Glow Plug Selections
A note to my readers: As you probably noted, there was not an FAQ column in the March 2012 issue. Some of the columnists will now be submitting bimonthly columns. Content will still be the same, and I will continue to answer your questions, in both print and privately, to the best of my ability. Please realize answers may take longer.
I will no longer have a preamble each month. You know how this column works, so I'm saving some space. From now on I will get directly to the questions and answers.
Q545 — Fred Mintz: Glow-plug temperature selection
Question: "I have been in the hobby for a long time and always on the glow-power side of things. However, I have never been able to determine what temperature range of glow plug is best for a given setup that includes engine size, rpm operating range, two- or four-stroke, inverted mounting, cooling method, fuel nitro content, or winter/summer.
I see advertised everything from 'ultra hot' to 'cold,' but I don't have a clue as to where they are intended to be used. Without doing extensive testing (which would be expensive), I don't know what range to select to get the best from my engines.
The manufacturers may have had a suggested range, but since I buy most of my engines secondhand I don't have that information available.
I have the same problem with glow plugs themselves. If I have a plug that is unknown, how can I tell the temperature range for which it is rated? Is there a place where I can reference these factors and get a chance of selecting the correct temperature range or identifying a plug type? This would be very helpful when diagnosing an engine problem or peaking performance."
Answer: First of all, Fred, I'm so happy to receive a glow-engine question. My readers have been getting on my case for concentrating too much on electric power. I assure you that I always want to grant equal time, but people have to keep writing in with questions.
Although I have been away from glow-engine power for some time, I still know how to find reference material. In this case I used the Google search "Glow Plug Temperatures for Model Aircraft Engines." The results were extensive and surprisingly good.
The best resource I noted was from the Raleigh-Durham (North Carolina) Radio Control Club: "Glow Plug Specification (a guide for selecting the correct glow plug)," authored by James McCarty, Brian Cooper, and Brian Gardner. It is available on the RCUniverse forum. The guide begins by describing all of the major glow-plug makers, such as O.S., Fox, Enya, McCoy, and Rossi, then goes into glow-plug usage tips.
The guide asks practical questions such as "What happens when your glow plug temperature range is too hot?" and gives plug recommendations for specific fuels: low-nitro and FAI, 10% to 15% nitro, and high-nitro (over 25%). Additional chapters cover four-stroke engine glow plugs, idle bars, and a discussion of cold plugs versus hot plugs.
I suggest you start with that information and then search beyond it using Google. Thank you, Fred, for an excellent question!
Q546: Doculam / ClearFilm covering
Question: "Every once in a while I read about a model covering product called either Doculam or ClearFilm. Could you give me an idea as to what this covering is all about and what properties it has that might make it worth trying?"
Answer: Doculam (also known as ClearFilm) was originally developed as a laminating material for the graphic-arts hobbyist or professional. It has several properties that make it ideal for model aircraft use:
- Lightweight.
- Built-in adhesive that can be applied with a hobby iron or a hot-air gun.
- Slightly milky as it comes off the roll; turns clear after heat is applied.
- Requires relatively high heat to adhere properly (I set my Top Flite iron to maximum or the heat gun to its highest setting).
- Can be shrunk like any iron-on covering.
- The adhesive is built-in and there is no protective backing to remove.
- Does not easily stick to itself until heat is applied, so it’s easier to handle during application.
- Does not curl up into a ball like some iron-on films.
The clear finish is attractive, but you may want to add colored trim. Doculam can be painted; it accepts spray paints such as water-based latex or acrylic enamels. Always make a test piece before painting your aircraft.
Recommended painting technique:
- Lightly sand with 320- or 400-grit paper.
- Wipe clean with denatured alcohol or common vinegar.
- Let the surface dry thoroughly (preferably overnight).
- Apply spray paint. Do not use primer — primer does not stick well to the Doculam surface.
After painting, you can apply masking tape and spray on trim colors. Someone even reported using wetted newspaper or paper towel as a mask; if you try that, test it first on a scrap.
The real advantage of Doculam is for scale or scalelike aircraft — there are many spray-paint colors available, and you can apply gloss or matte clears later to protect decals. Because Doculam covers and primes the raw wood in one step, the finished surface is lighter in weight than many traditional finishing methods.
Where to buy:
- The thinnest version (1.5 mil) is generally what you want; for very large models, consider 3.0 mil.
- Rolls are 25 inches wide. Some suppliers sell 10- or 25-foot rolls; full rolls are commonly 500 feet and some suppliers require a minimum purchase of two rolls.
- New Creations RC in Texas has 10-foot rolls for roughly $7.50 (Catalog No. MATCOV-010). Kirk Massey of New Creations has a large website worth checking.
- Oregon Laminating Company is willing to sell a 500-foot x 25-inch roll of 1.5 mil Doculam for about $45 plus shipping. That would be enough for an entire club; consider buying a roll and selling lengths to club members.
If you want more application information, search the Internet — there is a lot out there.
Q547: Archive of past FAQs
Question: "Is there a place I could go to look up all the past questions and answers published in your FAQ column?"
Answer: When I started this FAQ column eight years ago, we were placing all Q&As into a section on the AMA website. I have listed that URL in the Sources section. Postings were made for approximately two years, but changes in personnel at the magazine suspended the project.
More than 500 FAQs have appeared in the pages of Model Aviation. I asked editor Jay Smith about resuming an archive, and he replied: "An archive of every published issue of Model Aviation will be made available to our members early next year. It will have a robust search engine. This may prove to work well for members who wish to search for answers that were published in your FAQ column."
As soon as the search system is up and running, I will report it here and provide instructions for its use. Stay tuned!
Follow-up to Q530 (December 2011, p. 76)
I made an error in my December FAQ column when discussing the use of the Castle Creations CC/BEC to reduce the voltage of a two-cell LiPo pack to a lower voltage for an RC receiver and servos.
That FAQ was intended for glow-fueled pilots who wanted to use a two-cell LiPo to power their receiver and servos at reduced voltage. In my original answer I omitted the RC system switch from my photo and showed the battery going directly to the CC/BEC. As many of you pointed out, with that wiring the CC/BEC always had some power applied and drew its idle current continuously.
In my own use I remove the battery pack when not flying and therefore never used a switch. A fueled pilot should wire the system with a regular RC system switch harness. The correct wiring is: battery → system switch → CC/BEC → receiver battery port.
The CC/BEC idle current was measured at only 10 mA, but over a long period that would reduce the battery voltage to a level that might damage the battery. I thank AMA member Alan Buckner for being the first to bring this error to my attention.
SOURCES:
- Glow Plug Specifications
www.rcuniverse.com/forum/m_8376353/printable.htm
- New Creations RC
(936) 856-4630 www.newcreations-rc.com
- Oregon Laminating Company
(800) 574-9814 www.oregonlam.com/index.html
- Frequently Asked Questions (AMA / Model Aviation)
www.modelaircraft.org/mag/faq/index.asp
Transcribed from original scans by AI. Minor OCR errors may remain.
