NELSON FAI TUNING? (Full Version)

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combatpigg -> NELSON FAI TUNING? (9/3/2007 7:39:42 PM)

Are there any experienced handlers of this engine here? I've got a few questions.
First has to do with securing the pipe to the cylinder and how to get the best seal at the exhaust stack / pipe junction.
Second question is about which props allow the engine to do its' best work.
Third question is about compression adjustment. The engine I got was delivered with a huge stack of shims. With 10% nitro and a 7.0x8.25 prop, the only way I can get the engine to run and hold a peak setting is with just a single .005" shim.
I am just aiming for best straight line speed, not lap times.



Ed Smith -> RE: NELSON FAI TUNING? (9/3/2007 9:48:19 PM)

Which Nelson FAI engine do you have? The rear intake, rear exhaust or the Front intake rear exhaust?

Ed S



combatpigg -> RE: NELSON FAI TUNING? (9/3/2007 11:58:29 PM)

It is the front intake. It looks to be about 13mm.

I would like to pack some high temp silicone caulk into the exhaust stack coupling instead of using the standard O-ring.

The best I can come up with to hold the pipe to the engine is .032" music wire.... there must be a better way?

I wonder if any plug can be expected to survive a real good run? I know it is playing Russian Roulette to have the element go out the exhaust every run....sooner or later it will leave a gouge. There doesn't seem to be any middle ground with tuning, I suppose the prop load is the final tuning stage now.



Terryoc -> RE: NELSON FAI TUNING? (9/4/2007 12:17:32 AM)

I have always used stainless steel lock wire to hold the pipe on and so does every one else just the wire may change but the method stays the same.
Dont use Nitro it is an FAI engine made for FAI fuel being 80/20 castor oil.
Head should have 18 to 22 thou clearance depending on where you are atmosphere wise. Start at 20 thou.
You should see 26 800 minimum on the ground but I never went over 27500.
It most likely will not hold peak for more than a few seconds on the ground dont go looking for peak again as it wont happen , from peak go about 1/4 turn rich it should hold there and should have smoke in exhaust then try flying.
I used to get 6 or more races per plug.
Hope this helps
Terry



Ed Smith -> RE: NELSON FAI TUNING? (9/4/2007 1:59:54 AM)

Do exactly as Terry says.

quote:

I would like to pack some high temp silicone caulk into the exhaust stack coupling instead of using the standard O-ring.


Forget the silicone. Use the coupling as intended. You will need a high temperature "O" ring, should have been supplied with the engine. If not purchase the correct "O" ring. I used "Viton" "O" rings. Viton is the name of the material. There are probably equivalents. There is a technology to "O" rings. The correct size groove and fit on the ring. You will need to support the stinger. Enough to stop it from vibrating but not too tight that the pipe cannot expand. I used a piece of silicon tubing and a nylon cable tie on a support.

Your prop sounds a bit heavy on pitch. With true FAI fuel a 7.0 x 7.5 would be a better starting point.

Ed S



combatpigg -> RE: NELSON FAI TUNING? (9/4/2007 3:06:22 AM)

Thanks guys, The only advice I got from Nelson when he was out here 2 summers ago was to be careful if running any nitro in it. As it turns out, I have been running it with .021" and 10% and the piston is developing a pit after a dozen runs. I'll get some 0% fuel and try less pitch next weekend.

The stock O-ring works very well so far, but the replacements I bought from PSPEC don't seal as well. Is Nelson the only source of good replacements?



luv to race -> RE: NELSON FAI TUNING? (9/4/2007 11:35:32 AM)

The piston is developing a "pit"?? like it is on its' way to burning a hole through the top of the piston? If that is true, it will never run very good from this point forward... just too much abuse. Have Dave Shadel rebuild the top end and start over. If you are losing the element every run or close to every run, something is certainly wrong. It should run 10 laps and the element still be there. Pitting the piston and head is not good, just means you are too lean... which could be the nitro, get rid of that and run FAI fuel as intended. Like Ed said, your prop may have too much pitch. Buy a couple props from Ed, he has excellent Nelson props. Keep using safety wire to tie the pipe to the engine case too. You do not want the pipe move back or away from the header, it makes the engine think the pipe is getting longer while it's running.. that changes the way the engine runs.

