The Zenith CH-701 + CH-750 and ICP Savannah VG, XL and S Comparison :-)

[eightyknots]

I decided to put together a table which gives a fair comparison between Zenith's and ICP's high-wing, STOL, two-seater planes. In this table I have compared Zenith's CH-701 and CH-750 and ICP's Savannah VG, Savannah XL and Savannah S. The Savannah XL and S have identical specifications and performance figures so I have treated them as one.

 

I have added some difference columns so that a proper comparison can be made between makes and also between models from the same factory. I believe the figures make pretty interesting reading:

 

 

So far, there have been bits-and-pieces discussions in a number of threads, often as 'asides' from the main topic of those threads. Also, on other 'places' on the internet, discussions have arisen about these two manufacturers. Unlike the forumites at aircraftpilots, those people have become very heated in their discussions. I felt that, more often than not, there was a copious quantity of angry, partisan heat :ranting:but very little light.

 

I hope that, by viewing the manufacturer-provided figures, a proper discussion can follow ...based on light rather than heat.

 

Enjoy!

 

 

[winsor68]

The school Sav S that I have done a few hours as in my Avatar photo... cruises at 85 knots maximum in my experience... I reckon there are kit built Savs around that are quite a bit slower than that... Doesn't change the fact they are a great Aircraft. It seems in my experience that there are some manufacturers...not all of them overseas... that make some wild claims. Perhaps with a constant speed prop in the best conditions the aircraft would do 97 knots... the Sav is certainly strong enough to go that fast but... why bother. The other figures stated are achievable in my experience. They are a great aircraft... but 97 knots as from the factory???

 

 

[eightyknots]

The school Sav S that I have done a few hours as in my Avatar photo... cruises at 85 knots maximum in my experience... I reckon there are kit built Savs around that are quite a bit slower than that... Doesn't change the fact they are a great Aircraft. It seems in my experience that there are some manufacturers...not all of them overseas... that make some wild claims. Perhaps with a constant speed prop in the best conditions the aircraft would do 97 knots... the Sav is certainly strong enough to go that fast but... why bother. The other figures stated are achievable in my experience. They are a great aircraft... but 97 knots as from the factory???

It's great to hear -from people actually flying these five planes- how the factory-supplied figures stack up. Thanks W68!

 

 

[eightyknots]

I forgot to add that the ultimate load design factor for the two Zenith and three ICP aircraft is: +6 / -3

 

 

[David Isaac]

I forgot to add that the ultimate load design factor for the two Zenith and three ICP aircraft is: +6 / -3

That comment of yours worries me 80 ...

Are you quoting the 'Ultimate' or 'maximum design' load factor.

 

Usually 'ultimate' means the point just before permanent deformation occurs and is usually 1.5 x the design load factor (unless I have it wrong). +6 / -3 is a big number to claim, standard utility GA aircraft are usually +3.8 / -1.8.

 

 

[rankamateur]

That comment of yours worries me 80 ...Are you quoting the 'Ultimate' or 'maximum design' load factor.

 

Usually 'ultimate' means the point just before permanent deformation occurs and is usually 1.5 x the design load factor (unless I have it wrong). +6 / -3 is a big number to claim, standard utility GA aircraft are usually +3.8 / -1.8.

I have seen that figure quoted too, often in the company of MTOW 450Kg!

 

 

[David Isaac]

What many people do not understand with STOL aircraft is that you generally cannot have it both ways ... i.e. STOL and high cruise speed . The two are mutually exclusive unless you can change the shape of the wing in various flight configurations like jet passenger liners do.

 

High lift wings by their nature have very limited maneuvering speeds because the load factors are easily exceeded in gusting conditions at speed.

 

There is no way a STOL aircraft like the Savannah or Zenith will have a cruise speed of 97 knots .. that is more likely to be VNE due to the high loads induced at high speed. There is no magic formula here, these are all calculable speeds.

 

 

[rankamateur]

But the VNE is now 112 knots, and 95 knot cruise is quite achievable BUT the price is economy.

 

 

[turboplanner]

Ultimate and Rosary Beads go together.

 

 

[skyfox1]

That comment of yours worries me 80 ...Are you quoting the 'Ultimate' or 'maximum design' load factor.

 

Usually 'ultimate' means the point just before permanent deformation occurs and is usually 1.5 x the design load factor (unless I have it wrong). +6 / -3 is a big number to claim, standard utility GA aircraft are usually +3.8 / -1.8.

Hi David l have just bought a ch701 and the figures in the performance manual are +6G/-3G design load factor (ultimate)

Gross weight 500 kg.

