Glide Distance to meet 135 Requirements over open water.

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mjonesr

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mjonesr
Located Guam. To meet FAR Part 135 over water requirements with passengers, we need to glide 16 miles with loss of an engine (Rota to Guam). We have a Cessna 207 but the glide distance would require a climb to 10,000 feet. Would wing tip extensions make the glide distance better, can you use excess speed to weigh in on the formula. That is, how much distance is used when transitioning from 150 MPH to 90 MPH. Do any high lift devices weigh into the formula. Just thinking outlaid.
 
Best glide is (L/D)max and since L is effectively constant (it's equal to aircraft weight), it's the decrease in drag you want, not an increase in lift. So high lift devices are out. Wingtip extensions might help, however, drooping wingtips might help. Vortex generators might help.

None of these things are likely to help enough to be with the cost and trouble, though.
 
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Best bang for the drag reduction buck is likely up front - cooling drag is big. Also, gap seals. What kind of speed mods are out there?
Clip4 said:
I have a lot of 207 time. It is a dirty airframe. I can’t see how any modifications are going in increase your glide distance enough to warrant the expense.
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Lipstick on a pig?
 
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mjonesr said:
we need to glide 16 miles with loss of an engine
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Doubtful there are any modifications to give you that distance in any single. And if there were you would be money ahead to simply install life vests to meet the requirement.
 
Realistically, you’d have to talk to your POI and find out what kind of proof of improved glide performance they’d need to see…I’m sure none of the mods you mentioned will publish the change and the excess speed thing will need to be quantified.
 
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I fly a C207 for a living. They glide like a greased anvil. I'm flying a T-28 across the country right now and it might be a toss up as to which one makes a crater first.

I would assume that wing tip extensions would be an STC to include a POH supplement that would have numbers for change in performance. Your answer lies in that supplement.
 
aftCG said:
I would assume that wing tip extensions would be an STC to include a POH supplement that would have numbers for change in performance. Your answer lies in that supplement.
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I wouldn’t make any assumptions in that regard…more than likely, it just says performance will be the same as or better than the unmodified airplane.
 
I believe Cessna only made 120 Model 207s and 4 pilots here have time in them”. Small world.
 
If you think 8.4 to one is like an anvil, you should try a flight in a helicopter. :D

FYI, a 172 is 9.6 to 1
 
Clip4 said:
I believe Cessna only made 120 Model 207s and 4 pilots here have time in them”. Small world.
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120, wow. Well we have more than 10% of them on our ramp, ten of them flying 20k hours per year. Including our competitors we most have over half of them operating out of PABE.
Pinecone said:
If you think 8.4 to one is like an anvil, you should try a flight in a helicopter. :D

FYI, a 172 is 9.6 to 1
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No way in hell the sled glides at 8.4.
1/4 mile out on down wind, pull the power abeam the numbers. With 15" MP you can just barely make the runway if you turn immediately. Power off, not a chance.

Way high on final? Reduce to idle for 2-3 seconds. The sink rate is mind blowing.
 
That is what Cessna says.

Try testing at altitude.
 
I was very surprised to read the glide ratio of a Cessna 208. The Caravan's glide ratio (1:14) is better than the Skyhawk's (1:9). Is there another single engine aircraft with anything close to the glide performance of the Caravan. I cant seem to find one.
 
A Malibu might








































































































mjonesr said:
I was very surprised to read the glide ratio of a Cessna 208. The Caravan's glide ratio (1:14) is better than the Skyhawk's (1:9). Is there another single engine aircraft with anything close to the glide performance of the Caravan. I cant seem to find one.
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Not a bad glide ratio, about 12:1. But priced near 1 million for a late model. Might as well spring for a Caravan. Im guessing there are no piston powered aircraft near 12:1 or more.
 
I couldn't find this requirement in Pt 135.
Can you point it out? Interested.
Or, maybe it's in your OpCert?
 
Its goes further in the requirements on reaching land. You don't want to be faced with the "White Cliffs of Dover" at the end of the glide to a shoreline.
 
The required crossing altitude of a Cessna Caravan, Rota to Guam would be 5700 feet. But in the process of slowing from cruise speed to gliding speed, there is some distances. To bleed off 100 mph, you undoubtedly will move down the road a few more miles. Can that be calculated into a displaced descent point and so a lower altitude for crossing. An ETOPS ETP takes into consideration other factors, although FAR 135.183 doesn't highlight such factors, seems head or tailwinds, residual airspeeds, improved aircraft performance devices might help. But, thats my simpleton point of view.
 
Clip4 said:
I believe Cessna only made 120 Model 207s and 4 pilots here have time in them”. Small world.
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They made a little less than 1,000 IIRC.

Interestingly enough, we’ve probably all flown the same 207s.
 
A few ideas here that might help with the modification program.

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Still working island flying and the right aircraft. FAR 135.183 requires single engine aircraft with the loss of an engine to glide to a shoreline. The Cessna Caravan cruises at 180K. The descent engine out is 95K. How far down the road can you go, maintaining your altitude and beginning at 180K, to decelerate to 95K. I recall that in the 737, its 1 mile per 10K but with a fixed gear, feathered prop and dirty airframe, can you get 1 mile per 20K and maybe its much great. I cant find anyone in the know or a chart.
 
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