I've said it before, but it's worth repeating: Increasing your RF4's engine size will not result in much speed increase.

Top speed is mostly proportional to drag (although my propeller guy says it's also proportional to wing area, and RF4s sure do have a lot of that, making 110 knots/125 mph a practical maximum). So, to go faster, fair your outrigger legs, turn your antenna upside-down and put it inside the fuselage (wood is transparent to radio waves) or install an internal tape style antenna, and tape up all the holes and gaps in your airframe. You might get three more knots from what is already an incredibly low drag airframe, thanks to Rene's genius.

More power just increases your climb rate and fuel consumption. Increase your VW's capacity from 1200cc to 1800cc (50 per cent) and you will increase fuel consumption by fifty per cent too, from 10 to 15 litres per hour (2.5 to 4 US gph). However, your climb rate might double.

BUT... 50 per cent more fuel burned and 50 per cent more power means you have to get rid of 50 per cent more heat, or your shiny new motor won't last very long. If it has aluminum (Nikasyl) cylinders, they will quickly warp and you're stuffed!

In fact, if your engine becomes excessively hot, the power output actually drops off! So you want to keep it as cool as possible.

If you didn't care about the drag, you could simply increase the front cowling inlet's area and the hot air outlet area both by 50 per cent. But we care about the drag, so how can we improve the cowlings' inner airflow without increasing weight (much) or drag?

First, ensure your baffles fit tightly. Not like these on WGN when we got it.

One good idea is to fair in the front cowling lip with foam, see http://www.fournieruk.com, click 'technical', 'miscellaneous', and 'Bob's mods'. Mod 8 is the inlet foam thing. This noticeably reduced my oil temperature (the only gauge I have).

An aeronautical design engineer buddy suggested it's important to similarly fair the flow of the outlet air. Commonly, after the air goes past the engine's fins, manufacturers stop bothering, and let it all just pile up in the lower cowlings and tumble around, fighting to get out. This guy said to make semi-circular outlet fairings like this:

This also made a small improvement in my oil temp, although not as much as I had hoped.

Then I looked at the oil cooler outlet, and saw it was flowing straight at the upright rear flange thingy. So I cut off and smoothed the semi-circular top of that. Oil temp dropped further.

Not satisfied, I fitted this tiny little fairing plate, and would you believe, that made the biggest difference of all to the oil temps -- dropped it by ten degrees Celsius (twenty Fahrehnheit). Cost: a scrap bit of aluminum, weight, nothing, time five minutes.

Even the outlet fairings and inlet foam only took half a day each.

Go to it.

Yours, Bob

[Edit by Bob Grimstead on Wednesday, November 19, 2008 @ 11:36 PM]

[Edit by Bob Grimstead on Wednesday, November 19, 2008 @ 11:41 PM]

A RF3 oir RF4 with a 1200 cc Rectmo will not be able to follow a RF5 squadron unless the RF3/4 followers fly with full throtlle at 3400 rpm !!! An this is not good for the engine !
Increasing the egnihe to 1400 or 1600 ccm with an adequate prop ( 133/100) and a good oil cooler will make the RF3 or RF4 175 kmh fast, this means good 90 knots and allow to swim with the big brothers and sisters.

On the RF5 the increase of power will not bring a tremandous increase of speed but in any case quite a higher fuel consumption. My RF5 with a 2500 cc Sauer engine needs at least 14 to 15 liters per hours at 180 kmh/ cruise.

But the big difference is the shorter take-off distance and the better rate of climb. During the summer time ( hot temp.) and being well loaded (means 20 or 40 kg over weight) it is risky to fly to some airstripes with short runway, obstacles, or steep runway. Then the engine power is not a luxury but an important factor for safety.

Patrick

--------------------
Patrick, Speyer - Germany RF5 D-KOPF

That is interesting what you say about a 1200cc RF4 being unable to fly with a standard RF5. I didn't know that.

I have increased my engine power for the same reason. Not to go faster, but to have the same performance in high temperatures. I fly aerobatics in summer air temperatures up to 40°C (occasionally, even more!)

Yes, on a reasonable day (25°C) my 1400cc Fournier with RF5 wooden Hoffmann propeller, will fly at 100 knots maximum, and cruises at 90 kt.

I am very interested to know how you deal with all the excess heat your big 2500cc engine produces. Do you have bigger cooling air inlets and a cowl flap?

Yours, Bob

The problem is known for a long time : engine temp. can differ strongly from one a/c to the other and nobodies knows why.
On my RF5 with a SAUER 2500 I have the contrary problem: My engine does not get warm !
It is a tough matter of discussions ... for our GAP event !
Patrick

--------------------
Patrick, Speyer - Germany RF5 D-KOPF

Steve

That really doesn't have a lot to do with cooling (or in a couple of ways does), but as the cruise speed issue come up, I would like to ask about your top speeds. Our baby can do about 185 (100 kts) at max allowed RPM, but is not supposed to be done for a long time. The previous one we had was a bit slower. I think it could do the 180 at 3300. Anyway, everyone of the four RF4Ds I have flown have been able to beat that 175 km/ without not having to go to red line. I haven't flown the example here in Finland that has a 1700 cc engine, but have heard it has a cruise speed of about 200-210 km/h (108-113 kts).

