1965 Citabria 7ECA O-200 Max RPM

65Citabria

65Citabria

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Hi folks. I recently purchased a 1965 Champion Aircraft Citabria 7ECA with a low time Continental O-200A, and would like to get some feedback. My main issue is the engine never sees more than 2450 rpm which from what I've read is simply cruise rpm. Basically my takeoff and climb performance has been only based on cruise rpm, not the 2750 redline rpm.

Compressions are good, mag check is good. Carb heat door is fully closing. The log books show the correct prop. At 2450 rpm I'm climbing at about 400 fpm, and cruising at 85 mph when solo, full tanks, and near sea level. My mechanic did say an incorrect (overly long) throttle cable was used and it appears the throttle lever arm on the Marvel Schebler MA-3SPA carb isn't getting the full throw by about 1/4" prior to the stop.

Can another 300 rpm be gained by such a small amount of additional opening of the butterfly valve? Or...are there any other recommendations on what to look for?

Thanks in advance!
-Matt
 
I have your plane’s twin - another 1965 7ECA with the O-200 engine. I can’t quite turn 2700 RPM in level flight, but it will turn 2650 pretty easily. But that may (or may not) be related to the fact that I have my wheel pants removed (less wt, but more drag). Static RPM on run-up on mine is well within the TCDS requirements (min=2400, max=2600 static RPM at full throttle), but you didn’t say what yours is doing. This is a good “health indicator” before every flight.

The throttle linkage travel “shortage” you describe could well be the source of your issue. If it’s not that, i would check for a blockage in the exhaust system - the flame cone can come loose inside the exhaust system, and partially block the exhaust. If neither of those is it, you might have a carburetor adjustment problem. And there is always the remote possibly that someone installed an incorrect propeller (the right prop is the McCauley 1C172MCM74, with diameter between 67.5 and 69 inches). I would check all of those before jumping to the conclusion that it’s an engine issue.

Good hunting!
 
Thank you for the reply Jim! I'm SN 305...maybe they were under the same roof at some point. :).

My static is around 2350. I haven't checked exhaust but will if the correct throttle linkage doesn't help.

Speaking of throttle...does yours have the Bowden type cable? Do you happen to have pics of your carb setup? I have to order the correct cable assembly for my mechanic and it seems there isnt one clear throttle cable assembly for this model. Any help is greatly appreciated!

Thanks!
Matt
 
If you get 2350 at sea level on a standard day, you are certainly low on static RPM. With good compressions, I would check the log books to see what your prop pitch is. I assume it's a hi pitch. If that is the problem you can have it repitched. If your cruise speed seams hi, that is also an indication that your pitch is too high.
 
Thx for the input. According to the logs, the prop is a McCauley 1A100ACM69. I've not confirmed model or diameter. One note, both climb and cruise are subpar.
 
Matt,

Google and download a copy of TCDS A-759. That will list all approved props and required static RPMs for each. A lot of other very useful information there too.
 
Thank you Ron. It looks like the prop shown in my logs matches the TCDS. I will get a better check on static rpm next flight.

15. McCauley 1A100ACM69 24 lb. (-58)
(a) Models 7ECA with Continental O-200-A engine
Static r.p.m. at maximum permissible throttle setting:
(No additional tolerance permitted).
Not over 2600, not under 2400
Diameter: not over 69 in., not under 67.5 in
 
I also have a 65 o-200 Citabria. Mine will run about 2550 to 2600 level. I usually run it about 2500 for cruise. Climb is fairly anemic. I have the standard prop.

Dale
 
Thanks Dale. Just curious what kind of cruise speed and climb rate you're seeing. Since I'm only maxing at 2450 rpm on takeoff and climb, in fairly standard conditions I'm only seeing 400 fpm climb and 85 mph cruise (solo with full fuel). I'm guessing I should be closer to 700 fpm and 95 mph...but maybe I'm being optimistic.
 
Mine is pretty close to that. On a cool day (florida panhandle) it will climb about 400-500 fpm. On a warm day it is way less than that. On a hot humid day, I try not to fly with a passenger. Also, I rarely fill the tanks. Cruise is around 90 mph, sometimes a little more, sometimes a little less.

It sounds like yours is pretty close to mine.

One other note, mine sinks like a rock at less than 70 mph. I have a friend who has a 74 model. He can make approaches much slower than I can. I am thinking it is the extra drag of the double struts of the oleo gear.
 
Thank you Dale. Makes sense on the fuel...the plane is new to me, so I've been filling the tanks until I really get a good feel for burn numbers.

I found this article from '66: https://books.google.com/books?id=c...page&q=citabria 7eca o-200 climb rate&f=false
Based on your numbers and these, it looks like I'm just being a little too optimistic on the O-200. I think if I can get my rpm's closer to 2600 I'll be able to get closer to 550 fpm which should help.
Performance.png
 
Keep in mind those numbers were developed with a pristine airplane flown by an experienced test pilot. "Your results may Vary!" :lol:

I bought mine as a TW time builder since I am constructing a Nieuport 17 replica. It sure is not a cross country cruiser. But it is nice to putt around the area. I do periodically fly with the friend with the 74 model to shake bad habits with the "no bounce" gear.

As an aside, I have rolled it, but have not yet looped it. I have had it up to 145 mph in a dive to see what it did when and if I decide to try to loop it. (I have a friend who is an aerobatic instructor who rode with me. He also owns the parachutes.) We did the test dive to see if the RPM would redline - Yes it did easily.

Also, I refer to mine as the "missing link". Not quite a Champ, but not quite a full Citabria.

Dale
 
1/4" short of the stop could be quite a bit of power left "on the table".

Several years ago when getting my TW and mountain checkout we did some high density altitude work in very high outside temps. I got a real good look at the treetops at the end of the dirt runway coming out of Lake Wentachee. I had left my carb heat on and all I was missing was 50rpm. Up until that moment I used to think leaving the carb heat on was really no big deal. Never again.

The 65 Club
I've crossed paths on the web with Jim Parker before. I have s/n 290, but it's been converted to 150hp O-320. At gross I expect about 1000ft/min. Solo in cold weather as high as 1500 ft/min.
 
Thanks for all the input fellas! Got a quick picture of the carb at full throttle this week, and thought it might be worth a share. I purchased a new cable this week, so at least I can rule out this missing 15 degrees (or so) of throttle arm rotation.

Carb.png
 
Have you checked your RPM with some sort of optical device? Could be as simple as your RPM indicator in the plane is inaccurate.
 
Hi Greg...no not yet, but that will the be one of the next steps if we still aren't seeing max rpm improvements after getting full throttle. Thanks for the suggestion!
 
2 Quick updates on the original post:
1. New (shorter) throttle cable installed, now getting full throw on carb throttle arm (image below).
2. Mechanic found right mag was retarded by a few degrees.

Hoping to get it in the air early next week and will report back on the results.

Carb_After.png
 
Final report out on the original post...full throttle and corrected mag timing gave me 2550 static rpm (acceptable range for this engine is 2400-2600). Test flight yesterday was producing 2600 rpm consistently which was a reasonable improvement on takeoff and climb rate. It also got me to 10,000 ft which was one of my goals for an anticipated long cross country later this year.

Thanks to those who provided feedback. It was great to see how helpful this community is on my first forum post. For those interested, I created a quick video with a few highlights from yesterday's flight...

https://www.youtube.com/watch?v=uc9z583Ba6s&t

IMG_6673.jpg
 
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