Weight and other issues

Now the questions. From a lightness and durability standpoint, is it better to build the cowl in the usual fashion or go with a fiberglass molded job? Same question for the wheelpants (wing mounted gear)? The elevators are built and came in at about an ounce (both). I'm just starting on the flaps, but hope to keep them under 2oz. I also need to do the cockpit detail and canopy, but that won't weight much.

So, any ideas to save weight at this stage of constuction?

I used a bit heavier construction than I had planned in the wing because the structure is my own design and I wasn't sure how it was going to hold up. If the wing structure holds up well, I can probably lighten it 2 or 3 oz with the next one. But, that's the next one.

Thanks for comments.

Now, on to your other questions. Matt was going to mold cowls and wheel pants out of fiberglass figuring that even if he changed the design (does it every time) the cowl and the wheel pants would work on the next one. The advantage of molding is the ability to make duplicates quicker. Making the first one is a bear, however, and when he weighed his present wood cowl, it was less than half an ounce. The wheel pants were a quarter. It is doubtful that a fiberglass part of the same strength would be lighter and would probably even end up heavier. Matt's finish, from bare wood to final front row at the Nats, was a total of 7 ounces. All Brodak dope. Medium silkspan overall with a bit of carbon fiber veil added in selective places for added strength. It has an all white top (Matt said, "Never again") and white takes more to cover, although the Brodak dope again has much more pigment in it than the SIG stuff we relegated to the basement. With the SIG he always had to add pigment to get it to cover properly.

Now, are you using equal panel wings or do you have some assymetry. With some assymetry you will need to have to add less tip weight. Matt has about 2 1/2 ounces of tip weight using equal panels, but we feel the use of equal panels and added tip weight is worth it in the added line tension that you gain--especially overhead. Still, you would come out with less if you have assymetry built in. Do you have the engine already? If not, why the 40 or 51? Putting in a 61 or 65 would give you added thrust (with the right prop) and added tension all around with minimal increase in weight. Forget the weight of the added fuel (less than 6 1/2 ounces will still get you through the pattern). Most of the fuel is burned off by the time you get to the critical portions of the pattern (hourglass through clover). Fuel weight is a non issue. But some of the people (Gieseke for one, even with his extremely light weight) will tell you the added power and ability to turn the larger prop are well worth it. There is no substitute for the aiblity to turn a larger prop, as some of the people now experimenting with 4-cycle engines are suddenly finding out.

Medium Silkspan is too heavy and hard to fill adequately. Try doing what I do for lightness. Cover the fuselage and tail surfaces with OO light silkspan, iron it, make sure there are NO wrinkles in it (this is important). Then cover the wing out to just where the tip begins with starline polyspan. It is only slightly heavier than the OO light silkspan, but much, much tougher and easier to fill it's somewhat tighter grain. You can then cover the tips with light silkspan for solid tips, medium for those using covered tips. The polyspan is waterproof, and it shrinks by heat and does fill much easier than medium silkspan. You need about 3 light coats of clear under the polyspan so it will stick down good. After shrinking the polyspan spray on the 1st coat of clear thinned only enough to get the paint to flow onto the surface. You don't want it penetrating through and running on the underside. After 3-4 more fairly thin coats of clear sanding lightly between, use one only coat of zinc serate filler that you can obtain from Randy Smith. Wet sand and fix slight blemished with either Elmers spackle for light wood, or the 3M blue glazing putty. When done, spray on a light coat of clear as a sealer and lightly wet sand this too. Then a coat of Silver mixed with Polar Gray 50-50, If all is OK you can use this as your base coat or for even more lightness you final base color coat, if not wet sand this one down too, then spray on another one. Any bad areas here are spot fixed. For the greatest lighness mask of your trim areas and spray your base color, then go back and do the trim. Always, Alway remember to use just enough color paint to get adequate coverage, don't worry about gloss, that will come with clear coats. Just remember to use the minimum amount of clear that you can adequately fine sand with 1200 and buff to a shine. When you want to spruce up the bird for appearance judging, just get a bottle of Son of A Gun, spray it on & wipe it off, makes the plane shine even more than just being rubbed out!

Other lightening tricks, use the mimimum amount of header pipe and connector material, use carbon fiber gear if fuselage mounted gear is used. You can get carbon fibre spinner backplates too.

If you are going to build the same type cowling all the time them a fiberglass mould may be a good investment, however, I don't think there would be a substantial weight savings. One other thing I might try on my next plane is to use 1/20 sheeting and geodesic construction on flaps stab and elevator and cover them with light carbon veil.

