hand-turned, on a short bench test run I found it to be very smooth and vibration free [even though I was spinning it in reverse 'cos I hadn't got around to reversing the motor leads!]. You could go the planetary route. I have several of the MJ805x and MJ806x versions which are extremely well-made but I have not been terribly impressed with the meshing of the gears (especially on the one on my 480). I also have a VMGM 6:1 planetary g/box for my Mini AC and even that, at $45, is not all that smooth (and I've run it in as recommended for about 45mins now).
Good luck, and hang tough with Hobby-Lobby - they ought to be ashamed of themselves! Cheers, Phil

[bluemax1962]

Phil,

Hobby Lobby has agreed to refund my purchase.

They made it sound like this is a cheep unit, but if I want to spend $59 I could go much better....Better yet "why not go brushless and skip the gearbox"...HeeHeeHe..Yeah right!

Will keep you posted.

Perry

[Dr Kiwi]

Hey Perry - I'm glad Hobby-Lobby came through, but disappointed that you obviously did not get the whole story. I forgot to mention in my previous post that I have a Mini-Olympus which came with my 400 powered RADAR kit from Cavanos Sailplane Design. There are no identifying marks but I'll bet it is the same g/box that Hobby-Lobby USED to sell - it is beautifully made, and the nylon/nylon mesh of pinion and spur gear is as smooth as you could want. They MUST have acquired a really cheap version and are passing it off as the original.
On the subject of brushless/gearboxless flight: I have been disappointed with just about every gearbox I have ever owned - they are all noisy and the meshing of teeth leaves much to be desired (I don't have an Astro or similar - they may indeed be superb). However, a thought for your 400 aircraft. I recently acquired an AXI 2808/20 (79g, or about 120g with wires, mount, prop and adapter). A Speed 400 with Mini Olympus or MJ gearbox and associated prop etc is also about 120g! (and with an MJ planetary it is 138g). The AXI is incredibly smooth and turns an 8"x4" prop at almost 11000 revs on 8 cells at 13.5A, the same prop on only 6 cells at 9200 revs at 9.5A. It turns a 9"x5" at 9100 at 17A on 8 cells and 8000 revs at 13.7A on 6 cells. That sort of performance beats the 400 hands down, so it might be worth a look if you want to avoid the hassles of grungy gearboxes. Go for it! [maybe?]. Cheers, Phil

[bluemax1962]

Thanks Doc.

I will be looking into this based on what you have said. This site really does save time and wasted trial and error of the old days before the net.

Doc, you wouldn't have a pic of your AXI 2808/20 setup would you? What was the cost (motor/contl/adapt)? What was your mounting like?

Thanks

[Dr Kiwi]

Dear bluemax1962 - Sorry, I don't have a photo of the set-up but if you can wait a day or two I have a film I want to finish up so I'll get one of it for you.
The AXI 2808/20 I bought from toddsmodels.com for $69.95
The controller is a Jeti brushless 30-3P that I've had for several years I see its at Hobby-Lobby (JEC 303) for $77
Connectors are Jeti 3.5mm (JEC 001 and 002) at $4.20 and $6.20 a 3-pack at Hobby-Lobby
The mount is a Graupner HLAN 2096 horizontal mount ($8.50) - simply use a Dremel to grind away the vertical parts of the mounting lugs to allow free rotation of the motor case.
Mounting screws are standard Speed 400 2.5mm (HLH 8725) from Hobby-Lobby at about $2 a packet.

I ran some tests on my Mini AC1215/20 with the Graupner 2.33:1 gearbox - interestingly on 8 cells, at around its maximum draw of 9.2amps, it is spinning an 8x4 prop at 9300 revs - that is only fractionally less than the AXI in the same configuration (c. 9500revs), so their efficiencies are about the same [and the Mini AC weighs somewhat less]. Of course the AXi will keep on cranking to about 11000 revs at 13.5amps but if you have a smaller plane which only needs the thrust produced by each of these at c.10amps, you would be better with the Mini AC (but then you have to deal with a gearbox!] Cheers, Phil

[Dr Kiwi]

Dear bluemax1962 - I didn't have motor etc weights at hand when I did the last post. Just for your interest here are some figures which might be useful in deciding what to fit into your various aircraft:

