N421GM with new GAMI’s

Home 2024 Forums Opening Section Operational Issues N421GM with new GAMI’s

Viewing 15 posts - 1 through 15 (of 17 total)
  • Author
    Posts
  • #83529

    I told the board we would post results of GAMI installation along with JPI engine monitor and FF.

    This is a pre GAMI flight. We tried FL250 at around 150PPH per side and got 225 KTS. Then dropped to FL210 at similar FF and got about 215KTS. If I remember right we might have had a slight tailwind. Sorry I did not take notes! On other flights the a/c did about 200KTS TAS @ FL200 at just over 100PPH per side pretty much by the Cessna book at maybe 55% power. The engine instrumentation was pure Cessna stock.

    GAMIs are now in a/c as well as a JPI 760. First test flight was yesterday here are the test results so far.

    I believe MP was 30″

    Plane will be enroute to KRZN (near my lake home) Monday 7/25 then to OSH early Tuesday. Will have more data from that flight and perhaps post it online Monday evening. The JPI has not been fine tuned for K factor meaning FF is in the ballpark but not a certainty. The transducers were out of a 421B as was the JPI. Ignition was set up at annual with new fine wire plugs. I cannot remember what magnetos are in the plane but mechanic said they will do fine LOP. Ignition harnesses were in great shape.

    We have a new interior from the same salvaged 421B (don’t ask) but headliner did not work so we have our old ragged one in the plane. We have some completion to do on interior but for the most part the big pieces are finished.

    Avionics n a/c at this time are vintage. We plan on replacing them after OSH w/G600 and GTN 750/650 series. We will keep the RDR 2000 and control head. I am not paying Garmin $3000 so so I can read it on the G600 or the G750 unless one of you guys wants to but the “stabilized” RDR 2000 VP (12″) . Autopilot plan is new 55X w/FD and auto-trim. We will have lots of older avionics for sale shortly.

    Short list of avionics to be removed:
    Audio KMA-24
    Nav/Com #1 KX-155
    Nav/Com #2 KX-155
    Compass Collins PN-101 w/slaving unit
    Nav Indicator KI-209 w/ glide
    ADF KR-87
    Trpdr Collins TDR-90
    Encoder Ameri-King AK-350
    Flt-Dir Collins FD-112V w remote gyro
    Dual Inverters (new avionics do not require inverters)
    Auto-pilot Bendix M4-D
    RMI Aeronetics 3137L -B-6-3-C
    Scope Insight Strike Finder
    DME Collins DME-40
    GPS King KLN-90B
    Radar RDR-2000 VP
    Rad Alt KRA-10A
    Map Argus 7000
    Davtron M 811B Clock & M655 Density Alt;

    #94922

    How were the engines running? It seams like there was still a large spread on the peak EGTs with the gami’s (but its hard to tell from a photo). Were you LOP at 16.3 gph?

    #94931
    quote TJOHNSONJR:

    How were the engines running? It seams like there was still a large spread on the peak EGTs with the gami’s (but its hard to tell from a photo). Were you LOP at 16.3 gph?

    Both engines subsequent to that flight, required quite a bit of fuel tuning. We think we got it pretty close now. Plane went to avionics bay for new panel. Will resume playing with GAMI spread etc once panel is installed. We’ll try a lot of different setting etc. Right now we think its sweet spot is going to end up around 200KTS at FL190-210. The fuel flows low, high and mid range were a mess. Time will tell.

    #94936

    Well keep us posted, I’m very interested in seeing the performance of a well tuned 421. If your able to knock a few gallons per hour per side thats alot of savings and it increases the utility if you can make longer legs. Thanks

    tim

    #94975
    quote TJOHNSONJR:

    Well keep us posted, I’m very interested in seeing the performance of a well tuned 421. If your able to knock a few gallons per hour per side thats alot of savings and it increases the utility if you can make longer legs. Thanks

    tim

    It turns out there are three fuel flow adjustments needed and all have been worked to death and then the a/c went into the avionics bay. We’ll let you guys know once its out and flying again.

    There are a million things to do to get an old airplane into shape. A C421 that can do 220kts @ FL 210 or there about on 33 GPH is the goal. Takes work, patience, fuel, and $$.