We use the carbon fiber gear and belcranks, but have a problem with the spinner backplates. They flex too much and make tightening more difficult as you can end up pushing the backplate right into the nose of the plane. Better are the titanium back plates that are available for the spinners at about the same weight.

I can supply any of this, but it is rather exotic stuff that the top flyers will use (to whom price is unimportant, but the last point from the judges is) and the average flyer is probably better off ignoring.

One helpful hint to keep the dope from penetrating through the covering on open bays and causing a mess with those inside "drops" is to brush or spray the open bays from the bottom. Hold the plane above you. Apply the dope, then turn the plane over and apply the dope to the second side with it again above you. Any drips will, thus, be formed on the outside of the covering where they can be wiped or sanded off with relative ease.

No problem disagree away! It could be that my medium silkspan could have come from a more loosely woven batch than yours? Where do you get yours anyway? I'd like to try some if it fills better than light in your opinion. For covering just the open bays, you can't beat polyspan for it's weight to strength ratio!
It's not as heavy as medium silkspan and a little heavier than light silkspan and fills pretty easily. Example, the finish on my Intrepid is 4 coats clear, 1 coat zinc sterate filler, 1 coat clear, 1 coat silver/polar gray wetsanded, 1 coat silver/polar gray as final base color, 1 coat of trim white, blue, red and yellow, mist clear on ink lines and decals, then two medium wet coats clear, sand with 1200, buff with Gorhams and/or McGuire's polish, some Son of a Gun and Wah-Lah.

Matt sands with 600, 1200, then 2000, before going to the Brasso or Gorhams, and, also, experiences a few sand throughs. Adding another hint of Windy's is to pre spray an extra coat or two along the edges, the ribs, etc., in those places where you may tend to sand through so you have extra material to work with.

Anybody know how to spell zinc stearite (starate) ?? A more common filler is talcum powder or corn starch which all work well. As long as you sand well and let the filler fill the grain only, little extra weight is added with any of these. If you don't sand, however, it can be like lead.

Hmm, let's see. The plane is 692sq inches (nearly as I can calculate it). Equal panels (I will never build an asymetrical plane again---long story). The flaps are built up D-tube, sorta. They are quite thick (another design quirk of mine) and very, very stiff longitudinally and diagonally. As I noted, they look to come in around an ounce each. The elevators are just solid wood with some veil. Light, stiff, simple. It has a wing mounted gear (first I've built in awhile).

Len,

I'm using the PA.40 because it's the best running engine I own. Very strong, very consistent and relatively insensitive to weather changes. Only problem I've had with it is that if the plane gets at or above 60oz, it doesn't have enough poop in strong wind (the only kind of weather we have for contests). My PA.61 is not only broken, but lost. I sent it to Smith for repairs but he didn't get it. UPS says they delivered it, but... Will be resolved eventully, I suppose. Even it I had it, I wouldn't use it. The thing has never run right.... Well, If I get off on that, I'll rant for an hour. sufice it to say, I have no love for that PA.61 and after hearing Paul and Ted talk about them, I'm not that hot to try another. I would like to try a PA.51.

My next ship is Pat Johnston's Epiphany. I flew his and I really like this plane. It's an eliptical wing job that if very solid in the air. Nothing real fancy, just a good flyer. I plan to use a Magnum .51 if your able to get me the one we talked about or use the Stalker .61RE I have. Back to 4-2-4 for a bit.

Whoaaa! Can't let that go out in public without a disclaimer, Randy. I am truly pleased with the performance of my .61s. Sure, like any engine I've had my "moments" with them, but by and large they've performed very well and have power to spare.

The only thing I can think of that I might have said which could be construed as a negative is that the PAs are more demanding of detail than, say, the OS engines. I think the difference is that the PAs were built with ultimate performance in mind whereas the OS VFs were mass production units set up to be pretty much bullet proof to even the roughest the RC crowd could bring to them. The result seems to be that they run exactly the same every time with little need to adjust for conditions.

The PA's respond noticably to climate and set-up changes and thus require a bit finer ability to diagnose and refine the run for changing conditions. While this sounds like a negative at first glance, the corallary is that they are much more amenable to refined tuning for ultimate performance. When you change something (head clearance, pipe length, nitro content, etc) the result is measurable and predictable.

