Why Are Nearly All Kits and ARFs Incorrectly Designed?

Why Are Nearly All Kits and ARFs Incorrectly Designed?
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Why Are Nearly All Kits and ARFs Incorrectly Designed? - 11/6/2006 9:04:24 AM

DarZeelon

Posts: 7109
Joined: 4/9/2003
From: Rosh-Ha'Ayin, ISRAEL
Status: offline

Most glow engine models; at least 98%, I believe, do not use a fuel pump.

But all the kits/ARFs I have ever seen mount the engine at the wrong height in relationship to the fuel-tank.

I.e. the tank is mounted so the fuel tube(s) exits the firewall in the middle of the engine mount, which for most engines means the tank center-line is at the crankshaft level; about 1.5" below the carburettor.

This does not apply to those 'rear intake' racing engines, with their carburettors mounted onto the back-plate drum/disk valve, but one of how many engines are like that?

A solution is to mount the engine sideways...
Another solution is to mount the engine upright under the engine-bearers, or inverted, over the bearers (according the what the model is designed for). But most engines are wider over the mounting-lugs than they are under them... Could be a problem.

...But there is another problem there; as the thrust-line would be lower (not as the model was designed) and so would the propeller ground-clearance...

Another solution is to use one of those rectangular 'slant-tanks' (that is wider than it is tall) and mount it, for an upright engine, inverted and snug against the top of the tank-compartment, or for an inverted engine, upright and snug against the bottom of the tank-compartment.
But that would usually mean having to use a smaller fuel-tank...

The obvious last solution is to use an on-board pump/regulator...

But, how many kits/ARFs did you ever see with such tank-mounting (or engine mounting) instructions?

So, will all those of us that are not scratch builders have to 'bite the bullet' and just live with an incorrectly leveled power-system???

Or will ALL kit/ARF manufacturers ever GET SMART?

Or will future engine mounts be designed so the hole in the firewall will be at carburettor level?

< Message edited by DarZeelon -- 11/6/2006 10:46:42 AM >

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RE: Why Are Nearly All Kits and ARFs Incorrectly Designed? - 11/6/2006 10:31:56 AM

BillS

Posts: 3052
Joined: 9/6/2004
From: Greensboro, NC, USA
Status: offline

Maybe it’s possible that there was no design effort and most of the ARF’s have never been test flown.

If the design does not test for reasonableness I would never purchase the airplane. Unfortunately often the purchaser is uninformed until after the disaster. A P-38 with improperly mounted tanks is absolutely insane.

And no I don’t intend to use pumps nor heat.

The manufacturers will not get smart until we stop purchasing improperly designed junk.

Bill

(in reply to DarZeelon)

Post #: 2

RE: Why Are Nearly All Kits and ARFs Incorrectly Designed? - 11/6/2006 12:44:21 PM

majortom-RCU

Posts: 1579
Joined: 12/11/2001
From: Merrimack, NH, USA
Status: offline

Dar, you have put your finger on a widespread problem. Many's the time I've rebuilt an ARF tank compartment to get the tank at the right level. Often I take the easy way out and side-mount, when I'd rather not side-mount. More often I will resort to a trusty YS pumped four-stroke or put a pump/regulator on a two-stroke. Like many kit-builders, I read the manufacturer's manual, then proceed to build it how I want it, instructions be damned. As soon as I clear out a little larger building space, this will be less of a problem with my gassers.

(in reply to DarZeelon)

Post #: 3

RE: Why Are Nearly All Kits and ARFs Incorrectly Designed? - 11/6/2006 2:01:06 PM

AllTheGoodNamesAreTaken

Posts: 601
Joined: 8/31/2002
From: Oak Ridge, NC, USA
Status: offline

quote:

ORIGINAL: DarZeelon

Most glow engine models; at least 98%, I believe, do not use a fuel pump.

But all the kits/ARFs I have ever seen mount the engine at the wrong height in relationship to the fuel-tank.

I.e. the tank is mounted so the fuel tube(s) exits the firewall in the middle of the engine mount, which for most engines means the tank center-line is at the crankshaft level; about 1.5" below the carburettor.

This does not apply to those 'rear intake' racing engines, with their carburettors mounted onto the back-plate drum/disk valve, but one of how many engines are like that?

