otrcman

Wow, I just received a Spitfire kit which I had won on eBay. I know some people have said Sterling kits had some heavy wood, but my experience back in the 60's was that they weren't all that bad. Well, this one bears out what the others have said. The big nose block weighs a ton, and feels more like a piece of oak rather than balsa.

Of course this in no way reflects on the eBay seller, just on Sterling. This kit looks like a late edition, having nylon bellcranks rather than plywood with bushings. It also shows screws holding the wing to the fuselage rather than rubber bands. I wonder if Sterling got into really hard balsa (I'm giving them the benefit of the doubt here, assuming it's balsa) in their later years?

I built a Sterling Spitfire in 1964 and had no complaints about the wood. Don't recall what the final weight was, but it flew very well and didn't seem like a lead sled. Think I'll be doing some wood substitution on this one.

Dick

Jeff Worsham

My Feedback: (28)

Boy, growing up and learning to build in the 70's, I came to regard most Sterling and Guillow's kits as...well at least their smaller kits as....dare I say...."junk" unless they were being built for controlline. After building a few, I gained the perception that anything they offered would come out too heavy for FF or RC. Probably unfair and not 100% right, but that was my perception as kid.

stuntflyr

Hi Dick,
I found this thread wandering through the forum and saw another Sterling guy. And it's you!
Not knowing what was going on in 1969, as a 10 year old I went to the Sterling factory and got a tour during the Nats at Willow Grove. Terry Prather had just had his Winder combat ship kitted and he and a bunch of us in our C/L club went along. Dad didn't seem too impressed by the R/C Mustang top blocks being shaped. It started with a block that had a nice slot for the fin, once it was shaped the slot was gone, replaced with a flat spot. I thought maybe the tool was badly out of calibration (though I didn't know those words then).
As far as weight, after collecting kits for the last 35 years I have seen a bit of interesting and puzzling trends in materials. In Berkeley kits the ply became luan, and then finally cardboard! It'd work I'm sure, but it just wasn't high quality anymore. Metal stamped parts became plastic (good as far as I'm concerned for flight). It seems that when buying large quantities of wood during the Viet Nam war, light stuff was hard to get cheap. Also, during the 60's and 70's the aerospace industry was using balsa for airliners and that put a big strain on the supply of cheap wood. I kind of thought of Ed, the owner of Sterling when I toured the place, as a business man that happened to have a model kit manufacturing plant. Could be he was keeping the place going when times were hard, or just watching the bottom line. Must be hard balancing the needs of business and modelers desires, anyway.
I used the top block from a Sterling Skylark C/L Stunt kit and found that it was very light after I mototooled it down to about a 1/8th to 1/16th. Easy to carve as it didn't get brittle or tear of on the corners, (takes some sharp tools though) It was still pretty solid after hollowing!

So are you going to build that Sterling Spitfire? Any updates on construction? How about pics of yours from long ago?

Chris...

otrcman

Hi Chris,

What you said about quality materials getting more expensive in the 1960's and 70's must be true. The Spitfire kit I recently bought on eBay seems to be a far cry from the one I built in the early 1960's. Just this morning I took an hour to remove the contents from the box and really look everything over. The balsa density varies from fairly hard to unbelievably hard. Die cutting doesn't seem to suffer much, which surprised me. The lower nose block is the hardest piece of balsa I have ever seen. I measured the part, calculated the volume, and then weighed it. Worked out to be 23 lb. density. According to my wood density table, white pine is 26 lbs, so this nose block is a lot closer to pine than to balsa.

Some of the plywood is indeed luan as you mentioned about the Berkeley kits.

There are a number of things that make me think this Spitfire is a late-production kit. The nylon bellcranks I mentioned before. Also, the plans show the wing attached with dowels and screws rather than rubber bands. The instruction mentions "four channel fully proportional system of aircraft only frequency..", which certainly wasn't state of the art in 1964.

As far as building the Spitfire, I'm not sure. I really want to do it, but my list of projects seems to be getting longer instead of shorter. Right now I'm winding up a full scale Curtiss Robin and I have another Robin waiting in the wings. In addition, I have a full size Jenny project that has been waiting to move to front & center. I also have an L-2 Taylorcraft that I use for tailwheel training and it's really needing to be re-covered. Then there are the models. I'm in the middle of an Aristo Craft F3F right now.

All this stuff about diet and exercise & longevity gets a lot more relevant when you look at the things you want to do and then look at yourself in the mirror. Wow, got to get busy.

Happy new year to all, Dick

otrcman

How about pics of yours from long ago?

