Letters to the Editor
All letters will be carefully considered, those of general interest used. Send to Model Aviation, 815 15th St., N.W., Washington, D.C. 20005.
"His" Sniffer
I've just finished reading the "For Openers" column in the April 1977 issue of Model Aviation. When I read what you had to say about Midwest's Sniffer kit (P. 58) I just couldn't believe it. I had to read it over again to make sure that I wasn't seeing wrong.
You see, I've been modeling only about 2 years now and the Super Sniffer (48" span?) was my first and second model airplane. I had decided to try a balsawood model and walked into the local hobbyshop expecting to buy a small rubberband powered type. The owner asked me a lot of questions (interests, financial status, spare time available, etc.) and recommended the Super Sniffer.
Well, I said why not. He told me that it was easy to build, cheap, and that even a rank beginner should have little trouble getting it to fly. To make a long story a little shorter, I built it, and flew it, (with a Cox Baby Bee) and this was what convinced me to take up modeling!
After a few extremely successful flights I decided that no matter what I did I couldn't keep it from drifting with the wind, and thought maybe I could afford to put a cheap radio in it to bring it back closer to our field. (Chased that darned thing 3 miles once. Circle climb—circle glide—5 mph wind!) That's when my troubles started! Nobody told me about CG, control surface area, and I didn't have an instructor with pulse single-channel experience. Well, the first one bit the dust shortly thereafter, but I knew it was my fault, not Sniffer's. I had started reading some model magazines by then and knew that I could make the plane fly properly with my single-channel radio.
I proceeded to build a second Super Sniffer. The first one was blue and white (dope and tissue) which was awfully hard to see against a blue sky, so I got smart and lazy and the results are shown in the enclosed picture. (Monokote).
The second one used an ORC .049 which I really appreciate. (Soft ears?) It is about 1 year old and has had many successful flights. I recently sold the complete outfit to some local kids and they are having a lot of fun with it. But that's not the end of my story. I have the plans and will soon be building two more Super Sniffers—one free flight (only this time with the dethermalizer) and one w/micro 2 ch flight pack. The f/f one will be back to traditional tissue and dope while I intend to use transparent Monokote on the RC.
Now for the point of my letter. I think you are talking about the "Sniffer" (37" span), not the "Super Sniffer," but aside from the size they are the same airplane. I've tried in vain to find out more about the history of this model, but have only run into blank stares.
You might be able to help me by telling me how to get ahold of this Wally Simmers or someone else to share some of my experiences with this model. I currently am flying some sailplanes; I am in the Rocky Mountain Soaring Association and compete regularly. But this Sniffer model has got so much character that I think I'll always have one around and will recommend it to any beginner! Although I don't think that Midwest is doing justice (no advertising!) and it is getting to be difficult to buy it in hobbyshops. I do truly believe that the Sniffer is one of the most enjoyable kits a person can have. Hey thanks from me for the shot in the arm. (ego?)
Bill Thomas Fort Collins, CO
The Sniffer we described was kitted shortly after the war. For an .049, it undoubtedly was the smaller one referred to by Thomas. Wally Simmers is the "S" in K & S Engineering, 6917 W. 59th St., Chicago, IL 60638. It is interesting to note that a good design and kit, and a sage dealer's advice, produced a new modeler who became an R/Cer.
Still More on Props
In the June issue you published a letter from a Mr. Sidwell regarding timed speeds of his Formula 1 racer. Your comment that his high speeds were probably due to error in timing are undoubtedly correct (he would have had to increase available power by 40% to go from 165 to 187 mph).
The mention of the Prather 8½ x 6½ prop reminded me of some theoretical calculations I did some months ago on what size prop would be best for the newer engines in view of their higher rpm, lower torque values at maximum power output. Using information available at that time, the calculations suggested that 8½ x 6½ would be best all around. This is within about 3% of the diameter value of the Prather prop, which can be readily explained by a slight difference in dynamic solidity between the Prather prop and the model I used for calculation purposes. I used 24,000 rpm to arrive at the ideal prop.
If you will recall Mr. deBolt's article in the May, 1977 issue, these conditions are supposed to limit maximum speed to about 118 mph (80% efficiency). Considering all the speed lost in turns, if this is true (118 mph max) then a Formula I plane using the Series 2 Prather prop at 24,000 rpm would seem to be non-competitive in Formula I.
On the other hand, if the Vortex Theory by which I made the calculations is correct, the maximum speed should be in the 145-150 mph range (100% by the currently held notion of efficiency in modeling circles).
Since theory and practical experience do not always agree, I would like to ask if you would publish this in hopes that some racers using the 6½ inch prop would respond giving the following information:
1) What are your best race times with the prop? 2) What ground rpm do you turn? 3) How many miles do you think you actually travelled for the times reported? 4) What air rpm do you think you get?
If these answers verify my calculations, I would be glad to work up an article or two on propeller efficiency to clear up the propeller mystery. The whole thing can be reduced to a single equation which, unlike Mrs. Watson's "outerves yaw" equation, really works for any engine, flight speed, reduction ratio, etc. a modeler might encounter or imagine.
J. L. Brownlee 2407 Quince Drive, SE Decatur, AL 35601
Mr. Brownlee's full address is given to facilitate correspondence on this important matter. Perhaps, someday, we'll all know more about these fickle fans. Incidentally, we did not specifically state that Mr. Sidwell's speeds were the result of a timing error. Mr. Brownlee does say "probably."
