My Berkeley Stinson SR-7

[E-Challenged]

I have a detailed and lengthy build thread on E-Zone about this model. The 70's era SR-9 kit was designed for freeflight or control line .099 glow power. I converted from the "modern" curved windshield SR-9 to the more classic 1937 SR-7 version with flat plate windshield following Wylam drawings. This is a short nosed radial engine design so I had to minimize weight in tail and mount lipo pack protruding through the firewall to the front of the cowl ( lessons learned on GWS Zero) I'm using an AXI 2212/20, Polyquest 1100mah 3S lipo and 8x6 GWS slowflyer prop. Balance is perfect with no extra nose weight. Linkage to rudder and elevator is via Dubro micro pull-pull set up. Tailwheel is linked to rudder by sort pushrod.
Ailreons are controlled by a single servo and linkage is by bellcranks set up for differntial throw ( not much down elevator). Cowl ring is held on by Velcro. Battery changes require removing prop, remove cowl insertand connect pack, install prop , taxi out and go fly. I still need to install short step ladders on the sides under the side doors and install windshield panels and side windows. Pilot is a Williams Bros bust. I made him a torso arms/hands and legs and a seat. I made a three spoke "steering wheel"
from brass tube and solder for the pilot to hang onto

[Big_Bird]

E, great looking plane. Could you provide us a link to the build thread? You gonna paint the prop?

Ken

[E-Challenged]

http://www.rcgroups.com/forums/showthread.php?t=304704

[Doppelganger]

Some of you people are truely amazing. If I had half the patience, and a 3rd of the talent, I'd be a happy camper.

Steve

[E-Challenged]

I'm slow but sloppy and change my mind a lot . I had a lot of good suggestions from others during the build. I've been gluing sticks to formers and ribs since about 1950. Biggest breakthrough was learning to mount lipo packs protruding through the firewall into the cowl to get plane balanced. Use of brushless and lipo technology greatly improves power to weight and weight to wing area ratios making small scale models fly a lot better and longer with less damage during landings.

[mmmdowning]

Wow, really nice job. It looks like a large scale. Well done.

[Doppelganger]

Originally Posted by mmmdowning

Wow, really nice job. It looks like a large scale. Well done.

I thought it was a large scale at first also.

[Boomerang]

Lovely job, looks great! A friend has a large ARF Boeing Peashooter he converted to electric, batteries in a similar position, & he loads them from the front through the cowl & under the motor without removing the prop, is this an option that you didn't consider? - John.

[E-Challenged]

Originally Posted by Boomerang

Lovely job, looks great! A friend has a large ARF Boeing Peashooter he converted to electric, batteries in a similar position, & he loads them from the front through the cowl & under the motor without removing the prop, is this an option that you didn't consider? - John.

The cowl ring opening is a little too small to get battery pack in or out, so must remove prop and cowl ring. I really need a non-metallic prop nut wrench to avoid prop twitching. I firmly hang onto prop while removing nut just in case it wants to try spinning. Same situation with my Guillows PT-17 with ring cowl and 12mm Faigao in DXA gearbox/400mah 3S Lipo.

[E-Challenged]

I started a new "Pre-Maiden" thread on E-Zone and posted these pics showing Ham Standard display prop, cockpit door step ladders and windshield and side windows installed. Dremeled, carved, filed and sanded old wood IC prop to look like Ham Std ground adjustable pitch prop as used on the SR-7. Covered it with chrome monokote. Should have painted it with Balsarite and stretched monokote tighter, some wrinkles but looks good from a distance. Ham Std logos copied from a website and resized on my PC.Gotta cut wing numerals from orange trimfilm and it'll be finished. (I give up trying to post pics on this forum, file size must be too small to show details)

[E-Challenged]

Have read good reviews of the DX-6 spread spectrum system intended to protect park flyers from interference from other modelers, RF in the enviornment, and electrical noise from inside your model. The system is relatively inexpensive at $199.95 if it will protect my "labor of love" Stinson sR-7 so I ordered one from Horizon Hobbies in Ontario, Cal, some 40 miles away. It showed up via UPS the next day. The receiver is tiny and weighs next to nothing, has two 3.5" antennae. The transmitter utilizes multi-use progammable switches for dual rates etc. The 4 servos are about same size as Hitec HS-55's . The receiver can use any brand of servos. The transmitter can store memories for 10 models. Extra receivers cost aorund $60 each and are currently on back order. The setup procedures for dual rates, mixes, etc., in the user's manual are more complex than I expected. The flap feature has only one position. This system is intended for park flyers and has adequate range for them. The "full range" system will probably have more features.

