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Take-off roll reality check...

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dave(at)thecoverts.com
Guest

Posted: Sat Jan 07, 2006 10:47 am Post subject: Take-off roll reality check...



I have 5 acres of land and a desire to fly off of it. I own a GA plane now

(Grumman AA5), but the airport is nearly an hour each way and I just don't

fly it near as much as I should. So I am selling it and want to build

something I can use from my own place. That limits me to either a helicopter

(like a Rotorway) or a gyrocopter or a true STOL fixed wing. Since I already

have a fixed wing license (and frankly big spinning blades make me nervous)

I certainly tend toward the STOL.

The CH-701 seems to be the best supported and 'most experienced' home built

STOL in the market and it is currently way way up on my list. Before I start

bending metal tho, I thought I would ask the 'group mind' for a reality

check.

Like I said, I have 5 acres, shaped like a long rectangle (3: pointing

about 30 degrees off of the prevailing sea breeze (20 miles inland at 32ft

above sea level), but it is a thicket and about 1/3 of it is now

house/shop/yard. On the remaining 2/3 I have room to bulldoze a 50'x400'

strip with 30' trees at the end or, if I ran it a bit more diagonally into

the wind maybe a 40'x500' strip with the same 30' trees at the end. The

surface would be hard-packed earth with bermuda grass growth. Worst mid-day

take off conditions would be 95F, no wind, 95% rel humidity. (density

altitude approx 2,900'?)

Common take off conditions would be 85F, 10mph breeze, 95% humidity. (d.a.

2,000')

So... given those dimensions, and conditions, would a full gross 75hp CH-701

operate safely out of that strip? How about a full gross 100hp CH-701?

Dave

jon(at)joncroke.com
Guest

Posted: Sat Jan 07, 2006 11:11 am Post subject: Take-off roll reality check...



Hi Dave,

I have a grass strip on my property... it is about 1000' feet with 20'

obstacles at both ends. I would NOT want anything significantly shorter

than this... as the safety of margin and your brain want to see more length

than the 701 actually needs.. I have flown serveral ultalight models off

this strip also with STOL capability... there are days when you wished you

had 2000'... so my point is that for ME: 1000' is the minimum for all round

safety, enjoyment and margin of errors...

just one opinion and worth every cent you paid for it!

Jon

701 rebuild at 94.8%

do not archive

larrymc(at)qconline.com
Guest

Posted: Sat Jan 07, 2006 1:47 pm Post subject: Take-off roll reality check...



Dave,

The 701 is a great machine, will easily takeoff and land in 2000 feet.

If you have the funds to

build and fly a Rotorway, you might seriously consider the 801. It is

just more capacity with

nearly the same performance.

Larry McFarland

do not archive

Dave Covert wrote:

I have 5 acres of land and a desire to fly off of it. I own a GA plane now

(Grumman AA5), but the airport is nearly an hour each way and I just don't

fly it near as much as I should. So I am selling it and want to build

something I can use from my own place. That limits me to either a helicopter

(like a Rotorway) or a gyrocopter or a true STOL fixed wing. Since I already

have a fixed wing license (and frankly big spinning blades make me nervous)

I certainly tend toward the STOL.

The CH-701 seems to be the best supported and 'most experienced' home built

STOL in the market and it is currently way way up on my list. Before I start

bending metal tho, I thought I would ask the 'group mind' for a reality

check.

Like I said, I have 5 acres, shaped like a long rectangle (3: pointing

about 30 degrees off of the prevailing sea breeze (20 miles inland at 32ft

above sea level), but it is a thicket and about 1/3 of it is now

house/shop/yard. On the remaining 2/3 I have room to bulldoze a 50'x400'

strip with 30' trees at the end or, if I ran it a bit more diagonally into

the wind maybe a 40'x500' strip with the same 30' trees at the end. The

surface would be hard-packed earth with bermuda grass growth. Worst mid-day

take off conditions would be 95F, no wind, 95% rel humidity. (density

altitude approx 2,900'?)

Common take off conditions would be 85F, 10mph breeze, 95% humidity. (d.a.

2,000')

So... given those dimensions, and conditions, would a full gross 75hp CH-701

operate safely out of that strip? How about a full gross 100hp CH-701?

Dave

dxj(at)comcast.net
Guest

Posted: Sun Jan 08, 2006 8:06 pm Post subject: Take-off roll reality check...



