CEF speed contest Design Discussions (2014)

Details of my high tech intake system:

Firewall has two holes, an intake for the engine and an intake for the "airbox" that directs air to the engine.


Detail of the airbox cut into the cheek block.

The intake tube.


What it looks like all put together.

Jim

I know from experience getting the intake off the firewall via a bore hole, or a choke tube really makes a difference in ease of operation. I have noticed some difference in engine strength, but it is not very large, maybe a couple hundred RPM. I have not tached the same engine on different mountings to be more precise.

Does ram air into he intake really make any difference?

Phil

pkrankow wrote:I know from experience getting the intake off the firewall via a bore hole, or a choke tube really makes a difference in ease of operation.  I have noticed some difference in engine strength, but it is not very large, maybe a couple hundred RPM.  I have not tached the same engine on different mountings to be more precise.  

Does ram air into he intake really make any difference?

Phil

It might on a rotary valve intake.. but I doubt it on a reed-valve engine. You can't blow any more air past a reed than it's design dictates. All you can do is insure that there's ample fuel/air at the venturi for a steady mixture to flow. How well the engines "internal" components are fitted.. along with proper sealing.. will dictate the reed engine's output on a given fuel, cylinder-porting and compression. (IMHO)

pkrankow wrote:
Does ram air into he intake really make any difference?

Phil

Phil,
 Think of it as fresh air intake, not ram air.

The opening on the left of the cowling is larger than the exit around the cylinder. That ensures positive pressure in the cowling so exhaust is forced out the exit. The opening is directly in front of the cylinder to supply plenty of airflow for spi as the exhaust ports are buried in the cowling. I didn't want the positive pressure in the cowling feeding exhaust to the engines intake. I was going to vent the intake to a hole on the side of the cheek block but was afraid air flowing past would create a vacuum and pull exhaust past the intake. I could have done that and added an air scoop but I didn't want to add unnecessary frontal area so I plumbed through the cowling.
Plus it just looks cool.    

Jim

It does look cool. And I agree, fresh clean air is what you are getting. Forced air in a reedy could potentially float the reed and slow its sealing action, I hope my "Art of Simplicity" can keep up with your sophisticated machines. That's what I need to name it this time, Art. Or Simp... Simp the Blimp. Naaa!
Looking good guys.
Rudimentary Rusty

I like it Jim! It seems well thought-out. Fresh/cooler air is better for combustion.. and you can't get much fresher than that set-up, when cowling-in an engine. It's an air-flow management system for the whole engine!

When I designed my sport muffler.. I had several ideas in mind. Make it simple and easy to install, provide adjustable degrees of silencing and a pressure-tap. I was discussing with Rusty; experimenting with cross-flow.. by using different orifice sizes in a dual-pipe configuration. It's a "stretch".. but you never know. It's said that "Cox"mufflers on SPI cylinders don't work well.. but the Cox design is quite restrictive. My design is more of an adjustable expansion chamber. All you can do is experiment to see if you can attain a "scavenging" effect.


The two interchangeable pipes shown, have .060" difference in orifice size. The .204" pipe is the maximum that a pipe can be drilled, and the .144" pipe is the smallest of several sizes I made; in graduated increments of between .007"/.010" to experiment with. It would be interesting to calculate the total exhaust port area on different cylinders vs. total pipe-orifice area.

The aluminum ring is the internal muffler chamber and gets drilled-out for the pipe(s)/location(s) that you're using. The one in the foreground has a pressure-tap and two holes for dual pipes spaced 180 degrees apart.



Rusty had trouble with the kit I sent him, when mounting on his Tee Dee. There isn't much clearance between the cylinder and carb-body. I'm wondering if the muffler-body's rubber flange could be tucked "up" and in between. It's pretty flexible. It may even act as an air-scoop.

getback wrote:Sorry Mike I was thinking about what you said and........https://www.youtube.com/watch?v=ODZYrrkoJxg  Man I don't know what u guy over there are smoking !!! Getback 

I watched up to 1:10.. and gasped... and at 1:40 I just clicked the stop button.    

