Twin Commander
General Category => General Discussion => Topic started by: ghancock on August 30, 2019, 09:08:29 pm
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So I really love my Commander but I really hate the engines on it. I’m not sure what if anything can be done about it but the airplane is such an awesome plane if I didn’t constantly have engine crap to deal with. So my question:
Is there anyway to put different engines on the plane that don’t run so hard that might allow the cylinders to last longer than 300 hours? I’ve combed through my logbooks on the plane and it appears even from the early days people have been replacing cylinders starting around 300 hours after engine rebuilds. I’ve personally had 4 failures, 1 resulting in having to shut down during a flight and another 2 preventing me from coming home. Add to it the skydrol 3000psi pumps and Simmons fuel injectors and wow...
The problem for me is the Commander is by far the best flying airplane I’ve ever flown and honestly at the moment I have 12 new jugs on the engines so I can get at least 300 hours or so before I have more trouble but I want something more reliable.
Is there anyway the airplane can be converted to experimental so that I could put whatever engine I want on it or is the airplane just doomed to the dust bin?
I watch the Draco guy doing all sorts of stuff to his production airplane and I’m not sure how he gets away with it. I guess I should ask him but was wondering if any of you had any thoughts on the matter?
Thanks,
Glenn
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Anyone know if it is possible to still put 720’s on it?
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Glen,
I have no details, but before Morris passed he’d mentioned the possibility of using a 541 that’s on the Duke and creating a Stc for the 680 series. He believed the weight savings alone would be worth it not to mention converting the hydraulic to 1000psi and replacing the pressurization with turbos. He started to have problems with his shop and health before we could go any further. But if Morris thought it was feasible and practical it might be worth investigating. Good luck, long time follower of your videos and your 680.
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Wasn't there a Mr. RPM conversion to 720s or something like that? I'm pretty sure there was one for the 680FLP, but maybe not the FP?
If you want to be practical, I would sell the 680 and buy a 500B. That would be a nice complement to your 18, and would still fly very nice.
Let someone who wants to own and operate a museum piece have the 680.
I would think Bruce could help you out, and maybe even take a trade.
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There was a Mr. RPM conversion on a 680F that Morris had in his shop that met with demise; I think it was something like hydraulic failure while taxiing and it hit a fence or something. So I'm quite positive there is an STC for the 680F. As for the 680 FP, I'm not sure.
Try tracking down Barry Collman? He pretty much tracked every AC there was, not just pictures.
I'm with Don; a nice 500B (with RayJays) is a nice plane, and the RayJays didn't seem to need near the attention as the geared motors you have. Even a nice straight aspirated -B model is nice as well.
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Yeah, I know there is an STC for the 720's but no one is making any of that stuff anymore. So it would probably be a pretty big job to do the conversion. The 541 option is really just a slightly larger 540 as far as I know and to get over 380hp you'd end up having to go to the geared side which is really no different than where I already stand. I'm not sure of the price on these engines but they also don't run upside down so would need to redo quite a few things to have the exhaust coming out the bottom instead of the top.
As for selling the plane I'd love to get it into someone's hands that will fly it. The problem is, no one really wants to step into this type of a project. I mean, to be clear, with new engines I'd probably be having none of these issues, at least for a while, but the market for a pressurized Twin Commander with piston engines probably isn't very large.
As for trading, that might be an option but not sure Bruce would want to get involved in trying to move this type of plane.
I hope to have her back in a hanger in the next couple of months where I can start working on getting annual done as well as the gearbox on the left engine.
Just don't want to see her die. :-(
Glenn
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The TIO-541's on Dukes do produce 380HP, but it takes 2900 RPM to do so. Never liked the thought of spinning them up that fast in the ~15-20 hours of Duke time I had, but it was obviously by design.
Roy
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Could you buy an airplane like the one Roy mentioned (damaged) and take the conversion bits and engines from that?
You'd still need the STC, but I assume that's available in some shape or form?
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Duke engine will cost as much as the ones on now. They were only used on the Duke and there isn't a good infrastructure behind it. It also has cam problems. I would try to make the ones you got on now reliable.
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The Duke engine does not have a pretty history. Talk to any shop that has maintained a Duke and you will get the same story. great airframe, terrible engines.
I would talk to a DER and ask what he would need if you found a Mr RPM Commander (any model) that has big airframe issues so it will be cheap to use as a engine donor. There is no replacement for displacement. I flew with a guy who had a 400 horse Comanche and I was pretty impressed. Butter smooth and this one was sitting at 1600 hours and had all original cylinders. 8)
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Yeah that is what I would like is the 720's. And btw: 2900rpm? Is that all? I'm turning 3400rpm on take off. I feel like I'm sitting on a monster about to go wild every time I push those throttles forward. I must have missed the damaged commander with the Mr RPM conversion. Will have to go back and look for it.
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Oh, you're talking about the one in Morris's shop. Someone told me that most things in his shop are property of the airport now due to being behind on the bills but not sure how factual that is. Also not sure if Morris owned the plane or if it was someone else's.
I guess I could look into that and see. I'm also not sure what would be required to swap something like that nor how I'd get the STC since it is no longer available as far as I understand. Maybe a field approval would work...
