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Those are good points, Al. I laid out my system to take advantage of ram pressure. The pressure is additive, so it is just goodness on top of goodness.
The 180 bend should not make much of a difference. My layout will have a 90 degree bend to the intake.
I see your point about the venturi, but Dennis' test (D) incorporated a SCAT tube, just like test (C), with the blower. The only variable I see between the two is the inclusion of the air filter in test (D). Dennis, depending upon the size and condition of your filter, you could be losing between 1" and 2" right there. The air filter could be accounting for the entire gain seen by the blower.
From my previous calculations, I expect the blower to consume between 3 and 4 Hp. The blower I've designed has approximately the same diameter as a backpack blower. I believe their speed is around 6000rpm. Those are averaging numbers in the high 400s for CFM, with air speeds around 170mph.
In any case, I would take the rated capacity of the blower with a large grain of salt. Unless independently tested, those are going to be marketing numbers. Given only a 0.9" increase in MP with the blower and without the filter, I have to wonder if the engine might have been driving the blower in that case.
Dennis, do you care to try your experiment again with a few modifications? The blower effect should be independent of the prop blast and air filter. On test (B), fit some sort of cone to the intake to eliminate the sharp edge. I think that would compare equitably to a test with the blower at the end of a SCAT tube.
What do you think, Al?
Al Gietzen wrote:
Before we get too excited about putting leaf blowers under the cowl; you might consider this. The baseline case here (no blower) is with the plane standing still with at sharp edge intake at the TB – correct? Fairly significant inlet pressure loss for that configuration.
You may get a similar increase in manifold pressure by putting a nice bell-mouth entrance on the TB. And you will get a similar increase in manifold pressure with a ram inlet scoop flying at about 160 Kts.
Al G
-----Original Message-----
*From:* Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] *On Behalf Of *Dennis Haverlah
*Sent:* Monday, February 15, 2010 7:58 PM
*To:* Rotary motors in aircraft
*Subject:* [FlyRotary] Re: Air Pump
Bill:
Thanks to my younger brother who was brave enough (use younger brothers for dangerous stuff) to operate the leaf blower I ran the leaf blower test for the group. I used a fairly new hand held Echo leaf blower Model PB 251 I "borrowed" from my neighbors hangar.
Specs - 25 cc 2 stroke,
Average Air Volume (cfm-pipe)
390
Average Air Volume (cfm-housing)
509
Maximum Air Speed (mph-pipe)
145
No information on rpm's at these data points were listed. I would guess that the 2 stroke engines are operated between 6000 and
8000 rpm. but I'd like to have real rpm data.
Four tests were conducted as shown below. Local air pressure was 30.2 in Baro. - 0.5 in for 1000" = 29.7 in hg. air pressure at field elevation.
Weather was Clear, low humidity and 53 deg. OAT. All tests were at WOT.
Pictures are attached for each test. Note the 180 deg. bend in the Scat tubing during the (C) test.
The (C) test picture was taken after we had taken the Scat tube but my brother was holding it in place.
_Test condition_ _Static max. RPM_ _Manifold Pressure _ _Engine Temp._
(A) Standard intake, 5870 28.9 Barely warm
air filter etc.
(B) W/O air filter & 5660 28.7 Fully warm
prop blast
(C) Leaf Blower full 5925 29.9 Fully warm
throttle into throttle
body - 180 deg turn.
(D) Same as (A) 5700 29.0 Fully warm
It appears that the blower raised the inlet pressure by 1.2 in Hg. and the engine rpm increased from 5700 to 5925 rpm.
I needed to turn the mixture knob slightly richer with the blower running to get max. power.
Also note that the tube feeding the intake had to make a 180 deg. bend just before the throttle body.
The leaf blower used in this test was the_ smallest Echo makes_. Their web site lists approximately 15 blowers and the largest is a 63.3 cc 2 stroke as follows:
Average Air Volume (cfm-pipe)
620
Average Air Volume (cfm-housing)
1240
Maximum Air Speed (mph-pipe)
205
My thought is that several blowers are available that probably would provide the needed blower capacity.
I believe we need a system that is adaptable to using Tracy'c RD-1 drive. I also believe it is not likely a centrifugal blower can be placed between the engine and gear box because the spacing between the gear box plate and the engine is about 2.5 inches and the ring gear is approximately in the middle of the space. _If someone is interested in adding a direct drive blower why not attach it to the rear of the engine with the centrifugal fan attached to the crankshaft pulley?_ The fans from the big blowers may have enough capacity to work at our crankshaft speeds. If this could be made to work it would fit the majority of the rotary installations and be an inexpensive way to add _More Power Scotty_.
PS I have all the power I need with my DIE intake - if someone can find a way to build it that may solve most of the power needs.
Dennis Haverlah
Bill Bradburry wrote:
Has anybody ever tried hooking up a leaf blower to the throttle body inlet and see what that would do to the static rpm and manifold pressure at WOT?
Bill B
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Ernest Christley, President
Ernest@TechnicalTakedown.com
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Cary, NC 27518
(919) 741-9397
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