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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 18 Jul 2019, 16:15 
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Joined: 12/25/10
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Company: Occasionally Pleasant
Location: Bourland Field 50F Cresson, TX
Aircraft: H35, C-172
Username Protected wrote:
Just finished up a several year restoration on a 1956 C172 with an AVCON Conversion. Everything is new engine, prop, power flow exhaust, Sportsman STOL kit etc. Flew it for the first time the other day and the plane leaped off the ground handled great but the top end speed is only indicating 110 MPH. Had the Avionics shop recheck the pitot system and confirmed all is good. The rigging on the airframe is straight. One thought that was brought to my attention was the engine incidence. Does anyone know what the engine incidence is on an AVCON conversion or have any other suggestions on what to look for. Also what kind of indicated airspeeds are you getting from the conversion.

Flew again tonight. At 2000 feet the winds were almost nothing. Flew four different directions with the GPS showing ground speeds almost the same speed all four directions. Tanks at half full. Two 200 lbs Guys in the front seats. Noticed the elevator just slightly down, elevator trimmed pretty close to middle. I would of thought with two people in the front seats the plane would of required some up elevator to stay level not down elevator. Plane seems to be making full power on takeoff. The engine analyzer shows 18.5 gph full throttle and 2650 RPM on the prop. The engine is sitting straight forward 90 degrees of the firewall and now has .3 degrees of down tilt. We added some washers under the engine mount to tip it down and back to the left. The neighbor in the hanger next to me has a 58 with the stock Continental so I measured his engine incidence. It didn't change anything maybe 1 MPH

Make the engine incidence corrections at the firewall (washer 0550156)not on the motor mount vibration isolator. Make sure the (055015 bushing is like new.) Changes mostly adjust for p factor. Speed should come from correct aircraft rigging. Seems as if yours is set to fly straight while in a crab. You ought to easily get 120 kts.
Check timing, prop hi and low stops. Does it have wheel pants?


For another data point, my 1956 172 got 110kts. Stone stock.


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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 18 Jul 2019, 18:38 
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Joined: 01/10/16
Posts: 1111
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Location: KLBO
Aircraft: Cessna 172
I have a 1975 M with the stock O320-E2D 150hp Lycoming. Have a full set of fairings, two year old paint and prop overhaul. Mine will true out at 128 mph at 2,500 rpm with just me on board. Before the paint job, it would true out at 124 mph at 2,500 rpm.

That airframe is only going to go so fast with the built-in headwind it has.


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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 18 Jul 2019, 20:28 
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Joined: 12/26/16
Posts: 110
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Location: Hernando, Ms
Aircraft: 7ECA, B19
How is this?


Please login or Register for a free account via the link in the red bar above to download files.

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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 19 Jul 2019, 07:06 
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Joined: 12/20/10
Posts: 35
Aircraft: Panther Navajo
If I am reading the drawing right it looks like they are adding a washer between the lower mount and the engine which is going to raise the engine a bit. What I don't know is what is the 825-1 spacer they are talking about?


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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 19 Jul 2019, 07:27 
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Posts: 35
Aircraft: Panther Navajo
Username Protected wrote:
Just finished up a several year restoration on a 1956 C172 with an AVCON Conversion. Everything is new engine, prop, power flow exhaust, Sportsman STOL kit etc. Flew it for the first time the other day and the plane leaped off the ground handled great but the top end speed is only indicating 110 MPH. Had the Avionics shop recheck the pitot system and confirmed all is good. The rigging on the airframe is straight. One thought that was brought to my attention was the engine incidence. Does anyone know what the engine incidence is on an AVCON conversion or have any other suggestions on what to look for. Also what kind of indicated airspeeds are you getting from the conversion.