Glenn
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I like the idea of getting your engines working well, really.
Considering that you have the 18, 300 hours might last you several years.
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Yes, the Duke engines have a history. 100% agree there.
The 680F I was talking about Morris had with the Mr. RPM conversion was circa late 1980's-early 1990'. In the end he did end up owning it according to FAA records, a part of the "bad ending" the plane had. However that plane is long-since parted out, verified according to the last picture I saw of it labeled at 2016 in KHWD with lots of stuff missing. As for where the STC went, this is too long ago and I was not privy to that part of his business; I bet someone bought it from him knowing him. So that plane is not an option, I just offered it up that a 680F had Mr. RPM with STC on it.
Re: 2900 RPM, please accept my ignorance if this is the case. A geared engine, yes the props are turning 3400 RPM, but aren't the engines turning much less than that? I forget what the gear box ratio is (if I have this right). Note I'm talking about my limited Commander history circa 1985-1994.
Wish I had more experience, and circa today ;)
Roy
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Roy, the geared engines go the other way- the engine turns at say 3200, but the gearbox(and I'm referencing the GO-300) has a 3:4 ratio- so the prop turns at 2400 rpms. Hope this helps a little!
Steve
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Glenn
I have available 2 720’s, the props, and probably most of the parts to convert a 680FL(p) to 720 power. STC’s get rid of the 3000 psi hydraulic system and it’s supercharger too.
If you want to do it, it’s probably doable with enough time and money!
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Glenn,
Don’t know what you’re willing to try, but there’s also at least 1 680 fp in Germany with fresh <100 hr engines. 67’ model used in aerial survey, that apparently they can no longer certify due to EASA regulations. One add stated for export or part out. No price was given. The add was on “aircraft24.com”. Hope this was useful.
https://www.aircraft24.com/multiprop/commander/680fl--xi130880.htm
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Thanks for all the info. And I'm weighing all my options at the moment. Things will start to move as soon as this hanger is finished so I can get her back inside to start work. Having the Beech 18 does give me more time to do things as I won't be in a rush to get her flying immediately. The 720's project does sound interesting but need to get all the parts and processes lined up ahead of time to make sure I don't work myself into a hole.
As for the gearbox on this particular engine, the engine turns at 3400rpm on takeoff and 47" of manifold. The prop is only turning around 60% of that on this engine. It makes for an exciting takeoff roll and makes it even more interesting that it will push well over 46" so you have to watch what you're doing on each takeoff.
I've been talking to Bill Leff about it and he's telling me to just let her drink the gas and the engines will last. He said the reason people have so much trouble with them is trying to lean them out too much and that most people throughout the years have always tried to do that. But there are others that just keep them fed and they last like a normal engine.
I may give that a shot too but still trying to decide. We'd be talking about 60gph for an airplane that barely flies 200knots. Not sure if I'd be able to do that for long. :-)
Glenn
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@ Steve, thanks, I showed my ignorance in public on how the gear boxes work. Thought it was the other way around.
Roy
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Hi, Glenn, et. al.
My 685 is very similar, with the GTSIO-520K's. 3400RPM, 44.5 inches MP at takeoff to generate 435hp. Thankfully, I have not had as much difficulty with cylinders. I think it's because of my constant monitoring of CHT's via my EDM-800's. At any reasonable kind of altitude (thinner air, less effective at cooling), I cannot run with the cowl flaps anywhere near full closed and still keep the CHT's under 435 (I like to leave a margin for error below the 460 max) with a properly-leaned mixture. That generates about a 5kt airspeed loss due to the drag, but I'll take it vs. cooking the cylinders.
By the way... I rely heavily on the engine analyzers to show me the individual CHT's. The OEM gauge shows just one cylinder... and it's not the hottest one. I likely would have cooked off several cylinders by now without even knowing why.
Wilson
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Thanks,
Yeah, I use my monitors as well and I generally kept my CHT's below 400. I ran LOP though with generally 390 F temps. The problem though is when running LOP your EGT's are generally higher and I am burning Exhaust valves. So I'm thinking of switching back to ROP. However, we're talking 38gph at LOP and 60GPH ROP. When flying ROP I can barely lean the mixtures at all before the CHT's go through the roof.
Are you running ROP or LOP?
Glenn
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Hi, Glenn.
I run ROP.
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Glenn,
I run LOP.
ed
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But the 500 really isn't a fair comparison to the big geared engines on the 680/685, is it?
Glenn,
I run LOP.
ed
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I am sure you are right. I just jumped in there, not thinking about that ... ;-)
Ed
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Yeah, the issue is not the CHT as I keep all mine below 390F. The issue is with EGT's when LOP as they do run higher and 100% of my cylinder problems have been with burnt exhaust valves. I may just try running ROP once I get her in annual again and see how that goes. Problem is we're talking 38GPH LOP and 60GPH ROP.
Glenn
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Heyy Glen...how about some allisons?? Perhaps talk to lycoming for a recommended engine and do an STC?? I am on the same boat, but I do run ROP instead of LOP. They go for about 800 hrs.