Horsepower, RPM, and Supercharging

XBe02Drvr · Jul 5, 2019

Snowygrouch said:
Feel free to list a suggested improved story-board, and a list of recommended equiptment.

Well, to start with, more diffuse and brighter lighting would make the board easier to read, along with broader, more contrasty markers with more vibrant colors. This isn't rocket science. Two or three cheap clip lamps with daylight LED bulbs and thin, whispy white muslin or cheesecloth draped over the front, strategically aimed, can do a lot for short money. The goal is multi source light and shadow minimization.
The audio leaves a lot to be desired. It sounds like a cheap consumer grade video camera's built in mike. A shotgun mike mounted on the camera or on a stand in front of the lecturer, but out of the picture, would help. A "studio room" with sound dampening(even some heavy drapes or rolls of fiberglass) would also help if you can manage it.
When editing, it pays to address the audio level in the finished product, as these videos were a little on the low side. I've seen many student videos where truly stunning camera work was marred by too loud, too soft, distorted, or inconsistent audio.
When you've got your final edited product, I would suggest "test flying" it on as many different platforms as you can access. A production that looks good on your typical editing computer may not look or sound so good on an Android, an iPhone, a tablet or other device.
I hesitate to recommend specific models of equipment, as I've been retired now for four years, and the marketplace has changed. The school I worked for couldn't afford to outfit an entire class with professional grade equipment, so I used to buy "prosumer" stuff, and had good luck with Panasonic. If I was going professional, I would probably go with Canon or Sony, but not without a lot of research first. Until you get into top grade professional work, it's really less about the equipment you use and more about what you do with it. I've seen stunning videos shot by teenagers on Flip cams and carefully edited, and sloppy stuff done by rich kids who "borrowed" their parents' professional equipment and brought it to school to show off.
Well, my apologies for getting so deep into lecture mode. Hope this helps.
Cheers,
Wes

tommayer · Jul 5, 2019

tommayer said:
best, Tom

Wes,
Just finished proving I can read runway markings right 10 times out of 10. Feel all tingly with self satisfaction.
I have been doing the CFI drudgery on line for years. A matter of sheer necessity. I think AOPA is the best of several I've tried. I live in the boondocks in NM some of the year, in Mexico most of the year. Nobody holds seminars in rural Nayarit. AOPA online eFirc charges $128.00 (I think). Whatever it is, it's much cheaper than flying my Staggerwing to PHX or ABQ. No matter how you do it, it gets old, no? I HATE this new ACS stuff.
Where are you? Sometimes I can still arrange rides in a 47 working strips in the sierra that make anything in Alaska look like LAX. For a few years one had an 1820 on one side and an 1830-94 on the other. Kind of fun to fly something where the throttles are split 6 inches in cruise.
Who'd you fly for?

best, Tom

tommayer · Jul 5, 2019

XBe02Drvr said:
Navy Key West Flying Club, Mansfield Aviation, Vermont Flying Service, Scan America Corp, Sugarbush Soaring, Brockway Air/Metro Air Northeast, and Wiggins Airways. A "checkered resume", you might say. All little stuff, nothing bigger than a Beech 1900.
Which engine does your Staggerwing have? I've flown a bunch of different Beeches, but all were of the "modern" variety. Staggerwings make me drool. My first complex was a T34 at the Navy club, in the days of young and foolish. That plane kept me alive through many a stupid (but educational) escapade.
Do you instruct for a school, an FBO, or on your own? A lot, or a little from time time, just for grins?
Back in the 80s, there was a local cancelled check and UPS feeder operator who had a small fleet of C47s done up in D-Day color schemes. One 1820 and three 1830s. They came into MPV twice a day for UPS, I knew most of the guys who flew them, but the promised ride never materialized. I eventually flew that UPS route for Wiggins in a Be99.
Cheers,
Wes

