The International Cessna^® 170 Association

There are about 50 different threads on all of these items but today I have hit questions and answers in every catagory.
I am going to post a bunch of info and probably follow it up with some photos and a few more posts. Not so much for argument, but just for info for the next guy.

KLIPTIP

We currently have a dm7653 prop (bought brand new 400 hours ago) on the c-145-2 motor with the 8 bolt hub. Our spinner is a bullet nose type with front and rear backing plates.

We bought a overhauled dm7651 prop and when it arrived found it had the KLIPTIP stamped on the hub. I was not expecting the klip tip. Anyway shape of the tips are the same which puzzled me because I thought the kliptip meant a different shape. The prop is about 1 inch shorter, still within the allowable length, but otherwise they look identical.

PROP BOLTS

Our newly overhauled prop came with AN6H-37A bolts but the bolts on the old prop were -43a. That is because our spinner appeared to have some repair work done on it adding a doubler to the backing plate. Thuse the -37A bolts were too short. Looking at the repair work on the backing plate we decided to not reuse the current spinner. We also found some corrosion on 2 bolts.
I was suprised at the corrosion considering the bolts were new 3 years ago when the 7653 prop was put on.

SPINNER

I just ordered a skull cap type spinner from spruce and will be putting it on monday. We decide to go with the skull cap over repairing or replacing the bullet nose just because of simplicity. Less parts. I am hoping the -37a bolts that came with the prop will fit with this new type spinner because there will be no backing plates. My mechanic said that we could use a few an960-6 and -6l washers if the bolts are too long otherwise we will need to get new bolts.

CRUISE SPEED

To be determined. We currently get 109kts running the motor pretty hard on the 7653 prop. We were getting 105kts but seemed to gain 4 kts after a mag overhaul and replacing one cylinder. Once the new prop is on I will post my unscientific comparison of cruise speed, climb performance, and static rpm between the 2 props.

Opinion
I read a lot of posts on prop bolts. We got the -37a bolts based on the posts but they didn't work because our spinner backing plate is thicker than most. Now with a new spinner coming I have no idea what size we are going to end up using. There is not a lot a margin for error. Too long and you can bottom out the shank of the bolt, too short you don't have enough thread. Bottom line I would just measure what size bolt you need instead of guessing in advance.
As for the Kliptip, I will take some detailed photos and length measurements but I can't tell the difference between the Kliptip and the non kliptip prop. As for the spinner, I like the look of the bullet type (and it is painted) but I bought the skull cap spinner because it is a simple design. (Unfortunately it only comes in polished aluminum and the airplane is white).

End of Ramble.

More posts and photos to follow.

Steve

Klip-tip is a squared-off tip. A non-Klip-tip (rounded) may be altered to a Klip-tip provided it does not make the prop too short in accordance with the application and type certificate. A rounded tip is sometimes altered to a Klip-tip at overhaul as a method of ridding it of tip damage. That may explain why the prop is shorter than the other.

I Love the new prop!!!!!

Kliptip
Here is a pic of the old 7653 prop



Here is a pic of the new (overhauled) dm7651 Kliptip prop



The second pic is at a slightly different angle but they are the exact same shape and when we measured them they are the exact same length. Both 76 inches on the dot.

Prop Bolts
The -37A prop bolts work perfect with the skull cap type spinner.

Spinner



The skull cap spinner from spruce looks good but required some modifications to the bracket to make it fit. The cap is from aircraft spruce and the bracket was too short. We riveted a nut plate to the back and added a spacer and used a beefier screw. As with everything on a 1952 aircraft, nothing I buy fits without modification.

Cruise Speed.
We got an extra 100 static rpm on run up and that makes this a new airplane. We lost 5 knots off the top end so we are cruising at 104kts. The climb is impressive. I would say we got 15%-20% better performance on takeoff and initial climb below 1000ft.

Opinion

The 7651 prop is the right prop for my application. I still can't figure out the difference in the kliptip and don't care. This prop gives me a shorter takeoff roll, 300fpm better initial climb and the airplane accelerates a lot better. No longer that mushy area on takeoff trying to go past 60 or get the last notch of flaps up. The top end loss is only about 5% but I get at least a 15% gain on the climb and takeoff. I figure on my average daily hop and short field operations it is going to make a big difference. On my longer hops, I fly a lot of 150NM trips, it will add only 1-2 minutes to the flight but I will climb to cooler smoother air a lot quicker (ie wife happier). As for the spinner... looks good to me and I saved about 5 lbs.

What rpm on the 76/53 was (Running engine hard) in your first post to get 109knts ?

2600 rpm. I tend to cruise for long periods at around 2550.
So far all my testing with the new prop has been below 1000ft agl. Later in the week I will head into the sierras and see how it performs at high altitude.

This topic brings up a new development in Props.
I had a 1948 C170 with the C-145-2 (O-300) motor and metal prop with skullcap spinner. After purchasing a majority interest in a large volume MT Propeller distributorship, I looked to see if I could put an MT Natural Composite Fixed Pitch Propeller on this plane.

Answer is YES. Here is how:
1. The TCDS for this plane in the Propeller section describes an approved Sensenich wood propeller and includes the continuation phrase "...or any other wood propeller with a maximum diameter of ##" and max. static RPM of ####..."
2. The MT fixed pitch Propellers are all certified and the TCDS lists them as 'wooden propeller'.
3. I asked our FAA ACO rep that works with us on our STC's if I could install the MT prop to this plane with a logbook entry. He reveiwed the TCDS of the plane and prop and said 'no problem'.
4. I had MT Propeller engineers design a prop that would be an 'all around general use prop' for this plane and engine. They did...then I sold my C170 and did not get the prop ordered or installed.
5. The MT prop weighs only 16lbs, is a wood core with carbon fiber cloth covering and a full length stainless steel leading edge. Cost is $2500. There is no life limits and the TBO is 'on condition'.

My experience recently involving a 160HP RV6 that we swapped props from a wooden Sterba to a MT. We saw less vibration, 25% increased thrust (as measured by a digital thrust guage), inproved climb and much faster cruise. Best part is the plane can now run in rain and snow without worry of damage and it operates off a sand strip so there is no issues any longer with erosion.

.... I have no idea how it will perform on the 170, ... They do not use a US standard pitch measurment so there is no way to simply compare a 74x46 to the MT.

John Nielsen
...

I'd be glad to test that prop out for you. Just send me the prop or pop on down to CA and we will bolt it on and try it out for a few weeks.

Here's the pertinent words of the TCDS. (Be aware that unless you have a dampered crankshaft that new installations of wood propellers is not approved.)

1(b) Sensenich 73BR-50 or any other fixed pitch wood (prop)
Static r.p.m. at max. permissible throttle setting:
Not over 2320, not under 2220
No additional tolerance permitted
Diameter: Not over 74 in., not under 71.5 in.
(Not eligible on seaplane. Not eligible for
new installations on Continental C-145-2
engines having undampered crankshafts after November 1, 1951)

I could look it up but it is easier to ask gahorn.
How do I tell if I have an dampered crankshaft on my 145-2

buzzlatka wrote:I could look it up but it is easier to ask gahorn.
How do I tell if I have an dampered crankshaft on my 145-2

This has been answered several times, for instance here: http://www.cessna170.org/forums/viewtop ... 745&p=5183. George's explanation is about halfway down the page.

John

The only sure way to tell it is dampened is to remove one of rear cylinders and look. While the 1/4" hole in the flange is referenced in the TCM manual, I have now encountered several that are dampened with the hole including my own.