Re: Sig Akromaster build.

**Cribbs74** Sat Jan 11, 2014 9:14 am

Yeah perhaps not, the Fox 15 is 3.6oz and the Cox is 4.2oz

Not surprising really, Foxes are usually lighter than other engines of the same displacement.

I would bet the Cox is more powerful though.

Ron

Ken Cook Sat Jan 11, 2014 9:28 am

There was a great article in the 80's, possibly Flying Model's that featured the Akromaster with mods using the Medallion .15. The Cox .15 Medallion would work fine in my opinion. Certain features of the Akro which I don't approve of is the split elevator for instance. The kit uses a piece of basswood to attach both halves. For those interested in using the Enya, your going to require almost 3/4 oz. of tail weight even with foamy wheels up front. This still leaves the Akro nose heavy. I was also using a tongue muffler which is far lighter than the stock Enya. If your not using any muffler, which I would highly recommend the balance should be just right. To assist in the cg shift and to improve the design, I would make the entire elevator from a piece of basswood. Tanks can be a bit of chore locating them on the nose due to conflicts with gear wire and muffler placement if used. However, I would highly recommend taking a bit of the nose off to once again shift the cg. Why keep adding weight to the plane due to it already being over worked. The Akro needs a touch bit more wing area and you will improve the flying ability of this plane by adding one rib bay to each wing tip.

I have built a few of these over the years and the last one I did had the wing shifted forward in the fuse about 3/4". In addition, swap the stock control horn to a larger horn as this will calm the twitchiness that's readily apparent with .15 sized models. Start out with the bottom hole and fly the model working the pushrod wire up a hole at a time until your desired turn rate is achieved. This was the best flyer out of the ones I had. I would highly recommend having the centerline of gear axles finish out in front of the leading edge 1 1/4"- 1 1/2" otherwise the plane trips on it's gear and flips rapidly over on landing. Here's a pic of my last Akro built about 12 years ago. My son flew this plane forever. It now collects dust hanging on the wall with it's covering all split. THis was the covering job that taught me how to use plasticizer.WHile the picture does this plane a lot of justice, the silkspan is splitting right next to several of the ribs. All ribs and gussest have a radius sanded on them which is a real good practice to avoid issues like this. Dave Brown makes an excellent product which can be added to dope which is Dave brown's Flex All. The dope on this plane is Brodak's which is really broken down by UV. This is exactly what happened to this covering and while Brodak used to make a rejuvenator for this problem, it's no longer made. The only fix for this is to completely strip the model and recover. Dad's stripper from the home center will make quick , clean work of that task. I just have a ton of projects to finish so this one now will sit and be a dust collector for some more time. The last outing with the plane we were flying a "Stinky" engine which is the diesel on it in the pic. What a shaker that was. Ken
Sig Akromaster build. - Page 2 Dscn2124

duke.johnson Sat Jan 11, 2014 10:32 am

You do want to keep this plane light and engine will help. For Mark and Richard, flying at Delta Park, no mufflers required will help.

I've read a lot about the Mod's for this plane, if I were a new builder and just wanted a good flying plane, I would build it stock and put a unmuffled Fox 15 in it. I think I'm going to lengthen the fuse and wing span on my next one. But mostly because I want to go electric with it.

We have had a few of these and they are great little planes. Ken is right on about the control horn length, that will help tons. If you read up on this plane , you'll find about half the guys say use the mod's and the others not.

RK Flyer Sat Jan 11, 2014 10:57 am

WoW! Thanks to Ken & Duke for the heads up!
I knew there was a good reason I havnt started the build yet, now I can do a little more research.

RK Flyer

Edit for a couple of questions,

Jim, What is the length of the wing? What would you recommend to hold the Landing Gear?

Ken, Since you moved the wing forward 3/4" & the landing gear in front of the wing, and the plane builds tail heavy, would you recommend cutting a new fuse 3/4" longer?

Thanks to every for the info!!

Ken Cook Sat Jan 11, 2014 11:32 am

The Akro doesn't build tail heavy. The Enya will make it nose heavy. I shifted the wing to throw some tail weight to the rear. In the pic, you can see the lead weights buried into the fuse on the one side. This really isn't enough weight. I will say this, every kit is different and therefore, I'm giving a generalization of engine vs cg. Not everyone builds the same in terms of glue, paint, wood choice. Directly out of the box, the plane will fly just fine if balanced correctly. I just felt there was a lot of room for improvement. If you did choose to build the fuse longer, I feel it would benefit the engine choice your deciding to use. It really doesn't take much weight in the rear to compensate for a nose heavy plane. When it builds tail heavy is when you run into problems due to it requiring a lot of weight up front. I had this similar problem with the Ringmaster JR. I lengthened the Ring fuse 1 1/2" to get it to balance with the Enya. One thing I found through the years was keeping a log in terms of building and flying. Lately, I've been very lazy in filling it out. I found that the Enya really liked to turn up a bit and using a APC 7x6 improved the speed and maneuverability of the plane. Ken

RK Flyer Sat Jan 11, 2014 12:10 pm

Ken,

You are right about everyone & every kit being different, so many variables!
This will be my first build of a larger than 1/2A plane so I want to start off on the right foot.

