| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 770.14 | tight fit in the cowl | LEDS::LEWIS | | Tue Nov 10 1987 16:47 | 26 |
|
I need advice on three things.
1. This has to do with the engine mounting in my CAP 21. I am
putting an OS .45FSR in it and have to turn the carburetor 180
degrees so the needle valve won't stick out the top of the cowl.
Does anyone know of this being a problem (other than the fact
that I'm going to have to make a special 90 degree fuel nipple
so the fuel tubing doesn't stick out into the prop arc)?
2. The cheek cowl will barely fit over the engine head if I grind
off some of the glo plug tip. I was going to solder a remote
wire to the glo plug and have the clip underneath the cowl.
Now I'm worried that the cheek cowl will melt, as the head will
be within 1/16" of the cheek at some points. I planned on cutting
out the underside of the cowl to maximize air flow, but am I
kidding myself thinking that the cowl won't melt? I'd like to
hide the entire engine, but that cheek is going to be CLOSE.
3. What can I use to replace the stock tailwheel configuration they
give in the G.P. kit? I don't want to put force on the rudder
hinges if I can help it.
That's it for now, any advice would be appreciated.
Bill
|
| 770.15 | WELL, IF IT WERE ME, I'D......... | GHANI::CASEYA | THE DESERT RAT RC-AV8R | Tue Nov 10 1987 17:47 | 60 |
|
> 1. This has to do with the engine mounting in my CAP 21. I am
> putting an OS .45FSR in it and have to turn the carburetor 180
> degrees so the needle valve won't stick out the top of the cowl.
> Does anyone know of this being a problem (other than the fact
> that I'm going to have to make a special 90 degree fuel nipple
> so the fuel tubing doesn't stick out into the prop arc)?
* Also, be very careful regarding the position of the hole or slot in the carb
spray bar (if applicable). It needs to point directly down the throat of the
carb venturi or you'll have no end of grief with it. What's wrong with the
needle-valve sticking out the top of the cowl? I'd rather have it there where
it's easily accessible than on the bottom, under the cheek-cowl where you may
have to grope for it and fumble yer' fingers into the prop. I like to cut (or
extend) my needle-valve shafts to where they just barely protrude from the sur-
face, then silver-solder the head of a 6-32 hex-head bolt on the end so I can
adjust the needle using a ball-driver. Another possible option is to obtain one
of the O.S. remote needle valve assy's and relocate the needle "anywhere" you
like.
> 2. The cheek cowl will barely fit over the engine head if I grind
> off some of the glo plug tip. I was going to solder a remote
> wire to the glo plug and have the clip underneath the cowl.
> Now I'm worried that the cheek cowl will melt, as the head will
> be within 1/16" of the cheek at some points. I planned on cutting
> out the underside of the cowl to maximize air flow, but am I
> kidding myself thinking that the cowl won't melt? I'd like to
> hide the entire engine, but that cheek is going to be CLOSE.
* Don't solder a wire to the glo-plug...I guarantee it'll constantly break off
and be a real source of irritation. If you need to make a remote glo-plug con-
nection, take it from one who's had the experience, attach the wire to the plug
via a solderless clip affair of some sort or you'll live to regret it. This
probably means you won't have room in the 1/16" clearance you describe but I'm
a great believer in keeping things "functional" and easy to handle/service,
"first and foremost," so if it were me, I'd simply cut the cheek open about 1/16
-1/8" larger than the head diameter and solve "all" the problems yer' fretting
over. I guarantee you'll never see it on a 100 mph low pass or from the saddle
of a bucking horse. No sweat with cooling or with connecting to/replacing the
glo-plug that way.
> 3. What can I use to replace the stock tailwheel configuration they
> give in the G.P. kit? I don't want to put force on the rudder
> hinges if I can help it.
* Try to pick up one of the very scalelike CB Associates (I think) leaf spring
tailwheel assy's. These, just like a full scale light-plane, bolt to the bottom
of the fuse and connect to the rudder via a pair of springs, removing any/all
loads from the rudder/rudder servo. If you know someone who's had the misfortune
to've crashed one of the E-Z type ARF's, e.g. Laser, Citabria, Pitts, Christen
Eagle, talk `em out of the tailwheel assy as it's identical in function to the
CB Associates item which "can" be difficult to obtain in the .60 size you prob-
ably require.