AXI 2808/20 with Graupner 400 horiz. mount, ESC, 8x4 Slim Prop and adapter: 160g

Mini AC 1215/20 with Graupner 2.33:1, ESC, 8x4 Slim Prop and adapter: 122g

Speed 400 with MPJ gearbox, ESC, 8x6 APC E prop and adapter: 122g - yes, same as the much more powerful AC 1215/20

Phasor 15/4 with Graupner 600 horiz. mount, ESC, 8x4 Slim Prop and adapter: 222g

Cheers, Phil

[bluemax1962]

Well I finally got some aluminum tubing to make the gear plug in.:D Now the bottom of the plane is clean (no thread tied to the bottom). I can think of swapping for floats later. The Trexler #3 wheels make a good match. Some brass bushings and hub caps will top it off.

[bluemax1962]

Here is a detail shot of the plug system

[bluemax1962]

Sorry about the big photos. i gotta work on those digital camera skills!

Anyhow...Here is a shot of the tail wheel. It is 1/32 wire with two trimmed Tyco rear hubs. The tire is a dried out sponge rubber tire from my slot car days in the 60's

Who said I wouldn't have time for models with the new baby? I must admit time is much more limited.

Perry

[bluemax1962]

Shot 1 of 2

[bluemax1962]

I'm getting better HAHAHAHAH

[CalmAir]

Hey Bluemax,

She is looking real sweeeet!

[bluemax1962]

Hey Phil,

I have been looking into the AXI alternative. Sure sounds like a torquey devil. Looking forward to hearing Mounting alternatives.

While I have everyones attention, the kit has no definition of thrust angles for this cub. From my gas days knowledge I will guess that the light loaded flat wing will be about 2 degrees down and 1 degree right.

I am new to electrics, but with turning a larger prop slower (compared to gass) do I need to worry about right thrust at all?

Anyone got thoughts on this issue (2 dwn.1 rht)? Anyone bulit this (or similar cub) and have thoughts? 2NG How about you? Still flying your cub?

Thanks
Perry

[bluemax1962]

Phil (or anyone with an opinion)

I finally have had the time (yes you all were right about babys :-)) to evaluate some other power systems.

I think I have it down to the Mini AC 20 with an all metal gearbox or the 280 MP Jet Brushlessmotor w.plastic gearbox. The AC system will weight out .5 oz heavier, cost $30 more, but offers some flexability later.

The Mini AC is only 2oz and is cheaper, but will it pull a 46in span plane at about 16-17oz? They rate it at 18oz max for park fliers. Starting to wonder if I go the larger s400 MP Jet brushless if that will pay for itself. The trick is 27 oz thrust for the same price, but at a weight of 3.2 oz.

Do I go for super light or heavy but powerful? I know the old addage "you can always throttle back".....but a plane built to fly at just that perfect combo is just soooooo sweet.

Part of the delema comes from maybe adding floates later. I got real motivated when I saw the foamfloats.com web site. Nice site worth a look.

Thoughts?

Thanks as usual Perry

[Dr Kiwi]

Hey, Perry - I'm not much help here, since I'm not quite ready to give you any definitive answer on the MiniAC performance yet, nor on these new MPJet beasts, since I have not rushed out to buy both models (25/25-26 and 25/35-20) just for testing purposes!

I do think that Hobby-Lobby's claims of watts-in and thrust need to be taken with many grains of salt. After testing a bunch of my motors including the MiniAC, my AXI and my Phasor, I would suggest their figures are way too high for their stated prop and gearbox combinations. Yes, if they had a constant voltage source rather than a battery perhaps they could obtain figures of this order but I would defy them to do it in the "real world" - i.e in an aircraft.

I found that the Northeast Sailplanes site

http://www.nesail.com/MPJet/2525gear.html

has more believable figures for these two motors, suggesting 10-12oz thrust at 6-7amps for the 25 and 20-21oz at 11-12amps for the 35.

You'll have seen Hobby-Lobby's 18oz at 15amps and 26oz at 16amps respectively. For 9x6 props the 18oz thrust figure [for the MPJET 25 on 5:1] would need about 7000rpm prop speed and 26oz [for the MPJet 35 on 4.1:1] about 8500rpm. Even if they could pull those sorts of currents and get those sorts of thrust figures, which I doubt, the motors would probably be close to frying, because they would need to be turning at around 35,000rpm.