What do you think of a Mc Coy 19 size engine? Would it be to big & to fast ? I have both types the red head & the Testors series 21.

RK Flyer

Ken Cook Sat Jan 11, 2014 12:56 pm

If your asking in regards to using those engines on the Akromaster, both engines weigh far too heavy for this plane. I did have a Akrmoster using the redhead Mccoy .19. This took a chunk of lead so large in the rear that if it ever fell off it would've knocked someone out. Your Enya .15 would outpower the .19 . The series .21 is too heavy period. I do believe the Akro states engine sizes from .15-.19. The best flying example I've witnessed was using a FP .10. The .19 size displacement was somewhat of a funny size in terms of kits. They were recommended on most .35 size models as the box would state .19-.35. A general rule of thumb is if the plans state 2 engines sizes, go for the larger. The .19 though would fly most .35 models which suited the beginner just fine. In the situation of the Akro, the .15 would suit the model far better due to wing loading. The Mccoy .19 wouldn't make the plane fly any faster than your Enya. In fact just the opposite.

The Mccoy redhead line of engines just didn't have very good quality control. While many have used them successfully including myself, I can list dozens of problems associated with them. The Enya that you plan on using is made far superior to the Mccoy. The series .21 engines were Dyke's ringed engines which was a giant leap for Mccoy but the case known as the "Brick" was just heavy. While the series .21 engines far outlasted the redhead series, they came out too late in the game and never really had the support that the other foreign engines were gaining rapidly. Ken

OVERLORD Sat Jan 11, 2014 1:38 pm

I don't know if you saw this video concerning an Akromaster with an ENYA .19. It shows the CG.

https://www.youtube.com/watch?v=9STm_rWn97g

Lieven

batjac Sat Jan 11, 2014 2:51 pm

Cool! There's a video on YouTube of a guy flying an Akromaster with a Medallion .15! Even has the muffler on and closed. It seems to have plenty of power to pull the plane around. He does several consecutive loops a couple of times in the video. He didn't do any inverted, but maybe he's not comfortable with that yet.

https://www.youtube.com/watch?v=Ly3w7yLJTpI

I can't tell by looking at the video whether he's making the plane oscillate up and down on purpose, or if it's unstable due to a rearward C.G. and that's making it oscillate. Ah, well. My question about whether it's enough power is answered. Anyone got a guess as to how long his lines are?

Thanks for the input, Duke and Ken. I'll think on it for a while whether I mod it or not. Duke, where did you read about the mods? Stunthanger? And Ken, any idea where I might find the article about the Akromaster with the Medallion?

The Answered Mark

Ken Cook Sat Jan 11, 2014 3:13 pm

I have the article but like most, I saved the magazine but didn't mark which one it was. I had all intentions of doing exactly what was in the article. It maybe very well possible that the Medallion might require a touch of nose weight due to it's weight. As Duke mentioned, the Fox .15 was I believe the engine of choice. Many would rather throw the Fox .15 as it's achieved hurling status amongst a certain group. I like the angled plug Fox .15's. They're little screamers and truly a pleasure to use. A modern prop like the APC combined with shifting the engine out on the beams slightly may just correct any issues. I didn't watch the video, but hunting can be caused by several issues aside from a incorrect CG. You have my vote, build it and go fly it. We need some video!!!. Ken

I just went and watched the video, looks to be an excellent build. I also like this fellow due to prop choice. If you take note, the Medallion he's using is on a muffler which I find also impressive as it doesn't seem to be struggling for power. Very cool. A typical line length for a .15 size plane is 52' center to center .012's would work fine, but .015's could be substituted. I feel if you wanted to experiment a bit, Spectra lines might even work equally as well due to their weight which would assist in speed.

JPvelo Sat Jan 11, 2014 6:21 pm

RK,
I removed the original tips and will be using 1/2" balsa "cap ribs" for tips. That will give me a span of 35". This is my first build bigger than 1/2a and the majority of those don't have landing gear. So I'm probably not the best guy around to ask about mounting the landing gear.

Jim

JPvelo Sat Jan 11, 2014 6:51 pm

Ken, and others,

How of you feel about rudder offset on this model? I have not been using any on 1/2a builds and it seems fine.

Jim

Ken Cook Sat Jan 11, 2014 7:08 pm

Jim, I don't personally see the need for rudder offset and all of my builds for the past several years have 0 deg offset. I don't use it period. I've personally found it to be useless as it just yaws the plane out. This causes a lot of drag where it's most needed like in the overheads as the plane is literally strangling itself to go over the top due to it trying to fight itself. I fly most models with o deg offset and I sweep the leadouts fwd. While most would panic doing so, I've found no better substitute than power. Many times the suggested prop from the engine manufacturer or within the kit for me at least is oversized and overpitched. I prefer the engine rpm's slightly higher than most.