> That's it for now, any advice would be appreciated.
> Bill
* Pornada, amigo, Al
|
| 770.16 | | SPKALI::THOMAS | | Wed Nov 11 1987 10:27 | 11 |
| For a tailwheel the CB is great. Another type which I like better
is made by Ohio Superstar's. It not a springy.
If you still go the alternate glow plug way you can make one using
some wire and a wheel collar. Drill a hole in the collar and sand
the exterior adjacent to the hole. Tin the wire and the insert it
into the hole and solder. This then is secured to the glow plug
vai the set screw.
Tom
|
| 770.17 | WATCH THE WICKING........ | GHANI::CASEYA | THE DESERT RAT RC-AV8R | Wed Nov 11 1987 12:50 | 19 |
| Re: -.184,
This method "will" work but there are two things which must be
considered: 1.) When soldering the wire into the wheel collar,
the "utmost" care must be taken to get the solder joint done quickly
enough to prevent the solder from wicking back up under the insulation
as the resulting stiffness of the wire (due to the solder-wicking)
makes it vulnerable to vibration/breakage. 2.) Use the smallest,
lightest wheel collar possible as the weight added to the the plug
can make it susceptible to breakage, again, due to vibration of
the mass added to the plug.
I've had the best luck with a simple "bobby-pin" like clip bent
from small dia. music wire with the electrical wire carefully soldered
to it. The almost non-existance of weight protects the plug from breakage
and the fact that it is a non-rigid sort of connection seems to
prevent breakage of the soldered wire.
Adios, Al
|
| 770.18 | on keeping the cowl tidy | LEDS::LEWIS | | Wed Nov 11 1987 13:15 | 62 |
|
> Also, be very careful regarding the position of the hole or slot
> in the carb spray bar (if applicable). It needs to point directly
> down the throat of the carb venturi or you'll have no end of grief
> with it.
I just turned the carb around without touching the needle valve
assy - so I would think the spray bar orientation wouldn't be
affected.
> What's wrong with the needle-valve sticking out the top of the cowl?
> I'd rather have it there where it's easily accessible than on the
> bottom, under the cheek-cowl where you may have to grope for it and
> fumble yer' fingers into the prop.
YUCK! The same thing that's wrong with having a huge hole in the
side of the cheek cowl for the cylinder head! Thought I'd try my
best to imitate you scale masters that manage to hide everything
that makes a plane look like a model. From experience I've found
that I usually need to make one needle valve adjustment per day,
so even if it's a little more difficult to do (from underneath) I
didn't think it would be too bad. Your point is well taken though,
I think I'll experiment with it to see just how difficult it's going
to be.
> Don't solder a wire to the glo-plug...I guarantee it'll constantly
> break off and be a real source of irritation.
I meant to say silver-solder. Are you talking about the problem
that the engine heat melts the solder, or vibration breaking the
joint? I've used silver solder to build a custom pipe and found
it CAN stand the heat these engines produce (while regular solder can't).
I went through the same pain you mentioned after trying to solder
a wire on the plug of my Enya 46-4C (they REQUIRE remote plugs!).
I thought silver solder would solve the problem. No?
Tom's wheel collar suggestion is a good one but I just don't have
the room - like I said, it's TIGHT. I was planning on grinding
off all but 1/16 of the glo plug tip.
> if it were me, I'd simply cut the cheek open about 1/16
> -1/8" larger than the head diameter
Say it ain't so! I was AFRAID that's the message I was gonna get.
I was hoping you were gonna point me to some special insulating
material made of 1/32 teflon sheet or somethin like that, that I
could put inside the cheek cowl. D**M! I can already picture
the melting cheek cowl on my prize posession after all this work!
I may have to just give in on this and cut it out. Aargh!
> Try to pick up one of the very scalelike CB Associates (I think) leaf
> spring tailwheel assy's.
