doxilia

My Feedback: (3)

Lamar,

it is possible to use non retract servos for retracts but these days, it is not particularly desirable considering that modern retract servos DO have end point adjustment. The Spektrum 7000 series servo is one such example. Further, the advantage of retract servos is that they are designed to "disengage" once their cycle is complete. This means that the servo can't "hang" your radio by continuously drawing current. In other words, the servo powers up, rotates, and powers down. This way the battery is unaffected by these servos once the model is in flight and the retracts are up.

You can mount the servo on it's side but the other advantage of retract servos is that they are low profile allowing them to be set into the wing vertically providing easier access to the output wheel and any necessary adjustment. With modern servos these days, you basically hook up your pushrods, set the end points to "low" on your Tx and increase the end points until the retracts have fully cycled and locked. Sometimes it's 180 degrees (max throw) but sometimes the units require less. If they do, the advantage is that you can keep your output wheel smaller keeping things neat and tidy.

The main detractor of mechanical retracts is potential servo/gear hangup (due to usage and gear/linkage misalignment) if using the same power source used for the control servos. Using modern retract servos provides both EPA as well as servo cutoff so you can rely on the use of a single battery (to the extent that is actually reliable). Whatever the case, I'd strongly suggest you use a LiFe 2s battery when using digital servos as you are.

David

lamarkeiko

My Feedback: (1)

David,
Thanks for the reply back on retract servos. I never knew about the Spektrum retract servos with end point adjustment. The point that the retract servos only rotated 180 deg was a main concern for me, thinking that may give me more grief setting up. Unfortunately I have already ordered a Hitec HS-77BB low profile servo. It should fit in the wing fine, and have plenty of torque to operate the retracts. Just to understand your mention of a non retract servo drawing current, are you saying that it doesn't matter which direction, retract up or down, the servo will be drawing current? And if so, isn't that going to be a slow draw just like any other servo with sticks in a neutral position?
Lamar

doxilia

My Feedback: (3)

Lamar,

yes and no. Basically using a standard control servo on retracts is more risky because mechanical retracts have a potential for binding since they are subject to takeoff and landing forces. Any misalignment of the gear can cause the unit to bind (a wheel against the wing rather than the well for example) leaving the servo drawing current as it’s on a two throw switch.

Control servos are less prone to binding because controls don’t typically bind if setup properly at first and also, they are on proportional centered channels rather than an “end points” channel.

The HiTec will be fine but you’ll have to verify it has zero draw and/or binding at each end and use the output shaft to measure and locate required throw. Standard analog retract servos are 180 degree rotation end to end.

David

kdunlap

My Feedback: (12)

For what its worth, I just burnt up a hitec 225MG in a main gear installation on a Curare. The servo got jammed by the linkage and before I knew it, it was smoking. Totally torched the controller in the servo. That made me rethink the wisdom of using a conventional analog servo for the main gear. On the next go I used a TowerHobby low profile 180 retract servo. Tower Hobbies TS-59 Low-Profile Aileron BB Servo U Cost $29 and followed these instructions to the letter. End result is that they operate perfectly fine. Just a thought.

lamarkeiko

My Feedback: (1)

kdunlap,
The Tower Hobbies TS-59 servo has almost exactly the same specifications as the Hitec HS-77BB low profile servo I have on order. The Tower specifications on the TS-59 servo, do not call it a retract serve, just low profile. There is no mention of 180 deg rotation. So I am encouraged that my Hitec servo will work. Thanks for the link for mechanical retract installation. I've read the first page so far, and it is very informative.

Lamar

dhal22

Great thread.

doxilia

My Feedback: (3)

Hey Lamar,

any progress?

I’ve pulled my DB40 build from the rafters with the intention of making some progress over the holiday season. Hopefully I can get some traction early December as I’ll have some time available.

The honey do’s seems to pop up every time I get some time off...

Anyway, one wing panel built, one to go.

David

lamarkeiko

My Feedback: (1)

