Author Topic: Maple motor mounts vs firewall mount (Read 4544 times)

Paul Taylor · « **on:** May 05, 2012, 02:54:51 PM »

What is the main reason RC mounts are not used. Seem like you have more options with motor orientation with the RC mount.

Tim Wescott · « **Reply #1 on:** May 05, 2012, 03:18:33 PM »

Size, strength and weight?

For a firewall mount you need to make the structure up to the firewall strong, and you need a strong firewall, then you need strong mounts to bolt to the firewall.

For a beam mount, the motor mount crutch becomes part of the front fuselage structure, so all the weight that you're using to hold the motor with is also strengthening the nose.

And, you can build your fuselage sides right up to the motor mount.

Bob Reeves · « **Reply #2 on:** May 05, 2012, 05:21:18 PM »

Reason is because that is the way it's always been done..

I use RC mounts for my 4 strokes and like them, have posted several times all the reasons I decided to switch. Only reason not to is because you think if it's used in RC it can't work for CL.

Will Hinton · « **Reply #3 on:** May 05, 2012, 05:49:13 PM »

I started using r/c mounts a long time back, still do beams occasionally, but mostly radials. I have been building the nose area an ounce LIGHTER than with beams. We tend to overbuild so often. Go to your local airport and get them to let you look in the back of the fuse, sometime. Ain't much back there, but what's there is engineered for the lightest and strongest it can be. I have a r/c mount TP based ship with several hundred flights on it using a PA65 and pipe setup, no problems.
Just engineer the nose right and go for it.

Randy Powell · « **Reply #4 on:** May 05, 2012, 06:03:26 PM »

Alignment is often easier with beam mounts. I've used both. I've also used a combination mount that uses beams but is built like a radial mount. Al Rabe did this a lot. Comes down to what you are trying to accomplish. Radial setups are generally heavier than beam mounts, all things being equal, but they don't have to be.

Paul Taylor · « **Reply #5 on:** May 06, 2012, 07:37:14 AM »

I saw a RC plane with a tube muffler and the way the engine was setting on the mount the stinger came out of the bottom of the fuse. Very clean looking.

Peter Ferguson · « **Reply #6 on:** May 06, 2012, 10:39:42 AM »

There is the same discussion going on in the Senior Pattern Flyers group as a lot of the old Pattern designs used beam mounts and they are now being replaced with firewall mounts. The thinking over there is that the firewall mount looses some of the benefit of distributing the loads into the fuse sides rather than through the firewall mount joint. I think I agree, but firewall mounts have worked well for many years and planes.

proparc · « **Reply #7 on:** May 06, 2012, 11:10:15 AM »

Tradition,

RC guys have traditionally used radial,and stunt guys traditionally have used beam. Of course, either one can work in either scenario.

Beam tends to make a nicer looking nose which we like in stunt. Radial allows for changing different motors which they like in RC.

Brian Massey · « **Reply #8 on:** May 06, 2012, 01:53:59 PM »

Never used a firewall mount, but have one in the ready position for my next build. I want to use a Saito and want to mount it on it's side instead of inverted. I have plans to make sure it's well gusseted and braced.

Brian

Ward Van Duzer · « **Reply #9 on:** May 06, 2012, 02:01:02 PM »

Consider also, that engine angles may be adjusted using radials without chewing up engines!

W.

larry borden · « **Reply #10 on:** May 06, 2012, 02:02:08 PM »

I'm using a Dave Brown mount on the SWIFT.

riley wooten · « **Reply #11 on:** May 06, 2012, 08:55:53 PM »

I have a lot of faith in radial mounts and think they are much easier to build. They also give a lot more tank room.
Our quickie 500 kit "Scat Cat 500" only had a 2" square 1/4" ply firewall. For years we sold appx. 500 a month and
I don't remember ever having a complaint about firewall failure. We used bass triangles and corner doublers in the
nose and recommended .5 glass cloth inside and out. We know many only used plastic film on outside. They had to
weigh 3-1/2 pounds (56 oz) ready to fly with at least 12 oz. of radio and if you wanted to win you had to be at the
min. They had honking 40's and flew 150 mph. I think if they will stand up to that they will be ok in control line......
RW

Chris Wilson · « **Reply #12 on:** May 06, 2012, 09:51:43 PM »

With a beam mount you can definitely get the tank closer up behind the engine by virtue of not having any firewall mounting system spacing you forward.
So the beam mount is the most compact of all.
Thrust line alignment also becomes a no-brainer because of the obviousness of the extended lines.
Beam mount is also cheaper, well its simply a forked piece of wood or a shaped beam.

