Performance report 447

RICK MARTIN

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Most of the guys who were at Essex days know about this, but I thought I'd share it with everyone:

I arrived early on Thursday. When I tried to fly Thursday afternoon I had three aborted takeoffs. I couldn't get enough climb.
My bee is about 315 lbs, 447 single carb, 60 Ivo, me at 220 lbs.
Even with this situation, all of you know I fly fine at Wauchula in the heat(I'm guessing Wauchula is about 150' ASL).

Scott's field is at about 800' and was hotter than home.

We took out a half turn of pitch (increase engine rpm). I waited until the next morning and flew but it was marginal.

Later that day the heat caused the same problem. My tiny tach had just died so we were re-pitching blind until Ron showed up with his optical tach.
So we used his tach and pitched it to 6500 static......my usual static is 6250-6300. So we thought......this should do it! It was a dog! I couldn't fly it. He couldn't fly it.

All we could think of was that we had taken out too much pitch..........so we put two and a half turns back in and ............problem solved (sorry but i don't think we took another reading). We both had a good time flying it. It still didn't climb like Barry's 503, but it was adequate.

Scott and I were still scratching our heads so I told him when I got home, I would fly at Wauchula without changing anything and give him a report. Here is what I sent him this evening:
--------------------
Sorry Scott,

I forgot to get back to you about this.

After fitting a temporary fuel tank (I think I told you mine had a hole in it when I got home) and three of us looking the Bee over very carefully, I flew at Wauchula without adjusting anything. It was about 90 degrees and humid with a bout a 5 mph head wind. The old girl leapt into the air and flew as good or better than she ever has on a cool morning here....very good climb. The engine rpm said 6250 to 6300 on climb out. This is lower than normal for here. I usually turn about 6350 to 6400.
So I guess the logic works....................if it's set for best performance at a higher density altitude then it will fly better at a lower density altitude. I have flown well two days in a row, so it wasn't a fluke. By the way I was discussing this reverse-logic phenomenon (higher engine rpm is supposed to give better thrust) with my friend K.C. who flies a fixed wind 912 with an Ivo. He confirmed that it was fairly common knowledge that you can go too far with taking pitch out of a prop (to hell with the suggested engine rpm). So I guess the best indicator is to just do a thrust test for each new set up. I doubt whether running/cruising etc at anything over 5000 would cause the engine to load up.......................tell me I'm correct please and have no concerns here.
 

PW_Plack

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Would a single-carb engine make peak HP at lower RPM than the dual carbs?

Could this also suggest a restriction or other issue with exhaust?
 

GyroRon

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I am feeling pretty certain that Rick has something wrong with his engine, most likely the carb. Fix the engine, turn the most rpms the engine is rated for and you will get the best possible performance.
 

Ralph

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Our approach was always to adjust the prop to get 6300 rpm at full-throttle with the aircraft tied down/restrained. As I remember, this happened with 14-degrees of pitch cranked into the 60-inch, two-blade IVO.

This approach assures that the engine is properly loaded. The thrust you get will then depend, to a large extent, on how good your prop might be. Depending on the specific prop, a 447 can crank out between 250 and 300 pounds with a single carb. I would not settle for a pull of under 250 pounds (measured on a smooth surface). If you are getting anything above 300 is suspect.

If you are measuring CHT and EGT readings, that could give you a clue if it is a carb problem. Also, the torsion rods on an IVO can sometimes start to take a set with time, reducing effective pitch. Still another possibility is that your muffler/exhaust may be accumulating carbon. To compensate, you either have to clean the unit (sometimes difficult and always messy) or rejet. The latter works fine, but you have to remember to go back to stock jets if you clean the muffler or replace it.

Ralph
 

RICK MARTIN

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Ron,

Because of this engine seeming to have a mind of it's own, I wouldn't be completely surprised to find out that your hunch is correct, but it sure flew great yesterday. What a blast!

Ralph

Thanks for the info. You gave me some stuff I was not aware of. My hunch is that the prop is just very flexible and or like you said has started to take a "set". There have definitely been times in the past where I have decreased the pitch and gained thrust, but maybe I was below a certain threshold which we crossed at Essex Days.

Anyway, it's pulling great now, and I did have about three hours of great flying while up at Scotts. I'm shopping for a 503, but I still love that little engine.
 

Dale Young

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Rick, I have experienced the same thing with my 503dc . It seems to push better and perform all around stronger with the pitch set at 6400/6500 full throttle. I'm staying at around 5750 rpm at cruise.
 

gyropilot

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Hey Rick,

Keep in mind the main jet in the carb is only going to be optimal for a relatively narrow combination of temperatures and density altitudes. Outside of these ranges, poor engine power can result. Besides referencing jetting charts published by either Bing or Rotax, the best way to be sure the carb has optimal jetting is by referencing EGT's and CHT's.