This is an interesting problem, and I hope you don't mind the long answer

... but I would hate to see a fellow pilot get hurt or killed ... so read

on. Don't let your desires over-ride your common sense. That might get you

divorced in case of marriage, but it will kill you in the case of airplanes.

A quick look at the specs on Zenair's site for the CH701:

http://www.zenithair.com/stolch701/7-perf.html

Assumptions:

============

Let's assume you're going to be attempting takeoff at maximum gross weight.

The web site quotes 38 as the stall speed with "dual" ... but it's not clear

if that's maximum gross or not. For the purposes of discussion, let's use 38

as Vso.

The best rate of climb (Vy) of 1000 FPM quoted on the site probably doesn't

account for the worst case density altitude and humidity either. Let's

assume Vy is 1.5 times Vso - or 57 MPH at 900 FPM. That's 84 feet per second

(FPS) horizontally for every 15 FPS vertically.

The best rate of climb (Vy) is also not the same as best angle of climb

(Vx). On a short runway, you'll definitely want to use Vx; which means the

rate of climb is going to be less than Vy! Lets assume Vx is 1.4 times Vso -

or 54 MPH at 850 FPM. That's 80 FPS horizontally and 14 FPS vertically.

The web site indicates you'll need about 115 feet for take-off roll at max

gross weight, presumably on a hard runway surface. Let's assume a 50%

increase in rolling distance for wet/soft/high grass and low density air due

to high temperature and humidity ... so your take-off roll will be about 170

feet.

The web site indicates a landing roll of 140 feet, presumably on a hard

runway surface. Let's assume landing roll on grass is 25% longer because you

don't want to be too aggressive with the brakes on a grass surface. That

puts landing roll at 175 feet.

You'll want to clear the trees by at least 50 feet, so you need to be 80 AGL

at the end of the runway. Runway length is 500 feet.

Takeoff:

========

You'll need a little less than 6 seconds (80 feet AGL divided by 14 FPS

vertical) after liftoff to clear the trees by 50 feet. At 80 FPS

(horizontal) you'll use up another 450 feet of runway in that time to clear

the trees by 50 feet. Add that to the 170 feet of ground roll for a total of

620 feet. You're 120 feet short. In fact, with a 500 foot runway you only

have about 4 seconds of runway left after take-off; which would put you only

25 feet above the trees at the end of the runway. That's less than a wing

span from disaster or death. So, technically, your 500 foot runway would

work for takeoff so long as everything went well and you don't mind skimming

trees on occasion.

Aborted takeoff:

================

Let's say things don't go as planned: You get off or are about to get off

the ground and things just don't seem right. Perhaps you forgot to put the

flaps in the right position or the carb heat was on or the tires are

under-inflated or the grass is wet/soft/tall etc. Maybe a suicidal deer

jumped on the runway.

You'll need perhaps 175 feet to stop if your wheels are on the ground at the

time you abort. If you abort before liftoff, you'll need 345 feet (170+175),

leaving 165 feet to spare.

Let's say you lift off before aborting. You're traveling at about 80 FPS, so

you'll have about 2 seconds of in-the-air time on an abort. How long will it

take you make an abort decision once airborne? There is really no margin for

error once you are off the ground - perhaps 1 second to decide to abort once

airborne ... because if you climbed for 1 second, you'll presumably descend

for 1 second before back to mother earth.

Landing:

========

Approach is typically done at best glide speed for safety. Let's assume best

glide is the same as Vy - or 84 FPS horizontally - and you're a minimum of

50 feet above the trees at the approach end of the runway. You could use up

as much as 450 feet of the runway on approach while descending 80 AGL and

bleeding off your air speed during the flare etc. High-lift planes tend to

have long flares. Add another 175 feet of ground roll to stop for a total of

625 feet. You're 125 feet short. Ok, maybe you can come in steep and slow

and closer to the trees. Maybe you can force it on the ground sooner and

brake for longer. Would 500 feet be enough? I don't know, but it would be

very close.

Aborted landing:

================

Let's say things don't go as planned again and you have to abort the

landing, perhaps even a few feet off the ground. It's that damned suicidal

deer again! You already know that you can barely make it above the trees on

take-off after a 170 ground roll, so it follows that you can only abort the

landing in the first 170 feet of runway.

Unfortunately, that deer did his math and knows that if he pops out anywhere

on the last half of the runway, you'll either have to kill him or kill

yourself (and passenger) on a go-around attempt.