Yes, I have had my experience with honey do's. After 46 years of marriage, I have had my share. The returns have made them all worth while though.
I have made some progress since my last post. I finally have the retracts installed, and I believe they work satisfactorily. It took a bit of figuring out on my part. The low profile servo I purchased had to be mounted higher in the wing cavity than I would have liked in order to keep from touching my nose gear retract linkage and servo. With the servo sitting up higher in the wing cavity, it was then necessary to have a higher upward bend in the linkage. I had the retracts operating fine with my transmitter when I noticed that the spring on the left wheel strut was facing forward instead of to the rear. I didn't think this could be right, so I loosened the set screw for the strut and rotated it 180 deg. along with the axle. With that done, I then had to gouge out a new clearance for the strut spring to the rear. Once that was done, it brought me to the next problem. The wheel then fit much deeper in the wheel well than before, and now I needed additional bending of the left retract linkage so the wheel wouldn't make contact in the retracted position. With all that done, I operated the retracts many times with my transmitter, and all seems fine now.
Now I'm trying to figure the best way to construct a hatch cover for my retract servo and how it is suppose to blend into the wing. I'm planning on making the cover, then installing the rest of the 3/32" balsa covering on the bottom of the wing and around the retracts.
One thing that does concern me now is once all that covering is in place, how hard will it be to install the retracts and linkage back to the retract servo. If I'm missing something here David, I'd sure appreciate some advice before I went too far. I'm attaching pictures of the retracts before reversing the left strut and then the completed retracts and linkages. The final picture is where I'm at now making a retract servo hatch.

Lamar
2245920[/attach]')]DSCN2807 (2).JPG
2245921[/attach]')]DSCN2867 (2).JPG
2245922[/attach]')]DSCN2869 (2).JPG
2245923[/attach]')]DSCN2884 (2).JPG

lamarkeiko

My Feedback: (1)

A new update on my restoration progress. I completed making and installing the wheel wells. I had some concerns about being able to get the retracts and linkages hooked up to the retract servo once all the covering was on, but now I don't think that will be an issue. With the wheel wells installed, I didn't have any problem inserting everything back into place by using the hatch opening for the retract servo. So far, I have hooked up to my radio, and the retracts seem to work good.
Now I'm going to proceed to finish covering the wing bottom with 3/32" balsa. Then finish the Hatch. I'll post progress as I go.

Lamar

doxilia

My Feedback: (3)

Lamar,

good to see you making progress. FWIW, 3/32" sheeting is overkill on framed up classic wings. Particularly if you use vertical grain shear webs spanning the spars and rib bays.

The 21st century approach to framed up wings is 1/16" sheeting throughout (this actually goes back to the 1980's) and 1/32" skins on foam core surfaces (ideally reinforced in between with some CF or FG in strategic locations).

I guess the philosophy is to keep 'em light!

David

lamarkeiko

My Feedback: (1)

Yes David, I'm sure your correct as the 3/32" as being over kill, but that is what I took off the bottom, and that is the space needed between the ribs, leading and trailing edge sheeting. This plane was built with lots of heavy thick balsa. I don't know what it may have weighed originally as completed, but I'm sure I will be lightening it up some during my restoration with mini servos, foam wheels, and I believe the retracts are lighter.

Lamar

lamarkeiko

My Feedback: (1)

I finished applying the sheeting on the bottom around the retracts, and did some sanding and blending in the bottom hatch. This was a fairly easy process.
I could now use a little advice as I move on the next phase of the wing restoration. I want to glass the top and bottom center sheeted portions of the wing. I don't want to add any unnecessary weight if I can avoid it. My initial thought is to just glass the middle top and bottom portions of the wing, then cover the entire wing with Koverall and paint. Does this sound like the correct approach?
The next question I have is about the large gap between the wing fillet on the fuselage and the wing, once the wing is bolted down. Should this just be filled in with a bead of epoxy and micro balloons on the bottom of the wing fillet, or is there another method that should be done. Also the wing incidence. I don't know what it should be, or how to check it. Should I also be concerned about that now?

Lamar

bentwings

You are doing very well. Not sure why you have the gap around the wing. The fillet is important on these planes as I recall. Something to do with air flow. I always had smooth blended fillets and a pretty sharp edged where it contacted the wing. So say fill,it in with something light and blend it to the wing. Look at P 51 fillets, the DB is similar. I used to use a silicone rubber sealer too so there was no leakage into the fuselage. This came from the older guys back then, not my invention.

Im pretty sure all of my DB's both 40 and 60' had 0-0 incidence. My original,incidence gage was purchased when I built the first one.

i used to use 2-4 oz glass cloth installed with thinned epoxy on the wing center. Probably over kill as noted above. The first couple DB's survived crashes with minor repairs but the really high speed ones.....well the wind usual blew most of the pieces away before I got to them. Kicked dirt over the rest. LOL. I was Into top fuel drag racing then too so model airplanes were small change compared to the $$$$ turned over in drag racing.

as far as weight goes my 40's used to weigh in the 5 1/2 -6 pound area. Radio stuff was pretty heavy back then. I did use the Kraft streamlined wheels which were very light. All but my first one also had muffled tuned pipes. The later ones with the 6.5 and 7.5 ducted fan motors ran through the canopy. About 4-5 years ago I finally tossed the fiber glass canopy mold in the trash. Sorry.