Wes,
Just read your reply, 7/5.
Sounds like you had a neat career.
I was a college English teacher who worked merely to eat and to pay for airplane parts. Back in the dark ages I did some instructing, but found I hate flying with people who don't know how to fly. Now confine myself to BFRs for people I like who have airplanes I like. Spent ten years making a video of Mexican bush flying. Nobody wanted to see it but the guys in it, and they're mostly dead now. One of the places I went to regularly was Chapo's home town, though I did not know that until years later. I spray mangoes for a friend sometimes.
Staggerwing. Have had the thing since 1970. Got it cause I was working off a rocky, hump-backed 2300 foot strip at 6700 msl & high OATs. I wanted a C-185, but, back then, the old Beech was cheaper. Found out via experience it is better at high DAs too. Fun factoid. Manual from WWII says a GB-1-2 (the Navy version of the D-17S, P&W R-985 AN1 or 3) needs only 50 feet more on T/O to clear 50 feet at a DA of 6000 than at SL. Ground run at 6000 is a shade longer, but the crate climbs a shade better up high.
They are fun to fly. Feel a lot like straight tail Bonanzas or T-34s, only they have better rudders. You'd think you were back in your 34, but suddenly had enough power and enough rudder to really hold the stops in a point roll.
Visibility on the ground sucks, as you'd imagine. Touchdowns and roll outs are easy, if you have educated feet. One oddity: they have a 15:1 glide ratio clean. Drop the gear and flaps and you need almost 25 inches to hold 90-100 IAS in level flight. Pull power on the backside of the curve with flaps + gear extended, and you've turned a near sailplane into a free-falling elevator. I check people out by making them treat 100 IAS as if it were a blue line. This raises eyebrows, since the thing actually stalls at 50-55 IAS, so 100 IAS is a lot higher than 1.3-1.5 Vso. But as soon as you break the glide it's as if you'd run into a pillow, amazing deceleration is instantaneous. Best ROC is also 90-100, at which speeds torque is no problem if you need to go round.
Full span ailerons give you pretty good roll rate, but acro involves some muscle. They'll loop from cruise, though of course that's something I've never tried. They'll carry anything. I'd tell you true stories, but some Fed might read this. I have invented my own CAFE race to specs I know will make a Beech 17 the winner, 1) T/O from muddy strip of 1500 feet at 5000 msl, 50 foot cement barrier at 1750 feet. 2) You get extra points for each SOB besides the pilot. The Beech will have 3 fatties or four skinnies in addition to me. 3) course is 500 nm. 4) MEA for some of it is 15K 5) big penalty for any TAS under 160 K 6) Destination also muddy, unimproved, less than 2000 feet usable, and 5000 msl or higher. 7) You are disqualified if you don't land with 1.5 hours of fuel remaining. 8) W&B must be within factory limits. 9) No Porters or C-130s or turbine Gooney birds allowed.
If you ever come to northern NM or southern Sinaloa, let me know.

best, Tom

tommayer · Jul 5, 2019

11bwmech said:
Times have sure changed when I went to A&E school (1951), I was told the purpose of the supercharger wa to bulls-t the carburetor. That is, to make it think it was at sea level. Never knew it was such a complicated subject. Keep at it, guys. Someone may learn something, although probably not I. I just know that the turbos on the B-36 ruined my hearing in the days before ear plugs. In the early days, they pulled 64" Hg on the ground during run up. What a scream!

Snowygrouch said:
I posted two videos explaining exactly how that all works within the context of supercharging on 28th, same day the question was posted. Does mean you have to actually sit through the videos though....

Again--just open the throttle if you want a bigger explosion in each jug. The prop governor will keep the RPM the same. Get out of your head the idea that a C/S prop responds like a car gear box when you goose or retard the throttle. It does NOT.

XBe02Drvr · Jul 5, 2019

tommayer said:
I did some instructing, but found I hate flying with people who don't know how to fly.