They have 'em in the Tower Hobbies book - 0-9 lbs, .60-size planes
for about ten bucks. I hadn't planned for it when I built the fuse
and it looks like it needs a separate pushrod. True?
Thanks again, wish I'd asked these questions sooner!
Bill
|
| 770.19 | MY VOTE REMAINS "KEEP IT FUNCTIONAL".... | GHANI::CASEYA | THE DESERT RAT RC-AV8R | Wed Nov 11 1987 14:03 | 70 |
| > I just turned the carb around without touching the needle valve
> assy - so I would think the spray bar orientation wouldn't be
> affected.
* Ah yes, but what if (as is common) the spray-bar hole/slot was already an-
gled back into the throat to take advantage of the intake air direction? By
turning the carb 180-degrees, the hole/slot will now angle forward and the po-
tential of a fuel draw/feed problem "may" exist. I don't "know" that this will
be the case, or even that it'll cause a problem but it needs to be considered
and thoroughly checked out "before" committing yer'self to this installation.
> YUCK! The same thing that's wrong with having a huge hole in the
> side of the cheek cowl for the cylinder head! Thought I'd try my
> best to imitate you scale masters that manage to hide everything
> that makes a plane look like a model.
* Then why not cut a small hole, centered on the glo-plug and just large enough
to accomodate yer' glo-plug connector and/or remove/change the plug?? That's how
I did the Bucker and Bob Frey did the exact same thing on his new Jug. H*ll, the
whole head hangs out under the nose of my MiG-3 and, to the best of my know-
ledge, it's never cost me a point in static as it's strictly prohibited by the
rules to deduct points for concessions to model hardware. Why invite Masters-
class frustration to the bird unless you actually plan to compete it? Hiding
everything "does" have a price and it's usually increased aggravation regarding
everyday, normal operation of the model; engine overheating problems, 1-hour to
change plugs, etc., ad infinitum.
> I meant to say silver-solder. Are you talking about the problem
> that the engine heat melts the solder, or vibration breaking the
> joint?
* I was talking about breakage due to the effects of vibration on the wire
which has become hard/stiff due to the wicking of the solder back from the
actual joint.
> I was hoping you were gonna point me to some special insulating
> material made of 1/32 teflon sheet or somethin like that, that I
> could put inside the cheek cowl.
* I'm not gonna' stick my neck out and say that such a miracle material
doesn't exist but, if it does, I've never heard of it. Proper/adequate ven-
ting of cooling air through the cheek cowl "might" prevent melting of the plas-
tic but how do you predict the result without actually exposing yer'self to the
possibility of a melt-down. A good alternative, if you could find the means
to do it, might be to make a fiberglass cheek-cowl (or purchase an aftermarket
item, if available) and substitute it for the plastic one. Glass would be much
more heat resistant.
> They have 'em in the Tower Hobbies book - 0-9 lbs, .60-size planes
> for about ten bucks. I hadn't planned for it when I built the fuse
> and it looks like it needs a separate pushrod. True?
* That's the one you want. The only thing you might have to do to adapt this
unit to yer' ship is to install a plywood mounting plate on the bottom of the
fuse. No extra pushrod is needed; the wheel is driven by a pair of springs
running from small horns on each side of the bottom of the rudder to a tiller
bar atop the tailwheel strut. The springs provide the steering while isolating
the rudder (and servo) from tailwheel loads, identical to full-scale applica-
tion.
> Thanks again, wish I'd asked these questions sooner!
> Bill
It doesn't sound like you've "painted yer'self into a corner" yet, Bill...you
just have some decisions to make before proceeding. I'd still recommend going
for the functional/serviceable approach...you'll get a lot more enjoyment and a
lot less hassle in the long run.
Adios, Al
|
| 770.20 | roll your own | LEDS::HUGHES | Dave Hughes (LEDS::HUGHES) NKS-1/E3 291-7214 | Wed Nov 11 1987 15:05 | 12 |
| I was going to suggest trying to fabricate a slightly deeper cowl
that would give you some more room and would be unlikely to be noticed
as being out of scale. If you take Al's suggestion and make one
out of fiberglass you'd solve both problems at once - give yourself
a tad more room and get heat protection too. That cowl isn't very
complex, I would think you could make a simple form out of balsa
and lay up some fiberglass on it.
