We learned that the fiberglass mounts break, saving expensive engine parts. The beams did not.
Why is it that we almost never see models built these days with hardwood
> engine mounting beams? I've seen quite a few firewall-mounted engines
> ripped off their mounts in crashes, but don't ever remember one coming
> off a hardwood mount that ran back through two or three formers. To be
> sure, fiberglass/nylon mounts don't oil soak, but neither does
> epoxy-coated wood. Whaddaya say, old-timers?
>
I don't use them because the wood compresses with time and the engines keep coming loose. Other main reason is it is hard to change engine types with wood rails. You get too many holes in the wood!
If the firewall is properly engineered and installed, it shouldn't come loose. One of the main advantages to the plastic engine mounts is that it will usually break, saving the crankcase and airframe from more damage.
When I was still building with wooden beam mounts I had learned to insert tubular, hard aluminum sleeves into the engine mounting holes, the same thickness as the wood, to prevent the engine mounting bolts from eventually crushing the wood. This meant that the beams had to be wide enough to work with the over-size holes required for the sleeves.
If I wanted to change engine types, not really a common occurance back then, and the mounting holes didn't match, which they never seemed to do, the additional holes just weakend the beams.
Most of the aircraft designs then were so "well flown" by the time I got around to building them that the correct side and down thrust had been designed into the position of the beams during construction.
I "build to fly" which means I tried to make the ship as light as possible. But, seeing as the beams usually were long enough to reach back to at least the second former in the nose, the Maple, in combination with the aluminum sleeves, was probably as heavy as one of the "new" composite, fiber-filled mounts.
I never had a beam mount break, this also means that the force of a nose-in "accident" wasn't dissipated by the mount structure and the crank and case took more of a beating.
The one advantage of a all-wood beam mount that I think may still remain is the vibration dampening effect of the wood. The wood beams are much better at dampening vibration and spreading it out through the aircraft's forward fuselage structure than is a composite mount. The composite or aluminum mounts appear to act like a stiff vibration "hammer" on the "drum face" of the firewall. I saw an example of this with a Spinks Acro.
I owned the thing for many, many years and flew it with the engines on the Maple beam mounts. This is one model that lasted long enough to see three generations of engine power to weight improvements. As a result the beam mounts finally got to the point where it was prudent to cut them out and replace them - which would have necessitated a major fuselage re-build - or saw them off at the firewall and replace them with a composite mount. I used the composite mount and re-mounted the same OS FS.46 (the Prefix "FS" did not mean four stroke in that model line) that I had been flying it with for half of the season. After the change, I could actually hear and see the difference in the nature of the vibration at various throttle settings. It was noticable enought that I re-checked the security of the mount and the firewall and pulled the propellor off and checked its balance. On about the fifth or sixth flight after the change the throttle servo failed. Interesting coincidence.
The only aircraft that I still have in my stable with beam mounts is a plans-built Super Telemaster (12' span) with a Saito 1.50 on the nose for the power required for glider towing. This early edition of the 1.50 seems to have a little more vibration than the newer ones and the beam mount handles it well without much "shake" being transmitted to the wings or tail feathers. Here is a note for other owner's of the early Saito 1.50s - the idle and low throttle setting vibration is much improved by setting the idle as lean as you can get it and still have a reasonable throttle transition.
Yeah, my years qualify me as an "old fart" in this hobby - started flying in the early 50's. However, my nightly bed-side mantra is "Please don't let me ever think or act like an old fart."
Following the trend towards ARF's, the bolt on engine mounts are easier to install and change. A lot of modellers are either lazy, or don't have time/space to build like we used to back in the 60's, 70's, and 80's. On the plus side, they break in a crash, often saving engine parts and the fuselage from damage. They also allow more freedom in fuselage/cowl design than fixed beams would.
I have used both but prefer the glass mounts. It's just easier to get things done that way plus the ability to make quick repairs and/or thrust changes.
The Goldberg Eagle 2 has wooden rails, but the engine didn't mount on them. You screwed a piece of plywood cut into a U shape on to the rails. The engine then mounted to this piece of plywood. This made it nice that you could change the piece of plywood if you wanted to mount a different engine, or your could cut the U shape with more right thrust.
But nylon engine mounts are still nicer and easier.
Dont think I qualify as an old fart yet, but a big advantage the nylon mounts have over the hardwood mounts, in my opinion, is being able to drill and tap the nylon mounts. Crank down the socket head screws, add a nylon insert nut for a keeper and that engine will never become loose yet is easy to remove if needed. Would also prefer to break a mount than break a fuse or engine case. Sometimes an improvement really IS an improvement!
======================================== "Fubar of The HillPeople" wrote in message news:G%O1b.1485$ snipped-for-privacy@twister.socal.rr.com... Dont think I qualify as an old fart yet, but a big advantage the nylon mounts have over the hardwood mounts, in my opinion, is being able to drill and tap the nylon mounts. Crank down the socket head screws, add a nylon insert nut for a keeper and that engine will never become loose yet is easy to remove if needed. Would also prefer to break a mount than break a fuse or engine case. Sometimes an improvement really IS an improvement!