The only time I had a huge problem with a PA was the one year I ran the .51 at the nats in 1996. I was thrilled with the performance at home. I got to the nats, however, and it was not the same. Way too much power at all the wrong places. I looked around for my little motor buddy and he was off in Sweden doing battle with the Brits, French, Chinese and the rest of the world. Bottom line was I gave Bob Baron just a little help at kicking my butt. (five or ten thousandths additional head clearance would have mellowed it right out)

I found out that year that I'd better learn more about tuning these engines myself. So, instead of just asking David "what to do", I've learned to ask "why" as well. Things have come around pretty well since then!

Sorry, I didn't mean to make it sound like you or Paul or anyone else said that they were somehow "bad" engines. But I have heard you both say that they were sometimes difficult engines to get to run consistently from one flight session to another. As you note, this is a learning curve. It's obvious that they run very well in the hands of those that have the knowledge and experience required.

I've talked to you and Paul periodically about the one I had. At different times you both commented that I should send it back to Smith to be looked at because it didn't seem very happy. I was more answering Len on why I wanted to use the PA.40 I have rather than a PA.61. As I noted, I've been very happy with the PA.40. It is certainly less critical of weather and fuel factors than the PA.61 I had, but that could be related to something else wrong with that particular engine or just my inexperience with it.

I've heard pretty consistently from many people that the PA.40 and PA.51 are for whatever reason, perhaps, less critical of adjustment, weather, fuel and set up than the 61. Doesn't make them better or worse and is certainly not a comment on the ability of the .61. My comments on probably not wanting another PA.61 are for the reasons you note. I have a lot to work on and I'd rather not, at this stage, spend a great deal of time trying to understand the intricacies of running this engine when I've been successful getting the PA.40 to perform.

If UPS ever pays off on the PA.61 that I sent to Smith and they lost, I'll probably just use the money to get another PA engine, but it will probably be a .51.

Did you try pushing the pipe in from where it was at the NWR, like I suggested? It was a bit too long, which made the engine a little flat, to the trained ears of the illustrious Mr. Cox and myself. The 40 should have no problem up to the mid 60's, and can be easily set to give more boost with some compromises if it's heavier.

>My
>PA.61 is not only broken,
>but lost. I sent it
>to Smith for repairs but
>he didn't get it. UPS
>says they delivered it, but...
>Will be resolved eventully, I
>suppose. Even it I had
>it, I wouldn't use it.
>The thing has never run
>right.... Well, If I get
>off on that, I'll rant
>for an hour. sufice it
>to say, I have no
>love for that PA.61 and
>after hearing Paul and Ted
>talk about them, I'm not
>that hot to try another.

Eek! I think I'll start digging a bomb shelter.

Mine runs great, as long as I don't get mislabelled fuel (like at the NATS).

See what happens when you post something when you're tired.

As I noted above, I probably wasn't very clear. I've seen others run the PA.61 and they run great. I just never had that much luck with the one I owned. I think it had more to do with that particular engine and, perhaps my inexperience with it. It wasn't a comment on the design.

>Did you try pushing the pipe in from where it was at the NWR, >like I suggested? It was a bit too long, which made the engine >a little flat, to the trained ears of the illustrious Mr. Cox >and myself. The 40 should have no problem up to the mid 60's, >and can be easily set to give more boost with some compromises >if it's heavier.

Yea, I shortened it up a couple of times. I got some additional power, but the sweet characteristics I love in that engine went away to some extent. I started off at about 17.75 inches (too long, as you and Chris noted) and ended up somewhere around 16.25. The best compromise was at about 17.00 inches. Enough power to pretty much carry the load with not too hard a charge out of the corners or surging in round manouvers. While that plane wasn't a pig, it was too heavy at about 65oz. and not enough wing area to really carry it well. Part of it may have been the pipe I was using too.

Add a small head shim to the PA and it will solve the surge. Like they say in the cookbook, add to your taste.

Amazing how this got off line. Guess it falls under the "other issues" catagory

I should know better than to make off hand comments.

Is this still off the subject?

Len,

I was just looking for some comments on the merits of using a fiberglass cowl. Thought I might pick up some other weight saving tips for the stage I'm at with the plane. This plane is going to interesting enough due to the design (which I'm sure will garner nevering ending comments and cracks from the folks around here when they see it). It's the first time in about 4 or 5 years that I've built something that's not based or copied from someone else. Everything from the airfoil, layout and areas to the constuction techniques all pretty much my own ideas or are based on a conglomerate of things I've learned. It's different, anyway. Should be fun.

Still no word on my lost PA.61. If UPS doesn't come up with something next week, I suppose I'll file a claim.