Conclusion:

===========

You need at least 650 feet if everything goes well, but 1000 feet if they

don't. You need an additional 5 acres.

dave(at)thecoverts.com
Guest

Posted: Sun Jan 08, 2006 9:33 pm Post subject: Take-off roll reality check...



Very good thoughts, I didn't re-run your math on this, but if that stupid

deer gets in the way, I will likely not care if I clear the trees by 50'...

I will likely be quite happy with 50". In the emergency sitation I will in

effect only have to obtain about 50% of the altittude I would normally like

to see. (40' vs 80')

Based on all of that I think that tailhook and arresting wires idea I have

been toying with is sounding better and better. That and use the grass at a

local airport until I get proficient at launching and landing the craft at

it true capabilities. I have seen a number of references (by people who

replied directly to me) that they make short final in the 30's and roll on

in the 20s. Being able to land in the 30s will still get you hurt, but it

sure isn't like landing my Grumman at 75-80mph.

Out of curiosity what sort of strip do you usually operate your 701 out of?

Dave

ronflys701(at)hotmail.com
Guest

Posted: Mon Jan 09, 2006 5:29 am Post subject: Take-off roll reality check...



Just curious do u fly a 701? Or are u a math teacher?Every 701 is different

they are not alike we have 5 of them and they all fly at different speeds

and take off some sooner then others and land according to the pilots

experience.....You need to flys and know your limitations,,,Lets be honest,

the best is no trees or wires on either end and 2000 ft of runway but thats

not what the plane is about if u look in the archives u will see a couple of

guys who have almost met disaster taking off even with full flaps and

stalled? If u want to be safe don t push the plane to its limits when the

pilots limits can t match the plane....Like the zenith site says it takes

alot of practice and sometimes new gear from bending to perfect the stol

caracteristics of the 701 expecially at full gross....Regards Ron

 	  Quote: 	
		  From: "David X" <dxj(at)comcast.net>

Reply-To: zenith-list(at)matronics.com

To: <zenith-list(at)matronics.com>

Subject: Re: Zenith-List: Take-off roll reality check...

Date: Sun, 8 Jan 2006 23:06:17 -0500

This is an interesting problem, and I hope you don't mind the long answer

... but I would hate to see a fellow pilot get hurt or killed ... so read

on. Don't let your desires over-ride your common sense. That might get you

divorced in case of marriage, but it will kill you in the case of

airplanes.

A quick look at the specs on Zenair's site for the CH701:

http://www.zenithair.com/stolch701/7-perf.html

Assumptions:

============

Let's assume you're going to be attempting takeoff at maximum gross weight.

The web site quotes 38 as the stall speed with "dual" ... but it's not

clear

if that's maximum gross or not. For the purposes of discussion, let's use

38

as Vso.

The best rate of climb (Vy) of 1000 FPM quoted on the site probably doesn't

account for the worst case density altitude and humidity either. Let's

assume Vy is 1.5 times Vso - or 57 MPH at 900 FPM. That's 84 feet per

second

(FPS) horizontally for every 15 FPS vertically.

The best rate of climb (Vy) is also not the same as best angle of climb

(Vx). On a short runway, you'll definitely want to use Vx; which means the

rate of climb is going to be less than Vy! Lets assume Vx is 1.4 times Vso

-

or 54 MPH at 850 FPM. That's 80 FPS horizontally and 14 FPS vertically.

The web site indicates you'll need about 115 feet for take-off roll at max

gross weight, presumably on a hard runway surface. Let's assume a 50%

increase in rolling distance for wet/soft/high grass and low density air

due

to high temperature and humidity ... so your take-off roll will be about

170

feet.

The web site indicates a landing roll of 140 feet, presumably on a hard

runway surface. Let's assume landing roll on grass is 25% longer because

you

don't want to be too aggressive with the brakes on a grass surface. That

puts landing roll at 175 feet.

You'll want to clear the trees by at least 50 feet, so you need to be 80

AGL

at the end of the runway. Runway length is 500 feet.

Takeoff:

========

You'll need a little less than 6 seconds (80 feet AGL divided by 14 FPS

vertical) after liftoff to clear the trees by 50 feet. At 80 FPS

(horizontal) you'll use up another 450 feet of runway in that time to clear

the trees by 50 feet. Add that to the 170 feet of ground roll for a total

of

620 feet. You're 120 feet short. In fact, with a 500 foot runway you only

have about 4 seconds of runway left after take-off; which would put you

only

25 feet above the trees at the end of the runway. That's less than a wing

span from disaster or death. So, technically, your 500 foot runway would

work for takeoff so long as everything went well and you don't mind

skimming

trees on occasion.