Flew again tonight. At 2000 feet the winds were almost nothing. Flew four different directions with the GPS showing ground speeds almost the same speed all four directions. Tanks at half full. Two 200 lbs Guys in the front seats. Noticed the elevator just slightly down, elevator trimmed pretty close to middle. I would of thought with two people in the front seats the plane would of required some up elevator to stay level not down elevator. Plane seems to be making full power on takeoff. The engine analyzer shows 18.5 gph full throttle and 2650 RPM on the prop. The engine is sitting straight forward 90 degrees of the firewall and now has .3 degrees of down tilt. We added some washers under the engine mount to tip it down and back to the left. The neighbor in the hanger next to me has a 58 with the stock Continental so I measured his engine incidence. It didn't change anything maybe 1 MPH

Make the engine incidence corrections at the firewall (washer 0550156)not on the motor mount vibration isolator. Make sure the (055015 bushing is like new.) Changes mostly adjust for p factor. Speed should come from correct aircraft rigging. Seems as if yours is set to fly straight while in a crab. You ought to easily get 120 kts.
Check timing, prop hi and low stops. Does it have wheel pants?


For another data point, my 1956 172 got 110kts. Stone stock.


The bushings at the firewall were replaced with the bushings that are used on the float planes. They are aluminum bushings without the rubber mounts so the engine mount to the firewall is solid and no chance of the engine sagging from the rubber mounts as they get older

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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 19 Jul 2019, 08:17 
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Joined: 11/25/11
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Location: KGNF, Grenada, MS
Aircraft: Baron, 180,195,J-3
Greg,

This is a little like trying to tell a guy why he has a headache. Lots of things come into play here. Please take my comments for the almost nothing they are worth.

Just because and airplane flies straight does not mean it is in proper rig.

Lots of "old" airplanes get bent and there is no record of it. Ask me how I know? I own the Psycho Billy Skywagon.

Is your nose wheel straight in cruise?

Cooling Drag is often over looked.

The proper rigging of the airplane can get complicated. There is "a guy", don't recall his name, that specializes in rigging Cessnas. I believe he is in Dallas area.

A structural shop, like Del Lehman, has the real expertise. How far are you from Mena, AR?

Your speeds, unfortunately, are probably not far off. Craig's wife's 172 is a good comparison.

Jg

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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 19 Jul 2019, 08:22 
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Joined: 12/25/10
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Company: Occasionally Pleasant
Location: Bourland Field 50F Cresson, TX
Aircraft: H35, C-172
In a good thermal I could get 140mph straight and level but the horizontals would vibrate. Very unnerving. I put the fuselage to horizontal fairings from a 182 on in place of the little rubber junk seal and eliminated the flutter. Kind of like a poor mans version of the cuff on a V-tail. Oddly, though they are mirror images of each other, one is twice as expensive as the other. Even from the salvage yard.


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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 19 Jul 2019, 08:30 
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Joined: 05/29/09
Posts: 4181
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Company: Craft Air Services, LLC
Location: Hertford, NC
Aircraft: D50A
Username Protected wrote:
Greg,

This is a little like trying to tell a guy why he has a headache. Lots of things come into play here. Please take my comments for the almost nothing they are worth.

Just because and airplane flies straight does not mean it is in proper rig.

Lots of "old" airplanes get bent and there is no record of it. Ask me how I know? I own the Psycho Billy Skywagon.

Is your nose wheel straight in cruise?

Cooling Drag is often over looked.

The proper rigging of the airplane can get complicated. There is "a guy", don't recall his name, that specializes in rigging Cessnas. I believe he is in Dallas area.

A structural shop, like Del Lehman, has the real expertise. How far are you from Mena, AR?

Your speeds, unfortunately, are probably not far off. Craig's wife's 172 is a good comparison.

Jg


One thing I find a little strange is just how slow the older 172s are, even with the 180hp conversion. When I was still in school, Aubie and I somehow ended up flying around in someone's 180hp 172 and it was relatively fast. If I remember correctly, it had a constant speed prop and a rear window, so it was at least a 1963 model. That plane trued somewhere just under 140mph, which is in line with 172XP performance numbers.

Conventional wisdom has it that the constant speed prop doesn't help that much on a 172, and others say that the STOL leading edges don't hurt that much. Does the old straight tail airframe have that much more drag than the "Omnivision" models? It sure doesn't look like it would, but then again, I've never understood how an Aeronca Chief can so easily outrun a Champ. :shrug:

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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 19 Jul 2019, 08:35 
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Joined: 03/24/08
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Username Protected wrote:
The proper rigging of the airplane can get complicated. There is "a guy", don't recall his name, that specializes in rigging Cessnas. I believe he is in Dallas area.