[E-Challenged]

After a number of attempts at flight I found that the model was grossly nose heavy and over powered with the AXI 2212/20. I changed from the long 2200mah Lipo pack to a much lighter and shorter 1100mah 3S lipo located farther back to help nose heaviness. I installed one of my $19.00 Esskay 400XT outrunners with 3mm apapter. Plane now ROG's much better reponding well to ailerons or rudder or a mix of both. Plane still needs ome up elevator. I plan to increase the wing incidence from the "control-line" to "free-flight" angles shown on the ancient Berkeley plans which should make it an easy scale-like flyer. I have been flying with wheel pants off, yech!, but will soon have it flying well enough to land fly pants-on.

[E-Challenged]

Increased incidence helped a little, still needs a little up elevator trim. Tends to drop one wing or the other needing frequent leveling of wings.One of the wise men noted that the outboard ends of both ailerons were twisted downward giving a possible "wash-in" effect. The sharply tapered gull-wings are tip stall prone anyway and "wash-in" can't help. I'll make some new ailerons with an upward twist to give some wash-out effect. Maybe I'll install two aileron servos and use differential settings for up aileron and no down.I'm tempted to build a straight wing for it and call it an SR-5. It would fly slower and more scale-like with increased wing area.

[Don Sims]

E-Challenged, thanks for posting your comments on a fantastic looking plane. Good luck on the wash-in elimination!

[E-Challenged]

I heated and twisted ailerons and adjusted them to give wash-out and went flying. Connected ailerons to aileron channel and rudder to rudder channel. Took off, trying to keep wings level with ailerons, plane circled to right and bounced, no aileron response. I switched on aileron/rudder mix and it took off and flew fine with a little left rudder trim. I now realize that I should have built the wing flat without dihedral to get better aileron response. I also decided that I had way too much down and right thrust based on the tendency to circle to the right. The plane responds to ailerons well when in cruise flight or faster but may need rudder to keep wings level during take-off run.

I am no beginner at this scale model stuff but have learned and re-learned a lot with the Stinson project.

[easytiger]

Nice work! But you found out the Achilles heel of Berkeley kits...weight.

[Big_Bird]

Originally Posted by easytiger

Nice work! But you found out the Achilles heel of Berkeley kits...weight.

I'm a bit puzzled, just how does this tie into his warped wing problem?

[easytiger]

Huh? Wing is not warped. Plane suffers from being overweight and therefore critical. Not the end of the world, it will still fly.
The dihedral/ailerons thing is another issue, but can probably be managed with C-A-R mix.

[E-Challenged]

The durn thing has settled down into a predictable flyer with no bad habits using coupled aileron and rudder. I even put 'er into a short dive and looped 'er yesterday, recovery was smooth. So now it's one of those scale models that takes off and flies racetrack style and flies and lands a little faster than the real thing. If I ever get ambitious, I might build a new wing without dihedral and increase aileron size a little. Gotta get some flight pics.

[E-Challenged]

Really lousy shot just to prove it does fly. Loops nicely, lands with pants on.!

[Big_Bird]

Must be from a cell phone. It's really a neat looking plane. Congratulations on your accomplishment.

[E-Challenged]

Originally Posted by Big_Bird

Must be from a cell phone. It's really a neat looking plane. Congratulations on your accomplishment.

My friend Gene shot those with my digital Oly camera, forgot to zoom in, had to crop. Flight pics I took of his plane came out great

[E-Challenged]

Here's a better flight shot, looks good in air with pants on. On to next project, 70's Sig J-3 Cub with old Astro 25 geared and 16 cell 1950AUP Nimh pack. Have "clip wing" kit.

[Big_Bird]

Looks great. A bit off the subject but since you mentioned an Oly camera.... I took this photo on July 4 2005 with my Olympus C-750 UltraZoom. The plane is a Buccaneer.

[E-Challenged]

Originally Posted by Big_Bird

Looks great. A bit off the subject but since you mentioned an Oly camera.... I took this photo on July 4 2005 with my Olympus C-750 UltraZoom. The plane is a Buccaneer.

Mine's the C2100UZ ( 12X optical zoom), here's a pic I took of buddy Gene's new Wattage Camelphokker yesterday. Power is Esskay 400XT outrunner and 1100mah 3S Lipo 9x5 DD prop