The MiniAC1215/20 is midway between these two motors in size so you may be interested in some preliminary data I've gathered on it:
Here are some Peak thrust/rpm/amp figures for different gear and prop combos, each time using an 8-cell 1250SCR Nicd pack:

Geared 2.3:1
8.5x5 prop: 15.7oz at 8880rpm @10.5amps
9x6 prop: 19.0oz at 7200rpm @14.3amps
10x4 prop: 20.1oz at 8250rpm @13.0amps
10x7 prop: 18.6oz at c.6200rpm @16.0amps

Geared 3.0:1
9.5x6 prop: 14.2oz at 6780rpm @10.2amps (still could have gone higher, but didn't in this test)
10x7 prop: 19.4oz at c.7000rpm @13.0amps


Here's some comparable data for the AXI since I have it in front of me:

8.5x5 prop: 22.9oz at 10350rpm @ 16.5amps
9.5x6 prop: 20.1oz at 7700rpm @ 19.0amps
10x7 prop: 18.6oz at 6000rpm @ 11.6amps


Lots more trials are needed!

Cheers, Phil

[bluemax1962]

Phil,

As usual you are a big help. I wondered about the numbers posted in the Hobby Lobby catalog. Seemed too good to be true. Even the write up in Bakyard Flier and Model Airplane News seemed a bit crazy when I did some quick math. They describe flights of 20min with a 1350 mah Nmh and the larger MP Jet brushless. All While turning a 9x6! Seems like a strech. So I'll be holding onto my $'s a little longer and checking out NorthEast Sailplanes' site.

Cub Update. After much fiddling, I finally got the two wing halfs joined and strong enough to not use struts. I will anyway. Managed to cut some of the weight too. Center section helped because it was simpler and far fewer parts. For those thinking of building the Hobby Lobby Cub (Modified or not) save yor self some hassle and DON'T install the leading edge sheeting till the wing halfs are joined.

Thanks again Phil. Let me know if you do anymore testing :-)

Perry

[Dr Kiwi]

Hey Perry - just a few more scattered bits of info which might interest you [my Geology students are demanding my attention and this is essentially an instant message!]

1. For the 25/25: I don't understand why Hobby-Lobby suggests an 18oz max aircraft if their motor is truly taking in 122W - for high-wing, slow flyer/trainers etc 40W/pound [2.5W/oz] is considered adequate - that means you should be able to fly a 3lb monster with the 25/25 motor. Their figure of 122W should be enough power to sustain a vertical hover in an 18oz super aerobatic aircraft! Normally for slow flyers a thrust figure of about half the weight of the aircraft is enough, so why they suggest you need 18oz for an 18oz aircraft is beyond me.

2. The 20min flight on 1350mAh NiMH with the 25/35 would be possible only if you ran at partial throttle alternating with gliding! Using my MiniAC figures, I reckon that, at 4amps, you could get about 8oz thrust from a 9x6 [marginally adequate for an 18oz aircraft]. An 8-cell NiMH pack, even at that relatively low current draw, is going to suffer decreased voltage as the flight progresses - probably down to 8.5V or less within minutes - so your power in is going to be only 40W at the start and approaching 30W soon after. I've looked at lots of battery tests and most packs actually only provide more than 1V per cell for about 1/2 to 2/3 of their mAh capacity. Let 'em try sucking 16amps out of a 1350NiMH - Buena suerte!

3. Your 18oz, 42" plane should be fine with any motor which can give you 8-10oz thrust - a MiniAC, one of these MPJet's, an AXI, even a geared Speed 400 will give you that at around 4-5amps. If you want more thrust the 400 will, realistically, peak at only about 12oz @ 8-9amps, the MiniAC could get you up to 16oz @10amps, and the AXI will go to 20+oz (but at 16-20amps!). Reach for the sky and 30oz or so and you need a Phasor at 30+amps!

4. In my testing so far it is clear that output (in ounces of thrust per amp current draw) decreases dramatically as current increases. Most typical motor/prop combinations give you about 2.5oz of thrust per amp at 1.0amp draw, they gradually fall below 2oz/amp through the mid-range (4-8amp draw) and finally, as their limits are reached, drop down to no more than 1.5oz/amp. For motors like the AXI and Phasor, which are capable of sucking currents much higher than any can motor can accept, their output may drop below 1.0oz/amp at 20-30amps.