Good luck.
RB



SSGSPEEDMAN -> RE: NELSON FAI TUNING? (9/5/2007 6:32:15 PM)


quote:

ORIGINAL: luv to race

The piston is developing a "pit"?? like it is on its' way to burning a hole through the top of the piston? If that is true, it will never run very good from this point forward... just too much abuse. Have Dave Shadel rebuild the top end and start over. If you are losing the element every run or close to every run, something is certainly wrong. It should run 10 laps and the element still be there. Pitting the piston and head is not good, just means you are too lean... which could be the nitro, get rid of that and run FAI fuel as intended. Like Ed said, your prop may have too much pitch. Buy a couple props from Ed, he has excellent Nelson props. Keep using safety wire to tie the pipe to the engine case too. You do not want the pipe move back or away from the header, it makes the engine think the pipe is getting longer while it's running.. that changes the way the engine runs.

Good luck.
RB



Guess I'll just keep the FAI fuel and not try 2% nitro [:D]

Kevin



luv to race -> RE: NELSON FAI TUNING? (9/5/2007 7:34:36 PM)

Nitro is probably really fun.. but as most people probably expereince, when running an FAI engine on Nitro...just a tad lean equals hole in piston. I burnt a hole in a piston at the WC and we weren't running Nitro. And any pitting or detination is bad, hurt performance and reliability.

RB



combatpigg -> RE: NELSON FAI TUNING? (9/6/2007 2:48:39 AM)

I'm only interested in straight line speed [but please don't disown me]. I ran it on 0% nitro yesterday and the performance was good with a 7x8.25 prop. It was easier to needle, but noticably down on power. I'm going to use a K&B 6.5 F-1 combustion chamber as a model to make a nitro head for this Nelson engine. That, combined with removing some weight from the piston and rod should allow this engine to run somewhat harder. Until I get a purpose built speed plane, I realize that there won't be any speed gains with my delta and also realize that the plane has to work with the engine and prop to get the massive unloading that I'll be looking for with a high pitched prop.



luv to race -> RE: NELSON FAI TUNING? (9/6/2007 11:30:05 AM)

Make a nitro head for the Nelson engine? huh? The current FAI head of a Nelson is perfectly suited for Nitro. Are you thinking about changine the shape of the bowl in the head? Why don't you call Dave Shadel at Performance Specialties and get his thoughts on "re-vamping" the Nelson engine to improve performance. This is just me, but I would think that if there was a way to make the Nelson FAI engine perform better, Henry Nelson would of already made the change.

Here is the best advise one can give a non-pylon guy who is just looking for speed.... Sell all that FAI stuff, and buy a Q40 engine from PSPEC.COM... That engine will pull a modern day Q40 airplane well over 200mph out of a dive, and you can tear up your sport field with a big smile on your face. And it is about 1,000,000,000,000,000,000 (that about a "gazzilion) times easier to operate than an FAI engine. You run it on standard 15% fuel, and you don't burn plugs like crazy.

On the flip side of that, I completely understand that some people like the challenge. So good luck with that...

R.Bridge



Ed Smith -> RE: NELSON FAI TUNING? (9/6/2007 12:48:51 PM)

quote:

I'm only interested in straight line speed


Do you want to go fast or dick around with engines and go nowhere? Follow Randy's advice. Read it again below.


quote:

Here is the best advise one can give a non-pylon guy who is just looking for speed.... Sell all that FAI stuff, and buy a Q40 engine from PSPEC.COM... That engine will pull a modern day Q40 airplane well over 200mph out of a dive, and you can tear up your sport field with a big smile on your face. And it is about 1,000,000,000,000,000,000 (that about a "gazzilion) times easier to operate than an FAI engine. You run it on standard 15% fuel, and you don't burn plugs like crazy.


Ed S



daven -> RE: NELSON FAI TUNING? (9/6/2007 4:59:32 PM)

Randy and Ed,

I completely understand with what each of you are saying, and completely agree, but some people just like to experiment and try and get the most possible out of a certain motor despite costs or effort. From what I know about Combatpig (still love that name), I think he is one of these people :)

I wish him the best of luck, and am glad you two are here to answer his questions, because there are not many people in the Country that can run these things succesfully.



Ed Smith -> RE: NELSON FAI TUNING? (9/6/2007 7:57:48 PM)

Dave,

I would agree with you but for this sentence in Combatpig's very first post. No mention there of the desire to tinker.

quote:

I am just aiming for best straight line speed,.....


Combatpig
If you wish to tinker then purchase the SS Q40 engine liner and head. The liner has the same timing as the F3D engine. The Q40 combustion chamber shape is set up for Nitro. You now have the base from which you can work with pipe set-up.