What I don't understand about the proponents of radial mounts is that 99.9% of engines have beam mount lugs cast into them as a given so you are virtually forced to use a heavier hybrid combination of both systems anyway.

Radial mounts seem to be supremely flexible in use though and although some say that the weight is less than an equivalent beam system I have trouble grasping exactly what is 'equivalent' as it becomes an apples and oranges debate the more you dig into it.

larry borden · « **Reply #13 on:** May 07, 2012, 07:27:41 PM »

I flew many of Riley's Skooter IIs and all had the Hayes mounts. The Skooter had a small firewall also and I was flying them with ST G21 46. We also drilled the mount to install the nose gear, never had a problem.

RogerGreene · « **Reply #14 on:** May 08, 2012, 06:21:14 AM »

What are the names of the radial mounts used for stunt and where can they be bought?

Roger

Avaiojet · « **Reply #15 on:** May 08, 2012, 06:37:09 AM »

I have at least eight "firewall" mounts left over from my R/C days and was going to put them on ebay along with 100 other R/C HDWE items and things. Actually the second time I've sold firewall mounts this way with 100 other items in a Lot. Last time I had close to a dozen mounts!

Now you have me rethinking to keep them. I'd have to take the photos all over again. Plus, with servos operating things in Scale CL models, I shouldn't get rid of anything! Egads!

Nah, still going on ebay.

Charles

larry borden · « **Reply #16 on:** May 08, 2012, 07:22:05 AM »

Quote from: RogerGreene on May 08, 2012, 06:21:14 AM

What are the names of the radial mounts used for stunt and where can they be bought?

Roger

I'm using Dave Brown mounts and most hobby shops stock them. I got mine from Roy's here in the DFW area.

Bob Reeves · « **Reply #17 on:** May 08, 2012, 10:36:28 AM »

Quote from: RogerGreene on May 08, 2012, 06:21:14 AM

What are the names of the radial mounts used for stunt and where can they be bought?

Roger

I like the two piece SIG mounts mainly because they are light and I can put the carb on a 4 stroke right back against the firewall.

This is a thread showing the nose of my Latency before it was finished.

http://stunthanger.com/smf/index.php?topic=11564.0

RogerGreene · « **Reply #18 on:** May 08, 2012, 10:58:39 AM »

Great on the Dave Brown mount. Here is my application.

Roger

Avaiojet · « **Reply #19 on:** May 08, 2012, 11:09:49 AM »

Roger,

Nice work!

What's the model?

Allows for a wider fuselage for scale or unusual models.

Nice.

Roger, tank cover!! I'll be lookin'

Charles

Chris Wilson · « **Reply #20 on:** May 08, 2012, 05:42:25 PM »

Another point about the use of RC style mounts is that the mounting ring on the firewall, and in fact the need for any firewall at all, has the potential to disrupt the cooling airflow in certain designs.

larry borden · « **Reply #21 on:** May 08, 2012, 05:50:35 PM »

Quote from: Chris Wilson on May 08, 2012, 05:42:25 PM

Another point about the use of RC style mounts is that the mounting ring on the firewall, and in fact the need for any firewall at all, has the potential to disrupt the cooling airflow in certain designs.

Why would the mount disprupt air flow?