    #94976
    quote :

    A C421 that can do 220kts @ FL 210 or there about on 33 GPH is the goal

    220 Kts in a 421 and on 33 GPH? We used to get 200 – 205 Kts at 42 GPH in a 421C when the engines were 80 – 100 ROP. What mods do you need to make to achieve those numbers? LOP can provide better economy – does anyone get higher performance and economy together? Also, what were your TITs when you were running 1584 EGT in the photo above.

    Geoff

    #94977
    quote COCHRANE:

    quote :

    A C421 that can do 220kts @ FL 210 or there about on 33 GPH is the goal

    220 Kts in a 421 and on 33 GPH? We used to get 200 – 205 Kts at 42 GPH in a 421C when the engines were 80 – 100 ROP. What mods do you need to make to achieve those numbers? LOP can provide better economy – does anyone get higher performance and economy together? Also, what were your TITs when you were running 1584 EGT in the photo above.

    Geoff

    Geoff, we’re trying, I said we’re trying. Some cold day, north of Nebraska I will show you. Now.. right as of this second, 205 maybe? How about we clean up 17 antenna’s, fix the sagging landing lights, fix the gear doors and add winglets (Oh! we already have those) strakes maybe, fly by night go fast fluid and and flux capacitor. Then point is down hill slowly while adjusting the set screw in the VSI (damn, that’s electronic). OK, we’ll just fly through a thunderstorm in an updraft. Not!

    I will simply do a minor software adjustment to the co-pilot. Or I will read the Cessna C421 brochure from 1976 again.

    Laughs,

    Tim

    #94985
    rwelsh
    Participant

      Tim, I expect you will end up using 37 to 38 GPH and get about 200 to 205 KTAS at FL210 to 230 assuming your engines are properly baffled to be able to stay under 390 dF CHT while LOP. On the non-geared engines most run out of boost at FL220 and above unless you increase the RPM by at least 100 to get more mass airflow to spin the turbos. I don’t know how the geared engines will react to LOP at altitude, but an increase of RPM will recover the boost. If you don’t have the true airspeed indicator installed and working, then the Garmin 530 has one or you can use a whiz wheel to figure out the TAS. Flying a round trip course to find the average for TAS can be a pain depending where you are and what airspace so having a TAS indicator is handy.

      If you really want to experiment, put 250 pounds of movable baggage in the aft compartment and fly a test run. Then move the 250 pounds to the forward passenger seats and do a test run. I have found in the 340 that we got 3 to 5 knots better with the weight forward.

      #94989

      The G600 (w/750/650) will compute TAS. We are at 205 now (we think) at the LOP settings FL 190-210. With FF properly set up (subject to more testing) and strakes and a skinny co-pilot who knows how to adjust his seat for proper CG calibration maybe we gain a few knots. I have yet to see a standard ISA (really). We’ve done FL 240 at max book ROP and did not see much of a gain but for noise.

      We’ve lightened the plane an estimated 100lbs by the end of the avionics project. The 421 does not seem to gain much speed with fuel burn like a Baron does. What are the VG’s costing us speed-wise but what do they add back for safety.

      All things are relative. I really want to make Naples (KAPF) to Teterboro Airport (KTEB) non-stop with NBAA reserves. The rest is relative to my patience level. The real trick is to get up there fast and then do the big pull.

      I really have to find a 1976 brochure then communicate with Lopresti from my reverse engineered communications device I stole from the Chinese. I will see if I can get him, Ted Smith and Mike Smith on a conference call. Then I am going to Ada and Waco to explain to them the principals of thrust and drag follow by a visit to Allen Klapmeier and Jim Bede.

      Wichita is not in the 421 business anymore which is a pity but with today’s advances, you could probably on carry 100 gallons of fuel.

      #94994
      rwelsh
      Participant

        I must say 205 KTAS with a 421 running LOP is quite good. Can you share the good and the bad with the strakes? They are supposed to be ready for the 340 and I was interested. Over on the CPA twin Cessna forum, there was a major discussion on how the strakes work and how the engineer types didn’t think strakes could increase cruise speed with the same fuel burn from prestrake time.
        Dick Welsh

        #95008

        Dick,

        Once we get them on, I will let you know. We have a lot of testing to do.. I think the VG’s cost about 8 knots. The winglets add 7kts back. The Vg’s give you a lower landing speed and VMC than what winglets alone do nobody can tell us, I am not sure other than I believe give you get 100lbs with winglets but nothing for VMC . I like more rudder power for lower VMC. I am not sure the t/o speed or landing speed is all that relevant if you have winglets.