Me, I'll stick to sport ships and monokote for the time being!
Good luck!
Dave
|
| 770.21 | Spring, Sprang, Sprung... | K::FISHER | Battery, Mags, & Gas Off! | Wed Nov 11 1987 18:08 | 14 |
| Speaking of glow connectors - I bought one of these on-board ignitions
several months ago and it came with two springs. You pick a spring
according to the size of the connector on your glow plug and solder the
wire to the spring. I didn't know glow plugs came with different size
tops - but anyway. The spring works great and if I ever saw some for
sale someplace I would buy a gaggle of them - but where does one find
itty bitty springs that you can solder?
_!_
Bye ----O----
Kay R. Fisher / \
================================================================================
|
| 770.22 | Good advice | LEDS::LEWIS | | Thu Nov 12 1987 00:22 | 27 |
|
RE .-1 I like that idea - just looked around for some small springs,
the ones in ball-point pens are too big, but I found one in
an old micro-switch that's just about right (slightly narrower,
wouldn't be able to fall off even with vibration). Might do the
trick if I decide to go that way.
I might try making a slightly larger cheek out of fiberglass as
suggested, even if I decide to take Al's advice and cut a hole for
the plug in the cheek (I like that better than cutting around the
entire head). With the extra clearance and fiberglass I shouldn't
have melting problems, but I still might have engine overheating problems
(D**M, just talked my way back into needing clearance for the whole
head again!). Well, time to go work on the wing again, I'm
gettin tired of going around in circles on this one - wait! I've
got it! I'll make new cheeks out of fiberglass, build the thing
to hide the engine completely, then TRY IT! If I have problems
with getting at the glo plug or engine overheating I can just cut out
the cheek then! Phew, glad that's over with.
RE: tail wheel - that's great news, I didn't know how I was going
to get another pushrod to the wheel. Sounds like just the thing
I need.
THANKS GUYS!
Bill
|
| 770.23 | | SPKALI::THOMAS | | Thu Nov 12 1987 10:41 | 25 |
|
Bill I don't know what engine your using but you may be able
ti adapt it to "in flight adjustment". With some needle valve set
ups you can solder an arm to the end to hook it up to another
servo. This gives you needle valve adjustment. You will also need
to remove the spring from the needle valve and replace it with a
small length of fuel tubing. This tubing will apply pressure to
the needle valve to help prevent itfrom backing out and also
allow for smooth movement rather than the ratcheted movement produced
by the spring.
Tom
I like Al's idea about a hair clip.....
Oh yes, If your concerned about heat make a baffle that divides
the entire engine compartment into two sections. The baffle should
act to split the airflow form the cylinder fins up. This will force
the air to flow over the head and actually help to cool it. This
is what done on most racing ships. The hot air is then expelled
at the rear and or bottom of the cheek.
|
| 770.24 | More good ideas | LEDS::LEWIS | | Thu Nov 12 1987 12:11 | 15 |
|
I don't think I'm gonna need to adjust the needle valve that often,
if the engine behaves like most OS FSRs that I've seen. I'm planning
on using a fuel pump (didn't want Al to hear that, I know how he
feels about pumps), mainly because I have one of those Pitts mufflers
with no pressure tap. Hopefully that will keep the fuel flow
constant throughout the flight. Thanks for the suggestion though-
Yes the baffle is a good idea, that was recommended to me by Charlie
Nelson a while back. I figured I'd need a baffle to maximize air
flow over the cylinder head in a fully enclosed setup. Most of
the bottom of the cheek will have to be cut out. I suppose I should
build the baffle right into the cowl.
Bill
|
| 770.25 | Nice lookin' cheeks... | LEDS::LEWIS | | Mon Nov 16 1987 11:32 | 42 |
|
Well, this weekend I made new cheek cowls out of glass as recommended.