 

cheers Geoff.

 

 

[Wayne T Mathews]

What many people do not understand with STOL aircraft is that you generally cannot have it both ways ... i.e. STOL and high cruise speed . The two are mutually exclusive unless you can change the shape of the wing in various flight configurations like jet passenger liners do.High lift wings by their nature have very limited maneuvering speeds because the load factors are easily exceeded in gusting conditions at speed.

 

There is no way a STOL aircraft like the Savannah or Zenith will have a cruise speed of 97 knots .. that is more likely to be VNE due to the high loads induced at high speed. There is no magic formula here, these are all calculable speeds.

What you have said is generally true David. But (here's that "but" word again) it's not impossable to get the numbers being quoted. I was told a long time ago that if you can get 1 Knot per horsepower, you've got an efficient airframe. It's one of the things that made CG Taylor famous in his time. He was getting 65 kts out of the 65 HP the J3 had. Then he built the Taylorcraft and got 75kts out of 65 HP. Yee Har... He did that in the mid to late '30s.

 

Been a lot of water under the bridge since the '30s & '40s, David. Been a lot of advances in designs too. So there's no way I'd have the balls to say, "There is no way a STOL aircraft like the Savannah or Zenith will have a cruise speed of 97 knots.." I reckon with the right prop on a 100 HP 912 at altitude (which would probably be delivering around 90 HP), it's just possable the Savanah might true out at 97 kts. I agree it's not probable. But hey, it just might be possable. I'd want to fly one and try it before I'd commit to a definate opinion.

 

 

[winsor68]

Regardless... one thing the Sav S does have is bloody terrific flying qualities IMO... I reckon 80-85 knots is a fine cruise speed for the aircraft... and I believe with a different prop set up you would get 90 knots indicated... that is about as fast as you would want to go in one without the possibility of flying outside the aircraft limits (again IMO)...

 

 

[eightyknots]

That comment of yours worries me 80 ...Are you quoting the 'Ultimate' or 'maximum design' load factor.

 

Usually 'ultimate' means the point just before permanent deformation occurs and is usually 1.5 x the design load factor (unless I have it wrong). +6 / -3 is a big number to claim, standard utility GA aircraft are usually +3.8 / -1.8.

Regardless... one thing the Sav S does have is bloody terrific flying qualities IMO... I reckon 80-85 knots is a fine cruise speed for the aircraft......

That's my kind of speed Winsor .

 

I wonder if the higher than usual ultimate load design factors for both the Zenith and ICP STOL aircraft is because they have fatter than usual wings. This thickness may lead to extra strength carrying capacity, perhaps simply as a byproduct of the design?

 

 

[David Isaac]

What you have said is generally true David. But (here's that "but" word again) it's not impossable to get the numbers being quoted. I was told a long time ago that if you can get 1 Knot per horsepower, you've got an efficient airframe. It's one of the things that made CG Taylor famous in his time. He was getting 65 kts out of the 65 HP the J3 had. Then he built the Taylorcraft and got 75kts out of 65 HP. Yee Har... He did that in the mid to late '30s.Been a lot of water under the bridge since the '30s & '40s, David. Been a lot of advances in designs too. So there's no way I'd have the balls to say, "There is no way a STOL aircraft like the Savannah or Zenith will have a cruise speed of 97 knots.." I reckon with the right prop on a 100 HP 912 at altitude (which would probably be delivering around 90 HP), it's just possable the Savanah might true out at 97 kts. I agree it's not probable. But hey, it just might be possable. I'd want to fly one and try it before I'd commit to a definate opinion.

Well sweety, maybe I'm just an opinionated SOB.

It all depends on how you define cruise speed. I would hardly call a speed at WOT 'cruise'. More importantly, I would hardly call any speed right on or just below maneuvering speed 'cruise' speed either. Cruise is supposed to be the trimmed speed at 75% power is it not, and measured as TAS.

 

 

[David Isaac]

Hi David l have just bought a ch701 and the figures in the performance manual are +6G/-3G design load factor (ultimate)Gross weight 500 kg.

cheers Geoff.

There is that term again. So what is the load factor ... design or ultimate?