5. Note on Phasor 15/4: Phasor's seem to need so much current initially that they give less than 1oz/amp even at 1-2amp draws, improve a bit to peak at around 1.3oz/amp in their mid-range, then fall back again to just below 1oz/amp at their maximum of 30amps or so.

Remember that, theoretically, to double your rpm (obviously related to thrust) you need 8 times the amps!!

Got to dash - more later - Cheers, Phil

[bluemax1962]

Phil,

Thanks for taking the time to help me out. I want to order either the AC Mini 20 or the AXI 20 by next week. I even considered the AXI 10. The flexability to swap ratios at a lesser weight is a real draw towards the AC Mini. However the silence and extra power of the AXI is pulling me that way. The AXI means floats will not be a problem later, but also cuts the flights to a little more than half!

Decided on a coil antenna and RA Micro lite for covering. I will be vacuforming the windows for a better fit/look. The spinner is gonna be a vacume project too, but low on the list. The two hatches will be buried in the bottom in front of and behind the gear. Film hinges in the front and rare-earth magenets at the rear should hold them shut in flight

I managed to get the wheels blind mounted with hubcaps. Had to make perfect washers of .007 shim stock but turned out clean.

I have drawn up my mental notes for the ailerons, but still debating hinge line/type. Do I go with a top hinge tape arrange ment (gap on bottom only), a mid line spilt (gap top and bottom) or go fancy and make full length pivot with the centers inside the control surface. The later will look better and give a cleaner line, however this thing will need to fly some day here soon! :D

I will stop rambling for now. Will write more when my order comes in.

Perry

[Dave Robelen]

Hi Perry,
I would opt for the center hinge with the ailerons having a sharp wedge at the LE. A good fit for an aerodynamic seal will go far in keeping the wing from "tip stalling" in tight turns at low speed.
On models such as the Cub, differential in the ailerons is very important for smooth turns. About twice as much up movement as down. Part of this can be achieved by locating the aileron horn on the bottom, and well aft of the hinge line. The rest would depend on how you plan to connect to the servo(s).
Many model J3 Cubs have gained a bad rep because the builder set up the ailerons with equal throw, and then ignored the rudder when banking. I have flown in, and controlled a full scale J3. It is very much a "rudder" plane. That is, if you do not coordinate the rudder with the stick, you will get some mighty funny attitudes. The first time I moved the stick to bank as I would with a peppy model, the plane banked OK, but it also started skidding until I was looking up at the sky. A lesson quickly learned.
Modern Piper and Cessna planes have as much as 3-1 differential, and ca be banked with little or no rudder.
Happy building, Dave

[bluemax1962]

Dave,

I agree with you that differential throws will aid the performance of the cub. It is in my plan to include this in the control setup. Maybe the setup will give you picture of what I am confronting.

Each wing has a digital micro servo. It will be mixed with rudder and also will have flaperons. A little elevator mix will solve any ballooning.

Here is were I get unsure....I am dealing with flaps that are the length of the wing and (most likely) never see as much deflection as separate flaps/ailerons. So........ Do I get fancy and make offset pivoting ailerons that are half rounds at the leading edge with mating surface fit to seal (Scale)? Or do I go the modeler's hinge with gaps top and bottom and a wedge shaped hinge line. This would assure a 100% seal if film used full length (or tape). It would be easier to make. Would the gaps disrupt the airflow on such a (hopefully) slow flying model.

I have even thought of goning a simpler route, but not sure of the effects in flight. What if I use a modeling hinge and leave the gap only at the bottom? Hinge at the top would not disrupt airflow over the wing where lift is from and would not be too ugly from above. However...the ugly gap on the underside could cause turbulance that would affect my short field take offs!

Thoughts? Anyone try and like something different?