Just an FYI...

In late summer I fly my 503 equipped Bee from a dry lake bed in southern Oregon with an elevation of 4,100 feet. Before I installed an HAC (High Altitude Compensator) system on my carbs, to keep the EGT's in the proper range, I had to change jets at least once (and sometimes twice) during the day as the chilly morning temps soared to near 100 degrees F in the afternoon.

Best regards,

John L.
 

RICK MARTIN

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Thanks Dale,

Thanks john,

That all makes perfect sense to me and probably everyone else. But when I said that this engine has a mind of it's own I was talking about things like this:

When I change to a richer main jet (or two sizes larger), it makes very little difference, if any, in the EGT reading at full power. The only thing that seems to make a noticeable difference is prop pitch. I'll check all my jets and the needle on Saturday so we can know the parameters we're talking about here.
 

RICK MARTIN

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Dale, What prop and size are you using?

How about you john? And how does the HAC work?
 

gyropilot

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RICK MARTIN said:
How about you john? And how does the HAC work?
Rick,

I'm using a 60" 3-blade Ivoprop on my 503 equipped Bee. I have it pitched so that the engine might reach 6500-6600 rpm at sea level, full throttle, and 70 mph. Max engine rpm at 45 mph is closer to 6300-6400 rpm. Climb performance is more than adequate like that.

Regarding the HAC...

The High Altitude Compensator works by gradually restricting the venting to the carburetor float bowls as density altitude increases. This has the effect of keeping the air/fuel mixture at the optimum ratio as density altitude increases. I believe it was primarily designed and tested in the late 80's by Rotax and Bing to address the problem of an excessively rich air/fuel mixture when pilots climbed and flew at high altitudes using these carburetors.

Sadly, the "chamber" device (which regulates the carburetor float bowl venting and is the heart of the system) was discontinued from manufacture in the late 90's or early 2000's. Therefore the HAC kit is no longer available. I bought one used on eBay several years ago.

Of course I don't normally fly at high altitudes (8000 feet MSL is my record), but I installed one anyway because it means I'll never have to change the main jetting again... no matter what the temp or altitude. Once everything was dialed in after I installed the HAC, my 503 has near perfect EGT's under all flight conditions.

Best regards,

John L.
 

gyropilot

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gyromike said:
High Altitude Compensator kits from Green Sky Adventures.
Mike,

Unfortunately that *automatic* mixture control kit hasn't been available for more than a couple of years now when the supply of HAC chambers were exhausted.

Green Sky now only sells a *manual* mixture control system.

Best regards,

John L.
 

gyromike

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Hmmm, they mention on the website that they have both the automatic and manual mixture systems.

I guess their website is out of date.
 

RICK MARTIN

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Thanks gentlemen!

You just keep on talkin' and I'll just keep on learnin'
 

greywuuf

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Snowmobile guys run into this problem all of the time. The HAC system was advertised as designed and marketed by SKIDOO on their rotax powered sleds.he other brands have followed suite with varing degree's of sucess. DO a google search on "Holtzman Racing" or ATAC Altitude Temperature compensation having the same aneroid chamber and working on the carb vents. they work very well on ground based two strokes and run a bit over 200 bucks.
 

bshamblin

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did you say what diameter rotor you use with the 447 gyrobee? 220lb + 320 lb = 540lb. to keep the disc area close to 1 lb/sqft youd want 26' rotors as Taggart speaks of for good flying with the 447, wouldnt you?? or am i missing something?

bshamblin
morganton nc
 

scottessex

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Depends on the rotors, Low performance draggy rotors like rotorhawks or Brocks you will be fine, If you plan on using Dragon wings they are a high performance blade and require more disc loading, around 1.3 I think, somebody correct me if I am wrong here.


So if you and the gyro weigh 540 lbs you would need 23 ft blades if you were using dragon wings, if you were using Sportcopters you could add a foot.

I'm no engineer so I hope I didn't give any bogus info.
 

RICK MARTIN

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Sorry,

I've neglected this thread for a while.

My Bee is about 310 lbs.
I'm 225 lbs
447 single carb
23' Dragon Wings
60" 3-blade Ivo
Wide open I turn 6200 rpm, and I pretty much fly wide open all the time.

All I can tell you is that I fly every weekend, hot or cold, at Wauchula without a problem. Would I like more power? Yes. But it flies like a dream.
 

Udi

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...I fly every weekend, hot or cold, at Wauchula...
Now, THAT made me laugh... :whip:

Right now it's 10°F outside and tomorrow will be a nice sunny day with highs at 25°F. Friday will cool down again to 16°F so I think I will wear a coat to work...

Udi
 
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