I was so pleased with the way they came out and how simple it was,
I'll put the procedure in here (I guess the scale note is as good
a place as any) - you can use it for making replacement cowlings,
wheel pants, etc.
1. I wanted to add about 1/8" clearance so I glued the plastic
cheeks to a piece of 1/8" balsa sheet with CA, then sanded the balsa
base flush with the outer contour of the cheeks.
2. Lay Handi-Wrap plastic food wrap down to ease removal, then
lay down 6 oz fiberglass cloth (pull tight around bottom and pin
in place).
3. Apply at least two heavy coats of polyester resin and let it
cure (if you add a couple extra drops of hardener it's hard as rock
in a couple hours).
4. Rough sand outside and bottom with 80 grit. Once the bottom
is sanded flush with the balsa base you can remove it from the
plastic "mold" to check the strength.
5. I found it still a bit too flimsy at this point, so I added
another layer of .75 oz cloth and three more coats of polyester
resin (I put it back on the "mold" before doing this).
This brought it up to about the same strength as the plastic
part, and about the same weight. Lots of sanding and you have a
part that is only slightly larger than the original. Don't forget
to peel the Handi-Wrap off the inside of the pieces when done.
With the new cheeks, I have enough clearance to fit the whole
glo plug tip under the cheek cowl, and I don't think the size
increase is noticeable (I didn't use the full 1/8" added height,
after sanding it was more like 1/16" or 3/32"). I think my
engine will be a lot happier with some "breathing room".
Making new cheeks was the answer to my problem, just shows what
can happen when we put our heads together - thanks for all the
help guys.
Bill
|
| 770.26 | REALLY SOUNDS SIMPLE, BILL....... | GHANI::CASEYA | THE DESERT RAT (I-RC-AV8) | Tue Nov 17 1987 12:57 | 9 |
| Bill,
Thanx fer' sharing yer method with us. I know "I" enjoyed reading
it as I'm one of the balsa, silk and dope people who are still a
little intimidated by new materials/methods like making my own glass
parts. You made it sound simple enough that I feel less inhibited
to give it a try the next time an occasion arises.
Gracias, Al
|
| 770.1 | YA' DOES IT LAK' THIS HERE..... | PNO::CASEYA | THE DESERT RAT (I-RC-AV8) | Mon Nov 28 1988 19:56 | 21 |
| Tom,
Whatcha' do is put a 1/8" ply baffle just behind the lip of the
cowl. This plate can be utilized to mount dummy radial engine
cylinders, like those from Williams Bros. to. Now, cut/fit the
baffle plate such that the crankshaft is allowed to protrude then
open the cutout vertically to clear carb/needle-valve, etc. and
expose _just_ the engine cylinder to the incoming air. In other
words, the only cutting out of the baffle will be directly in front
of the cylinder. No intake is necessary for the bottom areas of
the crankcase. As long as adequate cooling air exit area is provided,
via the cowl flaps in the case of a Corsair or other radial engined
ship, the incoming air will be forced right through the engines
cooling fins and cause sufficient circulation in the engine compartment
to keep the crankcase adequately cool.
|
| | 00 Adios, Al
|_|_| ( >o
| Z__(O_\_ (The Desert Rat)
|
| 770.2 | but but what about those dummies? | RICKS::KLADD | | Mon Nov 28 1988 22:55 | 9 |
| al,
if you use a dummy engine in front of the baffle, like williams
bros., how much of the opening in the baffle (in front of the
cylinder) can be obstructed by dummy engines? do you need to
cut off a dummy cylinder or 2?
thanks
kevin
|
| 770.3 | YOU GOT IT, KEV....!! | PNO::CASEYA | THE DESERT RAT (I-RC-AV8) | Tue Nov 29 1988 12:47 | 11 |
| Kevin,
Right, you simply cut away or omit any parts of the dummy engine
which would obstruct the baffle opening. *NO* obstruction in front
of the opening is desireable as heating problems _will_ result!
|
| | 00 Adios, Al
|_|_| ( >o
| Z__(O_\_ (The Desert Rat)
|
| 770.4 | Space?? | MPGS::PERCUOCO | | Tue Nov 29 1988 12:56 | 10 |
| Al,
Do the dummy cylinders from Williams bros. have space
between the cylinders so I can offset them to provide
space for the baffle?? Do you know how I can get some
info on Williams Bros. accessories, catalog....etc???
