Thread Tools
Sep 17, 2019, 06:55 PM
Big gov never Works
St. Martin's Avatar
Thats right, Bill. And having the bulkhead patterns, on the plan, allowed accurate pre-assembly of the bulkheads and notch check. I would build the vertical keel assembly over the plans, with tacked 1/16 sq balsa vertically for bulkhead locators. Start at the tail with the side keels then stringers. I think doing this type of assembly and learning what CG means, helped them start flying! Of course learning how to read, helped a lot, too.
Sign up now
to remove ads between posts
Sep 24, 2019, 10:33 PM
Registered User
AntiArf's Avatar
Thread OP
Strung the fuselage about as far as I can go, before installing the nose retract and tail feathers with internal linkage, as both areas need to be accessible to install the linkage. The nose has inset planking in highly curved areas to help form the 1/32" sheeting and provide sanding latitude for the thin sheeting in those areas. The cocpit area on this subject is more difficult that the Lear 23 I built a few years ago, as it has individual panes with straight borders, versus curved glass which is easier to terminate against the fuselage. This subject requires flat areas for the bases of the individual cocpit panes to rest against, which will need to be sculpted when the panes are fitted. The internal rudder linkage uses a bellcrank to correct the geometry, which is a more proper arrangement than running the servo driven pushrod into the rudder linkage arm at an angle. In the past I've routed the pushrod in from the top of the fuselage which worked fine, still at some angle to the rudder linkage arm. Doing that locates the servo higher in the fuselage, which I don't want to do with this build. The wing panels have 1/32" LE sheeting and sheer webbing between two stringers that run out to the aileron headers. Still a good deal of work remaining, constructing the nacelles.
Sep 26, 2019, 01:32 PM
Pro Hoarder
turbonut's Avatar
Nice work..I like the bellcrank! its well thought out!
Latest blog entry: In flight
Sep 26, 2019, 02:26 PM
Big gov never Works
St. Martin's Avatar
Very nice, Bill. I have had to use bellcranks in a few Mig-15's. I found the round wheels perfect for changing throw and geometry. A lot of variables can be had.
Sep 30, 2019, 07:58 PM
Registered User
AntiArf's Avatar
Thread OP
Not much to show as this precision work takes time, setting the retract mounts and nacelle construction. The retract mounts should require no thicker than 0.005" sheet plastic shims or thinner, to tweak their positioning. The subject has a high dihedral angle and sits with the nose pointing slightly downward, which need to be taken into account when setting the gear mounts, so that the struts are straight when deployed. That includes determining the incidence setting, so that the struts will not be leaning forward or rearward. The landing gear will retract less than a full 90 degrees, or the wheels would protrude through the top of the wing panels. Nice thing about mechanical retracts is that you can retract them as far as desired. The small Goldberg 1/16" wheel collars were drilled out to fit on the retract strut wires, and use #2-56 screws for the axles. Wish I had bought more of those collars when they were available, as they're smaller than the 1/16" Dubro collars.
Oct 08, 2019, 10:46 PM
Registered User
AntiArf's Avatar
Thread OP
Constructed the nacelle front portions, with the model sized for a tight fit using Hurc 250 Plus outrnners, no longer available. C20s would be a possible replacement, although I prefer the lower kv outrunners which run on 3s, not straining 12A ESCs with 7030 props, or 6030 3-blade props which will be used on this model. The motor mounting screws will be fed through the slots in the nacelle fronts, and then rounded scale caps will be added to the nacelle fronts. Thin shims will be required to tweak the prop angles.

The retract bellcrank arrangement was worth the added effort to construct, versus routing the retract pushrods directly into opposing arms of the servo horn. I've done that before, which requires elongated slots in the wing ribs to accommodate the back and forth pushrod movement, as well as bending the pushrods to route into the servo horn, which causes the pushrods to have a tendency to bow. The arrangement used provides more linear travel of the pushrods. The retract servo is a 180 degree pan servo, with 1.8 kg-cm of torque. The servo will also drive the nose retract, where the throw rate will be synced to the main gear. The push-pull logic for the nose retract is the opposite of the main gear, which is not an issue a ratio increasing bellcrank will be required between the servo and the nose retract, with the pushrods attached to opposite arms of the bellcrank which reverses the motion. Not adding the weight of an additional servo although I have one, and the throw rate would still have to be synced anyway to the main gear servo, or it would require a mix, which would eliminate the ability for dual aileron programming with a 6 channel radio.