Jg


The guy in Dallas is John Efinger:

http://cessnarigging.com/

I suspect Del L and John are in fact brothers from different mothers....at least when it comes to working on airplanes.

RAS


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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 19 Jul 2019, 09:06 
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Posts: 35
Aircraft: Panther Navajo
I will give him a call. The Guy that helped me restore this plane is considered to be one of those experts in the Midwest. He has the cessna jigs for the airframe, wings, and the control surfaces. I am being told that the straight tails are faster than the newer planes. My neighbor has a 58 bone stock and he indicates 120mph all day long. One of the local Mechanics used to fly this plane 40 years ago and he said this plane was 140 MPH all day. The restoration on this plane was quite extensive. All the surfaces were rebuilt. Quite a few panels on the fuselage were replaced either due to holes, dents or corrosion. Engine is new, prop is new, Sportsman STOL kit, LED wingtips from Stene, Modern day panel from Avion Research, All glass inside, the list goes on. I should of added to the title that it is the most expensive 172 also :scratch:


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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 19 Jul 2019, 12:21 
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Joined: 07/16/17
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Location: KYIP Willow Run (Detroit MI)
Aircraft: BE58/7AC/C140
I’m no help, but our stock ‘61 would cruise at 115 mph. Seems like you should be at least that fast.


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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 19 Jul 2019, 15:36 
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Joined: 11/25/11
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Location: KGNF, Grenada, MS
Aircraft: Baron, 180,195,J-3
Craig,

I learned to fly in 1960 in a new 1960 Cessna 172. Mr. Bob Christopher, the FBO, had a Piper Super Cruiser with 135 hp. It would flat out run away from the new 172. As you said, the early ones simply were not very fast.

And, how did you fit in the front of a 172 with Aubie? :bugeye:

Jg

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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 19 Jul 2019, 15:44 
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Joined: 12/25/10
Posts: 5743
Post Likes: +3434
Company: Occasionally Pleasant
Location: Bourland Field 50F Cresson, TX
Aircraft: H35, C-172
Username Protected wrote:
The proper rigging of the airplane can get complicated. There is "a guy", don't recall his name, that specializes in rigging Cessnas. I believe he is in Dallas area.

Jg


The guy in Dallas is John Efinger:

http://cessnarigging.com/

I suspect Del L and John are in fact brothers from different mothers....at least when it comes to working on airplanes.

RAS


Effinger is busier than a one armed paper hangar and in the process of moving from Hicks to here at Bourland Field SW of Fort Worth. He will be in Oshkosh for the mass arrival Saturday.

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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 19 Jul 2019, 17:19 
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Joined: 05/29/09
Posts: 4181
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Company: Craft Air Services, LLC
Location: Hertford, NC
Aircraft: D50A
Username Protected wrote:
Craig,

I learned to fly in 1960 in a new 1960 Cessna 172. Mr. Bob Christopher, the FBO, had a Piper Super Cruiser with 135 hp. It would flat out run away from the new 172. As you said, the early ones simply were not very fast.

And, how did you fit in the front of a 172 with Aubie? :bugeye:

Jg


Heck, 25 years ago we could both fit in a Luscombe with enough room left over for a case of beer! :cheers:

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 Post subject: Re: Slowest 56 C172 with AVCON Conversion HELP
PostPosted: 19 Jul 2019, 18:03 
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Joined: 01/10/16
Posts: 1111
Post Likes: +1257
Location: KLBO
Aircraft: Cessna 172
Username Protected wrote:
Craig,

I learned to fly in 1960 in a new 1960 Cessna 172. Mr. Bob Christopher, the FBO, had a Piper Super Cruiser with 135 hp. It would flat out run away from the new 172. As you said, the early ones simply were not very fast.

And, how did you fit in the front of a 172 with Aubie? :bugeye:

Jg


Heck, 25 years ago we could both fit in a Luscombe with enough room left over for a case of beer! :cheers:


it’s funny how airplanes shrink over the years...

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