Electric Varable Pitch Constant Speed Propellers for the 170

[N1277D]

Based on my needs of operating in Idaho/Western US and some items I saw on the forum I checked around and found a propeller manufacture that produces electric varable pitch and constant speed propellers. MT-Propeller in Germany manufactures several types of varable and constant speed propellers that are electric. Some of their propellers have US type certificates, and some of their certified propellers are used on the Maule and other aircraft with US type certificates.

I spoke to Larry Schlasinger of MT-Propeller, he is conferring with the MT engineers to see which model would work best for the 170/170A/170B using the C145 engine. He has a good write up in Northern Pilot (October/November 2002 issue) He indicated that the SAE 3 or 8 bolt flange is not a problem as would be any required paper work, and that MT engineering would identify the best electric hub and blade combination and would get back to me soon concerning their recommendations.

[Bruce Fenstermacher]

Great. Can't waith to hear. I've thought for sometime now that the first manufature that produces a electricly adjustable variable pitch prop for the Cessna 172/Cherokee 140 and the like would have a big market. If the prop is affordable!

[wa4jr]

YESSSSSS! Please keep us updated as to this project. If we could get the full 145 HP out of our O-300s on takeoff, then there would be much less motivation to convert to another engine that cost's nearly as much as the airplane itself!

[Watkinsnv]

I just saw one of these props on a Velocity yesterday. The owner said he sets it for takeoff rpm and then for cruise rpm, its not a c/s. He wouldn't tell me what he paid for it, just that it cost him dearly. LANCE

[Bruce Fenstermacher]

2 settings would be fine with me. I doubt if the prop cost him the $30k or more that a larger engine would! A friend has done some experimenting for a prop company with his experimental. I was talking to the prop guy about this very thing. He said the prop we are talking about would be fairly easy to do although all props take time to develop. He though he could probably bring one to market for about $5k or $6K. Problem is he is more interested in making my friends LanceAir IVP do over 300Kts.

[N1277D]

I sure will keep the forum updated on this.

Some time ago I was reading an article about 170 engine conversions. One individual had used an 0-320 with a constant speed prop and was amazed at the performance, the article claimed the C170 O-320 conversion to be close to his friends C170 O-360 conversion in performance. (I think the article is in the 170 book published by the association) This made no sense since it has 30 less hp.

Coming back from Alaska, we ran into someone with a 170 with the O-340 and a constant speed prop. He was faster than us and used less gas (go figure) and claimed he out performed the O-360 conversions. Again this made no sense.

Recently a new exhaust system was STC'd for the O-360 claiming as much as 23 additional hp. The claim is that the exhaust system used at the Lyc factory for rating the engine was different than that used by the OEMs. The OEMs exhausts were not permitting the full 180 hp to be developed and in some cases the O-360 was putting out only 157 hp.

So things now make perhaps some sense why the O-320 with a 150 hp and constant speed propeller can almost match performance with the O-360 with a constant speed with an OEM exhaust system.

Anyway I was taking to some old timers about why the 172 with a higher gross weight and that draggy noise wheel has higher performance numbers than the 170 with almost the same engine. They indicated that during the design process of the early 172's the additional drag/weight slowed them down, so they had to do something to get it to sell and what they did was to improve the prop over that found on the 170. So the 172 outperforms the 170 even though it is draggier and heavier becouse it has a better prop design.

So it might be possible that a "new blade design" varable pictch or constant speed prop on the old C145 might yield 170 performance numbers close to some of the O-360 conversions with the OEM exhaust system. One can never can tell but it sure is worthwhile looking at.

[zero.one.victor]

A guy at my airport has a Velocity on which he is running either a Hoffman or MT prop. He likes it,I guess. Don't know much about it. He used to run an in-flight adjustable (electric?) Ivoprop,but had trouble with the composite blades splintering. Not good! I think the current prop cost a bunch more than the Ivoprop,but it works !

Eric

[ak2711c]

The MT props are also composite with a stainless leading edge. That is some thing to consider if a guy is going to do a lot of off airport work. You can't just dress out a nick. That article in Northern Pilot on them was really good. They seem to have there stuff together.
Shawn

[GAHorn]

I sure will keep the forum updated on this.


Anyway I was taking to some old timers about why the 172 with a higher gross weight and that draggy noise wheel has higher performance numbers than the 170 with almost the same engine. They indicated that during the design process of the early 172's the additional drag/weight slowed them down, so they had to do something to get it to sell and what they did was to improve the prop over that found on the 170. So the 172 outperforms the 170 even though it is draggier and heavier becouse it has a better prop design.

So it might be possible that a "new blade design" varable pictch or constant speed prop on the old C145 might yield 170 performance numbers close to some of the O-360 conversions with the OEM exhaust system. One can never can tell but it sure is worthwhile looking at.

Excuse me if I say this too loudly.......BALONEY!!

Don't listen to "old timers" and believe their BS.
Let's look at the facts. The performance numbers for the 170B and the last 172 made with the O-300 engine---a 1967 172H: (All specs from "Standard Catalog of Cessna Single Engine Aircraft":

Model 170B 172H
Cruise: 136mph 138 mph
LR cruise: 126 102 (!!!)
Gross: 2200 2300
empty: 980 1275
useful 1220 1025
CLIMB 690 645
Land dist 1145 1250
TO roll 618 865
Svc Ceiling 15500 13100

On top of that, notice that in order to try to make the figures look better they dropped the so-called Long range cruising speed by 14 mph! and then ran the airplane completely out of gas ! so they could publish a 670 mile max range on the later airplane. (The 170B was listed as having a 511 mile max range with a 30 minute reserve. Now just how the blazes they proved their wild claim for the later airplane which was heavier with the same engine and carrying the same fuel is worthy of Enron accountants!)
The ONLY difference in the two aircraft propellers was that the 172H used a McCauley EM7653 (76-inch diameter and 53-inches of pitch) prop that had 6 bolt holes instead of the 170B's McCauley DM7653 (76" diameter and 53" pitch) with 8 bolt holes. Go tell the "old timers" their BS has been found out and they've been busted!