Thanks
Perry

[Dave Robelen]

Hello Perry,
Of all the hinge arrangements I have used on wings of this general size, and with a "flat bottom" airfoil, the one with the gap on the top, and hinged on the bottom is the best performer. This is on the Lil Luscomb Sport, A Bulgarian ARF that is one terrific model.
What this has shown me is that the flow is more thorougly seperated on the upper surface than the lower. I felt the comprimise solution of a hinge line along the center with a wedge shape would be more acceptable cosmetically, and would fly just as well. The half round style seald hinge is very attractive, and would perform fine, but if it were me it would be difficult to justify the extra work. But, then I have a lazy streak, and as with most any model you will spend far more time looking at it than flyimg, the solution that appeals to your aesthetics will be the best. The version with all of the gap alng the bottom gives away the most performance, so that is why I would avoid that approach.
Regards, Dave

[bluemax1962]

dave,

Thanks for the direction. I wondered about using the bottom approach. I would be much simpler. I have little experimentation with flat bottom wings with ailerons. Spent too much time zooming around with symetrical wings and aerobatics in the past.

I will be able to build either of your ideas with the layout I have, so based on looks I will send photos of the out come.

Thanks again

Perry

[bluemax1962]

Phil,

Last Questions before I oreder my motor Phil..........

AXI rated at 10-20 Amps...Does this mean I need 10 Amps just to start the thing turning or is this the Max output range. (example...can I glide around at 1/4 throttle and only burn 3 amps?) I just don't want all that power all the time. Does your answer depend on the controller being programmable?

Speaking of controllers...You recommended the Jeti 30/3. What do you think of the Castle Creations Pheniox 25? It is sensorless, it's weight is less it cost about the same and is programable with slow ramp up.

I know your time is short. A couple blerbs will set me straight.

Soon to be brushless.....Perry

[Dr Kiwi]

Dear Perry -

The 10-20amps is the best range for the motor - you can certainly cruise around at less than that [provided you do actually have enough power to provide level flight at, say, your arbitrary figure of 4amps - by my crude estimates you may have 7-8oz thrust at 4amps.].

I talked to the owner of one our local hobby shops today and he was in raptures over his AXI (although his is a larger version than you are getting - a 2820-12 on 10-cells - everything I've seen of my 2808-20 suggests that the smaller versions are just as good). He was impressed by the smoothness and power and he got 8 minutes of extreme aerobatics (rolls, loops, inverted, knife-edge flight....yes, he is a VERY proficient pilot!) + taxiing, out of a 2400mAh pack with plenty to spare.

I haven't yet tried my AXI in flight but I do happen to have a few figures from bench tests for your interest. I could put these in a table but I don't know if these posts support the formatting - here they are in crude form: these are one-off measurements and battery performance may not have been exactly comparable [I should have recorded "watts in" as well as amp draw to keep a handle on voltage drop].

AXI 2808/20 on 8-cell 1250mAh pack - Jeti 30-3P controller.

8.5x5 Aeronaut prop: at 5amps, static thrust 236g (8.3oz): at 8amps, static thrust 368g (13oz) - peak thrust 650g ((22.9oz) at 16.5amps.

9.5x6 Aeronaut prop: at 5amps, static thrust 240g (8.4oz): at 8amps, static thrust 340g (12oz) - peak thrust 650g (22.9oz) at 21.0amps.

10x7 Aeronaut prop: at 5amps, static thrust 280g (9.9oz): at 8amps, static thrust 396g (13.9oz) - peak thrust 528g (18.6oz) at 11.6amps.

Simplistic conclusion - it seems to be best with the 10x7 since the thrust/amp figure is higher at each stage and though peak thrust is not as high (18.6oz v. 22.9oz), it is obtained at a significantly lower amp draw than it is with smaller props.

As far as the controller goes - Castle Creation makes brilliant controllers - though my Jeti seems okay, I got it because it was part of a package - I would have preferred a Castle Creation since I have three others of theirs (Pixie 14, Pixie 20 and Sprite 25) and I love 'em.

[bluemax1962]

Phil,

You are a time/dollar saver. Thanks so much for such in depth advise and research. I know it took some time. If I can ever return the favor..... (as if you ever would need advise yourself :D )

Todd's seems to have a good price on everthing I need. I just need to finish the "while I'm ordering I might as well get this too" list.

Thanks again for all the efforts you put into helping me figure out what's what.

Perry

[bluemax1962]

Well my order of the power system is in.
AXI Motor,Castle 25 ESC and a loaded antenna.
Thanks again Phil for all the help.
I am working on the mont forthe motor as I write.
Should have pics posted soon.