Chris...
[/quote]

Forgot to answer your last question. I don't believe I have any pics of my first Spitfire. It originally flew with a K&B 45 and Kraft reed 10 channel radio. The K&B was soon replaced by an Orwick 64. The Orwick was more powerful but the idle was lousy with the primitive throttle I adapted onto it. So I retired it for a few years.

Then in the early 70's I resurrected it with a proportional radio and ST 60 Bluehead. Now it was a real airplane Even with the 60 it wasn't particularly fast, but looked very cool coming out of a prolonged dive and sweeping by at 10 feet or so and finishing up with a victory roll.

When the airplane reached the point of needing a major refurb I gave it to a promising young teenager who flew it some more before hitting a farm implement on landing approach. Sterling made tough models, but International Harvester was tougher.

Dick

stuntflyr

Hi Dick,
I see your problem. Full scale airplanes! Two Robins! Wright's or OX? (I remember Perry Schreffler's Newsboy, he thought he'd never finish it.) Very cool, a Jenny. L-2, huh? Not just a BC! Just sold my Pitts Special last year, wondering if I can find a cheap 120 or 140 for my son and I as the acro and expensive stuff is now out of the question.

I have an Aristocraft Staggerwing kit, I feel your pain.

(I pulled a canopy the other day on the old King Cobra. Too grainy of a mix on the hydrocal. I need to mix it differently. It should work though. Trying again tomorrow.)

I love the 25 lbs balsa. Usually with age the stuff gets lighter! I wonder what it was when they boxed it!? A buddy built a Sterling Spitfire Sunter by tracing all of the kit parts, simplifying some structure and using real wood. He saved a bunch of weight and it was very straight and tight. It sure would be cool to see your F3F and Spitfire both flying! (Do you use ancient engines and radios?)

I got my King Cobra graphics done and the cutter is mailing them right away. I'm excited about it again. I'm going to finish that model next. Should be interesting with the 91 and those stock ailerons. I'll be posting on it soon in the Pattern thread.

Happy New Year,
Chris...

otrcman

Hi Chris,

Looking forward to seeing your completed P-63 and also hearing a pilot report. The local hotshot I knew in the 1960's said his King Cobra flew great. By the time I met him he was flying a highly modified Kwik Fly, making low inverted passes, then pushing upward and doing outside snaps starting at about 5 feet all with a 10 channel Orbit reed radio ! At that time the King Cobra was so far out of my league skill-wise that I didn't even consider building one. But all these years I've been thinking .......

Yes, the big airplanes consume a lot of time. The Robin that's almost ready to cover is a model J-1, which has the Wright J6-5 engine. The other Robin is OX-5 powered. Cessna 120/140 airplanes seem to remain pretty cheap compared to most other types. I've never understood that, as they're good little airplanes. One of the local guys at Santa Maria recently bought a 140 off eBay (sight unseen, no less) for about $18K. I've seen the plane and it is airworthy, but not exactly a show stopper.

As far as R/C radios and engines, I'm not a glutton for punishment. The F3F will have a Saito 50 and modern radio. Those old radios were a disaster when they were new and I doubt they improved with age. The F3F has numerous mods to make it more scale-like scale dihedral, bolted on wings, etc.

One interesting thing about the Spitfire. It has the same positive incidence in both wing and stab as does the P-63. I have the original George Harris magazine construction article stored away in a box, but haven't dug it out to see if the prototype used the same angles. One of my friends has a Sterling P-51 kit, so I'll have to look at his plan to see if it has similar incidence angles. I still wonder why they did that. Maybe it was a hold over from when all radio models had lots of incidence in the wing and they simply raised the stabilizer LE for faster models rather than reducing wing incidence. Or, maybe as somebody said before, they wanted the model to fly with the fuselage nosed down a bit to make it look like it was going faster.

Dick

pimmnz

The full size Spit flys with the rear fuselage top almost level. You may find that this set up will be just the ticket to reproduce the full size attitude.
Evan, WB #12.

otrcman

I now have in my possession what I think of as the "big three" Sterling kits. Breitling P-51, Harris Spitfire, and Hester P-63. The P-51 isn't mine yet. A friend has offered it to me at a very reasonable price with the provision that it has to be my next project. Not sure I want to commit to that.

But comparing the three kits is interesting. First the quality. Both the P-51 and the P-63 have quite good balsa. They're not as light as a really premium kit, but both are plenty acceptable. The Spitfire, as I've mentioned before, is a disaster in wood selection. I'm not sure, but it looks like the P-51 and P-63 are early 1960's production and the Spitfire may be early 1970's.

