Speed,Combat,Scale,Racing > Scale Models
Small scale ship retracts, air or mechanical?
Chris McMillin:
Dear scalers,
I have a couple of Top Flite C/L Mustangs designed by Jerry Worth. I have one that I'm going to finish stock, fixed gear with a 3-line JRoberts throttle and electric flaps and radiator/oil cooler flaps for the optional operational stuff, because they're easy.
Retracts are hard. The spar is in the way. The wing is too thin. I dunno which system is best for C/L and it's CF issues. Can air systems overcome the CF? Is mechanical better? Can the little units hold up to the stresses of taxiing in a circle (or my landings)?
Any help is appreciated.
Chris...
chuck snyder:
Chris,
I use almost exclusively pneumatic retracts (Robart, Century Junk, and Rhom) , but do have a mechanical set that was in an R/C model. It seems to me that the real difference is in the quality of the construction. The mechanicals seem to be designed and built down to a lower selling price. Theoretically you could use as high torque a servo as necessary to move the mechanical linkage, but remember that one pushrod will be in compression and trying to buckle. I tried to build a set of retracts for a 1/7th scale Typhoon and set up to test for the CF as follows. Find the CG and weight of leg and wheel. Run a string from the CG horizontally to go over a pulley to a weight. I used a weight 3 times the weight of the leg and wheel. That's about right for 60' lines and 50 mph. Then see if your driver can move the retracts. With the Typhoon--long strut and heavy wheel--all I did was detroy the mechanism I had built. It had a jackscrew drive with plenty of torque. I decided the weight of a sufficiently strong retract mechanism would be too heavy for the model so built it as a fixed gear Sport Scale model. Once upon a time I had an FW-190, 1/8th scale, with pneumatic retracts. They sort of worked after I doubled up the number of cylinders and added a huge balance spring. My models since then have had rearwards retracting gear.
On the other hand, the Mustang gear, especially at the scale you are considering, is pretty short with a small wheel.
If you plan to use retracts as an option in competition you will probably have to retract the tailwheel too to get a good score.
Chuck
Chris McMillin:
Thanks Chuck,
If only I was a super machinist! But I am not even a bad one, so I'll have to use commercially available stuff.
Bob Whitely had a good mechanical system in his Rabe Mustang, but the wing was much bigger than this little 1/12th job, so I don't know if anything will work. It would look great though, if I could get all of the doors to close! I agree on the tailwheel, which I also had to figure out. The model is just too small...but Robart does have some small scale equipment.
The test rig sounds simple, sorry about your Typhoon gear. It is a beautiful model in the pics, BTW.
I feel like a 60 inch span model is about the smallest a fighter can be for reasonable retracts, weight and wing loading. I have redrawn (outline) a Red Box Top Flite P-39 kit. It isn't too bad and all of the Robart stuff seems to fit alright even though the new Gold Edition kit is really for which it is specifically designed.
I just wish I was a machinist (did I already say that?) so I could build a drive shaft to move the engine back enough to bury it. R/C car stuff?
Scale is hard.
Thanks again,
Chris...
chuck snyder:
Chris, I agree on the size of a model that can handle the "bells and whistles." I have also heard that mental challenges and exercise can prevent Alzheizmers disease. Scale guys should be in pretty good shape (if they don't go nuts from frustration first).
Chuck
Chris McMillin:
--- Quote from: chuck snyder on September 26, 2007, 06:54:44 PM ---Chris, I agree on the size of a model that can handle the "bells and whistles." I have also heard that mental challenges and exercise can prevent Alzheizmers disease. Scale guys should be in pretty good shape (if they don't go nuts from frustration first).
Chuck
--- End quote ---
I see what you mean, I have become a kit manufacturer for my 11 year old, and engineering is a tough deal when it has to look like something real when you are finished. Profile is even hard!
Chris...
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