        I am not saying I am going to take the VG’s off, I am saying that they may not really do what they are worth if you have winglets. Nobody has completely tested the two and done the engineering work. Adding strakes is supposed to give you up to a 10% IAS (at altitude) increase or some such thing was that tested with winglets and VG’s, no. I think it changes the angle of incidence therefor reducing drag in climb and cruise. I think it acts like an aft CG and lightens the downward lift of the tail without adding much if any weight.

        So add up, winglets, strakes and VG’s and what do you have, a tricked out, faster climbing 421 that can do the big pull quicker than a stock bird without overheating the engines on climb. Flatter faster climb attitude = cooler engines, 100 FPM more, run the engines hard ROP for 15 minutes and you are at FL 210, then pull back the FF and see what you get.

        In many ways this plane have been tested by STC holders with all trucks installed. I guess we will find out.

        We will try numerous altitudes, FF (%hp) and see if we can make new sweet-spot. All I want is Naples – Teterboro non-stop with reserves consistently anything other than that is a bonus. Maybe to do that we go to 28 GPH at 200 kts, I don’t know yet. Should know pretty much by November.

        #95377

        Any update to your performance enhancements? Did you add strakes? Any difference?
        I am soon to be in the market for a 421 with similar “demands” (I want to be able to get from MI to TX, 950-1000 miles). For now, still reading the forum and old magazines and gathering info. This is a great group with lots of great discussions.

        #95380

        JKOZIARSKI

        We just put overhauled engines from Performance out of Opa Locka on the bird. No strakes yet. The engines we had were lower time engines but the right one threw a bolt on the alternator gear putting metal through the engine and the left engine would not hold compression well enough. I could have probably topped them but not knowing what I had in the bottom half negated that idea.

        As for this second we are a bit high on TIT on the right engine which is being pursued as to cause. The engines now have 25 hours on them so we are past the break-in period. Once we get the cause of TIT spike on right engine figured out we’ll go out to Colorado and put stakes on it. We also rebuilt the fuel selector as the seals had dried out and the right engine would not run smoothly without low boost.

        We saw 203 KTS at 32 inches and 1800 RPM running 21.5 on the left and 23.5 GPH on right engine (in deference to TIT temps) at FL200 Friday. This was with a the mains full and 6 (4 very pretty ladies) on board. We were well under gross. On an FYI basis, we dropped to 16,500 ft to avoid a circuitous ATC routing and lost only 3 KTS at same power settings. We also picked up 15 KTS of ground speed due to wind changes as we descended.

        That is probably the best thing about a 421. You have the option of flying lower to find more favorable winds and not lose too much airspeed. Turbo props don’t have that luxury. At 11,000 ft a week ago I saw 193 KTS at similar power settings.

        Tim

        #95381
        rwelsh
        Participant

          Tim, check the timing on the engine running high CHTs. There should be no advance from the factory number and a tad retarded can help to lower CHTs. Also check the baffles, especially the innercylinder baffles. The baffles should be super tight with no air leaks anyplace. Put a drop light behind the rear baffles when in a dark hangar, and you should see no light when looking through the nose cowl. There should be no gaps between the innercylinder baffles and the engine case. I put a 12 inch plastic tube nozzel on a large tube of high temp red silicon obtained from the autoparts store and fill all the gaps between the engine and baffles, even the smallest holes. There should be a tight seal between the baffle seal that goes between the baffles on both sides of the front and under the propshaft. The difference between very tight baffles and sloppy ones can be 20dF on the CHTs.

          #95384

          Tim, Thanks for the update. Those numbers sound pretty respectable. Sorry to hear about the new engine. It will be interesting to see what happens after the break in and the strakes. You are right about the altitude issue. Right now I fly an Aero Commander. Today I got walloped with headwinds.

          John

        Viewing 15 posts - 1 through 15 (of 17 total)
        • You must be logged in to reply to this topic.