lamarkeiko

My Feedback: (1)

My center wing joint is already covered with a 2" wide heavy glass/epoxy reinforcement. I need to cover the rest of the bare sheeted balsa top and bottom center section with 3/4" glass cloth & resin.
My wing fillet flairs up from the outer edge where it should be contacting the wing, about 1/16" all the way around. It is bare plywood on the bottom. I'm guessing about 1/32" thick, with epoxy built up on the top.
I'm thinking I could laminate a 1/16" layer of plywood to the bottom edge to fill in the gap between the wing, then sand and fill voids on the top side with a epoxy/micro balloons mix to make a nice smooth fillet to the body. I'd appreciate any recommendations.

Lamar

bentwings

I think the original filet probably has epoxy and filler. You could use 1/64 ply too. It would make a more durable sharp edge. This may have shrunk over the years thus leaving the gap. Yeah just fill it in. I think I'd just use some balsa to save a bit of weight. Then 3/4 oz glass it.

When I was building and flying these, I worked in a shop and did some paining. Auto acrylic enamel with hardener was popular. I painted most of the planes I built with this stuff. I thinned it heavily. Also there was very light auto primer. It was super light so I thinned it too. I glassed the models with 3/4 or 5/8 oz cloth and epoxy thinned with alcohol. Not rubbing alcohol but " pure" stuff we used in the race cars. This only has a bare minimum of water less than 1 % or so. I know you are not supposed to thin epoxy like this but all it had to do was attach the glass cloth. Some of the guys I flew with went a step further and used thinned dope for this instead. From there one coat of thinned light primer. I sanded with 400 grit and one thin coat of paint. In painting I only painted the white ares that showed white. The colored areas only overlapped an inch or so. I didn't paint the whole plane white then half of it orange or other color over it. Too much excess paint weight.

i would not use acrylic enamel and hardener today. This stuff is extremely toxic and you need an air supplied respirator to safely work with it. Automotive paint is far too expensive today plus it's very complex to get a system together. I had almost $400 in paint supplies just to paint a fender on my truck.

there are water based paints but you will,have to test compatibility with nitro fuels. Paints are quite a bit different today. It's probably why modeler so generally use films.

I'd just use model,paints. My last Warbird was painted with house paint but that's a "gasser".

lamarkeiko

My Feedback: (1)

Thanks bentwings for the reply back. I like the idea of using balsa as a filler and then covering that with 3/4 oz glass. That will be much easier to shape, and the glass & resin should give plenty of strength.
I have been considering using Minwax polycrylic for the glassing instead of resin. I read & saved a procedure on using it, and I thought that might save some weight. I have used it in the past for attaching and sealing Sig Koverall with good results. For painting, I'm planning on using an automotive primer from a can, but for the final paint, I haven't figured that out yet. I've used Rustoleum in the past with good success, and it is fuel proof. The only problem with Rustoleum is the color choices are limited. My neighbor recently purchased a 2017 Camaro , and the color is called Crypton green. I'd love to use that color. Should be very high visibility. I just don't know how I could come up with that color.
Lamar

lamarkeiko

My Feedback: (1)

The latest update. I tried the suggestion bentwings had on filling the wing fillet gap with balsa, and it was very easy, and I think it will work great. I still need to cover the bottom of the fillet with 3/4 oz glass & resin, then shape the top edge of the fillet to a finer edge. Last will be add some more epoxy & micro balloons to the top of the fillet.
One thing I'm not sure of is the bottom of the fillet behind the wing. Should this part be built up to blend in with the bottom of the fuselage? If anyone could submit me a photo of this part on a Dirty Birdy, I'd appreciate it.
Lamar

bentwings

Yeah, that area needs to be filled in nice and smooth. You will probably have a notch where it blends with the wing. I think on your restoration I'd lay a piece of 1/64 ply from the fuselage edge out to maybe a 1/4 lunch past the existing filet. The object is to keep a nice sharp hard edge up to the filet on the wing. Obviously make both sides the same. Since your filet has lifted with age try to blend in as well as you can the wing side should be as sharp as possible. The sharp edge gets a bit delicate that's why the 1/164 ply base. You'll have to use some light weight filler too.

imhad a large dowel about 1 1/4" diameter to blend the final shape. Wrap it with sticky back sand paper.

byron

lamarkeiko

My Feedback: (1)

Byron, do you mean to put the 1/64" plywood on top of the built up balsa I did to get rid of the gap? Is that so I can make a nice sharp edge where the fillet meets the wing? I don't have any 1/64" balsa, but I think if I put on a bottom layer of fiber glass cloth and resin, that should be able allow me to shape a nice smooth sharp contact with the wing and be fairly strong. Let me know if I'm understanding you correct.