[N3243A]

George,
Speaking of BS: The Empty weight of a 170B is published at 980?? I think that book got its figures for empty weight and useful load transposed?

Bruce

[zero.one.victor]

George,speaking of baloney,a lot of them factory figures match that description. "Cruise speed:136 mph,138 mph"--who they trying to kid?
I run a DM-7651 prop and see about 115 IAS,the GPS bears this out. I'm talking about real everyday flying and airspeed,not "true airspeed" up in the flight levels.
Are you saying that the EM & DM series props are the same except for 6 & 8 hole configuration? Did you get this info from McCauley? I know that some similar-sounding prop series have different airfoil designs. As an example,the DM & MDM seem to indicate similar performance but with about 2" different pitches. There's there's the "California twist" prop,what does that mod actually entail?
Just like back in my Harley-riding days,I believe that "there ain't no substitute for cubic inches"! But airplanes are individuals: weight,rigging,aerodynamics (fairings,venturi's,cleanlines,wax job,engine baffling,etc!) all make a (sometimes big) difference.
I don't think a 145 horse 170 is gonna match a 180 conversion on all fronts,but a light 145-powered 170 with a seaplane prop just might beat a (heavy)180 horse c/s propped 170 off the ground & up to pattern altitude.I think the 180-horse is gonna kick ass in the speed area,but with a super-coarse cruise prop & plenty of time to get up on the step,a 145-horser might come out looking pretty good.Who knows?
Regarding the old timers,the 172's might indeed have outrun the earlier 170's in speed,but I'm sure they gave up TO/climb performance--there ain't no free lunch.
To get back to the point,when somebody finds an approved variable pitch prop that weighs & costs no more than the stock McCauley,put me down for one! Til then,it's fun to daydream out loud,isn't it?

Eric

[N1277D]

George interesting data, but I will always wonder why those older late 1950's 172s with the O300 seem to pass the 170s with the same prop pitch. Those old timers flew B17s and other stuff during the war. I think I will learn from their experiences and at the same time wade through the BS and all the old stories and not get them too pissed off. The next time one passess me in his 1959 172, I wont believe it is the airframe design he is just a better pilot and can read the winds better. It can't be the airplane design

Maybe Dick L can shead some light on the prop changes between the early 172s and the 170.

[N1277D]

I just remembered another embarassing moment. Last year at the annual Montana Antique Fly In held at Three Forks, MT a bunch of us headed out to a dirt strip for a fly in breakfast. I rode along with a friend of mine in his 1953 or 54 170B. Would you believe we got passed by a Super Cub with 22,000 hours on it and could just barely keep up at full power. Ouch

[GAHorn]

Flying alonside one another you might feel like you've been "whipped" pretty soundly when you watch your buddy ease on by you and leave you behind. But the next time that happens, try to estimate his actual speed advantage.
Consider this: A fast walk is 3-4 mph. Stand still and watch someone walk briskly by you, and imagine they are an airplane passing you in formation. It looks pretty fast, huh? But that's only 3-4 mph and it represents less than a 3% improvement in speed. That much speed advantage can be due entirely to individual aircraft rigging and condition of paint and fairings. Go to the front of your aircraft and look at it like you were a molecule of relative wind. What's there to hit you?
Are the brake lines exposed from behind the gear legs? Are there 3 or 4 antennas on the airplane? (Are all of them actually hooked up to something that's operational?) Are the flight controls trimmed and in proper streamline? Are the wheel pants slanted tail-down to look cool? (They become air-scoops in flight that way.)
See what I mean?

Re: Eric's question about props: The EM props and the MDM props are the same prop with different bolt holes. They are thinner and lighter than the earlier DM. The EM/MDM blade tapers slightly closer to the hub than the DM. This gives the EM/MDM series a slight efficiency advantage, requires less horsepower for the same thrust and therefore may be pitched slightly more to produce the same performance. This translates to better cruise performance and less theoretical engine wear (due to 4 lbs. less wt/momentum thereby reducing gyroscopic forces) which in theory may be at a slight penalty in low-speed thrust but is supposedly offset by a slight advantage in engine acceleration. The only practical drawback is that similar damage from stones, FOD, etc., is more likely to condemn the EM/MDM than the more robust DM which has more material reserves to work with.
I'm not too familiar with the "California twist" prop, but understand it to be a more highly pitched (think- cruise prop) blade that has been thinned considerably so as to allow it to flex at the tips to a lower pitch during takeoff. It is modified from a standard McCauley.

[Dave Clark]

There is a fellow in Phoenix who has a 170 with a 180 Lyc and a fixed pitch prop. My mechanic friend here says that this fellow seems to lack the performance one would expect from the conversion on takeoff and climb here at 5000 ft. I saw the owner yesterday and as we talked he mentioned he only gets 100 knots cruise @9gph also which is what I got with the C-145 @7gph! He was in a rush so I couldn't ask him any more questions. Seems to me the constant speed is the way to go.