 

 

[Kyle Communications]

As far as I know the quoted figures are design specs and the ultimate is 1.5 times the design spec.....BUT (theres that word again).......thats what I have read in my research thats all. At 560kg the Sav is +4 g -2g and max rough air speed is 74kts on mine the VNE is 108 knots

 

 

[David Isaac]

As far as I know the quoted figures are design specs and the ultimate is 1.5 times the design spec.....BUT (theres that word again).......thats what I have read in my research thats all. At 560kg the Sav is +4 g -2g and max rough air speed is 74kts on mine the VNE is 108 knots

Those Sav figures sound more realistic to me. Quoting 'ultimate' load factors is mischievous IMHO. The 'turbulence penetration' speed is the key indicator on high lift wings and the Sav data proves that point. For the same reason high VNE speeds are not normal on high lift STOL wings, again for load factor reasons.

 

 

[eightyknots]

As far as I know the quoted figures are design specs and the ultimate is 1.5 times the design spec.....BUT (theres that word again).......thats what I have read in my research thats all. At 560kg the Sav is +4 g -2g and max rough air speed is 74kts on mine the VNE is 108 knots

I have not ever come across the +4/-2g quoted in ICP literature. It's consistently +6/-3. Do you remember where your figures come from?

 

 

[Kyle Communications]

The +6 and -3 is for the 450kg version in europe...when it became 560kg it changed

 

 

[Kyle Communications]

The following 2 pages are from the current Sav flight manual from the USA you will note on page 20 the upgrade note to 560kg if the mods are done. The kits we get here are the 560kg modified ones the specs remain the same

 

Mark

 

Page20 from savannahvgmanual-2.pdf

 

Page19 from savannahvgmanual.pdf

 

Page20 from savannahvgmanual-2.pdf

 

Page19 from savannahvgmanual.pdf

 

Page20 from savannahvgmanual-2.pdf

Page19 from savannahvgmanual.pdf

[eightyknots]

+4/-2 appear to be the load factor for the Savannah and multiplied for 1.5 to obtain the ultimate load factor (i.e. +6/-3)

 

This is how they tested the negative g factor. A dozen more men on either side would have reached the "ultimate" factor :

 

 

The load distribution is approximated by piling more guys on in the middle compared to the outside of the wing .

 

Now, to test the positive g, you'll have to turn your plane upside down:

 

 

 

[Wayne T Mathews]

Well sweety, maybe I'm just an opinionated SOB.It all depends on how you define cruise speed. I would hardly call a speed at WOT 'cruise'. More importantly, I would hardly call any speed right on or just below maneuvering speed 'cruise' speed either. Cruise is supposed to be the trimmed speed at 75% power is it not, and measured as TAS.

Oh stop it you beast David. You're doing it again. You're applying logic. And nobody else can win when you apply logic...

 

You know as well as I do that the Italians' English is not so good. When they say "cruise speed", they mean Vmo...

 

Now,,, play nice David,,, no naughty natter, y'hear?...

 

 

[David Isaac]

The following 2 pages are from the current Sav flight manual from the USA you will note on page 20 the upgrade note to 560kg if the mods are done. The kits we get here are the 560kg modified ones the specs remain the sameMark

Mark,

Page 19 you attached clearly states the design load factor is +4 / -2 at 454 Kg. it also clearly states that the ultimate is 1.5x the design load factor. This is the same safety margin we use in standard GA aircraft, except we rarely quote 'ultimate' figures because it is bloody irresponsible in my view because some D head will push the limit and tear the bloody wings off. If Zenith are stating figures that are actually the ultimate load they should be castigated for it ... unbelievable.

 

This is what buggers up the credibility of the ultralight industry when BS figures are quoted that fly in the face of conventional wisdom. Just like some of the BS VSo figures quoted by some.

 

 

[eightyknots]

Mark,Page 19 you attached clearly states the design load factor is +4 / -2 at 454 Kg. it also clearly states that the ultimate is 1.5x the design load factor. T.

I made the point about load and ultimate load (i.e. destruction force) in post #21 above but you have added another dimension when you wrote your post which is that the factors are for 454 kg only.

 

Zenith CH701s are designed for a maximum ("gross") weight of 500 kg while the ICP Savannah in North America, South Africa, Australia and New Zealand is for 560 kg. Many will appreciate that -in the case of the Savannah- if the weight increases from 454 kg (the European maximum ultralight limit) to 560 kg, the design load factor should either be de-rated or the plane has to be beefed up for the extra design load. I understand that ICP's 560 kg version is a stronger aeroplane. It is strange therefore that the Savannah flight manual in the USA (600 kg LSA territory!) has the loading figures for 454 kg.

 

Where is the page from the manual that actually lists the load factors for the strengthened 560 kg Savannah?

 

 

[Kyle Communications]

The loads are the same as the aircraft has been strengthened with the upgrade kit. The +4 and -2 are the load factors for the 560kg version the same as the lighter version due to the upgrade.