PAINLESS

My Feedback: (19)

The one thing I don't see mentioned on this forum is increasing nitro content of fuel to get some more speed. Granted this would cost a little more but if you really want to go fast.....

The boat guys don't use anything less than 40% (for racing) and some use as high as 60%. One of the hydro classes, (.67 or 90 I forget) is running over 100 MPH. I think the record is around 109 or so for 1/16 mile straight away.

gubbs3

My Feedback: (1)

Increasing nitro can give you more power (can being the keyword). When you increase nitro you have a much higher chance of getting detonation, where the fuel explodes rather than burning quickly and that can cause engine damage. Also high nitro tends to kill plugs. These boat guys running 40%+ nitro probably put in a new plug for every run, and that gets very expensive. And then there's the cost. The lowest possible price you will ever pay for 40% would be around $25 per gallon, more as the nitro increases.

PAINLESS

My Feedback: (19)

Yes, you need to increase head clearance (more shims) when going up in nitro to prevent detonation. It wouldn't be hard to find the info on what to set it to. It seems most engines I've bought lately have way to much head clearance. I like to set it at .010-.014 for 15% fuel. Any less and I see detonation.

I did some boat racing about 10 years ago, and while I did occasionally blow a plug, it was usually from a lean run. They would easily last for a day of racing.

I'm already paying $17 for a gallon of 15% at the local hobby store, so $25 wouldn't break the bank.

It just seems like an easy way to gain some more MPH out of a particular engine/prop/airframe combination.

ChuckAuger

My Feedback: (12)

Are water cooled and are propped to turn up some serious R's...both of these will allow you to run more nitro. Running 10% with 2 head shims on the 46VRDF propped to turn in the 22K ~ 24K range I could get a few flights out of a plug..but even a little lean and pop goes the plug.

I had 20% and 30% nitro setting right here, and never even considered it...just sounded like blown plug city to me.

PAINLESS

My Feedback: (19)

I don't think blown plugs would happen as frequently as you all seem to think.

Cars run 25% nitro and heli's run 20 -25%, you don't see them changing plugs every run.

You can bet if there was a pure speed contest, guys would use high nitro and replace plugs every flight to win. Speed costs money.

There's an idea, a contest for the "fastest prop driven plane on glow fuel".

ChuckAuger

My Feedback: (12)

Cars run more nitro..they are geared to where the engine is not loaded very heavy, and the don't run WOT for extended periods.

Helis run more nitro because they run very rich to keep them cool, and the extra nito helps them get some power back....and again are geared to where the engine is not loaded as much (yes, I know that heavy 3D does load the engine...that's why they use .91 sized engines in a .60 sized machine...)

I think you are expecting too much from just increasing nitro...I haven't run the tests, but I have read that you can only expect a couple hundred RPM increase for every 10% jump in nitro content.

IMO there are lots of ways to increase speed other than running more nitro..FAI pylon planes are some of the "fastest prop driven planes" and they run 0% nitro.

Try running the numbers...an inch of pitch will get you more speed than a bucket of RPM's...

The main reason I don't care about running more nitro is if I am planning on going fast, I run a pipe...in my experience it is a real pain to get a piped engine to work well with lots of nitro..you can only run so many head shims, etc...a pipe is a supercharger, look at the compression ratio of supercharged car (automobile)engines compared to normally aspirated car engines..it is 25~30% lower...anybody can blow one up, it is making it run that is the key.

But if running more nitro is the path you want to take, knock yourself out...what do I know?

PAINLESS

My Feedback: (19)

Simply adding nitro will not boost speed to much. There are other things that need to be changed as well. Like the above mentioned head clearance, pipe length, port timing, richening the mixture and probably a colder plug to optimize the whole package. Going from 15% to 40 % would probably only require a .010-.015 head shim. For serious speed I would always use a tuned pipe over a stock muffler.

"Try running the numbers...an inch of pitch will get you more speed than a bucket of RPM's..."

Sooner or later your going to run out of horsepower to turn that "inch of pitch" which is exactly where more nitro would help.