Aborted takeoff:

================

Let's say things don't go as planned: You get off or are about to get off

the ground and things just don't seem right. Perhaps you forgot to put the

flaps in the right position or the carb heat was on or the tires are

under-inflated or the grass is wet/soft/tall etc. Maybe a suicidal deer

jumped on the runway.

You'll need perhaps 175 feet to stop if your wheels are on the ground at

the

time you abort. If you abort before liftoff, you'll need 345 feet

(170+175),

leaving 165 feet to spare.

Let's say you lift off before aborting. You're traveling at about 80 FPS,

so

you'll have about 2 seconds of in-the-air time on an abort. How long will

it

take you make an abort decision once airborne? There is really no margin

for

error once you are off the ground - perhaps 1 second to decide to abort

once

airborne ... because if you climbed for 1 second, you'll presumably descend

for 1 second before back to mother earth.

Landing:

========

Approach is typically done at best glide speed for safety. Let's assume

best

glide is the same as Vy - or 84 FPS horizontally - and you're a minimum of

50 feet above the trees at the approach end of the runway. You could use up

as much as 450 feet of the runway on approach while descending 80 AGL and

bleeding off your air speed during the flare etc. High-lift planes tend to

have long flares. Add another 175 feet of ground roll to stop for a total

of

625 feet. You're 125 feet short. Ok, maybe you can come in steep and slow

and closer to the trees. Maybe you can force it on the ground sooner and

brake for longer. Would 500 feet be enough? I don't know, but it would be

very close.

Aborted landing:

================

Let's say things don't go as planned again and you have to abort the

landing, perhaps even a few feet off the ground. It's that damned suicidal

deer again! You already know that you can barely make it above the trees on

take-off after a 170 ground roll, so it follows that you can only abort the

landing in the first 170 feet of runway.

Unfortunately, that deer did his math and knows that if he pops out

anywhere

on the last half of the runway, you'll either have to kill him or kill

yourself (and passenger) on a go-around attempt.

Conclusion:

===========

You need at least 650 feet if everything goes well, but 1000 feet if they

don't. You need an additional 5 acres.

	


Take charge with a pop-up guard built on patented Microsoft SmartScreen

Technology

Start enjoying all the benefits of MSN Premium right now and get the

first two months FREE*.

p.mulwitz(at)worldnet.att
Guest

Posted: Mon Jan 09, 2006 6:07 am Post subject: Take-off roll reality check...



I am surprised nobody has mentioned AOA or LRI device use to minimize

take off and landing distances for the 701.

Is anyone using these devices on a 701? What results?

Paul

XL wings

do not archive

At 05:29 AM 1/9/2006, you wrote:

 	  Quote: 	
		  Just curious do u fly a 701? Or are u a math teacher?Every 701 is different

they are not alike we have 5 of them and they all fly at different speeds

and take off some sooner then others and land according to the pilots

experience.....You need to flys and know your limitations,,,Lets be honest,

the best is no trees or wires on either end and 2000 ft of runway but thats

not what the plane is about if u look in the archives u will see a couple of

guys who have almost met disaster taking off even with full flaps and

stalled? If u want to be safe don t push the plane to its limits when the

pilots limits can t match the plane....Like the zenith site says it takes

alot of practice and sometimes new gear from bending to perfect the stol

caracteristics of the 701 expecially at full gross....Regards Ron

dxj(at)comcast.net
Guest

Posted: Mon Jan 09, 2006 7:13 am Post subject: Take-off roll reality check...



 	  Quote: 	
		   Out of curiosity what sort of strip do you usually operate your 701 out

of? 	


Dave,

I fly a CH601 and a CH2000, but the principal applies to any aircraft. It's

not just what the aircraft and pilot can do when everything goes right ...

think about the contingencies ...

There were a number of antidotal accounts in the list about what the 701

could do. I've seen it operate. It's an impressive aircraft in the right

hands. However, don't bet your own life on antidotal accounts.

I think the best advice was to get some training or a demo to see what could

be done. Tell them what you want to do at your proposed field, then have

them go through a few simulations, like aborted landings and take-offs.

Consider worst case scenario, because it will happen eventually.

ronflys701(at)hotmail.com
Guest

Posted: Mon Jan 09, 2006 7:51 am Post subject: Take-off roll reality check...



