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General questions on a couple of slow low powered aircraft

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Erttrab

New Member
Joined
Apr 29, 2016
Messages
2
Location
Big Clifty, KY, US
Non-pilot neophyte here with a compare and contrast and a few questions.


In the corner to my left weighing in at 395 lbs (gross) is an aircraft the only details I have is a single short post on this forum by user sigrana.

https://www.homebuiltairplanes.com/forums/light-stuff-area/12916-static-prop-engine-thrust-2.html post #18.

I think its a Moyes XT with 165 sq ft wing area, with 15 hp engine and 72x16 prop. Stated top speed around 35 mph, stated climb rate 600fpm.

In the corner to my right weighing in at 375 lbs (gross) is Mike Sandlin's Bloop. Various data points gleaned from his site, 25 hp Moster engine (7800 rpm), 51 1/2 inch prop. Level flight speed 24 mph, climb rate about 160 fpm. At an engine rpm of 5800 it is slowly descending. Wing area 194 sq ft, and a biplane.

Okay, my knowledge of flight physics is pretty limited (on a steep learning curve right now) but I want to look at some generalities for the sparse data points available for the two aircraft and ask some questions.


The Moyes XT, 165 sq ft of single surface wing area, 600 fpm climb with 395 lbs gross weight. Its pulling 395 lbs up at 10 ft/sec. That's 3950 ft-lbs/sec giving 7.18 thrust hp for climb. If prop efficiency is 70%, he needs 10.25 surplus engine hp to produce that 7.18 surplus thrust hp, and he only has 15 engine hp to start with. And how can it get to 35 mph with 16 inches of pitch on a slow turning prop?

The Bloop. 160 fpm climb with 375 lbs gross weight. Within .025 of 1000 ft-lbs/sec. That's 1.82 surplus thrust hp for climb, 2.5 surplus engine hp using the assumed 70% prop efficiency as in the Moyes XT.


Okay, looking at the Bloop another way. I know the Moyes is a delta wing and the Bloop is a strut and wire biplane so a comparison would be somewhat general. From Mike Sandlin's Q&A he stated the Bloop is slowly descending at 5800 rpm. Giving a tiny edge in its favor, lets assume it can maintain level flight at 5800 rpm. I don't have the torque curve for the Moster 185 so I'll assume its flat (spherical cow of uniform density in a vacuum), which yields us approximately 18 engine hp consumed for level flight, and about 12.6 thrust hp if prop efficiency is 70%. Okay, this is one of my foggy points on flight physics, but if we need 12.6 thrust hp for level flight, does that mean the sink rate is consuming 12.6 thrust hp? If so, 12.6 hp is 6930 ft-lbs/sec and with 375 lbs gross weight, that would put the sink rate at 18.5 ftp/sec. 24 mph works out to 35 ftp/sec forward velocity giving a glide ratio of 1.9.

I've watched all the Bloop videos numerous times, there is a video of the Bloop 3 doing a power off landing. I'm sure the glide ratio of the Bloop is considerably better than 1.9 from watching the videos, but, where's all the engine power going? I know the Bloop's prop is only 51 1/2 inches compared to the 72 inch on the Moyer but I don't understand how the heavier (gross weight) Moyes XT based PHG performs better than the Bloop which has considerably more power.
 
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