Thanks...
Tom
|
| 770.6 | ARE WE ON THE SAME WAVELENGTH....?? | PNO::CASEYA | THE DESERT RAT (I-RC-AV8) | Tue Nov 29 1988 15:34 | 19 |
| Tom,
I'm not sure yer' getting the picture I'm trying to paint. The
so-called baffle is nothing more than a flat piece of 1/16-1/8"
ply mounted in the front of the radial cowl, just behind the lip
by such distance as to allow scale dummy cylinders to be attaqched
to it. You's lay out the dummy engine with the scale number of
visible cylinders but cut away or omit those that would block the
opening cut directly in front of the model engine cylinder. Doe
that help some??
Williams Bros. advertise in nearly all the major model mags. I'm
sure a card or call to them would produce a catalog of some sort.
|
| | 00 Adios, Al
|_|_| ( >o
| Z__(O_\_ (The Desert Rat)
|
| 770.7 | I got you..... | MPGS::PERCUOCO | | Tue Nov 29 1988 18:14 | 7 |
| I got you ,Al.... I was writing the last reply and the
one before my reply got snuck in and explained that there
was probably no way of ducting air thru the baffle unless
I cut out a cylinder or two...anyway, should not be a problem!
Thanks again, my friend....
Tom
|
| 770.8 | IF ANY QUESTION REMAINS, HERE'S A PIC... | PNO::CASEYA | THE DESERT RAT (I-RC-AV8) | Tue Nov 29 1988 19:13 | 30 |
| Here's what I've been trying to describe. Drawing's still crude and cannot
show much detail but maybe it'll help to visualize what I've been talking
about.
CUTOUT FOR (Drawing assumes)
ENGINE CYLINDER (upright engine.)
---------------
|
|
|
- V -
- | | -
- | | -
- | | -
- | | <-------- INSTALL DUMMY CYLINDERS
- \ / - TO BAFFLE PLATE. CUT OUT
- \_____/ - OR OMIT PARTS THAT OBSCURE
- - CUTOUT. CYLINDERS ADDED
- - AFTER PLATE INSTALLED IN
- - COWL.
- - -
MAKE BAFFLE PLATE (Fiberglass to inside of)
FROM 1/16-1/8" PLY. (cowl, just behind lip.)
-------------------
|
| | 00 Adios, Al
|_|_| ( >o
| Z__(O_\_ (The Desert Rat)
|
| 770.9 | pontiac calls it ramair | RICKS::KLADD | | Tue Nov 29 1988 20:39 | 27 |
| al,
let me beat the dead horse! i understand your picture which is
well done considering 80 column resolution.
my observation is (and i may be wrong or this may only apply to
giant scale)
that some people, somehow, have managed to install a dummy
engine without any extra openings in the dummy engine. i say
"extra" cause there is some open area between and outside of dummy
cylinders. how do they get away with this?
an idea i had was that, since the baffle is near the front lip of
the cowl, and the engine cylinder is set back, a "funnel" could
be built. the front of the funnel is extra big and glued to the
now oversized hole in the baffle. this funnel extends straight
back and the small opening of the funnel is the same outline as
the cylinder. the sole purpose of this funnel is to compensate
for the obstructions of the dummy cylinders, or said another way,
the funnel allows the open area at the baffle to be equal to the
area of the real cylinder in spite of dummy engine.
am i crazy? is this ever done? i know this contradicts your
philosophy of keeping the engine as functional/reliable as
possible. i agree with that philosophy wholeheartedly!
kevin
|
| 770.10 | My 2c worth | CURIE::ANKER | Anker Berg-Sonne | Wed Nov 30 1988 11:46 | 26 |
| Re:< Note 772.16 by RICKS::KLADD >
Kevin,
I think the funnel will make things worse. There's lots
of turbulence inside a cowl and most of the air will end up
getting close to the cylinder. The funnel will restrict the
amount of air coming through the cowl and I don't believe the
benefit of directing it to the cylinder outweighs the reduced
total airflow.
