Convert an MX7-160 to 180hp

Wyflyer · Post by **Wyflyer** » Tue Jan 20, 2015 5:57 pm

My airplane has been in for paint and recover all winter and is nearing the point where my shop will reassemble it all and make it fly again.
While it's been down I have aquired most of the parts to upgrade it to a 180B: O-360-C1F, Hartzell prop, spinner, prop governor cable, etc.

Before I commit to turn it into a 180b at this time, I need to make sure I understand the sequence of events to return it to service:

All the modifications described in the Mod kit must be done completely, then a 337 completed to capture the major alteration.
The 337 along with the Mod Kit #30 documentation will provide documentation needed to receive approval from a FSDO for an amended airworthiness certificate, which is needed to fly it as a MX7-180B.

With the new airworthiness certificate I can obtain the final data plate from Maule to install on the airplane which is a final step to return it to service.

This is my understanding of the process. Keep in mind i'm not an A&P so it may seem overcomplicated to me and may be simple to those of you who do this regularly.
What I don't know is how long it might take for the FAA to approve all this. I'm thinking they can generate a new airworthiness certificate fairly quickly. If it's a 6 week process I may hold off and do it all later.

aero101 · Post by **aero101** » Wed Jan 21, 2015 11:17 am

First of all, this is already an approved mod, doesn't need to go to FAA for approval, just a form 337 documenting mod as per Maule paperwork just like you'd do with an STC. Depending upon Maule's instructions, you may have to go to your FSDO, to modify your Airworthiness Cert, and Registration. Sometimes this is part of mod, sometimes not... It will be spelled out in directions. I did a long wing conversion onto an M5 several years ago, on that one, I think we changed the model to an MX7 or M6, not sure which anymore, and this was all called out in Maule's paperwork. If new airworthiness certificate required, FAA will issue on the spot, no waiting period required. You will probably have to fill out an 8130-6 (application for airworthiness cert) for FAA, as well as re-register as updated model...

Wyflyer · Post by **Wyflyer** » Thu Dec 10, 2015 6:27 am

Aero, i'm not sure but I think you paraphrased what I already described?

In any event, i'm at the end of the process. In my case the FSDO wanted to look at the airplane even though the Mod Kit 30 was approved by my A/P and FAA in person inspection is not required.
All the work is done, logbooks updated, A/W cert in hand and all I lack now is submitting it for new registration as a model MX-7-180b which will be done today.

I can't speak for them directly of course, but I think the FAA just wanted to become more familiar with this mod and see it for himself. Other areas would likely just sign off the mod and move on.

I'll post more about the airplane performance when i've put some hours on the tach. In a short time i've messed with it the increase in power is very noticable. more later

aero101 · Post by **aero101** » Thu Dec 10, 2015 7:45 am

Yes, sometimes FAA does want to look at aircraft prior to issuing a new airworthiness certificate.. They generally want to see logs and aircraft to verify aircraft is in fact airworthy and not just a pile of project or something. They do not need to approve the 337 for the mod, and technically per their own rules you really don't even need a 337, but I'd do one anyway, just to document the mod in Oak City.... Sounds like you've got it well in hand!!

Wyflyer · Post by **Wyflyer** » Mon Dec 21, 2015 6:43 pm

I"ve put 4 hours on the tach now after getting my airplane out of the shop. The rigging is complete and it now flies wings level and straight. The rudder trim tab is set with the trailing edge of the trim tab 1/8" inch to the right of centered.

In the 160 hp configuration I could only detect approx 1 or 2 knots of speed increase using the +7 flaps. My last flight I set it up in cruise at 25mp/2500 and applied the + flaps and observed a 9 knot speed increase. wow!
So far with limited flight time i've observed 138 mph at 25/2500. My fuel monitor indicates 11.5 gph, but I need to make a few flights and check it for accuracy on some longer flights before I determine how accurate it is. Prior to sending the airplane to the shop it was accurate within 1%..

When it was a 160hp most takeoffs were 800', now it's more like 450-500'. I'll learn more about this with time also.
These are just some preliminary observations, i'll be better informed in a few months. But one thing is certain, I love the c/s prop and more horsepower!
It takes off shorter and flies faster, both are good things;)

rjb · Post by **rjb** » Tue Dec 22, 2015 4:40 am

My IAS also shows a 9 knot increase with +7 flaps

However my Garmin shows only a ground speed increase of 1 to 2 knots.

Wyflyer · Post by **Wyflyer** » Tue Dec 22, 2015 6:57 am

My speed increase was observed simultaneously on my Garmin 430 and Foreflight

SlowFlyer · Post by **SlowFlyer** » Tue Dec 22, 2015 2:28 pm

With a power setting of 25´´/2500rpm you should be above 75% power. 11.5GPH sounds reasonable at that power setting. 138mph does seem fast! I am still trying to get it up to 125mph with the big wheel up front.

Wyflyer · Post by **Wyflyer** » Sun Feb 28, 2016 2:43 pm

One more milestone in this project, I checked FAA registration records today and see that the FAA has approved the model change. The documentation has been with them for a couple of months waiting it's turn. So my airplane is officially an MX-7-180B.
One less thing to worry about.

Convert an MX7-160 to 180hp

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