So, opinions, please

--------------------
***** Antti Laukkanen, Helsinki, Finland - RF4D OH-371 - RF4D OH-370 - RF5 OH-386 *****

Might it be possible to get a better picture of your oil cooler installation. It seems to be mounted quite far back from the standard position directly over the oil feed ports on the top of the case. Do you have a different adapter that positions the cooler more rearward? It would sure help with cowl clearance.

Thanks.

--------------------
Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

It's odd you just mentioned this, because I only became aware last week that my oil cooler 'adaptor' was not standard. Having looked through the documentation I got with HDO, I discovered the adaptor was made and supplied to the previous owners ten years ago by Mike Woollard (joint author of an excellent book on glider aerobatics).

I need another adaptor for my new engine, otherwise the upper cowling will not fit. I would also like an oil cooler on my British RF4, which has the 1400cc motor, but no oil cooler. Tim Kroeger, who recently imported his RF4 into a hot part of Australia would also like one. Maybe there are others, too?

Last week I e-mailed Mike W, but as yet have had no reply. I'll leave it a week, and if I don't hear, I shall phone him (I'm in Australia, he's 10,000 miles away in England, with an eight-hour time change). Whatever happens, I shall put the relevant information on this thread.

Yours, Bob

Eugenio makes a nice adaptor that moves the cooler back. I will post a picture later today.

--------------------
Collin Gyenes

A WARNING!!!

I have just discovered that, contrary to assurances I was given at the time, the two-pack foam I used to fair the insides of my cowlings is flammable. When you apply a match to it, not only does it burn freely, but it gives off quantities of nasty dark smoke which made my eyes water and made me cough.

Until I find out more, I cannot recommend you use either the two pack foam illustrated in my mods section, or the 'builders foam' you can buy in cans at your local hardware store. I know this stuff burns in a similar way, because I tested that last summer.

It might be possible to render the foam inert by covering it with a layer of glassfiber mat and non-flammable resin, but I need to investigate that further, and I do not have the time right now.

Can anybody else help with suggestions as to how to ensure this foam does not burn if there's a fire in our cowlings?

Yours, Bob

Here is a link to Great Plains oil cooler page. Have a look at the Sonerai adaptor.

http://www.greatplainsas.com/scoilcooler.html

I took a look at the Great Plains page, but there is no mention or photo of how far back the oil cooler will be when using that plate. There is also mention further down the page of an adaptor which can be used 'where the builder can't or doesn't want to drill and tap the cases and/or oil pump', so presumably this adaptor requires drilling or tapping the crankcase. I think the Woollard adaptor on my Australian Fournier does not need the crankcase to be drilled or tapped. Not certain, but I think not.

As we have recently discovered, the oil cooler has to be right back against the rear flange of the engine to fit under the stock Fournier cowling (which of course we do not want to make ugly bumps in).

I just got an e-mail from Mike Woollard. He says the price for his plates would be £350 (approx $700US) per plate if we want three, dropping to £275 ($550 US) if he makes six together. The high price is because they are complex, with lots of holes and machining to get around the hand starter mechanism etc. I need two and Tim K wants one, so are there any other takers out there?

Alternatively, does Eugenio still make an alternative design, and would his be less expensive?

Yours, Bob

I have another image that shows this same adapter and the cooler is right back where Bob's is. Hard to tell how low it is, but certainly no higher that the standard adapter.

Dann

--------------------
Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

Here is a picture of my adapter. It is a std Great Plains unit. I machined it so I can I mount it upside down and machined thiner to clear the cowling it still works with the pull starter.

http://www.cfiamerica.com/images/2182-oil_cooler.JPG

http://picasaweb.google.com/dannsparks/RF4D_N2188/photo#5186632225728886130

Here is another image with a different adapter. It is hard to see it, but I don't think it is a Soneria style. Is this Eugenio's plane?

http://picasaweb.google.com/dannsparks/RF4D_N2188/photo#5186634970212988306

[Edit by dannparks on Monday, April 7, 2008 @ 07:49 PM]

[Edit by dannparks on Monday, April 7, 2008 @ 07:51 PM]

--------------------
Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

Collin, the adaptor plate you are using is the Sonerai Oil Cooler Adapter Plate from Great Plains, cost $69.95? and you just had to make it thinner and mount it upside down plus cut out a corner for the pull starter tube?

If so, it is much better value than Mike Wollard's unit, presumably because they can make and sell them in quantity -- although Mike's comes with all the hardware, special seals etc.

Mike's adaptor not only moves the standard VW oil cooler right back against the rear flange (well, nearly anyway) but also moves it over to the left a little so it's absolutely central on the engine centerline. Otherwise it would still foul the upper cowling.

It that also true of the $69.95 Great Plains unit? It sure looks like it.

Of course, if Eugenio makes one and the price is ismilar to Great Plains, then I would prefer to give him my money (as I would prefer to buy from Mike W) but as always, price is important.