Your theory is also that more air will pass at higher
velocity because of the funnel. Unless you somehow manage to
increase pressure in the funnel the airflow will NOT increase, on
the contrary.
_
/ |
| _====____/==|
|-/____________|
| | o \
O \
O
Hang in there! o_|_
|
Anker \_|_/
|
| 770.11 | Really Works | SA1794::TENEROWICZT | | Wed Nov 30 1988 12:43 | 23 |
| I Kevin had worked for a Jet engine manufacturing company I'd have
to disagree with you Anker, but he hasn't so.........
In actuality shape of a funnel within a jet engine does effect it's
efficiency and that what we're really talking about.
Kevin. I have seen something not quite exotic as you discribed in
an RC aircraft that worked really well. seems that the majority
of the heat the needs to be dissipated is located along the sides
and top of the cylinder. This makes sence. The lower crank case
sees a limited heat rise and doesn't require the heat dissipation
the cylinder needs. What I saw was a plywood plate that had cutouts
in it so that the plate could be mounted parallel to the crank shaft
just below the finned section of the cylinder. This plate extended
from the cowl front over the engine (as discribed) back to the firewall
where cut outs existed to get the warm air out of the engine
compartment. It isolated the engines cylinder in a direct airflow.
Tom
P.S. This technique is used on most racing and control line aerobatic
ships. I think also on most RC Formula 1 and FAI racing ships. Perhaps
John Chadd our DUB (Down Under Buddy) can shed some light on the matter.
|
| 770.12 | LIKELY MORE TROUBLE THAN IT'S WORTH | PNO::CASEYA | THE DESERT RAT (I-RC-AV8) | Wed Nov 30 1988 12:47 | 36 |
| Kevin,
I believe close inspection will reveal that "some" allowance for
model engine cooling is made in _any_ installation. Those models
which do not are plagued with engine heating problems, certain death,
sooner-or-later, for a scale model (or any other for that matter).
Uncowled radials with the model engine sitting behind the dummy
cylinders have little problem as the cylinder head is exposed to
the airflow. I'm pretty sure, however, you'll find that, in cowled
installations, some part of the dummy engine is cut away/omitted
to permit adequate airflow over the model engine cylinder.
As Anker points out, exotic ductwork has many complications and
doesn't always produce the desired result. Believe it or not, there
_is_ such a thing as too much air intake; have you ever seen a cowled
engine with no baffling overheat? I have and it's quite common.
The why of it is that air passing the cylinder must absorb and remove
heat and too much intake air with considerably less exit area just
balls up in the cowl and is prevented from removing heat...result:
overheat!
This simple baffle I recommend directs incoming air around the cylinder
where it's needed and also reduces the volume such that the exit
area provided by scale openings, cowl-flaps, etc. is adequate to
promote constant air exchange in the engine compartment.
Believe it or not, the removed/missing dummy engine parts are barely
noticeable and certainly can't be seen during a 100 mph low pass
viewed from the back of a galloping horse.
|
| | 00 Adios, Al
|_|_| ( >o
| Z__(O_\_ (The Desert Rat)
|
| 770.13 | hmmm | RICKS::KLADD | | Wed Nov 30 1988 16:06 | 22 |
| anker, tom, al,
great replies, thanks! i agree with most everything said and will
take all into consideration.
ultimately i will probably chicken out and use the proven method
that al advocates. i remember how i fretted about the exposed
(non-scale) aileron linkages but now that the plane is built i
never notice them so they dont bother me one bit. same would
undoubted be true for a slightly butchered dummy engine.
still, i find the funnel/ducting ideal intriguing.
i had hoped to test my dummy engine installation on the jug while
it was in primer (the stakes are high). however, i didnt get the
shaft extension till way late. besides, you dont really know what
you've got till you've flown in a hot hot july day!
btw, with the bully unbaffled and inverted in the jug, it did seem
to run hot, tho not catastrophically hot.
kevin
|