Seriously, guys, I asked the original question after looking at some of the old plans I've got kicking around here that show hardwood beams. On a plan that was properly sorted out before publication, the thrust change issue would be moot, but the idea of breaking a mount before breaking a crankcase makes sense. But, then, the way I fly, the breakaway mount doesn't matter. Three weeks ago I hit on the left wingtip, cartwheeled and bashed the tail, then belly-flopped on the landing gear. The prop and spinner never touched ground! Oh, well... ;-)
I was away from this hobby for many years, then returned five years ago, so a lot has changed. Heck, I'd still rather cover a plane with silk and dope than mess with mylar and irons! Which brings up a whole 'nuther topic: Anybody still cover the old-fashioned way?
At first I decided not to respond. Whoever does runs the high risk of offending you. So... don't take this as a negative :)
There is no such thing as a set of plans that have been "properly sorted out before publication". Engines, even engine/prop combinations differ wildly in the thrust that is generated. Ignoring the determination of the proper thrust angles is right there with ignoring the determination of the proper setting of the CG. Both can only be done properly by trial and error on the finished plane in flight.
I suppose there are many of us who can still cover with silk and dope. The question is why? The convenience of heat shrinkable Mylar makes producing a beautiful finish easy, less time consuming and less costly. In the instances were the weave is desirable, there are plastic films that will duplicate the appearance. The stuff is easier to repair.
Now, having said that, the correct answer for you is to reply to my question with: "Because I can and because I want to." There is certainly nothing wrong with that. In my case, I don't much like instant glues and I detest epoxy as an adhesive. I prefer making joints that fit and using aliphatic resin. Most would disagree.. it's a personal thing.
The knowledge from being able to use the classic methods of construction is something I would not want to give up, but, using modern methods and materials also has merit. In today's ARF world, just showing up with a plane that is built, as opposed to bought, is enough of a "WOW" factor at the field. Rather a sad situation.
Thanks. I was beginning to feel out of step again.
I don't recall the last time I BOUGHT CA (I generally 'win' one a year somewhere) and I have had epoxy spoil on the shelf. Tower told me it was over 3 years old when I called and complained that the working time on their
30 minute stuff was on the order of 4 minutes. I apologized.
There is NO plastic covering that will match the depth, high shine, or lustre of a properly applied dope finish over silk. for those who know, it's like comparing a hand-rubbed French finish on a piece of mahogany to a sprayed-on stain and poly-u finish on a piece of pine.
Yes there are. Most compantie test-fly their planes before finalizing the plans and related details. The Piranha II, which I designed and have flown for over 10 years, has been through many changes, and the plans changed with the plane. It's all up to date and correct, and it flys GREAT! Dr.1 Driver "There's a Hun in the sun!"
Funny you should mention that, Paul, as I just walked in with some of it - the UK-made stuff sold here under the Worldtex brand.
As for another poster's saying there's no such thing as a "sorted out" plan, I'll buy your argument to a degree, but only partially. If one uses an engine/prop combo similar in thrust and torque to what's called for in the plan, I would certainly expect those little slidey-clicky things alongside the radio sticks on non-computer radios to be able to trim out any variances.
Second, using the trims switches on the Tx are what cause things like corkscrews when you attempt to do a loop.
Try it for yourself. Trim the plane with the trim switches for straight and level flight, and then, in dead air, point the plane straight up at full throttle. If your trim settings work to correct the thrust, the plane will go straight up, not to the left or right, nor to the canopy or wheels. If it does not, you need to adjust the engine thrust. Let us know how you come out with your method of trimming. For further info check out the trim chart I posted. It does NOT just apply to pattern planes. Trimming your plane properly can take a dog and make it a joy to fly.
In addition, there is the dress shop polyester that can be applied either with cement or nitrate dope and it can be heated to super tight. Then it must be painted. Very easy to work with. Have to use care with the dope and paint thing as it has a tendency to pull away from multiple coats of dope. Had 2 4-star 40s that each became very ragged after a couple years. There was one of the famous Home-Built designers that lost his life when a rather new polyester wing covering, doped on in the usual way, left the wing in flight. Was it Whitman?
I agree with you except for the epoxy part. I do like epoxy in a few areas such as wing hold downs and firewall , otherwise it's tightbond everywhere. I do usually have a small bottle of CA so I can glue fingers together and patch cuts.lol I'm with you on the fitting of parts. My wife say's "why take so much pains, no one will see it" but thats the way I like to do it. Now that we have all these hot shot young pilots building skills are sort of an equalizer...at least I would like to think so. :-)
I do have a couple fun fly ARF's. They were cheaper than a kit and covering and they are just that , "fun fly", to beat around with.But I still like to build'em myself. Like you said , it's nice to show up at the field with one. I like it when they say "what is it , never saw that in the catalog". It is a sad situation in most ways, but I think overall it's a good thing in that people get started in the hobby that otherwise would not have invested their time building. We have had few that started that way and us older farts kept stressing the merits of building and some have started buying and building kits. I'm afraid that we will keep seeing fewer and fewer kits on the market. I do like to build from plans but not everything. I guess time will tell.
Old Fart here... I think it's for two reasons. First, the engine mounts available are more convenient and allow for easier changing of thrust angles. Hardwood mounts are usually epoxied in and are pretty much permanent. All you can do is either shim for up or down, or re-drill for lateral thrust change which seems kind of brutal. Store bought mounts are easier. Second, aah, well, I forgot the second reason. Like I said, I'm an Old Fart and those things happen.
Ah, we're talking about a breakaway plate! I have a Telemaster 40 that uses said animal to keep the engine and the fuse from parting company, and I've made different plates as I've put different engines on the plane. The system seems to work fine, although the glass-filled nylon mounts are just so convenient! However, if you got the maple and the plywood, go for it!
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.