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Old Feb 27, 2002, 10:29 PM
Registered User
Gladstone, NJ. USA
Joined May 2000
408 Posts
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Dumas Bearcat with GWS Retracts..Need Input!

Hi Guys:
I purchased a Dumas Bearcat and a set of GWS retracts at the WRAMS show last week. I am determined to get this right! "Measure twice - cut once!" I really want to keep the airframe and finish as light as possible ...using any tricks and or advice the you (all) can offer. I've seen the article in RC Microflight where the builder used a brushed 280 motor...but I want to go somewhat lighter. Since I have not yet received the kit (Back ordered ). Lets start with the "Finish"..I'm planning to use the very light 5 micron Risteen "Micro-lite" covering which i've seen on a few models..dark blue of course! Receiver...I'm looking for the lightest "dual conversion" available.....Servos..I'm considering the "Wes-Technic" 3 gram variety..I've done some reading on them..It seems they will probably be up to the job. Retracts...Hmmmmmmm...well I've been thinking of using one of the same servos there also.(I have been looking for a really light weight retract servo...(one that cycles to the disired stroke and then either shuts off or powers down, to minimize the battery drain)but I have another idea..How about using an escapement mechanism similar in setup to the old single channel variety...rubber band driven..with a small relay as the trigger....It would give me positive movement (stroke)and cycles for as long as the rubber is wound! The only problem is how does one "Fire" a relay from the current type receivers that are designed for use with servos??? Can this be done. The advantage would be A. some possible weight savings. B. very little battery drain..(only to energize the escapement to cycle up or down retracts) Ailerons...I'm pretty sure I could use another Westechnic servo here also. Motor....Since I have had a great success with my Hacker B20-15L in my ol'timer, I would prefer a
really small brushless (smaller and lighter than the Hacker) or at least coreless motor. Perhaps mating 2 coreles motors on the same geartrain?
Batteries...perhaps Lithium polymer? BEC...thats a good question...i really could use your help here..I need a BEC that will cope with all this! That's rudder, elevator, ailerons, retract mechanism or servo...4 servos...
I have yet to run this through MotoCalc...but I intend to very soon.
Thanks for all your help in the past and future!
Sincerely,
Jon B. Shereshaw
PS. The GWS retracts are quite clever, but not exactly the little jewels I had expected. Whats with that klunker steel (music wire) strut? I would like to replace it with some very small carbon fiber tubing.
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Last edited by JonB; Feb 28, 2002 at 06:52 PM.
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Old Feb 28, 2002, 12:31 PM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
6,719 Posts
Good luck

A couple of pointers- the GWS R4P does pretty well for non dual conversion- otherwise FMA Extreme. Motor choices- how about an Astro 010 using a CC controller- reasonably light- very rugged. Maybe direct drive it it'll swing a 6.5 inch prop (8 cells NiMH?) Other choices- MTM S-100 Hummingbird?

Westech's are best left indoors. They break. Hard to argue with the HS-50s but give Pat a call and see what he thinks the lowest drain servos are.

Retracts- well if you haven't built anything like this before, maybe you should omit the retracts for your first try. Otherwise, I doubt you'll save all that much weight with your proposed escapement- just add a servo.

By the way, if I remember Tom Hunt's review- when he dropped in an 8 cell 350 pack, this litte 'Cat hummed. If you've got retracts in it, you want to be ahead of the power curve.

Sam
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Old Feb 28, 2002, 04:54 PM
Function Over Form
BillH's Avatar
Connecticut
Joined Feb 2000
1,043 Posts
I watched Tom Hunt fly that little bearcat at our clubs fun fly we did a few years back. All I can say is that plane is awsome the way he flew it.
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Old Mar 01, 2002, 06:47 AM
got any foam to bash?
Tom Hunt's Avatar
Lake Grove,LI, NY
Joined Aug 2000
5,406 Posts
Jon

The Dumas bearcat at 30" is physically the same size as a "ryan" speed 400 bearcat. It gets away with "good" performance with a geared 280 system because it weighed between 10-12 ounces, rather than 18-20 as a "400 version" would.

It requires more power than most models in the "30" class because of that big radial cowl up front. It glided like a brick at 11 ounces, but was a lot of fun under power.

To let the cat out of the bag so-to-speak, this weekend I plan to begin kit-bashing the hawker hurricane in the same series, though I plan on using a GWS IPS S-1 or S-2 system and the micro retracts. I hope it works well enough to take it to the Toledo Indoor fly-in April 6th.

I hope to keep it to 8 ounces with this lighter weight motor system and the corresponding lighter weight pack. even with the retracts and the extra servo, I think it is possible.

Regards
Tom Hunt
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