The topic of rudder offset comes up frequently. While most plans from back in the day called for rudder offset, modern planes generally have none. I've had much better success using a offset phenolic pad under the engine lugs opposed to rudder offset. I wouldn't suggest washers under the front lug as sometimes shown on plans as this generally crushes into the motor mount due to not a large enough footprint. A tad of rudder offset isn't going to hurt, but I would certainly keep it mild.

What I've done in the past is to not glue the back half of the rudder onto the main vertical section. Instead, I've used .030 brass strips and slotted both halves the same way you would hinge a flap. Epoxy the brass strips in and you now have a adjustable rudder tab. Just bend to the desired offset, if it's not flying to your expectations, straighten it out. It stays put perfectly. Another method of offset is to use a slightly thicker piece of stock say 3/16" and sand a airfoil shape from front of rudder to rear. The flat side facing the outside of the circle while the airfoil shape is the entire inboard side of the rudder. Ken

JPvelo Sat Jan 11, 2014 7:09 pm

Rusty,
Tried spackle on the fuse today, pretty cool. Will probably start silkspan/ polycrylic on Monday.

Jim

JPvelo Sat Jan 11, 2014 7:12 pm

Ken,
I figure if a combat wing can keep the lines tight with zero rudder a few degrees offset on a stunter probably isn't needed.

Jim

duke.johnson Sat Jan 11, 2014 9:44 pm

Mark-most of my reading for Akromaster mod's would come from stunthanger. We have had a few of these and the were all stock out of the box.

Richard-just my opinion, but I'd still build my first per the plans. You can't go wrong. I would try to find a old fox 15 or an OS 10-15FP or LA. And go without a muffler.

Jim-I'm mostly with Ken on the rudder offset. I've been leaving it out on my last couple of planes, all the Expert PA guys that I know set the rudder straight. I have not noticed any bad habits. The basic three ways to keep the lines tight are, lead outs, engines offset, and rudder. I feel the rudder does the least.

Now that all said, I have only been flying CL for a few years and I'm just a dumb plumber.

**RknRusty** Sat Jan 11, 2014 11:23 pm

Jim, I haven't tried it, but Ken suggests that thinned(I think) white glue is better and lighter than poly for laying the silk down. I have to admit, I like the look of my Poly-silk fuse though. Try to get the silk grain running lengthwise. For our purpose it probably doesn't matter though. I expect to be painting this coming week.

Rusty

JPvelo Sun Jan 12, 2014 12:41 am

RknRusty wrote:Jim, I haven't tried it, but Ken suggests that thinned(I think) white glue is better and lighter than poly for laying the silk down. I have to admit, I like the look of my Poly-silk fuse though. Try to get the silk grain running lengthwise. For our purpose it probably doesn't matter though. I expect to be painting this coming week.

Rusty

I used poly to silkspan the fins on a rocket my son and I are building. I have two coats of poly on top and they look real good, can't wait to see how paint looks. Will probably do the fuse the same way.

Jim

**RknRusty** Sun Jan 12, 2014 2:03 am

I am going to do a primer coat between the poly and the paint. Do you plan to prime too, or just go straight on with the paint? I bet paint sticks to poly just fine, but I want ultra glassy. I wish my flaps weren't primed already, as I'd like the extra stiffness the poly might add.

JPvelo Sun Jan 12, 2014 8:08 am

RknRusty wrote:I am going to do a primer coat between the poly and the paint. Do you plan to prime too, or just go straight on with the paint? I bet paint sticks to poly just fine, but I want ultra glassy. I wish my flaps weren't primed already, as I'd like the extra stiffness the poly might add.

Definitely primer. I did primer over poly on my speed planes. If nothing else it's an extra layer of fuel proofing.

Jim

JPvelo Mon Jan 13, 2014 6:37 pm

Managed to silkspan the fuse today and get a second coat of poly on.

Jim

**RknRusty** Mon Jan 13, 2014 9:52 pm

I sanded my second coat almost back down to the paper. It's not as "rock hard" as I expected from what I read, but still a lot more dent resistant than plain balsa.

Rusty

JPvelo Mon Jan 13, 2014 10:03 pm

RknRusty wrote:I sanded my second coat almost back down to the paper. It's not as "rock hard" as I expected from what I read, but still a lot more dent resistant than plain balsa.

Rusty

How many coats are you doing? I am planning on at least three including the initial silkspan coat.

Jim

**RknRusty** Tue Jan 14, 2014 7:20 am

I laid one coat down and applied the damp silkspan. Then brushed on one more thin coat, making sure all the overlaps and corners of the silk were stuck down firmly. I lightly squeegeed it and cleaned the runoff with a wet paper towel, double checking the corners and overlaps. After a couple of days I sanded that down until I thought I was about to hit the silkspan.

It sanded very easily and quickly, and I used 220 grit 3M paper with an open coat. I forget their name for it, but it was more aggressive than I expected. I liked it, just have to be careful. I'll go to the shop later and get the exact name in case anyone is interested. I shook off the paper frequently while sanding.

Rusty

JPvelo Wed Jan 15, 2014 7:52 am

I put a third coat of poly on the fuse last nite and it's as smooth and shiney as a baby's bottom this morning.

Jim

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