Oh lordy, I see my name being dropped in the Roddie muffler conversation again. I better put that Altoids box full of experimental parts on my table where I can see it. I actually am curious about it.
Rusty

roddie wrote:

getback wrote:Sorry Mike I was thinking about what you said and........https://www.youtube.com/watch?v=ODZYrrkoJxg  Man I don't know what u guy over there are smoking !!! Getback 

I watched up to 1:10.. and gasped... and at 1:40 I just clicked the stop button.    

I got a few seconds farther... I could have had that back in the air at the field with some 5- 10 minute epoxy.

Phil

getback wrote:

RknRusty wrote:Oh lordy, I see my name being dropped in the Roddie muffler conversation again. I better put that Altoids box full of experimental parts on my table where I can see it. I actually am curious about it.
Rusty

       Thank You Brother Rusty 

Yes Brother Eric, Brother Roddimus, I will commence testing. As they say in Jamaica, Soon come man, soon come.

Jim

That front end looks really great. Nice clean air is always what a engine wants.

I am waiting in anticipation to see this biplane. If I can get my Nemesis done in time, I will also try and build a biplane. I am a big fan of biplanes.

I am now busy doing the airfoil on the wing. It is coming along quite nicely.

Theo

Theo Kleynhans wrote:Jim

That front end looks really great. Nice clean air is always what a engine wants.

I am waiting in anticipation to see this biplane. If I can get my Nemesis done in time, I will also try and build a biplane. I am a big fan of biplanes.

I am now busy doing the airfoil on the wing. It is coming along quite nicely.

Theo

I hope we can see some pics soon, Theo! Like I said, I can't wait to see how your Nemisis progresses.

I'm thinking a biplane would be fun too. Jim, is the 12.5" minimum span for both wings? A lot of biplanes have smaller span on the lower wing, should we think about extending it for minimum span compliance?

Mike Mulligan wrote:

Theo Kleynhans wrote:Jim

That front end looks really great. Nice clean air is always what a engine wants.

I am waiting in anticipation to see this biplane. If I can get my Nemesis done in time, I will also try and build a biplane. I am a big fan of biplanes.

I am now busy doing the airfoil on the wing. It is coming along quite nicely.

Theo

I hope we can see some pics soon, Theo! Like I said, I can't wait to see how your Nemisis progresses.

I'm thinking a biplane would be fun too. Jim, is the 12.5" minimum span for both wings? A lot of biplanes have smaller span on the lower wing, should we think about extending it for minimum span compliance?

biplanes are still subject to the 45 square inch portion of the rule, so it shouldn't matter that the lower wing is shorter.

Phil

pkrankow wrote:

Mike Mulligan wrote:

Theo Kleynhans wrote:Jim

That front end looks really great. Nice clean air is always what a engine wants.

I am waiting in anticipation to see this biplane. If I can get my Nemesis done in time, I will also try and build a biplane. I am a big fan of biplanes.

I am now busy doing the airfoil on the wing. It is coming along quite nicely.

Theo

I hope we can see some pics soon, Theo! Like I said, I can't wait to see how your Nemisis progresses.

I'm thinking a biplane would be fun too. Jim, is the 12.5" minimum span for both wings? A lot of biplanes have smaller span on the lower wing, should we think about extending it for minimum span compliance?

biplanes are still subject to the 45 square inch portion of the rule, so it shouldn't matter that the lower wing is shorter.

Phil

Good question Mike and good point Phil.
I hadn't really thought about it until now. I lifted the rules for this from 1/2a profile proto and we've adapted them along the way to incorporate scale and try to get more speed from a reed powered plane.
The 12.5 biplane span is from the proto rules. That's a combined span of 25 inches. To me it would make sense to change the biplane rule to minimum combined wingspan of 25" with minimum 45 square inch wing area. That way you can make top and bottom span whatever you like as long as they hit the 25" combined span mark.

Thoughts?

Jim

JPvelo wrote:

pkrankow wrote:

Mike Mulligan wrote:

Theo Kleynhans wrote:Jim

That front end looks really great. Nice clean air is always what a engine wants.