The wing airfoils look almost the same on all three planes. The thickness percentages vary slightly, but they all look generally like NACA 24xx series, which were very much in vogue at the time on such planes as the Astro Hog and Taurus. Wing and tail incidences vary wildly. Here are the measurements that I got off the plans:

P-51 Wing +1° Stab +4.2° Engine 0°

Spitfire Wing +3.4° Stab +1.3° Engine 0°

P-63 Wing +2.2° Stab +4.5° Engine 0°


To an aero engineer, this is like looking at a mystery novel. Why so different on each plane? I didn't check the fuselage sides to confirm that the wood matches the plans, but assuming the plans are correct then some construction mods are probably in order. The zero lift angle of the NACA 2415 is -2°, so we would like the stab to about 1° positive relative to wing chord line. Here is what I'd suggest:


P-51: Reduce stab incidence from +4.2 to more like +2°

Spitfire: Reduce wing incidence to about + 0.5, or maybe a combination of wing at +2° and stab at +3°

P-63 This one is just about right. Maybe reduce stab to +3.5° But if you're using a fairly heavy modern engine, +4.5 will probably work out.



Dick

stuntflyr

Hi Dick,
I didn't realize that the zero lift angle was so low on the 23000 series airfoil. I guess these guys knew what they were doing. The stab angle should be a little bit more than the wing, I guess? 2 degrees will get it?

If this is the case, what, if any benefit could I derive from setting the wing to +1 and the stab to +3 or even +2? I'm thinking better inside to outside balance, better slow roll coordination and more predictable slow speed, high speed trimming.

Whadda' you think? Stock, or lower them a bit? I'm planning on balancing it at about 28 to 30% MAC. Good, too far forward?

Chris...

otrcman

Hi Chris,

I'm presuming from your question that you're talking about your P-63, so that's how I'll reply. First, I should plead insanity as far as the effect of wing/stab incidence upon aerobatic maneuvers. That's a really complicated subject and I don't know enough to even make educated guesses. So now that you know my limits, I'll comment on your questions.

First the airfoil. It's about 14% thick at the root, and the shape looks like it would work out to be a NACA 2414. Note that the four digit 24xx series is a completely different animal than the five digit 23xxx series. The four digit series is semi-symmetrical and has pretty good stall characteristics but not particularly low drag. The five digit 23xxx series, also semi-symmetrical (like on a Taylorcraft), has lower drag but comes at the expense of a sharper stall.

My suggestion for relative incidence angles was based primarily on being able to trim the airplane for level, upright flight with little or no elevator deflection. Obviously if your stab is incorrectly angled relative to the wing you can trim for level flight with some elevator deflection, but we usually shoot for no elevator. So what I was suggesting was that the angular difference between wing zero lift angle and stab zero lift angle should be about 1°. That is, the stab should be about 1° negative relative to the wing. If you are going to run a really powerful engine you might want to go down to 1/2° and if you have a low powered engine you might go up to 2°. Your CG at 28 to 30% sounds like a good starting point.

Now, to really get into the guesswork involving aerobatics. The only comment I can venture here is that you probably want to rotate the airplane around the fuselage principal axis for cleanest rolls. If the fuselage is well aligned with the velocity vector then the tail will not describe an arc as you roll, and fewer yaw and pitch excursions will be mixed in with the rolling motion. For this, it seems like the lower wing incidence the better. I'd expect that with your 90FS you will be moving right along in level flight and your angle of attack will be very low, maybe 1 to 2° above zero lift. So to have your fuselage aligned with the velocity vector you would need the wing to be at +1 to +2° above the zero lift angle.

Most of my career as an engineer was in flight test, so I have a healthy appreciation for just how wrong the theoretical guys can be. In the end, it's called cut and try. That's what is so neat about RC models: Doesn't cost all that much to cut, and you don't get hurt too badly when you try.

Dick

Joe Nagy

My Feedback: (3)

Hi Everyone;

Hey; another good thread and read on the old Sterling Kits and incidence settings.

Re Incidence Settings: I am no expert at all, but you can learn a lot about these settings from almost any of the late Hal deBolt's many design articles, especially on his aerobatic/pattern designs, and pylon racers. He usually recommended +11/2 degrees for the wing, and +2 1/4 degrees for the stab, reasoning that once you rolled inverted the stab setting would almost automatically drop the tail and raise the nose. I don't know for sure, but I build all my ships to Hal's formulas, and they fly straight and true, and track like they are on rails. So dig into your magazine piles/archives and read Hal's design works.

