M7-235 to M7-260

[asa]

Time to overhaul engine, there’s a $5600 option to change from W1A5D to V4A5, 235hp to 260hp.

I thought this would obviously be legal or a mod kit because it’s a factory option.. however looking at the mod kits it’s not in there that I can find. Is it legal via the fact it’s a type certificate option? Am I blind and missing the mod kit? Not legal?

I’ll call Maule on Monday but figured I’d ask here first. Seems like a simple thing.

Thanks,
Asa

[montana maule]

The Type Certificate Data Sheet says M7 260 same as M7 235B except for engine and prop.

[gbarrier]

You'll need a few other things. For starters you will need a five point engine mount and will need to drill and weld bung in your fuselage to bolt the fifth point in. You will also need a different oil cooler that vents a little different. Might be a few other things I have forgotten. Looked at it a few years ago when I overhauled. Wish I had now.

[onfinal]

Mod 63 addresses your requirements... (my bold highlights)

Modification description
M-5-235C, M-6-235, MX-7-235 or M-8-235 modified by replacing the existing –235
engine with a Lycoming IO-540-V4A5 (260 hp) Engine or an M-7-235B/C modified
to M-7-260/C by replacing the existing engine with a Lycoming IO-540-V4A5 (260
hp) Engine. (Approved)

Models affected
M-5-235C, M-6-235, MX-7-235, M-7-235B/C, M-8-235

[asa]

Thanks everyone. That mod kit makes it seem like only the universal wing M7’s are eligible. I’ll call them Monday and ask about mine which is a M7-235, no letter suffix.

[FARMAULE]

This swap has crossed my mind as well. Anyone know the weight penalty? Also what options do we have to bump the 235 horsepower numbers? Port polish, cold air intake, timing, RPM, electronic ignition etc.? If you could get 250hp out of a 235 and not gain weight that may be a better avenue then a 260 if there is a substantial weight difference?

[Andy Young]

Lycoming lists the V4A5 as weighing 14 pounds more than the W1A5. Of course, that does not include the weight of the extra attach point on the engine mount.

[asa]

Trebor that was my thought as well.

Thought this might be nice to have for others considering the same. Lycon quotes a $5600 charge to go to V4A5. Not a bad up charge for the power but I didn’t realize there were airframe mods.

[gbarrier]

That's about the same price rebuilder quoted to build me the 260 istead of my 235. Having flown both I feel the power greatly out shadows the small weight penalty. Besides the increase in price my airplane was in a not totally enclosed hangar and am pretty sure the windshield, boot cowl, and firewall would have needed to be removed with winter coming. Still wish I had.

[maules.com]

From W1A5 to V4A5 shows 14 lbs, however W1A5D to V4A5 will be more as the single drive mag setup is lighter.
V4A5 burns more fuel per hour than the W1A5D and that extra fuel to be carried also comes into play.
V4A5 runs at 2700rpm versus W1A5D at 2400rpm so 11% higher wear factors. This also affects prop length because of noise requirements.
At sea level on a standard day in tests many years ago the takeoff distance amounted to be the same.
A appreciable takeoff distance (less than 100ft) did not show until over 3000msl.
The 260 proved about 5mph faster in cruise but at a weight and fuel cost.
High altitude operators will like the more hp but sea level operators, not so much.

[andy]

Takeoff distances don't seem to be much different for the 235 vs. 260 but with the heavier engine I would expect landing distance to be slightly longer for the 260. A heavier engine on landing also means that you have to be more careful applying brakes to avoid a nose-over. I would expect the biggest difference to be in climb rate at higher density altitudes and heavier weights. For that matter I haven't seen that much difference in takeoff and landing distances between the 180 hp and 235/260 hp engines. The big differences are in climb rate at higher density altitudes and heavier weights. The 235/260 engines allow the installation of a higher thrust prop, which might be a bigger factor in short takeoff performance. I've read that the single drive mag isn't as reliable as dual mags. Maybe one of the A&Ps can chime in on that.

Back when I was flying the Cessna A185F with the Continental IO-520-D 300 hp engine and 3-blade Black Mac prop for work, the takeoff distance was about the same as my 180 hp Maule but the 185F would climb over 2,000 fpm up to 10,000 MSL while my MX-7-180 would only do 500 - 1,000 fpm up to about 4,500 MSL. Landing distance was a lot shorter with the Maule, though. The 185F was fuel injected while my MX-7-180 is carbureted so that made a difference too. If you are interested in shorter takeoff distance, then a larger wing, lighter weight and higher thrust prop with a 235 hp engine might be more effective than switching to the 260 hp engine. Lightening up the weight and lowering the final approach speed are the best ways to shorten landing distance. Vortex generators help a lot with lowering the final approach speed. If you are operating primarily out of high density altitude airstrips with high terrain around, then the increased hp of the 260 makes more sense. That was the conclusion that I reached comparing the operation of the 185F with my MX-7-180.

[asa]

Thanks for that Jeremy. I don’t understand how the 260hp is any faster in cruise or burn more fuel unless you’re using a higher cruise rpm. Seems like it would only be a takeoff/climb advantage when you can spin it over 2400. 2400 and below shouldn’t it be the same power curve?

Sounds like you’re more a fan of the 235

[maules.com]

Climb, speed performance is depicted by thrust which is a combination of hp, rpm, and prop blade.
Higher rpm does not necessarily improve thrust, in fact too high rpm will decrease thrust.
The higher rpm of the 260 eliminates use of the long prop because of noise regulations . Tip speed goes supersonic which reduces thrust. Listen to the long prop C185 which produces incredibly damaging noise but not as much thrust as if the rpm was reduced to less than 1 mach, which by the way changes according to OAT on that day.

[Andy Young]

Hi Jeremy,
So from what you’ve said, I understand that the 86” Mac would not be approved on the 260 due to noise. That aside, would the 86” see reduced thrust (due to tip speed) at, say, 2650 rpm?

[maules.com]

http://www.pponk.com/HTML PAGES/propcalc.html
On this site one can find the table to enter prop length, blade length and temperature, to calculate tip speed. There is also a discussion re mach speeds and performance, altitude changes etc.
Noise limits were not as limiting as they used to be, but with good reason we should attempt to be neighborly especially to the non flyers who live only on the ground.
For fresh certification, there are specific noise limits and ground clearance limits.
Different types of blades produce different reaction so certification is dependent on proving specific props on specific engines/airframe combinations.