Lamar

bentwings

Sorry I didn't look close enough at your pictures. Your filets have shrunk or lifted which ever way you look at it. You don't have much choice but to continue the blend even if it extends the filet a bit. Just guessing it looks like you can add about a 1/4 ". In your case I think glassing will be ok. On the bottom just use your favorite light weight filler and blend with the wing. You are going to have a step there but it will blend in ok I think. Again glassing to stiffen the sharp edge will be ok. Just be carefull handling the plane.

Fillers like sparkle and the hobby version tend to shrink over time so you see the result. The 1/64 plywood comment I made was probably in error....typing before observing and thinking..sorry if I confused you. You will be ok as you are doing. It's a lot of work forming those filets but they look nice and are supposed to help aerodynamically. I never built one without them so I can't give hard data.

i like to use the 1/64 plywood on these as it is easier to get a razor edge. I often build trailing edges with 1/64 plywood too so they are more ding proof. Sharp trailing edges also have an aerodynamic effect. Again I have not tested this only followed the leaders and full scale. Many full scale planes have very shap trailing edges. If you were to scale these down to model size, a razor blade might be considered dull. Years ago there were endless debates on model construction whether to just round over the trailing edges or sharpen them. Some said the controls were less sensitive around neutral with blunt edges, some claimed more or less chance of flutter both ways. I guess I just felt the planes looked like the builder took more time to make a good looking model.

Byron

lamarkeiko

My Feedback: (1)

Thanks Byron, for the info. I want to give an update on a discovery and correction I made on my main retracts last week. If you go back and read over post #33 I made, maybe the experts can figure out the cause of my problem. I had issues with the right retract. Last week I had been looking over a lot of Dirty Birdy photos I had saved, and one photo was of a set of Hobbico mechanical retracts from the Tower Hobbies web site. As I looked at the photo, I noticed that spring on the struts was wound in opposite directions on the main retracts, so that the springs would both be facing rearward once installed. I went back to look at my struts and discovered that my strut springs were the same. What I had was two right hand retracts that I had been trying to make work. I went back on to the Tower web site and found that the Hobbico retracts were no longer carried, but Tower still had some replacement parts available, and that included the left and right struts. I had purchased the Hobbico retracts last March, but I decided to call Tower customer service and explain my problem. To my pleasant surprise, Tower sent me a left hand strut free of charge, and it arrived in two days. I immediately changed out the strut, and fortunately had not cut out the clearance for the strut spring yet in the bottom sheeting. The wheel now doesn't sit real deep in the wheel well as before. and now matches the right side in how it sits. Gives me plenty of clearance from my linkage.
Lamar

bentwings

Nice bit of detective work. I think you are in line for detective lieutenant.

lamarkeiko

My Feedback: (1)

I'm still slowly making progress on my restoration. I covered the top and bottom wing sheeting with 3/4 oz glass using Minnwax polycrylic. The process was very easy with the Minnwax. I finished up the balsa filled wing gap, by first coating the sanded balsa filling with thin ca to harden the surface. I then coated the wing fillet surface with Z-Poxy finishing resin, laid on one layer of 6 oz glass cloth, applying more resin to soak in, then mounted the wing firmly in place until hard. I had applied a non stick teflon tape I had around the wing prior to attaching the wing. I think the results turned out fairly well. Once the glass was trimmed around the wing fillet, I had a nice solid edge on my wing fillet.
I've also finished filling in the rear portion of the wing fillet with plywood and epoxy, blending it in better to the fuselage. I'm now in the process of filling in the top of the wing fillets with epoxy & micro balloons. One side is done, and will do the other side today. I'll attach photos once complete.
I have one request for anyone who knows. I don't know what the control throws are for the DB 40 or where the CG is. I haven't been able to find that info on line. It would be nice to have a copy of the original DB 40 build manual if that was possible. Does anyone have a pdf file of that they could PM me?
Lamar

bentwings

Can’t help much there. I remember there was not much weight on the nose wheel.

doxilia

My Feedback: (3)

Lamar,

can't help you with the instructions as I have none. However, I can tell you that the CG is 6" from the straight TE (or from the rear bulkhead if that helps). As for control throws, I would go with standars for classics like 3/8" up and down on ailerons, 1/2" on elevators and 2" on rudder. On high rates. Then dial down on low rates to suit, Say 60-70%.

David