A solution is to mount the engine sideways...
Another solution is to mount the engine upright under the engine-bearers, or inverted, over the bearers (according the what the model is designed for). But most engines are wider over the mounting-lugs than they are under them... Could be a problem.

...But there is another problem there; as the thrust-line would be lower (not as the model was designed) and so would the propeller ground-clearance...

Another solution is to use one of those rectangular 'slant-tanks' (that is wider than it is tall) and mount it, for an upright engine, inverted and snug against the top of the tank-compartment, or for an inverted engine, upright and snug against the bottom of the tank-compartment.
But that would usually mean having to use a smaller fuel-tank...

The obvious last solution is to use an on-board pump/regulator...

But, how many kits/ARFs did you ever see with such tank-mounting (or engine mounting) instructions?

So, will all those of us that are not scratch builders have to 'bite the bullet' and just live with an incorrectly leveled power-system???

Or will ALL kit/ARF manufacturers ever GET SMART?

Or will future engine mounts be designed so the hole in the firewall will be at carburettor level?

And how may people blame brand X engine due to this issue??? You never hear someone compaining that they can't get their engine to run right on the test stand.

< Message edited by AllTheGoodNamesAreTaken -- 11/7/2006 12:03:10 AM >

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Jeff Walker

(in reply to DarZeelon)

Post #: 4

RE: Why Are Nearly All Kits and ARFs Incorrectly Designed? - 11/6/2006 3:39:43 PM

fancman

Posts: 1266
Joined: 11/21/2002
From: N. Charleston, SC, USA
Status: offline

I really don't see the purpose of your post. No way are kit MFG's going to look at this and all of a sudden start to redesign all their kits. I've had many ARF's and while the fuel tank location isn't optimal, it really isn't a big deal. My engines run jus t fine when the carbs are needled in correctly.

quote:

ORIGINAL: DarZeelon

Most glow engine models; at least 98%, I believe, do not use a fuel pump.

But all the kits/ARFs I have ever seen mount the engine at the wrong height in relationship to the fuel-tank.

I.e. the tank is mounted so the fuel tube(s) exits the firewall in the middle of the engine mount, which for most engines means the tank center-line is at the crankshaft level; about 1.5" below the carburettor.

This does not apply to those 'rear intake' racing engines, with their carburettors mounted onto the back-plate drum/disk valve, but one of how many engines are like that?

A solution is to mount the engine sideways...
Another solution is to mount the engine upright under the engine-bearers, or inverted, over the bearers (according the what the model is designed for). But most engines are wider over the mounting-lugs than they are under them... Could be a problem.

...But there is another problem there; as the thrust-line would be lower (not as the model was designed) and so would the propeller ground-clearance...

Another solution is to use one of those rectangular 'slant-tanks' (that is wider than it is tall) and mount it, for an upright engine, inverted and snug against the top of the tank-compartment, or for an inverted engine, upright and snug against the bottom of the tank-compartment.
But that would usually mean having to use a smaller fuel-tank...

The obvious last solution is to use an on-board pump/regulator...

But, how many kits/ARFs did you ever see with such tank-mounting (or engine mounting) instructions?

So, will all those of us that are not scratch builders have to 'bite the bullet' and just live with an incorrectly leveled power-system???

Or will ALL kit/ARF manufacturers ever GET SMART?

Or will future engine mounts be designed so the hole in the firewall will be at carburettor level?

(in reply to DarZeelon)

Post #: 5

RE: Why Are Nearly All Kits and ARFs Incorrectly Designed? - 11/6/2006 4:08:55 PM

rainedave

Posts: 5193
Joined: 7/21/2005
From: Greensboro, NC, USA
Status: offline

I think the point of DarZeelon's post is that arf manufactures are focused on producing planes that they think will sell in today's r/c market based primarily on visual appeal. That's a lot different than designing and thoroughly testing models for optimum performance. The two cannot be confused or conflated. Now, whether or not that's what arf manufacturers are actually doing is a different issue.

(in reply to fancman)

Post #: 6

RE: Why Are Nearly All Kits and ARFs Incorrectly Designed? - 11/6/2006 4:39:09 PM

Gizmo-RCU

Posts: 976
Joined: 9/17/2002
From: Athol, ID, USA
Status: offline

I fully support Dar's position. Case in point is the UCD's with their inverted engine and very high tank. Some of the others like the Harrier have about the same problems and can cause a lot of anguish when trying to tune and successfully fly them.
It's seems to be all about looks, the narrow deep Fush. for knife edge and clean looks. A pump/regulator, side mount or tank re-location are your only options. A proper design would eliminate much of this and most likley sell more models.........