Perry

[bluemax1962]

For those who were curious about the ailerons, I have them framed. The hinge line is all I really have left.

[bluemax1962]

Still working on the mount for the motor. Looking good, but ready for pic yet. Here is a progress shot.

[Dr Kiwi]

Hey Perry - Looking very good!

Just one word of warning - I see you have an Aeronaut style grub-screwed 4mm prop adapter - I'd replace it, IMMEDIATELY, with a collet type such as is offered by Hobby-Lobby, and I'm sure other suppliers, as CPA0406 -$4.30.

A trip to the emergency room will be a lot more expensive than that! The AXI is a very high torque motor, yet its shaft does not have a flat machined on it, so grub screws have little to grip on - during testing I've twice had props fly off at 8000rpm+ - I got lucky and only had one minor scratch on my arm from the rogue prop, but it could easily have been very serious. A carbon reinforced nylon prop letting loose at 10,000rpm+ can do a lot of damage if you get in its way - collet type props can be really securely tightened down, and you won't have a problem.

My local Hobby Shop proprietor had just fitted an AXI 2820 to one of his aircraft and, after losing a prop (and attached Aeronaut adapter!) in flight, was happy to accept my collet suggestion before he lost an eye or appendage!

Cheers, Phil

[bluemax1962]

Phil,

I had thought of flatting a spot on the shaft for that very reason. I also was planning to use loc-tite on all hardware. Being an ex- Huey Crewchief I am well aware of vibrating hardware.

Is a collet type that more secure? I see it is used on some high speed prop combinations. Is it more balanced as well? Sounds like I can still use a loc-tite on it too.

I plan on taking your advise. Thank you again.

Sounds like you could start a thread of "Close Calls/Lessons learned". I know as the once Safety Officer at a Club that I could share a story or two!

Thank You Phil. I am sure others may benifit by reading what you have shared with this thread.

Perry

[Dr Kiwi]

Dear Perry - Yes, I have every faith in collet type adaptors to hold REALLY tight - you can put a big wrench [ maybe 20ft.lb of torque or more] on the nut on about a 1/4" diameter threaded shaft, and the split collet grips the whole length of the motor shaft - that has got to better than the holding ability of two skimpy little grub screws with point contact, and which you can only tighten with a slender Allen screwdriver or L-tool. While Loc-tite will help with holding, you are going to have one hell of a job getting the adaptor off again whenever you want or need to change props!

I don't see any problem with balance - all these adaptors seem to be well machined and imbalance of the adaptor is going to be far less of a problem than prop imbalance [obviously one can static balance the prop fairly well, but I don't believe ever PERFECTLY]. Unless you have found some way to exceed 20,000rpm on your prop, you'll be okay!!!

Cheers, Phil


Cheers, Phil

[bluemax1962]

Well I finally got the AXI mounted. I had to invert my mount design due to the large diameter pushed the limit of the cowl size. We suceeded none the less. A couple more cooling holes and I will be firing this thing up.

With the mount I could finally do a rough balance with (mostly) everything sitting on the bird. Lucky for me my desire to put the servos in the tail work out as workable. My intent to keep the battery under the CG seem possible. This is so I can swap large for small batteries and play with light performance vs. Heavy endurance and not loose my CG range.

Perry

[bluemax1962]

Well I finally made progress on the flaperons. I decided to go with off center scale hinge points. Servo mounts are in. Just some gap seals and hinge point reinforcements and I will be almost done. He is some pics to update.

[bluemax1962]

Another shot

[bluemax1962]

Well everyone......

After moving, job search and childcare I finally finished my Cub.

All the mods have worked out well (good advise got me there) :-)

All up weight came out at a somewhat disapointing 23 oz's. With the 1100 ma battery, the AXI and mods I shouldn't be real upset.

With a Lipoly I can shave another 2 oz and that is the same as stock weight. I feel better already .....:-)

Anyone have thoughts on control throws? I tend to put too much in for 1st flights! Suggestions please!!!!

Any how here is a pic of her. I will return to let everyone know how she flys. Just waiting for the Snow to thaw....(Hopeful for Saturday)

Thanks in advance

Perry