I am waiting in anticipation to see this biplane. If I can get my Nemesis done in time, I will also try and build a biplane. I am a big fan of biplanes.

I am now busy doing the airfoil on the wing. It is coming along quite nicely.

Theo

I hope we can see some pics soon, Theo! Like I said, I can't wait to see how your Nemisis progresses.

I'm thinking a biplane would be fun too. Jim, is the 12.5" minimum span for both wings? A lot of biplanes have smaller span on the lower wing, should we think about extending it for minimum span compliance?

biplanes are still subject to the 45 square inch portion of the rule, so it shouldn't matter that the lower wing is shorter.

Phil

Good question Mike and good point Phil.
I hadn't really thought about it until now. I lifted the rules for this from 1/2a profile proto and we've adapted them along the way to incorporate scale and try to get more speed from a reed powered plane.
The 12.5 biplane span is from the proto rules. That's a combined span of 25 inches. To me it would make sense to change the biplane rule to minimum combined wingspan of 25" with minimum 45 square inch wing area. That way you can make top and bottom span whatever you like as long as they hit the 25" combined span mark.

Thoughts?

Jim

Leave it alone. Combined span will produce some maverick possibilities, it "forces" a wing chord of 1.8 inch. If, say, the top wing is 12.5 and the bottom wing is 7.75 so total span less fuse is 20, the wing chord is about 2.25 inch.

Phil

That sounds good Jim. It makes it quite simple and easy to understand that way.

Theo

Theo Kleynhans wrote:Jim

That front end looks really great. Nice clean air is always what a engine wants.

I am waiting in anticipation to see this biplane. If I can get my Nemesis done in time, I will also try and build a biplane. I am a big fan of biplanes.

I am now busy doing the airfoil on the wing. It is coming along quite nicely.

Theo

Theo,
Can't wait to see the finished Nemesis, I seriously considered doing one for the first contest. It should be a real performer with the proper engine and prop.

Jim

Mike Mulligan wrote:
I hope we can see some pics soon, Theo! Like I said, I can't wait to see how your Nemisis progresses.

Thanks Mike. I will be showing some pics tomorrow. I have done the big work on the wing. I now just need to do the finishing sanding and shaping tonight on the wing. I am enjoying it thoroughly. Then I need to shape the Stab. Only after that will I be slotting and sanding the fuse.

JPvelo wrote:
Theo,
Can't wait to see the finished Nemesis, I seriously considered doing one for the first contest. It should be a real performer with the proper engine and prop.
Jim

Thanks Jim. It really is a beautiful plane in real life. Wish I could get a flight in one. It will still be some time to finish it, I am really busy at work and can only get a little bit of time at night to work on it. But I am getting there.

The biggest problem for me regarding the engines is that here in South Africa we do not get any spares for Cox engines. If I want something I have to order from Cox and it is quite expensive for us. Our currency (Rand) is a bit weak at the moment, so it is difficult to buy. I have a few engines and I will be using a Estes Black Widow front end on a 5cc Baby bee tank. This is my fastest engine that I have tested. It is decent, but not nearly as fast as the ones that I have seen you guys doing. The other problem is the props. I could only get a few APC 5.7 x 3 props and I have 1 cox 5 x 4 that I can use for this purpose. I cannot get the bigger pitch props here. Like you guys are using a 4.5 x 4. The only ones they have here with bigger pitches is the APC electric props. Will those electric APC props work on a cox, or is it a big  NO NO?

Theo

Theo the electric props don't have the big thick hubs to reinforce against engine vibrations, the shock of pulsed combustion. One is in danger of having an e prop fly apart.
Rusty

RknRusty wrote:Theo the electric props don't have the big thick hubs to reinforce against engine vibrations, the shock of pulsed combustion. One is in danger of having an e prop fly apart.
Rusty

Not only that - but they are sharp, very sharp and make excellent finger choppers.

Another drawback is that they are light as well as thin. The IC engine may not react well to this.