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Feb 23, 2009, 06:47 PM
Pronounced "High Duck"
haiduk's Avatar
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Build Log

AmpMaster JR


I recently found some free plans for the AmpMaster Jr by Al Eastman and would like to build one. As usual I do a preliminary build in RealFlight to check flight characteristics and to use as a platform to test changes, etc. First I'm looking to scratch build a park-sized electric plane that is capable of 3D but mostly I'm after a good responsive sport aerobatic type plane. 400-450 sized outrunner would be perfect.

By looking at the plans it looks to be a fairly straight forward build, but I'd like to talk about some of the issues. Al's plans call for an inrunner in a gearbox using NiCads/NiMh batteries. I will be using an outrunner with a 3S lipo.

I wanted a 44" Wingspan, so the original plans were scaled down. The flat bottomed airfoil didn't provide the performance I was after so I built the RealFlight model with a fully symmetrical airfoil and that did the trick.

The mounting of the outrunner and the airflow through the fuselage is my biggest concern. There really isn't a lot of provision for airflow in Al's plans. I figured I'd add scoops to the right and left of the nose and a small hole at the tail for an air exit. Air should be forced around the motor and through the firewall then over the ESC and battery pack.

Here's the problem. When using an outrunner, the motor shaft protrudes out the back of the motor. In the event of a nose in, the lipo could shift forward and impale itself on the motor shaft. A destroyed fuselage is one thing, but electronics destroyed due to a LiPo fire is yet another.

To solve the problem, I was thinking about adding a second "firewall" to the front of the battery tray to keep the battery from shifting forward into the motor shaft. This might also have a secondary effect of channeling airflow over the battery and ESC better.

Any idea's here would be helpful. If any of you have a better method of handling this I'd love to hear it. I'd like to get these little details hashed out before starting to build the plane.

EDIT: Build Log starts here.
Last edited by haiduk; Mar 23, 2009 at 01:13 PM. Reason: Post formatting
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Feb 24, 2009, 04:51 AM
hul
hul
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I built one of these a while ago, 39" span: https://www.rcgroups.com/forums/show...1&postcount=14
My Axi was mounted to the back of the firewall. Cooling opening at the chin. And I ended up extending the nose by 40mm (from memory), but it could use more.

Eventually flew it with the Axi 2212/26, 9x5 on a 1200mAh pack. It was a good sports flyer with this lighter pack (first flights were on a heavier 2100 pack).

Hans
Feb 24, 2009, 05:14 AM
Pronounced "High Duck"
haiduk's Avatar
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I'm looking to build mine with a 44" wingspan. Hopefully in the 25-27oz AUW range. Probably use a 450-480 class outrunner. I modeled the plane in RealFlight and found I personally like the symmetrical airfoil over the clark Y. It seems to be considerably more stable during slow flight and handles inverted flight much better. I'm more interested in pattern type aerobatics than 3d stuff, but it would be nice to grow into a bit of 3d too. The sim model convinced me to build one, it really is a fun plane to fly. I think I will just mount the outrunner on a firewall with standoffs so there is a smaller chance that the LiPo will impale itself on the motor shaft during one of those unplanned immediate deceleration events.

At this point it's a matter of building light and strong enough to handle rough landings.

Quote:
Originally Posted by hul
... And I ended up extending the nose by 40mm (from memory), but it could use more....
Is there an issue with this design being tail heavy?
Feb 24, 2009, 01:01 PM
hul
hul
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it's ok with a heavy motor, todays little outrunners are too light to balance with the short nose. This is a screen shot of mine, side view is with the extended nose, top view has only the spinner moved.

Hans
Feb 24, 2009, 01:18 PM
Registered User
Not sure of your flying experience but I would lean toward the larger size (48 inch) if you are just learning aerobatics - even in close quarters. I built an Acro400 (18oz) with a 33 inch wing span after flying a Traveler 20 (43oz) with its 48 inch wing span and find the smaller plane to be almost too quick. Both are powered around 100 watts per pound.

I've been flying for about 5 summers and am at the stage of performing classical aerobatic: loops, Immelmans, Split Ss, Cuban 8's, rolls to inverted, stall turns and turns while inverted. I crashed the little plane twice last year while trying learn a knife edge - it went from wings vertical to inverter going down in a heart-beat. In general, when things get out of sorts, I find the little plane to be almost too quick for me to recover where in comparison, the 48 incher seems to be going in slow motion. Maybe it is just a size thing.

