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Real World M7 Cruise Speeds
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TxAgfisher
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PostPosted: Tue Oct 08, 2019 5:30 pm    Post subject: Real World M7 Cruise Speeds Reply with quote

Those of you with M7’s, particularly on oleo gear and 29’s or 31’s what kind of cruise speeds are you seeing?
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TJ Van Matre
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Mog
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PostPosted: Tue Oct 08, 2019 6:41 pm    Post subject: Reply with quote

They aren’t any faster than your last M4. Expect between 110-125. Tone down the tires and fair the gear and you will do a bit better.
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TxAgfisher
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PostPosted: Wed Oct 09, 2019 7:57 am    Post subject: Reply with quote

Mog wrote:
They aren’t any faster than your last M4. Expect between 110-125. Tone down the tires and fair the gear and you will do a bit better.


Say it ain't so! Maule claims 164mph cruise if I remember correctly, I thought they might be at least capable of mid to high 130's on a man's size tire.
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Mog
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PostPosted: Wed Oct 09, 2019 9:05 am    Post subject: Reply with quote

Yeah, in a dive!!

-Andrew


But honestly, no they can’t do that unless you put tiny tires. Might even need wheel pants to truely get there. The M4 is the fastest recip Maule to my knowledge. I think you are trying to find a unicorn. You will need to spend a lot more cash to get what you are looking for. By a lot, I mean a whole lot. The horse power needed to overcome all the drag of a small 4 place STOL aircraft is insane. 300hp would be a start, but still won’t get you there so far as I know.
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Undaunted
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PostPosted: Wed Oct 09, 2019 9:23 am    Post subject: Reply with quote

M7-235C on 31" cruise at 118 kts
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andy
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PostPosted: Wed Oct 09, 2019 9:31 am    Post subject: Reply with quote

I lose about 5 mph at 100 mph cruise in my MX-7-180 with 31" tundra tires and ABI standard length HD main gear legs with no fairings. Drag increases as the square of airspeed so you can expect to lose more airspeed at faster cruise airspeeds. I can't tell you the airspeed at which your engine and propeller cannot overcome the parasite drag with an increase in power since each airplane's configuration is so different. Maule Air Inc.'s website shows 158 mph cruise TAS airspeed for the M-7-235B at 75% power and optimum altitude. That's probably with stock 7.00x6 tires and gear leg fairings. I think you would be lucky to see 140 mph and you'd probably be burning at least 15 gph.
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Andy Young
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PostPosted: Wed Oct 09, 2019 9:52 am    Post subject: Reply with quote

My M-6-235, on 31” tires, with faired, extended oleo gear, at 22”/2200 rpm, goes about 115-120 mph, while burning 12 gph. Same scenario, but with 8.50s, yields 135-140 mph.

I suspect the M-7-235 would have very similar numbers; perhaps just a bit slower, as it MAY be a little draggier due to the the slightly larger fuselage and slightly increased wing area.
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TxAgfisher
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PostPosted: Wed Oct 09, 2019 11:41 am    Post subject: Reply with quote

You guys are depressing! Laughing
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Andy Young
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PostPosted: Wed Oct 09, 2019 11:51 am    Post subject: Reply with quote

Undaunted wrote:
M7-235C on 31" cruise at 118 kts


118 knots, not mph!?

That’s quite impressive on 31”s! What are your power settings at that speed?
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benflyn
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PostPosted: Wed Oct 09, 2019 4:31 pm    Post subject: Reply with quote

andy wrote:
optimum altitude.


Not to high jack the thread, but what is optimum altitude?
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VA Maule
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PostPosted: Wed Oct 09, 2019 5:05 pm    Post subject: Reply with quote

As high as you can get before you or the airplane pass out Wink
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Andy Young
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PostPosted: Wed Oct 09, 2019 5:08 pm    Post subject: Reply with quote

benflyn wrote:
andy wrote:
optimum altitude.


Not to high jack the thread, but what is optimum altitude?


Andy might have a different response. Mine is:

As you go higher, drag is reduced, resulting in a higher airspeed for a given amount of thrust, all other things being equal. However, all other things are NOT equal; thrust and lift are also reduced with altitude. As regards lift, as you go higher, a higher angle of attack is required to maintain level flight. At some point, the higher induced drag from the higher angle of attack equals the reduced drag from the thinner air, and it’s a net zero gain. Go higher still, and you actually go slower. Also, at some point, the engine and prop combination cannot make enough horsepower and thrust to take advantage of the thinner air to pull you faster through it. This altitude depends on the specific engine/prop combination. Total weight and CG also have an effect.

So you could say the optimum altitude is that at which highest true airspeed can be achieved for any particular combination of airframe/engine/prop/loading configuration.

Overall, I have found that for most light aircraft, this optimum altitude is at about 8000’. There are exceptions, of course.
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andy
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PostPosted: Thu Oct 10, 2019 2:08 am    Post subject: Reply with quote

Andy Young said it best. I was referring to overcoming the parasite drag of the large tires.

Air density decreases as altitude, temperature and humidity increase. Parasite drag is created by the impact of air molecules on the large frontal surface area of the tires and other frontal impact areas on the airframe, such as unfaired (round) main gear legs. The shape of the frontal surface area has an effect as well. Round surfaces generate more drag than aerodynamic surfaces. Flat surfaces generate the most drag. There are several forces at work: thrust, gravity, lift, parasite drag, induced drag; generated by a variety of sources: propeller efficiency and RPM, engine power, angle of attack, airframe and tire frontal surface area, air density. As density altitude increases there is a point where thrust and lift are maximized and total drag is minimized. That would be optimum altitude.

At optimum altitude in level flight as a pilot increases engine power and adjusts propeller pitch and RPM (constant speed prop) to increase airspeed and elevator pitch to maintain altitude, there is another point where the engine and propeller can no longer overcome the combination of parasite and induced drag. Airspeed is maximized at this point. You can imagine with all of the forces at work and the variety of airplane configurations, that finding this point would be tricky.

If you want to find maximum airspeed at a particular altitude in level flight, adjust propeller pitch (constant speed prop) without changing throttle and watch the airspeed indicator. When you maximize airspeed, increase the throttle until airspeed no longer increases. Record your manifold pressure, propeller RPM, fuel burn and air temperature every 1000 feet as you increase altitude and make a table out of it. There's no easy way to record humidity but it has less of an effect on density altitude than air temperature. After the flight, convert your table's indicated altitudes to density altitudes based on the air temperatures that you observed. The Lycoming Engine Operator's Manual has a table like this for each engine type but it only considers the engine, not the propeller or airframe configuration.
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Paul Amstutz



Joined: 28 Nov 2010
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Location: Cottonwood Heights, Utah

PostPosted: Thu Oct 10, 2019 11:36 am    Post subject: M7 cruise speed Reply with quote

M7 260B

29" tires 110mph at 10-12K, 10gph or slightly less, plus 1 gal/hour or so at 6000', but I don't do much long distance at that altitude in UT, running WOT/LOP, 2150RPM, CHT in mid 300's, loafing along for the 260.

Put the old 8.50's on the other day and got 5-7mph better.

I travel to see things, not to get anywhere fast. With larger tires, the extra speed costs a lot for very little.
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diebroke



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PostPosted: Fri Oct 11, 2019 5:03 am    Post subject: Reply with quote

My M5 235C with 29” shaved Airhawks cruising at 8,500’ and 9,500’ at 65% power trues out at 146 mph while burning 12-13 gal/hr.
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