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RE: Why Are Nearly All Kits and ARFs Incorrectly Designed? - 11/6/2006 5:36:05 PM

Motorboy

Posts: 1693
Joined: 2/7/2004
From: Bergen, NORWAY
Status: offline

Same here i fully support Dar's position....
I had problems with Kyosho Me 190 with 4 stroke engine 0.52 inverted, there was difficult to make idling nice. Tried difference 4 stroke glowplug and adjusted for each glow plugbrand before the problem was solvent since tank position was not correct in height.

Jens Eirik

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Jens Eirik
All landings are just controlled crashes!

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RE: Why Are Nearly All Kits and ARFs Incorrectly Desig... - 11/6/2006 6:20:42 PM

GrantK

Posts: 136
Joined: 8/3/2003
From: Ruston, LA, USA
Status: offline

Seems to me that tank placment isn't a real big issue. Few of my planes have the tank well below carb level but the only i'll affect is I have to do a little extra priming. But I do agree that arf manufactors shouldn't compromise a design to make it more marketable. Thats why I try to avoid arfs and build kits.

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RE: Why Are Nearly All Kits and ARFs Incorrectly Designed? - 11/6/2006 6:49:58 PM

Ed Cregger

Posts: 7749
Joined: 1/31/2002
From: Ringgold, GA, USA
Status: online

I think that the real problem is the lack of a properly fuel supplied glow engine. Expecting suction to meet the demands of a model engine's fuel requirements is outdated, obsolete and disastrous, in many instances. Just think of how many models have been lost or damaged due to this single factor. For most folks, buying a pressure fed/fuel regulated engine in the beginning would have been a far less expensive affair.

Ed Cregger

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Artisan

"Flying models since the Fifties - I'll get the hang of this yet!!!"

(in reply to DarZeelon)

Post #: 10

RE: Why Are Nearly All Kits and ARFs Incorrectly Desig... - 11/6/2006 7:00:46 PM

XJet

Posts: 3465
Joined: 3/31/2003
From: Tokoroa, NEW ZEALAND
Status: online

What surprises me is that we're still using engines with such a crude fuel system. No pump, no pressure regulation just a basic venturi-spraybar setup (albeit with twin needles).

You won't find any gas engines that are this primitive -- and that's probably why so many folks find that gassers are so much more reliable than glow.

How hard can it be to build a small diaphram pump into the backplate of an engine and add a regulator (like the Cline or IronBay) to the fuel system?

Sure, it would cost a bit more and add a bit of weight -- but I suspect that this cost would be recouped the frist time you avoided a dead-stick on take-off or at an inopportune time when you're not within gliding distance of the field.

Yes, I know that some glow engines have been made like this -- but why aren't more?

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RE: Why Are Nearly All Kits and ARFs Incorrectly Desig... - 11/6/2006 7:19:20 PM

submikester

Posts: 1253
Joined: 8/13/2004
From: El Segundo, CA, USA
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I asked the same question a while back...

http://www.rcuniverse.com/forum/m_3994496/anchors_3994496/mpage_1/key_/anchor/tm.htm#3994496

(in reply to XJet)

Post #: 12

RE: Why Are Nearly All Kits and ARFs Incorrectly Desig... - 11/6/2006 7:51:23 PM

fancman

Posts: 1266
Joined: 11/21/2002
From: N. Charleston, SC, USA
Status: offline

I hear what's being said here but in the club I belong to 95% of the members fly ARF's and I haven't witnessed all the problems mentioned here. Everyone seems to be able to adjust their engines and fly just fine without any excessive number of dead sticks which could be attributed to ARF design. I've been flying all kinds of kits and ARF's for more than 20 yrs and tank placement is not always optimal but I've never considered blaming the kit MFG for my inability to properly set up my engines to work no matter what the kit design. I suppose it would be nice if they took more time to get the tank placement more correct but does anyone think that is going to happen?

(in reply to submikester)

Post #: 13

RE: Why Are Nearly All Kits and ARFs Incorrectly Desig... - 11/6/2006 7:58:42 PM