Will close, just my contribution to a really great thread, best regards from Phoenix,

Joe Nagy.

stuntflyr

Hi Dick,
Yes, I was speaking of the King Cobra and I didn't make that clear but you caught on.
I am confused, as usual. In the post about the Sterling kits, you listed the stabs as having the + (leading edge up) values that are more than the wing. Am I reading this or interpreting this incorrectly?
In the latest, you describe a stab incidence - (leading edge down) from the wing value, and that's where I am stuck. These two posts seem contradictory.
I'm just the pilot in the FTE/PIC scenario, so I just kinda follow along and move the sticks to the test card here. More knowledge transferal may be necessary!
Thanks,
Chris...

stuntflyr

Hi Joe,
Interesting tidbit there. Thanks for that, and your back-up of your personal experience with it.
Chris...

otrcman

Hi Chris,

Sorry to take so long in replying to your question on incidence, but I changed internet service providers and it took longer than expected to get back on line.

Regarding my inconsistencies in incidence angles, I'm afraid I played fast and loose with with how the angles are measured. The "chord line" of an airfoil is typically a line drawn from the center of the leading edge radius to the point of the trailing edge. If the airfoil is symmetrical, such as on a stabilizer, then the "chord line" and the angle of zero lift are the same. But for non-symmetrical airfoils, the angle of zero lift doesn't coincide with the chord line. To be consistent, I should have used all chord lines or all zero lift angles, but not mixed the two.

In my January 5 post, I said, "the stab should be about 1° negative relative to the wing". What I was trying to express there is the angular difference between the zero lift line of the wing and the zero lift line of the stab. When we use the chord lines in a discussion it is very common to find the stab positive relative to the wing if the wing airfoil isn't symmetrical.

Did I clear it up or just make it worse?

Dick

stuntflyr

Thanks Dick,
I now understand the differences in chord line and zero lift angle for asymetrical airfoils.
If I understand this correctly, the difference for the fuse reference line to zero lift angle would be about 4.2 degrees (assuming minus 2 for 0 lift angle)? Therefore making the stab then about .3 positive? Thence; your suggestion to reduce the stab angle to about 3.5, or minus .7? Or; leave it where it is for high speed operation over the original's ability?
I hope I have this right as it took me 20 minutes with the TV off to think it out!!!
Thanks again, Dick.
Chris...

flysrc

Good day guys,
I have this little gem about 2 hours away from being ready to paint. Problem I have is that I built it with no plans so therefore balance point. This is no good as I don't like to guess at this. Could someone post the balance point for please...
Dave

otrcman

Dave,

We've been going back and forth talking about Sterling Spitfires and Sterling P-63's. Which model are you inquiring about?


Chris,

Yes, I think you've got it now. Always comes down to drawing a picture for me to get it right.



Dick

flysrc

Balance point for the Sterling Spitfire.
Thank you in advance
Dave

otrcman

Hi Dave,

According to the plan, the CG of the Sterling Spitfire is 4.65 inches aft of the wing leading edge, measured at the center of the wing.

My old Spitfire was very stable in pitch. I initially balanced it at the point shown on the plan, but later put an 8mm movie camera in the cockpit area (pointing out the windshield) to take in-flight pictures. The camera was light by 1970's standards, but still pretty heavy for the airplane. I don't recall how far this mod moved the CG aft, but it still flew fine.

Dick

flysrc

THANK YOU very much, I really appreciate it. Guessing balance is no fun at the best of times.
Dave

otrcman

Glad you got the CG information OK Dave. One other thing worth mentioning relative to CG is that my old Spit was prone to nosing over on landing if I failed to touch down just right. Think I bent the gear forward out of desperation at some point. You might want to put some anti-scuff tape on the bottom of the nose at first until you get used to the plane. Knowing this now, I intend to take a look at the main gear location on the real plane. If the real gear were farther forward, I will change the model accordingly.

Dick

Tony Babington

I have put radio gear back into my Sterling Spitfire after 40 years of it being in the lofts of many houses I have moved to over time. It took me about 18 months to build and cover with doped nylon and another 6 weeks to airbrush ( a few hours a week ). In the interim I have been flying other IC's then electric, petrol and now turbines. I remember that the bell cranks were brass bushed plywood so it must have been one of the original kits. It flew on a twin plug Merco 60 but to try make sure it does not stall on take off ( that would be a disaster after such a long time) I have put an OPS 61 in this time. It weighs 8.5 lbs dry. Does anyone know what the wing area is so I can see what the wing loading comes out at?

stuntflyr

Hi Tony,
690 sq in for the Spifire.
Chris...

stuntflyr

Hi Dick (otrcman),
I noticed along the way that you have been posting about the F3F but wondered if you ever did anything with the Sterling Spitfire?
Hope all is well.
Chris...