Comet "balsa" P38 rubber job

Ken Cook wrote:              The conversions I've made from rubber to glow never really flew well. I can only contribute that to the fact that the models true intent was free flight therefore it's construction doesn't lend itself to the rigors of glow. They require balsa sheeting from F-1 typically back at least 2 formers and the longerons usually need a bit of beefing as well. Comet kits were all generally print wood sheets. This is far superior to die cut due to it allowing you to make all the pieces the same by stack sanding. The wood however is mismatched at times for it's purpose and therefore when trying to cut a radius the wood wants to split with the grain.

I do know of a fellow who's plane was featured in Model Aviation and was also displayed on the Guillows website. I believe his name was John Reckner. He used a Thunder Tiger .07 for power in a ME-109 due to it's needed weight for the nose. I watched this plane fly and although it wasn't very aerobatic, it was truly a beautiful looking plane. He used many of the kit parts but cut Dow board blue foam for leading edge for many of the intricate parts that wouldn't allow the balsa to curve properly. Water based model paints were used in a airbrush and this plane looked great in the camo scheme. Ken

Thanks Ken, Yea... I had no experience with Comet kits at the time... and AHM's description was vague in their mailer/flyer catalog... (you remember those?) I now have the scroll-saw (Dremel) that I knew I'd "want"... to allow me to cut those printed pcs. out of their sheets... if I ever do decide to build it. Parts with questionable grain direction/hardness could just be traced and re-cut from a better sheet. I don't mind sanding... It was the thought of "knife-cutting" all those little pieces out "whole"... without breaking any, that kept me from building.



I made a plywood table-insert with a small hole for cutting small thin pieces. It works really well.

Geez...... I forgot I even had this... I gave it to my Dad for his Birthday back in 1993... along with everything needed to build it, except the engines! He's given me several un-built kits over the years, that he just didn't have any more interest in building.  I paid $19.95 for this kit in 9/93 at a local hobby shop.

The Sterling P-38 in my opinion would fly terrifically with 2 OS .10 MAX S engines. If you ever have a need for somewhat anemic engines, just place them on a twin. This twin would be perfect for them. My thoughts were also using 2 Medallion .09's which I think would be terrific. Too many people put 15's on this plane and when the power quits the plane makes craters in the ground. It has very little wing area. Ken

Ken Cook wrote:             The Sterling P-38 in my opinion would fly terrifically with 2 OS .10 MAX S engines. If you ever have a need for somewhat anemic engines, just place them on a twin. This twin would be perfect for them. My thoughts were also using 2 Medallion .09's which I think would be terrific. Too many people put 15's on this plane and when the power quits the plane makes craters in the ground. It has very little wing area. Ken

Ken... "Thanks for that advice"!!! Now I know "NOT" to use 2 Fox .15's that I have... One is good... the other was seized... and I mushroomed the piston when freeing it up; tapping with a wooden dowel...  

Ok...  concerning "making craters when the power quits with .15's..." are you meaning an "engine-out" scenario? If so; do C/L mechanics start their twins' outboard engine "first"... so it quits before the inboard engine? Should this be routine procedure on any C/L twin? Am I correct in assuming that it's better to have an "outboard engine-out" or quit first?

So I will have to obtain engines/motors for this model. CEF member Phil (pkrankow) is building an elec. powered Jr. Ringmaster... and I'm going to pay attention to how he sets it up. He's using a KRPKG-V2 governor/timer system w/esc for motor control using an 8-4 prop. Maybe X2 of his motor choice.. w/an esc to handle the extra current, would be a less docile yet "safer" way to go? The electronics/battery(ies) could reside in a "modified/built-up" center section with lightweight styrene fairings for a more "scale" appearance, attached with Velcro...  Maybe this would be too much weight... Is it the weight of x2 glow .15's that's too much for this models' wing area, in "general"?

Phil attached these links for his project:

http://www.rsmdistribution.com/index-2.htm
http://www.keithrenecle.co.za/Electric%20CL.htm
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=36717
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=37778
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=20331
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=35038

I have a N.I.B. mid-90's era OS .10FP r/c... but it's destination is planned for 1 of 2 un-built r/c kits that I have... an Ace "All-Star Bipe" or Sig/Herr Eng. "Little Extra" ARF.

Have you any experience with modern elec. control line systems? I am just learning about them.

Thanks again,
Roddie

Kieth's timer/governor is a single engine unit to provide a "piped run" effect.  It won't work on a twin.  (I probably shouldn't say "won't work on a twin" though.  There is currently published information for the concept from Kieth that I am aware of)

Using a "dumb" timer like an e-flite (which has retracts and not much else) with some high end computer programmable esc's with internal governors is a choice, although I seem to recall that someone on Stunthanger has a multi-engine governor/timer arrangement.

Of course if you go scale you can put 2.4gHz on and have proper throttle and retracts, and other features at will.  It's not like stunt where it has to run on its own.  This is naturally a whole lot more simple in today's technology.

The drive line I am putting on my Jr. Ringmaster is sized to swing a 8x4 prop with 5 minute run time on a 1300mAh battery.  It should compare favorably to a .15 size engine for power, but will weigh less.

I ruined a slant-head fox that way not long ago.  Traded it in on a Fox Stunt 35.  I should have soaked it in antifreeze or anti-seize  something.

Not an expert here, this is my first electric CL job.  I was just introduced to the concept of sizing a motor via the desired prop and thrust instead of power output.

Phil

Thanks Phil, You already know waaaayyy more than I, about elec. propulsion.

Just for the sake of conversation... would a motor/switch/battery config. w/a low voltage cut-off work for control line? Sure; a "timer" and ESC will "dial-in" contest timed runs, provide delayed-start and govern RPM's... But if you start with a "target-max" rpm elec. motor; given a certain voltage... to mimic a glow equivalent... which also runs a constant rpm (on a good run...) you could make it work?

I don't know SQUAT about "brushless" motors... Do they require an ESC, even for "single-speed" operation?

Thanks again,
Roddie

Yes they do. They use an electronic switching circuit in place of a commutator and cannot run at all without it. The circuit is of course placed in the ESC.

If you are going to take advantage of brushless motors and their efficiency and power, then you need an ESC. The difference between a brushless model motor and an industrial 3-phase motor is mostly scale (and permanent magnets) The ESC does the real work.

Similarly if you are going to take advantage of the long life of lipo batteries they need to be treated well, so using low voltage cutoff as your timer will shorten the life of the batteries, and provide inconsistent run time.

To drive the ESC you need a servo controller of some type. The EASIEST is to hook up a reciever and control it like RC, which is commonly done for scale and carrier.

The timer replaces the Rx to control the ESC, and may actively govern the motor.

Phil

Thanks very much. This helps me understand things better.

I have the 1/2A Sterling P-38 kit.

i have been planning to build a replica by tracing the parts.

I built this kit when it was new, and originally had a hard time getting it airborne.

I found it flew off the ground if I flew off of a hard surface and replaced the tires with streamlined types.

It was a lot of fun, and a real odd ball at the flying field. The sound of 2 Cox .049s was real cool.

Tim