Bill Hummel · « **Reply #22 on:** May 08, 2012, 06:23:54 PM »

A properly designed and built beam front end on a stunter allows you to tie the engine vibration into the ply fuse doublers, and likely into the wing structure. In the older 2 strokes, vibration was a serious concern, and this structure allowed for fairly good control of the vibration, giving better and more consistent engine runs. I believe the newer, better built and balanced 2- and 4-stroke engines develop considerably less vibration, so the radial mounts may indeed give adequate strength for good engine runs. We played with the Score ARF for a season with the stock firewall and radial mounts. The PA engines ran very well in this set-up, while the old ST 60 just didn't seem happy. The late Jim Greenaway talked often about the critical need for the front end to be able to distribute the vibration throughout the airframe...his "reference" was primarily the older ST 60-style engine runs.

Chris Wilson · « **Reply #23 on:** May 08, 2012, 06:34:13 PM »

Quote from: larry borden on May 08, 2012, 05:50:35 PM

Why would the mount disprupt air flow?

Because a firewall mount by default needs a firewall, and walls block airflow, especially perpendicular ones

And since all of this is one vs the other topic, beam mounts do not need a firewall - so no wall, no potential blockage.

Looking at this in its simplest terms, the task is to link the thrust unit to the lifting surface, and a straight line provided by a beam between the two undoubtedly is the simplest method. An RC style firewall mount adds complexity and personally I would prefer to mount directly off the engines back plate to the firewall 'if' I went for that system and that is something that is not possible with most four strokes because their back plate is obstructed.

Igor Burger I believe went for the direct back plate system with his 'Max' model as do some RC fliers with their indirect modified and combined back plate/ radial mount systems.

Its not that I don't like RC style mounts, its just that I prefer it differently.

Cheers.

Chris Wilson · « **Reply #24 on:** May 08, 2012, 06:45:04 PM »

Quote from: Bill Hummel on May 08, 2012, 06:23:54 PM

A properly designed and built beam front end on a stunter allows you to tie the engine vibration into the ply fuse doublers, and likely into the wing structure. In the older 2 strokes, vibration was a serious concern, and this structure allowed for fairly good control of the vibration, giving better and more consistent engine runs. I believe the newer, better built and balanced 2- and 4-stroke engines develop considerably less vibration, so the radial mounts may indeed give adequate strength for good engine runs. We played with the Score ARF for a season with the stock firewall and radial mounts. The PA engines ran very well in this set-up, while the old ST 60 just didn't seem happy. The late Jim Greenaway talked often about the critical need for the front end to be able to distribute the vibration throughout the airframe...his "reference" was primarily the older ST 60-style engine runs.

This strikes a chord with me Bill, I like my diesels and have two PAW 40's waiting for their 'Freebird' homes to be completed.

Now these engines have quite substantial cast iron pistons lumping up and down coupled with a goodly amount of rapid ignition diesel thump, and their purpose designed models have, in the first inverted engine version, tapered beam mounts running the entire length of the fuselage to 'spread' the love the best they can and in the later side mounted version beams running right back to the inboard wing root/fuselage corner.

A more solid design I can't think of!

Bob Reeves · « **Reply #25 on:** May 09, 2012, 03:49:42 AM »

Don't think anybody is really pushing one or the other, you need to do what works for you and what you are comfortable with. We all know maple beam mounts work but in some situations an RC mount can be a better choice. I run my 4 strokes side mounted, using beam mounts would really complicate the nose structure so I choose to use an RC mount.

RogerGreene · « **Reply #26 on:** May 09, 2012, 08:30:55 AM »

Reply #19

Its my own design called 'Altair'. It was first an enlargement of my AETOS design. The AETOS is a 42" wing span profile design and the Altair is 52" wing span full fuselage. Both straight wings.

Joseph Patterson · « **Reply #27 on:** May 09, 2012, 08:49:34 AM »

I've used both, beam and radial and found no noticeable difference as far as the way vibration effects one more than the other. In fact, I converted one of my planes from beam to radial and it seemed to be less with the radial( actually it had more mass which probably changed the harmonics of the airframe). However, that is only my limited experience, it amounts to how well the firewall system is made, and what a person prefers. I like both.
Doug