"FAI pylon planes are some of the "fastest prop driven planes" and they run 0% nitro. "

Their port timing and exhaust extractors are optimized for that, if you tried 10 or 15 % nitro they would run poorly. Why is Formula 1 dead in this country... because it turned into an engine builders nightmare, among other things. Why do you think they limit the fuel to 15% in Q500 racing... so nobody shows up with "spiked" fuel and smokes everyone else.

As far as comparing 2 strokes with tuned pipes to 4 strokes with super chargers, thats apples and oranges. Although detonation can still be the end result in both types if not handled properly. A super charger increases cylinder pressure, thats the reason for lower compression.
A tuned pipe works because of pressure waves and must be tuned for a given RPM and must be re-tuned if you do some thing to increase RPM like more nitro or a smaller prop. Most if not all sport engine don't have the right port timing to make full use of a tuned pipe.
Nitros is an oxidizer (I think thats the term) which allows the fuel to carry more oxygen into the cylinder. It requires a richer needle setting. This is similar to nitrous oxide injection in a car engine, and requires almost double the amount of gas at wide open throttle while "on the bottle" to keep from melting a piston.

Anyway, I plan to do some testing to atleast prove to myself what more nitro will do. I'm sure I'll see performance gains, whether or not it is worth the dollar increase vs. reliability remains to be seen .

ChuckAuger

My Feedback: (12)

You seem to have almost an identical outlook as mine...The inch of pitch was, of course, just for comparison, it is pretty coarse. I now know you are aware of the minute pitch differences used in high nitro/high RPM operation. I thought I was just talking to another seeker of speed

The supercharged compression ratio analogy was also aimed at someone who I perceived to not be as well informed as you..it was just that, an analogy.

You are correct..a properly set up engine on a pipe could run higher nitro and see a gain..but as you pointed out at the end..it (the little nitro gain) is just not worth the cost X aggravation for me vs the much easier to obtain (for lower nitro use) other avenues.

Good luck in your testing, not trying to dissuade you from trying..I just didn't realize the depth of your knowledge.

PAINLESS

My Feedback: (19)

I should have been more clear in my original post, its more complicated than just doubling or tripling nitro content.

One of the things I enjoy about this hobby is tinkering with engines to increase their performance, like 2000 rpm increases from raising exhaust ports. All the little things add up in the end.

I'm going to try the first test tomorrow. I have a Thunder Tigre Pro 40 w/ a Macs pipe and header. I'll try some 15% and 25% fuel with no other changes except needle adjustments and tach both.

mec

see:
http://www.rcuniverse.com/showthread...76&forumid=162

post #1

mecc

PAINLESS

My Feedback: (19)

Just performed the test mentioned above. TT40 pro, MACS muffled pipe and header, APC 10x6 prop.

15% wildcat fuel....14000 rpm
25% sig fuel....14900 rpm

Had to richen the needle 4 or 5 clicks with the 25%, I expected that though.

What do you think 900 rpm would be worth mph wise?

JCM

My Feedback: (2)

Looks like about 5 mph.
Try the calculator at Limey Bob's
I'm interested in high percents myself,
going to try up to 40% in a couple big
cheap engines,curious to see what you develope.

PAINLESS

My Feedback: (19)

When using anything above 40% nitro a colder plug is needed. OS makes one called an R5, McCoy and K&B had high nitro plugs at one time also.

I have an onbord tach that records the highest RPM reached. I used to have it on a Scat Cat with TT40 Pro, stock muffler, 9x6 prop and 15% fuel. I made two flights and was careful not to put it in a dive. It was taching 16.8k on the ground and I got two readings of 22k and 22.5k after landing. I was surprised at the high reading, (I had a witness) and one could certainly question the accuracy of the tach.

I'm going to try the tach again with the TT and a pipe as soon as I get another plane to put it in. I'm waffling between buying something and scratch building.

ChuckAuger

My Feedback: (12)

This is pretty much what I would have expected...not really gonna set the world on fire, but if you are after absolutely every last RPM, I guess it means something..

In my experiences, mostly on Rossi's, but some others..a 12 ~15 degree increase in exhaust duration will give 1K~1.5K increase...just adding a pipe will give up to 2K (more if the exhaust duration is increased and the pipe is properly set)...this was my point, there are lots of ways to gain R's, and increasing nitro content is fairly far down my list.

Glad to hear your nitro experiments are going well, keep us informed of any future developments.