The main gear struts are on the opposite side of the wheels from scale correct, which would not retract the wheels far enough into the wing if done scale like. The gear strut pants will still be on the correct side of the wheels however. The full scale subject has the wing skin flared outward around the wheel bays, which works well as the lower ends of my gear struts and pants would otherwise protrude below the wing bottom surface. As it is now the pants will need to notched at the lower ends to fit around the strut wires, and not protrude downward any further from the strut wires.
Oct 09, 2019, 11:59 AM
Big gov never Works
St. Martin's Avatar
I think this RLG system, is just too simple, for you, Bill..not enough tinkering. Looks real nice.
Oct 09, 2019, 06:12 PM
Registered User
AntiArf's Avatar
Thread OP
Thanks Fuzz. There's a few details I forgot to mention with the setup also. The retracts only need 11.5mm of pushrod travel, which doesn't take advantage of the travel ability of the servo, which would place a higher load on it. The arrangement now has 16.5mm of servo travel at the outer holes. The additional EZ link on the servo horn will be used to drive the nose gear, which now is fairly close to the position where it gains maximum mechanical advantage in the retracted position, taking load off of the servo. The nose gear will have a mechanical stop against the nose strut in the down position, so there's no issue with straining the servo there. Interesting to note that there's a small offset bend in the right retract pushrod in the previous photos, which was causing a slight bow in the pushrod when retracting the gear (not a problem though) at a mere mm or so. Bending the pushrods to fit into opposing ends of a servo horn which is commonly done, would have had issues that I've ran into in the past. The retract pushrod wire is also thicker than standard 0.032" wire, at around 0.039".
Oct 09, 2019, 07:54 PM
Or current resident
glewis's Avatar
Lot of moving parts in that linkage! Nice.
Where did you get those retract units? They look like the GWS ones.
Oct 09, 2019, 10:33 PM
Registered User
AntiArf's Avatar
Thread OP
Thanks Glenn, they're the GWS "blue" units. Probably wouldn't want them with stork looking leg length using the full strut length, but they seem adequately strong with the struts cut down to the length needed for this model.
Oct 16, 2019, 04:45 PM
Registered User
AntiArf's Avatar
Thread OP
Slowly getting something done. Finished inset planking around the wheel bays, and sheeting the retract/wheel bay areas with 1/32" balsa. The door shown below is dry fitted in place, where a notch is cut on the back side of the doors for the struts to recess into, making the doors flush with the wing bottom. The subject has raised farings around the wheel bays, which I assume reduce drag without the need for wheel bay doors, although the wheels do not appear to protrude much, if anything at all, below the wing bottom surface. Those parts were pre-sculpted and glued in place, with the wheel openings cut out to match the holes previously cut in the sheeting below. CA glue hardens the seam where the layers meet, making it easy to trim away the excess material with an exacto, while not cutting into the previously cut wheel bay holes.

Photo showing wing underside detail: https://www.planespotters.net/photo/...e-jetstream-t2

The nacelle caps will be rounded later, and are dry fitted to the nacelles with locator tabs. The back sides of the caps have a groove routed to clear the motor bells, which allows the motors to be mounted further forward, reducing the length of the already long prop adapters required for scale appearance.
Oct 28, 2019, 10:26 PM
Registered User
AntiArf's Avatar
Thread OP
More mechanisms finished. The nose gear doors will use a string closing mechanism, driven by a servo versus using the gear strut to pull the string and close the doors. When using the gear strut to pull the string, the nose wheels need to retract far enough into the fuse to avoid tire to door clashing, caused by closing the doors too early. In the past I've just managed to avoid clashes with little clearance to spare, as well as having to setup the string so that the doors fully close. This setup has a hysteresis mechanism driving a limit switch that will control servo power (pic 1). The fuzzy pic almost hides the off angle of the limit switch mounting block, as someone had the switch logic reversed initially late at night. I was able to easily relocate the switch and still use the mounting block, without having to alter it. The mechanism will ensure that the doors will fully deploy when extending the nose gear, but will only close the doors when the wheels are almost fully retracted into the fuselage. When the gear is fully deployed, the servo is de-powered. Not a great photo, but demonstrates the concept with the slide path in the bellcrank. It's likely the slide mechanism may not be needed and the switch could simply be driven by a bump on a bellcrank, as the switch has some hysteresis, and the door servo is faster than the retract servo, but best to ensure the doors are fully opened before the servo is de-powered.

The tail parts are now covered, with the tail attached to the fuselage and tail linkage/bellcranks installed. The remaining rear fuselage stringers can now be added and the fuselage sheeted, after a few pushrod support points are installed in the fuselage. The ailerons have been cut away and hinged, with the mass balancers also shaved for clearance. The balancers were cut away from the wingtips which were glued to the aileron ends, but not glued to the last wing rib in the area that needed to be cut away. The method avoided the effort of having to attach balancers to the ailerons and sculpt them to match the wing tip profile, as well as having to cut material away from the wingtips for the balancer paths.
Oct 29, 2019, 02:51 AM
Big gov never Works
St. Martin's Avatar
Moving along nicely, Bill! Balances are easy when done right, eh?
Oct 29, 2019, 04:51 PM
Registered User
AntiArf's Avatar
Thread OP
Thanks Fuzz. The only odd feature with building in the balancers, was angling the outer wing ribs to be parallel with the balancers. First time I remember building a subject and adding this type of balancer onto ailerons.
Oct 29, 2019, 05:13 PM
Big gov never Works
St. Martin's Avatar
I have never done an enclosed type balance, like that either. I suspect I would end up with a little filling.


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Build Log Handley Page Victor 46.5" span 30mm QX fans flight video AntiArf Scratchbuilt EDFs 124 Nov 06, 2019 02:54 PM
Build Log Giant Scale Airacobra P-39, 84" span Rengine Foamies (Scratchbuilt) 65 Apr 28, 2016 07:38 PM
Help! Handley Page Type 39 Gugnunc buildawyvern Free Flight 10 Oct 25, 2006 08:31 AM
"free" p51 scale plan (39" span) download Bare Scale Kit/Scratch Built 7 Mar 08, 2004 01:09 PM