Ed S



combatpigg -> RE: NELSON FAI TUNING? (9/7/2007 1:16:57 AM)

Ed, that was going to be my next question, whether or not the Q-40 head is interchangable with the FAI liner. If not, I would buy a few FAI heads and tinker with them.
This engine isn't that hard to run compared with 1/2A speed engines. They are much less forgiving of mistakes and you can't ever be totally sold on a change until you see the engine do the same thing twice in a row.
I think this engine would be a bear to compete with on a race course though, no thankyou.
So far, taking a 7.4x8.25 APC down to 7 inches and thinning the blades near the tips has turned out pretty well. For $10 and an average life expectancy of 4 flights, it is hard to beat. I am anxious to see it perform on a faster plane. I will try a 7x7.5 when I get an order in to Steve Wilk, but all I think that will do is make the engine easier to run at the expense of top speed..



Ed Smith -> RE: NELSON FAI TUNING? (9/7/2007 5:47:27 PM)

The bore is the same on both engines. The Q40 head has what we called the "Double Bubble" head, one hemispherical shape blending into a smaller one where the plug enters.

Ed S



Terryoc -> RE: NELSON FAI TUNING? (9/10/2007 12:11:07 PM)

If you are going for nothing but speed get an inflight mixture and an onboard glow set up and put a BIG prop on.
If you can get the prop on the pipe on the ground it is to small.
You need the glow to help it climb onto the pipe and the inflight mixture is so you can take off nice and rich get height put it in a dive and lean it out to get up onto the pipe and fly big circles to keep it there.
Then you will see it unload
Terry



combatpigg -> RE: NELSON FAI TUNING? (9/11/2007 4:17:40 AM)

Terry, I think another aid will be launching with a high start.....it will allow ridiculous diameter / pitch combinations.
Should be able to try that 6x10 prop I've been lugging around for 20 years. [;)]
An onboard glow is a good idea, it probably doesn't need much capacity to maintain combustion.



daven -> RE: NELSON FAI TUNING? (9/11/2007 5:09:41 AM)

CombatPigg,

What I love about what your trying to do, is that no consistency is necessary. You are looking for ONE good run out of five or six flights.

Most of us racers sacrifice top speed over repetitieve competitive runs, which is contrary to what the German "speed cup" guys are after.



Terryoc -> RE: NELSON FAI TUNING? (9/11/2007 3:18:05 PM)

A highstart sounds like a good idea but a bit tricky to keep it away from the prop.
Could set it up like a bow and arrow the plane being the arrow.
Really dont think you would need the high start as evan off the pipe you would have quite a bit of thrust , but would add to the fun factor a little
The onboard glow really only needs to be a switch feed by 2 1300mah cells or something similar which can handle a 5 amp draw.
Have fun
Terry



combatpigg -> RE: NELSON FAI TUNING? (9/12/2007 3:34:16 AM)

You're exactly right, Dave. It is like trying to catch that perfect wave. I've tried to watch the C/L speed guys during breaks at the combat circle and it is excruciating to watch. It is like watching someone else fish [8|]. You might see just a handful of totally dead on runs all weekend, but they are just magical when it all comes together. It looks like a guy who is just holding a handle, flying some invisible, shrieking noise out there. The sound is purely satanic, it sends dogs into convulsions [;)] There are always lots of burnt and twisted parts laying around, no shame in trying. Nothing ventured, nothing gained. I imagine the pace at the Speed Cup isn't too much better, maybe 1/3 of the attempts are within 90% of the record? Just a guess.
I wish some of the C/L speed guys would get interested in RC speed,[before it's too late] their numbers are shrinking, very few youngun's want any part of this stuff.



jaka -> RE: NELSON FAI TUNING? (9/28/2007 8:23:51 PM)

Hi!
The Nelson FAI engine is easy to run provided you use 80/20 fuel, Nelson glow bee plugs and the correct carbon fiber prop...as any othet FAI engine. What's the fuzz about???



RabC -> RE: NELSON FAI TUNING? (1/12/2008 9:49:31 PM)

Guys this sounds disappointing,i was getting 27 on the ground with straight mix 8x8 apc on an irvine ducted fan engine really reliable and got about 10 8 minuite flights per plug,just sounds a bit weak for pylon,no?



adec4 -> RE: NELSON FAI TUNING? (5/14/2008 4:02:05 PM)

hey boys
can anyone tell me whats the best combo to use as a plug igniter ??
i have to travel soon to the other side of the country and im trying to keep my weight
down so the airline wankers dont slug me a fortune in freight
im just running an old power panel at the moment coz it doesnt drop the voltage
on the plug which seems to work well ,,
have any of you used just something like a D cell battery and clips for the plug
with any success ?

any help would be greatly appreciated

vb (adec4)



djlyon -> RE: NELSON FAI TUNING? (5/14/2008 8:36:58 PM)

Rechargeable "C" cell with a clip. That's all I use.



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