And Still More on Props
Subject: Hal deBolt's article on making
Continued on page 84
Letters to the Editor
high performance propellers (June, '78, vol. 4, #6, p. 30).
Even though pylon racers (or whatever they are) are out of my province I found deBolt's article interesting and provocative but I came away with a few misgivings.
I think that the idea presented that identical pitch can be maintained while substituting different types of airfoils can be very misleading and can lead easily to specious reasoning. Determining pitch by some arbitrary datum line seems largely a matter of choice that merely lends itself to the flat driving face of a standard propeller section. I would think that a more meaningful approach in this case would be to calculate pitch from the zero lift angle of the blade airfoil. Since there could be as much as six or seven degrees difference in zero lift angles between a symmetrically shaped airfoil and a thick flat bottomed section we would have a big difference in aerodynamic pitch also.
So where does that leave us? I would suggest setting propeller blade elements for given lift coefficients at design advance angles and let "pitch" take care of itself.
As a point of interest regarding the use of symmetrical airfoils in propeller design, I recall N.A.C.A. tests on a Navy propeller that had a speedy, biconvex airfoil on the outer fifty percent with it developing to a more standard airfoil inboard. The combination gave very high maximum efficiency but climb acceleration was poor.
Hal states that the widest part of the blade should be near the .6r station...yet a developed view of the planform seems to put it much closer to the hub. I would be interested to know how he came to this conclusion. To confuse the issue in my mind was an N.A.C.A. propeller comparison test against a standard propeller looking much like Hal's. The propeller giving highest maximum efficiency had its maximum width around .38r with nearly straight taper to the rounded tip. The gain was 3%, I believe. (3% gain in propeller efficiency means only a 1% gain in flight speed.)
I was taken aback by the fact that Hal was turning a nine inch diameter prop at 27K. Is this a common occurance? A tip speed well over 1000' per sec seems to be pushing it even for a full-scale metal propeller with ultra thin tip profile. It's hard for me to believe that a miniature propeller with its lower Reynolds Numbers wouldn't suffer a severe loss of efficiency. I have thought (perhaps wrongly) that 900' sec was about as high as we could go even with thin, carbon/epoxy props. I, for one, would like to hear more about compressibility phenomena as it relates to model props...should (pylon racers) be going to three bladed props?
To anticipate part #2 of Hal's article I would like to pass on a warning to those carving their own props. Don't depend alone on the template markings to give you the anticipated blade angle. It looks good on paper but small errors creep in that can really screw things up. Recently I went through batches of old props that I had carved using markings only and was shocked to find them many times off the original design intentions. Simple angle templates made from stiff paper (file cards, folders, etc.) will make sure you have it right. And, finally, be sure to balance the prop. It is not enough to balance it horizontally...it must be balanced on the vertical axis as well. (As a friend of mine put it, "pretend that is a four bladed prop and balance the phantom blades.")
Bill Gieseking, Jr. Denver, CO
About Interplane Struts
I do not know if anyone has called your attention to the plans of "The Comedian" July 1976 by Henry Farrell, #149. I have been in the process of building it. Have run into trouble with the plans.
Everything was going along nicely until I made the interplane struts, then trouble developed. Either the cabane struts are too short or the interplane struts are too long. I did not think much of it at first, but on assembly it was obvious the upper wing would be too far forward, and had to be moved back, upsetting the alignment. To solve the problem I cut two strips of 1/8" balsa 3/8" wide and glued them on the inside of the cabane struts to build them up at the top. That brought the upper wing back into alignment. The top wing now rests on the cabane instead of being attached to the top of the fuselage as the plans call for. I have written to Mr. Farrell and am awaiting his reply. I thought other builders might run into the same trouble.
I think the plans are a good job otherwise and hope to finish the model soon.
R. H. Hurd Northbridge, Mass. I have read an article on biplanes that the distance between top and bottom wing is to be spaced the same distance apart as is the chord of the wing to be a good flying bipe.
One thing that I can see wrong with the plans is no dihedral allowed for the lower wing. Or am I overlooking something?
Charles Kolodziejsky Stone Ridge, NY
Many draftsmen and designers of biplanes who show the root rib profiles on both top and bottom wings but without display on the side view of the actual appearance of the dihedral incorporated, innocently show the interplane strut(s) extending the full depth of the gap between the wings at a point close to the aircraft center line. With dihedral in the lower wing (none, or not as much, dihedral in the top wing), the true length of the interplane strut(s) is less than what is drawn. Our suggestion to Charles was that he place the wing panels in the mounted position and then measure the actual length of the strut at its station on the span. We do appreciate hearing from readers about plan problems. Corrections are sometimes made on plans during their life in the Plan Service.
Wylam Plan Books
I am trying to locate copies or reprints of any of Wylam's Plans Books. To date, I have been able to purchase only book #4. I am especially interested in book #2. Any help you can give me for the location and/or prices of these books would be greatly appreciated. Enclosed is a self-addressed and stamped envelope.
Matt Jacobson 10423 112th St. SW Tacoma, WA 98498
The Wylam Books are marketed by Model Airplane News. We gather from Matt's letter that some of them are out of print. We've included Matt's full address in the hope that someone may have pleasant news for him.
Transcribed from original scans by AI. Minor OCR errors may remain.