Best of luck,
Alan

PS I left space between the spinner and fuselage on the Traveler to let in cooling air - check out its nose in the picture.
And, I use Hans' exact power setup on the Acro400 - it almost lifts the plane into the air from a dead stop.
Last edited by Al Offt; Feb 26, 2009 at 07:47 PM.
Feb 24, 2009, 02:41 PM
Pronounced "High Duck"
haiduk's Avatar
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I've been flying since the mid '70s. Can handle most sport type aerobatics with the right plane, but as always, need more practice. 44" wingspan fit's nicely in the back of my car. About the biggest that will easily fit without removing the wings.

Looks like I will need to look for ways to lighten the tail a bit too.
Feb 25, 2009, 03:38 AM
Pronounced "High Duck"
haiduk's Avatar
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I am beginning to think I would be better off just building a StevensAero - G480 V2 (Re-Groove). There is a ton if info in these forums. Looks like it is the same size and similar weight. It would definitely be easier to build and would probably end up with a lighter final AUW.
Feb 25, 2009, 04:25 AM
hul
hul
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but where is the fun in building a kit?

Hans
Feb 25, 2009, 05:03 AM
Pronounced "High Duck"
haiduk's Avatar
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Easier I suppose. Still trying to make up my mind as to what I want to build next. I did spend about 100 hours or so modeling the AmpMaster for RealFlight. It flies very well in the sim. I just wish I had a laser cutter!
Feb 25, 2009, 08:30 AM
Build it, Fly it, Fix it!
Balsahack's Avatar

Ampmaster


Haiduk,
This is a great little aircraft. I used Al's plans for the Ampmaster and made a few changes to the build. I put in a JEN.37 2-stroke, with tuned pipe under the wing, seperate aileron servos, 6v lipo flight pack, etc. Goes like the clappers and does all the sports manoeuvres. I kept the Clark-Y and have not had too many cases of tip stall, but it will catch you out if pulled up too slow. Is very fast, especially in the landing and now use full length 1.5 inch ailerons in flaperon mode to slow things down. Extra throw from oversized ailerons, 52 inch wing and increased rudder area allow for some good 3D tricks, but hindered by Clark-Y. Found tail build to be light enough and with plenty of strength, although not sure if there are major differences between Ampmaster and Jnr versions. I am definitely a great supporter of this plan and think you should go for it. Much more fun than a kit build and a very versatile plane.

By the way, do you have the profile you designed for RealFlight? I run v3.5 and would love an Ampmaster profile for the rainy days - which we get lots of in the UK! Best of luck with your project and great design work too!
Feb 25, 2009, 08:42 AM
Pronounced "High Duck"
haiduk's Avatar
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The AmpMaster Jr I made for RealFlight is only for G4.5. I think I can do the conversion back to G3.5, but I'd have to reinstall the old software. I will see what I can do.

Here's a link to the G4.5 version if anyone is interested:

AmpMaster Jr 44


EDIT: Here's the G3.5 version:

AmpMaster Jr G3.5
Last edited by haiduk; Feb 27, 2009 at 02:32 AM.
Feb 26, 2009, 04:38 AM
Pronounced "High Duck"
haiduk's Avatar
Thread OP
Balsahack,

By chance do you have any photo's of your AmpMaster?

Duk
Feb 26, 2009, 04:54 PM
Build it, Fly it, Fix it!
Balsahack's Avatar

Pictures


Haiduk,
Currently as my avatar - that was before I made the canopy. Fitted an Acrowot cowl to hide the engine and ease maintenance. Will find some bigger pictures and post. Thanks for looking into the RealFlight matter.
Feb 26, 2009, 08:19 PM
Pronounced "High Duck"
haiduk's Avatar
Thread OP
Quote:
Originally Posted by Balsahack
Haiduk,
Currently as my avatar - that was before I made the canopy. Fitted an Acrowot cowl to hide the engine and ease maintenance. Will find some bigger pictures and post. Thanks for looking into the RealFlight matter.
Actually, I've been working on the RealFlight G3.5 version of the AmpMaster. Was thinking it would be cool to include the color scheme of your plane. I can't really make out enough detail from your avatar photo though.

EDIT: Posted the AmpMaster for RealFlight G3.5. Check the link in post #11. Remember this is a 44" version with symmetrical airfoil as opposed to the clark y.
Last edited by haiduk; Feb 27, 2009 at 02:45 AM.
Feb 27, 2009, 02:39 AM
Pronounced "High Duck"
haiduk's Avatar
Thread OP
I think I have decided to go ahead and build one of these AmpMasters. I went ahead and placed an order for a TR 35-30C 1100kv Brushless Outrunner (Eq AXi 2808). I have an extra 25amp ESC to use.

I'm guessing I can build a 44" version with a flying weight between 26-30 ounces like in the sim. That motor with a 10x6 should perform well and stay nice and cool.

Now to try out a few color schemes in the sim while waiting for the motor to arrive.


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