I fly a 701 out of a 1800 ft ,but land and then taxi to the 500 ft mark to

taxi off the grass strip.you can fly the plane in at 50 mph or drop it in

and stop with a stall 1 ft above the field and come to a stop in 100

ft.........there is no substitute for practice and build your confidence you

will know your limitations.How many pilots have died trying to return to the

field on takeoff?Yet they hear about others... and have been told time and

time again to point down and land ahead. Go for a flight with someone who

has the plane, and really knows how to use the stol performance and see how

it performs and you will see if it is the right plane for u or not?I have

bent the spring learning how to perform this with a zenith instructor so I

know personally how fast it can drop .....just like a helicopter..Just

always be ready for the unexpected...there is a point where u will be

committed and u have to follow through even on takeoff....Regards Ron PS

....Im not an expert just had a bit of experience and seen some of the

problems u can run into with this plane........ 250 hrs .1 bent spring

and because Im using the old style, Had a wheel fork break ( had a hairline

crack between the bolt holes and slid along the grass with no damage to the

pro;p or the plane ..some luck as well).Regards Ron

 	  Quote: 	
		  From: "David X" <dxj(at)comcast.net>

Reply-To: zenith-list(at)matronics.com

To: <zenith-list(at)matronics.com>

Subject: Re: Zenith-List: Take-off roll reality check...

Date: Mon, 9 Jan 2006 10:12:32 -0500

> Out of curiosity what sort of strip do you usually operate your 701 out

of?

Dave,

I fly a CH601 and a CH2000, but the principal applies to any aircraft. It's

not just what the aircraft and pilot can do when everything goes right ...

think about the contingencies ...

There were a number of antidotal accounts in the list about what the 701

could do. I've seen it operate. It's an impressive aircraft in the right

hands. However, don't bet your own life on antidotal accounts.

I think the best advice was to get some training or a demo to see what

could

be done. Tell them what you want to do at your proposed field, then have

them go through a few simulations, like aborted landings and take-offs.

Consider worst case scenario, because it will happen eventually.

	


Don't just Search. Find! http://search.sympatico.msn.ca/default.aspx The new

dxj(at)comcast.net
Guest

Posted: Mon Jan 09, 2006 8:41 pm Post subject: Take-off roll reality check...



 	  Quote: 	
		   Or are u a math teacher?

	


Any safe pilot will add to the minimums some margin for pilot error and

unforeseen events. The approach I outlined is a tried and true way to

thumb-nail a reality check . so I was required to demonstrate using a POH

before being granted a pilot's license.

Ok, so I got Vso, Vx and Vy wrong, but anyone with a 6th grade education can

redo the math . in case you were wondering.

Some people like living on the edge . but the gentleman asked for opinions

from the peanut gallery . so I suggested he think about adding a healthy

margin for error so he can continue to enjoy that fine wife, faithful dog,

hard earned house and beautiful 5 acres of tall trees. There are obviously

going to be differences in opinion. On the other hand, if my novice opinion

prompted another to reply in more useful terms, even if it were to insult me

. then the gentleman has all the more opinion to weigh 

The article linked to previously (

http://www.acomodata.com/zenair701/flying.htm ) was a good read. There are

some useful quotes there about margin of error:

"the speed will bleed amazingly quickly. This is particularly pronounced

when approaching with full flap, (30 deg.) Early power reduction and speed

decay can result in loss of elevator authority." Sounds like potential

trouble if too close to the trees during a power loss. But, leaving more

margin over the trees also means a longer runway is required.

"any strip with a fence at each end less than 200 m long requires the pilot

to be well versed with the STOL capabilities of the 701" So, 200 meters is

156 feet longer than the gentleman's proposed field. I recall that I told

him he was 120 feet too short based on a thumbnail calculation.

"I believe it's absolute minimum length, in still air, fenced at both ends,

level, at sea level and moderate temperatures is 100m with no margin for

error" That's 328 feet, and I doubt the "fence" is 30 feet tall. I recall

that I told the gentlemen 345 was the absolute minimum landing distance

based on a thumbnail calculation.

"if you do attempt continued climb at this low speed and high body angle

and then suffer an engine failure below 100' agl, [then] recovery is not

possible before hitting the ground." So, you need more runway to pick up

speed in ground affect so not to be forced to climb at 30 knots, and you

need more runway incase of an engine failure.

"A low experience pilot wanting to buy a 701 to operate a really short field

on the strength of the advertised figures could be in for disappointment." I

think that sums it up nicely.

Math is your friend. Don't be afraid of it.

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