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Old 02-22-2017, 07:32 AM
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doxilia
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Originally Posted by lamarkeiko
I've been reading over again all the advice that David gave me, then going back to look at the DB to help put everything together in my mind. The first thing I've been trying to figure out is the best way to do a mechanical nose gear retract. I looked at some pictures of the Hobbico nose gear retract, and from what I can tell, this retract needs to be mounted on a horizontal plane to the fuselage. I don't think this is possible on this DB, because the fuel tank is right there.
Lamar,

If you are able to keep the Goldberg NG then this is moot but if you need a new retract you can install a belly/pan mount retract by first installing a 1/16" ply plate separating the tank bay from the gear bay. If you brace the sides with 1/4 or 3/8" tristock and epoxy everything in place, it should provide a good base for a 3/16" ply NG only plate glued to the FW, tank plate and sides, again with bracing on the sides. You will notice the Hobbico NG is quite shallow so this makes things a little easier.

I've set my DB40 up using a belly mount NG and just used a 1/4" ply horizontal former keyed into the FW and side doublers so it can be done space wise. I'm using a Sullivan 10 oz round tank which is supported around the cap by a 1/16" ply partial former between the end of the NG plate, side doublers and the fuse top blocks.

I think I need to stick with the original nose gear retract which is mounted vertically to the FW. I've had doubts that I could fit a mini servo in the retract compartment, but I got to thinking that could run the retract linkage back in the fuselage and put a mini servo close to where the other servos will be located. See attachment.
If you prefer to use the FW style mount then the Dave Brown (DB) unit is designed like that. You might have to drill two new holes in the top portion of the brackets in case your engine mount bolts interfere with the NG top bolts. My only complaint about the DB NG is size as otherwise it's well designed and works well. With that in mind, if you need to replace the FW, you can install a fresh mount and the DB gear while the FW is free. If on the other hand you're leaving the front portion of the model much as it is, then I'd suggest either keeping the CG gear or use a flat mount unit per suggestions above.

My thought has then been going to the main retracts in the wing. David first said he would personally go with electric retracts to clean up the unsightly bottom of the wing. this seems to be the easiest option. Do you feel David that the electrics will work as well as the mechanical? I want to install ones that have the least chance of problems later.
Electrics have had their issues and it varies a fair bit by brand. The main issue is that the electronics in the gear can fail due to vibration. This is more of a concern with the NG as it's clearly closer to the source and there have been many reports of electric NG failures in glow models. There have been fewer issues with electric mains but again it varies by users and manufacturers. There seems to be no correlation betweeen failures and cost so the less expensive units don't necessarily fail more often than the expensive units. That said, electrics are still not as fool proof as mechanicals but the latter can also have their issues.

In a earlier post I said that all three retracts were operated by one servo. I thought that the hatch on the bottom of the wing was to access the servo, and I placed a servo there thinking that was how it mounted. As I look at the top of the wing now, it looks like the servo mounted on top. I think the only reason the hatch is there on the bottom is so the nose gear servo linkage could be disconnected for removal of the wing. Maybe that would be still the best way to operate the main retracts. I can still get rid of that ugly hatch on the bottom. let me know what you think.
The mechanical approach with a central servo has been used for decades and it works. Use a servo such as the Spektrum suggested and setting it up should be simple. Note how the pushrods on the existing CG units are bent at the servo arm and you can copy it. Otherwise, you can use Sullivan spring loaded ball links which attach to the top of the servo arm with a 20-30 degree bend on the pushrods close to the ball links. This prevents the pushrods from binding when they are in the retracted position at the far end of the output arm.

I started stripping the cover fabric off the fuselage today. The canopy came up with the fabric, because it was glued on after the fabric covering was installed. I believe I can salvage it. One other thing that also came off with me pulling off the fabric covering was the ventral fin. It was apparently glued on also after the fabric was covered on the fuselage. That seemed a little odd
I'd recommend that you do all wood work repairs on a clean fuse after having brought some fresh grain to the surface. Do any needed fillets and when done you can glass the wood. I'd install the canopy after glassing as it's much easier. The canopy can be held in place by first constructing a 3/32" balsa canopy floor that fits inside the canopy. It will then have a large surface to fix it to the fuse. A finishing fillet around the canopy blends it in nicely and makes it all solid. If you plan to paint the canopy with the rest of the model, sand it up to give it a little tooth before primer. If you want to leave it clear, then you should finish the interior floor and other details you desire before gluing it to the fuse.

David

Last edited by doxilia; 02-22-2017 at 07:41 AM.