Yours, Bob

[size=small][Edit by Bob Grimstead on [TIME]1241809424[/TIME]][/size]

[size=small][Edit by Bob Grimstead on [TIME]1241809472[/TIME]][/size]

Much smaller than the Soneria design ($69 from GPAS), but it seems like it might be just a bit thicker -- although it obviously fits in an RF4D cowl.

Looking at the standard GPAS adapter (the $29 one), it seems like it should be possible to machine the adapter much thinner, and cut out a bit of the oil cooler case and fins on the bottom oil cooler (without hitting the oil channels) where they contact the engine bolts on the engine case. This could lower the thing by as much as 3/8", which would go a long ways. Some filing on the top of the cooler could ad even more clearance. I'm going to try it on an old cooler I have.

--------------------
Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

[Edit by dannparks on Thursday, April 10, 2008 @ 10:01 PM]

--------------------
Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

I've just uploaded some additional photos for the above thread, because I think this is probably the most important thread of the lot.

Also, I'm now going to buy one of each of the Great Plains oil cooler adaptors, and see how I get on with them.

I'll let you all know the results.

Yours, Bob

Here is a picture of the std Great Plains oil cooler adapter modified to keep the pull starter. I machined it thinner for more cowling room and flipped, rotated and machined to use countersunk allen head bolts.

A visual reminder.
These are the most important baffles (although they were missing on WGN when we bought it.
And you have to take off the heads to fit them!

With this second photo, note on the left how closely the rear baffle curls around and fits under the lower cylinder head.
If it's not like that, it's pointless, and all the cooling air escapes.

Yours, Bob

[Edit by Bob Grimstead on Saturday, November 29, 2008 @ 04:43 AM]

Cany anybody enlighten me.

Should I continue trying to get hold of two pairs of these baffles and retro-fit them to HDO and WGN?
Or doesn't it matter?

Yours, Bob

[Edit by Bob Grimstead on Saturday, November 22, 2008 @ 07:53 PM]

Just a warning.
The rear right cylinder tends to be the one to suffer, because it is furthest back, and gets hottest.

Yours, Bob

on RF 5 b SE-UDI´s Limbach L 2000 I didn´t find any of these smaller baffle inserts under (or rather over) the bigger, black painted "inter-cylinder" placed baffles (or "forget-plates" as I saw them called on a Swedish VW-site). I´ve never noticed any critically high cylinder temps either, but then again we don´t have your Perth-kind of outside temperatures. On RF 4 SE-XST I haven´t dismanteled the heads (yet), so I don´t know if there are any "inserts" under the "forget plates".

Increased airflow should increase cooling, but I wonder if these inserts improves airflow if you have the bigger "inter-cylinder" baffles properly in place.

Take 5(b) just 4 fun/ Jörgen

I would just like to amplify Patrick's earlier post.

It is nice to have a cylinder head temperature gauge as well as our standard oil gauge, but actually neither tells you about what is happening in the very hot combustion chamber.
And, of course, it is important to check calibrate your gauges before coming to any conclusions.

When Matthew and I bought WGN one year ago, we found that it always ran cool according to its only gauge, the oil temperature. And yet, when I took off the cowlings after a flight, it felt red-hot in there. Now we suspect that the oil temp gauge tells lies.

The important factor is engine life.

My Australian RF4, blue HDO still has its original engine. It has flown 1,300 hours, the last 300 hours in my 5 years ownership mostly at full throttle. It runs well, still has good oil pressure, and the heads only came off once in its life, when I upgraded to 83mm cylinders (1,400cc). That was the only time the valves were lightly ground, with no apparent wear. The aeroplane climbs at 600+ feet per minute.

The other one, red WGN had a replacement engine around 15 years ago. Since then, its heads have been removed at least 4 times, and on one of these occasions it had a snapped valve. 'Top overhauls' seem to last 150 hours or less (the last one was just over 100 hours).
It only climbs at 520 feet per minute (with the exact same propeller).

The only significant difference is that its 'forget' baffles were missing and the rear baffles that curve down behind the rear cylinders were as seen on the photos higher up on this post.

In other words, all its important baffles were missing or leaked badly.

It seems that, whatever your gauges say, an engine which has tight, properly-sealed baffles will last at least ten times as long as one with poorly-fitting baffling.

Half a day spent fixing your baffling by careful bending and with a $5 tube of high-temp silicone sealant might save months and many dollars getting your engine (or at least, the rare, almost-irreplacable single-port heads) rebuilt.

Just a suggestion for these otherwise-boring winter months.

Yours, Bob

[Edit by Bob Grimstead on Friday, May 8, 2009 @ 03:08 PM]

I add a cowl flap in the summer months to help with cooling.

That's very interesting.

I know the theory.

Can you see a definite temperature difference with that flap in place?

I had been planning to design and fit an adjustable cowl flap when I fit my new engine, but if your fixed flap works well, it would be so much easier to make.

Yours, Bob

-A-

--------------------
***** Antti Laukkanen, Helsinki, Finland - RF4D OH-371 - RF4D OH-370 - RF5 OH-386 *****

On second thought, maybe it´s best you skip that picture....

Take 5(b) just 4 fun/ Jörgen