I always enjoyed flying with people who, by the time I was done with them DID know how to fly. Have ridden through some unintentional aerobatics perpetrated by ham handed students but due to my time early on in the T34 and 150 Acrobat, didn't have any problem with it. Almost none of my students soloed without first demonstrating spin recoveries. My first two or three did slip through unspun, but then I cracked down and started sending "spinaphobes" to other instructors.
Love that 985. The local duster outfit back in the day had two W670 Stearmans and one 985. The Continentals would shake, rattle, and roll at idle, while the 985 would just tick over quietly, steady as a rock. Duster pilots were unwelcome in the terminal building, so if they needed to make a comfort stop, they would land in the grass, climb out, and visit the bushes. The 670s had to shut down and restart, but that 985 would just sit there ticking over and waiting for her master's return. They made a point of doing this in a spot visible from the restaurant windows.

tommayer said:
If you ever come to northern NM or southern Sinaloa, let me know.

Thanks, Tom, but not likely. Vermont summers are too hot for me as it is. We drove through ABQ on the old Route 66, on our way to LA when I was a kid, and I liked to have died. If you're ever in New England, give me a shout. I don't fly any more (eyes too bad), so I've turned into a water rat.
Cheers,
Wes

Sid327 · Sep 18, 2019

Definitely recommend tommayer's post #33

about recommending this site:

Greg's Airplanes and Automobiles

Zipper730 · Feb 1, 2020

D Deleted member 68059

So the problem with the butterfly valve and throttling losses are that...

You have a lower absolute inlet pressure due to throttling
The restricted airflow is forcing the compressor to work harder, and getting nothing out of it like if I was trying to breathe with a pillow in my face?

Does the higher pressure ratio produced have anything to do with the angle of the airflow relative to the blade? I'm just curious because the swirl throttle looks like the variable stator vanes seen on General Electric's J79...

tomo pauk · Feb 2, 2020

Snowygrouch said:
You understand that from where exactly ? The slip coupling gave it about 100bhp MORE at sea level that it would otherwise have had if it had a gear driven supercharger from something like a Merlin-III.

...

To come back a bit here.
Would this not be a more fair comparison: Merlin X (gear-driven supercharger) vs. DB 601A?

Deleted member 68059 · Feb 4, 2020

Zipper730 said:
D Deleted member 68059

So the problem with the butterfly valve and throttling losses are that...

You have a lower absolute inlet pressure due to throttling

The restricted airflow is forcing the compressor to work harder, and getting nothing out of it like if I was trying to breathe with a pillow in my face?

Does the higher pressure ratio produced have anything to do with the angle of the airflow relative to the blade? I'm just curious because the swirl throttle looks like the variable stator vanes seen on General Electric's J79...

It is very difficult to answer that fully without lots of maths - which I already made a video on, but...

1) Yes the butterfly (or barell) throttle work by reducing the area of the intake, since the engine still wants to ingest a certain volume of air,
it will then give you a higher speed flow through the throttle, which is then at lower pressure (bernoulli).

2) The restricted flow does NOT make the compressor work harder, it uses less power because there is less mass of air flowing through,
HOWEVER.... it would use EVEN LESS power, if you simply reduced the speed of the supercharger, instead of closing the throttle. The difference
in a 1000hp class aero engine is easily 100 to 150bhp at sea level (where the throttle is at its most closed position).

The swirl throttle does (eventually) reduce the flow area when its virtually shut, but its not really made to work like that, by spinning the air entering
the compressor, it basically fools the supercharger into acting as if it IS spinning more slowly, because the spinning air off the
vanes, effectively means that relative to the air, it IS spinning more slowly.

Variable stator vanes like the J79 are made to stop the air stalling when the compressor is working "off-design-point", not as a throttle.

However, a swirl throttle, can also be used to help the airflow into the supercharger valves come in at a more favourable angle when its running
at very low speeds, which can also extend the operational range of the supercharger before it stalls (meaning it will be able to run at
slower speeds and still work).

You can do lots of things with variable vanes, but in a Jumo213 or AM35/38, its being used primarily as a throttle.

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